Calcium oxalate crystals, influence

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

White DJ, Nancollas GEI. Triamterene renal stone formation the influence of triamterene and triamterene stones on calcium oxalate crystallization. Calcif. Tissue Int 1987 40 79. 

Unfortunately nephrolithiasis is a recirrrent disease and about 75% of patients suffer the recurrence within 10 years. Therefore it is important to develop new more efficient preventative therapies, which can inhibit the formation of kidney stones or possess properties of dissolution of calciitm oxalate deposits. The possible approach constitutes modeling the potential inhibitors forming calcium oxalate crystals. On the other hand there are available compoimds directly influencing the calciiun oxalate formation (inhibitory or dissolution effect) e.g. citrate. It should be noted that compounds possessing dissolution properties of calcimn oxalate carmot interfere too much into the whole calcimn economy. 

Brecevic, Lj. and Kralj, D., 1989. Factors influencing the distribution of hydrates in calcium oxalate precipitation. Journal of Crystal Growth, 97, 460M68. 

When particles or large molecules make contact with water or an aqueous solution, the polarity of the solvent promotes the formation of an electrically charged interface. The accumulation of charge can result from at least three mechanisms (a) ionization of acid and/or base groups on the particle s surface (b) the adsorption of anions, cations, ampholytes, and/or protons and (c) dissolution of ion-pairs that are discrete subunits of the crystalline particle, such as calcium-oxalate and calcium-phosphate complexes that are building blocks of kidney stone and bone crystal, respectively. The electric charging of the surface also influences how other solutes, ions, and water molecules are attracted to that surface. These interactions and the random thermal motion of ionic and polar solvent molecules establishes a diffuse part of what is termed the electric double layer, with the surface being the other part of this double layer. 

A. Millan, O. Sohnel, F. Grases, The influence of crystal morphology on the kinetics of growth of calcium oxalate monohydrate, J. Crystal Growth 179 (1997) 231. 

On the other hand there is the opinion of Robertson, who emphasizes the influence of the uric acid concentration of the urine on the formation of calcium-containing concrements ments due to the process of crystallization. He assumes that increased uric acid concentration stops the blocking activity for crystallization of calcium oxalate, which derives from the acid mucopolysaccharides. 

Specifically, the influence of biodegradable, environmentally friendly carboxyl-ated polysaccharide additives, such as carboxymethyl inulin (CMI), has been used to delineate the crystallization kinetics of calcium oxalate. The retardation in crystal growth is controlled by the carboxylation degree of CMI and its concentration [96]. CMI is produced by chemical reaction of the biopolymer inulin [97]. Inulin (Fig. 5.8)... 

By determining the mass loss due to dehydration (rfwi and dm2 in Fig. 4), it is possible to quantitatively determine the phase composition of mixtures of crystal hydrates provided it was qualitatively ascertained by some other method (for instance, by X-ray powder diffraction). This method has been used to determine the influence of various experimental parameters on the phase composition of calcium oxalate precipitates. Several examples are given in Figs. 5-9. 

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