Dialkyl Sulfides Research Articles

A non-covalent strategy for the assembly of supramolecular photocurrent-generating systems.

Three photocurrent-generating thin films were assembled on gold surfaces. SAM I was constructed from molecules consisting of an alkyl disulfide group linked covalently to a 12-residue helical peptide and terminated with an alanine residue containing a pyrene chromophore. SAM I served as a benchmark for multilayered films II and III in photocurrent generation experiments. Films II and III were assembled from several components that were linked noncovalently by metal-ligand complexation. Cyclic voltammetry and contact angle measurements suggest that the films consist of ordered layers with relatively few defects. Photoexcitation of SAM I by the output of a 350 nm lamp ( approximately 0.2 mW power incident on the sample) results in current generation in the range 5-10 nA/cm2. Photoexcitation of II and III yields higher current in the range 10-30 nA/cm2, representing a quantum efficiency of approximately 1%. The observation of comparable or higher current from noncovalently assembled multicomponent films indicates that this method of assembly may obviate the problems associated with the covalent assembly of devices from large molecules.

Surface and Adsorption Structures of Dialkyl Sulfide Self-Assembled Monolayers on Au(111)

Surface and adsorption structures of dioctadecyl sulfide (DOS) self-assembled monolayers (SAMs) on Au(111) were examined by scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS). In comparison with alkanethiol or dialkyl disulfide SAMs, the molecularly resolved STM images clearly showed that DOS SAMs have significant structural differences in the formation of depressions and ordered domains, and in the lattice structure, including the presence of conformational defects in the ordered domains. In addition, the clear red shift of the Au−S stretching mode and the existence of the C−S stretching mode were also observed for DOS SAMs by HREELS measurements. The unique surface structure and the existence of such characteristic features at the Au−S and C−S stretching modes for DOS SAMs strongly support the intact adsorption of DOS molecules on Au(111).

PB03 ディスコティック液晶の自己組織化膜修飾基板上での配向挙動(化学・材料)

PB03 ディスコティック液晶の自己組織化膜修飾基板上での配向挙動(化学・材料)

Syntheses, Oxidations, and Palladium Complexes of Fluorous Dialkyl Sulfides: New Precursors to Highly Active Catalysts for the Suzuki Coupling.

Abstract Reactions of Rf8(CH2)nI (Rf8=CF3(CF2)7) with Li2S give the fluorous dialkyl sulfides (Rf8(CH2)n)2S (n=2, 1 , 71%; 3, 2 , 67%) as low melting white solids that are soluble in most fluorous and organic solvents. Reactions of 1 and 2 with CH3CO3H yield the corresponding sulfoxides (Rf8(CH2)n)2SO (85; 80%), which are soluble in CF3C6F5 at room temperature, but insoluble in most other solvents. At higher temperatures, solubilities can become appreciable. Reactions of 1 and 2 with Na2PdCl4 (ca. 0.5 equiv.) give palladium complexes [(Rf8(CH2)n)2S]2PdCl2 ( 5 , 94%; 6 , 95%), which are soluble in only a limited range of fluorinated solvents at room temperature. The CF3C6F11/toluene partition coefficients of 1 and 2 are 98.7:1.3 and 96.6:3.4 (24°C). The Suzuki coupling of aryl bromides and PhB(OH)2 to biaryls is catalyzed by 5 and 6 (0.02 mol%) in CF3C6F11/DMF/H2O in the presence of K3PO4, generally at room temperature. Turnover numbers of 4500–5000 are easily achieved. However, activities decrease under fluorous biphase recycling conditions, and implications for the nature of the catalytically active species are discussed.

Impact of Host Structure on Guest−Host Recognition at Self-Assembled Surfaces of Tetrathiol and Tetrasulfide Derivatives of Calix[4]resorcinarene

Guest−host recognition at self-assembled surfaces of two different synthetic calix[4]resorcinarene receptors, a tetrasulfide (R4SC7) and a tetrathiol (R4SH) host, was performed. The host structure was found to impact the molecular organization within the monolayers as well as the interfacial properties. Comparison of structural characterization of the SAMs formed from R4SC7 and R4SH on gold substrates revealed a larger area per molecule for the tetrasulfide host, which indicated that the dialkyl sulfide chains do not pack commensurately below the calix[4]resorcinarene headgroup and can lead to interstitial cavities. As a consequence, the self-assembled surfaces formed from R4SC7 are slightly more hydrophobic and thinner than the SAMs formed from R4SH. Guest−host recognition of a small neutral molecule, α-hydroxy-γ-butyrolactone (HBL), occurred from aqueous solutions on both surfaces on a time scale of several hundred seconds. Adsorption isotherms for the two surfaces revealed that the difference in the free energy change due to adsorption is comparable to thermal energy. Whereas HBL bound to the SAMs formed from R4SH was found to almost completely desorb into an organic solvent, the binding to the R4SC7 surface was largely irreversible. Despite R4SH and R4SC7 possessing macrocyclic cavities of geometrically similar size, the significant difference in the desorption behavior indicates the role of incommensurate packing of the dialkyl sulfide chains below the calix[4]resorcinarene headgroup and the impact of monolayer structure on guest−host recognition at self-assembled surfaces.

ChemInform Abstract: Dioxygenase‐Catalyzed Mono‐, Di‐, and Tri‐oxygenation of Dialkyl Sulfides and Thioacetals: Chemoenzymatic Synthesis of Enantiopure cis‐Diol Sulfoxides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Syntheses, oxidations, and palladium complexes of fluorous dialkyl sulfides: new precursors to highly active catalysts for the Suzuki coupling

Reactions of R f8(CH 2) n I (R f8=CF 3(CF 2) 7) with Li 2S give the fluorous dialkyl sulfides (R f8(CH 2) n ) 2S ( n=2, 1 , 71%; 3, 2 , 67%) as low melting white solids that are soluble in most fluorous and organic solvents. Reactions of 1 and 2 with CH 3CO 3H yield the corresponding sulfoxides (R f8(CH 2) n ) 2SO (85; 80%), which are soluble in CF 3C 6F 5 at room temperature, but insoluble in most other solvents. At higher temperatures, solubilities can become appreciable. Reactions of 1 and 2 with Na 2PdCl 4 (ca. 0.5 equiv.) give palladium complexes [(R f8(CH 2) n ) 2S] 2PdCl 2 ( 5 , 94%; 6 , 95%), which are soluble in only a limited range of fluorinated solvents at room temperature. The CF 3C 6F 11/toluene partition coefficients of 1 and 2 are 98.7:1.3 and 96.6:3.4 (24°C). The Suzuki coupling of aryl bromides and PhB(OH) 2 to biaryls is catalyzed by 5 and 6 (0.02 mol%) in CF 3C 6F 11/DMF/H 2O in the presence of K 3PO 4, generally at room temperature. Turnover numbers of 4500–5000 are easily achieved. However, activities decrease under fluorous biphase recycling conditions, and implications for the nature of the catalytically active species are discussed.

Oxorhenium(V) Dithiolates Catalyze the Oxidation by tert-Butyl Hydroperoxide of Sulfoxides and Sulfides, Including 4,6-Dimethyldibenzothiophene

tert-Butyl hydroperoxide (TBHP) efficiently converts a wide variety of sulfides to sulfoxides and sulfones. The method offers the advantage that one product or the other can be obtained in high purity by a modest variation of conditions. The reactions occur smoothly at 25minus sign50 C in chloroform and, to the extent studied, in toluene and methylene chloride. A catalyst is required; the most extensively studied was MeReO(mtp)PPh(3), 1, where mtpH(2) is 2-(mercaptomethyl)thiophenol. Other chelating dithiolate ligands can be used with comparable results. These oxidations were tested for dialkyl, alkylminus signaryl, and diaryl sulfides; thiophenes; and thianthrene. Even the "hard" sulfide, 4,6-dimethyldibenzothiophene (DMDBT) was quantitatively oxidized to the dioxide with TBHP:DMDBT 3.0-3.5 and 0.05-3.8 mol % 1. The mechanism was explored in kinetics studies carried out only for methyl tolyl sulfide. The product buildup curve was complex, with an induction period followed by a rapid growth phase. The kinetic data could be modeled adequately but not perfectly by allowing five rate constants to refine. Their values are consistent with the chemical sense of the mechanism.

Dialkyl Sulfides: Novel Passivating Agents for Gold Nanoparticles

Gold nanoparticles passivated with symmetrical and unsymmetrical dialkyl sulfides (H21C10SC10H21 and H37C18SC10H21) have been synthesized via the borohydride reduction of HAuCl4 and characterized by 1H NMR, FTIR, UV-vis, Auger Electron, XPS spectroscopies, and TEM. Under equivalent conditions of formation, the size and polydispersity of the gold cores obtained was greater for dialkyl sulfide ligands (d(C10SC10) = 5.3 ± 0.8 nm; d(C18SC10) = 6.3 ± 1.1 nm) than alkanethiol ligands (d(C10H22SH) = 2.2 ± 0.1 nm). Edge-edge interparticle spacing of 2-D arrays of the nanoparticles is found to be dependent on the length of the longest alkyl chain passivating the nanoparticles and is independent of the asymmetry of the alkyl chains in the dialkyl sulfide.

The fate of sulfur-bound hydrogen on formation of self-assembled thiol monolayers on gold: (1)H NMR spectroscopic evidence from solutions of gold clusters.

It is demonstrated that thiols can adsorb to gold without losing hydrogen. Dodecyl sulfide-capped gold clusters have been prepared and subjected to ligand exchange reactions in perdeuterated benzene by addition of dodecanethiol and subsequently dodecyl disulfide. It is shown by 1H NMR spectroscopy that dodecanethiol molecules are readily taken up as ligands producing characteristic broad signals corresponding to the alpha-methylene and S-H protons, with chemical shifts close to those found for thiol in solution; these signals are absent in spectra of thiolate-capped clusters. Addition of excess disulfide to such clusters capped with both dialkyl sulfides and thiols leads to the appearance of sharp signals for free dialkyl sulfide and intact thiol. Amounts of thiols up to 50% of the ligand shell are, however, taken up by the clusters under rapid and irreversible loss of hydrogen.

Preparation of Dendritic Multisulfides and Their Assembly on Air/Water Interfaces and Gold Surfaces

Poly(propylene imine) (PPI) dendrimers of generations 1−5 have been derivatized with dialkyl sulfide chains. On water, these dendrimers form stable LB films with densely packed alkyl chains pointing to the air and cores exposed to the aqueous solution. Self-assembly of the same dendrimers from solution onto a gold surface leads to a flattened orientation of the molecules on the surface, as shown by high contact angle hystereses, high electrochemical capacitances, and low charge transfer resistances. X-ray photoelectron spectroscopy data indicate that the formation of the flattened structure can be attributed to adsorption to the gold surface of not only part of the sulfide moieties in the alkyl chains, but also part of the tertiary amines in the core. The electrochemically determined surface coverages of ferrocene-modified dendritic wedges (with similar molecular structures as those of the dialkyl sulfide PPI dendrimers) confirm the proposed flattened, surface-spread dendritic structure. In contrast, LB films of the sulfide PPI dendrimers that were transferred onto gold appear to largely remain their original, densely packed state, as for these films smaller contact angle hystereses and higher charge transfer resistances are measured than those observed for the monolayers prepared by self-assembly from solution. Additionally, the electrochemical capacitances of the transferred LB films point to a layer thickness comparable to the thickness of a densely packed didecylsulfide monolayer. The results in this study demonstrate that different surface architectures can be prepared of the same compounds by solely varying the preparation procedure.

HREELS studies of gold nanoparticles with dialkyl sulphide ligands

We have employed high resolution electron energy loss spectroscopy (HREELS) to study low energy electron impact on films of gold nanoparticles passivated with dialkyl sulphide (H 21C 10SC 10H 21). HREEL spectra obtained in UHV show energy loss peaks due to CH x and CC vibrational modes of the organic ligands together with a mode at 230 cm −1 assigned to the Au–S stretch. Measurements as a function of impact energy reveal resonances in the intensities centred between 9 and 12 eV. Prolonged exposure of the film to an electron beam at 50 eV, with a dosage of approximately 360 μC cm −2, causes significant changes in the HREEL spectra, consistent with cleavage of the Au–S bond.

Structural Study of Dialkyl Sulfide Self-Assembled Monolayers on Au(111)

Dialkyl sulfide self-assembled monolayers on gold were characterized by Fourier transform infrared reflective absorption spectroscopy (FTIR-RAS) and scanning tunneling microscopy (STM). It was found that dialkyl sulfide SAMs have quite different surface characteristics compared to alkanethiol SAMs. Our STM result clearly elucidated that dialkyl sulfide SAMs are composed of the liquid-like disorder phase with many small nucleations, not the ordered phase.

Structural Study of Dialkyl Sulfide Self-Assembled Monolayers on Au(111)

Dialkyl sulfide self-assembled monolayers on gold were characterized by Fourier transform infrared reflective absorption spectroscopy (FTIR-RAS) and scanning tunneling microscopy (STM). It was found that dialkyl sulfide SAMs have quite different surface characteristics compared to alkanethiol SAMs. Our STM result clearly elucidated that dialkyl sulfide SAMs are composed of the liquid-like disorder phase with many small nucleations, not the ordered phase.

Optimizing disulfide fungitoxicity: Adjustment of hydrocarbon chain length

Previously identified classes of antifungal disulfides are modified by extending alkyl substituents. Although, the principal focus is on f -sulfone disulfides, one nitrophenyl alkyl disulfide and a pair of f -ester disulfides were also prepared and examined. Optimum fungitoxicity is associated with structures which have seven to ten carbon atoms in the form of unbranched chains and/or phenyl rings.

Dioxygenase-catalysed mono-, di- and tri-oxygenation of dialkyl sulfides and thioacetals: chemoenzymatic synthesis of enantiopure cis-diol sulfoxides

Toluene dioxygenase (TDO)-catalysed monooxygenation of methylsulfanylmethyl phenyl sulfide 1 and methylsulfanylmethyl 2-pyridyl sulfide 4, using whole cells of Pseudomonas putida UV4, occurred exclusively at the alkyl aryl sulfur centre to yield the alkyl aryl sulfoxides 2 and 5 respectively. These sulfoxides, accompanied by the dialkyl sulfoxides 3 and 6, were also obtained from naphthalene dioxygenase (NDO)-catalysed sulfoxidation of thioacetals 1 and 4 using intact cells of P. putida NCIMB 8859. Enzymatic oxidation of methyl benzyl sulfide 7, 2-phenyl-1,3-dithiane 19, and 2-phenyl-1,3-dithiolane 23, using TDO, gave the corresponding dialkyl sulfoxides 8, 20 and 24 as minor bioproducts. TDO-catalysed dioxygenation of the alkyl benzyl sulfides 7, 15 and 17 and the thioacetals 19 and 23, with P. putida UV4, yielded the corresponding enantiopure cis-dihydrodiols 9, 16, 18, 21 and 25 as major metabolites and cis-dihydrodiol sulfoxides 14, 22 and 26 as minor metabolites, resulting from a tandem trioxygenation of substrates 7, 19 and 23 respectively. Chemical oxidation, of the enantiopure cis-dihydrodiol sulfides 9, 16, 18 and 21 with dimethyldioxirane (DMD), gave separable mixtures of the corresponding pairs of cis-dihydrodiol sulfoxide diastereoisomers 14 and 27, 28 and 29, 30 and 31, 22 and 32. While dialkyl sulfoxide bioproducts 3, 6, 20 and 24 were of variable enantiopurity (27–≥98% ee), alkyl aryl monosulfoxides 2 and 5, cis-dihydrodiols 9, 16, 18, 21 and 25 and cis-dihydrodiol sulfoxide bioproducts 14, 22 and 26 were all single enantiomers (≥98% ee). The absolute configurations of the products, obtained from enzyme-catalysed (TDO and NDO) and chemical (DMD) oxidation methods, were determined by stereochemical correlation, circular dichroism, and X-ray crystallographic methods.

Reactions in clay media: photooxidation of sulfides by clay-bound methylene blue

Photooxidation of dialkyl and alkyl aryl sulfides to the corresponding sulfoxides with clay-bound methylene blue is studied in acetonitrile. A significant increase in sulfoxide/sulfone ratio and a marginal increase in cooxidation of a second sulfide molecule are observed. The results are explained in terms of a suitable mechanism involving persulfoxide and thiadioxirane intermediates.

Generation of peracetic acid on aging of perborate solution in acetic acid: Kinetics of oxidation of organic sulfides

Perborate in acetic acid generates peracetic acid on aging and affords H2O2 in ethylene glycol; the oxidations of dialkyl, alkyl aryl and diaryl sulfides in ethylene glycol–acetic acid are second order and uncatalysed by acid, and follow a common mechanism.

An efficient and selective aerobic oxidation of sulfides to sulfoxides catalyzed by Fe(NO3)3–FeBr3

The binary system Fe(NO3)3–FeBr3 is a very efficient catalyst for the selective air-oxidation of sulfides to sulfoxides. Since the oxidation is selective, it may be applied to any type of dialkyl and alkyl aryl sulfide, as well as to substrates of biological interest. It develops in mild conditions, giving a high yield in the presence of different functional groups on the sulfide. Other binary systems such as Fe(NO3)3–FeBr2 and Cu(NO3)2–CuBr2 are also effective catalysts for sulfoxidation. In contrast to previous oxygenation methods, this oxidation requires neither an aldehyde nor a transition metal complex.

Flavor-protein binding: disulfide interchange reactions between ovalbumin and volatile disulfides.

The irreversible binding of selected sulfur-containing flavor compounds to proteins was investigated in aqueous solutions containing ovalbumin and a mixture of disulfides (diethyl, dipropyl, dibutyl, diallyl, and 2-furfuryl methyl) using solid-phase micro-extraction (SPME). In systems which had not been heated, the recovery of disulfides from the headspace above the protein at the native pH (6.7) was similar to that from an aqueous blank. However, significant losses were observed when the pH of the solution was increased to 8.0. When the protein was denatured by heating, much greater losses were observed and some free thiols were produced. In similar heat-denatured systems at pH 2.0, no losses of disulfides were observed. Disulfides containing allyl or furfuryl groups were more reactive than saturated alkyl disulfides. Interchange reactions between protein sulfhydryl groups and the disulfides are believed to be responsible for the loss of the disulfides.