Phase Diagram of Colloidal Solutions

Abstract

The phase diagram of globular colloids is studied using a combined analytic and computational representation of the relevant chemical potentials. It is shown how the relative positions of the phase boundaries are related to the range of interaction and the number of contacts made per particle in the solid phase. The theory presented successfully describes the features of the phase diagrams observed in a wide variety of colloidal systems. [S0031-9007(96)

Macromolecular crystal growth as revealed by atomic force microscopy

“…The existence of a liquid protein phase in concentrated protein solutions, the multilayer stacks discussed here being one manifestation, has been dealt with in greater detail elsewhere, and it is the source of much current interest in the field of colloids as well as crystal growth (Asherie et al, 1996;Haas and Drenth, 1999;Kuznetsov et al, 1999b;Lui et al, 1995;Ten Wolde and Frenkel, 1997). It was one of the more unexpected results to emerge from AFM studies of macromolecular crystal growth.…”

“…Such a phenomenon fails, however, to explain the perfect alignment of all of the stacks with the underlying lattice and with one another. A second explanation, for which there is now substantial and persuasive evidence, suggests that they arise from liquid protein phase droplets that exist in concentrated macromolecular solutions (Asherie et al, 1996;Kuznetsov et al, 1998;Lui et al, 1995). These liquid protein phase droplets are composed of many thousands of molecules exhibiting short-range order, mediated principally by nonspecific hydrophobic interactions and random arrangements of hydrogen bonds.…”

“…Because the former involves spontaneous, singular events that are unpredictable in time and place, nucleation is difficult to directly visualize and characterize by most imaging techniques, including atomic force microscopy (AFM). It is best studied using neutron or small-angle X-ray scattering from solution (Tardieu et al, 2001) or light scattering methods (Asherie et al, 1996;McPherson, 1993, 1994;George and Wilson, 1994). Growth of crystals, on the other hand, occurs at predictable sites on the surfaces of existing crystals, and the size range and time scale are ideally suited to direct visualization and recording by AFM.…”

How fluorescent labelling alters the solution behaviour of proteins

“…Phase diagrams are used to characterize the interactions between macromolecules, including colloidal particles and proteins. 8,25,33,34 These studies have shown that the effective inter-protein interaction potential results from the complex interplay of both attractive and repulsive contributions. 35 Proteins are inherently anisotropic, since each surface exposed amino acid contributes to varying degrees to the overall net-interaction potential.…”

“…26,33,36,37 Liquid-liquid phase separation (LLPS) occurs for proteins interacting via short-ranged net attractive forces. 25,33,34 Indeed, the temperature at which LLPS occurs is sensitive to the strength of net attraction between proteins in solution and can be used to probe the relative changes in protein inter-particle interactions as a result of altered protein chemistry, changing solution conditions or the presence of a second protein type. 38,39 In this study, we experimentally assess the phase diagram for human gD-crystallin (HGD), which is a structural protein in the eye lens that undergoes LLPS due to short-ranged attractive interactions which dominate its behaviour at physiological pH (at the pI of the protein).…”