SYNTHESIS AND STRUCTURAL-ANALYSIS OF NEW IRON(III) POLYHYDROXAMINO COMPLEXES WITH POTENTIAL APPLICATION TO NUCLEAR-MAGNETIC-RESONANCE IMAGING .2. STUDIES ON COMPLEXES FORMED IN-SITU FROM HYDROXAMIC ACIDS - RELAXIVITY OF THE COMPLEX L)-4-(4''-AMINOBUTYLOXY)-2,6-PYRIDINEDICARBOXAMIDE

Numerous analogous dihydroxamates of rhodotorulic acid have been prepa red, and their mode of complexation of iron(III) and the stability of these complexes studied as a function of pH, for comparison with ferri oxamine B and the complex of acetohydroxamic acid with iron(III). This study has shown that the stoichiometry of the complexes is 2:3 (at a pH of 7) and 1:1 (at a pH of 2), and that, in spite of a complete comp lexation, their electrochemical behaviour varies greatly with pH. The very strong complexation constant observed (log beta(110) = 21.3) at a pH of 1 with the ligand N,N'-bis(acetylhydroxamino-3' propyl)-pentylo xy-4 pyridine-2,6-dicarboxamide confirms the strong complexation capac ity of iron(III) by these complexes. The high relaxivity of the comple x of iron(III) with the -(amino-4''-butyloxy)-4-pyridine-2,6-dicarboxa mide suggests that this product could be a useful contrasting agent fo r nuclear magnetic imaging.