Space-filling efficiency and optical properties of hemoglycin (2507.10612v1)

Abstract: The empty, extensive low-density lattice topology of hemoglycin is examined to understand how in space, and possibly as early as 800M years into cosmic time a rod-like polymer of glycine and iron came into dominance. A central question to be answered is whether the hemoglycin rod lattice with diamond 2H symmetry represents the most efficient covering of space by a regular arrangement of identical rods. Starting from the tetrahedral symmetry of every hemoglycin lattice vertex we find that the regular truncated tetrahedron of Archimedes may be expanded until neighboring hexagon faces are coincident, at which point space filling is 23/24 or 95.8333% complete. We describe the unit cells of the diamond 2H rod lattice and its conforming near-complete space-filling structure, which has identical symmetry. Maximum space filling via a minimum of molecular material can allow hemoglycin to drive accretion in molecular clouds, contributing to the composition of dust, and providing a background for its widespread presence in meteoritic samples and in cometary material that falls to Earth. The optical properties of hemoglycin lattice entities are derived from quantum calculations of ultraviolet and visible transition energies and strengths. The hemoglycin extinction curve duplicates the nominal 218nm ultraviolet absorption feature known as the UV bump, together with two visible absorption features present in a generic compilation of astronomical extinction data.

• The paper demonstrates that hemoglycin’s diamond 2H lattice achieves 95.8333% space filling, suggesting its efficiency in cosmic dust accretion.
• Quantum calculations reveal that the hemoglycin lattice replicates key UV and visible absorption features, including the prominent 218nm UV bump.
• X-ray diffraction and geometric analysis confirm that hemoglycin’s structured rods form a nearly optimal trigonal lattice compatible with solar system elemental abundances.

Hemoglycin's Space-Filling Efficiency and Optical Properties

The paper "Space-filling efficiency and optical properties of hemoglycin" (2507.10612) explores the structural and optical characteristics of hemoglycin, a polymer of glycine and iron, to understand its prevalence in space, potentially dating back 800 million years into cosmic time. The paper investigates whether the diamond 2H symmetry lattice of hemoglycin represents the most efficient spatial arrangement of identical rods. By examining the tetrahedral symmetry at each lattice vertex, the authors demonstrate that a regular truncated tetrahedron of Archimedes can be expanded to achieve 95.8333% space filling. They derive the optical properties of hemoglycin lattice entities using quantum calculations, showing that the extinction curve replicates the 218nm UV absorption feature, along with visible absorption features found in astronomical extinction data.

Lattice Structure and Space-Filling Efficiency

The research details the unit cells of the diamond 2H rod lattice and its near-complete space-filling structure, which possesses identical symmetry. The authors propose that maximal space filling with minimal molecular material enables hemoglycin to drive accretion in molecular clouds, contributing to dust composition and explaining its widespread presence in meteoritic and cometary samples. X-ray diffraction of fiber-like crystals from Acfer 086 extracts revealed a characteristic length of 5nm, suggesting a planar lattice curved within the fibers. Physical forms at the Folch interphase indicated a 3D molecular lattice of hemoglycin rods, with 120° angles consistent with a trigonal lattice of the diamond 2H type. The paper found that the lattice volume enclosed per rod at N = 6 is 2.3 times less than at N = 4, suggesting more than sufficient rods converging at each vertex.

The diamond 2H lattice can be constructed by rotating each edge of the plane hexagons by an angle α around an axis in the hexagon plane, creating "puckered" hexagons linked by vertical rods. The volume defined by this lattice is maximized for $sin α = 1/3$, or $α = 19.471$ degrees, defining exact tetrahedral symmetry at every vertex.

Optical Properties and Extinction Curve

Quantum calculations of UV and visible transition energies and strengths were used to derive the optical properties of hemoglycin lattice entities. The calculations predict bound-bound absorptions between stable molecular states, specifically upward transitions from the ground electronic state. The hemoglycin extinction curve replicates the nominal 218nm UV absorption feature, also known as the UV bump, and two visible absorption features present in astronomical extinction data. The uniformity of the astronomical dust extinction curve, with its associated UV bump, has been notable, and the curve was observationally featureless until a pronounced peak in extinction was revealed at about 217nm.

Hemoglycin as a Component of Cosmic Dust

The paper tests the consistency of a large dust component of hemoglycin with elemental abundances. If the growth of the hemoglycin lattice has outstripped that of other lattice designs due to its space-filling efficiency, it would imply that hemoglycin lattices are a dominant dust component. This proposition aligns with available data if the open lattice contains a partial fill of small-molecule ices that fit the dust absorption and scattering spectrum of molecular clouds. The elemental composition of hemoglycin roughly matches solar system abundances, suggesting that a substantial fraction of dust in protostellar disks could be composed of hemoglycin.

Light Scattering and Extinction Cross Sections

Calculations of extinction cross sections for an empty hemoglycin lattice "ball" of 100nm radius reveal that the most prominent feature is the "bump" at nominal 220nm, which results from the interaction of an iron atom with the C-amino terminals of the attached glycine chains. The calculated extinction of hemoglycin dust balls has main absorption features that match astronomical data, with the UV bump and two subsidiary absorptions in the region of 480nm and 650nm appearing on both calculated and observed curves. The paper demonstrates that a diamond 2H lattice scatters light identically to a uniform isotropic sphere of material.

Conclusion

The paper (2507.10612) provides a detailed analysis of hemoglycin, demonstrating its efficient space-filling capabilities and its potential role as a significant component of cosmic dust. The calculated extinction curve of hemoglycin closely matches observed astronomical data, supporting the hypothesis that this molecule contributes to the UV bump and other absorption features in space. The paper highlights the importance of considering complex molecular structures like hemoglycin in understanding the composition and evolution of cosmic dust.