title: Intrinsic conformational characteristics of alpha,alpha-diphenylglycine.
abstract: Quantum mechanical calculations at the B3LYP/6-31+G(d,p) level have been used to investigate the intrinsic conformational preferences of alpha,alpha-diphenylglycine, a simple alpha,alpha-dialkylated amino acid bearing two phenyl substituents on the alpha-carbon, in both the gas phase and aqueous solution. Nine minimum energy conformations have been characterized for the N-acetyl-N'-methylamide derivative within a relative energy range of about 9 kcal/mol. The relative stability of these structures is largely influenced by specific backbone...side chain and side chain...side chain interactions that can be attractive (N-H...pi and C-H...pi) or repulsive (C=O...pi). On the other hand, comparison with the minimum energy conformations calculated for alpha-aminoisobutyric acid, in which the two phenyl substituents are replaced by methyl groups, revealed that the bulky aromatic rings of alpha,alpha-diphenylglycine induce strain in the internal geometry of the peptide. Finally, a set of force-field parameters for classical Molecular Mechanics calculations was developed for the investigated amino acid. Molecular Dynamics simulations in aqueous solutions have been carried out to validate the parameters obtained.
authors.affiliation: Departament de Química, Escola Politècnica Superior, Universitat de Lleida, Spain. jcasanovas@quimica.udl.es
authors.forename: Jordi
authors.initials: J
authors.lastname: Casanovas
authors.forename: David
authors.initials: D
authors.lastname: Zanuy
authors.forename: Ruth
authors.initials: R
authors.lastname: Nussinov
authors.forename: Carlos
authors.initials: C
authors.lastname: Alemán
mesh_terms: D003198:Computer Simulation; D005740:Gases; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D009038:Motion; D011789:Quantum Theory; D012996:Solutions
chemical_list: D005740:Gases; D012996:Solutions; C405270:diphenyl glycine; D005998:Glycine