Lugo-Mas Priscilla, Taylor Wendy, Schweitzer Dirk, Theisen Roslyn M, Xu Liang, Shearer Jason, Swartz Rodney D, Gleaves Morgan C, Dipasquale Antonio, Kaminsky Werner, Kovacs Julie A
The Department of Chemistry, University of Washington, Box 351700 Seattle, Washington 98195-1700, USA.
Inorg Chem. 2008 Dec 1;47(23):11228-36. doi: 10.1021/ic801704n.
The syntheses and structures of three new coordinatively unsaturated, monomeric, square-pyramidal thiolate-ligated Fe(III) complexes are described, Fe(III)((tame-N(3))S(2)(Me2)) (1), Fe(III)(Et-N(2)S(2)(Me2))(py) (3), and Fe(III)((tame-N(2)S)S(2)(Me2)) (15). The anionic bis-carboxamide, tris-thiolate N(2)S(3) coordination sphere of 15 is potentially similar to that of the yet-to-be characterized unmodified form of NHase. Comparison of the magnetic and reactivity properties of these reveals how anionic charge build up (from cationic 1 to anionic 3 and dianionic 15) and spin-state influence apical ligand affinity. For all of the ligand-field combinations examined, an intermediate S = 3/2 spin state was shown to be favored by a strong N(2)S(2) basal plane ligand field, and this was found to reduce the affinity for apical ligands, even when they are built in. This is in contrast to the post-translationally modified NHase active site, which is low spin and displays a higher affinity for apical ligands. Cationic 1 and its reduced Fe(II) precursor are shown to bind NO and CO, respectively, to afford Fe(III)((tame-N(3))S(2)(Me))(NO) (18, nu(NuO) = 1865 cm(-1)), an analogue of NO-inactivated NHase, and [Fe(II)((tame-N(3))S(2)(Me))(CO)] (16; nu(CO) stretch (1895 cm(-1)). Anions (N(3)(-), CN(-)) are shown to be unreactive toward 1, 3, and 15 and neutral ligands unreactive toward 3 and 15, even when present in 100-fold excess and at low temperatures. The curtailed reactivity of 15, an analogue of the unmodified form of NHase, and its apical-oxygenated S = 3/2 derivative Fe(III)((tame-N(2)SO(2))S(2)(Me2)) (20) suggests that regioselective post-translational oxygenation of the basal plane NHase cysteinate sulfurs plays an important role in promoting substrate binding. This is supported by previously reported theoretical (DFT) calculations.
本文描述了三种新的配位不饱和、单体、四方锥型硫醇盐配位的Fe(III)配合物的合成与结构，分别为Fe(III)((tame-N(3))S(2)(Me2)) (1)、Fe(III)(Et-N(2)S(2)(Me2))(py) (3)和Fe(III)((tame-N(2)S)S(2)(Me2)) (15)。15的阴离子双羧酰胺、三硫醇盐N(2)S(3)配位环境可能与尚未表征的未修饰形式的NHase相似。对这些配合物的磁性和反应性性质的比较揭示了阴离子电荷积累（从阳离子1到阴离子3和二阴离子15）以及自旋态如何影响顶端配体亲和力。对于所研究的所有配体场组合，结果表明，强N(2)S(2)基面配体场有利于中间S = 3/2自旋态，并且发现这会降低对顶端配体的亲和力，即使顶端配体已内置。这与翻译后修饰的NHase活性位点形成对比，后者是低自旋的，并且对顶端配体表现出更高的亲和力。阳离子1及其还原的Fe(II)前体分别被证明能结合NO和CO，生成Fe(III)((tame-N(3))S(2)(Me))(NO) (18, ν(NO) = 1865 cm(-1))，一种NO失活的NHase类似物，以及[Fe(II)((tame-N(3))S(2)(Me))(CO)] (16; ν(CO)伸缩振动 (1895 cm(-1))。阴离子（N(3)(-)、CN(-)）被证明对1、3和15无反应，中性配体对3和15也无反应，即使在100倍过量且低温的情况下。15（一种未修饰形式的NHase类似物）及其顶端氧化的S = 3/2衍生物Fe(III)((tame-N(2)SO(2))S(2)(Me2)) (20)的反应活性受限表明，基面NHase半胱氨酸硫的区域选择性翻译后氧化在促进底物结合中起重要作用。先前报道的理论（DFT）计算支持了这一点。
