Analysis of a novel phenomenon in a solidlike structure in ovalbumin aqueous colloids using the Yukawa potential

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Abstract
A solidlike structure in ovalbumin (OA) aqueous colloids was investigated at various ionic concentrations of the phosphate buffer solution (0–1.5 M) and was analyzed using the Yukawa potential. Rigidity and yield stress due to the solidlike structure increase with increasing ionic concentration and decrease passing through a maximum. This is novel behavior which has never been reported. This behavior is very different from the behavior of the usual (conventional) colloids. From the theoretical consideration by the Yukawa potential, it turns out that the novel behavior of the OA colloid is caused by the fact that the dispersing particles in the colloid, i.e., dimeric molecules composed of the OA globular molecules, are extremely small compared with polymer particles and lattices, etc. That is, the theoretical curve of rigidity versus κ (Debye–Hückel parameter) shifts to a region of large values of κ with decreasing particle radius. A phase diagram is shown in the logarithmic relationship between the OA concentration c and the concentration of buffer solutionc b . The boundary between the liquid phase and the solid phase can be represented by a straight line with a slope of −1 over wide ranges of c and c b .