Biochemistry & Organic Chemistry

The Role of the CuCl Active Complex in the Stereoselectivity of the Salt-Induced Peptide Formation Reaction: Insights from Density Functional Theory Calculations

By Keith Cowing
Status Report
Life
October 8, 2023
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The Role of the CuCl Active Complex in the Stereoselectivity of the Salt-Induced Peptide Formation Reaction: Insights from Density Functional Theory Calculations
(A) The proposed active complex proposed by Rode et al. (1990) for the SIPF reaction for a protonated and neutral alanine molecule [18]. (B) Another plausible SIPF active complex between two neutral alanine molecules in a cis configuration as proposed by Rimola et al. (2007) [20]. Here, cis refers to the relative position of the N (or equivalently O) atoms on the same side of the plane containing the Cu atom. In this figure, red denotes oxygen, blue denotes nitrogen, gray denotes carbon, light gray denotes hydrogen, orange denotes copper, and green denotes chlorine. — Life

The salt-induced peptide formation (SIPF) reaction is a prebiotically plausible mechanism for the spontaneous polymerization of amino acids into peptides on early Earth.

Experimental investigations of the SIPF reaction have found that in certain conditions, the l enantiomer is more reactive than the d enantiomer, indicating its potential role in the rise of biohomochirality. Previous work hypothesized that the distortion of the CuCl active complex toward a tetrahedral-like structure increases the central chirality on the Cu ion, which amplifies the inherent parity-violating energy differences between l- and d-amino acid enantiomers, leading to stereoselectivity. Computational evaluations of this theory have been limited to the protonated–neutral l + l forms of the CuCl active complex.

Here, density functional theory methods were used to compare the energies and geometries of the homochiral (l + l and d + d) and heterochiral (l + d) CuCl–amino acid complexes for both the positive–neutral and neutral–neutral forms for alanine, valine, and proline. Significant energy differences were not observed between different chiral active complexes (i.e., d + d, l + l vs. l + d), and the distortions of active complexes between stereoselective systems and non-selective systems were not consistent, indicating that the geometry of the active complex is not the primary driver of the observed stereoselectivity of the SIPF reaction.

Allison C. Fox, Jason D. Boettger, Eve L. Berger and Aaron S. Burton
Life 2023, 13(9), 1796; DOI: 10.3390/life13091796
https://www.mdpi.com/2075-1729/13/9/1796

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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