Displacement Of Sulfur Research Articles

Влияние поверхностной ёмкости положительных электродов на длительность циклирования литий-серных аккумуляторов

The effect of sulfur content in positive electrodes (the surface capacity of sulfur electrodes) on the characteristics (such as the depth of sulfur electrochemical reduction, changes in capacitance and Coulomb efficiency during cycle life) of lithium-sulfur cells with electrolytes based on sulfolane was studied. It was shown that the reason for the capacitance decrease of the lithium-sulfur cells at the early stage of its cycle life is the displacement of sulfur of the porous positive electrode from the rear regions into the front ones. It was established that in order to achieve the maximum possible specific energy of the lithium-sulfur batteries with the electrolytes based on sulfolane, the surface capacitance of the positive electrodes should be in the range of 2-3 mA·h/cm2.

Sulfur oxidation on graphene-supported platinum nanocluster arrays

Nanocluster arrays grown on a graphene Moiré on Rh(1 1 1) are an excellent model system that can bridge the materials gap between single crystals and real catalysts. They feature different adsorption sites like edges, kinks, and facets, but are at the same time well-ordered with a small size distribution. Herein, we used platinum nanocluster arrays to investigate the oxidation of sulfur, which is a common catalyst poison, as a possible route to restore the catalyst. We studied the kinetics in a site-resolved manner with high-resolution XPS, despite the complex shape of the nanoparticles. Since SO3 and SO4 were the only observable SOx surface species, the reaction of S to SO was identified as the rate-determining step. As a secondary process, the displacement of sulfur from edge to facet sites caused by oxygen was observed.

A dual-response fluorescent probe for the discrimination of cysteine from glutathione and homocysteine

A highly selective and sensitive turn-on fluorescent BODIPY-based probe for the simultaneous and selective detection of Cys and Hcy/GSH from dual emission channels was developed. The spatial steric hindrance of the methyl groups at 1- and 7-positions in BODIPY skeleton prevented intramolecular displacement of sulfur with amino group of Hcy but not of Cys. GSH molecular skeleton is larger and amino is far away from sulfydryl group, and the product of the reaction of probe with GSH canstay in thiol phase. Therefore, the probe was successfully applied to the detection of Cys from GSH/Hcy. The confocal microscopy experiments implied that this probe is a promising candidate for imaging of Cys and Hcy/GSH in Hela cells.

Meso-heteroaryl BODIPY dyes as dual-responsive fluorescent probes for discrimination of Cys from Hcy and GSH

Two new BODIPY-based turn-on fluorescent probes (BDP-S-1 and BDP-O-6) contained tetramethyl at 1-, 3-, 5- and 7- positions, as well as O-, or S-aryl substituent at 8-position for the simultaneous and selective detection of Cys and Hcy/GSH from dual emission channels were developed. The spatial steric hindrance of the methyl groups at 1- and 7- positions prevented intramolecular displacement of sulfur with amino group of Hcy but not of Cys. Based on different thiols-induced SNAr substitution–rearrangement reaction with Cys and Hcy/GSH, leading to the corresponding amino- and thiol-BODIPY dyes with distinct photo-physical properties, these probes could simultaneously and selectively detect Cys and Hcy/GSH. With the help of laser scanning confocal microscope, we demonstrated that these probes could simultaneously sense Cys and GSH in Hela cells using multicolor imaging.

Uncoupling binding of substrate CO from turnover by vanadium nitrogenase

Biocatalysis by nitrogenase, particularly the reduction of N2 and CO by this enzyme, has tremendous significance in environment- and energy-related areas. Elucidation of the detailed mechanism of nitrogenase has been hampered by the inability to trap substrates or intermediates in a well-defined state. Here, we report the capture of substrate CO on the resting-state vanadium-nitrogenase in a catalytically competent conformation. The close resemblance of this active CO-bound conformation to the recently described structure of CO-inhibited molybdenum-nitrogenase points to the mechanistic relevance of sulfur displacement to the activation of iron sites in the cofactor for CO binding. Moreover, the ability of vanadium-nitrogenase to bind substrate in the resting-state uncouples substrate binding from subsequent turnover, providing a platform for generation of defined intermediate(s) of both CO and N2 reduction.

Ligand binding to the FeMo-cofactor: structures of CO-bound and reactivated nitrogenase.

The mechanism of nitrogenase remains enigmatic, with a major unresolved issue concerning how inhibitors and substrates bind to the active site. We report a crystal structure of carbon monoxide (CO)-inhibited nitrogenase molybdenum-iron (MoFe)-protein at 1.50 angstrom resolution, which reveals a CO molecule bridging Fe2 and Fe6 of the FeMo-cofactor. The μ2 binding geometry is achieved by replacing a belt-sulfur atom (S2B) and highlights the generation of a reactive iron species uncovered by the displacement of sulfur. The CO inhibition is fully reversible as established by regain of enzyme activity and reappearance of S2B in the 1.43 angstrom resolution structure of the reactivated enzyme. The substantial and reversible reorganization of the FeMo-cofactor accompanying CO binding was unanticipated and provides insights into a catalytically competent state of nitrogenase.

A near-infrared fluorescent sensor for selective detection of cysteine and its application in live cell imaging

Biological thiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play important roles in maintaining the appropriate redox status of biological systems. The discrimination between them is of great importance because of their different biological roles. Herein, we present a new near-infrared (NIR) fluorescent sensor Cy-NO2 for selective detection of Cys over Hcy/GSH. The nitrothiophenol group is introduced to quench the fluorescence through photo-induced electron transfer (PET). The sensor undergoes displacement of nitrothiophenol with thiol to turn on the fluorescence. The amino groups of Cys/Hcy further replace the thiolate to form amino-substituted products, which exhibit dramatically different photophysical properties compared to the sulfur-substituted product from the reaction with GSH. By means of more rapid intramolecular displacement of sulfur with the amino group of Cys than Hcy, the discrimination of Cys is achieved. Moreover, Cy-NO2 was successfully applied for bioimaging Cys in living cells.

Kinetic studies of the stability of Pt for NO oxidation: Effect of sulfur and long-term aging

The stability of Pt catalysts for NO oxidation was analyzed by observing the effect of pre-adsorbed sulfur on the reaction kinetics using a series of Pt/SBA-15 catalysts with varying Pt particle sizes ( ca 2–9 nm). Our results indicate that sulfur addition did not influence catalyst deactivation of any of the Pt catalysts, resulting in unchanged turnover rates (TOR) and reaction kinetics. The presence of sulfur on Pt was confirmed by X-ray absorption fine structure spectroscopy (EXAFS) under reducing environments. However, exposure of the catalyst to NO oxidation conditions displaced sulfur from the first coordination shell of Pt, yielding Pt–O bonds instead. Re-reduction fully recovered the Pt–S backscattering, implying that sulfur remained near the Pt under oxidizing conditions. X-ray photoelectron spectroscopy (XPS) and chemisorption measurements confirmed the presence of sulfur near platinum. The invariance of the NO oxidation reaction to sulfur poisoning is explained by sulfur displacement to interfacial sites and/or sulfur binding on kinetically irrelevant sites. Formation of Pt oxides remains as the main source of catalyst deactivation as observed by kinetic and X-ray absorption spectroscopy (XAS) measurements.

Ligand Structural Effects on Cu2S2 Bonding and Reactivity in Side-On Disulfido-Bridged Dicopper Complexes

To assess supporting ligand effects on S-S bond activation, a series of [Cu2(mu-eta2:eta2-S2)]2+ complexes supported by various beta-diketiminate or anilido-imine ligands (L) were synthesized via the reaction of Cu(I) precursors LCu(CH(3)CN) with S8. For the cases where L = beta-diketiminate, the syntheses were complicated by formation of clusters [Cu(SR)]4, where SR represents the ligand functionalized by sulfur at the central methine position. The [Cu2(mu-eta2:eta2-S2)]2+ products were characterized by X-ray crystallography and electronic absorption and resonance Raman spectroscopy. Correlations among the Cu-S, Cu-Cu, and S-S distances and the nu(S-S) values were observed and interpreted within the framework of a previously described bonding picture (Chen, P.; Fujisawa, K.; Helton, M. E.; Karlin, K. D.; Solomon, E. I. J. Am. Chem. Soc. 2003, 125, 6394). Comparison of these data to those for other relevant species revealed a remarkable degree of S-S bond activation in the compounds supported by the beta-diketiminate and anilido-imine ligands, which through strong electron donation increase backbonding from the copper ions into the S-S sigma* orbital and cause S-S bond weakening. Reactions of one of the complexes supported by an anilido-imine ligand with PPh(3) and xylyl isocyanide were explored, revealing facile transfer of sulfur to PPh(3) but only displacement of sulfur to yield a LCu(I)-CNAr (Ar = xylyl) complex with the isocyanide.

Pyridine-Carboxylate Complexes of Platinum. Effect of N,O-Chelate Formation on Model Bifunctional DNA−DNA and DNA−Protein Interactions

This paper reports on the chemistry of platinum complexes containing bidentate pyridine-carboxylate (pyAc = pyridin-2-yl-acetate and picEt = pyridine-2-ethylcarboxylate, ethylpicolinate) (N,O) ligands. The pyridine-2-acetate and ethylpicolinate ligands form six- and five-membered chelates, respectively, upon formation of the Pt-carboxylate bond. In all reactions with picEt with various platinum complex starting materials, spontaneous de-esterification of the pendant carboxylate ester occurs to give directly the chelates K[PtCl(2)(pic-N,O)]-trans-[Pt(pic-N,O)(2)] and SP-4,2-[PtCl(pic-N,O)(NH(3))] without any evidence of intermediates. The de-esterification is solvent dependent, and molecular modeling was used to explain this reaction. The reactions of the geometric isomers of [PtCl(pyAc-N,O)(NH(3))] with 5'-guanosine monophosphate, 5'-GMP, and N-acetyl-l-methionine, AcMet, were investigated by NMR spectroscopy. The objective was to ascertain by model chemistry the feasibility of formation of ternary DNA-Pt-protein adducts in biology. Model nucleotide and peptide compounds were formed in situ by chloride displacement giving [PtL(pyAc-N,O)(NH(3))](+) (L = 5'-GMP or AcMet). Competitive reactions were then examined by addition of the complementary ligand L. Sulfur displacement of coordinated 5'-GMP was slow. For SP-4,3-[Pt(AcMet)(NH(3))(PyAc-N,O)](+), a rapid displacement of the sulfur ligand by 5'-GMP was observed, giving SP-4,2-[Pt(5'-GMP-N7)(pyAc-N,O)(NH(3))](+).

Pseudoamide-type pyrrolidine and pyrrolizidine glycomimetics and their inhibitory activities against glycosidases.

Coupling reaction of (2R,3R,4R,5R)-2,5-hydroxymethyl-3,4-dihydroxypyrrolidine (DMDP) with isothiocyanates afforded the corresponding thiourea adducts, which were transformed into isourea-type bicyclic oxapyrrolizidine glycomimetics by mercury(II) oxide-assisted intramolecular sulfur displacement. Cyclic carbamate and thiocarbamate analogues were also prepared by direct carbonylation or thiocarbonylation of DMDP. Evaluation of the glycosidase inhibitory properties demonstrated that remarkable specificities in enzyme inhibition can be achieved upon modifications on the pseudoaglyconic side chain and on the nature of the sp(2)-hybridized endocyclic ring nitrogen.

Novel linker for the solid-phase synthesis of guanidines

A novel linker for the generation of alkyl-, acyl- and arylguanidines as an attachment point in solid phase synthesis has been developed. Introduction of a suitably functionalized thiourea to Wang resin via a carbamate linkage, followed by displacement of sulfur with a 1° or 2° amine affords resin bound guanidines suitably protected for further manipulation. Activation of the thiourea with Mukaiyama's reagent allows for the generation of arylguanidines. Mild acid treatment effects deprotection and liberation from the resin to afford guanidines in good yield and high purity.

Glutathione and N-acetylcysteine inactivations of mutagenic 2(5H)-furanones from the chlorination of humics in water.

The mutagenic 2(5H)-furanones resulting from the chlorination of lignohumic substances in water disinfection and paper pulp bleaching are known to be inactivated by thiols. The objectives of the present study were to characterize the kinetics of an inactivating reaction, isolate and characterize products, and determine their mutagenicity in relation to the starting, mutagenic 2(5H)-furanones. The Salmonella typhimurium (TA100) mutagenicity of mucochloric acid (MCA) had a mean value of 2800 revertants/mumol from four assays and was twice as potent as the C-5 isopropyl ether of MCA (MCA-IPE), whose mutagenicity was determined in the same four assays. A second-order reaction of MCA with GSH at pH 7 was observed. The major product, making up 70% of the total product mixture, was identified as a 1.5:1 mixture of two diastereomers formed by sulfur displacement of the C-4 Cl atom from MCA. The major diastereomer was isolated from the 1.5:1 mixture. Connectivity of GSH to the MCA moiety in the product was established by 2D long-range coupling NMR and fully coupled 13C NMR. On the basis of circular dichroism, the major diastereomer had the S configuration at the hydroxyl-bearing, C-5 ring carbon. MCA-IPE reacted with GSH and N-acetylcysteine (NAC), giving 1:1 mixtures of two diastereomers, again by displacement of the C-4 Cl atom from MCA. A single diastereomer was isolated from the 1:1 MCA-IPE plus NAC reaction. Its structure, determined by X-ray crystallography, had the 5R,8R configuration and was in agreement with the ross structure deduced from the NMR analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation of (hydroxyethyl)ferrocene by [2-pyridylmethylbis(2-ethylthioethyl)/amine]copper(II)

A kinetic study of the oxidation of (hydroxyethyl)ferrocene (HEF) by [2-pyridylmethylbis(2-ethyl-thioethyl)ainine]copper(II) (Cu(pmas) 2+) is reported, with the objective of documenting the influence of the two thioether sulfur ligands on the electron transfer rate. Both reactants exhibit a first-order dependence at pH 6, I = 0.1 M(NaNO 3); k(25°C) = 1.3 × 10 4 M −1sec −1, Δ H‡ = 10.1 kcal/mole, Δ S‡ = −6 eu. The apparent Cu(pmas) 2+/+ self-exchange electron transfer rate constant calculated from this reaction on the basis of relative Marcus theory (4.7 × 10 1 M −1 sec −1) agrees well with previous findings on ferrocytochrome c, Fe(CN) 6 4−, and Ru(NH 3) 5py 2+ oxidations. Spectrophotometric titrations of Cu(pmas) 2+ and Cu(tmpa) 2+ (tmpa = tris(2-pyridylmethyl)amine) with azide ion showed that both Cu(pmas)N 3) + ( K f1 = 3.1 × 10 3 M −1) and Cu(pmas)(N 3) 2 ( K f2 = 3.5 × 10 1 M −1) but Cu(tmpa)(N 3) + ( K f = 6.6 × 10 2 M −1) are formed up to 0.15 M N 3 − (25°C, pH 6, I = 0.2 M), suggesting that a thioether sulfur atom is displaced in the uptake of a second N 3 − ion by Cu(pmas)(N 3) +. The effect of thioether sulfur displacement by azide ion on the HEF-Cu(pmas) 2+ reaction rate may be understood entirely through the tendency of N 3 − to shift the position of the redox equilibrium towards the reactant side, without invoking any special role for the sulfur ligand in promoting electron transfer reactivity.

ChemInform Abstract: Stereospecific Displacement of Sulfur from Chiral Centers. Activation via Thiaphosphonium Salts.

AbstractEine neue Methode zur stereospezifischen, direkten nucleophilen Substitution der Mercaptogruppe bei chiralen Mercaptanen (I) wird beschrieben.

Stereospecific displacement of sulfur from chiral centers. activation via thiaphosphonium salts.

The first general method for direct displacement of sulfur from chiral carbon centers has been developed. Chiral mercaptans are readily converted to the corresponding thiaphosphonium salts by treatment with t-butyl hypochlorite and hexamethylphosphorous triamide. Metathesis with ammonium hexafluorophosphate provides stable, isolable, crystalline salts which undergo clean nucleophilic diplacement with a variety of heteroatom and carbon based nucleophiles, affording products in which the stereochemistry has been inverted.

Luminescence in electron irradiated CdS

Electron irradiation induced changes in both the photo- and cathodo-luminescence spectra of high purity CdS platelets have been monitored over a wavelength range from 4800Å to 2 μm. The irradiations were all performed near 10K using beam energies from 100 keV to 1 MeV. By irradiating with electron energies between the cadmium and sulfur displacement thresholds, and above the cadmium displacement threshold, the damage induced luminescence could be assigned to specific sublattices. In the bound exciton spectral region near the band edge, all exciton lines present before irradiation were observed to decrease in intensity with the exception of the emission line at 4867Å. This line was observed to grow in absolute intensity for irradiation energies above the sulfur displacement threshold. We attribute the 4867Å emission to the decay of an exciton bound to a shallow neutral donor state associated with the sulfur vacancy. The edge emission was found to decay in intensity when observed by photoluminescence but to increase in intensity when excited by 100 keV electrons following an irradiation above the sulfur displacement threshold. Broad band luminescence has also been produced by irradiation at 7200Å and 1.03 μm. The 7200 Å band is not observed, however, until a thermal anneal is performed above a recovery stage centered at 180 K. The edge emission and bound exciton emission partially recover in this same temperature range. Another annealing stage is observed at 230 K by monitoring the intensity of emission bands at 1.03 and 1.65 μm. The annealing stage at 180 K is associated with sulfur sublattice damage recovery while the stage at 230 K is due to recovery of cadmium sublattice damage.

Enzymatic hydrolysis of adenosine 3′,5′-cyclic phosphorothoate

3′,5′-AMPS (adenosine 3′,5′-cyclic phosphorothioate) does not serve as a substrate or inhibitor of 3′,5′-cyclic nucleotide phosphodiesterase from rat and rabbit brain and from beef heart. Other enzymes, presumably phosphodiesterases, present in the preparations hydrolyze 3′,5′-AMPS with simultaneous displacement of sulfur. Snake venom phosphodiesterases from Crotalus adamanteus and Crotalus terr. terr. hydrolyze 3′,5′-AMPS to 5′-AMP, with adenosine 5′-phosphorothioate (AMPS) as an intermediate.