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Chiral 480 nm absorption in the hemoglycin space polymer: a possible link to replication - PubMed

  • ️Sat Jan 01 2022

Chiral 480 nm absorption in the hemoglycin space polymer: a possible link to replication

Julie E M McGeoch et al. Sci Rep. 2022.

Abstract

A 1494 Dalton hemoglycin space polymer of Glycine18 Hydroxy-glycine4 Fe2O4 termed the "core unit" is part of a polymer of Glycine, Si, Fe and O that forms tubes, vesicles and a lattice structure. It has been isolated from four different CV3 meteorites and characterized by mass spectrometry, FIB/SIMS and X-ray analysis. In quantum calculations (HF and DF wB97X-D 6-31G) the polymer has an absorption at 480 nm that is dependent on rectus "R" (= dextro D) chirality in a hydroxy glycine residue whose C-terminus is bonded to an iron atom. The absorption originates in the Fe II state as a consequence of chiral symmetry breaking. In confirmation of theory, measurements at Diamond Light Source UK, on crystals of hemoglycin derived from Acfer-086 and Sutter's Mill meteorites have shown a strong 483 ± 3 nm absorption that confirms the proposed location of hydroxy glycine residues within the polymer. A high 483 nm to 580 nm absorption ratio points to an "R" chirality excess in hemoglycin, suggesting that 480 nm photons could have provided the energy for its replication in the protoplanetary disc.

© 2022. The Author(s).

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1

Lattice form of the polymer built of modified core units, here at 1638 Da, linked by silicon atoms. The tetrahedral angles have been confirmed in X-ray scattering. Space filling model. Atoms: hydrogen white, carbon black, nitrogen blue, oxygen red, iron green, silicon pink. Spartan '20 Version 1.1.5 (220607) (Mac OS 12.5.1).

Figure 2
Figure 2

(a) (Top) UV/visible/IR spectra from the core polymer where the 4 hydroxy-glycine units all have ‘S’ (sinister/laevo S/L) chirality. There is no absorption at 480 nm. Graph axes: Vertical; calculated transition strengths on a log10 scale: Horizontal; wavelength (nm). The molecular model format is ball and spoke. Atom labels: hydrogen white, carbon black, nitrogen blue, oxygen red, iron green. (b) (Bottom) spectrum from the core polymer with an ‘R’ chirality hydroxy-glycine adjacent to an Fe atom at the peptide C-terminal. Spartan '20 Version 1.1.5 (220607) (Mac OS 12.5.1).

Figure 3
Figure 3

Correlation between transitions in Fe II (Fe+) and RPA calculated transitions for molecular cases with R(D) chirality hydroxy-glycine in C-terminal contact with Fe.

Figure 4
Figure 4

IR absorption from the core of Glycine18 Hydroxy-glycine4 Fe2O4. An absorption peak around 1651–8 cm−1 (6.0 µm), shown here at 1656 cm−1 is the typical “amide I” absorption for the backbone of the anti-parallel beta sheet. This IR spectrum is typical of the core and of the pared down conformers. Molecule format is ball and spoke. Atom labels: hydrogen white, carbon black, nitrogen blue, oxygen red, iron green. Spartan '20 Version 1.1.5 (220607) (Mac OS 12.5.1).

Figure 5
Figure 5

Sutter’s Mill crystal SM2 mounted in preparation for absorbance and diffraction measurements. Scale box at lower right 79.2 µm × 79.6 µm. Image taken by Diamond Light Source Beam line I24 by the beam line staff for JEMMc proposal MX31420.

Figure 6
Figure 6

Absorbance of SM2 crystal, with fitted curve (black). The exposure time was 8 ms and number of accumulations 500. No data filter was applied. Curve fitting via Igor Pro 8 of Wavemetrics Inc.

Figure 7
Figure 7

Cartoon of “core” replication process. Line molecular format. A peptide of 4 glycine units has started a replication and aligned to the core with a single glycine coming in to form an amide bond to make a 5-mer glycine. Hydrogen bonds in red. R/S labeling denotes chirality of hydroxy-glycine units. Spartan '20 Version 1.1.5 (220607) (Mac OS 12.5.1).

Figure 8
Figure 8

Sheets and tubes of hemoglycin in watch glass prior to crystallography loop pick-up. Scale bar 100 µm. Nikon E4500 camera mounted on a Leica MZ8 zoom Microscope.

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