Studies on the morphology of human uric acid stones

Analysis of urinary calculi using an infrared microspectroscopic surface reflectance imaging technique

This investigation highlights the use of infrared microspectroscopy for the morphological analysis of urinary stones. The research presented here has utilized the reflectance mode of an infrared microscope for use in creating chemically specific maps of cross-sectioned renal calculi surfaces, precisely showing the placement of renal stone components in a calculus sample. The method has been applied to renal stones of both single and multiple components consisting primarily of hydroxyapatite, calcium oxalate monohydrate and calcium oxalate dihydrate. Factors discussed include the photometric accuracy of the spectra obtained, a comparison of the surface reflectance method with existing methods such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and attenuated total internal reflection (ATR) analysis, and the influence of specular reflectance between polished and unpolished sample spectra. Full spectral maps of cross-sectioned renal stones provided positive localization of components using qualitatively accurate spectra similar in appearance to DRIFTS spectra. Unlike ATR and DRIFTS spectra, surface reflectance spectra lack photometric accuracy and are therefore not quantifiable; at present, however, spectra are suitable for qualitative analysis. It was found that specular reflectance increases minimally with a highly polished stone cross-section surface, though qualitative data is not affected. Surface reflectance imaging of sections of renal stones is useful for determining the identity of stone components while simultaneously providing precise locations of mineral components within the stone using presently available instruments.

Dyeing uric acid crystals with methylene blue

The growth of anhydrous uric acid (UA) and uric acid dihydrate (UAD) crystals from supersaturated aqueous solutions containing methylene blue, a cationic organic dye, has been investigated. Low concentrations of dye molecules were found to be included in both types of crystal matrixes during the growth process. Incorporation of dye into UA crystals occurs with high specificity, affecting primarily [001] and [201] growth sectors, while UAD crystals grown from solutions of similar dye concentration show inclusion but little specificity. The orientation of the UA-trapped species was determined from polarization data obtained from visible light microspectrometry. To achieve charge neutrality, a second anionic species must also be included with the methylene blue into UA and UAD crystal matrices. Under high pH conditions, crystallization of 1:1 stoichiometric mixtures of methylene blue and urate yields methylene blue hexahydrate (MBU.6(H2O). The crystal structure of MBU.6(H2O) reveals continuous pi-pi stacks of planes of dye cations and urate anions mediated by water molecules. This structure provides an optimal geometry for methylene blue-urate pairs and additional support for the incorporation of these dimers in uric acid single-crystal matrices. The strikingly different inclusion patterns in UA and UAD demonstrate that subtle changes in the crystal surfaces and/or growth dynamics can greatly affect recognition events.