Stability of Cu(II) and Zn(II) Complexes with Pyridinecarbohydrazones of Pyridoxal-5-phosphate in Aqueous Solution

Dephosphorylation of pyridoxal 5′‐phosphate‐derived Schiff bases in the presence of bovine alkaline phosphatase

“…The gain in the luminescence of pyridoxal hydrazones studied by us earlier, 14 compared with their PLP analogs, can be explained by the difference in composition and structure of protonated species at pH 10. According to the protonation constants determined in Ref.…”

“…Unfortunately, the direct study of hydrazones binding to BAPim is complicated since, first, hydrazones undergo the chemical transformation and the products have a different affinity towards the protein than the reagents; second, the hydrazones are capable of chelating Zn(II) ions. 14,15 BAPim having a lot of tryptophan, tyrosine, and phenylalanine residues 44 shows strong fluorescence in the range of 300-400 nm with a maximum at 330 nm (λ ex = 290 nm). The luminescence intensity does not change much in the presence of increasing amounts of either PLP-Tris or PLP-T2H or EDTA (Figure S7 in the Supporting Information; the spectra were corrected on the inner filter effect).…”

“…The growth in the long-wavelength range confirms the dephosphorylation of the ligand, as the complex Zn(II)(PL-3NH) 2 demonstrated increased absorbance at 400 nm (pH 7.4) 15 compared with that of the Zn(II)(PLP-3NH) 2 complex. 14 Since the analogous hydrazones are three-dentate ligands, and they are prone to form bulky complexes with stoichiometry ML 2 , [45][46][47][48][49] it is unlikely that the complex undergoes the dephosphorylation as it hardly fits the active site. A more reasonable assumption is partial dissociation of the complex with consequent dephosphorylation of the free ligands.…”

“…9,11 However, the hydrazones formed by pyridoxal (PL) or PLP might also prove harmful due to their metal-chelating properties. 12,13 Though the stability constants of d-metal complexes with PLP-and PL-derived hydrazones defining their biological activity are similar in neutral aqueous solution, 14,15 the equilibrium constants of binding of different B 6 vitamers and their hydrazones to serum albumins differ. 16,17 Schiff bases formed by PL are also less soluble than those of PLP since the phosphate group capable of dissociating twice is substituted by less acidic proton.…”

Complexes of Gold(III) with Hydrazones Derived from Pyridoxal: Stability, Structure, and Nature of UV-Vis Spectra

“…The phosphate group located in the periphery of the molecule does not significantly influence the chelating properties (it is noteworthy that, in general, the peripheral substituents of the hydrazones can be changed significantly without the loss of the most important properties; see, e.g., papers [22][23][24][25][26]). The hydrazone formed by PLP and isoniazid can also show anti-oxidant properties, because it inhibits the copper(II)-mediated oxidation of ascorbic acid due to the ability of Cu 2+ [27] binding. Comparisons of the stability constants of the complexes formed by Ni 2+ , Zn 2+ ions, and PL-and PLP-derived hydrazones [28,29] show that introducing the phosphate group leads to negligible changes in the value of the decimal logarithm of the stability constant (log β).…”