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Hydrogen‐bonding effects, electrostatic potential, and the antitumor activity of flavone acetic acid and related compounds. III. Ab initio studies on the conformation space
Author(s) -
Fang JianYun,
Thomson Colin
Publication year - 1997
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/(sici)1097-461x(1997)62:1<97::aid-qua10>3.0.co;2-3
Subject(s) - hydrogen bond , chemistry , ab initio , computational chemistry , acetic acid , ab initio quantum chemistry methods , organic chemistry , molecule
Restricted geometry optimizations at the ab initio SCF level with the 3‐21G basis set were employed to investigate the conformation space of flavone acetic acid (FAA) and its related compounds. All the conformations are produced from a conformation which is, according to our previous work, probably the active conformation in terms of antitumor activity shown by these compounds. Detailed studies on FAA were carried out while only brief discussions are made on the analogs. The main results obtained are that (1) FAA is a very flexible molecule, e.g., with the energy barrier up to about 3 kcal mol −1 from the reference conformation, the important torsional angle τ 1 can change from 27.0° to 117.0°, τ 2 from −168.0° to 2.0°, and τ 3 from −50.0° to 30.0°; (2) the hydrogen‐bonding effect plays an important role in determining lower‐energy conformations; (3) among all the FAA conformations considered, some are active and some are inactive; (4) it seems that the analogs will have similar behavior to FAA when the torsional angle τ 3 is restricted to the values which are around the equilibrium values; and (5) the hypothesis put forward previously has been further developed in this work. Now, we postulate that efficient charge transfers will lower the energy and that proper charge transfers will activate the molecule. There are mainly two different types of charge transfer corresponding to two different types of conformation, which are specified in this article. © 1997 John Wiley & Sons, Inc.