1408
Ab Initio Calculations on Large Molecules Using Molecular Fragments. Model Peptide Studies'" Lester L. ShipmanIb and Ralph E. Christoffersen*lc Contribution f r o m the Department of Chemistry, University of Kansas, Lawrence, Kansas 66044. Received July 27, 1972
Abstract: An ab initio procedure designed for the investigation of large molecules and based upon studies of molecular fragments is applied to prototype peptide systems. The molecules investigated include formamide, N-methylacetamide, and 2-formamidoacetamide, which were chosen as models of interactions that are expected along a peptide chain. The ability of the procedure to describe these systems is assessed by comparisons with experimental and other theoretical studies, and recommendations regarding the general applicability of the procedure to polypeptide characterizations are given.
T
he importance of a detailed understanding of peptide bonds and their interactions to many problems of biological interest has long been recognized. Consequently, a systematic characterization of prototype molecules which exhibit the kinds of interactions that are expected to be found in polypeptides is particularly appropriate. The obvious importance of such studies has given rise to a number of previous quantum-mechanical studies of peptide systems. Some of these have been ab initio studies,2-10while the majority have used more In approximate methods, mostly semiempirical. (1) (a) This study was supported in part by the University of Kansas and by grants from the National Science Foundation and the Upjohn Co., I
