Electrochemical behavior of the Fe(III) complexes of the cyclic hydroxamate siderophores alcaligin and desferrioxamine E
Electrochemical behavior of the Fe(III) complexes of the cyclic hydroxamate siderophores alcaligin and desferrioxamine E
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DOI：
10.1021/ic980635n
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发表时间：
1999-02-08
影响因子：
4.6
通讯作者：
Crumbliss, AL
中科院分区：
文献类型：
--
作者：
Spasojevic, I;Armstrong, SK;Crumbliss, AL
用循环伏安法研究了环羟肟酸铁载体、碱化素和去铁胺E的铁（III）配合物的氧化还原行为。pH高于9的碱化酶的极限氧化还原电位（E-1/2 VS NHE）为-446 mV， pH高于7.5的铁胺E的极限氧化还原电位为-477 mV。在较低的pH值下，两种配合物的氧化还原电位都变为正值，伏安可逆性丧失，这被解释为铁（II）从配合物的还原形式中二次解离的结果。这些观察结果具有重要的生物学意义，因为它们提示了微生物细胞中利用这些铁载体获取铁的还原机制的可能性。为了比较，在相同的条件下，获得了铁（III）配合物与环三羟肟酸（铁肟胺E）和线性（铁肟胺B）结构，与环二羟肟酸（钙素）和线性（红脲酸和己二酸）结构，以及与单羟肟酸（乙酰羟肟酸和n -甲基乙酰羟肟酸）结构的循环伏安图。观察到的氧化还原电位使我们能够估计出完全配位的Fe（II）配合物的总体稳定性常数为log beta(II)(Fe(2)alcaligin(3)) = 24.6和log beta(II)（铁胺E） = 12.1。发现了E-1/2与pM之间的线性相关关系，并从结构（密度和环/无环）和所研究的{烷基- noh - co -烷基}型羟肟酸配体之间的电子差异方面讨论了这种关系的基础。
The redox behavior of Fe(III) complexes of the cyclic hydroxamate siderophores alcaligin and desferrioxamine E was investigated by cyclic voltammetry. The limiting, pH independent redox potential (E-1/2 VS NHE) is -446 mV for alcaligin above pH 9 and -477 mV for ferrioxamine E above pH 7.5. At lower pH values, the redox potential for both complexes shifts positive, with a loss of voltammetric reversibility which is interpreted to be the consequence of a secondary dissociation of Fe(II) from the reduced form of the complexes. These observations are of biological importance, since they suggest the possibility of a reductive mechanism in microbial cells which utilize these siderophores to acquire Fe. For comparison purposes, cyclic voltammograms were obtained for Fe(III) complexes with trihydroxamic acids of cyclic (ferrioxamine E) and linear (ferrioxamine B) structures, with dihydroxamic acids of cyclic (alcaligin) and linear (rhodotorulic and sebacic acids) structures, and with monohydroxamic acids (acetohydroxamic and N-methylacetohydroxamic acids) at identical conditions. The observed redox potentials allow us to estimate the overall stability constants for fully coordinated Fe(II) complexes as log beta(II)(Fe(2)alcaligin(3)) = 24.6 and log beta(II)(ferrioxamine E) = 12.1. A linear correlation between E-1/2 and pM was found, and the basis for this relationship is discussed in terms of structural (denticity and cyclic/acyclic) and electronic differences among the {alkyl-NOH-CO-alkyl} type of hydroxamic acid ligands studied.