DFT-Based Study of the Intramolecular Interactions of Some Aminoglycosides

Quantum chemical modeling and full geometry optimization of sisomicin and gentamicin was carried out by the correlation functional B3LYP using augmented with polarization functions for heavy atoms 6-311G(d) and Dunning's correlation consistent cc-pVDZ basis sets. The effect of the basis set on the calculation results of molecular structure and quantum chemical descriptors of the titled compounds was studied. Special atten-tion was paid to the intramolecular NH...N, OH...N, OH...O, NH...O hydrogen bonds in sisomicin and gen-tamicin. According to theoretical calculations, the distances between hydrogen and acceptor atoms are slight-ly larger than a typical length due to a significant deviation of the intramolecular H-bonds from a linearity. To evaluate the extent of electron density delocalization from the lone pairs of atoms into the antibonding neigh-boring orbitals and inside H-bonds within the systems, NBO (Natural Bond Orbital) analysis was used at two levels of theory. The most intensive interactions between electron donor and electron acceptor in the struc-tures under consideration were determined and their delocalization energies were evaluated. Based on the ob-tained data, classical electrostatic nature of the weak H-bonds and conjugation effects stabilizing the mole-cules were suggested.