SIDEROPHORE ANALOGS - CHELATING PROPERTIES OF A NEW CYCLIC DIAZADIHYDROXAMIC ACID

A new cyclic diaza-dihydroxamic acid, 1,4-diazacycloheptane-NN'-bis(N-methyl-acetohydroxamic acid) (DACHDMAHA) has been synthesized and studied. This paper is the second one devoted to finding synthetic ferric sequestering agents suitable for mimicking chemical and biological properties of the naturally occurring rhodotorulic acid. This ligand, having the hydroxamate arms bound to a seven-membered ring diamine, presents some biological activity, as was previously found for the corresponding six-membered compound (PIPDMAHA). Stability constants with iron(III) and iron(II) as well as with copper(II) and copper(I) have been determined by potentiometry, spectrophotometry and cyclic voltammetry, this latter technique being also useful for the interpretation of the electrochemical reaction and the determination of the rate constant of dissociation of iron(II) complexes. Comparing the complexes obtained with DACHDMAHA and PIPDMAHA it has been noticed that the complexes with the first ligand are more stable and that the rate constant of dissociation of the iron(II) complex is higher, showing that this ligand has more of the characteristics of a siderophore.