thiourea and acetonitrile

In this work, GO bonded monolith (pAS-GO@PS-DVB) as the stationary phase for capillary electrochromatography was fabricated, which was achieved by a simple one-step in-situ copolymerization of styrene and vinylized GO in the presence of divinylbenzene as a cross-linker. GO functionalization was primarily completed using p-aminostyrene based on condensation reaction between amino and carboxyl groups. The characterization by infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy proved the covalent bonding of GO on the monolith. The average pore diameter via Barrett-Joyner-Halenda, specific surface area and pore volume via Brunauer-Emmett-Teller equation by nitrogen adsorption/desorption were determined to be 112.4nm, 485.8m(2)g(-1) and 1.4cm(3)g(-1), respectively. The pAS-GO@PS-DVB monolithic column gave effective separation for a wide range of aromatic compounds, which was based on hydrogen bonding and π-π interactions of GO with polar and/or non-polar organic compounds. The reproducibility in terms of the precisions of migration time, peak height and peak area was estimated below 6% using thiourea and other aromatic compounds. Furthermore, the differences of migration time, peak height and peak area between the first-week analysis and the forth-week analysis were less than 19%, indicating good stability of the proposed monolithic column in one month. The applicability of the pAS-GO@PS-DVB monolith was also demonstrated by baseline separation of three phenols and three anilines.

Topics: Acetonitriles; Adsorption; Aniline Compounds; Capillary Electrochromatography; Electrolytes; Graphite; Hydrogen Bonding; Hydrogen-Ion Concentration; Microscopy, Electron, Scanning; Oxides; Phenols; Photoelectron Spectroscopy; Polystyrenes; Porosity; Reproducibility of Results; Spectrophotometry, Infrared; Thiourea; X-Ray Diffraction

To achieve the greatest peak capacity in two-dimensional high performance liquid chromatography (2D-HPLC) a gradient should be operated in both separation dimensions. However, it is known that when an injection solvent that is stronger than the initial mobile phase composition is deleterious to peak performance, thus causing problems when cutting a portion from one gradient into another. This was overcome when coupling hydrophilic interaction with reversed phase chromatography by introducing a counter gradient that changed the solvent strength of the second dimension injection. It was found that an injection solvent composition of 20% acetonitrile in water gave acceptable results in one-dimensional simulations with an initial composition of 5% acetonitrile. When this was transferred to a 2D-HPLC separation of standards it was found that a marked improvement in peak shape was gained for the moderately retained analytes (phenol and dimethyl phthalate), some improvement for the weakly retained caffeine and very little change for the strongly retained n-propylbenzene and anthracene which already displayed good chromatographic profiles. This effect was transferred when applied to a 2D-HPLC separation of a coffee extract where the indecipherable retention profile was transformed to a successful application multidimensional chromatography with peaks occupying 71% of the separation space according to the geometric approach to factor analysis.

Topics: Acetonitriles; Anthracenes; Benzene Derivatives; Caffeine; Chromatography, High Pressure Liquid; Chromatography, Reverse-Phase; Coffee; Hydrophobic and Hydrophilic Interactions; Phenol; Phthalic Acids; Plant Extracts; Solvents; Thiourea; Water

A novel amphiphilic silica-based monolithic column having surface-bound octanoyl-aminopropyl moieties was successfully prepared by a one-step in situ derivatization process. As expected, the amphiphilic monolithic column exhibited RP chromatographic behavior toward non-polar solutes (e.g., alkyl benzenes) with high column performance. As the pH of the buffer inside the column increases, the EOF changed from -2.65 x 10(-8) m(2) V(-1) s(-1) at pH 3.0 to 1.20 x 10(-8) m(2) V(-1) s(-1) at pH 8.0 with the reversion of EOF at about pH 6.4. Using acidic mobile phase, five aromatic acids can be efficiently separated in less than 6 min under co-EOF conditions. For basic compounds, symmetrical peaks were obtained due to the existence of hydrophilic acyl amide group, which can effectively minimize the adsorption of the positively charged basic analyte to the silica-based surface of the capillary column.

Topics: Acetonitriles; Adsorption; Benzene Derivatives; Benzoates; Capillary Electrochromatography; Caprylates; Electroosmosis; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Microscopy, Electron, Scanning; Silicon Dioxide; Surface Properties; Thiourea; Toluene

A systematic study of the behavior of several common mobile-phase volume markers using traditional and polar-group-containing reversed-phase stationary phases is presented. Examined mobile-phase volume markers include two neutral molecules, uracil and thiourea, concentrated (0.10 M) and dilute (0.0001 M) KNO(3), and D(2)O. Mobile-phase volumes are examined over the entire reversed-phase mobile-phase range of 100% water to 100% methanol or acetonitrile. The behavior of these mobile-phase volume markers is compared with a maximum theoretical value (i.e. the void volume), as determined by pycnometry. The data suggest that: (i) uracil begins to fail as a mobile-phase volume marker in mobile phases below about 40% strong solvent for polar group containing phases; (ii) in nearly all cases, the mobile-phase volume measured dynamically is smaller than the pycnometric void volume; (iii) a significant dependence of measured mobile-phase volume on salt concentration is seen on the polar endcapped phase, which is not observed on the traditional and embedded polar group phase; and (iv) D(2)O does not work well as a mobile-phase volume marker with polar-group-containing phases, possibly due to interaction with the stationary phase polar group.

Topics: Acetonitriles; Chromatography, Reverse-Phase; Methanol; Thiourea; Uracil; Water

Newly synthesised fluorescent chemosensor ADDTU contains the thiourea receptor connected to the acridinedione (ADD) fluorophore via a covalent bond, giving rise to a fluorophore-receptor motif. In this fluorescent chemosensor, the anion recognition takes place at the receptor site which result in the concomitant changes in the photophysical properties of a ADD fluorophore by modulation of photoinduced electron transfer (PET) process. The binding ability of these sensor with the anions F(-), Cl(-), Br(-), I(-), HSO(4)(-), ClO(4)(-), AcO(-), H(2)PO(4)(-) and BF(4)(-) (as their tetrabutylammounium salts) in acetonitrile were investigated using UV-vis, steady state and time-resolved emission techniques. ADDTU system allows for the selective fluorescent sensing of AcO(-), H(2)PO(4)(-) and F(-) over other anions in acetonitrile.

Topics: Acetonitriles; Acridines; Anions; Binding Sites; Biosensing Techniques; Electron Transport; Fluorescence; Fluorescent Dyes; Hydrogen Bonding; Molecular Structure; Oxidation-Reduction; Photochemistry; Solvents; Spectrophotometry, Ultraviolet; Thiourea; Time Factors; Titrimetry

The oxidation of tetramethylthiourea (TMTU) at gold electrodes in acetonitrile, leading to dissolution of the electrode, has been studied by electrochemical methods and by an electrochemical quartz crystal microbalance (EQCM). TMTU in acetonitrile readily adsorbs at gold electrodes and an estimated coverage of 5.5 x 10(-10) mol cm(-2) (30 A2 per molecule) was measured electrochemically. Nevertheless, the oxidation of TMTU in solution is a diffusion-controlled process and is strongly influenced by the electrode material, as observed by comparison of gold electrodes with glassy carbon and platinum working electrodes. In the absence of TMTU, EQCM cyclic voltammetry experiments showed dissolution of gold through a 1e- oxidation process at potentials more positive than 1.20 V vs saturated calomel electrode (SCE). Potential step and cyclic voltammetry EQCM experiments performed using gold surfaces in the presence of TMTU revealed TMTU-assisted etching of gold at potentials as low as 0.35 V vs SCE. In the potential region from 0.35 to 1.20 V the current response of TMTU oxidation mimics the response expected for a redox-active species in solution, including the presence of a mass-transfer-limited region, which supports the conclusion that the etching process in this potential region is initiated by the oxidation of TMTU at the gold surface. The current efficiency of the TMTU-assisted etching was found to vary between 12 electrons per gold atom dissolved (e/Au) (E = 0.50 V vs SCE) and 2 e/Au (0.90 V < E < 1.20 V). At potentials <0.90 V the dominant electrochemical process is the formation of TMTU+, whereas at higher potentials the etching of the gold surface by formation of a Au(I)-TMTU+ species becomes equally important. At potentials above 1.20 V the etching is no longer dependent on the diffusion of TMTU and the e/Au value approaches 1.

Topics: Acetonitriles; Electrochemistry; Gold; Microchemistry; Oxidation-Reduction; Quartz; Surface Properties; Thiourea

Thiourea and superoxide dismutase were effective antidotes to paraquat toxicity in an HL60 cell culture system, whereas other hydroxyl scavengers were ineffective. The efficacy of thioureas was not due to blockage of intracellular paraquat uptake, inhibition of NADPH-P-450 reductase, or reaction with the paraquat radical. Thiourea also competitively inhibited the reduction of cytochrome c by the xanthine/xanthine oxidase superoxide-generating system, and the release of iron from ferritin by superoxide radicals. The reaction of superoxide with thiourea produced a sulfhydryl compound distinct from products formed by hydrogen peroxide or hydroxyl radicals. Spectrophotometric and chromatographic studies indicated the carbon-sulfide double bond was converted to a sulfhydryl group which reacted with Ellman's reagent. Additional confirmatory evidence for the sulfhydryl compound was obtained with carbon-13 NMR and mass spectroscopies. Thus, thioureas are direct scavengers of superoxide radicals as well as hydroxyl radicals and hydrogen peroxide. The rate constant for the reduction of thiourea by superoxide was estimated at 1.1 x 10(3) M-1 s-1. The implication of this finding on free radical studies, the mechanism of paraquat toxicity, and the metabolism of thioureas is discussed.

Topics: Acetonitriles; Cell Line; Cell Survival; Cytochrome c Group; Ferritins; Free Radicals; Humans; Magnetic Resonance Spectroscopy; Oxidation-Reduction; Paraquat; Sulfhydryl Compounds; Superoxides; Thiourea; Uric Acid