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 COO(-) 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.