Mets motifs, which refer to methionine-rich sequences found in the high-affinity copper transporter Ctr1, also appear in other proteins involved in copper trafficking and homeostasis, including other Ctrs as well as Pco and Cop proteins isolated from copper-resistant bacteria. To understand the coordination chemistry utilized by these proteins, we studied the copper binding properties of a peptide labeled Mets7-PcoC with the sequence Met-Thr-Gly-Met-Lys-Gly-Met-Ser. By comparing this sequence to a series of mutants containing noncoordinating norleucine in place of methionine, we confirm that all three methionine residues are involved in a thioether-only binding site that is selective for Cu(I). Two independent methods, one based on mass spectrometry and one based on rate differences for the copper-catalyzed oxidation of ascorbic acid, provide an effective K(D) of approximately 2.5 microM at pH 4.5 for the 1:1 complex of Mets7-PcoC with Cu(I). These results establish that a relatively simple peptide containing an MX(2)MX(2)M motif is sufficient to bind Cu(I) with an affinity that corresponds well with its proposed biological function of extracellular copper acquisition.

Sulfur bridging interactions between three cis-planar NiII-S2N2 complexes and NiII, CuI,II, ZnII, and HgII reactants were investigated by synthesis and X-ray crystal structures of some 24 complexes. This work was stimulated by recent crystallographic structures of the A-cluster of carbon monoxide dehydrogenase/acetylcoenzyme A synthase. This bridged biological assembly has the minimal formulation [Fe4S4]-(micro2-SCys)-[M((micro2-SCys)2Gly)Ni] with M = NiII, CuI, and ZnII at sites distal and proximal, respectively, to the iron-sulfur cluster. Bridges supported by representations of the distal nickel site were sought by reactions of the complexes [NiII(LH-S2N2)]2- and [NiII(LR-S2N2)], with 5-5-5 chelate ring patterns. Reaction products implicate the bridges Ni-(micro2-S)1,2-M in a variety of molecular structures, some with previously unknown connectivities of bridge atoms. The most frequently encountered bridge units are the nonplanar rhombs Ni(2-S)2M involving both sulfur atoms of a given complex. Those with M = NiII are biologically relevant inasmuch as the catalytic metal at the proximal site is nickel. The complex [Ni(L-655)]2-, containing the 6-5-5 ring pattern and coordination sphere of the distal nickel site, was prepared and structurally characterized. It was shown to sustain Ni2(micro2-S)2 rhombic interactions in the form of trinuclear [[Ni(L-655)]2Ni]2- and [[Ni(L-655)]Ni(R2PCH2CH2PR2)] (R = Et, Ph) in which the second NiII simulates the proximal site. Bridging interactions of NiII-S2N2 complexes are summarized, and geometrical features of Ni2(2-S)2 rhombs in these complexes, as dependent on ring patterns, are considered (LH-S2N2 = N,N'-ethylenebis(2-mercaptoisobutyramide)(4-); LR-S2N2 = trans-rac-N,N'-bis(2-mercapto-2-methylprop-1-yl)-1,2-cyclohexanediamine(2-); L-655 = N-(2-mercaptopropyl)-N'-(2'-mercaptoethyl)glycinamide(4-)).

Dithiolate bridging Ni-Fe complexes [(dppe)Ni(II)(mu-SEt)(2)Fe(II)(CN)(2)(CO)(2)](6) and [(dppe)Ni(II)(mu-pdt)Fe(II)(CN)(2)(CO)(2)] [dppe = 1,2-bis(diphenylphosphino)ethane and pdt = 1,3-propanedithiolate] have been synthesized and structurally characterized as structural analogues of the active site of Ni-Fe hydrogenase enzymes. The synthesis starts from key intermediate fac-[Fe(CN)(2)(CO)(3)I](-). [(dppe)Ni(II)(mu-SEt)(2)Fe(II)(CN)(2)(CO)(2)](6), which features a near-planar diethanethiolate-bridged Ni-Fe rhomb, and the arrangement of 2CN(-) ligands is cis to each other. In contrast, [(dppe)Ni(II)(mu-pdt)Fe(II)(CN)(2)(CO)(2)] shows a much more folded NiS(2)Fe rhomb, a short Ni-Fe distance, trans 2CN(-) ligands, and a semibridging CN(-) between Ni and Fe.

Kinetics of the oxygen atom transfer reactions [M(IV)(QC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- + XO --> [M(VI)O(QC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- + X in acetonitrile with substrates XO = NO3- and (CH2)4SO have been determined. The reactants are bis(dithiolene) complexes with M = Mo, W and sterically encumbered axial ligands with Q = O, S to stabilize mononuclear square pyramidal structures. The complex [MoIV(SC6H2-2,4,6-Pr(i)3)(S2C2Me2)2]1- is an analogue of the active site of dissimilatory nitrate reductase which in the reduced state contains a molybdenum atom bound by two pyranopterindithiolene ligands and a cysteinate residue. Nitrate reduction was studied with tungsten complexes because of unfavorable stability properties of the molybdenum complexes. Product nitrite was detected by a colorimetric method. All reactions with both substrates are second-order with associative transition states (deltaS approximately -20 eu). Variation of atoms M and Q, together with data from prior work, allows certain kinetics comparisons to be made. Among them, k2W/k2Mo = 25 for (CH2)4SO reduction (Q = S), an expression of the kinetic metal effect. Further, k2S/k2O = 28 and approximately 10(4) for nitrate and (CH2)4SO reduction, respectively, effects attributed to relatively more steric congestion in achieving the transition state with hindered phenolate vs thiolate ligands. The effect is more pronounced with the larger substrate. These results demonstrate the feasibility of tungsten-mediated nitrate reduction by direct atom transfer using molecules with both axial thiolate and phenolate ligands. Complexes of the type [M(IV)(OR)(S2C2Me2)2] are capable of reducing biological N-oxide, S-oxide, and nitrate substrates and thus constitute functional analogue reaction systems of enzymic transformations.

Aminopolycarboxylic esters react with C60 under photolysis to produce fullerene multicarboxylates. Irradiation of tetramethyl ethylenediaminetetraacetate (EDTA) with C60 yields the EDTA-containing fullerene monoadduct C60(MeOOCCH)2NCH2CH2N(CH2COOMe)2. In addition, several other C60 monoadducts are also isolated and characterized, including compounds due to EDTA fragmentation. Similar results are observed with pentamethyldimethylenetriaminepentaacetate (DTPA). When partially methylated nitrilotriacetic acid is irradiated with C60, decarboxylation occurs and organodihydrofullerene derivatives such as C60(H)(CH2N(CH2COOMe)2) are formed. Radical mechanisms are proposed for both types of photoreactions. The fullerene derivatives are characterized by their spectroscopic data. Photoreactions of C60 with other analogous molecules also support the conclusions.

The construction of a synthetic analogue of the A-cluster of carbon monoxide dehydrogenase/acetylcoenzyme synthase, the site of acetylcoenzyme A formation, requires as a final step the formation of an unsupported [Fe(4)S(4)]-(mu(2)-SR)-Ni(II) bridge to a preformed cluster. Our previous results (Rao, P. V.; Bhaduri, S.; Jiang, J.; Holm, R. H. Inorg. Chem. 2004, 43, 5833) and the work of others have addressed synthesis of dinuclear complexes relevant to the A-cluster. This investigation concentrates on reactions pertinent to bridge formation by examining systems containing dinuclear and mononuclear Ni(II) complexes and the 3:1 site-differentiated clusters [Fe(4)S(4)(LS(3))L'](2-) (L' = TfO(-) (14), SEt (15)). The system 14/[{Ni(L(O)-S(2)N(2))}M(SCH(2)CH(2)PPh(2))](+) results in cleavage of the dinuclear complex and formation of [{Ni(L(O)-S(2)N(2))}Fe(4)S(4)(LS(3))]- (18), in which the Ni(II) complex binds at the unique cluster site with formation of a Ni(mu(2)-SR)(2)Fe bridge rhomb. Cluster 18 and the related species [{Ni(phma)}Fe(4)S(4)(LS(3))](3)- (19) are obtainable by direct reaction of the corresponding cis-planar Ni(II)-S(2)N(2) complexes with 14. The mononuclear complexes [M(pdmt)(SEt)]- (M = Ni(II), Pd(II)) with 14 in acetonitrile or Me(2)SO solution react by thiolate transfer to give 15 and [M(2)(pdmt)(2)]. However, in dichloromethane the Ni(II) reaction product is interpreted as [{Ni(pdmt)(mu(2)-SEt)}Fe(4)S(4)(LS(3))](2-) (20). Reaction of Et(3)NH(+) and 15 affords the double cubane [{Fe(4)S(4)(LS(3))}(2)(mu(2)-SEt)](3-) (21). Cluster 18 contains two mutually supportive Fe-(mu(2)-SR)-Ni(II) bridges, 19 exhibits one strong and one weaker bridge, 20 has one unsupported bridge (inferred from the (1)H NMR spectrum), and 21 has one unsupported Fe-(mu(2)-SR)-Fe bridge. Bridges in 18, 19, and 21 were established by X-ray structures. This work demonstrates that a bridge of the type found in the enzyme A-clusters is achievable by synthesis and implies that more stable, unsupported single thiolate bridges may require reinforcement by an additional covalent linkage between the Fe(4)S(4) and nickel-containing components. (LS(3) = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-); L(O)-S(2)N(2) = N,N'-diethyl-3,7-diazanonane-1,9-dithiolate(2-); pdmt = pyridine-2,6-methanedithiolate(2-); phma = N,N'-1,2-phenylenebis(2-acetylthio)acetamidate(4-); TfO = triflate.).

Although transition metal dichalcogenides (TMDs) are attractive for the next‐generation nanoelectronic era due to their unique optoelectronic and electronic properties, carrier scattering during the transmission of electronic devices, and the distinct contact barrier between the metal and the semiconductors, which is caused by inevitable defects in TMDs, remain formidable challenges. To address these issues, a facile, effective, and universal patching defect approach that uses a nitrogen plasma doping protocol is developed, via which the intrinsic vacancies are repaired effectively. To reveal sulfur vacancies and the nature of the nitrogen doping effects, a high‐resolution spherical aberration corrected scanning transmission electron microscopy is used, which confirms the N atoms doping in sulfur vacancies. In this study, a typical TMD material, namely tungsten disulfide, is employed to fabricate field‐effect transistors (FETs) as a preliminary paradigm to demonstrate the patching defects method. This doping method endows FETs with high electrical performance and excellent contact interface properties. As a result, an electron mobility of up to 184.2 cm2 V−1 s−1 and a threshold voltage of as low as 3.8 V are realized. This study provides a valuable approach to improve the performance of electronic devices that are based on TMDs in practical electronic applications.

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