Thornton Alyssa M, Fawcett Timothy G, Kaduk James A, Lin YuJai, Swift Jennifer A
Department of Chemistry, Georgetown University, Washington, District of Columbia 20057, United States.
International Centre for Diffraction Data, Newtown Square, Pennsylvania 19073, United States.
Cryst Growth Des. 2023 Aug 16;23(9):6953-6959. doi: 10.1021/acs.cgd.3c00789. eCollection 2023 Sep 6.
The pathological crystallization of ammonium urate inside the urinary tract is a well-documented medical condition; however, structural studies of the biogenic material have proven challenging owing to its propensity to precipitate as a powder and to exhibit diffraction patterns with widely varying intensities. Using block Rietveld refinement methods of powder diffraction data, here we identify ammonium urate hydrate (AUH) as a likely component in natural uroliths. AUH has a planar 2-D hydrogen-bonded organic framework of urate ions separated by ammonium ions with water molecules residing in bisecting channels. AUH is stable up to 150 °C for short time periods but begins to decompose with prolonged heating times and/or at higher temperatures. Changes in the solid-state structure and composition of synthetic material over a temperature range from 25 to 300 °C are elucidated through thermogravimetric and spectroscopic data, combustion analysis, and time-resolved synchrotron powder X-ray diffraction studies. We contend that biogenic ammonium urate is more accurately modeled as a mixture of AUH and anhydrous ammonium urate, in ratios that can vary depending on the growth environment. The similar but not identical diffraction patterns of these two forms likely account for much of the variability seen in natural ammonium urate samples.
尿路内尿酸铵的病理性结晶是一种有充分文献记载的医学病症；然而，对这种生物源物质的结构研究颇具挑战性，因为它易于以粉末形式沉淀，并呈现出强度差异很大的衍射图样。利用粉末衍射数据的块体Rietveld精修方法，我们在此确定尿酸铵水合物（AUH）是天然尿路结石中可能的成分。AUH具有由尿酸根离子构成的平面二维氢键有机骨架，这些离子被铵离子分隔开，水分子位于平分通道中。AUH在短时间内温度高达150℃时是稳定的，但随着加热时间延长和/或温度升高会开始分解。通过热重分析和光谱数据、燃烧分析以及时间分辨同步辐射粉末X射线衍射研究，阐明了合成材料在25至300℃温度范围内固态结构和组成的变化。我们认为，生物源尿酸铵更准确地应被模拟为AUH和无水尿酸铵的混合物，其比例可能因生长环境而异。这两种形式相似但不完全相同的衍射图样可能是天然尿酸铵样品中所见诸多变异性的主要原因。
