S. V. Dushina

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

Solvent effect of aqueous ethanol on complex formation and protolytic equilibria in nicotinic acid solutions

The protonation constants of nicotinate ion and the stability constants of iron(III) nicotinate complexes in aqueous ethanol were studied potentiometrically. The increasing ethanol proportion in the mixed solvent in general enhances the stability of complex species. Ultraviolet spectra were measured for nicotinic acid in solvents with various ethanol proportions. It is suggested that different nicotinate ion protonation mechanisms operate in water and aqueous ethanol.

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.

Effect of Ionic Strength on the Thermodynamic Characteristics of Complexation between Fe(III) Ion and Nicotinamide in Water-Ethanol and Water-Dimethyl Sulfoxide Mixtures

Solutions of iron(III) perchlorate in water, water-ethanol, and water-dimethyl sulfoxide solvents (

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

x_{H_2 O}

Complexation of nicotinamide with Ag+ ions in water-organic solvents

= 0.7 and 0.25 mole fractions) at ionic strength values I = 0.1, 0.25, and 0.5 are studied by IR spectroscopy. Analysis of the absorption bands of perchlorate ion shows that it does not participate in association processes. It is demonstrated that in the range of ionic strength values between 0 and 0.5 (NaClO4), it affects neither the results from potentiometric titration to determine the stability constants of the iron(III)-nicotinamide complex nor the thermal effects of complexation determined via direct calorimetry in a binary solvent containing 0.3 mole fractions (m.f.) of a non-aqueous component.

Enthalpies of Iron(III) perchlorate and Fe3+ ion transfer from water into aqueous ethanol solvents

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.

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

The effect of the water-ethanol and water-DMSO solvent composition on the stability of nicotinamide (NicNH2) complexes with Ag+ ions at an ionic strength of 0.25 (NaClO4) and a temperature of 25 ± 0.1°C is studied by potentiometric titration. An increase in the EtOH concentration in the mixed solvent is found to result in a higher stability of the nicotinamide complex with silver(I) ions; as the DMSO concentration increases, the complex becomes less stable. The results of the study are analyzed in terms of the solvation thermodynamic approach taking into account the electronic structure of the ligand and the solvation contributions of the fragments of the molecule.

Nicotinamide solvation state in aqueous dimethyl sulfoxide

Thermal effects of the transfer of iron(III) perchlorate from water into aqueous ethanol solutions at 25.00 ± 0.01°C are determined calorimetrically. The enthalpies of Fe3+ ion transfer are calculated. An increase in the enthalpies of iron(III) ion transfer upon a rise in the ethanol content in the system is observed. The Gibbs energies of Fe3+ transfer are calculated using the linear correlation of solvation energy on the solvent and ion parameters.

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

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.