The Synthesis, Crystal and Molecular Structure, and Oxidation State of Iron Complex from Pyridoxal Isonicotinoyl Hydrazone and Ferrous Sulphate

Abstract

The reaction of isonicotinoyl hydrazone of pyridoxal (PIH), a biologically active iron‐carrier, with FeSO4‐7H20 at pH ∼ 6 generates the delta, lamda species of the N,N‐trans‐O,O‐cis‐cis coordination isomer of an iron(III) complex with iron‐to‐ligand ratio of 1:2. The dark red‐brown crystals are monoclinic, space group C2/c, with unit‐cell dimensions a = 14.487(2), b = 18.586(2), c = 27.508(4) Å, β = 102.76(3)°, and Z = 8. The coordination around the metal is distorted octahedral and involves the protonated organic ligands, which are chelated through the phenolic oxygen [Fe‐O1 1.941(6), Fe‐O1′ 1.938(6)], an enolic form of the carbonyl oxygen [Fe‐O3 2.017(6), Fe‐O3′ 2.018(6)] and the azomethinic nitrogen [Fe‐N2 2.133(8), Fe‐N2′ 2.133(8)]. Packing is determined by systems of N‐H….O and O‐H….O hydrogen bonds involving the protonated pyridoxal nitrogens, the pyridoxal hydroxymethyl group, and the [SO4]2− group. The Mössbauer spectra at different temperatures (300 K, 88 K and 4.1 K) clearly prove that the iron atom in the complex is in a high‐spin trivalent state.

The Evolution of Iron Chelators for the Treatment of Iron Overload Disease and Cancer

“…and Fig. 13A) (Antholine et al, 1977;Avramovici-Grisaru et al, 1985;Garcia-Tojal et al, 2002). However, thiosemicarbazones feature a sulfur donor atom in the coordination sphere, whereas in hydrazones the analogous donor atom is a carbonyl oxygen (Fig.…”

“…Interestingly, PIH was also found to bind Fe(II) although with lower affinity . The ferrous complex of PIH was found to be sensitive to oxidation, forming ferric complexes in the presence of oxygen (Avramovici-Grisaru et al, 1985;Vitolo et al, 1990). The ability of PIH to bind Fe(II) is believed to be responsible in its role of protecting plasmid pUC-18 DNA against OH ⅐ -mediated strand breaks by scavenging Fe(II) and enhancing its autooxidation rate (Hermes-Lima et al, 1998).…”

Pyridoxal Isonicotinoyl Hydrazone (PIH), a Synthetic Ion-Chelating Agent

“…However, little is known about the structure of the title compound, although some spectroscopic and physico-chemical data are now available (Fakhrayan, Doucet & E1-Hage Chahine, 1993;Dubois, Fakhrayan, Doucet & E1-Hage Chahine, 1992;Richardson et al, 1990;Avramovici-Grisaru, Sarel, Cohen & Bauminger, 1985;Murphy, Rose, Schomaker & Aruffo, 1985;Colonna, Coss6-Barbi, Massat & Doucet, 1993;Colonna, Coss6-Barbi, Massat, Ben Abdelmoumene & Doucet, 1993). For this compound, various conformers are possible a priori, but neither IR nor NMR results, nor semi-empirical quantum calculations can give definitive conclusions (Colonna, Coss6-Barbi, Massat, Ben Abdelmoumene & Doucet, 1993).…”

Synthetic and Natural Products as Iron Chelators

“…The Fe-binding affinity of these ligands has been examined, revealing that H 2 PIH has high affinity for Fe III , being comparable to that of DFO [118]. Additionally, H 2 PIH was found to bind Fe II with lower affinity [118], with this ferrous complex being sensitive to oxidation converting to the ferric form in the presence of oxygen [118,119]. H 2 PIH and its analogues have also been shown to bind Ca II , Mg II and Zn II [120], although the affinity for these divalent metals was much lower than that of Fe III , indicating that the chelation of Fe III over other biologically important metal ions can be expected in biological systems [120].…”