Conformations and Properties of the L-Tryptophyl-Containing Peptides in Solution, Depending on the pH-Theoretical Study vs. Experiments

The conformational preference and electronic properties of three L-tryptophyl-containing dipeptides, i.e., glycyl-L-tryptophane (H-Gly-Trp-OH), L-alanyl-L-tryptophane (H-Ala-Trp-OH), and L-methionyl-L-tryptophane (L-Met-Trp-OH) in solution depending on the pH of the media are studied both theoretically and experimentally. The effect of the protonation of the COOO- and deprotonation of the NH3+ as well as the alkaline hydrolysis of the amide fragment in a strong basic media on the electronic spectra are discussed. Ab initio and density functional theory (DFT) methods as well as the time-dependent DFT (TD-DFT) method as a function of the basis set are performed with a view to obtain the geometry and electronic properties of all of the species as well as the intermediate, obtained in the alkaline hydrolysis mechanism. (C) 2010 Wiley Periodicals, Inc. Biopolymers 93: 727-734, 2010.