DFT investigation of role of N - H⋯O and N - H⋯π interactions in the stabilization of the hydrogen bonded complexes of anisole with aromatic amines.

Theoretical investigations have been performed on hydrogen (H-) bonded complexes of two aromatic amines with anisole to investigate the effect of the methyl substituent on N - H⋯O and N - -H⋯π interactions. Natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) analyses were done to elucidate the nature of H- bonding. In 1:1 complexes, the total interaction energy of N-methylaniline complex is higher than that of aniline complex. The existence of bond critical point between N-H of amine and oxygen of anisole confirms weak hydrogen bonding. The energy decomposition analysis showed the role of CT in stabilizing complexes.

Harmonic analysis of vibrations of morpholine-4-ylmethylthiourea: a DFT, midinfrared and Raman spectral study.

The FTIR and FT-Raman spectra of morpholine-4-ylmethylthiourea (MMTU) were recorded in the region of mid-IR (400-4,000 cm(-1)). Initial geometry generated from the standard geometrical parameters was relaxed without any constraint on the potential energy surface at MP2 and DFT levels adopting the standard 6-31++G and 6-311+G basis set. With the help of two specific scaling procedures the computed harmonic frequencies have been compared with the observed vibrational wave numbers of FTIR and FT-Raman spectra and assigned to different normal modes of the molecule. Most of the vibrational modes have wave numbers in the expected range. The appropriate theoretical spectrograms of the IR spectra of MMTU have been also constructed.

Investigations on the fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene by certain flavonoids.

The fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by seven flavonoids namely flavone, flavanone, quercetin, rutin, genistein, diadzein and chrysin has been investigated in acetonitrile and dichloromethane solvents. The bimolecular quenching rate constants lie in the range of 0.09-5.75 x 10(9)M(-1)s(-1) and are explained in terms of structure of the flavonoids studied. The reactivity of flavonoids are in the order: quercetin>rutin>genistein>diadzein>chrysin>flavone>flavanone. The quenching rate constants (k(q)) increase with increase in the number of -OH groups. The endergonic thermodynamic values of DeltaG(et) reveal that electron transfer quenching mechanism can be ruled out. Bond dissociation enthalpy calculations reveal that the position of -OH is important. Further in vitro-antioxidant activities of flavonoids were evaluated with rat liver catalase by gel electrophoresis. The deuterium isotope effect thus observed in this work provides evidence for hydrogen abstraction involved in the quenching process of singlet excited DBO by flavonoids. The data suggest the involvement of direct hydrogen atom transfer (radical scavenging) in the fluorescence quenching of DBO. Bond dissociation enthalpy calculation performed at B3LYP/6-31G(p')//B3LYP/3-21G level are in excellent agreement with the above observations and further reveal that the number OH groups and position of them decide the quenching ability of the flavonoids.