Redox Diversity of Interstellar Compounds and Human Nutrients Reveals a Potentially Universal Chemical Constraint for Life

1. Introduction

Redox processes are central to biological organization, energy transduction, and homeostasis. Life on Earth depends on a finely tuned interplay between electron donors, electron acceptors, and molecules capable of switching between these states (amphoteric species). This triad enables controlled metabolic reactions, cellular signaling, and the maintenance of oxidative balance [1].

Understanding whether this redox architecture is a contingent feature of Earth’s biology or reflects a more universal chemical principle requires comparative analysis across different molecular populations. Interstellar molecular inventories represent the chemical environment that precedes and accompanies star and planet formation, including potential prebiotic precursors [2]. Nutrient molecules, by contrast, represent a set shaped by billions of years of biological selection. PubChem, with tens of millions of heterogeneous compounds, reflects chemically possible structures without biological or cosmological selection pressures.

By comparing these three molecular spaces, it becomes possible to identify chemical signatures shared between prebiotic cosmic chemistry and biological functionality—and to separate them from signatures of random chemical diversity.

2. Materials and Methods

2.1. Molecular Descriptors: AQVN and EIIP

The electronic-structure descriptors AQVN (average quasivalence number) and EIIP (electron–ion interaction potential) are used to characterize the redox properties of organic molecules. These parameters originate from the “general model pseudopotential” [3] framework and are mathematically defined as follows.

The EIIP value of a molecule is given by:

EIIP = 0.25Z * sin(1.04π Z*)/2π

(1)

where Z* represents the AQVN, calculated according to

Z* = Σ_i(n_i Z_i)/N

(2)

Here, Zi denotes the valence of the i-th element, ni is the number of atoms of that element, m is the number of distinct atomic species present, and N is the total atom count within the molecule. EIIP values derived from these equations are expressed in Rydbergs (Ry).

Molecular descriptors AQVN and EIIP have served as the foundation for studying diverse biological properties of proteins, DNA, and small molecules (with more than 400 peer-reviewed articles available at https://electronicbiology.org/biomedical-articles/).

In earlier work, we analyzed 4,510,644 randomly selected molecules from the PubChem database [4]. Of these, 90.4% exhibited EIIP values between 0.00 and 0.10 Ry and AQVN values ranging from 2.4 to 3.2. This predominant region of the EIIP/AQVN space was designated the basic chemical space (BCS), as it contains the great majority of known chemical structures.

Molecules positioned to the left of the BCS show enhanced electron-donor capacity and correspond to pro-oxidant species. In contrast, those located to the right of the BCS act as pro-reductants with strong electron-accepting properties. These two groups represented 4.3% and 5.3% of the analyzed PubChem compounds, respectively. Molecules falling within the BCS display amphoteric behavior, with moderate redox characteristics.

2.2. Overview of Data and Classification Scheme

Interstellar compounds encompassing 380 molecules detected across astrophysical environments (Dataset 1 and Dataset 2) [5,6], 225 human nutrient molecules (Dataset 3) [4], and >40 million compounds sourced from PubChem [7] were classified into three redox categories:

1.

Prooxidants—predominant electron acceptors

2.

Proreductants—predominant electron donors

3.

Amphoteric molecules—able to act as either donors or acceptors depending on context.

While the PubChem dataset is vast and heterogeneous, its inclusion provides a baseline representing “chemistry at large,” free of biological or cosmic selection.

3. Results

In the Interstellar and nutritional molecules show nearly identical redox distributions in the AQVN/EIIP space. The two datasets exhibit a remarkably similar redox composition (Figure 1):

• Interstellar compounds (Dataset 1):

  o

  Prooxidant: ~15.5%

  o

  Proreductant: ~41%

  o

  Amphoteric: ~43.5%

• Interstellar compounds (Dataset 2):

  o

  Prooxidant: ~19%

  o

  Proreductant: ~38%

  o

  Amphoteric: ~43%

• Human nutrients [4]:

  o

  Prooxidant: ~26.2%

  o

  Proreductant: ~31.8%

  o

  Amphoteric: ~42%

Despite their completely different origins—cosmic molecular clouds vs. biologically selected metabolites—the distributions converge on a nearly identical tri-modal structure dominated by amfoteric molecules but with substantial fractions of specialized redox donors and acceptors.

The PubChem dataset stands in sharp contrast (Figure 1):

• PubChem (≥40 million analyzed molecules):

  o

  Prooxidant: 4.3%

  o

  Proreductant: 5.3%

  o

  Amphoteric: 90.4%

This distribution reflects the unconstrained nature of synthetic and theoretical chemical diversity: most possible molecules do not adopt strongly polarized redox roles.

4. Discussion

4.1. Redox Diversity as a Universal Constraint on Functional Chemistry

The close alignment between interstellar chemistry and nutrient chemistry suggests that life did not emerge from a random subset of possible molecules. Instead, both cosmic prebiotic chemistry and biological evolution appear to favor a balanced redox diversity:

• Enough prooxidants to support electron transfer chains
• Enough proreductants to drive reductive synthesis
• A large class of amphoteric molecules for buffering, stabilization, and dynamic switching

Such a distribution likely facilitates:

• Redox cycling
• Energy dissipation
• Chemical self-organization
• Metabolic-like reaction networks even before the appearance of life.

This implies that the precursors of life may have been drawn from a chemically privileged subset of the interstellar molecular inventory rather than from planet-specific contingencies.

4.2. Why PubChem Differs: The Distinction Between “Chemically Possible” and “Chemically Functional”

PubChem’s extreme skew toward amphoteric molecules highlights that most theoretically possible compounds do not support the balanced redox roles required for biological organization. The comparison suggests that redox specialization is not random but selected—cosmologically and biologically.

Thus, chemistry compatible with life appears to be a tiny, highly structured subset of all possible chemistry. PubChem serves as a control dataset, illustrating the extent to which life-relevant chemistry diverges from chemical arbitrariness.

4.3. Implications for Astrobiology: Redox Distribution as a Universal Biosignature

A central implication of this analysis is the following:

If the redox distribution observed in interstellar molecules is universal, then any life elsewhere in the universe—if it is based on chemical processes—would likely require a similar redox architecture. This does not imply identical biomolecules (e.g., DNA, proteins). Rather, it implies that the underlying chemical logic of life is constrained by redox balance:

• electron transfer chains,
• donor–acceptor coupling,
• amphoteric buffering,
• maintenance of non-equilibrium systems.

Therefore, a balanced distribution of redox species within extraterrestrial molecular populations may serve as a functional biosignature—a chemical fingerprint indicating an environment capable of supporting life-like processes.

5. Conclusions

The comparative redox analysis of interstellar molecules, human nutrients, and the PubChem chemical universe reveals that:

• Interstellar and biological molecules share a highly similar redox landscape, despite their radically different contexts.
• The general chemical space is overwhelmingly amphoteric, lacking the redox diversity required for metabolic-like networks.
• This pattern suggests a universal chemical constraint: life depends on balanced redox specialization, not on arbitrary molecular diversity.
• If redox distributions in interstellar chemistry are universal, then life elsewhere in the galaxy would likely resemble Earth-life in its core chemical architecture, even if structurally distinct.

These findings open a new perspective on the chemical preconditions for life and suggest that redox diversity may be a powerful, quantifiable biosignature for astrobiological exploration.