The self-diffusion coefficients of globular proteins (myoglobin, bovine serum albumin, barstar, lysozyme) in aqueous solutions at different temperatures and pH values are obtained by pulsed-gradient spin-echo NMR, and their concentration dependence is analyzed. The generalized concentration dependence of globular protein self-diffusion coefficients is empirically established, and compared to the concentration dependence of diffusion coefficients of flexible polymers and rigid Brownian particles.

The self-diffusion properties of hexane confined in porous glass with different filling fractions were studied by means of pulsed field-gradient spin echo diffusometry. The spin echo attenuation curves were analyzed over a range of 3.5 orders of magnitude. Only for the partially filled sample was the shape of the echo attenuation curves found to depend on diffusion time. This observation indicates a vapor phase contribution to the total diffusional displacements and is interpreted by molecular exchange between the liquid and vapor phases. The distribution of molecular residence times in the liquid phase is evaluated from experimental data. A thorough analysis of this distribution function yields information about the nature of inhomogeneities of the liquid's spatial distribution inside the porous matrix, including typical sizes of the inhomogeneous regions and characteristics of exchange processes at the liquid/vapor interface. The model is further substantiated by additional computer simulations.

The time dependence of the self-diffusion coefficient D(t) in porous media is investigated by Monte Carlo simulation of autocorrelation functions 〈f(t)f(0)〉, where f(t) is the force of interaction between a molecule and the surface at time t. At short times, D(t) is governed by the surface population of the molecules and the probability of their return to the surface. At times t>t*, where t* is the characteristic time for the autocorrelation function to converge to zero, the apparent dynamics of the molecules is completely determined by the geometry of the surface on the length scale of D0t*, where D0 is the bulk self-diffusion coefficient. D(t) in this limit is the sum of a constant D∞=limt→∞ D(t) and a time-dependent term R̄p2/2d⋅t, where R̄p2 is the mean-squared size of an effective unit cell of the porous space and d is the dimensionality of the space. The meaning of tortuosity for self-diffusion is discussed.

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Abstraer. Geometrical restrictions of water diffusion in different aqueous protein systems were studied using two versions of the NMR field gradient technique. The samples were aqueous systems of bovine serum albumin, gelatin and horse myoglobin at concentrations ranging from diluted solutions to almost dry powders being only partly hydrated. Hydrated protein aerogels were produced by the aid of a special preparation procedure and studied in addition. The experiments referred to the temperature and concentration dependences of the water diffusion coefficient above and below the free-water freezing temperature. The diffusion coefficient within clusters of overlapping hydration shells is reduced by one order of magnitude compared with that of bulk water. Geometrical restrictions manifest themselves (a) by the obstruction effect observed at low protein concentrations, Co) by the topologically two-dimensional diffusion in the network of overlapping hydration shells, (c) by the percolation threshold appearing at about 15~ water and (d) by the anomalous diffusion behaviour concluded from the protein aerogel study.