Interaction of pyridoxal-derived hydrazones with anions and Co²⁺, Co³⁺, Ni²⁺, Zn²⁺ cations

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

“…After the addition of 14.5 units of BAPim, the changes in the spectra (Figure S8 in the Supporting Information) are very quick, and only the end of the dephosphorylation process can be observed. 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.…”

“…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).…”

“…53 and 54 should lead to a significant demetallation of the enzyme and consequent loss in its activity, which is not observed in the experiment. The log β value of the reaction ( 11) is undefined; however, its lower boundary can be estimated as 9 units, 15 while the upper one can hardly exceed 15-16 log units. Under these assumptions, the free ligand content may vary from 89 μmol L -1 (no complexation with zinc(II) at all at log β = 9; evidently, Figure S8 in the Supporting Information, it is not correct) to 3 μmol L -1 (almost complete complexation with zinc(II) at log β = 16).…”

“…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.…”

“…Therefore, the enzymatic dephosphorylation of pyridoxal 5′phosphate derivatives is probably an important step of hydrazones metabolism in either liver or guts influencing their bioavailability and/or excretion. Different luminescent properties of PLP 10 and PL 15 hydrazones combined with the elevated levels of APs in the pathologic tissues provide a possible way to use these compounds as fluorescent bioimaging agents.…”