On the use of conformationally dependent geometry trends from ab initio dipeptide and oligopeptide studies in empirical peptide modeling

Abstract More than 600 structures of some 150 molecules are now available in the series “Ab Initio Studies of Structural Features Not Easily Amenable To Experiment”, maintained during the last decade by the structural chemistry group at the University of Arkansas. All structures were obtained by standard ab initio gradient procedures at the same computational level, HF/4-21G, because it was our intention to create a body of information that is internally consistent and allows for comparisons of similar parameters among different systems. In the recent past this work has found considerable utility in experimental studies of various types and, in special cases, to test calculations at lower levels. Specifically, geometry trends from 4-21G dipeptide studies were used to modify the parameters of CHARMM for empirical peptide conformational analyses. Various aspects of this procedure are discussed. Extensions of the ab initio geometry refinements to oli-gopeptides, specifically the N -formylpentaglycine amide, show the efficacy but also the limitations of the dipeptide model in peptide conformational analyses.

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