SYNTHESIS, CHARACTERIZATION, AND SOLUTION CHEMISTRY OF A FAMILY OF PROTEIN-BINDING INORGANIC COMPLEXES - BIS(IMIDAZOLE)(AMINO ACID-N,N-DIACETATO)CHROMIUM(III)

The synthesis and characterization of a family of transition-metal complexes containing amino acid substituents, which has shown an array of recognition characteristics relevant to association with proteins, is described. These molecules are based upon the bis(imida7ole)(nitrilotriacetato)chromium(III) core, with the series generated through substitutions of amino acid side chains onto the methylene position of one of the chelate rings. The synthesis of the series has been achieved through the intermediate bis(aquo)(nitrilotriacetato)chromium(III) (1), previously not isolated, and by the use of substituted analogues. The solvated, solid-state structures of two members of the family, bis(imidazolc)(/-lcucine-N,N-diacetato)chromium(III) (3a) and bis(imidazole)(/-phcnylalanine-N,N-diacetato)chromium(III) (4a) have been established by single-crystal X-ray diffraction studies. Crystal data: (3a, orthorhombic, space group P212121, a = 8.576 (3) Å, 6=15.784 (9) Å, c = 15.648 (6) Å, V = 2118 (2) Å3, Z = 4, R(Fo) = 0.0421 (RW(F0) = 0.0627); 4a, orthorhombic, space group P212I2I, a = 9.601 (4) Å, b = 14.045 (4) Å, c = 37.235 (11) Å, V = 5021 (3) Å3, Z = 8, R(F0) = 0.0846 (RW(F0) = 0.0985). The solid-state intermolecular interactions of these complexes arc relevant to protein binding and include not only hydrogen-bonding interactions but also aromatic-aromatic interactions (in 4a). Electronic and circular dichroic parameters for the complexes arc reported, and the stereochemical course of the aquation of the parent bis(imidazole)(nitrilotriacctato)chromium(lll) (2) in solution is described. When 2H NMR methods are used on the dcutcrated analogue, the imidazole cis to three carboxylates is found to be the leaving group. © 1990, American Chemical Society. All rights reserved.