Attractive potential effect on the self-diffusion coefficients of a solitary water molecule in organic solvents

Abstract

H 1 -Fourier-transform pulsed field-gradient spin-echo NMR method is applied at 30 °C to measure the self-diffusion coefficients of water, acetonitrile, and benzene in dilute organic solutions of carbon tetrachloride, benzene, chloroform, dichloromethane, acetonitrile, acetone, and water. The dependence of the translational friction coefficients ζT of the apolar solute molecule, benzene, on solvent viscosity η is linear as predicted by the simple hydrodynamic theory. The η dependence of ζT of the polar solute molecule, acetonitrile, is linear, though the slope is different in apolar and polar solvents. The η dependence of ζT of the hydrogen-bonding solute molecule, water, is nonlinear and dependent on the strength of the solvent as a proton acceptor. The breakdown of the hydrodynamic theory is discussed in terms of the attractive part of the solute–solvent interaction. The role of the attractive interaction is illustrated through a linear relationship between the proton chemical shift of water and the residual friction coefficient, which is defined by removing the repulsive component from the overall translational friction coefficient.