Factors affecting the metal ion–hydroxamate interactions: effect of the position of the peptide function in the connecting chain on the Fe(III), Mo(VI) and V(V) complexation of some new desferrioxamine B (DFB) model dihydroxamic acids

Three new dihydroxamic acids (HO(CH3)NCO(CH2)xCONH(CH2)yCON(CH3)OH, where the related x and y values are as follows: 2,5; 3,4 and 3,3) with different length of the connecting chains containing the peptide group in different positions between the two functional groups were synthesized and their complexation with Fe(III), Mo(VI) and V(V) were studied by pH-potentiometric and spectrophotometric methods. Both the structure and length of the connecting chain in the 2,5-dihydroxamic acid (2,5-DIHA) are the same as those in the natural siderophore, desferrioxamine B (DFB). Although the stability of the monochelated complexes formed with all three dihydroxamic acids are similar, 2,5-DIHA forms significantly more stable bis-chelated complexes than the other two ligands with the three metal ions studied. The results support the hypothesis that the arrangement of the two chelating functions in 2,5-DIHA is in a proper preorganization for the coordination in octahedral complexes to metal ions having similar ionic radius as iron(III) has.