title: Interaction of flavins with electron-rich metals.
abstract: A complex of the electron-rich ion Cu(I) with the flavoquinone analogue 10-methylisoalloxazine has been synthesized and characterized by x-ray methods. The complex is unstable to oxygen. It is black-green in color, in contrast with the bright yellow, orange, or orange-brown crystalline complexes of 10-methylisoalloxazine or riboflavin with Cu(II), Ag(I), and Pb(II). These results are indicative of strong perturbation of the flavin electronic structure by the Cu(I) ion and suggest that this complex is a reasonable model for incipient transfer of an electron from a reduced metal to flavoquinone. the crystal structure is orthorhombic, Pna2-1, with unit cell constants a = 31.24(1) (figures in parentheses are estimated standard deviations), b = 12.862(4), c = 6.239(2) A, Pobs = 1.76 g per cm-3 and Pcalc = 1.77 g per cm-3 for Z = 4 and asymmetric formula CuClO4-2(C11H8N4O2). HCOOH. The final R factor based on 1250 counter-measured data is 8.8%. The 2 independent 10-methylisoalloxazine molecules, A and B, bind strongly to the cuprous ion throug N(5) of each flavin. The copper is approximately linearly coordinated with an N-Cu-N angle of 153(1) degrees, and Cu-N(5) distances of 1.94(2) A and 1.92(2) A. The next nearest atoms to Cu are the O(4) oxygens of each flavin, forming weak bonds with distances Cu-O(4) = 2.27(2) A and 2.21(2) A for molecules A and B. The dihedral angle between the 2 10-methylisoalloxazine molecules is 65.4 degrees.
mesh_terms: D001665:Binding Sites; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003300:Copper; D003460:Crystallization; D003461:Crystallography; D005415:Flavins; D005561:Formates; D008958:Models, Molecular; D008968:Molecular Conformation; D008970:Molecular Weight; D010472:Perchlorates; D012256:Riboflavin / Q000031:analogs & derivatives; D013696:Temperature; D013816:Thermodynamics
chemical_list: D005415:Flavins; D005561:Formates; D010472:Perchlorates; C009774:10-methylisoalloxazine; D003300:Copper; D012256:Riboflavin