Structure of pyridoxal isonicotinoyl hydrazone (PIH) and its analogs.

These compounds were synthesized by Schiff base condensation as described previously,12 and the absence of significant amounts of the starting materials in these preparations was confirmed by analytical thin-layer chromatography. Identity and purity of the hydrazones were confirmed by ¹H- and ¹³C-NMR.¹H spectra were similar to those reported previously.12 Solutions of the chelators were prepared in 0.1 M NaOH in 50% aqueous ethanol and were immediately used to prevent their base-catalyzed hydrolysis. Control experiments in which stock solutions were prepared in dimethyl sulfoxide yielded similar results (not shown), indicating that any hydrolysis that occurred in the basic solutions was negligible.