G.A. Gamov

Stability of H-complexes of nicotinamide nitrogen heteroatom with water and ethanol in mixed solvents by 13C NMR probing

The formation constants of the nicotinamide H‐complexes with protonic solvents such as water and ethanol in aqueous dimethyl sulfoxide and aqueous ethanol were determined using 13C NMR data. Free Gibbs energy of nicotinamide donor center (nitrogen heteroatom) solvation was calculated. Gibbs energy of entire nicotinamide molecule solvation was shown to be antibate towards Gibbs energy of a pyridine nitrogen solvation. The solvation state of this molecule fragment must be taken into consideration when analyzing the reagents contributions in the thermodynamics of complexation. Copyright

Solvation peculiarities of nicotinamide in aqueous ethanol

The solvation state of biologically active provitamin PP, viz., 3-pyridinecarboxamide, was studied in a water-ethanol solvent by 1H and 13C NMR and IR spectroscopy. The resolvation of the N heteroatom was found to occur at an EtOH content of 0.05–0.25 molar fraction. The degree of conjugation of the carbamide group with the heterocycle changes with an increase in the ethanol concentration. The structures of aqueous and ethanol nicotinamide solvates were optimized by the B3LYP/6-311G(d,p) method. The 13C chemical shifts (GIAO) and the IR spectra were calculated.

Complexation of nickel (II) ion with B3 vitamin in aqueous dimethyl sulfoxide

AbstractThe stability change of nickel(II) ion complexes including one and two nicotinamide (B3 vitamin) molecules in aqueous dimethyl sulfoxide (XDMSO = 0–0.85 m.f.) was studied at 298.2±0.1 K and 0.25 ionic strength value (NaClO4) using the potentiometric method. The first stage constant of complexation increased until organic solvent concentration was 0.5 m.f. and reduced at higher DMSO content. The difference between complex and central ions solvation is a dominating contribution into the Gibbs energy change of mononicotinamide complex formation reaction. When the second ligand molecule was bonded into the coordination compound, the nicotinamide contribution to ΔtrGr rose and became prevailing at XDMSO = 0.7–0.85. The ligand was found to replace a water molecule in the coordination sphere of the cation according to spectrophotometric study results.

Structure of pyridoxine solvates in aqueous solution from quantum-chemical calculations and NMR spectroscopy

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.

Solvation of reagents in a silver(I)-nicotinamide coordination equilibrium in water-ethanol solutions, according to NMR data

The solvation state of nicotinamide in water-ethanol solvent is investigated by means of 1H and 13C NMR spectroscopy. It is found that the nitrogen heteroatom is resolvated at xEtOH = 0.05–0.25. The resolvation boundary of the silver(I) ion is determined by nuclear magnetic relaxation. The relationship between the structural and thermodynamic characteristics of the solvation of nicotinamide and the silver(I) ion is demonstrated.

Nicotinamide solvation state in aqueous dimethyl sulfoxide

The solvation state of biologically active compound vitamin B3, viz., 3-pyridinecarboxamide, in an aqueous-dimethyl sulfoxide solvent of a variable composition was studied by 1H and 13C NMR and IR spectroscopy. Below XDMSO −0.65 molar fraction, the solvation of the N heteroatom due to hydrogen bonds with water molecules weakens. At XDMSO > 0.65 molar fraction, almost no changes are observed in the solvate state of the N heteroatom. The 1H NMR spectra indicate that the degree of conjugation of the carbamide group with the heterocycle increases with an increase in the DMSO concentration. The structures of the dimethyl sulfoxide and mixed aqueous-dimethyl sulfoxide solvates of nicotinamide were optimized by the B3LYP/6311++(DP) method, and their 13C chemical shifts (GIAO) and IR spectra were obtained. According to the IR spectroscopic data, the number of hydrogen bonds involving the carbamide group decreases on going from H2O to DMSO.

Complexation between nickel(II), cobalt(III) and hydrazones derived from pyridoxal 5’-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids in aqueous solution

abstract The present work reports on stoichiometry, apparent stability constants of biologically relevant complexes of nickel(II), cobalt(III) with hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids at pH 7.4, T = 25.0 °C, I = 0.25 determined using UV-Vis spectroscopy. The thermodynamic constants of some complexes formation (NiL, NiL2, NiL2H) were estimated. Cobalt(II) ion was found to be oxidized to cobalt(III). Co(II) and Co(III) form low-spin state complexes. Hydrazones binding ability (pL0.5) in the medium mimicking biological ones towards Ni(II) and Co(III) was estimated. Graphical abstract

The Schiff bases of pyridoxal-5-phosphate and hydrazides of certain pyrazoles: Stability, kinetics of formation, and synthesis

The interaction of pyridoxal-5-phosphate with 3-methyl-1Н-pyrazole-5-carbohydrazide, 2-(3,5-dimethyl-1Н-pyrazol-4-yl)acetohydrazide, and 1Н-pyrazole-3-carbohydrazide has yielded Schiff bases; the products have been characterized by 1Н NMR and IR spectra. The binding ability of these pyrazoles with respect to pyridoxal-5-phosphate under conditions modeling the living tissues has been evaluated. Rate constants of the formation of the Schiff bases have been determined.

Synthesis and thermal analysis of a Ni(II) complex of nicotinamide

Nickel(II) bisnicotinamide sulfate was synthesized, isolated, and studied by means of FTIR spectroscopy, thermogravimetry, and differential scanning calorimetry with simultaneous mass-spectrometry analysis of pyrolysis products. The order the molecules are evolved from the coordination compound during thermal treatment is determined. The total heat effects of the processes involved in pyrolysis are estimated.