Outer Sulfur Research Articles

Acidity of persulfides and its modulation by the protein environments in sulfide quinone oxidoreductase and thiosulfate sulfurtransferase

Persulfides (RSSH/RSS–) participate in sulfur metabolism and are proposed to transduce hydrogen sulfide (H2S) signaling. Their biochemical properties are poorly understood. Herein, we studied the acidity and nucleophilicity of several low molecular weight persulfides using the alkylating agent, monobromobimane. The different persulfides presented similar pKa values (4.6-6.3) and pH-independent rate constants (3.2-9.0 × 103 M–1 s–1), indicating that the substituents in persulfides affect properties to a lesser extent than in thiols because of the larger distance to the outer sulfur. The persulfides had higher reactivity with monobromobimane than analogous thiols and putative thiols with the same pKa, providing evidence for the alpha effect (enhanced nucleophilicity by the presence of a contiguous atom with high electron density). Additionally, we investigated two enzymes from the human mitochondrial H2S oxidation pathway that form catalytic persulfide intermediates, sulfide quinone oxidoreductase (SQOR) and thiosulfate sulfurtransferase (TST, rhodanese). The pH dependence of the activities of both enzymes were measured using sulfite and/or cyanide as sulfur acceptors. The TST half-reactions were also studied by stopped-flow fluorescence spectroscopy. Both persulfidated enzymes relied on protonated groups for reaction with the acceptors. Persulfidated SQOR appeared to have a pKa of 7.8 ± 0.2. Persulfidated TST presented a pKa of 9.38 ± 0.04, probably due to a critical active site residue rather than the persulfide itself. The apparent pKa for the TST thiol was 6.5 ± 0.1 and it reacted in the anionic state with thiosulfate. Overall, our study contributes to a fundamental understanding of persulfide properties and their modulation by protein environments.

3-Mercaptopyruvate sulfurtransferase: an enzyme at the crossroads of sulfane sulfur trafficking.

3-Mercaptopyruvate sulfurtransferase (MPST) catalyzes the desulfuration of 3-mercaptopyruvate to generate an enzyme-bound hydropersulfide. Subsequently, MPST transfers the persulfide's outer sulfur atom to proteins or small molecule acceptors. MPST activity is known to be involved in hydrogen sulfide generation, tRNA thiolation, protein urmylation and cyanide detoxification. Tissue-specific changes in MPST expression correlate with ageing and the development of metabolic disease. Deletion and overexpression experiments suggest that MPST contributes to oxidative stress resistance, mitochondrial respiratory function and the regulation of fatty acid metabolism. However, the role and regulation of MPST in the larger physiological context remain to be understood.

Well-Defined Hierarchically Porous Double-Shell Hollow Polypyrrole@Sulfur Microspheres with Outer Sulfur Shells for Lithium–Sulfur Batteries with Superior Electrochemical Performance

Polypyrrole (PPy) hollow micro/nanospheres have been widely designed to encapsulate active sulfur as cathodes in lithium–sulfur (Li–S) batteries to inhibit the polysulfide shuttle effect. Here, for...

Heat transfer analysis for design of RC sulfur pit structure under high temperature condition

Behaviors of the sulfur pit structure are governed with geometric constraints and thermal loads. The buried concrete structure stores sulfur in high temperature so sulfur pits are generally designed by performing structural analysis, which includes temperature gradient between inner and outer sulfur pit wall as load. The temperature gradient is strongly affected by the sphere of thermal influence in the ground surrounding the sulfur pit. However, there is no guideline to determine the value of the said sphere of thermal influence. This results in the designer using an arbitrary and empirical value for the sphere of thermal influence. For this reason, heat transfer analysis of the sulfur pit surrounded by ground is conducted. Considering the sulfur pit's wall thickness and thermal properties of insulator as parameters, the temperature variations with time in the sulfur pit wall and ambient ground are investigated numerically. A design formula for determining the thermal sphere is also proposed from the numerical results and would be utilized to calculate the temperature gradient of sulfur pit.

Redox regulation of mammalian 3-mercaptopyruvate sulfurtransferase.

A cystine-catabolizing enzyme, 3-mercaptopyruvate sulfurtransferase catalyzes the trans-sulfuration reaction of mercaptopyruvate or thiosulfate to thiol-containing compounds or cyanide. During the catalytic process, persulfide is formed at the catalytic site cysteine residue and a sulfur-acceptor substrate donates the outer sulfur of the persulfide to form a new persulfide molecule. Subsequently, the molecule can be reduced by thioredoxin to form hydrogen sulfide. The enzyme is regulated by redox changes via two redox-sensing molecular switches consisting redox-sensitive cysteine residues. One switch is the catalytic cysteine in itself, which is oxidized to form a cysteine-sulfenate resulting in inhibition of catalytic activity. The sulfenate can be reduced by thioredoxin resulting in restoration of the activity. The redox potential of sulfenate is lower than that of glutathione and greater than that of thioredoxin. The other switch involves cysteine residues positioned on the surface of the enzyme. The oxidation the intermolecular disulfide linkage at these cysteine residues, leading to dimer formation, inhibits enzyme activity. On the other hand, reduction-associated monomer formation increases catalytic activity. Thioredoxin reduces the disulfide bond more effectively than dithiothreitol, although the specificity mechanism has not been identified. Congenital defects in this enzyme result in, mercaptolactate-cysteine disulfiduria associated with or without mental retardation. However, the pathogenesis has not been identified. Because 3-mercaptopyruvate sulfurtransferase serves as a cellular antioxidative protein, the other biological functions related to the inhabitant disease are being investigated.

Oxidation at the Core–Ligand Interface of Au Lipoic Acid Nanoclusters That Enhances the Near-IR Luminescence

A new surface oxidation mechanism that enhances the luminescence of Au nanoclusters is discovered in Au nanoclusters synthesized with disulfide lipoic acid. The quantum efficiency increased from 1 to 2% up to 10% upon the sulfur oxidation at the Au–ligand interface. Relatively low quantum efficiency has been a bottleneck barrier to exploit the appealing near-infrared luminescence from molecular-like gold nanoclusters for broader and effective applications. Combined IR, XPS, and NMR analysis reveals that the outer sulfur atoms on ca. half of the lipoic acid ligands were partially oxidized accompanying the luminescence enhancement. Opposite to those from the widely studied monothiolate Au nanoclusters, the quantum efficiency increases at lower pH. The observation is explained by the electron density changes at the core–ligand interfaces under the ligand dielectric layer. Multivalent binding of the lipoic acid ligands on Au core drastically reduces the exchange or addition of monothiols into ligand monolayer. The improved resistance to excess thiols is significant because the stability of Au nanoclusters is a critical concern in their applications in thiol-rich physiological environment. The fundamental materials and chemistry insights suggest promising routes to further enhance the near-IR luminescence and chemical stability that are critical factors in biomedical and sensing applications.

S9-2 Mercaptopyruvate sulfurtransferase and hydrogen sulfide

Hydrogen persulfide (HP) generation is catalyzed by three enzymes: cystathionine β-synthase, cystathionine γ-lyase (cystathionase), and 3-mercaptopyruvate sulfurtransferase (MST). MST-catalyzed HP production is a three-step reaction. In the first step, a sulfur atom is transferred to a catalytic site cysteine residue to form a persulfide as a reaction intermediate. In the second step, the outer sulfur atom of this persulfide intermediate is transferred to a thiol compound (an acceptor substrate), resulting in the formation of another persulfide through a nucleophilic attack. In the final step, this persulfide is reduced by the substrate and/or a biological reductant such as thioredoxin to release HP. Considering the chemistry of redox reactions, all reactions proceed under physiological conditions. Moreover, HP production is only one of four physiological roles of MST. MST catalyzes cysteine degradation to pyruvate via the mercaptopyruvate pathway, a minor pathway in cysteine catabolism. MST also functions as an antioxidant through redox reactions involving its catalytic site cysteine (cysteine–sulfenate cycle) and an intersubunit disulfide bond (a monomer–dimer equilibrium). Finally, it contributes to the production of sulfur oxides through redox reactions involving the stable persulfide intermediate formed at the catalytic site cysteine.

Organo‐Gallium/Indium Chalcogenide Complexes of Copper(I): Molecular Structures and Thermal Decomposition to Ternary Semiconductors

Several organo-gallium/indium chalcogenide complexes of copper(I), stabilized by trialkylphosphines, were isolated, structurally characterized by using single-crystal X-ray diffraction, and investigated in thermolysis experiments. The syntheses with [E(Me3Si)2] (E=S, Se) as a starting material and a chalcogen source involve the elimination of volatile silyl acetate, silyl ethers, and methane from copper(I) acetate, and Group 13 metal trimethyl compounds, respectively. Chalcogenide complexes, according to the general formulas [(R3PCu)4(MeM)4E6] (1-6) and [(R3PCu)6(MeM)4M4S13] (7-9; with R=alkyl and M=Ga, In), and mixed chalcogenide-phenylchalcogenolate complexes [(iPr3PCuEPh)3(MeGaE)4] (10, 11) were isolated. The heavy atom cores of 1-6 consist of an octahedron of chalcogen atoms, interpenetrated by a cube of metal atoms. Depending on the steric demand of the phosphine ligands, two constitutions are observed; the metal atoms of the same element either forming tetrahedra, or parallelograms, respectively. This constitutional isomerism is further investigated by quantum chemical calculations. Complexes 7-9 contain a central sulfur atom, surrounded by two interpenetrating tetrahedra of Group 13 metal atoms, an octahedron of copper atoms, and an icosahedron of twelve outer sulfur atoms; the heavy atom framework of 10 and 11 is a "cut-out" of this structure. Thermolysis experiments include thermogravimetry measurements and subsequent Rietveld phase analysis of the residues by using powder X-ray diffraction. The homologous compounds 1, 3, 4, and 6 yield the respective crystalline ternary semiconductor material CuME2 at temperatures below 300 °C. Partial release of Me3 M during the thermolysis process results in excess copper in the residue and therefore in small amounts of additional binary copper chalcogenide phases or metallic CuM alloys. Compound 8 produces nanocrystalline CuGaS2 at about 300 °C.

The fate of Au25(SR)18 clusters upon ligand exchange with binaphthyl-dithiol: interstaple binding vs. decomposition

The ligand exchange reaction between monodisperse Au25(2-PET)18 (2-PET: 2-phenylethylthiolate) clusters and 1,1'-binaphthyl-2,2'-dithiol (BINAS) was long thought to induce decomposition of the cluster (Si et al., J. Phys. Chem. C, 2009). We repeated the experiment and analyzed the reaction products using MALDI-TOF mass spectrometry. The spectra clearly indicate successful ligand exchange, bidentate binding of the BINAS ligand and intact Au25 clusters. The reaction products are identified as Au25(2-PET)18-2x(BINAS)x (x = 1-4) for a 24 h reaction with a 50-fold molar excess of BINAS. Two likely binding motifs are discussed. Analysis of atomic distances in both the cluster and the free ligand indicates interstaple binding connecting the central sulfur atom of the protecting (SRAu)2SR with the outer sulfur atom of a second unit. The results presented have implications on the binding position of BINAS in Au38(SR)24-2x(BINAS)x clusters.

Anisotropic Chemical Pressure Effects in Single-Component Molecular Metals Based on Radical Dithiolene and Diselenolene Gold Complexes

On the basis of the reported radical neutral complex [Au(Et-thiazdt)(2)] (Et-thiazdt = N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate), a series of single-component conductors derived from [Au(Et-thiazdt)(2)], also noted as [AuS(4)(═S)(2)], has been developed, by replacing the outer sulfur atoms of the thiazoline-2-thione rings by oxygen atoms and/or by replacing the coordinating sulfur atoms by selenium atoms toward the corresponding diselenolene complexes. Comparison of the X-ray crystal structures and transport properties of the four isostructural complexes, noted as [AuS(4)(═S)(2)], [AuS(4)(═O)(2)], [AuSe(4)(═S)(2)], and [AuSe(4)(═O)(2)], shows that the oxygen substitution on the outer thiazoline ring actually decreases the conductivity by a factor of 100, despite a contracted unit cell volume reflecting a positive chemical pressure effect. On the other hand, the S/Se substitution increases the conductivity by a factor of 100, and the pressure needed to transform these semiconductors into the metallic state is shifted from 13 kbar in [AuS(4)(═S)(2)] to only ≈6 kbar in [AuSe(4)(═S)(2)]. Analysis of unit cell evolutions and ab initio band structure calculations demonstrates the strongly anisotropic nature of this chemical pressure effect and provides an explanation for the observed changes in conductivity. The greater sensitivity of these neutral single-component conductors to external pressure, as compared with "classical" radical salts, is also highlighted.

Is Novel Signal Transducer Sulfur Oxide Involved in the Redox Cycle of Persulfide at the Catalytic Site Cysteine in a Stable Reaction Intermediate of Mercaptopyruvate Sulfurtransferase?

Abstract In transsulfuration reaction catalyzed by rat mercaptopyruvate sulfurtransferase (MST), a stable persulfide is formed at the catalytic site cysteine Cys(247) as a reaction intermediate. The outer sulfur atom is donated by the substrate, thiosulfate, or by mercaptopyruvate. MST serves as a thioredoxin-dependent antioxidant possessing self-regulated enzymatic activity. After oxidation of persulfurated MST by treatment with hydrogen peroxide, mass spectrometric analysis showed that the outer sulfur atom of the persulfide is oxidized to form Cys-thiosulfenate (Cys-Sγ-SO(-)), Cys-thiosulfinate (Cys-Sγ-SO(2)(-)), and Cys-thiosulfonate (Cys-Sγ-SO(3)(-)). Next, sulfur acceptor substrates including reduced thioredoxin convert all modified cysteines to nonmodified cysteines. Another sulfur acceptor substrate, cyanide, also converted these cysteines via cyanolysis. Thus, sulfur oxides are suggested to release in the redox cycle of persulfide of MST.

Structural Basis for the Oxidation of Protein-bound Sulfur by the Sulfur Cycle Molybdohemo-Enzyme Sulfane Dehydrogenase SoxCD

The sulfur cycle enzyme sulfane dehydrogenase SoxCD is an essential component of the sulfur oxidation (Sox) enzyme system of Paracoccus pantotrophus. SoxCD catalyzes a six-electron oxidation reaction within the Sox cycle. SoxCD is an α(2)β(2) heterotetrameric complex of the molybdenum cofactor-containing SoxC protein and the diheme c-type cytochrome SoxD with the heme domains D(1) and D(2). SoxCD(1) misses the heme-2 domain D(2) and is catalytically as active as SoxCD. The crystal structure of SoxCD(1) was solved at 1.33 Å. The substrate of SoxCD is the outer (sulfane) sulfur of Cys-110-persulfide located at the C-terminal peptide swinging arm of SoxY of the SoxYZ carrier complex. The SoxCD(1) substrate funnel toward the molybdopterin is narrow and partially shielded by side-chain residues of SoxD(1). For access of the sulfane-sulfur of SoxY-Cys-110 persulfide we propose that (i) the blockage by SoxD-Arg-98 is opened via interaction with the C terminus of SoxY and (ii) the C-terminal peptide VTIGGCGG of SoxY provides interactions with the entrance path such that the cysteine-bound persulfide is optimally positioned near the molybdenum atom. The subsequent oxidation reactions of the sulfane-sulfur are initiated by the nucleophilic attack of the persulfide anion on the molybdenum atom that is, in turn, reduced. The close proximity of heme-1 to the molybdopterin allows easy acceptance of the electrons. Because SoxYZ, SoxXA, and SoxB are already structurally characterized, with SoxCD(1) the structures of all key enzymes of the Sox cycle are known with atomic resolution.

IF‐ReS2 with Covalently Linked Porphyrin Antennae

The preparation of inorganic and organic hybrid materials, of metals or semiconductor systems which are functionalized with functional molecules to fabricate devices — nanotechnology — is currently an area of intense activity in both fundamental science and applied science on an international scale. Principally, nanotechnology aims at manipulating atoms, molecules, and nanosize particles in a precise and controlled manner in order to build materials with a fundamentally new organization and novel properties. The embryonic stage of nanotechnology is atomic assembly, whereas the mature form of nanotechnology will be molecular assembly to make nano-building blocks for the design of nanocomposites or self-organizing nanodevices. In order to achieve the outstanding properties of nanomaterials, surface modification is the key to success, as any application in materials and devices is hindered by difficulties in processing and manipulation. For instance, the charge transport process across the interface between a semiconductor metal oxide and an organic dye or a biomolecule forms the basis for improving the performance of many optoelectronic devices, photovoltaic cells, and light emitting diodes (LEDS). Chalcogenide nanotubes and fullerenes are particularly useful components for inorganic hybrid structures because they find many potential applications as solid lubricants, catalysts for the hydrodesulfurization, and they are rigid and structurally well-defined. Many of the useful properties of inorganic layered metal chalcogenides are related to their crystal structures, which are characterized by weak van der Waals forces between the individual MQ2 (Q = S, Se) slabs containing metal atoms sandwiched between two inert chalcogen layers. Furthermore, they may have a broad range of chemical and physical properties that can be chosen according to the desired task. However, in order to utilize chalcogenide nanotubes and fullerenes in hybrid materials, their surfaces must be tailored with reactive groups, i. e., their surface chemistry has to be mastered. But the inertness of the chalcogen surface layer and the associated shielding of the metal atoms from nucleophilic attacks by organic ligands are the main obstacles for the functionalization of chalcogenide nanoparticles and nanotubes. Since direct anchoring of organic ligands to the surface of chalcogenides nanomaterials is difficult, we used a nitrilotriacetic acid that can be used to coordinate to Ni ions which, in turn, can use their vacant coordination sites for binding to the surface sulfur atoms of metal chalcogenides. A seemingly simple question to be addressed is the binding mode of the metal/scorpionate ligand block to the sidewalls of the metal chalcogenides nanoparticles. The most obvious model would assume a binding of the metal to defects on the chalcogenide surface. The second model assumes that the metal (e.g., Ni) is bonded to the ideally closed packed outer sulfur layer of the chalcogenide tube, and the metal is situated in a threefold hollow (or on a twofold coordinating or single site) of the closepacked sulfur layer. Herein, a step further, we report the surface functionalization of ReS2 fullerenes with polymeric ligands, the subsequent binding of protoporphyrin ligands, and the complexation of zinc. Our polymeric ligand incorporates (i) a nitrilotriacetic acid (NTA) anchor that can be used to coordinate to Ni ions which, in turn, can use their vacant coordination sites for binding to the surface S atoms of IF–ReS2; (ii) amine groups which can be used to immobilize protoporphyrins; and (iii) a piperazyl 4-chloro-7-nitrobenzofurazan (pipNBD) fluorescent dye as a recognition molecule to monitor microscopically the functionalization of the polymeric ligand to IF–ReS2. The amino groups were utilized for conjugating the protoporphyrin, which in turn complexates the Zn cation. The resulting functionalized IF– ReS2 particles can be dispersed in water and organic solvents. They were characterized by high-resolution trans-

Single-stage autotrophic nitrogen-removal process using a composite matrix immobilizing nitrifying and sulfur-denitrifying bacteria

We developed a novel single-stage autotrophic nitrogen-removal process comprised of two composite immobilized biomass layers-one of nitrifying bacteria and one of sulfur-denitrifying bacteria and elemental sulfur-in a Fe-Ni fibrous slag matrix. Nitrification and consumption of dissolved oxygen occurred in the outer part and sulfur denitrification in the anoxic inner part of the composite matrix, thus realizing autotrophic nitrogen removal in a single reactor. The complete conversion of ammonia into N2 in a single reactor was demonstrated in both batch-mode incubation and continuous-feed operation. The spatial profiles of the ammonia-oxidizing bacteria and denitrifying bacteria were evaluated by real-time PCR, targeting their functional genes, and stratification of these two types was observed in the matrix after several months of incubation. This process does not require any specific reactor type or conditions and thus has the potential to be applied to many different wastewater treatment processes due to its simplicity in both operation and construction.

Surface changes and role of buried water molecules during the sulfane sulfur transfer in rhodanese from Azotobacter vinelandii: a fluorescence quenching and nuclear magnetic relaxation dispersion spectroscopic study.

The Azotobacter vinelandii rhodanese is a sulfurtransferase enzyme that catalyzes the transfer of the outer sulfur atom from thiosulfate to cyanide. Recently, investigations by NMR relaxation on the (15)N-enriched protein reported that interdomain contacts are rigidly maintained upon the sulfane sulfur transfer from the enzyme to the substrate. The modality of the enzymatic mechanism is then confined to a surface interaction, including dynamics of water molecules buried in the tertiary structure. Thus, investigations have been carried out by fluorescence, circular dichroism, and nuclear magnetic relaxation dispersion measurements. The comparison of circular dichroism spectra of the persulfurated enzyme and the sulfur-free form indicated that small changes occur. Fluorescence quenching studies have been performed to evaluate the conformational changes during catalysis using the fluorescent probe 8-anilinonaphthalene-2-sulfonic acid, and acrylamide, iodide, and cesium ions as quenchers. Changes in exchange dynamics of water molecules buried in the structure with bulk water, observed by nuclear magnetic relaxation dispersion, are due to local conformational transitions, likely involving residues around the active site, and are consistent with the global correlation time found by (15)N relaxation. These results, taken together, provide important information for elucidating the conformational features of the mechanism of action of the enzyme either in the role of a selective donor of a sulfur atom to small-sized substrates (i.e., to cyanide, transforming it into thiocyanate) or in the role of sulfur insertase for the formation of the Fe(2)S(2) iron-sulfur cluster in sulfur-deprived ferredoxins.

Cyclic vinylogous TTF: a potential molecular clip triggered by electron transfer.

Cyclic vinylogous tetrathiafulvalenes (TTFs) where the two dithiole rings are linked through the outer sulfur atoms with an alkyl chain of various lengths were synthesized by oxidative intramolecular coupling of bis(dithiafulvenes). Upon oxidation, these systems exhibit large molecular movements associated with electron transfers. Their electrochemical behaviors were investigated together with the X-ray crystallographic structures of several derivatives and compared with molecular geometry calculations. Dependent on the length of the alkyl chain, either a stretch or a clip movement can be observed. These conformational modifications were found to be fast and fully reversible and required only low oxidation potentials. The movements seem to be almost insensitive to the nature of the substituents or its steric hindrance on the central conjugated spacer.

S-position isomers of BEDT-TTF and EDT-TTF: synthesis and influence of outer sulfur atoms on the electrochemical properties and crystallographic network of related organic metals.

The synthesis and characterization of new modified tetrathiafulvalenes (TTF), the S-position isomers of BEDT-TTF and EDT-TTF, are described. The synthetic strategy presented in this work is based on an efficient and unprecedented two-step sequence for the conversion of a vicinal bis(hydroxymethyl) functionality into a disulfide ring. Different routes are discussed in terms of efficiency for the synthesis of the symmetric S-position isomer of BEDT-TTF and that of EDT-TTF. Their electrochemical properties are combined with data obtained from UV/Vis spectroscopy and orbital calculations, and the electronic influence of peripheral sulfur atoms on the neutral and oxidized species is discussed. The introduction of these outer sulfur atoms at the periphery of the TTF core gives rise to specific intermolecular S...S interactions in the corresponding organic materials. Crystallographic studies of radical cation salts synthesized upon electrocrystallization clearly showed that the network obtained is dictated by the outer sulfur atoms, which are responsible for a characteristic and unprecedented "windmill" array.

Dinuclear molybdenum complexes containing the novel μ,η 1:3-AsS 2 ligand: synthesis and molecular structure of [{Cp* 2Mo 2(CO) 2As 2S 4}·2Cr(CO) 5]·0.5CH 2Cl 2 (Cp*=C 5Me 5)

The reaction of [Cp*Mo(CO) 3Cl] (Cp*=C 5Me 5) with K 3AsS 3 has been investigated under different conditions. At 56°C, the already known compounds [Cp* 2Mo 2S 4] ( 2), [Cp* 2Mo 2As 2S 3] ( 3), and [Cp* 2Mo 2S 4H 2] ( 4) are formed along with [Cp* 2Mo 2(CO) 2As 2S 4] ( 5). Reaction at 120°C only gives 2 and 3. Complex 5 was characterized by means of its bisadduct [{Cp* 2Mo 2(CO) 2As 2S 4}·2Cr(CO) 5] ( 6). An X-ray crystallographic study of 6 reveals the presence of two novel AsS 2 ligands, bridging in a pseudoallylic manner two Mo atoms. The Cr(CO) 5 fragments are coordinated to both the outer sulfur atoms. Thus, each AsS 2 ligand in 6 acts as a seven-electron ligand.

Oxygen-substituted derivatives of DHTTF-fused donors: synthesis and properties

The synthesis and electrochemical properties of novel oxygen-containing π-electron donors (3a,b and 4), in which only one outer sulfur atom of the DHTTF (dihydrotetrathiafulvalene)-fused donors (la,b and 2) is replaced by oxygen atom, has been investigated to explore new organic metals. Among the 3a-based CT (charge-transfer) complexes and salts, the TCNQ (tetracyanoquinodimethane) complex and the BF 4 salt exhibited metallic conducting behavior.

Carrier of reduced sulfur is a possible role for thiotaurine in symbiotic species from hydrothermal vents with thiotrophic symbionts

Experiments supporting the possible role of the free sulfur-containing amino acid thiotaurine, as a transport and storage compound for sulfide in invertebrates with thiotrophic symbionts are described. The free-living chemotrophic sulfur-oxidising bacterium, Thiobacillus hydrothermalis (strain DSMZ 7121), was used as a model for the symbionts as the actual symbionts have not been obtained in culture. Thiotaurine contains two sulfur atoms, namely the inner sulfone and the outer sulfane sulfur; the latter presents a potential source of reducing equivalents for the symbiont. Nevertheless, we observed no oxidation of thiotaurine when this compound was added to a culture of T. hydrothermalis pre-grown on sulfide. In contrast, when thiotaurine was added to the culture together with an extract of the trophosome of a vestimentiferan tubeworm from the Manus basin, we observed that thiotaurine was oxidised to hypotaurine with concomitant acidification and formation of bacterial biomass. Thus, the trophosome contains an unknown catalytic factor. We suggest that thiotaurine requires reduction prior to oxidation by T. hydrothermalisand that the host may catalyse the conversion of thiotaurine through the glutathione redox couple. This way, the host can accurately control energy delivery (as reduced sulfur) to the symbionts and can therefore control their symbiont biomass.