Pure Disulfide Research Articles

Dialkyl Disulfide Solvents of Asphalt-Resin-Wax Deposits

The structural group composition of samples of asphalt-resin-wax deposits (ARWD) has been studied. These samples were found to be of the wax-rich type. The effectiveness of disulfide oil as an ARWD solvent was studied. Pure disulfide oil was found ineffective for removing the most difficult to degrade wax-rich deposits. The addition of 0.1-0.5 wt. % nonionogenic surfactants and more than 40 wt.% aromatic hydrocarbons (liquid pyrolysis products, Bentol) markedly enhances the effectiveness of disulfide oil (up to 80-90 wt. % at 20-50°C), which justifies its commercial use as an ARWD solvent.

Thiol- and disulfide-modified oligonucleotide monolayer structures on polycrystalline and single-crystal Au(111) surfaces

We provide a comprehensive study of single- (ss) and double-strand (ds) oligonucleotides with either 25 or 10 bases or base pairs (bp) immobilized on polycrystalline and single-crystal Au(111) surfaces. The study is based on X-ray photoelectron spectroscopy, cyclic and differential pulse voltammetry, interfacial capacitance data, and electrochemical scanning tunnelling microscopy (in situ STM). The sequences used were the 25-bp sequence from the BRCA1 gene (25-mer), while the 10-bp oligonucleotides contained solely linear adenine and thymine sequences. The oligonucleotides were modified by the dimethoxytrityl group (DMT) via a disulfide group [DMT-S-S-ss25-mer and DMT-S-S-ds(AT)10], a pure disulfide group (A10-S-S-T10), or a thiol group [HS-ss25-mer and HS-ds-(AT)10], all via a hexamethylene linker. The overall pattern suggests strategies for controlled adsorption of DNA-based molecules and recognition of complementary strands or other molecules.

Oxidation chemistry of perfluoroalkyl-segmented thiols, disulfides, thiosulfinates and thiosulfonates: The role of the perfluoroalkyl group in searching out new chemistry

The oxidation chemistry of perfluoroalkyl-segmented thiols, R F–R–SH ( 1), thiosulfinates, R F–R–S(O)S–R–R F ( 3), thiosulfonates, R F–R–S(O 2)S–R–R F ( 4) and disulfides, R F–R–SS–R–R F ( 5) (in which R F= n-C 6F 13 or n-C 8F 17 and R=CH 2CH 2) is studied herein. Base catalyzed reaction of C6 thiol 1 with hydrogen peroxide gives pure disulfide 5, quantitatively. Other, less suitable methods for the oxidation of thiol 1 are also examined and compared. Selective oxidation of disulfide 5 by peroxy acids in chlorinated solvents gives excellent yields of thiosulfinate 3. Unlike their hydrocarbon analogues, which are unstable to heating or storage, the R F-segmented thiosulfinates 3 are relatively stable, crystalline compounds. Selective oxidation of 3 by sodium metaperiodate gives thiosulfonate 4 in high yield. Side reactions intervene with unfavorable conditions, or when peroxy acetic acid in acetic acid is used as oxidant,. Oxidation of 5 by hydrogen peroxide in low conversion gives 4 and two new compounds, 8 and 9. Compound 8 is n-C 6F 13S(O) 2CH 2CH 2C 6F 13 (probably the sulfinate ester and not the sulfone), and 9 is most likely the O, S-sulfenyl sulfinate or, possibly an isomer, the vic-disulfoxide. A free radical chain mechanism is proposed for conversion of 4 (or 9) to 8. Compounds 8 and 9 are stable in solution and are identified by MS/GC. In 3, 4 and 5, the ν CH bands correlate with NMR of CH 2 at C(1) and C(2) positions, both 1 H and 13 C NMR. The R F-segment in these unique sulfur compounds enhances their utility and modifies their chemical and physical properties in important and interesting ways.

Self-assembly of thiolipid molecular layers on gold surfaces: optical and electrochemical characterization

This paper describes the preparation and characterization of mono- and bilayers of three newly synthesized disulfide-bearing lipids and of mixed bilayers containing conventional phospholipids adsorbed onto gold substrates by the self-assembly technique. The polar group of the lipid is coupled to a spacer of variable length (1–3 ethoxy units) terminating at a disulfide group. The properties of these films were investigated by plasmon surface polariton (PSP) and electrochemical capacitance measurements. The capacitance data for all the pure disulfide lipid films suggest a low defect density, comparable to that found for thioalkane self-assembly films. While this is supported by the optical experiments for the films formed by the lipid with the longest spacer, for the films self-assembled from the other two lipids a relatively low refractive index must be assumed, indicating the influence of the spacer on the packing of the molecules. On the contrary, films of conventional phospholipids self-assembled onto thiolipid monolayers show a high optical density and a comparable pure electrical behaviour.

Effects of reducing agents on the determination of thiolic compounds in the presence of their disulfides using bimane pre-column derivatization

The influence of reducing agents (sodium borohydride, tributylphosphine, dithioerythritol and dithiothreitol) on the conversion of disulfides into their parent thiols, with specific application to cysteine was investigated. Dithioerythritol and dithiothreitol were found to be most suitable for this reaction. A contact time of one hour at room temperature provided quantitative reduction as tested using cystine as a pure disulfide standard. A modified fluorescence labelling procedure with monobromobimane followed by reversed-phase HPLC allows quantitation of the parent thiol and the disulfide content when completing the labelling reaction with and without preliminary treatment with reducing agent. The effects of various bimane reducing agent ratios on the yield of the reaction are discussed. Precautions should be taken when dealing with complex matrices with respect to reagent concentrations and ratios.

Reactions of thiyl radicals. II. The photolysis of methyl disulfide vapor

The photolysis of methyl disulfide vapor in the pressure range 2–25 Torr at wavelengths between 2 300 and 2 800 and at 2 288 Å has been examined and the effect of temperature, pressure, added inert gases, ethyl disulfide, and nitric oxide determined.The primary process is a direct production of two CH3S radicals which have excess energy and which can be observed as methyl thionitrite when NO is present during the decomposition. When pure disulfide is photolyzed the major observable product is methanethiol, although this material accounts for only a small fraction of the primarily produced thiyl radicals whose principal fate is recombination in a substrate-reforming reaction producing excited disulfide molecules. The latter species are deactivated by added gases, or by the substrate itself. The mode of mercaptan formation is by abstraction of H atoms from the substrate by excited CH3S radicals with an apparent activation energy of 1.5 kcal.