Aggregation patterns of bile salts: crystal structure of calcium cholate chloride heptahydrate.
Aggregation patterns of bile salts: crystal structure of calcium cholate chloride heptahydrate.
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发表时间：
1984-08
影响因子：
6.5
通讯作者：
A. Hogan;S. Ealick;C. Bugg;S. Barnes
中科院分区：
文献类型：
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作者：
A. Hogan;S. Ealick;C. Bugg;S. Barnes
七水胆酸钠氯化钙晶体，CaC 24 H39 O 7 Cl。7 H2O，属单斜晶系，空间群P2（1），a = 11.918（2），B = 8.636（1），c = 15.302（3）A，β = 97.93（3）度，V = 1559.9（8）A3，Z = 2。通过Patterson和傅立叶技术获得试验结构，并使用吸收校正的CuK-α衍射仪数据通过全矩阵最小二乘计算进行改进。最终R指数为0.047。晶体结构包含双层型排列，胆酸盐环的疏水部分夹在与钙离子和水分子相互作用的极性基团层之间。钙离子与五个水分子和胆酸盐残基的两个羧酸氧原子配位。另外两个水分子通过形成氢键仅参与晶体堆积。胆酸盐-胆酸盐疏水相互作用涉及羧酸酯侧链的烃部分与A和B环之间的接触。这导致交错堆积模式，其与胆酸钠和脱氧胆酸铷晶体中发现的几乎相同。类似的双层聚集模式也可能参与水介质中胆盐胶束的形成。特征双层包装安排可以容纳各种阳离子结合模式，证明了钙，钠，铷离子与极性面的双层以不同的方式相互作用的发现。在七水氯化胆酸钙的晶体结构中，羧酸侧链显示出两种不同的构象。侧链构象的变化可能是重要的调整，以适应不同的阳离子配位方案。
Crystals of calcium cholate chloride heptahydrate, CaC24H39O7Cl . 7H2O, are monoclinic, space group P2(1), with a = 11.918(2), b = 8.636(1), c = 15.302(3) A, beta = 97.93(3) degrees, V = 1559.9(8) A3, and Z = 2. A trial structure was obtained by Patterson and Fourier techniques and was refined by full-matrix least-squares calculations using absorption corrected CuK-alpha diffractometer data. The final R index is 0.047. The crystal structure contains bilayer-type arrangements, with hydrophobic portions of cholate rings sandwiched between layers of polar groups that are interacting with calcium ions and water molecules. The calcium ion is coordinated to five water molecules and to the two carboxylate oxygen atoms of the cholate residue. Two additional water molecules are involved only in crystal packing through the formation of hydrogen bonds. Cholate-cholate hydrophobic interactions involve contacts between the hydrocarbon portions of the carboxylate sidechains and the A and B rings. This results in a staggered packing pattern that is nearly identical to that found in crystals of sodium cholate and rubidium deoxycholate. Similar bilayer aggregation patterns may also be involved in the formation of bile salt micelles in aqueous media. The characteristic bilayer packing arrangement can accommodate a variety of cation-binding patterns, as evidenced by the finding that calcium, sodium, and rubidium ions interact with the polar faces of the bilayers in different ways. The carboxylate sidechain displays two different conformations in the crystal structure of calcium cholate chloride heptahydrate. Variation in sidechain conformation may be of importance in the adjustment required to accommodate different cation coordination schemes.