title: Systematic ab initio studies of the conformers and conformational distribution of gas-phase tyrosine.
abstract: A full structural assignment of the conformers of gaseous tyrosine is presented. A total of 1296 unique trial structures were generated by allowing for all combinations of internal single-bond rotamers and optimized at the B3LYP6-311G* level of theory and then subjected to further optimization at the B3LYP6-311++G** level. A total of 76 conformers are found and their dipole moments, rotational constants, and harmonic frequencies are determined. Accurate relative energies are given at the MP26-311G(2df,p)B3LYP6-311++G** level of theory. Characteristic H-bonding types are classified and listed for all the conformers. The four most stable conformers display an intramolecular H bond, COOH...NH(2), and an additional H-bonding interaction between the amino group and pi electron of the aromatic ring. The results further confirm that the global minimum conformations of the aromatic amino acids have the same H-bonding type. Combined with statistical mechanics principles, conformational distributions at various temperatures are computed and the temperatures with which the theoretical results match that of experiments are indicated.
authors.affiliation: Structure Research Laboratory, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Meiling
authors.initials: M
authors.lastname: Zhang
authors.forename: Zhijian
authors.initials: Z
authors.lastname: Huang
authors.forename: Zijing
authors.initials: Z
authors.lastname: Lin
mesh_terms: D005740:Gases; D008968:Molecular Conformation; D013057:Spectrum Analysis; D014443:Tyrosine / Q000737:chemistry*
chemical_list: D005740:Gases; D014443:Tyrosine