METAL-DEPENDENT COORDINATION OF BIOMOLECULAR LIGAND - X-RAY CRYSTAL-STRUCTURES OF COPPER, COBALT AND CALCIUM COMPLEXES OF (3-HYDROXY-5-(HYDROXYMETHYL)-2-METHYLISONICOTINIC ACID) 5-PHOSPHATE, AN OXIDIZED PYRIDOXAL 5-PHOSPHATE

X-ray crystal analyses of divalent copper, cobalt and calcium complexe s of monoanionic (3-hydroxy-5-(hydroxymethyl)-2-methylisonicotinic aci d) 5-phosphate (L, C8H9NO7P-) revealed the chemical compositions of Cu -1/2. L . 3H(2)O(1), Co-1/2. L . 5H(2)O (2) and Ca . L-2 . 7H(2)O(3) a nd the coordination structures which depend on the coordination abilit ies and chemical properties of the respective metal ions. Although I a nd 2 crystals showed similar features, i.e., presence of the metal ion at the crystallographic center of symmetry and octahedral six-coordin ation, the patterns of coordination with the ligand molecules differed . While direct coordination to the L carboxyl oxygen was observed in 1 crystals, all ligation positions in 2 crystals were occupied by water molecules. On the other hand, 3 crystals formed a pentagonal bipyrami dal structure (seven-coordination), where oxygens of L phosphates and water molecules coordinated to the calcium ion. Each of the complex st ructures showed characteristic molecular packing depending on the patt ern of coordination to the respective metal ion. L is monoanionic in a ll complex crystals, where the phosphate and carboxyl groups are depro tonated and pyridine nitrogen is protonated, and is neutralized by eac h metal ion. Crystal data: 1, monoclinic, space group P2(1)/c, a=5.412 9(6), b=10.515(2), c=22.770(2) Angstrom, beta=91.853(9)degrees, Z=4, R =0.0404 for 1834 observed reflections; 2, triclinic, space group P (1) over bar, a=7.514(2), b=16.976(4), c=6.789(3) Angstrom, alpha=96.84(3 ), beta=109.10(3), gamma=100.50(2)degrees, Z=2, R=0.0684 for 1605 obse rved reflections; 3, triclinic, P (1) over bar, a=10.069(2), b=14.501( 3), c=10.051(1) Angstrom, alpha=100.75(1), beta=97.28(2), gamma=76.18( 2)degrees, Z=2, R=0.0540 for 3637 observed reflections.