Effects of temperature on growth and aggregation of calcium oxalate in presence of various carboxylic acids in silica gel systems

A novel method for the separation of mono and ortho polymorphs of paracetamol in gel matrix

The nucleation control and separation of mono and ortho polymorphs of the important pharmaceutical solid paracetamol were carried out through a crystallization process in gel media for the first time. Crystallization of mono and ortho polymorphic forms of paracetamol was achieved by optimizing the experimental parameters such as the specific gravity, pH, height of the gel column and solute concentration at ambient temperature. The optimized experimental conditions favor the generation of necessary supersaturation responsible for the nucleation of preferred polymorph at different levels in the gel column and also endure the stability of the grown orthorhombic polymorphs at ambient conditions. Accordingly the needle like metastable orthorhombic polymorph nucleates at the top portion of the gel column whereas the prismatic stable monoclinic polymorph nucleates mostly at the bottom level. Morphology of the nucleated polymorphs was analyzed and their crystalline structures were confirmed by PXRD. FTIR analysis revealed the shifting of absorption peaks of few functional groups corresponding to both the polymorphs due to the difference in their structural nature. DSC analysis revealed that the grown ortho polymorph form II transforms to mono form I at 89.47°C while the grown mono form I retains its phase until melting.

Composition and morphology of nanocrystals in urines of lithogenic patients and healthy persons

The composition and morphology of nanocrystals in urines of healthy persons and lithogenic patients were comparatively investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was shown that the main composition of urinary nanocrystals in healthy persons were calcium oxalate dihydrate (COD), uric acid, and ammonium magnesium phosphate (struvite). However, the main compositions of urinary nanocrystals in lithogenic patients were struvite, β-tricalcium phosphate, uric acid, COD, and calcium oxalate monohydrate (COM). According to the XRD data, the size of nanocrystals was calculated to be 23∼72 nm in healthy urine and 12∼118 nm in lithogenic urine by Scherer formula. TEM results showed that the nanocrystals in healthy urine were dispersive and uniform with a mean size of about 38 nm. In contrast, the nanocrystals in lithogenic urine were much aggregated with a mean size of about 55 nm. The results in this work indicated that the urinary stone formation may be prevented by diminishing the aggregation and the size differentiation of urinary nanocrystals by physical or chemical methods.