Temperature and Concentration Dependences of Viscosity of Aqueous and Buffer Solutions of L-Arginine and Nicotinic Acid

The viscosity properties of binary systems containing the basic amino acid L-arginine (Arg) and nicotinic acid (NA) in water and buffer solution at different concentrations in the temperature range of 288.15–313.15 K were compared. The viscosity of Arg and NA solutions in a phosphate buffer (pH 7.4) was measured for the first time. The concentration dependences of viscosity of the systems obey the Jones–Dole equation for dilute solutions; the obtained values of the Bη coefficient tend to decrease with increasing temperature and reflect the cosmotropic effect of Arg and NA on the solvent. The temperature dependences of viscosity at a fixed solution composition were described using the Arrhenius equation. It was shown that the activation energies of the viscous flow ( $$E_{\eta }^{ \ne }$$ ) of the systems under study depend linearly on the solute concentration. This made it possible to determine the solvent and solute contributions to $$E_{\eta }^{ \ne }$$ . The Arg and NA solutions in water have lower activation energies than in the buffer. In the given range of concentrations, the $$E_{\eta }^{ \ne }$$ parameter was found to be mainly determined by the structural contribution of the solvent in which the solvated solute species move.