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首页> 外文期刊>Minerals >Thermal Behavior and Phase Transition of Uric Acid and Its Dihydrate Form, the Common Biominerals Uricite and Tinnunculite
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Thermal Behavior and Phase Transition of Uric Acid and Its Dihydrate Form, the Common Biominerals Uricite and Tinnunculite

机译：尿酸及其二水合物形式，常见的生物矿物尿石和锡云母的热行为和相变

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Single crystals and powder samples of uric acid and uric acid dihydrate, known as uricite and tinnunculite biominerals, were extracted from renal stones and studied using single-crystal and powder X-ray diffraction (SC and PXRD) at various temperatures, as well as IR spectroscopy. The results of high-temperature PXRD experiments revealed that the structure of uricite is stable up to 380 °C, and then it loses crystallinity. The crystal structure of tinnunculite is relatively stable up to 40 °C, whereas above this temperature, rapid release of H 2 O molecules occurs followed by the direct transition to uricite phase without intermediate hydration states. SCXRD studies and IR spectroscopy data confirmed the similarity of uricite and tinnunculite crystal structures. SCXRD at low temperatures allowed us to determine the dynamics of the unit cells induced by temperature variations. The thermal behavior of uricite and tinnunculite is essentially anisotropic; the structures not only expand, but also contract with temperature increase. The maximal expansion occurs along the unit cell parameter of 7 ? ( b in uricite and a in tinnunculite) as a result of the shifts of chains of H-bonded uric acid molecules and relaxation of the π-stacking forces, the weakest intermolecular interactions in these structures. The strongest contraction in the structure of uricite occurs perpendicular to the (101) plane, which is due to the orthogonalization of the monoclinic angle. The structure of tinnunculite also contracts along the [010] direction, which is mostly due to the stretching mechanism of the uric acid chains. These phase transitions that occur within the range of physiological temperatures emphasize the particular importance of the structural studies within the urate system, due to their importance in terms of human health. The removal of supersaturation in uric acid in urine at the initial stages of stone formation can occur due to the formation of metastable uric acid dihydrate in accordance with the Ostwald rule, which would serve as a nucleus for the subsequent growth of the stone at further formation stages; afterward, it irreversibly dehydrates into anhydrous uric acid.
机译：从肾结石中提取尿酸和二水合尿酸的单晶和粉末样品，称为尿石和锡云母生物矿物质，并在不同温度下使用单晶和粉末X射线衍射（SC和PXRD）以及红外进行研究光谱学。高温PXRD实验的结果表明，在380°C的温度下，堇青石的结构是稳定的，然后失去结晶性。锡云母的晶体结构在高达40°C的温度下相对稳定，而在此温度以上，H 2 O分子会快速释放，然后直接过渡为无水合状态的尿石相。 SCXRD研究和红外光谱数据证实了堇青石和锡云母晶体结构的相似性。低温下的SCXRD使我们能够确定温度变化引起的晶胞动力学。尿石和锡云母的热行为基本上是各向异性的。结构不仅会膨胀，还会随着温度的升高而收缩。最大膨胀沿单位晶胞参数7？发生。 （b为尿酸盐，a为锡云母）是由于H键合的尿酸分子链的移动和π堆积力的松弛，这些结构中最弱的分子间相互作用。垂直于（101）平面时，尿铁矿结构最强的收缩发生，这是由于单斜角的正交作用所致。锡云母的结构也沿[010]方向收缩，这主要归因于尿酸链的拉伸机理。在生理温度范围内发生的这些相变强调了尿酸盐系统中结构研究的特殊重要性，因为它们对人体健康具有重要意义。结石形成初期，尿液中尿酸过饱和的去除可能是由于按照Ostwald规则形成了亚稳态的二水合尿酸而形成的，该水合物将成为随后结石进一步生长时的核心阶段之后，它不可逆地脱水成无水尿酸。

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