Reductively activated nitrous oxide reductase reacts directly with substrate

In the terminal step of bacterial denitrification, N2O is converted to N2 at the mu4-sulfide bridged tetranuclear CuZ center of nitrous oxide reductase. The enzyme can be activated by reduced methyl viologen, with up to a 15-fold increase in specific activity. The reductively activated nitrous oxide reductase from Achromobacter cycloclastes was isolated and characterized by visible absorption and EPR spectroscopy, and both methods showed that the CuZ center can attain a [4Cu(I)] oxidation state. When N2O was added to the activated, reductant-free enzyme, distinct spectral changes were observed, indicating that this state of the enzyme interacts with substrate. This was further supported by the detection of 15N-labeled product in the absence of steady-state turnover conditions. A new absorption band around 970 nm appeared following reaction of activated nitrous oxide reductase with N2O, which may represent a catalytic intermediate state of the enzyme.     

Spectroscopic, computational, and kinetic studies of the mu4-sulfide-bridged tetranuclear CuZ cluster in N2O reductase: pH effect on the edge ligand and its contribution to reactivity

A combination of spectroscopy and density functional theory (DFT) calculations has been used to evaluate the pH effect at the CuZ site in Pseudomonas nautica (Pn) nitrous oxide reductase (N2OR) and Achromobacter cycloclastes (Ac) N2OR and its relevance to catalysis. Absorption, magnetic circular dichroism, and electron paramagnetic resonance with sulfur K-edge X-ray absorption spectra of the enzymes at high and low pH show minor changes. However, resonance Raman (rR) spectroscopy of PnN2OR at high pH shows that the 415 cm-1 Cu-S vibration (observed at low pH) shifts to higher frequency, loses intensity, and obtains a 9 cm-1 18O shift, implying significant Cu-O character, demonstrating the presence of a OH- ligand at the CuICuIV edge. From DFT calculations, protonation of either the OH- to H2O or the mu4-S2- to mu4-SH- would produce large spectral changes which are not observed. Alternatively, DFT calculations including a lysine residue at an H-bonding distance from the CuICuIV edge ligand show that the position of the OH- ligand depends on the protonation state of the lysine. This would change the coupling of the Cu-(OH) stretch with the Cu-S stretch, as observed in the rR spectrum. Thus, the observed pH effect (pKa approximately 9.2) likely reflects protonation equilibrium of the lysine residue, which would both raise E degrees and provide a proton for lowering the barrier for the N-O cleavage and for reduction of the [Cu4S(im)7OH]2+ to the fully reduced 4CuI active form for turnover.     

Electronic structure description of the mu(4)-sulfide bridged tetranuclear Cu(Z) center in N(2)O reductase

Spectroscopy coupled with density functional calculations has been used to define the spin state, oxidation states, spin distribution, and ground state wave function of the mu4-sulfide bridged tetranuclear CuZ cluster of nitrous oxide reductase. Initial insight into the electronic contribution to N2O reduction is developed, which involves a sigma superexchange pathway through the bridging sulfide.     

Formation of a cytochrome c-nitrous oxide reductase complex is obligatory for N2O reduction by Paracoccus pantotrophus

Nitrous oxide reductase (N2OR) catalyses the final step of bacterial denitrification, the two-electron reduction of nitrous oxide (N2O) to dinitrogen (N2). N2OR contains two metal centers; a binuclear copper center, CuA, that serves to receive electrons from soluble donors, and a tetranuclear copper-sulfide center, CuZ, at the active site. Stopped flow experiments at low ionic strengths reveal rapid electron transfer (kobs=150 s-1) between reduced horse heart (HH) cytochrome c and the CuA center in fully oxidized N2OR. When fully reduced N2OR was mixed with oxidized cytochrome c, a similar rate of electron transfer was recorded for the reverse reaction, followed by a much slower internal electron transfer from CuZ to CuA(kobs=0.1-0.4 s-1). The internal electron transfer process is likely to represent the rate-determining step in the catalytic cycle. Remarkably, in the absence of cytochrome c, fully reduced N2OR is inert towards its substrate, even though sufficient electrons are stored to initiate a single turnover. However, in the presence of reduced cytochrome c and N2O, a single turnover occurs after a lag-phase. We propose that a conformational change in N2OR is induced by its specific interaction with cytochrome c that in turn either permits electron transfer between CuA and CuZ or controls the rate of N2O decomposition at the active site.     

Polymerizing cluster helicates into high-connectivity networks

Solvothermal reactions of CuII salts and 3,5-bis(4-pyridyl)pyrazole (HL) under various conditions gave three different types of crystalline compound, namely [Cu2(Cu5L6)]BF(4).5 H2O (1 a), [Cu2(Cu5L6)]ClO(4).5 H2O (1 b), and [Cu7(CN)2(Cu5L6)2][BF4]3 (2). 1 a and b were obtained in ethanol and NH3.H2O, whereas 2 was obtained in methanol and NH3.H2O. The three complexes were constructed by incorporating new pentanuclear copper(I) pyrazolate bis(triple helical) cluster helicates (Cu5L6) as the second building units (SBUs), in which as many as twelve 4-pyridyl N atoms are available for further coordination and construction of high-connectivity topological networks. In 1 a and b, seven 4-pyridyl N atoms are linked to three three-coordinated CuI atoms and four four-coordinated CuI atoms, which results in 3,4,7-connected networks. In 2, as many as eleven 4-pyridyl N atoms coordinate to eleven CuI atoms, which results in a 4,10-connected topological network. The increasing connectivity of the cluster nodes in 2 is closely related to the in situ-formed CN- anion bridge around the periphery of the pentanuclear cluster helicates. The luminescenct properties of these compounds were also investigated.     

Construction of new heteroselenometallic clusters: formation of crownlike [Et4N]4[(mu5-WSe4)(CuI)5(mu-I)2] and octahedral polymeric [(mu6-WSe4)Cu6I4(py)4]n from planar [Et4N]4[(mu4-WSe4)Cu4I6] with additional faces

The coplanar cluster compound [Et4N]4[(mu4-WSe4)Cu4I6] (1) was prepared from reaction of [Et4N]2[WSe4] with 4 equiv of CuI in N,N-dimethylformamide (DMF) solution in the presence of [Et(4)N]I. Treatment of 1 with pyridine (py) in dry MeCN gave the neutral cluster [(mu4-WSe4)Cu4(py)6I2] (2) in good yield. Recrystallization of 1 from py/i-PrOH resulted in the reorganization of the coplanar WSe4Cu4 core and the formation of a neutral polymeric cluster [(mu3-WOSe3)Cu3(py)3(mu-I)]n (3) containing a nest-shaped OWSe3Cu3 core and a terminal W=O bond. The interaction of cluster 1 with excess PPh3 in CH3Cl3 gave [(mu3-WSe4)Cu3(PPh3)3(mu3-I)] (4) which has a cubanelike SeWSe3Cu3I core. Treatment of 1 with 1 equiv of CuI in dimethyl sulfoxide (DMSO) yielded [Et4N]4[(mu5-WSe4)(CuI)5(mu-I)2] (5) which has a crown-like core structure. Treatment of 1 in DMF with 2 equiv of CuI in the presence of py resulted in the formation of a two-dimensional polymeric cluster, [(mu6-WSe4)Cu6I4(py)4]n (6), consisting of an octahedral WSe4Cu6 repeating unit. The solid-state structures of clusters 3, 5, and 6 have been further established by X-ray crystallography. The nonlinear optical properties of 6 have been also investigated. Cluster 6 was found to exhibit good photostability and a large optical limiting effect with the limiting threshold being ca. 0.3 J cm(-2).     

Insights into the mechanism of N2O reduction by reductively activated N2O reductase from kinetics and spectroscopic studies of pH effects

Nitrous oxide reductase (N2OR) from Achromobacter cycloclastes (Ac) can be reductively activated with reduced methyl viologen over a broad range of pH. Activated Ac N2OR displays a complex activity profile as a function of the pH at which catalytic turnover is measured. Spectroscopic and steady-state kinetics data suggest that [H+] has multiple effects on both the activation and the catalytic reactions. These experimental results are in good agreement with previous theoretical studies, which suggested that the transition state is stabilized by H-bonding interactions between the active site and an N2O-derived intermediate bound to the catalytic CuZ cluster.     

Nature of the intermediate formed in the reduction of O(2) to H(2)O at the trinuclear copper cluster active site in native laccase

The multicopper oxidases contain at least four copper atoms and catalyze the four-electron reduction of O(2) to H(2)O at a trinuclear copper cluster. An intermediate, termed native intermediate, has been trapped by a rapid freeze-quench technique from Rhus vernicifera laccase when the fully reduced form reacts with dioxygen. This intermediate had been described as an oxygen-radical bound to the trinuclear copper cluster with one Cu site reduced. XAS, however, shows that all copper atoms are oxidized in this intermediate. A combination of EXAFS, multifrequency EPR, and VTVH MCD has been used to understand how this fully oxidized trinuclear Cu cluster relates to the fully oxidized resting form of the enzyme. It is determined that in the native intermediate all copper atoms of the cluster are bridged by the product of full O(2) reduction. In contrast, the resting form has one copper atom of the cluster (the T2 Cu) magnetically isolated from the others. The native intermediate decays to the resting oxidized form with a rate that is too slow to be in the catalytic cycle. Thus, the native intermediate appears to be the catalytically relevant fully oxidized form of the enzyme, and its role in catalysis is considered.     

The copper(II) adduct of the unstructured region of the amyloidogenic fragment derived from the human prion protein is redox-active at physiological pH

Prion diseases are caused by the misfolding and aggregation of the prion protein (PrP). Herein we provide evidence that the CuII adduct of the unstructured amyloidogenic fragment of the human PrP (PrP(91-126)) is redox active under physiological conditions. We have identified that the relevant high-affinity CuII binding region of PrP(91-126) is contained between residues 106 and 114. Both [CuII(PrP(91-126))] and [CuII(PrP(106-114))] have CuII Kd values of approximately 90 microM. Furthermore, the smaller PrP fragment PrP(106-114) coordinates CuII producing an electronic absorption spectrum nearly identical with [CuII(PrP(91-126))] (lambda max approximately 610 nm (epsilon approximately 125 M-1 cm-1)) suggesting a similar coordination environment for CuII. Cu K-edge X-ray absorption spectroscopy (XAS) reveals a nearly identical CuN(N/O)2S coordination environment for these two metallopeptides (2N/O at approximately 1.97 A; 1S at approximately 2.30 A; 1 imidazole N at approximately 1.95 A). Both display quasireversible CuII/CuI redox couples at approximately -350 mV vs Ag/AgCl. ESI-MS indicates that both peptides will coordinate CuI. However, XAS indicates differential coordination environments between [CuI(PrP(91-126))] and [CuI(PrP(106-114))]. These data indicate that [CuI(PrP(91-126))] contains Cu in a four coordinate (N/O)2S2 environment with similar (N/O)-Cu bond distances (Cu-(N/O) r = 2.048(4) A), while [CuI(PrP(106-114))] contains Cu in a four coordinate (N/O)2S2 environment with differential (N/O)-Cu bond distances (Cu-(N/O) r1 = 2.057(6) A; r2 = 2.159(3) A). Despite the differential coordination environments both Cu-metallopeptides will catalytically reduce O2 to O2*- at comparable rates.     

一个基于多钒酸盐与柔性吡啶基配体的三维非中心对称杂化物(英文)

基于柔性吡啶基配体和钒酸盐,合成得到了一个非中心对称的杂化化合物[CuⅠ4(bpp)4(VⅤ6O17)](1)(bpp=1,3-二(4-吡啶基)丙烷),并通过元素分析、红外光谱、X-射线单晶衍射、热重分析等测试对其进行了表征。晶体数据表明该化合物属于正交晶系,Pca21空间群。在化合物1中,一维链状的多钒酸根与[CuⅠ(bpp)]单元通过Cu-O键连接形成沿ab平面的层,这些层进一步通过Cu髣…Cu髣弱相互作用(Cu髣…Cu髣距离为0.281nm)连接成一个三维的框架结构。     

Synthesis,Crystal Structure,and Properties of a Dinuclear Cu(I) Cluster

Abstract

A new dinuclear copper(I) cluster complex, [(o-Tol)₃PCuI₂CuP(o-Tol)₃(DMF)] (1) ((o-Tol)₃P = tris(2- methylphenyl)phosphine, DMF = N, N′-dimethylformamide), has been synthesized and the crystal structure was determined by a single-crystal X-ray diffraction study. The dinuclear copper(I) cluster molecule containing an asymmetric Cu₂I₂P₂O core and the dinuclear clusters are fused together by a strong π–π stacking interaction to form asupramolecular one-dimensional (1D) chain. After having compared the relevant complexes composed of CuI and monodentate triarylphosphine ligands, the impact of the substituent of the triarylphosphine ligand to the subsequent complex structure has also been discussed.Except for a strong π–π* bond, the complex 1 also exhibits a weak metal-to-ligand charge transfer (MLCT) absorption bond in the 430–530-nm region and displays a weak green-yellow emission when irradiated by ultraviolet (UV) light. The thermogravimetric analysis demonstrates that its thermal stability is good, and the corresponding PXRD analysis has revealed that the final, organic-free decomposed product is CuI.     

Hard/soft heterometallic network complex of a macrocycle with endo/exocyclic coordination

One-pot assembly reactions of an S(2)O(4) macrocycle with CuI in the absence and presence of KI afforded an emissive one-dimensional looped coordination polymer linked with a cubane-type copper iodide cluster and an endocoordinated potassium(I) coordination polymer linked with a ribbon-type copper iodide cluster, respectively.     

Combination of lacunary polyoxometalates and high-nuclear transition metal clusters under hydrothermal conditions: IX. a series of novel polyoxotungstates sandwiched by octa-copper clusters

The reaction of CuCl(2).2 H2O with trivacant Keggin polyoxoanions K8Na2[A-alpha-GeW9O34].25 H2O or K10[A-alpha-SiW9O34].25 H2O in the presence of 1,2-diaminopropane (dap), ethylenediamine (en) or 2,2'-bipyridine (2,2'-bpy) under hydrothermal conditions afforded five novel hybrid inorganic-organic octa-Cu sandwiched polyoxotungstates (POTs): H4[CuII8(dap)4(H2O)2(B-alpha-GeW9O34)2].13 H2O (1), (H2en)2[CuII8-(en)4(H2O)2(B-alpha-GeW9O34)2].5 H2O(2), (H2en)2[CuII8(en)4(H2O)2(B-alpha-SiW9-O34)2].8 H2O (3), [CuII(H2O)2]H2[CuII8-(en)4(H2O)2(B-alpha-SiW9O34)2] (4), and [CuII2(H2O)2(2,2'-bpy)2]{[CuII(bdyl)]2-[CuII8(2,2'-bpy)4(H2O)2(B-alpha-GeW9-O34)2]}.4 H2O (bdyl=2,2'-bipyridinyl)(5). Additionally, CuCl(2).2 H2O reacts with the mixture of GeO2, Na2WO(4).2 H2O, H2SiW12O(40).2 H2O in the presence of 2,2'-bpy and 4,4'-bpy under hydrothermal conditions leading to another novel mixed-valent octa-Cu sandwiched POT hybrid: [CuI(2,2'-bpy)(4,4'-bpy)]2[{CuI2(2,2'-bpy)2(4,4'-bpy)]2[CuI2CuII6(2,2'-bpy)2(4,4'-bpy)2(B-alpha-GeW9O34)2}].2 H2O (6). 1, 2, and 3 are discrete dimers constructed from two trivacant Keggin [B-alpha-XW9O34]10- (X=GeIV/SiIV) fragments and an octa-Cu cluster whereas 4 displays the 3D (3,6)-connected nets with (4.6(2))(4(2).6(4).8(7).10(2)) topology, which are built by octa-Cu sandwiched polyoxometalate building blocks through copper cation bridges. 5 is a novel 2D layer based on octa-Cu sandwiched POT clusters and [CuII2(bdyl)] units. Interestingly, the rollover metalation of 2,2'-bpy is firstly observed in the system containing the copper complex under hydrothermal conditions. 6 is a discrete mixed-valent octa-Cu sandwiched POT supported by two CuI-complexes [CuI2-(2,2'-bpy)2(4,4'-bpy)]2+ through 4,4'-bpy bridges, which constructs a novel dodeca-copper cluster. Notably, the octa-Cu cluster in 6 is mixed-valent and is different from those in 1-5. To our knowledge, 1-6 represent a rare family of POTs incorporating novel octa-nuclear transition-metal clusters in polyoxometalate chemistry. They were structurally characterized by FT-IR spectra, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. The magnetic properties of 1, 4, and 5 were quantitatively analyzed by the MAGPACK software package.     

Polymorph and isomer conversion of complexes based on CuI and PPh3 easily observed via luminescence

Reactions between copper(I) iodide and triphenylphosphine have been explored in solution and in the solid state and six luminescent coordination complexes have been obtained and characterized by X-ray diffraction and UV-vis spectroscopy and photophysics. Solid-state reactions of CuI with PPh(3) in different conditions (kneading, vapour digestion) and stoichiometries resulted in the formation of high ratio ligand:metal compounds while tetrameric structures could be obtained only by solution reactions. Crystal structures were determined by single crystal X-ray diffraction while purity of the bulk product was checked by powder diffraction (XRPD). Three different tetrameric structures with 1:1 stoichiometry have been synthesized: two closed cubane-type polymorphs [CuI(PPh(3))](4) (form 1a) and [CuI(PPh(3))](4) (form 1b) and an open step-like isomer [CuI(PPh(3))](4) (form 2). The conversions between the polymorphs and isomers have been studied and characterized by XRPD. The most stable form [CuI(PPh(3))](4) (form 1b) can convert into the open step-like isomer [CuI(PPh(3))](4) (form 2) in a slurry experiment with EtOH or CH(2)Cl(2) or AcCN and converts back into [CuI(PPh(3))](4)1b when exposed to vapors of toluene. At room temperature all the tetrameric compounds exhibit luminescence in the solid state and, notably, the two polymorphs show a dissimilar dual emission at low temperature. The luminescence features in the solid state seem to be peculiarly related to the presence of the aromatic phosphine ligand and depend on the Cu-Cu distance in the cluster.     

Copper(I) complex O(2)-reactivity with a N(3)S thioether ligand: a copper-dioxygen adduct including sulfur ligation, ligand oxygenation, and comparisons with all nitrogen ligand analogues

In order to contribute to an understanding of the effects of thioether sulfur ligation in copper-O(2) reactivity, the tetradentate ligands L(N3S) (2-ethylthio-N,N-bis(pyridin-2-yl)methylethanamine) and L(N3S')(2-ethylthio-N,N-bis(pyridin-2-yl)ethylethanamine) have been synthesized. Corresponding copper(I) complexes, [CuI(L(N3S))]ClO(4) (1-ClO(4)), [CuI(L(N3S))]B(C(6)F(5))(4) (1-B(C(6)F(5))(4)), and [CuI(L(N3S'))]ClO(4) (2), were generated, and their redox properties, CO binding, and O(2)-reactivity were compared to the situation with analogous compounds having all nitrogen donor ligands, [CuI(TMPA)(MeCN)](+) and [Cu(I)(PMAP)](+) (TMPA = tris(2-pyridylmethyl)amine; PMAP = bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine). X-ray structures of 1-B(C(6)F(5))(4), a dimer, and copper(II) complex [Cu(II)(L(N3S))(MeOH)](ClO(4))(2) (3) were obtained; the latter possesses axial thioether coordination. At low temperature in CH(2)Cl(2), acetone, or 2-methyltetrahydrofuran (MeTHF), 1 reacts with O(2) and generates an adduct formulated as an end-on peroxodicopper(II) complex [{Cu(II)(L(N3S))}(2)(mu-1,2-O(2)(2-))](2+) (4)){lambda(max) = 530 (epsilon approximately 9200 M(-1) cm(-1)) and 605 nm (epsilon approximately 11,800 M(-1) cm(-1))}; the number and relative intensity of LMCT UV-vis bands vary from those for [{Cu(II)(TMPA)}(2)(O(2)(2-))](2+) {lambda(max) = 524 nm (epsilon = 11,300 M(-1) cm(-1)) and 615 nm (epsilon = 5800 M(-1) cm(-1))} and are ascribed to electronic structure variation due to coordination geometry changes with the L(N3S) ligand. Resonance Raman spectroscopy confirms the end-on peroxo-formulation {nu(O-O) = 817 cm(-1) (16-18O(2) Delta = 46 cm(-1)) and nu(Cu-O) = 545 cm(-1) (16-18O(2) Delta = 26 cm(-1)); these values are lower in energy than those for [{Cu(II)(TMPA)}(2)(O(2)(2-))](2+) {nu(Cu-O) = 561 cm(-1) and nu(O-O) = 827 cm(-1)} and can be attributed to less electron density donation from the peroxide pi* orbitals to the Cu(II) ion. Complex 4 is the first copper-dioxygen adduct with thioether ligation; direct evidence comes from EXAFS spectroscopy {Cu K-edge; Cu-S = 2.4 Angstrom}. Following a [Cu(I)(L(N3S))](+)/O(2) reaction and warming, the L(N3S) thioether ligand is oxidized to the sulfoxide in a reaction modeling copper monooxygenase activity. By contrast, 2 is unreactive toward dioxygen probably due to its significantly increased Cu(II)/Cu(I) redox potential, an effect of ligand chelate ring size (in comparison to 1). Discussion of the relevance of the chemistry to copper enzyme O(2)-activation, and situations of biological stress involving methionine oxidation, is provided.     

Interactions of selenate with copper(I) oxide particles

The chemical mechanisms responsible for the immobilization of selenate (SeO4(2-) from aqueous solutions on cuprite (Cu2O) particles were determined from batch experiments. This was achieved by performing both solution-phase analyses and characterization of solid particles by X-ray photoelectron spectroscopy and transmission electron microscopy techniques, after equilibration of cuprite particles with selenate-containing solutions at various pH values, solid-to-solution ratios, and ionic strengths. Two distinct mechanisms have been pointed out. In the acidic medium, where the acid-catalyzed dissolution of cuprite into CuI species occurs, the immobilization of selenate implies a redox reaction with transient CuI leading to the precipitation of copper(II) selenite, CuSeO3. In the absence of protons added in the medium, Cu2O is chemically stable and immobilization of SeO4(2-) is essentially due to adsorption in the form of an outer-sphere surface complex. The uptake level of selenate by Cu2O is markedly lower than that observed for selenite species in the same conditions.     

CuI NPs immobilized on a ternary hybrid system of magnetic nanosilica,PAMAM dendrimer and trypsin,as an efficient catalyst for A3‑coupling reaction

Research on Chemical Intermediates - Preparation of a nanocatalyst (Fe3O4@SiO2@DNHCS-Tr@CuI) containing PAMAM dendrimer and trypsin enzyme supported on magnetic nanosilica on which CuI NPs were...     

Mechanism of N2O reduction by the mu4-S tetranuclear CuZ cluster of nitrous oxide reductase

Reaction thermodynamics and potential energy surfaces are calculated using density functional theory to investigate the mechanism of the reductive cleavage of the N-O bond by the mu(4)-sulfide-bridged tetranuclear Cu(Z) site of nitrous oxide reductase. The Cu(Z) cluster provides an exogenous ligand-binding site, and, in its fully reduced 4Cu(I) state, the cluster turns off binding of stronger donor ligands while enabling the formation of the Cu(Z)-N(2)O complex through enhanced Cu(Z) --> N(2)O back-donation. The two copper atoms (Cu(I) and Cu(IV)) at the ligand-binding site of the cluster play a crucial role in the enzymatic function, as these atoms are directly involved in bridged N(2)O binding, bending the ligand to a configuration that resembles the transition state (TS) and contributing the two electrons for N(2)O reduction. The other atoms of the Cu(Z) cluster are required for extensive back-bonding with minimal sigma ligand-to-metal donation for the N(2)O activation. The low reaction barrier (18 kcal mol(-)(1)) of the direct cleavage of the N-O bond in the Cu(Z)-N(2)O complex is due to the stabilization of the TS by a strong Cu(IV)(2+)-O(-) bond. Due to the charge transfer from the Cu(Z) cluster to the N(2)O ligand, noncovalent interactions with the protein environment stabilize the polar TS and reduce the activation energy to an extent dependent on the strength of proton donor. After the N-O bond cleavage, the catalytic cycle consists of a sequence of alternating protonation/one-electron reduction steps which return the Cu(Z) cluster to the fully reduced (4Cu(I)) state for future turnover.     

Structural, electrochemical, and spectroscopic characterization of a redox pair of sulfite-based polyoxotungstates: alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-

The synthesis, isolation, and structural characterization of the fully oxidized sulfite-based polyoxotungstate cluster (Pr4N)4{alpha-[W18O54(SO3)2]}.2CH3CN and the one-electron reduced form (Pr4N)5{alpha-[W18O54(SO3)2]}.2CH3CN has been achieved. alpha-[W18O54(SO3)2]5- was obtained as a Pr4N+ salt by reducing the "Trojan Horse" [W18O56(SO3)2(H2O)2]8- cluster via a template orientation transformation. Acetonitrile solutions of pure alpha-[W18O54(SO3)2]5- also were prepared electrochemically by one-electron bulk reductive electrolysis of alpha-[W18O54(SO3)2]4-. Cyclic voltammetry of alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5- in CH3CN (0.1 M Hx4NClO4) produces evidence for an extensive series of reversible one-electron redox processes, that are associated with the tungsten-oxo framework of the polyoxometalate cluster. Hydrodynamic voltammograms in CH3CN exhibit the expected sign and magnitude of the steady-state limiting current values for the alpha-[W18O54(SO3)2]4-/5-/6- series and confirm the existence of a stable one-electron reduced species, alpha-[W18O54(SO3)2]5-. Employment of the Randles-Sevcik (cyclic voltammetry) and Levich (rotating disk electrode) equations at a glassy carbon electrode (d=3 mm) enable diffusion coefficient values of 3.7 and 3.8x10(-6) cm2 s-1 to be obtained for alpha-[W18O54(SO3)2]4- and alpha-[W18O54(SO3)2]5-, respectively. The tungsten polyoxometalates are highly photoactive, since measurable photocurrents and color changes are detected for both species upon irradiation with white light. EPR spectra obtained from both acetonitrile solution and solid samples, down to temperatures as low as 2.3 K, of the chemically and electrochemically prepared one-electron reduced species provided evidence that the unpaired electron in alpha-[W18O54(SO3)2]5- is delocalized over a number of atoms in the polyoxometalate structure, even at very low temperatures.