A preorganized siderophore: Thermodynamic and structural characterization of alcaligin and bisucaberin, microbial macrocyclic dihydroxamate chelating agents
A preorganized siderophore: Thermodynamic and structural characterization of alcaligin and bisucaberin, microbial macrocyclic dihydroxamate chelating agents
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DOI：
10.1021/ic9810182
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发表时间：
1998-12-28
影响因子：
4.6
通讯作者：
Nishio, T
中科院分区：
文献类型：
--
作者：
Hou, ZG;Raymond, KN;Nishio, T
本文从热力学和结构上研究了两种大环二羟肟酸铁载体碱性蛋白（AG）和双青素（BR）的铁配位化学。碱性蛋白是淡水细菌和哺乳动物病原体（包括导致人类百日咳的细菌）的铁蛋白，而与碱性蛋白结构类似的双角豆素则由海洋细菌产生。碱性蛋白和双青素在酸性条件下形成1:1的铁络合物（FeL+），在中性ph及以上形成2:3的铁络合物（Fe2L3）。这些大环二羟酸铁络合物的稳定性常数与线性二羟酸铁络合物红桃酸（RA）的稳定性常数有显著差异。值得注意的是，alcaligin的K-FeL是rhodtorulic的32倍，而随后Fe2L3的逐步形成常数是前者的3倍。碱性蛋白酶的Fe（III）配合物具有立体特异性；Fe2L3配合物的绝对构型（圆二色性和x射线结构）为Lambda。Fe2L3碱性络合物的结构是一种拓扑结构替代三螺旋结构的rhodotorruic络合物Fe-2(RA)(3)。FeL配合物中游离配体和双齿配体的结构基本相同，表明碱性蛋白对金属离子结合具有高度的预组织性。这解释了碱性蛋白和红桃酸之间K-FeL的差异，也解释了Fe2L3碱性蛋白复合物的单桥拓扑结构。碱解蛋白的质子化常数（log K-a1和log K-a2）分别为9.42(5)和8.61(1)，双角豆素的质子化常数为9.49(2)和8.76(3)。铁（III）配合物（log K-ML和log K-M2L3）的逐步形成常数分别为：碱解素的23.5(2)和17.7(2)，双角豆素的23.5(5)和17.2(5)。alcaligin和bisucaberin的总形成常数（log beta(230)）分别为64.7(1)和64.3(1)。在较低的配体与金属比（1:1）下，进一步研究了Fe（III）与碱素的溶液化学。在高pH下，一种新型的2:2铁铋-mu-氧桥式碱还原酶络合物（Fe2L2O22-）的对数β(22-4)为16.7(2)。该物种表现出与铁-铋-氧配合物一致的行为，包括反铁磁耦合。晶体数据：Fe-2(AG)(3)。25H(2)O在正交空间群P2(1)2(1)2(1)中结晶，a =13.3374(4)埃，b = 16.1879(5)埃，c = 37.886(1)埃，V = 8179.7(4), Z = 4。对于5512个F-0(2) bbb3 sigma（F-0(2)）的反射，最终R (R-w) = 0.053（0.068）。
The iron coordination chemistry of two macrocyclic dihydroxamate siderophores, alcaligin (AG) and bisucaberin (BR), has been investigated thermodynamically and structurally. Alcaligin is a siderophore of freshwater bacteria as well as mammalian pathogens, including the bacterium that causes whooping cough in humans, while bisucaberin, a structural analogue of alcaligin, is produced by marine bacteria. Both alcaligin and bisucaberin form 1:1 ferric complexes (FeL+) in acidic conditions and 2:3 ferric complexes (Fe2L3) at and above neutral pH. The stability constants of these macrocyclic dihydroxamate siderophores differ significantly from that of rhodotorulic acid (RA), a linear dihydroxamate siderophore. Notably, K-FeL Of alcaligin is 32 times greater than that of rhodotorulic acid, while the subsequent stepwise formation constant for Fe2L3 is 3 times less. The Fe(III) complexes of alcaligin are stereospecific; the absolute configuration of the Fe2L3 complex (circular dichroism and X-ray structure) is Lambda. The structure of the Fe2L3 alcaligin complex is a topological alternative to the triple-helicate structure of the rhodotorulic complex Fe-2(RA)(3). The structures of the free ligand and the bisbidentate ligand in the FeL complex are essentially identical, indicating that alcaligin is highly preorganized for metal ion binding. This explains the difference in K-FeL between alcaligin and rhodotorulic acid, as well as explaining the monobridged topology of the Fe2L3 alcaligin complex. The protonation constants (log K-a1 and log K-a2) are 9.42(5) and 8.61(1) for alcaligin and 9.49(2) and 8.76(3) for bisucaberin. The stepwise formation constants of the Fe(III) complexes (log K-ML and log K-M2L3) are 23.5(2) and 17.7(2) for alcaligin and 23.5(5) and 17.2(5) for bisucaberin. The overall formation constants (log beta(230)) Of alcaligin and bisucaberin are 64.7(1) and 64.3(1). The solution chemistry of Fe(III) and alcaligin was further investigated at a lower ligand to metal ratio (1:1). At high pH, a novel 2:2 ferric bis-mu-oxo-bridged complex of alcalagin forms (Fe2L2O22-) with a log beta(22-4) Of 16.7(2). This species exhibits behavior consistent with an iron bis-mu-oxo complex, including antiferromagnetic coupling. Crystal data: Fe-2(AG)(3). 25H(2)O crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a =13.3374(4) Angstrom, b = 16.1879(5) Angstrom, c = 37.886(1) Angstrom, V = 8179.7(4), Z = 4. For 5512 reflections with F-0(2) > 3 sigma(F-0(2)) the final R (R-w) = 0.053(0.068).