Crystallographic Studies of Interaction between Nucleotides and Metal Ions. I. Crystal Structures of the 1:1 Complexes of Cobalt and Nickel with Inosine 5′-Phosphate
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The crystal structures of the 1:1 complexes of inosine 5′-phosphate with cobalt (C<SUB>10</SUB>H<SUB>11</SUB>O<SUB>8</SUB>N<SUB>4</SUB>PCo,7H<SUB>2</SUB>O) and inosine 5′-phosphate with nickel(C<SUB>10</SUB>H<SUB>11</SUB>O<SUB>8</SUB>N<SUB>4</SUB>PNi,7H<SUB>2</SUB>O) have been determined from single-crystal X-ray data collected on an automated diffractometer. The both isomorphous crystals belong to orthorhombic system, space group P2<SUB>1</SUB>2<SUB>1</SUB>2<SUB>1</SUB> with four formula units in the unit cell of dimensions <I>a</I>=10.859, <I>b</I>=25.987, <I>c</I>=6.845 Å for the cobalt complex and <I>a</I>=10.812, <I>b</I>=25.898, <I>c</I>=6.845 Å for the nickel complex respectively. The structure of the cobalt complex was determined by three-dimensional Patterson and Fourier methods and that of the nickel complex was elucidated from that of the cobalt complex. Both were refined by the block-diagonal least-squares method including anisotropic temperature factors. The final <I>R</I> values were 0.051 and 0.075 for the cobalt and nickel complexes, respectively. All of the 25 hydrogen atoms in the case of the cobalt complex and 22 hydrogen atoms in the case of the nickel complex were found. The hypoxanthine bases related by the two-fold screw axis parallel to c are extensively overlapped at a distance of 3.42 Å for both complexes. The nucleotides have the preferred <I>anti</I> conformation about the glycoside linkage with the ribose ring showing the C(3′)-<I>endo</I> pucker. The torsion angles around the C(5′)–O(5′) bond are 161.6° (cobalt complex) and 162.0° (nickel complex). In the both complexes, therefore, the phosphate group has the extended conformation. The metals are not directly bonded to the phosphate oxygen atoms but are bonded to the nitrogen atom N(7) of the base and to five water oxygen atoms. There is extensive hydrogen bonding involving the hypoxanthine ring, the phosphate anion, the hydroxyl groups of the furanose ring and seven water molecules in the crystal.
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