The effect of metal ions on the amidolytic activity of human factor Xa (Activated Stuart-Prower Factor)

The effect of metal ions on human activated Factor X (Factor X_a) hydrolysis of the chromogenic substrate benzoyl-Ile-Glu-Gly-Arg-p-nitroanilide (S2222) was studied utilizing initial rate enzyme kinetics. The divalent metal ions Ca²⁺, Mn²⁺, and Mg²⁺ enhanced Factor X_a amidolytic activity with K_m values of 30 μm, 20 μm, and 1.4 mm, respectively. Na⁺ activation of Factor X_a amidolytic activity was also found. The K_m for Na⁺ activation was 0.31 m. Both the divalent metal ions and Na⁺ increased the affinity of Factor X_a for S2222 and had no effect on the maximal velocity of the reaction. Other monovalent cations were unable to activate Factor X_a. However, K⁺ was a competitive inhibitor of the Na⁺ activation (K_i = 0.14 m). Lanthanide ions inhibited Factor X_a amidolytic activity. Gd³⁺ inhibition of Factor X_a hydrolysis of S2222 was noncompetitive and had a K_i of 3 μm. The lanthanide ion inhibition could not be reversed by Ca²⁺ even when Ca²⁺ was present in a 1000-fold excess over its K_m indicating nonidentity of the Factor X_a lanthanide and Ca²⁺ binding sites. It is concluded that the Factor X_a Ca²⁺ binding sites have characteristics different from those previously described for the Factor X molecule and that Mg²⁺, Na⁺, and K⁺ may be physiological regulators of Factor X_a activity.     

Simulation of a multicolumn recirculated packed bed reactor (MRPBR) for penicillin acylase

Enzyme reactors for the industrial hydrolysis of penicillin are analyzed in terms of biocatalyst stability to pH. A multicolumn system with packed beds placed in parallel and operating under recirculating conditions is proposed as an adequate reactor for this process. The system is studied both experimentally and with the aid of a simulation program.List of Symbols A transversal area (cm²) - C _A ammonia concentration in the reaction mixture (M) - C ₁ concentration of KH₂PO₄ in buffer (M) - C ₂ concentration of K₂HPO₄ in buffer (M) - d _p biocatalyst diameter (cm) - E enzyme or biocatalyst concentration (gcat l^–1) - K _APA APA non competitive inhibition constant (M) - K _IS excess substrate inhibition constant (M) - Km constant Michaelis-Menten (M) - K _PAA PAA competitive inhibition constant (M) - Q recirculation flow rate (cm³ min^–1) - Q _T recirculation flow rate per column (cm³ min^–1) - Re Reynolds number - S _E substrate concentration entering the neutralization tank (M) - S ₀ initial substrate concentration (M) - S _T substrate concentration in neutralization tank (M) - t time (min) - v _i initial reactor rate (mol min^–1 gcat^–1) - V _s superficial velocity (cm seg^–1) - V _T volume of neutralization tank (cm³) - X _E substrate conversion entering tank - X _T substrate conversion in neutralization tank - X conversion - Z reactor length (cm) - z axial position in reactor (cm) - z ^* non-dimensional axial position in reactor - biocatalyst's density (gcat cm^–3) - p pressure drop in the packed-bed reactor     

Bioreduction of Cr(VI) by alkaliphilic Bacillus subtilis and interaction of the membrane groups

Detoxification of Cr(VI) under alkaline pH requires attention due to the alkaline nature of many effluents. An alkaliphilic gram-positive Bacillus subtilis isolated from tannery effluent contaminated soil was found to grow and reduce Cr(VI) up to 100% at an alkaline pH 9. Decrease in pH to acidic range with growth of the bacterium signified the role played by metabolites (organic acids) in chromium resistance and reduction mechanism. The XPS and FT-IR spectra confirmed the reduction of Cr(VI) by bacteria into +3 oxidation state. Chromate reductase assay indicated that the reduction was mediated by constitutive membrane bound enzymes. The kinetics of Cr(VI) reduction activity derived using the monod equation proved (K_s = 0.00032) high affinity of the organism to the metal. This study thus helped to localize the reduction activity at subcellular level in a chromium resistant alkaliphilic Bacillus sp.     

Performance evaluation of various bioreactors for the removal of Cr(VI) and organic matter from industrial effluent

Performances of various bioreactors under different operating conditions were evaluated with respect to hexavalent chromium (Cr(VI)) reduction and COD removal. Continuous reactor studies were carried out with (i) aerobic suspended growth system, (ii) aerobic attached growth system, and (iii) anoxic attached growth system, using both synthetic and actual industrial wastewater. Arthrobacter rhombi-RE (MTCC7048), a Cr(VI) reducing strain enriched and isolated from chromium contaminated soil, was used in all the bioreactors for Cr(VI) biotransformation and COD removal. Aerobic and anoxic batch experiments were conducted to evaluate the bio-kinetic parameters. The bio-kinetic parameters for aerobic system were: μ_max = 2.34/d, K_s = 190 mg/L (as COD), K_i = 3.8 mg/L of Cr(VI), and Y_T = 0.377. These parameters for anoxic conditions were: μ_max = 0.57/d, K_s = 710 mg/L (as COD), K_i = 8.77 mg/L of Cr(VI), and Y_T = 0.13. Aerobic attached growth system, operated at a hydraulic retention time (HRT) of 24 h and an organic loading rate (OLR) of 3 kg/m³/d, performed better than aerobic suspended and the anoxic attached growth systems operated under identical conditions, while treating synthetic wastewater as well as industrial effluent.     

Removal of Cr(VI) from ground water by Saccharomyces cerevisiae

Chromium can be removed from ground water by the unicellular yeast, Saccharomyces cerevisiae. Local ground water maintains chromium as CrO₄ ^2- because of bicarbonate buffering and pH and E _h conditions (8.2 and +343 mV, respectively). In laboratory studies, we used commercially available, nonpathogenic S. cerevisiae to remove hexavalent chromium [Cr(VI)] from ground water. The influence of parameters such as temperature, pH, and glucose concentration on Cr(VI) removal by yeast were also examined. S. cerevisiae removed Cr(VI) under aerobic and anaerobic conditions, with a slightly greater rate occurring under anaerobic conditions. Our kinetic studies reveal a reaction rate (V_max) of 0.227 mg h^-1 (g dry wt biomass)^-1 and a Michaelis constant (Km) of 145 mg/l in natural ground water using mature S. cerevisiae cultures. We found a rapid (within 2 minutes) initial removal of Cr(VI) with freshly hydrated cells [55–67 mg h^-1 (g dry wt biomass)^-1] followed by a much slower uptake [0.6–1.1 mg h^-1 (g dry wt biomass)^-1] that diminished with time. A materials-balance for a batch reactor over 24 hours resulted in an overall shift in redox potential from +321 to +90 mV, an increase in the bicarbonate concentration (150–3400 mg/l) and a decrease in the Cr(VI) concentration in the effluent (1.9-0 mg/l).     

Biosorption of chromium(VI) by spent cyanobacterial biomass from a hydrogen fermentor using Box-Behnken model

The study explores utilization of waste cyanobacterial biomass of Nostoc linckia from a lab-scale hydrogen fermentor for the biosorption of Cr(VI) from aqueous solution. The biomass immobilized in alginate beads was used for removal of the metal in batch mode optimizing the process conditions adopting response surface methodology (RSM). Kinetic studies were done to get useful information on the rate of chromium adsorption onto the cyanobacterial biomass, which was found to follow pseudo second-order model. Four important process parameters including initial metal concentration (10-100 mg/L), pH (2-6), temperature (25-45 °C) and cyanobacterial dose (0.1-2.0 g) were optimized to obtain the best response of Cr(VI) removal using the statistical Box-Behnken design. The response surface data indicated maximum Cr(VI) biosorption at pH 2-4 with different initial concentrations of the metal in the aqueous solution. The biosorbent could remove 80-90% chromium from solutions with initial metal concentration of 10-55 mg/L. Involvement of the surface characteristics of the biomass was studied through its scanning electron micrographs and Fourier transform infrared (FTIR) analysis.     

Kinetic Study and Mathematical Modeling of Chromium(VI) Reduction and Microorganism Growth Under Mixed Culture

The kinetics of chromium(VI) reduction by Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) was studied under both pure and mixed cultures. Initially, the study of kinetics was performed in pure culture. It was observed that the growth of the two bacteria was both inhibited in the presence of chromium(VI). The maximum specific growth rate (μ _m ) of P. aeruginosa decreased from 2.3942 h^?1 (without Cr(VI)) to 1.8551 h^?1 (with Cr(VI)). Under the mixed culture, the growth of E. coli was inhibited by P. aeruginosa. The maximum specific growth rate (μ _m ) of E. coli decreased form 0.871 h^?1 (in pure culture) to 0.153 h^?1 (in mixed culture). When the concentration of each bacterium was 4.5 × 10⁸ cells ml^?1, the half-velocity reduction rate constant (K _C) and the maximum specific reduction rate constant (v _max) of chromium(VI) were 80.05 mg chromium(VI) l^?1 and 3.674 mg chromium(VI) cells^?1 h^?1, respectively. The results showed that the simulation appeared in good agreement with the experimental data, supporting the series of mathematical models represented the bacteria growth and chromium(VI) reduction in both pure and mixed cultures usefully.     

Insights into the nature of Mo(V) species in solution: Modeling catalytic cycles for molybdenum enzymes

The tris(pyrazolyl)borate and related tripodal N-donor ligands originally developed by Trofimenko stabilize mononuclear compounds containing Mo^VIO₂, Mo^VIO, Mo^VO, and Mo^IVO units and effectively inhibit their polynucleation in organic solvents. Dioxo-Mo(VI) complexes of the type LMoO₂(SPh), where L = hydrotris(3,5-dimethylpyrazol-1-yl)borate (Tp^∗), hydrotris(3-isopropylpyrazol-1-yl)borate (Tp^iPr), and hydrotris(3,5-dimethyl-1,2,4-triazol-1-yl)borate (Tz) and related derivatives are the only model systems that mimic the complete reaction sequence of sulfite oxidase, in which oxygen from water is ultimately incorporated into product. The quasi-reversible, one-electron reduction of Tp^∗MoO₂(SPh) in acetonitrile exhibits a positive potential shift upon addition of a hydroxylic proton donor, and the magnitude of the shift correlates with the acidity of the proton donor. These reductions produce two Mo(V) species, [Tp^∗Mo^VO₂(SPh)]⁻ and Tp^∗Mo^VO(OH)(SPh), that are related by protonation. Measurement of the relative amounts of these two Mo(V) species by EPR spectroscopy enabled the pK_a of the Mo^V(OH) unit in acetonitrile to be determined and showed it to be several pK_a units smaller than that for water in acetonitrile. Similar electrochemical-EPR experiments for Tp^iPrMoO₂(SPh) indicated that the pK_a for its Mo^V(OH) unit was ∼1.7 units smaller than that for Tp^∗Mo^VO(OH)(SPh). Density functional theory calculations also predict a smaller pK_a for Tp^iPrMo^VO(OH)(SPh) compared to Tp^∗Mo^VO(OH)(SPh). Analysis of these results indicates that coupled electron-proton transfer (CEPT) is thermodynamically favored over the indirect process of metal reduction followed by protonation. The crystal structure of Tp^iPrMoO₂(SPh) is also presented.     

Mechanism of reduction of chromium(VI) ion by 2-mercaptosuccinic acid in aqueous solution

The kinetics of the reduction of the chromium(VI) ion by 2-mercaptosuccinic acid (thiomalic acid) were studied by rapid scanning stopped flow spectrophotometry. The conditions used were [Cr(VI)]_T=0.20 mM, [MSA]_T=5-90 mM, 3.0≤pH≤5.6 in citric acid-phosphate buffer, or 3.3≤pH≤5.4 in 0.40 M acetic acid-acetate buffer, 20.0≤T≤35.0 °C at I=0.50 M (NaClO₄). Spectrophotometric titration at 350 nm indicates the stoichiometry of the reaction to be 1:3. The kinetics of both formation and decay of the intermediate chromium(VI) thioester were followed at λ_max=425 nm and rate expressions, specific rate constants and corresponding activation parameters were derived from the proposed mechanism. The acetic acid-acetate buffer was found to catalyze the formation but not the decay rate of the intermediate. The citric acid-phosphate buffer and dissolved oxygen did not have any significant effect on the reaction rates. The justification of the mechanism was discussed in terms of standard biological conditions.     

Synthesis, molecular structure, and voltammetric behaviour of unusually stable cis-dioxobis(diisobutyldithiocarbamato)tungsten(VI)

The unusually stable cis-dioxobis(diisobutyldithiocarbamato)tungsten(VI) [WO₂(i-Bu₂dtc)₂] was synthesized by the reaction between WO₄ ²⁻ and i-Bu₂dtc⁻ in water under the air. The X-ray crystal structure and voltammetric behaviour of the complex are reported. The geometry of the WO₂S₄ core of the complex is distorted octahedral with two terminal oxo ligands in a cis position to each other. The average WO distance of the complex is 1.719 Å and the bond angle of O-W-O is 104.7°, which are in the range of those of cis-dioxotungsten(VI) complexes. The structural features of [WO₂(i-Bu₂dtc)₂] are very similar to those of corresponding cis-dioxomolybdenum(VI) analogues. The complex [WO₂(i-Bu₂dtc)₂] undergoes one-electron quasi-reversible reduction followed by a homogeneous chemical reaction at more negative potential (−1.40 V vs. SSCE) than the corresponding molybdenum analogue [MoO₂(i-Bu₂dtc)₂] (−0.92 V vs. SSCE) in dichloromethane.     

Evaluation and elimination of inhibitory effects of salts and heavy metal ions on biodegradation of Congo red by Pseudomonas sp. mutant

In this study, it was attempted to evaluate the influences and also recommended some elimination methods for inhibitory effects offered by salts and heavy metal ions. Congo red dye solution treated with mutant Pseudomonas sp. was taken as a model system for study. The salts used in this study are NaCl, CaCl₂ and MgSO₄·7H₂O. Though the growth was inhibited at concentrations above 4 g/l, toleration was achieved by acclimatization process. In case of heavy metal ions, Cr (VI) showed low inhibition up to 500 mg/l of concentration, compared to Zn (II) and Cu (II). It was due to the presence of chromium reductase enzyme which was confirmed by SDS-PAGE. Zn (II) and Cu (II) ion inhibitions were eliminated by chelation with EDTA. The critical ion concentrations obtained as per Han-Levenspiel model for Cr (VI), Zn (II) and Cu (II) were 0.8958, 0.3028 and 0.204 g/l respectively.     

Reduced Growth Yield of Activated Sludge in Organic Protonophore-Containing Batch Culture

Abstract The effects of organic protonophores 2,4-dinitrophenol (dNP) and para-nitrophenol (pNP) on the observed growth yield (Y _obs) was studied using batch cultures of activated sludge microorganisms. A growth yield model was proposed in relation to the ratio of initial protonophore concentration (C _u) to initial biomass concentration (X ₀) and was verified with experimental data. It was found that Y _obs decreased with the increase of the C _u/X ₀ ratio, while the specific rate of glucose consumption was increased. Results showed that the C _u/X ₀ ratio could more reasonably reflect the real strength of organic protonophore exerted to activated sludge than using C _u only. Based on the concept of growth yield, a model describing the uncoupling degree between energy generated via electron transport system and energy used for growth was further developed for protonophore-containing batch culture. It was shown that more than 60% of glucose was consumed through a futile cycle of energy rather than for growth at higher C _u/X ₀ ratios. This research usefully shows that the dissipation of energy via uncoupling biochemical processes can reduce excessive production of activated sludge markedly. Received: 28 April 1999; Accepted: 14 September 1999; Online Publication: 6 March 2000     

Using non‐invasive magnetic resonance imaging (MRI) to assess the reduction of Cr(VI) using a biofilm–palladium catalyst

Industrial waste streams may contain contaminants that are valuable like Pd(II) and/or toxic and mutagenic like Cr(VI). Using Serratia sp. biofilm the former was biomineralized to produce a supported nanocrystalline Pd(0) catalyst, and this biofilm–Pd heterogeneous catalyst was then used to reduce Cr(VI) to less dangerous Cr(III) at room temperature, with formate as the electron donor. Cr(VI)_(aq) is non‐paramagnetic while Cr(III)_(aq) is paramagnetic, which enabled spatial mapping of Cr species concentrations within the reactor cell using non‐invasive magnetic resonance (MR) imaging experiments. Spatial reactivity heterogeneities were thus examined. In batch reactions, these could be attributed primarily to heterogeneity of Pd(0) distribution and to the development of gas bubbles within the reactor. In continuous flow reactions, spatial reactivity heterogeneities resulted primarily from heterogeneity of Cr(VI) delivery. Biotechnol. Bioeng. 2010;107: 11–20. © 2010 Wiley Periodicals, Inc.     

Biosorption of Cr(VI) onto marine Aspergillus niger: experimental studies and pseudo-second order kinetics

The removal of hexavalent chromium from aqueous solution was studied in batch experiments using dead biomass of three different species of marine Aspergillus after alkali treatment. All the cultures exhibited potential to remove Cr(VI), out of which, Aspergillus niger was found to be the most promising one. This culture was further studied employing variation in pH, temperature, metal ion concentration and biomass concentration with a view to understand the effect of these parameters on biosorption of Cr(VI). Higher biosorption percentage was evidenced at lower initial concentration of Cr(VI) ion, while the sorption capacity of the biomass increased with rising concentration of ions. Biomass as low as 0.8 g l⁻¹ could biosorb 95% Cr(VI) ions within 2,880 min from an aqueous solution of 400 mg l⁻¹ Cr(VI) concentration. Optimum pH and temperature for Cr(VI) biosorption were 2.0 and 50°C, respectively. Kinetic studies based on pseudo second order models like Sobkowsk and Czerwinski, Ritchie, Blanchard and Ho and Mckay rate expressions have also been carried out. The nature of the possible cell–metal ion interactions was evaluated by FTIR, SEM and EDAX analysis.     

Study on Chromium (VI) Reduction Kinetics by Pseudomonas aeruginosa Using a Combined System of Acoustic Wave Impedance Analyzer and UV-Vis Spectrophotometer

A novel system combining acoustic wave impedance (AWI) analyzer with UV-vis spectrophotometer was developed for the study of chromium (VI) reduction kinetics by Pseudomonas aeruginosa. AWI gave information about the growth of Pseudomonas aeruginosa, and UV-vis spectrophotometer gave information about the concentration of chromium (VI) simultaneously. A combined system response model, for chromium (VI) reduction kinetics at lower initial chromium (VI) concentrations, was derived and proved based on the novel system. Taking into account the effect of bacterial growth on chromium (VI) reduction, the new model successfully simulated chromium (VI) bioremediation process. By fitting chromium (VI) reduction data toward the derived model, the kinetic parameters related to the process were obtained. When the concentration of peptone was 10 g L⁻¹, the half-velocity reduction rate constant K _C and the maximum specific chromium (VI) reduction rate constant ν_max were 0.7682 mg chromium (VI) L⁻¹ and 2.5814 × 10⁻¹² mg chromium (VI) cells⁻¹ h⁻¹, respectively. It was found that the combined system can provide real-time, reliable, and two-dimensional kinetic information, and can be applied to study other biological processes.     

Rapid phase change of lipid microdomains in giant vesicles induced by conversion of sphingomyelin to ceramide

To understand the role of sphingomyelinase (SMase) in the function of biological membranes, we have investigated the effect of conversion of sphingomyelin (SM) to ceramide (Cer) on the assembly of domains in giant unilamellar vesicles (GUVs). The GUVs were prepared from mixture of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), N-palmitoly-d-erythro-sphingosine (C₁₆Cer), N-palmitoyl-d-erythro-sphingosylphosphorylcholine (C₁₆SM) and cholesterol. The amounts of DOPC, sum of C₁₆Cer and C₁₆SM, and cholesterol were kept constant (the ratio of these four lipids is shown as 1:X:1-X:1 (molar ratio), i.e., X is C₁₆Cer/(C₁₆Cer + C₁₆SM)). Shape and distribution of domains formed in the GUVs were monitored by a fluorescent lipid, Texas Red 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine (0.1 mol%). In GUVs containing low C₁₆Cer (X = 0 and 0.25), round-shaped domains labeled by the fluorescent lipid were present, suggesting coexistence of liquid-ordered and disordered domains. In GUVs containing intermediate Cer concentration (X = 0.5), the fluorescent domain covered most of GUV surface, which was surrounded by gel-like domains. Differential scanning calorimetry of multilamellar vesicles prepared in the presence of higher Cer concentration (X ≥ 0.5) suggested existence of a Cer-enriched gel phase. Video microscopy showed that the enzymatic conversion of SM to Cer caused rapid change in the domain structure: several minutes after the SMase addition, the fluorescent region spread over the GUV surface, within which regions with darker contrast existed. Image-based measurement of generalized polarization (GP) of 6-dodecanoyl-2-dimethylaminonaphthalene (Laurdan), which is related to the acyl chain ordering of the lipids, was performed. Before the SMase treatment domains with high (0.65) and low (below 0.4) GP values coexisted, presumably reflecting the liquid-ordered and disordered domains; after the SMase treatment regions with intermediate GP values (0.5) and smaller regions with higher GP values (0.65) were present. Generation of Cer thus caused a phase transition from liquid-ordered and disordered phases to a gel and liquid phase.     

The effect of carbon source on microbial community structure and Cr(VI) reduction rate

In the present work, the effect of the carbon source on microbial community structure in batch cultures derived from industrial sludge and hexavalent chromium reduction was studied. Experiments in aerobic batch reactors were carried out by amending industrial sludge with two different carbon sources: sodium acetate and sucrose. In each of the experiments performed, four different initial Cr(VI) concentrations of: 6, 13, 30 and 115 mg/L were tested. The change of carbon source in the batch reactor from sodium acetate to sucrose led to a 1.3–2.1 fold increase in chromium reduction rate and to a 5‐ to 9.5‐fold increase in biomass. Analysis of the microbial structure in the batch reactor showed that the dominant communities were bacterial species (Acinetobacter lwoffii, Defluvibacter lusatiensis, Pseudoxanthomonas japonensis, Mesorhizium chacoense, and Flavobacterium suncheonense) when sodium acetate was used as carbon source and fungal strains (Trichoderma viride and Pichia jadinii), when sodium acetate was replaced by sucrose. These results indicate that the carbon source is a key parameter for microbial dynamics and enhanced chromium reduction and should be taken into account for efficient bioreactor design. Biotechnol. Bioeng. 2010;107: 478–487. © 2010 Wiley Periodicals, Inc.     

Bioaccumulation of copper(II), lead(II) and chromium(VI) by growing Aspergillus niger

The effect of copper(II), lead(II) and chromium(VI) ions on the growth and bioaccumulation properties of Aspergillus niger was investigated as a function of initial pH and initial metal ion concentration. The optimum pH values for growth and metal ion accumulation were determined as 5.0, 4.5 and 3.5 for copper(II), lead(II) and chromium(VI) ions, respectively. Although all metal ion concentrations caused an inhibition effect on the growth of A. niger, it was capable of removing of copper(II) and lead(II) with a maximum specific uptake capacity of 15.6 and 34.4 mg g⁻¹ at 100 mg dm⁻³ initial copper(II) and lead(II) concentration, respectively. Growth of A. niger was highly effected by chromium(VI) ions and inhibited by 75 mg dm⁻³ initial chromium(VI) concentration since some inhibition occurred at lower concentrations.     

Isovalent and mixed-valent molybdenum complexes containing Mo(μ-E)(μ-S2)Mo (E = O, S) core units

The reactions of Tp^iPrMoO(SR)(NCMe) (Tp^iPr = hydrotris(3-isopropylpyrazolyl)borate) with propylene sulfide in toluene result in the formation of the diamagnetic, isovalent Mo(V) complex, [Tp^iPrMo^VO]₂(μ-S)(μ-S₂). This complex and its previously reported μ-oxo analog, [Tp^iPrMo^VO]₂(μ-O)(μ-S₂), react with cobaltocene to produce one-electron-reduced, mixed-valent complexes, [CoCp₂][{Tp^iPrMo^IV,VO}₂(μ-E)(μ-S₂)] (E = S or O, respectively). All complexes have been isolated and characterized by microanalysis, mass spectrometry, IR and ¹H NMR or EPR spectroscopies, and X-ray crystallography. Neutral [Tp^iPrMo^VO]₂(μ-S)(μ-S₂) exhibits a pseudo-C₂ symmetric structure, with distorted octahedral anti oxo-Mo(IV) centers coordinated by Tp^iPr and linked by μ-sulfido and μ-disulfido ligands. A similar structure is adopted by the anion in mixed-valent [CoCp₂][{Tp^iPrMo^IV,VO}₂(μ-S)(μ-S₂)]; this compound adopts a hexagonal, supramolecular structure with columns of tight ion-pairs with interactions, interconnected through weaker contacts to three neighboring columns. The structure contains large interstitial voids filled with lattice solvent molecules. EPR investigation of the mixed-valent complexes gave rise to unusually broad signals with no evident hyperfine splitting. The synthesis and characterization of a number of cis-dioxo-Mo(VI) precursors are also reported.