Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Thiolate Environments

Comparison of the redox chemistry in Me2SO of 19-21 with their non-macrocyclic counterparts 22-24 is provided in Table I. Cyclic voltammetric studies demonstrated that clusters 19 and 20 can be oxidized and reduced by one electron in chemically reversible processes. The potentials for the [Pg.11]

3- and 3-,4- steps of 19 and 20 are shifted to more positive values when compared with the corresponding clusters 22 and 23. Cluster 21, which [Pg.11]


If cyanide is present, both the thiolate and the phosphine ligand can be displaced [56]. While the mixed thiol environment displacement is an equilibrium process, the right-hand reaction is much more favored in the reactions of phosphine and cyanide. [Pg.292]

Estimated from Eq. (3) and parameters in Tables I and II. c These ions are reduced by thiols. Since Cu(II) forms less stable complexes with thiols than Cu(II), this will always occur in an environment of thiols alone. However, log Ki for Fe(III) with thiols is larger than for Fe(II), and so log p4 for Fe(III) with ME should be proportionately much larger them with Fe(II). Thus, coordination of four thiolate groups, as occurs in electron transfer proteins, will lead to a very stable Fe(III) complex, which is much less easily reduced to Fe(II) than when only a single thiolate is coordinated. [Pg.141]

Nickel is found in thiolate/sulflde environment in the [NiFe]-hydrogenases and in CODH/ACS.33 In addition, either a mononuclear Ni-thiolate site or a dinuclear cysteine-S bridged structure are assumed plausible for the new class of Ni-containing superoxide dismutases, NiSOD (A).34 [NiFe]-hydrogenase catalyzes the two-electron redox chemistry of dihydrogen. Several crystal structures of [NiFe]-hydrogenases have demonstrated that the active site of the enzyme consists of a heterodinuclear Ni—Fe unit bound to thiolate sulfurs of cysteine residues with a Ni—Fe distance below 3 A (4) 35-39 This heterodinuclear active site has been the target of extensive model studies, which are summarized in Section 6.3.4.12.5. [Pg.250]

Nickel-selenium coordination compounds have received attention in recent years, because a unique Ni-selenocysteine interaction was revealed in the active site of [FeNiSe]-hydrogenases.1083,1084 Of particular interest in this regard are mixed CO/selenolate complexes. Distorted square planar (393) was prepared from [CpNi(CO)]2, PhSeSePh, and [Fe(CO)3(SePh)3] and provides the first example of CO bound to a square planar Ni11 center in thiolate/selenolate environment.1085,1086 Upon addition of RSSR, species of the series [Ni(CO)(SR) (SePh)3 ] are formed. //(CO) ranges from 2,023 cm-1 to 2,043 cm-1 and is regarded as a spectroscopic reference for the CO binding site in [NiFeSe] hydrogenases. [Pg.342]

The interest in low-valent Ni complexes in S-rich environments has been stimulated by the presence of Ni in [Ni,Fe] hydrogenase and CODH. While thiolate ligation usually favors higher oxidation states, thioethers stabilize Ni1 and Ni°. In most cases, however, Ni1 ions of an NiS4 chromophore are unstable with respect to disproportionation. The cyclic voltam-mogram of square planar (983) with homoleptic thioether coordination exhibits a quasi-reversible wave at —0.42V (vs. NHE), which on the basis of the rhombic EPR spectrum (gi 2.27, g2 2.11, and g3 2.03) of the chemically reduced species (Na/Hg) is assigned to metal-centered reduction. 8... [Pg.493]

Silver(I) trifluoromethanethiolate (AgSCF3) has been used to prepare trifluoromethyl aryl sulfides by reaction with iodide.996 A mixed silver-zinc thiolate complex [Ag4Zn2(SC6H2-Pr -2,4,6)6(OTf)2] has been prepared by reaction of AgOTf with Zn[N(TMS)2]2 in the presence of the thiol.99 Solid-state 109Ag NMR can be a sensitive environment probe for silver thiolates,998 overall for biological thiolates ligands as cysteine,999 or proteins such as metallothionein.1000,1001... [Pg.961]

As part of a study into the activation of metal catalysts in thiol or thiolate-rich environments, X-substituted coenzyme M and thioglycolate derivatives were investigated in a Ni-catalyzed crosscoupling reaction with a zinc co-factor the role of zinc was shown to be in a transmetallation process.571... [Pg.1197]

Dissolve the protein to be thiolated at a concentration of l-5mg/ml in 50 mM sodium phosphate, pH 7.5, containing 1-10 mM EDTA. Other non-amine containing buffers such as borate, HEPES, and bicarbonate also may be used as the reaction medium. The effective pH for the NHS ester modification reaction is in the range of 7.0-9.0, but environments closer to neutrality will limit the hydrolysis of the ester. [Pg.74]

Zinc is the active metal in the largest group of metalloproteins found in the nature. Recently a new class of zinc enzymes with a sulfur-rich environment has emerged the thiolate-alkylating enzimes, the most prominent of which is the cobalamine-independent methionine synthase.126 For these reasons several monothiolate zinc complexes have been prepared for the modelling of these enzymes with different N2S as (13),127 130 N20,13° 132 N3,132,133 S3,134 tripod ligands, or with Cd because of the favourable spectroscopic properties with an S3 tripod ligand.135... [Pg.40]

The pristine environment of the gas phase can give some surprising reactions, viewed from the perspective of condensed-phase chemistry (2). Silver nitrate dissolved in acetonitrile added to a solution of benzenethiol in acetonitrile gives an immediate white precipitate and a brown gas is given off. The insoluble polymeric layered silver thiolate (3) is formed as the solvent abstracts a proton forming nitric acid the acid attacks the solvent. [Pg.346]

The conversion (19) of thiols to disulphides coupled with reduction of flavin (vitamin B2 family) is a topic of import in connection with coenzyme reactivity in flavoenzymes. Since flavin oxidation of thiols involves nucleophilic attack of thiolate ion in the rate-determining step (Loechler and Hollocher, 1975 Yokoe and Bruice, 1975), this biologically important reaction would be markedly affected by hydrophobic environments. [Pg.468]


See other pages where Thiolate Environments is mentioned: [Pg.447]    [Pg.10]    [Pg.361]    [Pg.447]    [Pg.10]    [Pg.361]    [Pg.374]    [Pg.171]    [Pg.290]    [Pg.298]    [Pg.322]    [Pg.659]    [Pg.361]    [Pg.345]    [Pg.3]    [Pg.4]    [Pg.92]    [Pg.363]    [Pg.438]    [Pg.439]    [Pg.441]    [Pg.444]    [Pg.495]    [Pg.764]    [Pg.1190]    [Pg.210]    [Pg.301]    [Pg.85]    [Pg.32]    [Pg.88]    [Pg.123]    [Pg.97]    [Pg.304]    [Pg.339]    [Pg.536]    [Pg.454]    [Pg.196]    [Pg.442]    [Pg.411]    [Pg.256]    [Pg.270]   


SEARCH



Thiolate

Thiolates

Thiolation

© 2024 chempedia.info