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An MNDO molecular orbital study of the reactions of protonated oxirane with guanine
Author(s) -
Ford George P.,
Smith Christopher T.
Publication year - 1987
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560320810
Subject(s) - mndo , chemistry , protonation , molecular orbital , computational chemistry , transition state , guanine , photochemistry , molecule , organic chemistry , catalysis , ion , nucleotide , biochemistry , gene
Abstract The bimolecular hydroxyalkylation of the N 2 , 3‐, O 6 , and 7‐position of guanine by protonated oxirane has been studied using the MNDO molecular orbital procedure. The enthalpies of activation (relative to the isolated reactants) were calculated to be 12.5, 11.4, −4.8, and −4.9 kcal mol −1 , respectively. The transition state geometries were characteristically S N l‐like. The forming bonds reach ca . 0–2% of their final strengths while cleavage of the breaking bonds is ca. 77–87% complete. Their relative energies are dominated by electrostatic interactions between the reacting moieties with little to no charge transfer involved. The relevance of these results to the reactions of carcinogenic oxiranes and their derivatives with nucleic acids is discussed.