REACTIONS OF HYDROXAMIDOVANADATE WITH PEPTIDES - AQUEOUS EQUILIBRIA AND CRYSTAL-STRUCTURE OF OXOBIS(HYDROXAMIDO)-GLYCYLGLYCINATOVANADIUM(V)

Bis(hydroxamido)hydroxooxovanadate has been found to undergo favourabl e condensation reactions with simple peptides such as glycylglycine, g lycylglycylglycine, or glycyltyrosine to afford, in each case, three p roducts in the approximate ratio 1:3.5:0.2. The three products had the same ligand stoichiometry and, in the case of glycylglycine, an overa ll formation constant of 3.3 x 10(3) M-1 for the addition of GlyGly to bis(hydroxamido)vanadate. The V-51 chemical shift range of the produc ts (close to -850 ppm) overlaps that of the starting complexes and the products may well have a coordination geometry similar to the parent complexes. The chemical shifts observed for these materials are in the range of chemical shifts observed for peroxovanadium complexes. A cry stalline monomeric complex with a single glycylglycinato ligand was ob tained and its crystal structure determined. The complex is zwitterion ic and has a pentagonal bipyramidal coordination at vanadium with the glycine-NH2 functionality coordinated in the plane of the two hydroxya lamine ligands and the amido carbonyl oxygen in the apical position. S ome comparisons with peroxovanadium complexes are drawn. Crystal struc ture of V(O)(ONH2)(2)(GlyGly)H2O: monoclinic, space group Cc; Z= 4; a = 9.1340(9) Angstrom; b = 16.3355(15) Angstrom; c = 7.1149(6) Angstrom ; beta (degrees)= 103.020(7); V = 1034.31 Angstrom(3);T = 295 K; R-F = 0.21 for 2513 data (I-O greater than or equal to 2.5 sigma(I-O)) and 197 variables.