A Computational Investigation and the Conformational Analysis of Dimers, Anions, Cations, and Zwitterions of L-Phenylalanine

The structure and stability of various conformations of L-phenylalanine (PheN) and its zwitterions (PheZ), along with their ionized counterparts, cation (PheC) and anion (PheA), generated by adding and removing a proton respectively, have been investigated using first principle calculations in vacuum and in solution. This is followed by an extensive study on various possible dimer (PheD) conformations, which are noncovalently bound units without a peptide bond. This study results in 52, 31, 12, 9, and 11 minimum energy structures on the potential energy surfaces of PheD, PheN, PheC, PheA, and PheZ, respectively. Several important nonbonded interactions such as hydrogen bonds, NH-pi, CH-pi, OH-pi, and pi-pi interactions, which impart stability to the monomeric and dimeric units, have been analyzed. The capability and strength of the nonbonded interactions drastically changing the conformational orientations of monomeric units has been illustrated. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 33: 44-59, 2012