Interaction Enthalpy of Zinc Cation with Glycylglycine Dipeptide with DFT Calculation

In view to better understand the interactions of aminoacids and peptides with metallic cations, in the isolated state, the model system glycylglycine–Zn^2+ has been theoretically studied. Structures and energetic of complexes between glycylglycine dipeptide and zinc cation were investigated applying density functional theory (DFT). Zn^2+ cation was allowed to interact with different sites of glycylglycine and six stable isomers were obtained. Calculation for six different glycylglycine-Zn^2+ isomers were performed at BLYP and B3LYP level of theory using 6-31G* and 6-31G** basis sets. Relative energy calculations at different levels indicated that the most stable complex holds the structure, in which zinc cations are bound to the oxygen sites of carbonyl groups and the dipeptide of glycylglycine which acts as a bidentate ligand that has a structure of six-membered ring. Vibration frequency of most stable isomer is calculated by BLYP level and enthalpy, entropy and Gibbs energy of reaction was obtained.