Metalloflavoprotein models. The crystal structure of bis(riboflavin) bis(cupric perchlorate) dodecahydrate.

摘要: Abstract An orange crystalline copper(II) perchlorate complex of riboflavin, a possible model for enzymic metal-flavin interactions, has been prepared and characterized by x-ray techniques. The crystals are triclinic, with symmetry P1; unit cell constants = 7.701 (2) A (figures in parentheses following numerical values standard deviations the least significant digits cited), b 11.230 (3) A, c 17.336 (4) α 101.85 (2)°, β 96.41 γ 89.90 Z 1, ρobs 1.70 g per cm3, ρcalc 1.701 cm3 2 Cu-(CIO4)2·2C17H20N4O6·12H2O cell. crystal structure, refined use 3636 counter-measured reflections, gives an R factor 7.9%. There independent riboflavin molecules Cu(II) ions each One (RFa) is bound to both copper ions, Cu(1) via O(4) N(5) at distances 2.00 2.43 Cu(2) O(5'), O(4'), O(2) 2.30 (2), 1.97 2.49 A. other (RFb) only one copper, Cu(1), lengths 2.39 water, H2O(3) hydrogen-bonded RFb. These results confirm existence two separate chelate sites, N(1)-O(2) O(4)-N(5), flavoquinoid system offer further evidence that these sites will nearly always be occupied positive or dipoles. Supporting earlier prediction, ribityl groups approximate C(2')-C(5') extended planar conformation O(2') pointing over secondary site However, RFa alters relationship chain ring skeleton, producing 180° rotation about N(10)-C(1') bond. This change permits O(4') hydrogen bond N(1), O(5') coordinate copper. Water complete distorted octahedral coordination shells ions.