DESIGN OF LIGANDS CONTAINING THE O-HYDROXYBENZYL GROUP - METAL-COMPLEXING PROPERTIES OF YDROXYBENZYL)DIETHYLENETRIAMINE-N,N',N''-TRIACETIC ACID

The ligand ydroxybenzyl)diethylenetriamine-N,N',N''-triacetic acid (H( 5)L) has been synthesised and the protonation constants for L determin ed by potentiometric methods in 0.5 mol dm(-3) NaNO3, and spectrophoto metric methods in 0.5 and 0.1 mol dm(-3) NaCl, all at 25 degrees C. Th e sites of protonation have been inferred from H-1 NMR studies in D2O. The complex formation constants of Ca-II, Zn-II Cd-II, Cu-II, Pb-II a nd Bi-III have been determined at 25 degrees C by potentiometric metho ds in 0.5 mol dm(-3) NaNO3, and spectrophotometric methods in 0.5 mol dm(-3) NaCl. The results show that at biological pH the hydroxybenzyl groups tend to remain protonated, and over most of the pH range proton ated complexes dominate, with fully deprotonated complexes occurring o nly at pH values above 9 or 10. The ligand L is, compared to some of i ts analogues, effectively a weak complexing agent. This is rationalise d in terms of the six-membered chelate rings formed in the complex, wh ich include the hydroxybenzyl group. The six-membered chelate rings de stabilize complexes of the larger metal ions with which the octadentat e ligand should prefer to co-ordinate.