Dimer and Superstructure of the Active Form of a Vitamin D_3 ; 1α, 24(R)Dihydroxy-vitamin D_3 Monohydrate, C_<27>O_3H_<44>・H_2O

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The crystals of 1α, 24(R)dihydroxy-vitamin D_3 monohydrate, C_<27>O_3H_<44>・H_2O are orthorhombic in the space group P2_12_12_1 with cell dimensions a=25.719, b=42.572, c=9.851A and Z=16. The asymmetric unit consists of two subunits with b/8, and each subunit contains a dimer in which two molecules are hydrogen-bonded through water molecules into non-crystallographical symmetry of C_2. The two-fold axes are the straight lines, x=1/2, z=0.256 and x=1/2, z=0.623. The two dimers further make C_2 symmetry between the rigid ring part, but differ in the conformation of the flexible chains. The dimers further make C_2 symmetry between the rigid ring parts to form a superstructure, and the two-fold axis of the straight line, y=1/8, z=0.435 goes through a point that is a little apart from the hypercenter(1/2, 1/8, 1/2). The structure was solved by integrated Patterson and direct methods and refined on F^2_o under restraints. The final R_1 is 0.228 on F_o for 1623 reflections with F_o>3σ, resolutions 1.0-3.0A, 313 restraints, 490 parameters and average U_<eq>=0.120. Not all the atoms of the chains appeared nor the hydrogen atoms. The missing atoms of the dimer were modeled from another pair molecule by C_2 symmetry and hydrogen atoms were added. The structure of the dimer was optimized by ab initio molecular orbital of HF/6-31G^*.
公益社団法人日本薬学会の論文
2001-03-01