Ab Initio Study of the Geometry and Rotational Barrier of 4-Phenylimidazole.

摘要

The molecular design of several synthetic artificial enzymes, which mimic the action of the serine protease alpha-chymotrypsin, incorporates the phenylimidazole molecular fragment to play the role of the His-57 residue in the native enzyme active site. Study of these artificial enzymes by molecular modelling techniques requires accurate torsional force field parameters for the phenylimidazole inter-ring bond. This, in turn requires accurate characterization of the barrier to rotation around this bond. Previous semi-empirical calculations of this rotational barrier have neglected geometry optimization of the molecule at the points along the rotational pathway. The 4-phenylimidazole rotational barrier (5-16 kcal/mol) presented here was obtained by full ab initio geometry optimization at the 3-21G level at each of the points along the rotational pathway. (AW)