Bilirubin IXα is the major product of the degradation of heme from red blood cells and is of biological and medical relevance. It is insoluble in aqueous media leading to crystals in the gall bladder and urine indicating liver dysfunction. The degradation process leads to enantiomers – the M- and P-helical conformers – which are mirror versions of each other. The molecule is rigid because of strong intramolecular hydrogen bonding. We have grown two forms of bilirubin and analyzed another that was published in 1980. All forms crystallize in the space group P. Form I was first published in 1978, but the original authors mentioned that the molecules showed unresolved disorder. We have regrown this form and resolved the disorder. There are two molecular sites in the asymmetric unit in Form I, and both sites are a disordered mixture of M- and P-helical conformers, with no voids in the structure. Form II is a solvate (void space: 5% of the unit cell volume) and is a new form. It contains two molecular sites in the asymmetric unit with the same helical conformer in both sites, with an ordered molecule in one site and rotationally disordered molecules in the other site. Form III is also a solvate (void space: 25% of the unit cell volume) and contains methanol and chloroform. There is no strong intermolecular hydrogen bonding in any of the three forms, and the molecules aggregate through weak interactions. Despite this, CLP-PIXEL calculations showed that the three most stable molecule⋯molecule arrangements between the three forms are geometrically consistent.

中文翻译：

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胆红素及其晶体形式

胆红素 IXα 是红细胞血红素降解的主要产物，具有生物学和医学意义。它不溶于水介质，导致胆囊和尿液中形成晶体，表明肝功能障碍。降解过程产生对映体——M和P螺旋构象体——它们是彼此的镜像版本。由于分子内氢键强，该分子是刚性的。我们培养了两种形式的胆红素，并分析了 1980 年发表的另一种形式。所有形式都在空间群P中结晶。I型首次发表于1978年，但原作者提到这些分子表现出未解决的紊乱。我们已经重新培育了这种形式并解决了这种疾病。晶型I的不对称单元中有两个分子位点，这两个位点都是M-和P-螺旋构象异构体的无序混合物，结构中没有空隙。II 型是一种溶剂化物（空隙空间：晶胞体积的 5%），是一种新的形式。它在不对称单元中包含两个分子位点，两个位点具有相同的螺旋构象异构体，一个位点具有有序分子，另一个位点具有旋转无序分子。III 型也是溶剂化物（空隙空间：晶胞体积的 25%），含有甲醇和氯仿。三种形式均不存在强的分子间氢键，分子通过弱相互作用聚集。尽管如此，CLP-PIXEL 计算表明，三种形式之间的三种最稳定的分子…分子排列在几何上是一致的。