Organic Thiols Research Articles

Amperometric flow injection analysis of organic thiols and proteins

AbstractThe amperometric determination of thiols by injection into a mercury carrier stream is shown to be a sensitive method when using a tungsten wire as the working electrode in a three‐electrode flow cell. Hg2+ gives sharp peaks when injected into phosphate buffer at pH 3.1 at an operating voltage of −0.24V (against a Ag/AgCl reference electrode). Hg2+ was determined in the range 0.43 to 25.0 μM with linear response. Injection of cysteine into the mercury carrier causes a decrease in the cathodic current, and sharp flow injection peaks are observed with a peak width of approximately 60 s. Optimization of various parameters was performed, including buffer effects, mercury concentration, injection volume, and the effects of various cations and anions on the response were determined. Linear calibrations in the range 0.25 μM to 100 μM for cysteine and 1.3 to 1000 ng for the other thiols glutathione, thiourea, albumin, and DNA were found. The responses to cysteine and thiourea were most sensitive, and interference from silver and iodate was observed at concentrations in excess of the thiols. The method may be used as a rapid means of detecting thiols in various samples and as an HPLC detection method.

New Systems Related to CdS Nanoparticles in Sol-Gel Matrices

A process for the synthesis of CdS nanoparticles embedded in hybrid organic/inorganic silica matrices has been developed, based both on colloid and sol-gel chemistry. The large possibilities offered by these techniques allow the study of the influence of various parameters on the luminescence properties of the nanoparticles. Two directions were investigated: first, the authors characterized the surface of the nanoparticles complexed with an organic thiol using NMR spectroscopy. Then, they synthesized new systems to study the influence of chemical modifications, such as the composition of the aggregates (CdS:Mn), the surface (CdS/ZnS core/shell nanostructures) and the interface between the aggregate and the gel matrix.

Adenosine 5?-phosphosulfate sulfotransferase from the marine macroalgaPorphyra yezoensis Ueda (Rhodophyta): stabilization, purification, and properties

Adenosine 5′-phosphosulfate sulfotransferase (APSSTase) was purified over 2700-fold to homogeneity from the thalli of the marine macroalgaPorphyra yezoensis Ueda (Rhodophyta), using a combination of ammonium sulfate precipitation, hydrophobic chromatography, anion-exchange chromatography and gel-filtration. The native Mr measured by gel-filtration was 350 000. The subunit Mr was estimated to be 43 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. In addition, APSSTase had a relatively broad pH optimum of pH 9.0–9.8 with a peak at pH 9.5. The apparentKm value for adenosine 5′-phosphosulfate (APS) was 2.1 μM, when dithiothreitol was acceptor substrate. 3′-Phosphoadenosine 5′-phosphosulfate and inosine 5′-phosphosulfate could not substitute for APS as a sulfate donor. The enzyme utilized several organic thiols as acceptor substrates (artificial substrates): dithiothreitol (apparentKm = 1.5 mM) and dithioerythritol (apparentKm = 1.5 mM) gave the highest activity, and appreciable activity was also obtained usingl-glutathione (reduced form) which exhibited slight substrate inhibition (apparentKm = 0.6 mM; the initial velocity was maximal at 3.0–4.0 mM). While APSSTase was markedly unstable in vitro: the half-life for activity loss at 25°C and pH 9.5 was about 8 min, the instability was decreased in the presence of a relatively high concentration of Na2SO4 or (NH4)2SO4, and in the presence of APS or its analogs (AMP and β-methylene-APS). Most of the thiols, with the sole exception of glutathione, were found to inactivate APSSTase irreversibly. The thiol-mediated inactivation was completely inhibited by the high concentration of Na2SO4, and by the analogs of APS.

X-ray Photoelectron Spectroscopy Sulfur 2p Study of Organic Thiol and Disulfide Binding Interactions with Gold Surfaces

The presence of two sulfur species was detected in X-ray photoelectron spectroscopy (XPS) studies of thiol and disulfide molecules adsorbed onto gold surfaces. These species are assigned to bound thiolate (S2p3/2 binding energy of 162 eV) and unbound thiol/disulfide (S2p3/2 binding energy from 163.5 to 164 eV). These assignments are consistent with XPS data obtained from different thiols (C12, C16, C18, and C22 alkane thiols, a fluorinated thiol, and a cyclic polysiloxane thiol) and different adsorption conditions (solvent type, thiol concentration, temperature, and rinsing). In particular, the use of a poor solvent for thiol adsorption solutions (e.g., ethanol for long chain alkanethiols) and the lack of a rinsing step both resulted in unbound thiol molecules present at the surface of the bound thiolate monolayer. This has implications for recent studies asserting the presence of multiple binding sites for gold−thiolate species in organic monolayers.

Molecular Structure of Monolayers from Thiol-Terminated Polyimide Model Compounds on Gold. 2. Molecular Dynamics Simulations

Extensive molecular dynamics simulations of organic thiol monolayers self-assembled on gold were performed. Interaction parameters obtained from quantum mechanical calculations were used for the sulfur−metal bond. The first simulations concerned C20 alkane monolayers for comparison with experiment and previous theoretical studies. Then dynamics simulations of a (4-mercaptophenyl)phthalimide (4-MPP) self-assembled monolayer on a Au(111) surface were performed. The structure and dynamics of the interphase were simulated at several surface densities and for two bonding geometries, one with the sulfur atom sp hybridized and one with sp3 hybridization. The computed tilt angle for a high-density monolayer was 23° for the sp-hybridized case, in good agreement with the experiments presented in the previous paper. The nature of the sulfur-metal bond strongly affected the observed tilt angle, and the angle increased with decreasing surface density. The distribution of rotation angles of the imide ring was broad. The molecules of the interphase exhibited substantial thermal fluctuations at room temperature but did not freely rotate.

Near-surface electronic structure in GaAs (100) modified with self-assembled monolayers of octadecylthiol

Passivation of the GaAs (100) surface by self-assembled monolayers of octadecylthiol (ODT) has been studied using inelastic light scattering as a probe of the near-surface electronic structure. Application of the ODT self-assembled monolayers reduces the width of the depletion region at the surface of GaAs resulting in a reduction of the surface band bending, and the electron scattering time is increased as well. The ODT passivated surfaces are more stable to environmental degradation, over time and under temperature stress, than inorganic sulfide treated surfaces which have been reported. Organic thiol passivation may provide an attractive alternative to inorganic sulfide protocols for reduction of surface recombination velocities in III–V devices.

Tungsten sensor for amperometric detection of organic thiols and proteins

An amperometric sensor constructed with a metallic tungsten wire is reported for the indirect detection of organic thiols and proteins. Cysteine added to mercury(II) (40.0μM) buffered in 5.0 mM sodium acetate at pH 4.7 causes a decrease in the reduction current of mercury at −0.2 V (vs. SCE). Detection limits were found to be in the range 0.05�0.2 μg/mL for cysteine, thiourea and glutathione, but were poorer for albumin and DNA, showing this method is relatively selective for cysteine. The advantages of the tungsten electrode are its low cost, miniature size, and its inert oxide surface which does not amalgamate with mercury. Copyright © 1995 VCH Verlagsgesellschaft mbH

The reactivity of thiol compounds with different redox states of leghaemoglobin: evidence for competing reduction and addition pathways

Reaction of the ferric form of leghaemoglobin with hydrogen peroxide has been previously shown to give rise to an iron(IV)-oxo (ferryl) species, and a protein radical. Inclusion of a variety of thiol compounds in this system is shown to lead to rapid loss of the iron(IV)-oxo species and the regeneration of the ferric form and/or the formation of novel sulf species formed by nucleophilic attack of the thiol group on the tetrapyrrole ring. The reduction process also results in the generation of thiyl radicals which have been detected by EPR spin trapping. The relative yields of the products produced by these two competing pathways is shown to be highly dependent on the steric and electronic characteristics of the thiol compound. Evidence has also been obtained, in the absence of hydrogen peroxide, for both the reduction of the ferric form of the protein to the oxy-ferrous form, via a process believed to involve the deoxy-ferrous species, and the formation of sulf-leghaemoglobin species. Both of these pathways are again highly dependent on the structure of the thiol, and the former also results in the generation of thiyl radicals. Inclusion of the sulfide anion in place of the organic thiols results in somewhat different behaviour, in that this species appears to both reduce the iron centre and form a complex with the iron atom. This ligation process is reversible, and the sulfide complex is shown to react readily with both strong oxidizing and reducing agents. The behaviour of this protein, which is structurally related to myoglobin, is dramatically different to that demonstrated by myoglobin; this is rationalized in terms of the much more open heme site of leghaemoglobins, and the presence of an electronic gate which hinders access by negatively charged molecules. The contribution of these processes to the maintenance of the leghaemoglobin proteins in the oxy-ferrous form in vivo and the binding of oxygen is discussed.

Synthesis and reactions of functionalised gold nanoparticles

Stable functionalised gold nanoparticles are prepared by simultaneous reduction of tetrachloroaurate ions and attachment of bifunctional organic thiol molecules to the growing gold nuclei leading to a material whose chemical behaviour is characterised by the vacant functionality of the bifunctional thiol ligand.

Characterization of the conductivity of organic thiols by field emission microscopy and field emission spectroscopy

Characterization of the conductivity of organic thiols by field emission microscopy and field emission spectroscopy

Calculation of heats of vaporization of selected groups of organic compounds containing oxygen, sulphur or nitrogen by using saturated vapour pressure data

Basařová P., Svoboda V. and Kolská Z., 1992. Calculation of heats of vaporization of selected groups of organic compounds containing oxygen, sulphur or nitrogen by using saturated vapour pressure data. Using the Clapeyron equation the data on the temperature dependence of vaporization heats were calculated for selected groups of non-associating and weakly associated organic compounds, like ethers, esters, phenols, carbonyl compounds, amines, nitriles, sulphides, thiols, heterocyclic and miscellaneous compounds containing oxygen, sulphur or nitrogen. The parameters of the Wagner equation for vapour pressure correlation and of the modified Redlich-Kwong-Soave equation of state are given as well.

Time-of-flight secondary ion mass spectrometry investigations of self-assembled monolayers of organic thiols, sulfides, and disulfides on gold surfaces

Time-of-flight secondary ion mass spectrometry investigations of self-assembled monolayers of organic thiols, sulfides, and disulfides on gold surfaces

The reaction of CpRu(PPh 3) 2+ with organic thiols. Synthesis and characterization of [CpRu(PPh 3) 2(RSH)]BF 4 (R=benzyl, phenethyl) and the molecular and crystal structure of [CpRu(PPh 3) 2(C 6H 5CH 2CH 2SH)]BF 4·CH 2Cl 2

The isolation and characterization of two mercaptan complexes of the general formula [CpRu(PPh 3) 2(RSH)]BF 4, where R=benzyl and phenethyl, were undertaken to model the substrate/catalyst interaction of the hydrode-sulfurization (HDS) process. The IR data show a shift in the SH stretching frequency upon coordination. The structure of the [CpRu(PPh 3) 2(C 6H 5CH 2CH 2SH)]BF 4 complex was determined by X-ray diffraction techniques: monoclinic space group P2 1/ n, a=15.317(4), b=13.924(9), c=21.815(7) Å, β=95.20(2)°, Z=4, R=0.057, R w=0.073. The Ru is attached to two triphenylphosphine ligands, a cyclopentadienyl and the phenethylmercaptan. The Ru-S distance is 2.369(2) Å and the S-H distance is 1.18 Å.

Organic Thiols as Organolithotrophic Substrates for Growth of Phototrophic Bacteria

Rhodopseudomonas sp. strain BB1, isolated from a coastal marine sediment, immediately metabolized mercaptomalate when grown on mercaptomalate. Sulfide was detected as an intermediate. Extracts of cells grown on mercaptomalate converted mercaptomalate or 3-mercaptopropionate to equimolar amounts of sulfide and either fumarate or acrylate, respectively. Rhodopseudomonas sp. strain BB1 gave higher growth yields on mercaptomalate than on sulfide or malate, consistent with metabolism of the carbon chain of the thiol and the liberated sulfide; i.e., the organic thiol was an organolithotrophic substrate. In contrast, Thiocapsa roseopersicina, isolated previously from a marine microbial mat, had similar growth yields on sulfide, mercaptomalate, or 3-mercaptopropionate, with fumarate or acrylate accumulation from the thiols. T. roseopersicina did not grow photoorganotrophically on fumarate or acrylate, and the thiols were only a source of sulfide for photolithoautotrophic growth.

Organic Thiols as Pyrite Depressants in Oil Agglomeration of Coal

A group of bifunctional organosulfur compounds were tested as pyrite depressants for improving the separation of coal and pyrite by selective oil agglomeration. Preliminary screening tests of potential depressants were carried out with pyrite which had been sulfurized by treatment with a freshly acidified solution of sodium sulfide to increase its response to oil agglomeration. High-grade mineral pyrite was used for most of these tests, but pyrite extracted from coal was used for some tests. When heptane was used as an agglomerant, the following organic thiols were found to suppress the agglomeration of sulfurized pyrite: thioglycolic acid, thiolactic acid, mercaptosuccinic acid, 3-mercaplopropionic acid, and 2-mercaptoetbanesulfonic acid. Each of these materials contains both a sulfhydryl group (-SH) and a hydrophilic group. The materials were also shown to improve the separation of artificial mixtures of Illinois No. 6 coal and sulfurized pyrite in other tests involving agglomeration with heptane. However, the best separation was achieved when thioglycolic acid was employed.

Regiospecific synthesis of 3,5-bis(bromomethyl)benzoic acid, a cysteine crosslinking agent

Bridging two molecules of an organic thiol with the 3,5-dimethylenebenzoic acid (Dmb) group produces a rigid five-carbon Dmb crosslink that is stable to disulfide reducing agents. Radical bromination of 3,5-dimethylbenzoic acid or its succinimido ester gave four α-brominated products. So NMR-pure 3,5-bis(bromomethyl)benzoic acid (Br 2Dmb) was regiospecifically synthesized in 38% overall yield by a four-step route from 1,3,5-benzenetricarboxylic acid. S-Alkylation of cysteine methyl ester, a model thiol, with Br 2Dmb provided the 2:1 adduct (Cys-OCH 3) 2 Dmb in 79% yield. Subsequent N-protection with di( tert-butyl) dicarbonate gave (Boc-Cys-OCH 3) 2Dmb in 60% overall yield from cysteine methyl ester. This protected diamino acid is suitable for assembly of two Dmb-crosslinked peptide chains.

Molecular ordering of organosulfur compounds on Au(111) and Au(100): Adsorption from solution and in ultrahigh vacuum

Low-energy electron diffraction and reflection-absorption infrared spectroscopy were used to study the monolayers formed by the adsorption of n-alkane thiols [HS(CH2)mCH3] on both (111) and (100) single-crystal gold substrates. Samples were prepared by dosing either from solution (m=15, 17, 18, and 21) or in ultrahigh vacuum (m=0–9). On Au(111), ordered surface structures are obtained which can be indexed as (n√3×√3)R30°, where n varies from 1 to 6. On Au(100), the adsorption of short chain thiols leads to the formation of a c(2×2) overlayer while the longer chain homologs show additional diffraction spot splittings. It is also found that chain length influences both the character of the diffraction seen and perturbs the reactive sticking probability of molecules dosed in UHV. Infrared studies reveal that the polymethylene chains of the monolayers formed on Au(100) are comprised of nearly all-trans conformations and are less canted than the comparable structures formed on Au(111). A simple model is proposed to account for the differences seen on the two surfaces and a mechanism for the adsorption and assembly of organic thiols into ordered monolayer phases on gold is presented.

Catalytic capability of diaphorase bound to a self-assembled thiol monolayer at a gold electrode

Organic thiols adsorb strongly on gold surfaces and form self-assembled monolayers with well-ordered structure [l-20]. These unique characteristics of thiol are particularly suitable for modification of gold electrodes with closely packed, highly ordered organic monolayers. The influence of the surface monolayer on electrochemical reactions is a matter of great attention and has been investigated in detail by many researchers [8-161. Recent efforts [17-201 revealed that attachment of functional thiol molecules is a useful way to fabricate molecular-based devices such as electrochemical sensors. The molecular build-up in steps from thiol monolayers would also be attractive to immobilize functional molecules onto electrode surfaces. In this paper, we report the immobilization of an enzyme by step-by-step reactions from an Au electrode self-assembled with 2-aminoethanethiol. In this system the thiol monolayer acts as an anchor layer to stabilize the enzymes. The enzyme used in this study was diaphorase (Dp) [21,22] which catalyzes the oxidation of NADH. The self-assembled monolayer having a covalently bonded enzyme showed obvious catalytic capabilities for electrochemical oxidation of NADH. Such an enzyme monolayer could also be fabricated through silyl etherbased reactions [23]. The electrodes with immobilized enzyme monolayers will act as biosensors which exhibit rapid responses [221. In order to apply these immobilization procedures to biochemical devices, it is necessary to characterize the

A new class of self‐assembled monolayers: Organic thiols on gallium arsenide

The spontaneous assembly of long chain thiols on the clean oxide‐free surface of gallium arsenide has recently been reported by a group at Penn State University. In the past, the substrates on which this was possible were restricted to the group 10 and 11 metals Au, Ag, Pt, and Cu, and the oxides of silicon, aluminum and silver. The work and its consequences for GaAs‐based microelectronics are discussed.

MICROBIAL DESULFURIZATION OF COAL

ABSTRACT The sulfur found in coal is generally divided into three forms: pyritic, sulfate, and organic sulfur. Originating from irt-situ oxidation of metal sulfides, sulfates axe present in coal at low concentrations. Being soluble in water, they are relatively easy to be leached from the coal. Similarly, microbial depyritization promotes the oxidative conversion of inorganic sulfur compounds to water-soluble products. The pyrite removal results from the combined effects of direct bacterial attack and indirect chemical solubilization. In the former, pyrite (FeS2) is oxidized by bacteria into Fe2(SO4) 3; in the latter, ferric iron is the actual oxidizing agent and microorganisms serve to regenerate the ferric iron from ferrous iron. Organic sulfur is chemically bound to the carbon skeleton of coal. It is believed to be present mainly in the forms of organic sulfides, disulfides, thiols and thiophenes. Two pathways have been proposed for microbial desulfurization of heterocycles. One emphasized the oxidatio...