Bioinorganic Chemistry on Structure and Function of Unprecented Low-Spin Typed Non-Heme Iron(III) Complexes

1.从短杆菌R312和绿叶假单胞菌B23中分离得到的氰基水合酶是一种新的含铁酶。ESR研究表明，(1)腈水合酶是第一个具有典型的低自旋铁(III)配位环境的非血红素铁水合酶，(2)天然酶中铁(III)的轴向位置可能被硫酸盐和水基团占据，(3)脂肪腈底物通过水底物取代直接与铁(III)活性中心结合。基于博莱霉素铁(III)独特的配位位置，设计并合成了典型的低自旋铁(III)与非血红素铁(III)的模型配合物。含4-甲氧基吡啶和叔丁基团的N50给体集配体具有明显的低自旋铁(III)位的ESR和~1H-核磁共振特征。合成的模型化合物(PYML-8)显示了博莱霉素与4-二甲氨基吡啶核和叔丁基醚的金属结合部位的氧活化，最高可达天然博莱霉素的125%。由于样品的X射线分解和酶的小单晶，对氰基水合酶铁(III)活性中心的EXAFS和X射线结晶学研究没有提供有价值的信息。

1. Nitrile hydratase isolated from Brevibacterium R312 and Pseudomonas chlororaphis B23 is a new iron-containing enzyme. The ESR study reveals that (1) nitrile hydratase is the first non-heme iron enzyme with a typical low-spin iron(III)-coordination environment, (2) axial positions of the iron(III) site in the native enzyme may be occupied by thiolate and aquo groups, and (3) aliphatic nitrile substrates directly bind to the iron(III)-active center by water substrate replacement.2. On the basis of unique iron(III) coordination site of bleomycin, model non-heme iron(III) complexes with a typical low-spin iron(III) have been designed and synthesized. The N50 donor set ligand including 4-methoxypyridine and t-butyl groups clearly exhibited ESR and ^1H-NMR features characteristic of low-spin iron(III) site.3. A synthetic model compound(PYML-8) for the metal-binding site of bleomycin with a 4-dimethylaminopyridine nucleus and a tert-butyl ether group showed dioxygen activation up to 125 % of that of natural bleomycin.4. EXAFS and X-ray crystallographic studies of the iron(III)-active site of nitrile hydratase did not give valuable informations, because of decomposition of the sample by X-ray irradiation and of small single crystal of the enzyme.