Microcalorimetric and Small-Angle Light Scattering Studies on Nucleating Lysozyme Solutions

We have investigated the properties of nucleating lysozyme solutions, at various lysozyme and NaCl concentrations at pH 4.2, by isothermal conduction microcalorimetry and small-angle static light scattering. Both types of experiments were performed under stirring and differ drastically from their counterparts where stirring was not applied. Pronounced heat−power peaks, that can be attributed to nucleation and growth, appear at finite times which in turn depend on the supersaturation level. The calorimetric results are in qualitative accordance with the nucleation behavior deduced from small-angle scattering experiments. The implications of these experiments in the nucleation process of lysozyme are (i) without stirring, large fractal clusters with dimensionalities lower than ∼2.00 form and, after 1−2 days, large crystals appear and (ii) with stirring, nuclei of several micrometers in size appear within 2−13 h depending on conditions. Their dimensionalities vary between 2.5 and 3.0, indicating dense morphology; their appearance is accompanied by showers of microcrystals.