Diffusion in ternary aqueous systems containing human serum albumin and precipitants of different classes

Abstract

The mutual diffusion coefficients for two aqueous ternary systems, both containing a protein, human serum albumin (HSA, component 1), were measured. The first system contained a neutral polymer, polyethylene glycol (PEG, component 2), and the second an "organic solvent", 2-methyl-2,4-pentanediol (MPD, component 3). Both PEG and MPD are used as co-precipitants in HSA crystallization protocols. Measurements were performed at constant protein concentration, with increasing precipitant content. The results obtained for the two systems were discussed and compared. In both cases, the two main diffusion coefficients, relative to the motion of the protein and of the precipitant under their own concentration gradient, can be interpreted in terms of non-specific volume interactions between the solutes. Particularly, it was showed that any possible direct HSA-MPD interaction may not have a significant effect on the values of these two diffusion coefficients. Differences arise between the cross precipitant's diffusion coefficients, relative to the motion of the precipitant under the protein concentration gradient, D(i1) with i = 2, 3. In the case of PEG, the D(21) trend vs. c(2) can be simply interpreted in terms of an "exclude volume" effect. In contrast, in the case of MPD, the D(31)vs. c(3) trend seems to indicate a more complex mechanism of transport. Because the cross precipitant's diffusion coefficient plays an important role in the crystallization process, the implication of the observed difference on the crystallization procedure was also discussed.

Analysis of Main- and Cross-Term Diffusion Coefficients in Bile Salt Mixtures

“…Also for this technique details of apparatus and raw data treatment are reported in previous papers . A reasoned comparison between advantages and disadvantages of these alternative techniques has been illustrated elsewhere . However, the uncertainty in the results obtained by the Taylor approach is usually higher than that in Gouy interferometry results.…”

“…18 A reasoned comparison between advantages and disadvantages of these alternative techniques has been illustrated elsewhere. 19 However, the uncertainty in the results obtained by the Taylor approach is usually higher than that in Gouy interferometry results. This was found true also in our measurements, as can be seen by the uncertainties quoted in Table ESI1.…”

Contribution to the benchmark for ternary mixtures: Determination of Soret coefficients by the thermogravitational and the sliding symmetric tubes techniques

“…where S 1 and S 2 are the slopes formed by the variation of the concentration with the square root of time, L is the length of the tubes, A and B are the integration constants, α 1 and α 2 are function of the eigenvalues of the diffusion matrix, D 11 and D 22 are the diagonal diffusion coefficients and D 12 and D 21 are the cross-diagonal diffusion coefficients.…”

“…Nowadays, the focus is on ternary mixtures, because it is necessary to analyse and understand them before going to multicomponent mixtures. In the last years, some works have been published which try to determine the thermodiffusion, molecular diffusion or Soret coefficients in ternary mixtures [5][6][7][8][9][10][11][12][13][14]. However, as they are individual works and not all concerned with the same mixture, there was a high dispersion between the results, so they were not easily comparable.…”

Determination of the molecular diffusion coefficients in ternary mixtures by the sliding symmetric tubes technique

“…For example, Königer et al 10 tried to solve the problem applying a second wavelength for the determination by the Two Colour Optical Beam Deflection technique; Mialdun et al 11 devised a new instrument based on interferometry to determine the molecular diffusion coefficients. Leahy-Dios et al 12 used the OEC technique combining the density and refractive index measurements for the determination of the molecular diffusion coefficients and Santos et al 13 and Capuano et al 1 used the Taylor dispersion principle and the Gouy interferometer respectively. In addition, simulations based on molecular dynamics (Ref.…”