Fe(Ⅲ)与2,3-二羟基苯甲酸配位反应的动力学和机理

Kinetics and Mechanism of the Complexing of Fe (III) by 2, 3-Dihydroxybenzoic Acid

单细胞微生物在铁的浓度小于10^(-6)mol·dm^(-3)时分泌Siderophores,此物质在近中性的条件下摄取外界的铁。其中一类为他Catechloate Siderophores(例如enterobactin)。enterobactin 有很强的配合Fe(Ⅲ)的能力。但铁如何从 Fe(Ⅲ)的enterobactin的配合物中释放出来,目前尚不清楚。Fe(Ⅲ)的2,3-二羟基苯甲酸体系提供了研究该机理的模式。镰形细胞性贫血和重型库利氏贫血(β-thalasemia)的输血治疗引起铁在肝、胰和心脏中的不断积累,导致这些器官纤维损伤和功能丧失。虽然2,3-二羟基苯甲酸是治疗此类贫血病的制剂,但对Fe(Ⅲ)的2,3-二羟基苯甲酸体系的热力学性质还没有深入研究,其动力学和机理的研究亦未见报道。

The kinetics and the mechanism for complexing of aqueous Fe (Ⅲ) by 2, 3- dihydroxybenzoic acid (1) have been studied in 1.00 mol·dm^(-3) ionic strength between 1.00×10^(-2)mol·dm^(-3) and 0.700 mol·dm^(-3) [H^+] under condition of [Fe(Ⅲ)]/[1]≥10. The rate constants for complexing of FeOH_2^(3+) FeOH^(2+) and Fe^2(OH)_2^(4+) by 1 and 1 anion have been measured and calculated. The active enthalpy and active entropy decrease with the [H^+] increasing. This indicates the associate mechanism for FeOH_2^(3+) and the dissociate mechanism for FeOH^(2+) and Fe_2(OH)_2^(4+) The reaction rate equation shows the H^+ dependence typical for Fe(Ⅲ) complexation, but there is an unusual contribution from a kinetic term second order in [Fe(Ⅲ)]. A possible mechanism is proposed.