Natural flavonoids such as quercetin, (+)catechin and rutin as well as four methoxylated derivatives of quercetin used as models were investigated to elucidate their impact on the oxidant and antioxidant status of human red blood cells (RBCs) The impact of these compounds against metal toxicity was studied as well as their antiradical activities with DPPH assay Antihemolytic experiments were conducted on quercetin, (+)catechin and rutin with excess of Fe, Cu and Zn (400 μM), and the oxidant (malondialdehyde, carbonyl proteins) and antioxidant (reduced glutathione, catalase activity) markers were evaluated The results showed that Fe and Zn have the highest prooxidant effect (37 and 33% of hemolysis, respectively) Quercetin, rutin and (+)catechin exhibited strong antioxidant properties toward Fe, but this effect was decreased with respect to Zn ions However, the Cu showed a weak antioxidant effect at the highest flavonoid concentration (200 μM), while a prooxidant effect was observed at the lowest flavonoid concentration (100 μM) These results are in agreement with the physico-chemical and antiradical data which demonstrated that binding of the metal ions (for FeNTA: (+)Catechin, KLFeNTA = 16(1) × 106 M-1 > Rutin, KLFeNTA = 20(9) × 105 M-1 > Quercetin, KLFeNTA = 10(7) × 105 M-1 > Q35OH, KLFeNTA = 63(87) × 104 M-1 > Quercetin3'4'OH and Quercetin 3OH, KLFeNTA ~ 2 × 104 M-1) reflects the (anti)oxidant status of the RBCs This study reveals that flavonoids have both prooxidant and antioxidant activity depending on the nature and concentration of the flavonoids and metal ions

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In Vitro Antioxidant versus Metal Ion Chelating Properties of Flavonoids: A Structure-Activity Investigation

Oral iron chelators for clinical use

The kinetics and mechanism of the substitution of coordinated water in nitrilotriacetate complexes of iron(III) (Fe(NTA)(OH2)2 and Fe(NTA)(OH2)(OH)-) by phosphate (H2PO4- and HPO42-) and acetohydroxamic acid (CH3C(O)N(OH)H) were investigated. The phosphate reactions were found to be pH dependent in the range of 4−8. Phosphate substitution rates are independent of the degree of phosphate protonation, and pH dependence is due to the difference in reactivity of Fe(NTA)(OH2)2 (k = 3.6 × 105 M-1 s-1) and Fe(NTA)(OH2)(OH)- (k = 2.4 × 104 M-1 s-1). Substitution by acetohydroxamic acid is insensitive to pH in the range of 4−5.2, and Fe(NTA)(OH2)2 and Fe(NTA)(OH2)(OH)- react at equivalent rates (k = 4.2 × 104 and 3.8 × 104 M-1 s-1, respectively). Evidence for acid-dependent and acid-independent back-reactions was obtained for both the phosphate and acetohydroxamate complexes. Reactivity patterns were analyzed in the context of NTA labilization of coordinated water, and outer-sphere electrostatic and H-bonding infl...

Kinetics and mechanism of iron(III)-nitrilotriacetate complex reactions with phosphate and acetohydroxamic acid.

Metal-ion catalysed aquation of transition metal complexes

Coordination Modes of Hydroxamates in Neptunium (V) Complexes in Aqueous Solution

Thermodynamics and kinetics of 1:1 complexation of iron(III) with benzo- and several ortho-substituted (CH3, NH2, Cl and OH) benzohydroxamic acids (HL) forming FeL2+ have been investigated spectropho-tometrically in aqueous perchloric acid solution. Under the experimental conditions ([H+] « TFc « THL) complexation involves reactions of HL with Fe3+ (k1 path) and FeOH2+ (k2 path) ions leading to an equilibrium. Both k1 and k2 have been evaluated by stopped-flow spectrophotometry following the formation of FeL2+ and the dissociation of FeL2+ in acid solution. The AH* value (42.5 ± 4.8 Hmol-1) for the k2 path is close to that for the water exchange of FeOH2+ species, suggesting essentially a dissociative (Id) process, but that (54.5 + 3.8 kJmol-1) corresponding to the k1 path is perceptibly lower than that for the water exchange of Fe3+ species indicating associative (Ia) character. The reverse rate constants (k-1 and k_2) for the dissociation of the complexes by the two paths have also been evaluat...

Thermodynamic and Kinetic Studies on the Iron(III)-Hydroxamate Interaction in Acid Media

At elevated temperatures (⩾ 70 °C) the title complex aquates significantly in aqueous acid media, releasing one thiocyanate in the first step, which exhibits no acid dependence. For this spontaneous aquation, the rate constant (kspont.) at 25 °C, ΔH≠ and ΔS≠ are 1.2×10−8s−1, 132 kJ mol−1 and 59 JK−1mol−1, respectively. This first step is followed by a slower second step in which, the second thiocyanate is released as the Co(dmgH)2 moiety is cleaved. The rate of release of thiocyanate is enhanced considerably by addition of Hg2+ and the complex changes smoothly into the corresponding di(aqua) product, [Co(dmgH)2(OH2)2+, without any complicating side reactions. Both the steps of the process are linearly dependent on [Hg2+]. For the catalysed reaction, the second-order rate constant at 25 °C, ΔH≠ and ΔS≠ for the first and second steps are 2.85 M−1s−1, 89 kJ mol−1, 60 JK−1mol−1; and 1.48 M−1s−1, 63 kJ mol−1, −30 JK−1mol−1, respectively. The observed linearity of the kobsvs [Hg2+] plots over a wide range of [Hg2+] concentration suggests a direct electrophilic (SE2) attack of the Hg2+ on the leaving thiocyanate ligand of the substrate complex; there is CoIII-NCS bond fission without the involvement of any long-lived binuclear intermediate of the type CoIII-NCS-HgII.

Samir Gopal Bhattacharya

Papers

Thermodynamic and Kinetic Studies on the Iron(III)-Hydroxamate Interaction in Acid Media

Kinetics of reactions of bis(isothiocyanato)bis(dimethylglyoximato)cobaltate(III) in presence and absence of Hg2+ ion in acid perchlorate media