Abstract
The unified 'electroweak' theory of the electromagnetic and weak nuclear interactions in physics predicts a small energy difference (ΔE(pv)) between the left- and right-handed enantiomers of chiral molecules. Thus, electroweak theory provides one of several possible explanations for the origin of biomolecular homochirality (nature's preference for L-amino acids and D-monosaccharides). Recent systematic electroweak quantum-chemical studies find ΔE(pv) to be an order of magnitude larger than previously anticipated, which has sparked renewed interest in the subject. The present paper addresses, for the first time, the question of the relative stability of certain possible prebiotic precursor molecules suggested in the work of A. Eschenmoser and co-workers: aziridine-2-carbonitrile (CH2NHCHCN) and oxirane carbonitrile (CH2OCHCN), also commonly referred to as 2-cyanoaziridine and cyan oxirane, respectively. The cis/trans-isomerization pathway of aziridine-2-carbonitrile is initially characterized by standard quantum-chemical techniques. At the highest level of theory employed, the trans-isomer is found to lie by 4.0 kJ mol-1 above its cis-counterpart. The transition state connecting the two is another 74 kJ mol-1 higher in energy. After including unscaled, harmonic zero-point energy corrections, these values change to 3.7 and 69 kJ mol-1, respectively. Using the multi-configuration linear response (MCLR) approach to electroweak quantum chemistry (R. Berger, M. Quack, J. Chem. Phys. 2000, 112, 3148), the energy difference between the enantiomers of the various compounds and transition structures has been computed within the random phase approximation, a special case of the general MCLR technique. (S)-Oxirane carbonitrile and the (R)-configurations of aziridine-2-carbonitrile are found to be energetically more stable than their mirror images at their equilibrium nuclear configurations. Use of a solvation model to approximate an aqueous environment has a modest, but consistent, effect on the computed parity-violating energies. In the present examples, solvation increases the magnitude of the parity-violating energy by ca. 10%.
Recommended Citation
R. Berger et al., "Electroweak Quantum Chemistry for Possible Precursor Molecules in the Evolution of Biomolecular Homochirality," Helvetica Chimica Acta, vol. 83, no. 8, pp. 1919 - 1950, Wiley, Sep 2000.
The definitive version is available at https://doi.org/10.1002/1522-2675(20000809)83:8<1919::AID-HLCA1919>3.0.CO;2-D
Department(s)
Chemistry
International Standard Serial Number (ISSN)
0018-019X
Document Type
Article - Journal
Document Version
Citation
File Type
text
Language(s)
English
Rights
© 2024 Wiley, All rights reserved.
Publication Date
12 Sep 2000
