Büchi's model based analysis of local anesthetic action in procaine hydrochloride: Vibrational spectroscopic approach.

The drug action of ester type local anesthetic (LA) procaine hydrochloride (PRC HCl) is activated by blocking Na+ ion flow when it binds to the ion channel in the ligand gated sodium ion channel protein. Büchi's model, explains binding action of ester type LA drug with receptor in terms of charge transfer, dipole-dipole, hydrogen bonding and van der Waals interactions through lipophilic, ester and hydrophilic moieties. The present work investigates molecular structural and vibrational spectral features of para amino benzoate group, ester part and tertiary amino group respectively belonging to lipophilic, ester and hydrophilic moieties, accountable for the binding of drug to sodium channel. The electron transport mechanism through the ring responsible for structural deviation from benzenoid to quinonoid form and consequent dipolar nature of carbonyl group have been investigated, based on the analysis of XRD, DFT computed molecular structure, 8a ring mode and NBO charges. The characteristic UV absorption peaks and vibrational marker bands of LA drugs have been identified and the charge transfer interaction responsible for lipophilic binding has been investigated. The blocking of Na+ in the ion channel has been probed using attractive and repulsive energy profile. The molecular polarizability has been computed to substantiate the correlation between the structure activity relationship of LA drug molecule and molecular polarizability. The low toxicity of PRC HCl was evaluated using in vitro cytotoxicity study, confirming it as a potential short acting local anesthetic.

Spectroscopic analysis and charge transfer interaction studies of 4-benzyloxy-2-nitroaniline insecticide: a density functional theoretical approach.

A widespread exploration on the intra-molecular charge transfer interaction through an efficient π-conjugated path from a strong electron-donor group (amino) to a strong electron-acceptor group (nitro) has been carried out using FTIR, FT-Raman, UV-Vis, fluorescence and NMR spectra on insecticide compound 4-benzyloxy-2-nitroaniline. Density functional theory method is used to determine optimized molecular geometry, harmonic vibrational wavenumbers and intensities using 6-311G(d,p) basis set by means of Gaussian 09W program suit. A comprehensive investigation on the sp(2) to sp(3) hybridization and non-planarity property has been performed. Natural bond orbital analysis is used to study the existence of C-H⋯O, N-H⋯O and C-H⋯π proper and improper hydrogen bonds. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. A complete assignment of the experimental absorption peaks in the ultraviolet region has also been performed. Isotropic chemical shifts of (13)C, (1)H, (15)N and (18)O NMR and nuclear spin-spin coupling constants have been computed using the gauge-invariant atomic orbital method. The biological activity of substituent amino and nitro groups are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

DFT computation and experimental analysis of vibrational and electronic spectra of phenoxy acetic acid herbicides.

An absolute vibrational analysis has been attempted on the basis of experimental FTIR and NIR-FT Raman spectra with calculated vibrational wavenumbers and intensities of phenoxy acetic acids. The equilibrium geometry, bonding features and harmonic vibrational wavenumbers have been calculated with the help of B3LYP method with Dunning correlation consistent basis set aug-cc-pVTZ. The electronic structures of molecular fragments were described in terms of natural bond orbital analysis, which shows intermolecular O-H···O and intramolecular C-H···O hydrogen bonds. The electronic absorption spectra with different solvents have been investigated in combination with time-dependent density functional theory calculation. The pKa values of phenoxy acetic acids were compared.

Nonplanar property study of antifungal agent tolnaftate-spectroscopic approach.

Vibrational analysis of the thionocarbamate fungicide tolnaftate which is antidermatophytic, antitrichophytic and antimycotic agent, primarily inhibits the ergosterol biosynthesis in the fungus, was carried out using NIR FT-Raman and FTIR spectroscopic techniques. The equilibrium geometry, various bonding features, harmonic vibrational wavenumbers and torsional potential energy surface (PES) scan studies have been computed using density functional theory method. The detailed interpretation of the vibrational spectra has been carried out with the aid of VEDA.4 program. Vibrational spectra, natural bonding orbital (NBO) analysis and optimized molecular structure show the clear evidence for electronic interaction of thionocarbamate group with aromatic ring. Predicted electronic absorption spectrum from TD-DFT calculation has been compared with the UV-vis spectrum. The Mulliken population analysis on atomic charges and the HOMO-LUMO energy were also calculated. Vibrational analysis reveals that the simultaneous IR and Raman activation of the C-C stretching mode in the phenyl and naphthalene ring provide evidence for the charge transfer interaction between the donor and acceptor groups and is responsible for its bioactivity as a fungicide.

DFT computations and spectroscopic analysis of a pesticide: chlorothalonil.

NIR FT-Raman and IR spectra of the biologically active molecule, chlorothalonil have been recorded and analyzed. The molecular geometry and vibrational wavenumbers of the title compound in the ground state have been calculated by density functional theory (DFT) with 6-31G(d) basis set. In order to obtain the information about the influence of intramolecular interaction on the molecule, the calculated geometries of chlorothalonil molecule was compared with the experimental data. The results of the optimized molecular structure gave clear evidence for the intramolecular charge transfer (ICT). Time-dependent density functional theory (TD-DFT) calculation of the electronic spectra has been performed and compared with the experimental UV-visible spectrum. Mulliken's net charges have been calculated and compared with the atomic natural charges. The effects of chlorine and cyanide group substituent in benzene ring in the vibrational wavenumbers have been analyzed. NBO analysis is useful to understand the intramolecular hyperconjugative interaction between lone pair Cl and sigma*(C-C) bond orbital.