Imad A. Abu-Yousef

Carbon Nanotube−Ionic Liquid Composite Sensors and Biosensors

A new composite electrode has been fabricated using multiwall carbon nanotubes (MWCNT) and the ionic liquid n-octylpyridinum hexafluorophosphate (OPFP). This electrode shows very attractive electrochemical performances compared to other conventional electrodes using graphite and mineral oil, notably improved sensitivity and stability. One major advantage of this electrode compared to other electrodes using carbon nanotubes and other ionic liquids is its extremely low capacitance and background currents. A 10% (w/w) loading of MWCNT was selected as the optimal composition based on voltammetric results, as well as the stability of the background response in solution. The new composite electrode showed good activity toward hydrogen peroxide and NADH, with the possibility of fabricating a sensitive biosensor for glucose and alcohol using glucose oxidase and alcohol dehydrogenase, respectively, by simply incorporating the specific enzyme within the composite matrix. The marked electrode stability and antifouling features toward NADH oxidation was much higher for this composite compared to a bare glassy carbon electrode. While a loading of 2% MWCNT showed very poor electrochemical behavior, a large enhancement was observed upon gentle heating to 70 degrees C, which gave a response similar to the optimum composition of 10%. The ease of preparation, low background current, high sensitivity, stability, and small loading of nanotubes using this composite can create new novel avenues and applications for fabricating robust sensors and biosensors for many important species.

Semiconducting Metal Oxide Based Sensors for Selective Gas Pollutant Detection

A review of some papers published in the last fifty years that focus on the semiconducting metal oxide (SMO) based sensors for the selective and sensitive detection of various environmental pollutants is presented.

Recent chemistry of the chalcogen diatomics

Abstract The chemistry of the generation and trapping of diatomic sulfur (S 2 ) and sulfur monoxide (SO) are reviewed with special emphasis on recent work, including initial efforts to detect and trap diatomic selenium (Se 2 ).

Infrared study of UV-irradiated tungsten trioxide powders containing adsorbed dimethyl methyl phosphonate and trimethyl phosphate

The photodecomposition of dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) adsorbed on monoclinic WO3 powders when irradiated by ultraviolet light (UV) in air, oxygen, and under evacuation was investigated using infrared spectroscopy (IR). The IR spectra show that DMMP decomposes into methyl phosphonate upon exposure to 254 nm UV for 2 h at room temperature in air. The same decomposition of DMMP occurs only at temperatures above 300°C without UV illumination. TMP differs from DMMP in that the photodecomposition product is not the same as the decomposition product obtained by heating above 300°C. Thermal decomposition leads to formation of a phosphate on the surface, whereas photodecomposition leads to the same adsorbed methyl phosphonate as found for the thermal or photodecomposition of DMMP. Since TMP does not contain a P-CH3 bond, the formation of a methyl phosphonate on the surface after UV illumination involves a mechanism where CH3 groups migrate from the methoxy group to the phosphorous central atom. No decomposition is observed at room temperature when DMMP or TMP adsorbed on WO3 is irradiated under vacuum or in nitrogen atmosphere. Therefore, the photodecomposition of either DMMP or TMP adsorbed on WO3 at room temperature does not involve a reaction with the lattice oxygen but rather a reaction with the oxygen radicals produced by the decomposition of ozone.

Sulfenyl chloride chemistry. Sulfur transfer to double bonds

Abstract When triphenylmethanesulfenyl chloride (1) (or its thio homolog 2) are treated with various bicycles 1,2 addition reactions take place. Final products occur via an episulfide intermediate. The stereochemistry of addition has been determined by x-ray analysis. Finally, evidence has been obtained for the delivery of diatomic sulfur, likely via intermediate 3.

A useful precursor for sulfur monoxide transfer

Abstract When triphenylmethanesulfenyl chloride ( 8 ) (or its thio 9 and dithio 10 homolog) is treated with adamantylideneadamantane ( 11 ), adamantylideneadamantane thiirane ( 12 ) is produced (92%). Compound 12 was treated with m-chloroperoxybenzoic acid (m-CPBA) forming adamantylideneadamantane thiirane 1-oxide ( 13 ) in 99% isolated yield. The structures of 12 and 13 were established by 1 H and 13 C NMR, mass spectrometry as well as by X-ray analysis. Sulfoxide 13 decomposes smoothly to deliver sulfur monoxide in good yield to various dienes.

The organic chemistry of diatomic sulfur

This review summarizes work on the generation and trapping of diatomic sulfur (S2) as well as 2- and 4-sulfur transfer. †Dedicated to Professor David N. Harpp for his 70th birthday.

Three sulfur atom insertion into the SS bond—pentasulfide preparation

Abstract Chloro(triphenylmethyl)trisulfide (1) reacts under mild conditions with symmetric primary dialkyl disulfides and aromatic disulfides giving pentasulfides as the main products in good yield and selectivity. A mechanism involving a triphenylmethyl alkyl/phenyl tetrasulfide intermediate is discussed.

Sulfenyl chloride chemistry. Precursors for diatomic sulfur transfer

When triphenylmethanesulfenyl chloride (1) (or its thio homologue 2) are treated with various bicycles, norbornene (5), or bicyclo[2.2.2]octene (6), dithio adducts 7 and 8 were produced in good isolated yields. Final products were obtained via an episulfide intermediate. The stereochemistry of addition has been determined by X-ray analysis. Treatment of thiosulfenyl chloride 2 (or its dithio homologue 3) with other olefins, cyclopentene (10), cyclohexene (11), or 1,4-dioxene (12), leads to the formation of disulfides (13−15 from 2) and trisulfides (16 and 17 from 3) in high isolated yields (ca. 92%). The structures of 7, 8, and 13−17 were established by 1H and 13C NMR and elemental analysis as well as by X-ray determination. When these adducts are warmed with a 1,3-diene 42, they deliver diatomic sulfur-trapped derivatives, cyclic di-49 and tetrasulfide adducts 46. A variety of solvents, temperatures, times, and concentrations were employed to optimize the yield of 46 and 49. The tetrasulfide adduct 46 is...

A novel synthesis of organic diselenapolysulfides

Abstract A family of organic polychalcogenides with a common structure of RSeSxSeR (with x=1, 2, 3 and R=CH3, Ph, PhCH2, O2NC6H4CH2) as well as cyclic 5,5-dimethyl-1,2-dithia-3,7-diselenacycloheptane were synthesized in good yield and high purity from the reaction of Ph3CSxCl with corresponding diselenides in chloroform at room temperature. Mechanistic aspects of the insertion involving the formation of an intermediate (RSeSxCPh3) are discussed.