Clusters thiolates

Thiolation domains contain a conserved serine residue, to which a 4 -phosphopantetheinyl group is attached - it is this arm to which the growing peptide is attached. The phosphopantetheinyl group is itself attached by a specific enzyme known as a phosphopantetheinyl-transferase (PPTase), the gene for which is often found within the NRPS cluster. Thiolation and condensation domains are also known to influence the selection of amino acids, although to a lesser extent than the adenylation domains. Finally, each NRPS cluster usually possesses a single thioesterase domain, which cleaves the peptide from the protein complex, often cyclizing the released peptide in the process. 

Iron Sulfur Compounds. Many molecular compounds (18—20) are known in which iron is tetrahedraHy coordinated by a combination of thiolate and sulfide donors. Of the 10 or more stmcturaHy characterized classes of Fe—S compounds, the four shown in Figure 1 are known to occur in proteins. The mononuclear iron site REPLACE occurs in the one-iron bacterial electron-transfer protein mbredoxin. The [2Fe—2S] (10) and [4Fe—4S] (12) cubane stmctures are found in the 2-, 4-, and 8-iron ferredoxins, which are also electron-transfer proteins. The [3Fe—4S] voided cubane stmcture (11) has been found in some ferredoxins and in the inactive form of aconitase, the enzyme which catalyzes the stereospecific hydration—rehydration of citrate to isocitrate in the Krebs cycle. In addition, enzymes are known that contain either other types of iron sulfur clusters or iron sulfur clusters that include other metals. Examples include nitrogenase, which reduces N2 to NH at a MoFe Sg homocitrate cluster carbon monoxide dehydrogenase, which assembles acetyl-coenzyme A (acetyl-CoA) at a FeNiS site and hydrogenases, which catalyze the reversible reduction of protons to hydrogen gas. 

Several iron sulfide nitrosyl compounds are known. These have stmctures that in some cases are formally related to the FeS clusters by replacement of thiolate by NO. The compounds include the anions [Fe2S2(NO)4] and [Fe4S2(NO)2] (Roussin s red and black salts, respectively) and the neutral compounds [Fe2S2(NO)4] and [Fe4S4(NO)4]. Roussin s black salt has found use as a NO releasing vasodilator. 

Like gold, silver readily forms insoluble (yellow) thiolates [Ag(SR)] primary alkylthiolates are thought to have non-molecular structures but with bulky tertiary alkyls (n = 8), probably having a cyclic structure. Addition of excess thiolate leads to the formation of clusters like Ag6(SPh)g, Ag5(SPh)7 and Ag5(SBu )6 (phosphine adducts are known, too). 

In recent years, several model complexes have been synthesized and studied to understand the properties of these complexes, for example, the influence of S- or N-ligands or NO-releasing abilities [119]. It is not always easy to determine the electronic character of the NO-ligands in nitrosyliron complexes thus, forms of NO [120], neutral NO, or NO [121] have been postulated depending on each complex. Similarly, it is difficult to determine the oxidation state of Fe therefore, these complexes are categorized in the Enemark-Feltham notation [122], where the number of rf-electrons of Fe is indicated. In studies on the nitrosylation pathway of thiolate complexes, Liaw et al. could show that the nitrosylation of complexes [Fe(SR)4] (R = Ph, Et) led to the formation of air- and light-sensitive mono-nitrosyl complexes [Fe(NO)(SR)3] in which tetrathiolate iron(+3) complexes were reduced to Fe(+2) under formation of (SR)2. Further nitrosylation by NO yields the dinitrosyl complexes [(SR)2Fe(NO)2], while nitrosylation by NO forms the neutral complex [Fe(NO)2(SR)2] and subsequently Roussin s red ester [Fe2(p-SR)2(NO)4] under reductive elimination forming (SR)2. Thus, nitrosylation of biomimetic oxidized- and reduced-form rubredoxin was mimicked [121]. Lip-pard et al. showed that dinuclear Fe-clusters are susceptible to disassembly in the presence of NO [123]. 

Gronbeck, H., Walter, M. and Hakkinen, H. (2006) Theoretical Characterization of Cyclic Thiolated Gold Clusters. Journal of... 

Kruger, D., Fuchs, H., Rousseau, R., Marx, D. and Parinello, M. (2001) Interaction of short-chain alkane thiols and thiolates with small gold clusters Adsorption structures and energetics. Journal of Chemical Physics, 115, 4776-4786. 

Konopka, M., Rousseau, R., Stich, I. and Marx, D. (2004) Detaching Thiolates from Copper and Gold Clusters Which Bonds to Break Journal ofthe American Chemical Society, 126, 12103-12111. 

Liu, Z., Peng, L.and Yao, K. (2006) Intense blue luminescence from self-assembled Au-thiolate clusters. Materials Letters,... 

Formation of Missing Au SC via Thiolation of Polymer-Stabilized Gold Clusters... 

Thiolates (RS ) represent an extensive family of ligands, and include chelating forms. Thiolates are known to act as monodentate donors, but often act in a bridging role. There is a clear biological interest, through participation of thiolates (cysteine residues) as donors in many metalloproteins both as terminal S donors and bridging ligands in, for example, Fe S clusters. 

Chelation of ixo-maleonitriledithiolate (imdt) has been structurally characterized in the octahedral cobalt(III) complex trmw-[Co(imdt)2(P(ra-Bu)3)2], formed via reaction of cobalt(II) ion with K2(imdt) in the presence of the phosphine.1037 Simple chelating thiolates such as SCH2CH2S not only form mononuclear compounds, but participate in bridging in clusters such as [Co3(SCH2CH2S)3(PEt3)3]3+ (243).1038... 

Reaction of the Ni11 thiolate species [Ni(L)] (L = /V,/V -diethyl-7V,7V -bis(2-mercaptoethyl)-l,3-propanediamine) with the tetraiodo cluster anion [Fe4S4I4]2 yields [Ni(L)(Fe4S4I2)(L)Ni] (793).1984 It incorporates a dithiolate bridge between Ni and Fe centers with a Ni—Fe distance of 2.827(1) A and exhibits a quasi-reversible oxidation wave at 1/2 = +0.15V (vs. SCE). The corresponding monosubstituted cluster anion [Ni(L)Fe4S4I3] (794) was also reported.1985... 

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