Polymer amide as a source of the cosmic 6.2 micron emission and absorption

TL;DR

This paper proposes that the cosmic 6.2 micron emission and absorption features originate from hemoglycin, a polymer found in meteorites, which forms lattice structures capable of producing the observed infrared spectral features.

Contribution

It introduces hemoglycin as a candidate carrier for the cosmic 6.2 micron band, linking laboratory spectra and astrophysical observations with a specific organic polymer.

Findings

Hemoglycin's amide I band at 6.04 microns aligns with the cosmic 6.2 micron feature.

Laboratory poly-L-lysine shows a similar absorption at 6.21 microns.

Calculated UV absorption of hemoglycin matches the 2175 Angstroms feature.

Abstract

Cosmic infrared emission and absorption spectra often carry a well-defined and invariant 6.2 micron band that has been proposed to emanate from very small dust grains that may carry polyaromatic hydrocarbons. Hemoglycin, a well-defined polymer of glycine that also contains iron, has been found in meteorites of the primordial CV3 class and therefore originated in the solar protoplanetary disc. In approximate calculations, the principal amide I infrared absorption band of hemoglycin is at 6.04 microns. Hemoglycin, an antiparallel beta sheet structure with two 11-mer glycine chains, has an exact structural analog in antiparallel poly-L-lysine beta sheets which in the laboratory have an absorption peak at 6.21 microns. This wavelength coincidence, the demonstrated propensity of hemoglycin 4.9nm rods to form accreting lattice structures, and its proven existence in the solar protoplanetary disc strongly suggest that the cosmic 6.2 micron emission and absorption could be from small grains that are hemoglycin lattices or shell-like vesicles carrying internal organic molecules of various types. Calculated hemoglycin ultraviolet absorptions associated with iron in the molecule match the observed ultraviolet extinction feature at nominal 2175 Angstroms.