The effect of various organic solvents as well as the crystallization conditions on the crystal habit of anhydrous cholesterol have been studied. Both plates and needle-like crystals can be obtained in a particular solvent depending on the degree of supersaturation of the solution. However, the crystals grown at about the same supersaturation, from different solvents, show differences in their habit indicating dependence on the solvent-solute interaction. Thus, it is advisable not to identify needle-like crystals with anhydrous-cholesterol and plates with mono-hydrate cholesterol without specifying the crystallization conditions. A prediction on the crystal habit length to width ratios can be made using those parameters.
DTA analysis was used to confirm evidence from X‐ray diffraction studies for the existence of 1:1 mixed sitosterol—cholesterol crystals. The curve of melting point against composition has an inflection point at about 1:1 ratio. The DTA peaks for 1:1 mechanical mixtures and for 1:1 mixed crystals are different with respect to symmetry and width. The curve of the heat of enthalpy against the composition of crystals also changes indicating a change in entropy. This can be attributed to the difference between melting mixed crystals (high order) and solid solution (low order). The solubility curve in the sitosterol—cholesterol—alcohol system has also a region of inflection confirming the previous conclusions.
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