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An ab initio molecular orbital study of hydrogen bonding and ion‐molecule association in model systems for DNA bases
Author(s) -
Del Bene Janet E.
Publication year - 1988
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.560340712
Subject(s) - protonation , chemistry , hydrogen bond , amide , ab initio , molecule , binding energy , amidine , hydrogen , proton affinity , crystallography , basis set , ab initio quantum chemistry methods , computational chemistry , ion , stereochemistry , density functional theory , atomic physics , organic chemistry , physics
Ab initio calculations have been performed to investigate hydrogen bonding and ion‐molecule association in complexes of H 2 O with the neutral, protonated, and Li + complexes of N ‐formylformaldehyde and N ‐formylformamidine. In the complexes with the neutral bases, H 2 O assumes an in‐plane bridging position in the amide and amidine regions. The most stable complex is the bridging N ‐formylformamidine–H 2 O complex in the amidine region, which has an MP 2/6–31 + G (d,p) binding energy of −9 kcal/mol. Hydrogen bonded complexes of H 2 O with the oxygen‐protonated bases have open structures with the protonated bases as proton donors, and binding energies ranging from −16 to −24 kcal/mol. Nitrogen protonation of N ‐formylformamidine leads to an equilibrium chelated hydrogen bonded structure with a stabilization energy of –21 kcal/mol. When Li + associates with these bases at a carbonyl oxygen, hydrogen‐bonded bridging structures with H 2 O reappear, and wobble complexes exist in the amide and amidine regions of N ‐formylformaldehyde and N ‐formylformamidine. These complexes have binding energies of –13 to –14 kcal/mol. However, the most stable comples has H 2 O directly bonded to Li + , with an MP 2 binding energy of –30 kcal/mol. No hydrogen bonded structures of H 2 O with N ‐formylformamidine exist in the amide region when Li + associates with this base at the CN group. Hydrogen bond energies computed at the single‐determinant Hartree–Fock level with the 6−31 G (d) basis set approximate correlated MP 2/6–31 + G (d, p) energies to within 1 kcal/mol for all of the neutral and charged complexes. However, when H 2 O is bonded to Li + , HF 6–31 G (d) association energies overestimate MP 2/6–31 + G (d, p) energies by 3 kcal/mol.