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Electronic, vibrational, and electronic vibrational spectra of the 7-azaindole dimer, the 7-azaindole complex with a water molecule, and their tautomers are calculated. Transition states are considered based on the analysis of frequencies and shapes of low-frequency vibrations and the Mulliken charge redistribution. The performed quantum chemical calculation of chemical reactions enabled the determination of the structure of transition states and proton transfer conditions. It is shown that in the 7-AzI dimer the proton transfer has a consistent character with the formation of a zwitterionic form. The structure of excited states is calculated and the fluorescence spectra of the first electronic transitions that can be used as a criterion of the formation of 7-AzI tautomers as a result of chemical reactions proceeding through a proton transfer in the 7-azaindole dimer and the 7-azaindole complex with a water molecule are interpreted.

Conformational properties of a benzenesulfonic acid hydrazide molecule and its para -nitro and para -methyl derivatives, which have found wide application as porofors and biologically active compounds, are studied. It is found that the benzenesulfonic acid hydrazide molecule has six conformers with relative energies of 0//0 kcal/mol, 0.34//0.98 kcal/mol, 2.51//2.25 kcal/mol, 2.54//2.56 kcal/mol, 2.90//3.28 kcal/mol, 6.64//6.43 kcal/mol (MP2//DFT(B3LYP) with the cc-pVTZ basis set), each conformer has an enantiomer. Conformers differ from each other in the relative orientation of fragments of the -SO₂NHNH₂ group, energies of frontier orbitals, the direction and value of dipole moments. It is shown that the introduction of a nitro or methyl group into the para -position practically does not affect the conformational properties of the sulfonyl hydrazide group. A change in the structure of benzenesulfonic acid hydrazide in the crystal-gas transition is considered and it is revealed that in the crystal the conformation similar in structure to one of the high-energy conformers of the free molecule is stabilized. The NBO analysis of the electron density distribution is performed and it is shown that the occurrence of the gauche effect in all conformers of the molecules under study can be interpreted by the manifestation of the total action of strong anomeric effects between the lone pairs of nitrogen atoms and antibonding orbitals of S=O, N-H, C-S, and N-S bonds.

The Felbamate is a novel anticonvulsant and neuropathic pain drug that can exist as three possible tautomers. Herein, employing density functional theory (DFT) and handling the solvent effects with the PCM model, the structural parameters, energy behavior, natural bond orbital analysis (NBO), as well as the tautomerism of Felbamate are investigated. F1 is the kinetically and thermodynamically most stable tautomer of Felbamate, which contains the amide group in each of the carbamate moieties. The calculated NMR chemical shifts and IR vibrational frequencies are in good agreement with the experimental values, confirming the suitability of the optimized geometry for Felbamate. The tautomerization reaction of F1 to each of the other tautomers occurs via an intramolecular proton transfer. This reaction affects considerably the structural parameters and atomic charges of the Felbamate molecule. A large HOMO-LUMO energy gap implies a high stability of the F1 tautomer.

The structural and optical properties of 3-substitutedphenyl-1,5-diphenylformazans are studied by quantum chemical methods. The density functional theory (DFT) is employed to optimize the ground state geometries of formazans substituted with different electron donating and withdrawing groups in both gas and solvent phases. The absorption spectra of formazan derivatives are calculated using time dependent density functional theory (TD-DFT). The polarizable continuum model (PCM) calculations of 3-substitutedphenyl-1,5-diphenylformazans are performed for bulk solvent effects. The geometrical parameters, vibrational frequencies, and relative stabilities of isomers of 3-substitutedphenyl-1,5-diphenylformazans are studied. The results obtained by TD-DFT calculations reveal that the substitution of electron withdrawing and donating substituents affects the absorption spectra of 3-substitutedphenyl-1,5-diphenylformazans. The calculated maximum absorption wavelengths (λ_max) are highly consistent with the experimental values as found from UV-vis spectra.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most frequently prescribed drugs and have multiple therapeutic uses. These drugs are predominantly used for the treatment of musculoskeletal diseases because of their analgesic, antipyretic, and antiplatelet activities. Oxicams constitute an interesting class of organic compounds and have been investigated in the search for new analgesic and anti-inflammatory drugs. In the present work, a theoretical investigation of the molecular structure and spectroscopic properties of a series of five oxicams in different solvents was performed using density functional theory (DFT) methods. The geometric optimizations of the oxicams were carried out using the M06 density functional and the CBSB7 basis set. The infrared data were all obtained at the same theoretical level. The UV-Vis absorption and NMR data of some oxicams were calculated using the DFT and CBSB3 basis sets. The analysis of structural parameters, particularly the bond length and spectroscopic data, indicated that interactions occurred between the hydrogen bond types for 4-meloxicam, isoxicam, and normeloxicam. Stereoelectronic interactions caused by the substitution of alkyl groups caused the bond lengths to elongate. Similarly, the substitution of heteroatoms, such as nitrogen, sulfur, or oxygen, increased the bond lengths and angular stresses.

There are experimental evidences that in the methanol solution of glycyrrhizic acid (GA) and cholesterol in methanol, the cholesterol molecules have two different types of the environment. One corresponds to free molecules and another corresponds to the molecules associated with GA. However, the nature of these associates remains unclear. The all-atom molecular dynamics simulation of GA solutions in methanol is performed. It is shown that, on the contrary to aqueous solutions, GA in methanol does not form small stable clusters, including in the presence of cholesterol. The arising associates do not have distinct structures and exist for no longer than dozens of nanoseconds. The concentrations of these clusters and their stability constants are estimated. It is necessary to assume the existence of larger-scale associates to explain the experimental data.

A geometric optimization is performed for the neutral, zwitterionic, and protonated forms of pyridoxine in vacuum and in water with a solvent within the polarizable continuum model (PCM). The structural parameters are optimized for pyridoxine complexes in the neutral and zwitterionic forms with 4-10 water molecules. An analysis is performed of how the number of molecules of the solvent set by the model affects the agreement between the calculated and experimental NMR spectra.

Six new derivatives of perhydropyrimidine-2-ones obtained in a three-component system of urea, aromatic aldehydes, and dichloromethylacetylbenzoylmethanes are studied by single crystal X-ray diffraction. Molecules of the compounds studied have three chiral centers, but out of four possible diastereomeric pairs for each of compounds, the crystals of only one diastereomer are obtained, moreover, four of them crystallize as true racemates, two as racemic conglomerates. Crystals of five compounds are solvates with molecules of different nature (water, acetonitrile, dimethylformamide, dimethylsulfoxide). Crystals of the compounds studied are stabilized by both classical hydrogen bonds of N-H⋯O and O-H⋯O types and interactions of the С-H⋯O type.

The X-ray diffraction study of an indoline alkaloid of pseudokopsinine extracted from the plant Vinca erecta and its mono- and double salts is performed. The experimentally determined positions of Н atoms suggest the sp ³ hybridization of the indoline nitrogen atom in the base and salts. The pseudokopsinine base and double salt have an intramolecular Н bond between the NH group proton and the ether oxygen atom of the methoxycarbonyl group, which is absent in the monosalt and the related indolines. The intermolecular Н bonds and/or the packing efficiency cause a conformational change in F and Е heterocycles in the indoline hetero framework of pseudokopsinine salts in comparison with that observed in the base.

Schiff bases and their metal complexes have a number of biological activities such as antidepressant, analgesic, antimicrobial, antiviral, and antitumor. In the present studies, the 1-(( E )-(pentylimino)methyl)naphthalen-2-ol ligand is prepared by the reaction of 2-hydroxynaphthaldehyde with n -amyl amine. The ligand results in CoL₃, NiL₂ and CuL₂ complexes when reacted with the cobalt acetate, nickel acetate, and copper acetate salts respectively. The complexes along with their ligand are fully characterized by X-ray diffraction studies and biologically screened. The ligand structure reveals that it is a zwitterion species where the iminic nitrogen atom is protonated and the C-O bond shows a high double bond character. The cobalt complex has an octahedral geometry around the metal center and each nitrogen atom is in the trans position to the oxygen donor site. On the other hand, the copper complex shows a centrosymmetric square planar coordination, and in this case, the nitrogen sites are trans to each other. The complexes and the ligand are found to be more potent than the standard drugs used against some microbes in their preliminary biological studies.