Urochrome Pigment in Uric Acid Crystals

Renal stones are heterogeneous composites of numerous microscopic crystals (e.g., calcium oxalate, calcium phosphate, uric acid, etc.) and 2–3 wt % amorphous organic “matrix”. Uric acid kidney stones are often red–orange–brown in color, though uric acid crystals are colorless. The stone color originates from a variety of components in the matrix, some of which are a broad range of urinary pigments or urochrome. Herein, we report the first definitive structure of one of these pigments, urorosein, and its ability to form intracrystalline inclusions in single crystals of both anhydrous uric acid and uric acid dihydrate. The preferred orientation of the included urorosein molecules in the uric acid crystals was determined through polarized light microspectroscopy. On the basis of these results, it seems likely that other urochrome pigments can locate in both intercrystalline and intracrystalline spaces in urinary precipitates. This expands the conventional picture of where “matrix” resides in these composite materials.

肾结石是由多种显微晶体（如草酸钙、磷酸钙、尿酸等）与2%~3%重量百分比的无定形有机“基质”构成的异质复合材料。尽管尿酸晶体本身无色，但尿酸肾结石通常呈红-橙-棕色调。结石的颜色源自基质中的多种组分，其中涵盖了一类广泛存在的尿色素（urochrome）。本文首次报道了其中一种色素——尿玫瑰素（urorosein）的确切结构，以及它在无水尿酸（anhydrous uric acid）和二水尿酸（uric acid dihydrate）单晶中形成晶内包裹体的能力。通过偏振光显微光谱法，研究人员确定了尿酸晶体中包裹的尿玫瑰素分子的择优取向。基于上述研究结果，其他尿色素大概率也可分布于尿沉淀物的晶间与晶内空间中，这拓展了人们对这类复合材料中“基质”分布的传统认知。