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Molecular conformation of bilirubin from semiempirical molecular orbital calculations
Author(s) -
Shelver Weilin L.,
Rosenberg Harry,
Shelver William H.
Publication year - 1992
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.560440206
Subject(s) - dihedral angle , chemistry , hydrogen bond , molecular geometry , bond length , crystallography , molecular orbital , molecule , computational chemistry , diffraction , crystal structure , physics , optics , organic chemistry
Semiempirical methods were utilized in the computation of a fully optimized structure of bilirubin. Bond lengths and bond angles obtained using either AM1 or PM3 calculations showed excellent agreement with those obtained by X‐ray diffraction. This indicated that molecular orbital methods satisfactory reproduced the complex conjugation found in bilirubin. Dihedral angles of the crucial “hinge” and the dihedral angles of the propionic acid side chains agreed well with those found by X‐ray diffraction. Calculated hydrogen‐ bond parameters (distance and angles) showed substantial differences from experimental values, probably due to inherent weakness in the parameterization of the molecular orbital techniques. Conformational studies were carried out using AM1 by rotating the C9C10 bond in 5° increments showed that the most stable structure exhibited a minimum at about 125° and exhibited a structure similar to those postulated from X‐ray and NMR experiments. The hydrogen bonds showed remarkable tenacity during rotation of the C9C10 bond and resisted breaking until the molecule was under extreme strain. © 1992 John Wiley & Sons, Inc.