氧氣在許酵素的催化循環中扮演非常重要的角色。氧氣會與金屬蛋白的活性中心發生反應形成一些中間產物。在所有種類的金屬輔酶中，人體裡以鐵為中心的為大宗。Fe(III)-hydroxo、Fe(III)-superooxo和Fe(IV)-peroxo是最有反應性的中間產物。半胱胺酸雙加氧酶(Cysteine dioxygenase, CDO)在引入氧氣之後提高了半胱胺酸的氧化態並且透過氧化降解有毒的半胱胺酸。細胞色素酶(Cytochrome P450, cytP450)也是一種含鐵蛋白，含有一個卟啉和半胱胺酸。在氧氣進入催化循環後形成三價鐵超氧的結構，是為一個關鍵的中間產物。CDO和cytP450都是含有半胱胺酸配位的鐵蛋白, 含硫配位的酵素往往都和單純以氮作為配位的系統有著不同的本質。
我們實驗室利用利用富含硫的配位基H3[PS3”] (H3[PS3”]= H3[P(C6H3-3-SiMe3-2-SH)3])合成仿生錯合物，像是[PPh4][FeII(PS3”)(CH3CN)]和[PPh4][FeIII(PS3”)(OCH3)]。在這部分的研究中，我們專注於分離及探討與半胱胺酸配位的含鐵酵素中間產物相關的鐵硫錯合物。基於這個動機，合成以及鑑定了三個錯合物[PPh4][FeIII(PS3”)(OH)] (1)、[NMe4][FeIII(PS3”)(OAc)] (2)和[PPh4][Fe(PS3”)(O2)] (3)。這些錯合物都透過X光晶體學得到結構。錯合物1無法分離出純相，因此只能得到晶體數據。錯合物2透過光譜學了解其特性。最後，錯合物3由[PPh4][FeII(PS3”)(CH3CN)]與氧氣在低溫(~-40oC)反應形成。[Fe(O2)]2+官能基的電子組態經由不同種的物理方法，像是振動光譜、梅茲堡光譜及超導量子干涉儀確認。基於梅茲堡光譜的研究，鐵中心的氧化價數為三價鐵。而根據紅外光光譜，氧-氧的振動頻率在950cm-1被指認為超氧的模式。超導量子干涉儀數據顯示自旋態為S= 1。結合理論計算，S=1的總自旋是由S= 3/2的鐵中心及S= 1/2的超氧配位基經由強烈的反鐵磁耦合所組成。另外，還進行了錯合物3的反應性研究。錯合物3與TEMPO-H發生了奪氫反應(HAA)。自身衰退的產物經由光譜可以觀測到氧化膦的特徵，進而暗示了氧-氧鍵的斷裂伴隨著氧原子由金屬中心轉移到鍵結的膦配位基。

O2 plays an important role in catalytic cycle of many enzymes. Some intermediates would form after O2 involving in the active site of metalloprotein. In all category of metal cofactors, ones with iron centers are most abundant in human. Fe(III)-hydroxo, Fe(III)-superoxo and Fe(IV)-peroxo are the most reactive intermediates. Cysteine dioxygenase (CDO) introduces O2 to promote oxidation cysteine so that CDO can degrade toxic cysteine by oxygenation. Cytochrome P450 (cytP450) is also an iron-containing protein with porphyrin and a cysteine. Fe(III)-superoxo is a key intermediate after O2 involving in catalytic cycle. Both CDO and cytP450 are cysteinate-ligated iron enzymes, the thiolate-containing enzymes have different nature from only N donor ligand system.
Our laboratory has employed sulfur-rich ligand, H3[PS3”] (H3[PS3”]= H3[P(C6H3-3-SiMe3-2-SH)3]), to synthesize biomimetic complexes like [PPh4][FeII(PS3”)(CH3CN)] and [PPh4][FeIII(PS3”)(OCH3)]. In this work, we focus on isolating and studying iron thiolate complexes relevant to intermediates found in cysteinate-ligated iron enzymes. Based on this motivation, three complexes, [PPh4][FeIII(PS3”)(OH)] (1), [NMe4][FeIII(PS3”)(OAc)] (2) and [PPh4][Fe(PS3”)(O2)] (3) were synthesized and characterized. Structures of these complexes were determined by X-ray crystallography. [PPh4][FeIII(PS3”)(OH)] (1) can not be isolated in pure form, thus only the crystallographic data was obtained. The spectroscopic and structural data of complex 2 were characterized and investigated. Finally, complex 3 was formed by [PPh4][FeII(PS3”)(CH3CN)] reacting with O2(g) at low temperature (ca. -40oC). The electronic structure of [Fe(O2)]2+ moiety in 3 was confirmed by various physical methods such as vibrational spectroscopy, Mӧssbauer spectroscopy and SQUID magnetometry. The oxidation state of the iron center is assigned as a Fe(III) based on Mӧssbauer studies. According to the IR data, the O-O stretching frequency at 950 cm-1 is considered as a superoxo stretching mode. The SQUID data has shown a spin state of S= 1. Combined with the theoretic calculation, the total spin of S = 1 is attributed from a strong antiferromagnetic coupling between an S = 3/2 ferric center and an S = 1/2 superoxo ligand. In addition, reactivity studies of complex 3 were explored. Complex 3 was reacted with TEMPO-H via H-atom abstraction (HAA). The self-decay product characterized by spectroscopies gave a phosphine oxide characteristic, further implying O-O bond was cleaved followed by oxo-transfer from metal center to bound phosphine donor.

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