Biocentric nonmetals: H, C, N, O, P, S and Se

[Rene]

Colleagues, could I have some feedback on the following naming proposal?

Over the years suggestions have been made as to what to call the "leftover" nonmetals H, C, N, O, P, S and Se i.e. those other than the halogen nonmetals or the noble gases.

Along the way, Mark, Jess and Brian Gregory have expressed some interest in this question.

The suggestions have included:

HCN nonmetals

biogen

liminal

aminoid

selenoid

coactive

SeSPONCH

biosulfuroid

unclassified

bio elements

primary bioelements.

                         

The leftover nonmetals have never attracted an agreed category name, in part because naming and grouping in science often lag behind understanding — and because, until now, no one has compiled their many shared properties.

I now propose calling them biocentric nonmetals. These are the nonmetals that are naturally and covalently incorporated into the structure of biological macromolecules. As such, they play a central role in life’s cellular architecture. Examples of such macromolecules include enzymes, cholesterol, beeswax, glucose, fructose, starch and cellulose; and DNA and RNA.

Selenium is included here based on its presence in natural biological macromolecules. Although not all organisms retain the machinery to incorporate it, selenium’s genetically encoded use across all three domains of life affirms its evolutionary depth and structural role. By contrast, the biological roles of the halogen nonmetals are not macromolecular in nature.

The biocentric nonmetals, generally in ambient conditions, are further characterised by:

A. Their intrinsic atomic properties

1. Small to intermediate atomic radii

2. Moderate net nonmetallic character in terms of average ionisation energy, electron affinity, electronegativity, and metallicity ratio. In periodic table terms, most of the biocentric nonmetals are thus located between — on the left — the chemically weak metalloid elements and, on the right, the chemically active halogen nonmetals. Hydrogen may or may not appear in the proximity of its compatriots, depending on whether it is positioned above fluorine (group 17) or lithium (group 1).

3. Variegated appearance; brittle comportment if solid

4. Low-coordinate structures in their most stable forms

B. Their behavior in interaction with other atoms

5. Tendencies for catenation

6. Capacity to form interstitial and refractory compounds

7. Widespread roles in organocatalysis

C. Consequences and emergent characteristics

8. Multiple vertical, horizontal, and diagonal relationships within their patch of the periodic table

9. Foundational roles in biogeochemical cycles

10. Participation in luminescent compounds

11. Use in explosive materials

12. Use in nerve agents

13. A dualistic nature: Dr Jekyll in life-sustaining processes (e.g. #9), Mr Hyde in destructive or toxicological applications (#s 11, 12) — yet unified by a shared set of atomic and chemical traits, despite their diverse individual identities.

thank you, René

Postscript

There is some precedent for use of the word "biocentric" in the literature. Remick & Helmann (2023) published an article called "The elements of life: A biocentric tour of the periodic table" in Advances in Microbial Physiology, currently with 50 citations. Among the nonmetals, H, C, N, O, P and S were counted by them as elements essential for all life while Se was counted as essential for many organisms in all three domains of life. See: 

https://pmc.ncbi.nlm.nih.gov/articles/PMC10727122/#S79

[Jess Tauber]

https://en.wikipedia.org/wiki/CHNOPS

Se was left out of this sequence.

Jess Tauber

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[Rene]

On 16 Jun 2025, at 09:01, Jess Tauber <tetrahed...@gmail.com> wrote:

https://en.wikipedia.org/wiki/CHNOPS

Se was left out of this sequence.

Thanks Jess, what did you make of the exclusion of Se? My thoughts are below.

René

Se seems to have been left out of the CHNOPS (or SPONCH) acronym since it wasn't until 1957 that it was recognised as an essential trace element. This occured due to its role in the so-called 21st amino acid, selenocysteine. As well, the first selenoenzyme, glutathione peroxidase, was only isolated in 1973 — long after CHNOPS had become more or less established in biology education.

While most biological macromolecules are built from covalent combinations of the six CHNOPS nonmetals, stopping at six now seems arbitrary in light of selenium’s genetically encoded role in life across all domains. The acronym then becomes CHNOPSSe, which is still easy to remember. ‘SeSPONCH’ is just as easy — and has the bonus of ordering the elements by decreasing Z.

The other issue with CHNOPS is that it unintentionally casts Se into a kind of classificatory limbo — not noble like the noble gases, nor reactive like the halogens, yet also left out of the familiar group of biologically foundational elements. Including it completes the picture and acknowledges its evolutionary and biochemical relevance.

I was further interested to see that, in Fig. 1 of the article by Remick & Helmann (appended below), on the metal side of the periodic table, the plain (non-noble) transitions metals have the highest average biological importance due to the roles of Mo, Mn, Fe, Co, Ni, Cu and Zn. More broadly, the following correspondences can be drawn:

Metals Nonmetals

sf-block Halogen High reactivity, essential ionic roles (Na⁺, K⁺, Cl⁻, Ca²⁺)

transition (most) Biocentric

transition (noble) Noble gas

p-block Metalloid

Metals              Nonmetals    Description

------------------------------------------------------------------------------

sf-block            Halogen      High reactivity, essential ionic roles (Na⁺, K⁺, Cl⁻, Ca²⁺)

Transition (most)   Biocentric   Functionally diverse; central to redox and catalysis

Transition (noble)  Noble gase   Minimal reactivity; rarely biological but useful in medicine               

p-block             Metalloid    Trace biological or environmental roles

[Rene]

Misfire. Will, try again.

[Rene]

On 16 Jun 2025, at 09:01, Jess Tauber <tetrahed...@gmail.com> wrote:

https://en.wikipedia.org/wiki/CHNOPS

Se was left out of this sequence.

Thanks Jess, what did you make of the exclusion of Se? My thoughts are below.

René

The CHONPS story and the case of the missing nonmetal
Se seems to have been left out of the CHNOPS (or SPONCH) acronym because it wasn’t recognized as an essential trace element until 1957, when its role in the so-called 21st amino acid, selenocysteine, was discovered. The first selenoenzyme, glutathione peroxidase, wasn’t isolated until 1973 — long after CHNOPS had become entrenched in biology education.

While most biological macromolecules are built from covalent combinations of the six CHNOPS nonmetals, stopping at six now seems arbitrary in light of selenium’s genetically encoded role across all domains of life. The acronym becomes CHNOPSSe, which is still easy to remember. "SeSPONCH" is just as simple — and has the bonus of ordering the elements by decreasing atomic number.

Another issue with CHNOPS is that it unintentionally casts selenium into a kind of classificatory limbo — not noble like the noble gases, not reactive like the halogens, yet also omitted from the familiar group of biologically foundational elements. Including Se completes the picture and acknowledges its evolutionary and biochemical significance.

I was further struck by Figure 1 in the article by Remick & Helmann, which shows that among the metals, most transition metals have the highest average biological importance, due to the roles of Mo, Mn, Fe, Co, Ni, Cu, and Zn. Taken more broadly, we can propose the following table:

Fourfold complementarity: Metals and nonmetals

Metals Nonmetals Description

sf-block Halogen High reactivity, essential ionic roles (Na⁺, K⁺, Cl⁻, Ca²⁺)

------------------------------------------------------------------

Transition (most) Biocentric Functionally diverse; central to redox and catalysis

------------------------------------------------------------------

p-block Metalloid  Trace biological or environmental roles

------------------------------------------------------------------

Transition (noble) Noble gas Minimal reactivity; rare biologically; useful in medicine

For the first time I can get my head around the roles of metals and nonmetals in biochemistry.

[Jess Tauber]

Don't forget the less universal role of some of the rare earth elements in eubacterial biochemistry, and there the particular element isn't so important as the size of the ion.  I've speculated that initially even more of the periodic system was utilized during the transition to life from non-life. We know, for example, that oxygen was only the latest in a sequence of electron acceptors, and the Okolo atomic pile fossil deposit in Western Africa shows that early life (how many species, though?) was capable of using nuclear reactions as an energy source- and remember that some of the nuclear isomeric transitions involve the emission of electrons directly from these nuclei. So the trajectory of life has been a) to utilize less of the system generally, in the direction of lighter elements that also happen to be more common environmentally, and also more stable against nuclear decays. Early earth was likely far more surfacially radioactive than today, as those elements with half-lives (since their creation in stellar explosions or collisions) had not yet had time to decay to the point of nearly vanishing isotopic abundances.  I've speculated that the coordination chemistry of rare-earth and transition metals could have substituted for the more nuanced enzymatic biochemistry lifeforms have currently. And let us not forget that in the evolution of complex lifeforms, such as eukarya, also involve the elongation of proteins to include regulatory domains not present in more primitive forms, as well as much more involved stereochemistry of said proteins.

Looks like a grand conspiracy to me (even if not spiritual), much like the numerical trends in the PT and the nuclear shell systems (all that Pascal Triangle math, and the Leibniz Harmonic Triangle, etc.).

Jess Tauber

[Jess Tauber]

One would hope that these properties might be geometrically assorted in the depictions of the periodic system, as a means of distinguishing better ones from worse.

Also, note https://en.wikipedia.org/wiki/Trace_element

Jess Tauber

[Rene]

On 16 Jun 2025, at 23:26, in the Re: Biocentric nonmetals thread, Jess Tauber <tetrahed...@gmail.com> wrote:

Also, note https://en.wikipedia.org/wiki/Trace_element

I seem to have stumbled upon a pleasing three-flavoured perspective on the biocentric nonmetals, as per the attached image, and am wondering how others see this.

1. The acronym SeSPONCH, for selenium, sulfur, phosphorus, oxygen, nitrogen, carbon, and hydrogen, not only captures these seven elements but also echoes “seasponge,” often cited as one of our most ancient animal relatives. Thus: "Life begins with a SeSPONCH". 🤪

2. The seven symbols appear in reverse atomic number order, adding a touch of natural elegance, as if evolution left a mnemonic clue embedded in the very fabric of life’s chemistry.

3. The seven elements show a top down 1–2–4 pattern that reflects their roles in sustaining life: one trace element (Se), two "quantity" elements (S and P), and four abundant organic elements (O, N, C, H).

This cascading sequence mirrors the flourishing of life: from catalytic nuance to structural diversity to foundational abundance. Thus:

1 → Selenium: a trace element, catalytic and regulatory, a subtle but essential participant

2 → Sulfur and phosphorus: the “quantity” elements, central to energy transfer (ATP) and protein structure

4 → Oxygen, nitrogen, carbon, hydrogen: the basic organic elements, forming the bulk of biomolecular scaffolding.

After this, one only needs to recall metalloids, halogen nonmetals, and noble gases, and the nonmetals are down pat. Furthermore, the corresponding sets of metals fall into place too, effectively yielding a PT in "Eight Easy Pieces".

4. Threes are seen in:

• the triangle;
• the three layers;
• the 1-2-4 sequence; and
• the three domains of life.

The triangle appears very nice to me, as both a teaching tool and a conceptual framework, ready for presentation, publication, or sharing with educators and students alike.

René

PS. The atomic number sums of the three tiers follow a subtle symmetry: the difference between the top two layers (34 – 31 = 3) is the square root of the difference between the bottom two layers (31 – 22 = 9). Whether this is coincidence or chemical poetry is left to the reader (so to speak).

[Jess Tauber]

Some would call chemical poetry mere 'numerology' (but then the bulk of physics could also take that moniker. Don't forget that in the early prebiotic earth, after the Late Heavy Bombardment delivered scads of metallic elements to the surface of the planet (much probably radioactive from supernova nucleosynthesis), a lot more of the PT was probably involved in the development of early life than we give credit for. There were no large proteins yet to do all the specific catalytic and transportation work they currently do inside cells. Probably no coherent genetic (or other) codes either. But the coordination compounding behavior of many metal atoms, chelation, etc. played (at least in my mind) a supporting role here, being able to hold reactants closely together. Besides lightning (re Miller-Urey) energy sources here possibly also included UV from the young sun (no ozone to block it in our atmosphere yet), surface radioactivity (rather higher than today) as well as giant water waves crashing on shores. Later as many of the metallic elements settled out of the water column they became much less available to help catalysis along, and that is where I believe growing peptide chains and inorganic functional groups became indispensable. We traded the multiplicity of simpler substances present in the early prebiosphere for many fewer more complex forms (proteins) whose basic parts were much more common (in linguistic terms we traded paradigmaticity for syntagmaticity).

Jess Tauber

tetrahed...@gmail.com

[Larry T.]

That triangle is missing at least one major ingredient: iodine, the heaviest element that is essential for life.

Best Regards,

V. "Larry" Tsimmerman

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[ERIC SCERRI]

I like it!

Eric Scerri

On Jul 28, 2025, at 4:50 AM, 'Rene' via Periodic table mailing list <PT...@googlegroups.com> wrote:

On 16 Jun 2025, at 23:26, in the Re: Biocentric nonmetals thread, Jess Tauber <tetrahed...@gmail.com> wrote:

Also, note https://en.wikipedia.org/wiki/Trace_element

I seem to have stumbled upon a pleasing three-flavoured perspective on the biocentric nonmetals, as per the attached image, and am wondering how others see this.

<PastedGraphic-8.png>

1. The acronym SeSPONCH, for selenium, sulfur, phosphorus, oxygen, nitrogen, carbon, and hydrogen, not only captures these seven elements but also echoes “seasponge,” often cited as one of our most ancient animal relatives. Thus: "Life begins with a SeSPONCH". 🤪

2. The seven symbols appear in reverse atomic number order, adding a touch of natural elegance, as if evolution left a mnemonic clue embedded in the very fabric of life’s chemistry.

3. The seven elements show a top down 1–2–4 pattern that reflects their roles in sustaining life: one trace element (Se), two "quantity" elements (S and P), and four abundant organic elements (O, N, C, H).

This cascading sequence mirrors the flourishing of life: from catalytic nuance to structural diversity to foundational abundance. Thus:

1 → Selenium: a trace element, catalytic and regulatory, a subtle but essential participant

2 → Sulfur and phosphorus: the “quantity” elements, central to energy transfer (ATP) and protein structure

4 → Oxygen, nitrogen, carbon, hydrogen: the basic organic elements, forming the bulk of biomolecular scaffolding.

After this, one only needs to recall metalloids, halogen nonmetals, and noble gases, and the nonmetals are down pat. Furthermore, the corresponding sets of metals fall into place too, effectively yielding a PT in "Eight Easy Pieces".

4. Threes are seen in:

• the triangle;
• the three layers;
• the 1-2-4 sequence; and
• the three domains of life.

The triangle appears very nice to me, as both a teaching tool and a conceptual framework, ready for presentation, publication, or sharing with educators and students alike.

René

PS. The atomic number sums of the three tiers follow a subtle symmetry: the difference between the top two layers (34 – 31 = 3) is the square root of the difference between the bottom two layers (31 – 22 = 9). Whether this is coincidence or chemical poetry is left to the reader (so to speak).

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ERIC SCERRI

UCLA

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[Jess Tauber]

Re Larry's comment about iodine, I'm not sure it is vital to all living organisms. I know that it is often taken up by algae (which is a good dietary source), but what its function is in algae I couldn't tell you. In vertebrates it is used in the production of thyroid hormone (IIRC)- invertebrate animals (SFAIK) don't HAVE thyroid glands, so don't need the stuff, unless someone here knows better. And re Eric's 2 (re phosphorus), don't forget its role in information encoding, per the phosphate links between adenosinated nucleotide bases.  

Jess Tauber

tetrahed...@gmail.com

[Larry T.]

AI says: Iodine is crucial for the health of invertebrates, particularly in their growth and molting processes. Many invertebrates, such as shrimp, require iodine to successfully molt. A deficiency can lead to issues like opaque coloration and increased mortality during molting.

 It kills bacteria, though.

Best Regards,

V. "Larry" Tsimmerman

email: ora...@gmail.com

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[mavorte1]

A fascinating topic. Although I developed a periodic spiral, I'm actually a biochemist, so this subject really resonated with me.

I decided to create a variation of the previous design, adding a pair of ears. Instead of using purely French colors, I chose to blend French and Spanish colors. Beyond these fun choices, I’ve included my more scientific reasoning below the representation.

The first change I made was to reorder the elements so that lighter ones are positioned in the bottom-left corner and heavier ones in the top-right. This mimics the standard orientation of a typical graph, where the origin (0,0) lies at the bottom-left. At the same time, it retains the familiar left-to-right distribution of elements found in the traditional periodic table, even though I’m not the biggest fan of that layout.

I also updated the label “Quantity Nonmetals” to “Secondary Metals,” which aligns better with biochemical terminology.

Now, let’s talk about the trace metals and their “ears”.
Selenium is commonly found in all organisms, usually in the form of selenocysteine. But there are other trace elements that are important either in plants or animals:

- In plants, boron covalently binds to rhamnogalacturonan-II, and silicon to xyloglucan. In animals, these elements don't form covalent bonds with biomolecules, but they still interact with them, because we consume plants. Both boron and silicon are involved in signaling processes due to their interactions with carbohydrates. Boron can complex with SAM, NAD, and PIP/IP3 signaling molecules, while orthosilicic acid is involved in the PI3K and BMP-2 pathways, contributing to the synthesis of osteocalcin and collagen in bones.

- In animals iodine is well known for its role in the T3 and T4 thyroid hormones. Vertebrates have thyroid glands, while invertebrates, despite lacking a formal gland, still use these compounds and thyroid receptors. These hormones are formed via a covalent bond between the amino acid tyrosine and iodine, the least reactive halogen. This is no coincidence, the most reactive halogen available in nature, chlorine, is employed by immune cells (via myeloperoxidases) to chlorinate proteins and destroy pathogens. Nonetheless, inorganich chloride anion is essential to mantain osmotic balance.

What about bromine, which lies between iodine and chlorine in reactivity? Tyrosine bromination occurs in kidney basement membranes via peroxidasin, but also has been associated with inflammation, similar to chlorination.

And iodine in algae? They use inorganic iodide rather than organoiodine compounds, possibly for an antioxidant function.

I hope this offers a fresh perspective and specially helps clarify the biological role of iodine debated today.

Mario Rodríguez Peña

[Jess Tauber]

Bromine also is utilized by some (all?) salt-water algae, from what I've read.

Jess Tauber

tetrahed...@gmail.com

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[Mario Rodriguez]

You are correct. In algae, bromine is mainly present as the bromide anion, functioning similarly to iodide. It also forms various organic brominated compounds, such as bromoform, bromophenols, and brominated terpenes, which act as antimicrobial agents for defense. Algae also produce smaller amounts of organic iodine compounds (such as iodoform, iodophenols, and iodinated terpenes) with similar defensive functions. Additionally, algae can produce iodotyrosine, which can be used by marine invertebrates that lack a thyroid gland. Because the production of organic iodine compounds is relatively low, I wasn´t aware in my previous message. However, I have now decided to include both I and Br in the “animal ear”, which now also applies to algae.

I also found another important point. In animals, silicon is present as “silanolate bridges” bound to glycosaminoglycans. Therefore, Si should be moved to the central part of the diagram alongside Se.

While abundant elements are clear, trace ones are a more complex topic and sometimes it depends on the organism. To clarify, I am assuming that this representation only includes covalently bound elements. Otherwise, chlorine should also be considered, since chloride anions are essential for maintaining osmotic balance and function of various pumps, such as those in the kidneys and the stomach (for HCl production).

Mario Rodríguez Peña

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[mavorte1]

You are correct. In algae, bromine is mainly present as the bromide anion, functioning similarly to iodide. It also forms various organic brominated compounds, such as bromoform, bromophenols, and brominated terpenes, which act as antimicrobial agents for defense. Interestingly, algae also produce smaller amounts of organic iodine compounds (such as iodoform, iodophenols, and iodinated terpenes) with similar defensive functions. Additionally, algae can produce iodotyrosine, which can be utilized by marine invertebrates that lack a thyroid gland. Because the production of organic iodine compounds is relatively low, I wasn´t aware in my previous message. However, I have now decided to include both I and Br in the “animal ear”, which now also applies to algae.

I also found another important point. In animals, silicon is present as “silanolate bridges” bound to glycosaminoglycans. Therefore, Si should be moved to the central part of the diagram alongside Se.

While abundant elements are clear, trace ones are a more complicated topic and sometimes it depends on the organism. To clarify, I am assuming that this representation only includes covalently bound elements. Otherwise, chlorine should also be considered, since chloride ions are essential for maintaining osmotic balance and for the function of various pumps, such as those in the kidneys and the stomach (for HCl production).

Mario Rodríguez Peña

[mavorte1]

You are correct. In algae, bromine is mainly present as the bromide anion, functioning similarly to iodide. It also forms various organic brominated compounds, such as bromoform, bromophenols, and brominated terpenes, which act as antimicrobial agents for defense. Algae also produce smaller amounts of organic iodine compounds (such as iodoform, iodophenols, and iodinated terpenes) with similar defensive functions. Additionally, algae can produce iodotyrosine, which can be used by marine invertebrates that lack a thyroid gland. Because the production of organic iodine compounds is relatively low, I wasn´t aware in my previous message. However, I have now decided to include both I and Br in the “animal ear”, which now also applies to algae.

I also found another important point. In animals, silicon is present as “silanolate bridges” bound to glycosaminoglycans. Therefore, Si should be moved to the central part of the diagram alongside Se.

While abundant elements are clear, trace ones are a more complex topic and sometimes it depends on the organism. To clarify, I am assuming that this representation only includes covalently bound elements. Otherwise, chlorine should also be considered, since chloride anions are essential for maintaining osmotic balance and function of various pumps, such as those in the kidneys and the stomach (for HCl production).

Mario Rodríguez Peña

El lunes, 28 de julio de 2025 a las 23:57:52 UTC+2, tetrahed...@gmail.com escribió:

[Jess Tauber]

As I've written previously, I really do believe that initially far more of the periodic system was utilized in prebiotic and early biochemistry, both because of the relative availability of these materials in the ancient environment as well as their ability to help catalyze reactions and stabilize reactants spatiotemporally relative to each other (as with coordination compounding). Many of these elements ended up becoming far less accessible once the Late Heavy Bombardment of earth ceased, and many of these materials settled out of the water column. The Great Oxidation Event (where weakly oxidized iron precipitated out of the oceans and became (eventually) ore bodies probably removed the last conveniently available no-longer-standard elements, forcing early life to rely more and more on larger combinations of more common ones (CHON). I would predict that similar evolution would take place on other worlds where life has taken hold. Languages too show a similar pattern. It was discovered a couple of decades back that the languages with the smallest phonologies (the system of sounds used to generate meaningful strings of same) tended, at least statistically, to have the longest word roots, in terms of how many phonemes were in the average string. Conversely, those with the largest phonologies tend to have the shortest roots. A language in the Amazon has only SEVEN phonemes, while a click language from the Kalahari Desert in southern Africa has over One Hundred and Sixty. I've speculated that at the dawn of language evolution speakers made even larger numbers of distinct phonemes. Pushed to the extreme, a quantized series becomes effectively a continuum, which is the situation one often sees in animal communicative systems, where individual 'signs' come in a broad range of realizations rather than just one standard version, depending on context of use. As I mentioned in a recent thread, this kind of thing amounts to the distinction between paradigmaticity (that is how many basic combinable units you can substitute in strings) versus syntagmaticity (how long are your strings, and in what order do its elements appear?).

Jess Tauber

tetraher...@gmail.com

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[ERIC SCERRI]

Just to let you know that the 2nd edition of my 2012 book, 

A Tale of Seven Elements will be published on August 1st.

It includes a whole new chapter on the discovery of the rare earth elements and comes in paperback format.

[Rene]

On 28 Jul 2025, at 23:24, Larry T. <ora...@gmail.com> wrote:

That triangle is missing at least one major ingredient: iodine, the heaviest element that is essential for life.

Best Regards,

V. "Larry" Tsimmerman

Good to hear from you Larry.

AFAIK, the triangle isn’t missing anything.

This is because, as per the caption below the base of the triangle, it encompasses the seven nonmetals collectively found in macromolecules across the three domains of life.

AFAIK, iodine is not found in biological macromolecules. Nor is it a major ingredient of life: it's instead a trace element.

René

[Jess Tauber]

Actually, according to the wiki article on iodine in biology, a protein called thyroglobulin contains iodine. I think you'll agree that proteins count as macromolecules. I thought I'd remembered this from my undergraduate endocrinology class.

[Rene]

I happened to see this post in the middle of attempting to attend to various other items, and was immediately sucked in.

Jess: that’s an excellent observation. It’s good to stress-test things like The Triangle of Life.

Yes, thyroglobulin is a macromolecule.

No, iodine isn't found in macromolecules across the three domains of life. AFAIK iodine is biologically essential only in certain eukaryotes, notably vertebrates, where it's required for thyroid hormone synthesis.

Mario may wish to chime in here. Mario: I haven't yet had the time to consider your other thoughts on the Triangle.

René

[Mario Rodriguez]

Hi René,

Although, I answered these questions in my previous comments, I can blend the information in relation with your comments,

Iodine is present covalently bound in animals in T3 and T4 hormones, not only vertebrate with thyroid glands, but invertebrates also uses it and have thyroid receptors. They can generate it in other ways or take it from algae which can also produce iodotyrosine. Besides iodotyrosine, algae also produces iodoform, iodophenols, and iodinated terpenes with defensive functions. Additionally, bacteria and archaea can also produce methyliodide and some bacteria also iodotyrosines and iodophenols.

Bromine, has also implications in several realms. In animals, tyrosine bromination occurs in kidney basement membranes via peroxidasin for healthy funcion, In algae, they also produces iodoform, iodophenols, and iodinated terpenes with similar defensive functions. Methylbromide is produced also by bacteria and archaea, and some bacteria also bromophenols and bromopyrroles.

Terrestrial plants seem to be the only organisms not to have organic iodine and bromine compounds. Regarding chlorine, we must remember that, although it doesn´t form organic compounds in normal conditions, chloride anions are essential for maintaining osmotic balance and function of various pumps, such as those in the kidneys and the stomach (for HCl production). Chlorine is esential for any life, even though is not integrated in organic compounds. It´s the most reactive halogen available in nature, and for this reason is employed by immune cells (via myeloperoxidases) to chlorinate proteins and destroy pathogens.

Now, I want to remind silicon, in plants silicon binds to xyloglucan and in animals, silicon is present as “silanolate bridges” bound to glycosaminoglycans. it´s also involved  in the PI3K and BMP-2 pathways, contributing to the synthesis of osteocalcin and collagen in bones, although this signalling function doesn´t involve covalent bonds. The silica structures of diatoms and sponges are covalently bound to Ser and Thr of structural proteins.

In the case of boron, in plants covalently binds to rhamnogalacturonan-II. In animals, don´t bind covalently, but it can complex with SAM, NAD, and PIP/IP3 signaling molecules.

Abundant elements are clear, but trace ones are more complex to define and sometimes it depends on the organism. Additionally, a covalent bond is not neccesary to be essential for life.

Having all these in mind, I suggested some changes, that can also be discussed and changed:

- I reordered the elements so that lighter ones are positioned in the bottom-left corner and heavier ones in the top-right. This mimics the standard orientation of a typical graph, where the origin (0,0) lies at the bottom-left. At the same time, it retains the familiar left-to-right distribution of elements found in the traditional periodic table, even though I’m not the biggest fan of that layout.

- I changed the label “Quantity Nonmetals” to “Secondary Metals,” which aligns better with biochemical terminology.

- Si is involved almost in all realms and should be moved to the central part of the diagram alongside Se.

- I created 2 ears for elements that only affects some living beings "covalently" but not all: B in "plant ear", and Br and I in "animal and algae ear". Ears can be rearranged and more organisms included.

This email ended up longer that I wanted,

Mario Rodríguez Peña

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[Larry T.]

Regardless of the triangle, the fact is that iodine is the heaviest chemical element essential for vertebrates and invertebrates.

Best Regards,

V. "Larry" Tsimmerman, 

[ERIC SCERRI]

[Jess Tauber]

In the wiki piece I mentioned earlier (though it might have been another), it turned out that one or more of the enzymes producing iodine-containing hormones from thyroglobulin contained selenium. This makes me wonder whether it might be interesting and instructive to create internal links within the triangle showing such connections.  It's something linguists do all the time with regard to phrase and clause structure in syntactic analysis, including non-contiguous parts with links referred to as "traces".

[Rene]

On 30 Jul 2025, at 22:31, Larry T. <ora...@gmail.com> wrote:

Regardless of the triangle, the fact is that iodine is the heaviest chemical element essential for vertebrates and invertebrates.

Best Regards,

V. "Larry" Tsimmerman, 

Thanks Larry; I agree.

To include iodine meaningfully, the criterion could be reframed as "nonmetals essential for vertebrates and invertebrates", which yields:

• biocentric nonmetals (structural, universal across all domains of life); and
• some halogen nonmetals (functional, regulatory, often ion-based).

That broader grouping, though, tends to blur the line between structural foundations and physiological regulation, which is exactly why the SeSPONCH triangle remains useful: it highlights the core nonmetals embedded in the macromolecular architecture of life.

If the focus shifts to something narrower like “nonmetals essential for humans,” the distribution looks something like this:

Metalloids   Biocentric   Halogens   Noble metals

None         All          Some       None

The biocentric nonmetals clearly sit in the sweet spot: foundational, functionally diverse, and broadly retained.

Incidentally, selenium was only admitted to the club of essential nonmetals in the 1950s. There’s a good 2016 review titled “Why Nature chose selenium” with over 900 citations:

https://pubs.acs.org/doi/10.1021/acschembio.6b00031

It’s a little surprising that we still tend to hear so much about the CHONPS gang, overlooking selenium—with the result that the PT region between the metalloids and the halogen nonmetals is often treated as terra incognito. The SeSPONCH framework helps shine a light on this chemically rich but under-discussed zone.

Happy to hear any further thoughts you may have; this has been an engaging exchange.

René

PS: I’m behind in my responses to this thread, including to Mario.

[Mario Rodriguez]

Hi René,

I’d like to add to my previous comments that if you limit your classification to the essential elements found in biomolecules, you’ll notice that nearly all elements capable of forming covalent bonds are included. If you remove the strictly biological context and simply define the group as “covalent-bond-forming", characteristic of nonmetals, you are essentially describing the same set.

Regarding the halogens, the less reactive iodine and bromine can form covalent bonds in organic compounds (although they appear to be absent in terrestrial plants). Chlorine, being more reactive, primarily functions as the chloride anion, which is essential. Based on its concentration, it is classified as a secondary element rather than a trace element, and it fulfills its biological role without needing to form covalent bonds.

Noble metals, in most cases, cannot form covalent or any bonds, which explains their absence in biomolecules. As for the metalloids, I mentioned in my previous messages the roles of silicon and boron. Arsenic is largely avoided because it interferes with phosphorus. Germanium, antimony, and tellurium are simply too rare for life to depend on them.

Best regards,

Mario RP

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[Rene]

Hi Mario

Thanks for your examples of iodine, bromine, chlorine, silicon and boron across different biological systems. It seems to me like a reminder of how chemically inventive biochemistry can be.

However, the distinction I’m aiming to draw with the biocentric nonmetals (H, C, N, O, P, S, Se) isn’t based on whether other elements have biological roles: clearly many do. Rather, it's based on a dual criterion:

• covalent incorporation into biological macromolecules (not just small molecules or cofactors); and
• presence across all three domains of life i.e. archaea, bacteria, and eukarya.

To the best of my knowledge, only those seven elements (SeSPONCH) meet both criteria. The other nonmetals you mentioned certainly participate in important processes, sometimes even structurally, but their incorporation tends to be domain-specific, non-genetically encoded, or limited to regulatory or defensive functions rather than forming the macromolecular scaffolding of life.

So, while SeSPONCH may not cover all biologically active nonmetals, it highlights the ones with the deepest and most universal integration into life’s chemistry.

This framework is echoed in the biocentric periodic table presented by Remick and Helmann (2023), where CHNOPS elements are classified as essential for all life (Class i), and selenium is placed in Class ii — essential for many organisms across all three domains of life. This classification supports the core distinction of the biocentric nonmetals (H, C, N, O, P, S, Se): they are the only nonmetals collectively covalently embedded in biological macromolecules with evolutionary reach across archaea, bacteria, and eukarya. Elements like iodine, bromine, boron, and silicon appear in lower classes (iii or iv), reflecting their more limited, lineage-specific, or regulatory roles, consistent with the boundary between general biological activity and structurally foundational integration.

Remick KA, Helmann JD 2023, The elements of life: A biocentric tour of the periodic table, Advances in Microbial Physiology, vol. 82, pp. 1-127, https://pmc.ncbi.nlm.nih.gov/articles/PMC10727122/

I appreciate your perspective as a biochemist, and welcome any further thoughts, and apologise for any emails crossing the same territory before I have a chance to consider them.

René

On 30 Jul 2025, at 17:50, 'Mario Rodriguez' via Periodic table mailing list <PT...@googlegroups.com> wrote:

Hi René,

Although, I answered these questions in my previous comments, I can blend the information in relation with your comments,

Iodine is present covalently bound in animals in T3 and T4 hormones, not only vertebrate with thyroid glands, but invertebrates also uses it and have thyroid receptors. They can generate it in other ways or take it from algae which can also produce iodotyrosine. Besides iodotyrosine, algae also produces iodoform, iodophenols, and iodinated terpenes with defensive functions. Additionally, bacteria and archaea can also produce methyliodide and some bacteria also iodotyrosines and iodophenols.

Bromine, has also implications in several realms. In animals, tyrosine bromination occurs in kidney basement membranes via peroxidasin for healthy funcion, In algae, they also produces iodoform, iodophenols, and iodinated terpenes with similar defensive functions. Methylbromide is produced also by bacteria and archaea, and some bacteria also bromophenols and bromopyrroles.

Terrestrial plants seem to be the only organisms not to have organic iodine and bromine compounds. Regarding chlorine, we must remember that, although it doesn´t form organic compounds in normal conditions, chloride anions are essential for maintaining osmotic balance and function of various pumps, such as those in the kidneys and the stomach (for HCl production). Chlorine is esential for any life, even though is not integrated in organic compounds. It´s the most reactive halogen available in nature, and for this reason is employed by immune cells (via myeloperoxidases) to chlorinate proteins and destroy pathogens.

Now, I want to remind silicon, in plants silicon binds to xyloglucan and in animals, silicon is present as “silanolate bridges” bound to glycosaminoglycans. it´s also involved  in the PI3K and BMP-2 pathways, contributing to the synthesis of osteocalcin and collagen in bones, although this signalling function doesn´t involve covalent bonds. The silica structures of diatoms and sponges are covalently bound to Ser and Thr of structural proteins.

In the case of boron, in plants covalently binds to rhamnogalacturonan-II. In animals, don´t bind covalently, but it can complex with SAM, NAD, and PIP/IP3 signaling molecules.

Abundant elements are clear, but trace ones are more complex to define and sometimes it depends on the organism. Additionally, a covalent bond is not neccesary to be essential for life.

Having all these in mind, I suggested some changes, that can also be discussed and changed:

- I reordered the elements so that lighter ones are positioned in the bottom-left corner and heavier ones in the top-right. This mimics the standard orientation of a typical graph, where the origin (0,0) lies at the bottom-left. At the same time, it retains the familiar left-to-right distribution of elements found in the traditional periodic table, even though I’m not the biggest fan of that layout.

- I changed the label “Quantity Nonmetals” to “Secondary Metals,” which aligns better with biochemical terminology.

- Si is involved almost in all realms and should be moved to the central part of the diagram alongside Se.

- I created 2 ears for elements that only affects some living beings "covalently" but not all: B in "plant ear", and Br and I in "animal and algae ear". Ears can be rearranged and more organisms included.

<The Eared-Triangle of Life.png>

This email ended up longer that I wanted,

Mario Rodríguez Peña

[Jess Tauber]

Another set of parallels between elements utilized in biochemistry, genes, and languages- all these complex systems utilize a set of recombinable primitives to create functional units, and all apparently split these functions into two major sets. In languages we recognize the distinction between content words and functional words. In languages like Chinese, which have no bound morphology (that is, units which modify the meaning of the primitive units), function words are themselves full words and not prefixes, suffixes, or clitics. In the genetic system we have content genes which actually code for things like proteins, using the ribosomal translational complex, versus functional genetic material (which more and more appears to be largely housed in the so-called 'junk' DNA portion of chromosomes. Much of this is ancient 'defanged' retroviruses that have been repurposed to help regulate when, where, and how the content genes get utilized. Like Yin and Yang, OTOH, there is a little bit of the other in each of the two sets. That is, there are short stretches of regulatory material built into the content DNA, and content DNA still hiding within the regulatory DNA.

And now with the elements used in biochemical processes, we also have the split between content (structural) versus regulatory- often depending on whether or not covalent or ionic habits dominate.

We can further nuance these parallels- In human languages, we have the subfield of 'typology', where different parts of the structures and functions of the languages are more or less elaborated or reduced (often in complementary distribution)- A language like Chinese, mentioned above, has almost no morphology whatsoever, with almost all of the lexical elaboration either being through word compounding or phrasal/clausal. At the other end of the continuum we have so-called polysynthetic languages, like Cherokee (Tsalagi) or Inuktitut (an Eskimo language), where unbound, free forms are held to a minimum, and single phonological words are composed of all sorts of pieces, both content and regulatory. Most languages fall somewhere in between these extrema.

In genetic systems as well, we see major subdivisions. In prokaryotic organisms, such as eubacteria or archaea, there is generally a single chromosome of circular shape, where the genes that are functionally linked (for instance coding for different parts of the same complex protein) are all together in the string of DNA, serially. There are generally no gene-internal divisions ('split genes') in prokaryotes, so that the RNA transcript copied from the DNA is faithful to the latter and requires no elaborate editing. What you see is what you get. Eukaryotes (organisms with nucleated cells) have the split-gene motif for most proteins (circa 60%, IIRC). RNA transcripts off these then get variably edited (pieces of the intervening segments removed and the remainder stitched back together and then moved to the ribosomal translation system. So one underlying split gene is sometimes capable of producing, in the end, dozens or hundreds of slightly different protein products, each tailored to a specific environment of use. We have parallels to that for business products, adjusted to the needs of buyers.  And at the other end of the continuum we have viruses and viroids, whose genomes have been whittled down to such an extent that the only structures coded for are protein sheaths (viruses) that act like transport and entry vehicles for infecting hosts, or none at all (viroids) that basically hitch a ride into the host alongside normal viruses. The bulk of the genes in the usual sorts of viruses are used to make proteins that have regulatory function inside host cells so as to produce more virus. There ARE giant viruses that incorporate host genes (sometimes quite a few), but nobody is yet sure what that is all about.

Now, what sort of facts could parallel these but for the elements? Some are used primarily structurally but with a minor regulatory component, or vice versa?

Jess Tauber

tetrahed...@gmail.com

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[Rene]

On 31 Jul 2025, at 17:17, Mario Rodriguez <mavo...@yahoo.es> wrote:

Hi René,

I’d like to add to my previous comments that if you limit your classification to the essential elements found in biomolecules, you’ll notice that nearly all elements capable of forming covalent bonds are included. If you remove the strictly biological context and simply define the group as “covalent-bond-forming", characteristic of nonmetals, you are essentially describing the same set.

Regarding the halogens, the less reactive iodine and bromine can form covalent bonds in organic compounds (although they appear to be absent in terrestrial plants). Chlorine, being more reactive, primarily functions as the chloride anion, which is essential. Based on its concentration, it is classified as a secondary element rather than a trace element, and it fulfills its biological role without needing to form covalent bonds.

Noble metals, in most cases, cannot form covalent or any bonds, which explains their absence in biomolecules. As for the metalloids, I mentioned in my previous messages the roles of silicon and boron. Arsenic is largely avoided because it interferes with phosphorus. Germanium, antimony, and tellurium are simply too rare for life to depend on them.

Best regards,

Mario RP

Hi Mario

Thanks for your addition. I agree with your earlier comment: about this being a fascinating topic, especially given your role as a biochemist. I find it interesting from a taxonomical perspective.

Addressing your comments, it appears that the essential elements found in biomolecules are H, C, N, O, P, S, Se, Cl, Br, I, B, and Si. These 12 elements are all nonmetals (or metalloids) capable of forming covalent bonds with at least some other nonmetals. The set of 12 includes the biocentric nonmetals, three halogen nonmetals, and two metalloids.

If the biological context is removed, Ge, As, Sb, and Xe may be added to the group, as these three metalloids and one noble gas are also capable of forming covalent or polar covalent compounds with at least some nonmetals.

However, as I see it, neither the biologically derived set of 12 elements nor the expanded set of 16 has as much taxonomic utility as the more established groupings of metalloids, biocentric nonmetals, halogen nonmetals, and noble gases. These four categories seem especially useful in chunking the nonmetals of the PT into chemically meaningful sets, this being a challenge that has long accompanied this region of the table (aside from the halogen nonmetals and the noble gases).

I am curious as to how do you see all of this now?

René

P.S. For the metalloids Sb and Te, Remick & Helmann (2016) count them as having biological roles whereas Ge lacks such a role. Do you disagree?

[Rene]

Jess, Larry, Mario, Julio

Thanks; I appreciate your observations, queries and challenges.

To my mind, the Triangle is representative of "simplest sufficient complexity" i.e. these are the seven nonmetals collectively found in biological macromolecules, across the three domains of life, no more no less.

While it is true that B, Si, Cl, Br and iodine have biological roles, this is not the case in a macromolecular sense across all three domains, AFAIK.

Of course, one could augment the triangle with add-ons for these nonmetals but I think this detracts from its main point, which was to show the organisational poetry of the set of seven biocentric nonmetals.

A related benefit of the triangle is that it suggests that, in periodic table terms, the nonmetals mostly located between (to the left) the metalloids and (to the right) the halogen nonmetals do indeed have a collective identity rather than being traditionally referred to as leftover "other" nonmetals due to them seeming to have no unifying theme.

I mentioned another benefit in that the triangle is visually appealing, as both a teaching tool and a conceptual framework, ready for presentation, publication, or sharing with educators and students alike.

I’ve attached an AI-generated image of the associated mug, complete with spelling mistakes and omissions. The latter aside, the triangle strikes me as the kind of thoughtful, elegant science communication that looks good and sparks curiosity. I suggest it’s the kind of mug that a lot of scientists would not be displeased to sip from.

René

[Mario Rodriguez]

Hi René,

Because I'm travelling I may spend more time to reply.

I feel the name "biocentric nonmetals" seems to have a broad meaning, as if it includes all important nonmetals important to life. But the real meaning is quite tailored:

- They need to be covalently incorporated, this way you exclude a secondary element as Chlorine.

- It needs to be incorporated in macromolecules, not small molecules, nor cofactors, nor structural ones (which are indeed macromolecules). And the don't have to be limited to regulatory or defensive functions.

- And presence across all three domains of life. This way a lot of trace elements are excluded.

You also mentioned that they are not genetically encoded, and I would like to remind Selenocysteines are not genetically encoded either. Selenocystein is a proteinogenic amino acid but they are incorporated in the stop codon UGA with a special mechanism. 

Hence, I feel it's a quite tailored definition to reach the desired elements for a broad name as "biocentric nonmetals". Someone may feel chlorine is not central for all life when indeed it is, just doesn't fit in the aforementioned criteria. Most halogens participates in living beings as explained earlier, and also some metalloids.

Also, "triangle of life" may be a too ambitious name as well. I think it may be the triangle of macromolecules according to previous definition. Life needs more elements and not always covalently bound, not to mention all metal cations we are not considering because we are talking about nonmetals.

Regarding your question: For the metalloids Sb and Te, Remick & Helmann (2016) count them as having biological roles whereas Ge lacks such a role. Do you disagree?

I don't disagree but Sb and Te have a very limited role in biology because they are scarce. There's one author that proposes another layer of classification, "ultratrace elements", which I recommend: https://onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291520-670X%281998%2911%3A2/3%3C251%3A%3AAID-JTRA15%3E3.0.CO%3B2-Q

I sometimes feel we as humans are reluctant to accept nature is complex and we need to simplify to understand nature. That's not a bad thing as long as we don't oversimplify.

My recommendation is, if you want just a name for this set of elements, maybe a less ambitious name as "biocentric" or "tree of life" would be adequate. And if you actually want a real representation of elements important for life, the "tree of life" is a bit oversimplified and would need to incorporate more elements properly categorised.

Mario RP

[Jess Tauber]

Fluorine? See https://en.wikipedia.org/wiki/Fluorinase and https://en.wikipedia.org/wiki/Biological_aspects_of_fluorine. I wonder whether fluorine is utilized in any other types of biomineralization other than apatite-based ones.

Jess Tauber

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[Rene]

On 1 Aug 2025, at 23:48, Jess Tauber <tetrahed...@gmail.com> wrote:

Fluorine? See https://en.wikipedia.org/wiki/Fluorinase and https://en.wikipedia.org/wiki/Biological_aspects_of_fluorine. I wonder whether fluorine is utilized in any other types of biomineralization other than apatite-based ones.

Jess Tauber

Thanks Jess.

Fluorine isn't known to be essential to any organism.

Here’s the relevant part of Remick and Helmann (2023):

Fluorine is not known to be essential for any organism and is noted primarily for its toxicity (Johnston & Strobel, 2020). Nevertheless, F may have beneficial roles in some bacteria, plants, and animals and is therefore class (iv) [i.e. beneficial to at least some species]. In human biology, F helps strengthen the apatite mineral that makes up tooth enamel, which decreases dental caries (Aoun et al., 2018). Dietary sources of F can include tea, seafood, fluoridated toothpaste, and drinking water.

https://pmc.ncbi.nlm.nih.gov/articles/PMC10727122/

René

[Jess Tauber]

Flourinase, based on the diagram in the wiki article, is a pretty elaborate protein structure, exhibiting a n-mer composition as well as alpha helices. Not the sort of thing you'd expect unless it's products played some significant function.  That this enzyme can also catalyze chlorine-carbon bonds suggests a more general use, the way that most seventh last period rate earth ions can be cofactors in certain bacterial enzymes. Might it also work on bromine and iodine as well?

[Jess Tauber]

I sent the last reply through my phone, which autocorrected LST to 'last' and rare to 'rate'. And AI is supposed to take over our jobs??

Jess 

tetrahed...@gmail.com

[Rene]

Thanks Jess

Looking at this 2024 open access article...

"Reasons why life on Earth rarely makes fluorine-containing compounds and their implications for the search for life beyond Earth"

https://www.nature.com/articles/s41598-024-66265-w#Sec3

...I conclude that F is essential in rare cases.

The list of nonmetals regarded as being essential to at least some forms of life appears to be fifteen i.e. four metalloids (B, Si, Sb, Te), the seven biocentric nonmetals, and the four halogen nonmetals.

René

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[Jess Tauber]

Not that it matters in real life, but in the Star Trek: The Next Generation film entitled First Contact a Borg cube's smaller spherical escape pod manages to slip by the Enterprise through some sort of temporal vortex into Earth's past, so that in the present all life on the planet is now Borg, and the atmosphere contains significant amounts of fluorine. But then again, in the same movie it is established that Borg implants can cause significant skin irritation, and later in the film, after the ship has followed the sphere into the past (just before the first warp flight) and the Borg start taking over the ship, the Holographic Doctor, activated just to keep the Borg distracted while crew escape Sickbay, offers them a soothing cream as they try (unsuccessfully) to inject him with nanoprobes and assimilate him. I don't know what biological (or cybernetic, for that matter) role fluorine is supposed to play here, but us normal folks won't appreciate the chemical insult much.

Jess

[Mario Rodriguez]

I share with you the aforementioned review on ultratrace elements. It's from 1998 so it may miss some last discoveries but it's still a good review and can answer some questions.

Mario RP

To view this discussion visit https://groups.google.com/d/msgid/PT-L/CAO6d3h%2BQmtdusUbX0TCxrL2Dcwd%3DO0e1UjE7JRb%2B50f4dH%3DLKw%40mail.gmail.com.

[Jess Tauber]

I wonder whether, besides ultratrace elements, whose chemical identity is essential for their function, if any, the ISOTOPIC identity might also have some role.  We know, for example, that very light isotopes, such as deuterium, can inhibit certain reactions in cells and throw coordination out of whack, killing the cell ultimately if there is a too large concentration of D2O rather than H2O. Heavier element isotopes will have less discrepancy at least mass-wise and so one would expect effects to be felt only at even higher relative concentrations, but are there processes in living cells that are sensitive even here to such differences?

Jess Tauber

[Mario Rodriguez]

Hi Jess,

If I remember well, the kinetic isotope effect is only noticeable in hydrogen isotopes. Basically because the increase in mass is huge, deuterium is double mass than protium. Heavier isotopes vibrate slower so the bonds are stronger. If deuterium makes stronger bonds then is less reactive and cannot support life. However, when the element is heavier, the increase of 1 neutron doesn't change total mass that much, so the reactivity is considered similar. The increase in atomic weight is going to be the same regardless concentration. Indeed, in biochemistry isotopes labelling is used to mark biomolecules, assuming the isotopes have the same chemical behaviour in biochemical reactions.

Mario RP

[Rene]

Thank you Mario.

I intended for the name "biocentric" to refer to the nonmetals central to life i.e. those nonmetals found in the biological macromolecules which form the scaffolding of life.

Chlorine does not meet this criterion, as far as I can see. Without the biocentric nonmetals there would be no life for chlorine to interact with in the first place.

I didn't start out by looking for all of these tailored properties. I knew that CHNOPS represented the six most common elements in living organisms. I was then curious as to the status of Se. Cockell (2019), in The Equations of Life: How Physics Shapes Evolution, discussed the role of CHNOPS in being spread through life. He noted that Se was found in selenocysteine, the so-called 21st amino acid of life. From there I discovered the biological macromolecule theme linking CHNOPS and Se, and the fact that all seven nonmetals were essential across the three domains of life. It then took quite a while to come up with the biocentric nonmetals name. This is far better then the traditional term "other nonmetals", as if the nonmetals involved had been assigned to a taxonomical junkyard.

The metals of life would be irrelevant but for the Triangle of Life. We have known since the 19th century of the presence of CHON in all forms of life. It’s thus appropriate that they occupy the base of the triangle.

The threefold-flavour of The Triangle of Life is quite relevant given it takes three sides to make a structure.

Yes, Nature is complex and straightforward models such as these make it easier to grasp the basics. Such models are, I believe. widely present in most fields of science. From there, you can drill down into the details.

How do you see all of this now?

René

P.S. For the metalloids Sb and Te, Remick & Helmann (2016) count them as having biological roles whereas Ge lacks such a role. Do you disagree?.

[Rene]

I thought some metrics would be relevant to the question of parsing the nonmetals into categories.

The following table shows the atomic radii of the nonmetals, in picometres. 

               | Very small       | Small             | Intermediate                  | Largest            | Average

Category       | < 40 pm          | 40–80 pm          | 80–110 pm                     | > 110 pm           | (pm)

---------------+------------------+-------------------+-------------------------------+--------------------+---------

Metalloid      |                  | B^ 77.6           | As 100.1, Si 106.8, Ge 109    | Te 111.1, Sb 119.3 | 104

---------------+------------------+-------------------+-------------------------------+--------------------+---------

Biocentric     |                  | O 45^, N 52.1^,   | S 81, Se 91.8, P 91.9         |                    | 68.1

               |                  | H 52.9^, C 62^    |                               |                    |

---------------+------------------+-------------------+-------------------------------+--------------------+---------

Halogen        | F 39.6^          | Cl 72.5           | Br 85.1, I 104.4              |                    | 75.4

nonmetal       |                  |                   |                               |                    |

---------------+------------------+-------------------+-------------------------------+--------------------+---------

Noble gas      | He 29.1^         | Ne 35.4^          | Ar 65.9, Kr 79.5, Xe 98.6,    | Rn 109             | 69.6

               |                  |                   |                               |                    |

The figures are from Waber JT & Cromer DT 1965, Orbital radii of atoms and ions, Journal of Chemical Physics, vol. 42, no. 12, pp. 4116–4123 

Nearly all of the nonmetals have radii less than 110 pm. Antimony (Sb) and tellurium (Te), as is the case for nearly all metals, have radii > 110 pm. Nonmetals marked with a circumflex have smaller than expected radii.

It can be seen that the biocentric nonmetals have small to intermediate atomic radii, and the lowest average among the four subclasses. Since atomic radius correlates inversely with ionization energy, electron affinity, and electronegativity, as well as the energetics of bond formation, it would be expected that the biocentric nonmetals would have high values for the first three of these properties and be particularly energetic in nature. Yet this is not observed—the biocentric nonmetals, on a net basis, are more nonmetallic than the metalloids but less so than the halogen nonmetals, and the noble gases have some of the smallest the lowest radii of all. The latter would be expected to be the most chemically active of the nonmetals but for their filled valence shells, which make them largely reluctant to enter into chemical combination. The noble metals are likewise reluctant to react albeit for different reasons.

What is happening is that the lighter biocentric nonmetals namely hydrogen, carbon, nitrogen, and oxygen have smaller than expected atomic radii due to a lack of interelectron repulsions arising from electrons in lower occupied electron shells. That is to say, there is no 1p subshell for carbon, nitrogen and oxygen, and no zeroth shell for hydrogen. The net effect of the smaller radii is to increase the effective nuclear charge acting on the outer electrons of these biocentric nonmetals but not as much as would be expected if they had the commensurate effective nuclear charge in the first place. While smaller than expected radii also occur for boron, and for neon, boron is but one of six metalloids, and the latter two are but two of six noble gases, whereas hydrogen, carbon, nitrogen and oxygen are four of seven unclassified nonmetals. The overall nonmetallic character of the biocentric nonmetals is therefore as expected from their position in the periodic table between the weakly nonmetallic metalloids and the strongly nonmetallic halogen nonmetals.

René

[Mario Rodriguez]

Hi René,

My impression is biocentric means important for life and I understand not only macromolecules are important for life. If you say CHONPSSe are biocentric, it means that other nonmetals are not important for life, and that's not true as most of halogens and some metalloids participate as well. It also implies that if you create the label biocentric nonmetals, there should be a counterpart of biocentric metals with all the important metals for life.

Using the chlorine example (or chloride anions), you said "Without the biocentric nonmetals there would be no life for chlorine to interact with in the first place", the opposite is true as well, without chloride there won't be any life making macromolecules. So it's important too in a different way, and it's far more abundant in our bodies than selenium.

And then a true triangle of life should show all the important elements for life, nonmetals and metals, otherwise is a triangle of macromolecules.

You are making an equivalence that elements important for macromolecules are the only elements important for life. They are, but also other elements not involved in macromolecules. We also have a lot of ions and soluble compounds in our bodies essential for life 

Mario RP 

[Jess Tauber]

Re lack of chlorine-carbon bonds in biosynthetic pathways, consider the following: https://www1.udel.edu/chem/polenova/VHPO/BiosHalMetBact_AnnRevMicro_Pee1996.pdf

I'm guessing this sort of thing is a lot more common than folks may think.

As for fluorine, see https://pmc.ncbi.nlm.nih.gov/articles/PMC11227584/

Jess Tauber

tetrahed...@gmail.com

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[Rene]

On 3 Aug 2025, at 23:55, 'Mario Rodriguez' via Periodic table mailing list <PT...@googlegroups.com> wrote:

Hi René,

My impression is biocentric means important for life and I understand not only macromolecules are important for life. If you say CHONPSSe are biocentric, it means that other nonmetals are not important for life, and that's not true as most of halogens and some metalloids participate as well. It also implies that if you create the label biocentric nonmetals, there should be a counterpart of biocentric metals with all the important metals for life.

Using the chlorine example (or chloride anions), you said "Without the biocentric nonmetals there would be no life for chlorine to interact with in the first place", the opposite is true as well, without chloride there won't be any life making macromolecules. So it's important too in a different way, and it's far more abundant in our bodies than selenium.

And then a true triangle of life should show all the important elements for life, nonmetals and metals, otherwise is a triangle of macromolecules.

You are making an equivalence that elements important for macromolecules are the only elements important for life. They are, but also other elements not involved in macromolecules. We also have a lot of ions and soluble compounds in our bodies essential for life 

Mario RP

Thank you Mario.

The suffix -centric means “having a particular type of...thing as your most important interest” (Cambridge English Dictionary). Thus, biocentric nonmetals refers to those nonmetals that are most important to life. This is not to suggest that other nonmetals—such as Cl, I, or B—are unimportant. Rather, the key distinction lies between structural universality as the building blocks of life, and functional or regulatory significance.

Your point about a corresponding group of biocentric metals is well taken. These might reasonably include Mg, K, Ca, Mn through Zn, and Mo—metals with well-established roles in core biochemical processes. 

As for the name The Triangle of Life, I see it as a useful point of departure: a visual cue that highlights how certain nonmetals form the backbone of life’s molecular architecture, while others—though equally vital—serve to support and regulate that structure in complementary ways.

As a biochemist, you would appreciate that the central role of CHNOPS in life is widely recognized. NASA, for example, refers to them as life’s building blocks:

https://astrobiology.nasa.gov/education/alp/where-lifes-building-blocks-come-from/

By contrast, elements like chlorine, while essential in specific physiological roles, are not typically included among these core structural elements.

I’ve added selenium in recognition of its occurence in selenocysteine—sometimes called the 21st amino acid of life—giving us CHNOPSSe, or SeSPONCH.

From this perspective, the reactive nonmetals may be helpfully grouped as:

• Metalloids
• Biocentric nonmetals
• Halogen nonmetals

The term "biocentric nonmetals" is intended as a precise and meaningful way to characterize the elements in question, in the same what that e.g. the halogen nonmetals are characterised as salt-formers.

If you have any better suggestions for what to call the biocentric nonmetals could you please let me know.

René

[Jess Tauber]

In my CML tetrahedral models (all eight variations), only the p-block elements form a continuous ring around the equator of the tetrahedron, when said tetrahedron is oriented edge-on relative to a horizontally oriented reference plane. All other blocks are isolated.  I don't know if this has any significance beyond mere observation. 

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[Mark Leach]

Hi All,

If I remember correctly, C-3 and C-4 plants (which have different biosynthetic pathways) show a kinetic isotope effect with C-12 vs. C-13.

Mark

Mark Leach

meta-synthesis

To view this discussion visit https://groups.google.com/d/msgid/PT-L/2083950722.1781590.1754159199034%40mail.yahoo.com.

[Rene]

Would "polygen nonmetals" be better than biocentric nonmetals?

The polygen nonmetals—H, C, N, O, P, S, and Se—are those nonmetals most notable for generating a rich diversity of compounds and chemical functions, particularly within biological systems. Each brings a distinct set of valencies, bonding modes, and reactivities that together form the molecular fabric of life.

Carbon contributes unparalleled structural and bonding diversity; nitrogen, oxygen, phosphorus, and sulfur add polarity, reactivity, and functionality across a spectrum of oxidation states. Hydrogen, while simple, is universally present as a bond stabilizer and proton donor. Selenium, though rarer, plays a vital catalytic role in redox-active enzymes, with properties that surpass sulfur in resilience to over-oxidation. Its inclusion reflects not ubiquity but functional indispensability where life demands exceptional redox control.

In the quiet heart of matter, seven elements stir the drama of life.

Hydrogen, the patient spark, bonds where a single electron waits.

Carbon, the architect, spins webs of endless variety.

Nitrogen and oxygen bring tension and fire, polarity and breath.

Phosphorus lights the fuse of energy; sulfur tempers it with subtle force.

Selenium, the quiet sentinel, watches over redox storms with graceful resilience.

These are the polygen nonmetals—

not the loudest in weight or presence,

but the most generative,

weaving form, function, and fate from the elemental loom.

Cockell (2019, p. 206) wrote that, in broad terms, the four elements N, O, P and S are very good at forming a diversity of compounds with multifarious properties. That’s what got me going along this track.

René

Cockell C 2019, The Equations of Life: How Physics Shapes Evolution, Atlantic Books, London

[Mario Rodriguez]

Hi René

Sorry for my delay in reply but I'm travelling these days.

Answering your previous email, you have to make distinction in what are building blocks or important for macromolecules and what's important for life. All building blocks or important for macromolecules are important for life, but there are more things important for life.

Chlorine is not a building block but it's a secondary essential element. Its main action is in ionic form. Essential metals (biocentric metals if you want to call them this way) also act in ionic form. They don't participate in building macromolecules but they are essential.

Polygen could be a better name, although maybe a bit inespecific. If you make a portmanteau between biocentric and polygen, you can have a better one, biogen nonmetals. This way you are not saying these are the only important ones but you are saying these elements are the basis to generate life. There are more essential elements but these are the basis.

Regarding the triangle of life, it's linked to my previous reasoning. A true triangle or model of elements important for life would include more elements (nonmetal and metal) and it would be an interesting representation to develop. If the representation only contains the polygen/biogen elements, then it should be called in a more humble way, the triangle of macromolecules, the biogen triangle, etc

Mark, I haven't forgot your message. It's true there is a slight isotope kinetic effect favouring C-12 instead of C-13. After hydrogen, carbon is the lightest polygen/biogen atom. C-12 is a bit lighter than C-13, so it vibrates a bit more, it creates a slightly weaker bonds and it's slightly more reactive. But this difference is slight, not the difference found with hydrogen isotopes. Considering this effect slightly favours C-12 whose abundance is 99%, it doesn't affect the everyday life of plants. I don't know about differences between C-3 and C-4 plants in this regard. If you can share the paper, I would be glad to learn something new.

I hope all of this helps,

Mario RP

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[Jess Tauber]

https://en.wikipedia.org/wiki/Fractionation_of_carbon_isotopes_in_oxygenic_photosynthesis

Based on a brief scan of online papers/articles it seems that living organisms isotopically differentiate between all the light Triangle elements versus terrestrial abundances, Perhap all kinetic?

Jess Tauber

To view this discussion visit https://groups.google.com/d/msgid/PT-L/1307431595.3853678.1754503547399%40mail.yahoo.com.

[Jess Tauber]

Re isotopes, it is curious that the heaviest known stable isotope is Ca, with 20 neutrons as well as protons. This is interesting because from the perspective of the LST, Ca ends the fourth period out of eight, or in other words terminates the halfway point in the system re numbers of LS periods.  In my tetrahedral CML models, Ca also is the termination of the core tetrahedron surrounded by a jacket containing the last four LS periods.  Thus the end of equal numbers of neutrons and protons in the nucleus of a stable isotope ends as well halfway through the LST (period-wise) and at the filled state of the inner tetrahedral core of the CML model.

Jess Tauber

[Jess Tauber]

Another use for dietary lithium?

https://www.yahoo.com/news/articles/breakthrough-study-finds-alzheimer-could-091538126.html

Jess Tauber

[Rene]

I’ve been mulling upon referring to H, C, N, O, P, S, and Se as the macrogens.

The proposed name comes from the Greek makros (“large” or “long”) and -genēs (“producer of”). The “large” reflects their role in biological macromolecules, while the “long” refers to their ability to form homoatomic chains or rings—a phenomenon known as catenation.

In keeping with established names such as metalloids; halogens; and noble gases,  "macrogens" seem to offer a more versatile and descriptive term than earlier suggestions such as biocentric, polygen, or biogen nonmetals.

Details below.

René

Macromolecules. In biological systems, the macrogens occur in the covalent backbones or essential functional components of proteins, nucleic acids, and polysaccharides. While other elements may also occur in such structures, these seven are the most universally represented in the primary architecture and functional chemistry of macromolecules.

The electron structures of the macrogens enable the creation of stable bonds that can nevertheless be broken with sufficient ease to generate a high assortment of compounds useful to life. Thus:

“These elements have just the right atomic size and the right number of spare electrons to allow for binding to [one another] and…some other elements, to produce a molecular soup sufficient to build a self-replicating system.” (Cockell 2019, p. 212)

The size of selenium (as an outlying macrogen) and the behaviour of its electrons places it on the margin of being useful in many contexts. It nevertheless finds a specialised role, being included in the twenty-first amino acid of life, selenocysteine C3H7NO2Se. Selenium is the only essential dietary micronutrient that is genetically encoded in all domains of life. Being larger than sulfur it can: 

"…hand over its electrons more easily. This property plays a role in its ability to neutralize, if you will, the damaging free electrons in oxygen radicals. Once the selenium atoms have carried out this important function, they are more easily returned to their original state to carry out similar reactions. This reversibility, again because selenium can gain and lose electrons more easily than sulfur can, makes it useful in these roles." (Cockell 2019, p. 211)

Catenation. This is most prolific in carbon, whose ability to form stable, extended chains and rings underpins the structural diversity of organic chemistry.

Sulfur and selenium also form extensive chain and ring systems, with numerous allotropes featuring different ring sizes and chain lengths.

Oxygen catenation occurs in the well-known allotrope ozone (O3) and in compounds including peroxides R–O–O–R (where R is an element), ozonides (R–O–O–O), and higher oligomers such as hydrogen trioxide (H–O–O–O–H), proposed by Berthelot in 1880 and prepared in 1993 (metastable below −40 °C), and hydrogen tetroxide (H–O–O–O–O–H), suggested by Mendeleev in 1895 and characterized in 2011 below −125 °C.

While nitrogen is a reluctant player, long chains of it have attracted considerable attention in the research field of propellants, explosives, and gas generants. The longest known chain stops at eleven; compounds having five-membered nitrogen rings have been known since 1956. Lithium pentazolate (LiN5) is a five-ring nitrogen compound, only recently synthesized.

Red phosphorus can be viewed as a derivative of P4 in which one P–P bond is broken and an additional bond is formed with a neighbouring tetrahedron, resulting in chains of P21 molecules linked by van der Waals forces.

Hydrogen is the least prolific catenator in this group: the triangular trihydrogen cation (H3+) is thought to be one of the most abundant ions in the Universe, but belongs more to interstellar than terrestrial chemistry. Still, hydrogen shows unusual behaviour under extreme conditions—for example, a one-dimensional series of hydrogen molecules confined in a single-wall carbon nanotube is predicted to become metallic at 163.5 GPa, about 40 % of the ~400 GPa required for ordinary hydrogen metallization.

Analogous to group names such as pnictogen (“suffocation-producer”) and chalcogen (“ore-producer”), the defining properties of the macrogens are characteristic rather than exclusive. Just as gases other than nitrogen can cause asphyxiation yet only Group 15 elements are called pnictogens, other elements can form large or extended structures, yet only H, C, N, O, P, S, and Se are designated as macrogens.

Oher shared properties. The macrogens also have...

• associated biogeochemical cycles;
• a capacity to form interstitial or refractory compounds;
• applications in organocatalysis;
• involvement with luminal phenomena; and
• uses in combustion and explosives, and nerve agents

...suggesting they merit recognition as a discrete category of elements.

René

Cockell C 2019, The Equations of Life: How Physics Shapes Evolution, Atlantic Books, London.

[Jess Tauber]

From https://en.wikipedia.org/wiki/Cobalt_in_biology

Although far less common than other metalloproteins (e.g. those of zinc and iron), other cobaltoproteins are known besides B₁₂. These proteins include methionine aminopeptidase 2, an enzyme that occurs in humans and other mammals that does not use the corrin ring of B₁₂, but binds cobalt directly. Another non-corrin cobalt enzyme is nitrile hydratase, an enzyme in bacteria that metabolizes nitriles.^[6]

^{And I believe that vanadium (IIRC) is used in oxygen transport in some invertebrate lines.}

Jess.Tauber

tetrahed...@gmail.com

On Wed, Aug 20, 2025 at 9:20 AM Julio Gutiérrez Samanez <kut...@gmail.com> wrote:

Dear colleagues:

Since you're so immersed in biochemistry, how could we fail to consider cobalt, essential in the production of cyanocobalamin or vitamin B12, and zinc, essential in the production of the amino acid chains of the hormone insulin? 

Julio. 

Queridos colegas:

Ya que están tan inmersos en la bioquímica, cómo no considerar al cobalto, esencial en la producción de la cianocobalamina o vitamina B 12 y al zinc en la producción de las cadenas de aminoácidos de la hormona insulina. Julio

To view this discussion visit https://groups.google.com/d/msgid/PT-L/0D7FDDAD-1411-4295-8FB3-8E651145133E%40meta-synthesis.com.

[Jess Tauber]

See https://en.wikipedia.org/wiki/Hemovanadin

Jess Tauber

tetrahed...@gmail.com

[Jess Tauber]

Naturally occurring lithium in the brain- I don't know the URL of the original article, if any. https://www.yahoo.com/news/articles/breakthrough-study-finds-alzheimer-could-091538126.html

Jess Tauber

On Wed, Aug 20, 2025 at 10:22 AM Julio Gutiérrez Samanez <kut...@gmail.com> wrote:

This information is very interesting, although the discovery was made late. In 1955, an expedition of Cusco scientists to the Quero communities, led by anthropologist Dr. Oscar Núñez del Prado Castro, found that shepherds used khipus to keep track of their livestock. At least 10 khipus were described and drawn by Dr. Núñez del Prado in a pamphlet published by the University of Cusco and given to me by his son, the mathematical physicist and musician Wendell David Núñez del Prado Bejar. This proves the popular use of the khipu in Andean communities since ancient times.  However, it is important to use the latest science to verify the same thing by analyzing human hair from a five-century-old khipu:

: "The scientific team used an analysis of carbon, nitrogen, and sulfur isotopes present in the hair. These elements allow us to reconstruct an individual's diet, differentiating between high-prestige foods—such as meat or corn—and more common subsistence products, such as tubers and vegetables. The results were unequivocal. The person associated with the khipu consumed little meat and very little corn, staple foods in the diet of the elite."

JAGS

https://www.facebook.com/share/p/1CNC2Hq2DH/

Julio A. Gutiérrez Samanez 

[Julio Gutiérrez Samanez]

Dear colleagues:

Since you're so immersed in biochemistry, how could we fail to consider cobalt, essential in the production of cyanocobalamin or vitamin B12, and zinc, essential in the production of the amino acid chains of the hormone insulin? 

Julio. 

Queridos colegas:

Ya que están tan inmersos en la bioquímica, cómo no considerar al cobalto, esencial en la producción de la cianocobalamina o vitamina B 12 y al zinc en la producción de las cadenas de aminoácidos de la hormona insulina. Julio

El mar., 5 ago. 2025 6:42 a. m., Mark Leach <ma...@meta-synthesis.com> escribió:

To view this discussion visit https://groups.google.com/d/msgid/PT-L/0D7FDDAD-1411-4295-8FB3-8E651145133E%40meta-synthesis.com.

[Julio Gutiérrez Samanez]

This information is very interesting, although the discovery was made late. In 1955, an expedition of Cusco scientists to the Quero communities, led by anthropologist Dr. Oscar Núñez del Prado Castro, found that shepherds used khipus to keep track of their livestock. At least 10 khipus were described and drawn by Dr. Núñez del Prado in a pamphlet published by the University of Cusco and given to me by his son, the mathematical physicist and musician Wendell David Núñez del Prado Bejar. This proves the popular use of the khipu in Andean communities since ancient times.  However, it is important to use the latest science to verify the same thing by analyzing human hair from a five-century-old khipu:

: "The scientific team used an analysis of carbon, nitrogen, and sulfur isotopes present in the hair. These elements allow us to reconstruct an individual's diet, differentiating between high-prestige foods—such as meat or corn—and more common subsistence products, such as tubers and vegetables. The results were unequivocal. The person associated with the khipu consumed little meat and very little corn, staple foods in the diet of the elite."

JAGS

https://www.facebook.com/share/p/1CNC2Hq2DH/

Julio A. Gutiérrez Samanez 

El mié., 20 ago. 2025 8:31 a. m., Jess Tauber <tetrahed...@gmail.com> escribió:

[Mario Rodriguez]

Hi all,

This trend was originally about nonmetals in biochemistry. There are several metals involved in biochemistry. They usually act in ionic form and often with coordination bonds with organic backbones. As secondary Na, K, Ca and Mg (Cl would be the nonmetal in the secondary category I mentioned in my previous posts), and as trace ones Cr, Mn, Fe, Co, Ni, Cu, Zn, and Mo. Regarding V and Li, they are debated as ultratrace metals in humans.

But this would be a topic for a full representation of elements involved in biochemistry (whether human or universal),

Mario RP

To view this discussion visit https://groups.google.com/d/msgid/PT-L/CAO6d3hJ_UyXrrV%3Dgr%2BuLi%2Bq83%2BfQSGaZMZW5CcQJEBMCKO7%3D5Q%40mail.gmail.com.

Libre de virus.www.avast.com

[ERIC SCERRI]

Just published.

Website: http://www.ericscerri.com
PhilPeople https://philpeople.org/profiles/eric-scerri
Google Scholar https://scholar.google.com/citations?hl=en&user=8w1T5bEAAAAJ
ResearchGate https://www.researchgate.net/profile/Eric-Scerri

 

 

[Jess Tauber]

I've been updating myself on the proposed LUCA (Last Universal Common Ancestor) of living organisms (see https://en.wikipedia.org/wiki/Last_universal_common_ancestor). Given that all living cells exclude sodium and concentrate potassium within cells, I wonder whether the choice here was motivated more by existing chemical gradients in the world's early water bodies and less or random chance. By analogy, we know that several of the body's fluid systems have water solutes relatively close to what is found im sea water, and kidneys (as well as similar organ systems in other organisms) evolved for osmotic regulatory purposes to help maintain these balances. Could some of these gradients reflect the type of environment the earliest lifeforms evolved in? In the newsfeeds over the past few weeks stories about deep sea fluid seeps found with vast assortments of eukaryotes making a living off of chemosynthetic microorganisms it has been suggested that such places might be the sources of the first organisms on earth.

Jess Tauber

tetrahed...@gmail.com

[Jess Tauber]

In case this hasn't been posted previously: https://en.wikipedia.org/wiki/Molybdopterin

Jess Tauber

tetrahed...@gmail.com

[Mario Rodriguez]

Quickly answering your question, it is believed that the ionic composition of the cytoplasm reflects that of the ancient oceans where LUCA first emerged. Most of ion transporters are thought to have appeared when the composition of the seas began to change, allowing cells to maintain their internal ionic composition and thus remain alive.

Mario RP

To view this discussion visit https://groups.google.com/d/msgid/PT-L/CAO6d3hLnTpWy-FFBGbUSDcw-t5eBwiayRdmSTMD3nhLn0dL6BA%40mail.gmail.com.

[Rene]

I'd earlier written that:

"The acronym SeSPONCH—for selenium, sulfur, phosphorus, oxygen, nitrogen, carbon, and hydrogen—not only captures these seven elements but also echoes sea sponge, often cited as one of our most ancient animal relatives. Thus: Life begins with a SeSPONCH."

I now note that recent chemical evidence set out in an MIT study of 635-million-year-old rocks supports the view that ancient sea sponges were among the first animals on Earth, appearing well before the Cambrian explosion. Geochemists analyzed molecular 'fingerprints' in rocks from Oman, India, and Siberia, identifying sterol compounds—biomarkers—that closely match those produced by living sponges today. These chemical fossils, along with lab experiments and a 2009 discovery of a related 30-carbon sterol, strengthen the case that these filter-feeding organisms were early evolutionary pioneers.

https://www.newsweek.com/geologists-discover-earths-first-animals-sea-sponges-ediacaran-10804035

In the periodic table (extract attached), the bulk of the SeSPONCH nonmetals sit flanked by the metalloids to their left, the halogen nonmetals to their right, and the noble gases further beyond.

René

[ERIC SCERRI]

Thanks

Very interesting Rene!

Another 'tale of seven elements' in the making?

Eric

www.ericscerri.com

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<PastedGraphic-9.png>

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[Rene]

On 4 Oct 2025, at 07:59, ERIC SCERRI <sce...@g.ucla.edu> wrote:

Thanks

Very interesting Rene!

Another 'tale of seven elements' in the making?

Thank you Eric.

Perhaps so. The number seven seems to invite storytelling—whether it’s days, metals, or elements. In this case, the tale practically writes itself: seven nonmetals that bridge matter and life, chemistry and language.

On the last point, the SeSPONCH sequence could’ve been SeSPOAzCh 🤪 had nitrogen still been known as azote (“lifeless”)—a tangle of letters unpronounceable and lacking resonance with sea sponge.

Some of the story is found in the history of chemistry:

• CHON were recognised early on as being present in living organisms. I recall these four being referred to as organogens.
• Later, P and S were admitted to the club, giving rise to the sporadic acronyms CHONPS and CHNOPS.

Se hasn't traditionally been recognised as being on par with the big six due to its relatively low abundance in life. Nevertheless its involvement in a macromolecular sense across all three domains of life qualifies it. It otherwise ends up in kind of taxonomical limbo or is uncommonly recognised as a metalloid.

The broader issue, I think, is that the chemistry of these seven nonmetals is usually treated vertically, down the group “stove-pipes,” rather than across all of them. The all-encompassing connections have tended to be overlooked. 

The seven of them occupy a kind of transition zone, in terms of their chemical activity, between the metalloids and the halogen nonmetals. So the halogen nonmetals are quite active, the SeSPONCH nonmetals less so, and none of the metalloids are particularly noted for their chemical activity.

Quite interesting.

René

PS I'm still working on the knotty topic of the start and end of the f-block.