Vibrational spectroscopic analysis of cyanopyrazine-2-carboxamide derivatives and investigation of their reactive properties by DFT calculations and molecular dynamics simulations

Abstract

Using density functional theory technique in the B3LYP approximation and cc-pVDZ (5D, 7F) basis set, the molecular structural parameters and vibrational wave numbers of two cyanopyrazine-2-carboxamide derivatives have been investigated. On the basis of potential energy distribution detailed vibrational assignments of observed FT-IR and FT-Raman bands have been proposed. Using molecular electrostatic potential map relative reactivities towards electrophilic and nucleophilic attack are predicted. The first and second hyperpolarizabilities are calculated and the first hyperpolarizability of the title compounds are greater than that of the standard NLO material urea. Molecular studies reveal that the predicted binding affinities of the best poses were −8.7 kcal/mol for BACPC, −9.0 kcal/mol for CBACPC, and −8.8 kcal/mol for the original inhibitor. Efforts were made in order to investigate local reactivity properties of title compounds as well. In order to do so we have calculated average local ionization energy (ALIE) surfaces, Fukui functions, bond dissociation energies (BDE) (within the framework of DFT calculations) and radial distribution functions (RDF) (within the molecular dynamics simulations). ALIE surfaces and Fukui functions gave us initial information on the site reactivity towards electrophilic and nucleophilic attacks. BDE indicated locations that might be prone to autoxidation mechanism, while RDF indicated which atoms of title molecules are having pronounced interactions with water.