The analysis of human amniotic fluid using capillary electrophoresis

This study has investigated the composition of amniotic fluid (AF) using capillary electrophoresis (CE). A detailed optimisation investigation was undertaken to obtain the best resolution of the major peaks in amniotic fluid. In the final method, capillary zone electrophoresis (CZE) of AF was performed on a Hewlett Packard3D CE instrument using a fused-silica capillary of 44 cm total length (36 cm to the detector) with in internal diameter of 50 microm. The background electrolyte was 20 mM sodium tetraborate containing 0.8 mM EDTA adjusted to pH 9.0. AF was diluted 1 plus 1 with deionised water prior to hydrodynamic injection for 3 s at 50 mbar. The separation was performed at +22.5 kV and resulted in a current of 65 microA. The capillary temperature was 28 degrees C. Using this CZE method, some eight peaks were consistently resolved in AF samples and several other more transient peaks have been separated from AF in less than 10 min. A scheme for the identification of peaks once they had been separated was also developed. Four peaks have been identified as proteins, i.e., gamma-globulin, alpha1-antitrypsin, transferrin and albumin. Surprisingly, one major peak was shown to be the purine catabolite, xanthine.     

Structure and growth of oxides on polycrystalline nickel surfaces

The oxidation of polycrystalline nickel (Ni) metal surfaces after exposure to oxygen gas (O₂) at 25 and 300 °C and pressures near 130 Pa, was studied using X‐ray photoelectron spectroscopy (XPS). Oxide structures involving both divalent (Ni²⁺) and trivalent (Ni³⁺) species could be distinguished using Ni 2p spectra, while surface adsorbed O₂ and atomic oxygen (O) species could be differentiated from bulk oxide (O^2?) using O 1s spectra. Oxide thicknesses and distributions were determined using QUASES^?, and the average oxide thickness was verified using the Strohmeier formula. The reaction kinetics for oxide films grown at 300 °C followed a parabolic mechanism, with an oxide thickness of greater than 4 nm having formed after 60 min. Exposure at 25 °C followed a direct logarithmic mechanism with an oxide growth rate about four to five times slower than at 300 °C. Reaction of a Ni (100) single crystal under comparable conditions showed much slower reaction rates compared to polycrystalline specimens. The higher reaction rate of the polycrystalline materials is attributed to grain boundary transport of Ni cations. Oxide thickness was measured on a microscopic scale for polycrystalline Ni exposed to large doses of O₂ at 25 and 300 °C. The thickness of oxide was not strongly localized on this scale. However, the QUASES^? analysis suggests that there is localized growth on a nanometric scale—the result of island formation. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface chemistry of quantum-sized metal nanoparticles under light illumination

Size reduction of metal nanoparticles increases the exposure of metal surfaces significantly, favoring heterogeneous chemistry at the surface of the nanoparticles. The optical properties of metal nanoparticles, such as light absorption, also exhibit a strong dependence on their size. It is expected that there will be strong coupling of light absorption and surface chemistry when the metal nanoparticles are small enough. For instance, metal nanoparticles with sizes in the range of 2–10 nm exhibit both surface plasmon resonances, which can efficiently produce high-energy hot electrons near the surface of the nanoparticles under light illumination, and the Coulomb blockade effect, which favors electron transfer from the metal nanoparticles to the surface adsorbates. The synergy of efficient hot electron generation and electron transfer on the surface of small metal nanoparticles leads to double-faced effects: (i) surface (adsorption) chemistry influences optical absorption in the metal nanoparticles, and (ii) optical absorption in the metal nanoparticles promotes (or inhibits) surface adsorption and heterogeneous chemistry. This review article focuses on the discussion of typical quantum phenomena in metal nanoparticles of 2–10 nm in size, which are referred to as “quantum-sized metal nanoparticles”. Both theoretical and experimental examples and results are summarized to highlight the strong correlations between the optical absorption and surface chemistry for quantum-sized metal nanoparticles of various compositions. A comprehensive understanding of these correlations may shed light on achieving high-efficiency photocatalysis and photonics.

Size reduction of metal nanoparticles increases the exposure of metal surfaces significantly, favoring heterogeneous photochemistry at the surface of the nanoparticles.     

Hydrolytic polymerization of caprolactam. I. Hydrolysis—polycondensation kinetics

In a study aimed at process optimization of caprolactam polymerization, particular reference has been paid to the competing role of water in caprolactam hydrolysis and endgroup polycondensation. The dependence of the apparent equilibrium constant for polycondensation on water concentration indicated that there is a strong effect of the medium on the activities of the reacting species which can not be neglected in a kinetic study of the polycondensation reaction. The effect of a variation of the medium was taken into account by using a polycondensation rate constant which included a function of the water present at any given time. With the aid of analog computer curve-fitting techniques, good agreement with second-order kinetics was found. The validity of a second-order mechanism was confirmed in a kinetic study of the chain amide linkage hydrolysis. The hydrolysis of caprolactam follows substantially different kinetics, where the generation of carboxyl groups reduces the activation energy of the reaction, which follows predominantly a third-order mechanism.     

Collision-induced dissociations of deprotonated peptides,dipeptides and tripeptides with hydrogen and alkyl α groups. An aid to structure determination

The characteristic collision-induced dissociations of [M ? H]^? ions of dipeptides and tripeptides involve proton transfer to the carboxylate centre as a prelude to fragmentation. Dipeptides show the process NH₂CH(R¹)CONHCH(R²)CO₂^? → NH₂C(R¹)CONHCH(R²)CO₂H → ^?NHCH(R²)CO₂H + NH₂C(R¹)?C?O (R = H or alkyl) while tripeptides show the analogous processes NH₂CH(R¹)CONHCH(R²)CONHCH(R³)CO₂^? → NH₂CH(R¹)CONHC(R²)CONHCH(R³)CO₂^? → NHCH(R³)CO₂H + NH₂CH(R¹)CONHC(R²)?C?O and NH₂CH(R¹)CONHCH(R²)? CONHCH(R³)CO₂^? → NH₂C(R¹)CONHCH(R²)CONHCH(R³)CO₂H → ^?NHCH(R²)CONHCH(R³)CO₂H + NH₂C(R¹)?C?O. These fragmentations provide ready identification of the peptide.     

MS2Grouper: Group assessment and synthetic replacement of duplicate proteomic tandem mass spectra

Shotgun proteomics experiments require the collection of thousands of tandem mass spectra; these sets of data will continue to grow as new instruments become available that can scan at even higher rates. Such data contain substantial amounts of redundancy with spectra from a particular peptide being acquired many times during a single LC-MS/MS experiment. In this article, we present MS2Grouper, an algorithm that detects spectral duplication, assesses groups of related spectra, and replaces these groups with synthetic representative spectra. Errors in detecting spectral similarity are corrected using a paraclique criterion-spectra are only assessed as groups if they are part of a clique of at least three completely interrelated spectra or are subsequently added to such cliques by being similar to all but one of the clique members. A greedy algorithm constructs a representative spectrum for each group by iteratively removing the tallest peaks from the spectral collection and matching to peaks in the other spectra. This strategy is shown to be effective in reducing spectral counts by up to 20% in LC-MS/MS datasets from protein standard mixtures and proteomes, reducing database search times without a concomitant reduction in identified peptides.     

Voltammetric studies on the reduction of polyoxometalate anions in ionic liquids

The electrochemical reduction of tetrabutylammonium salts of isostructural pairs of polyoxometalates [Bu4N]2[M6O19], [Bu4N]4[alpha-SiM12O40], and [Bu4N]4[alpha-S2M18O62] (M = Mo or W) has been investigated at glassy carbon electrodes in dissolved and surface-confined states in ionic liquids and other media. In the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate [BMIM][PF(6)], between two and six reversible one-electron-transfer processes were detected. Detailed studies on the process [alpha-S2W18O62](4-/5-) in a range of ionic liquids, water, and conventional organic solvents (containing 0.1 M electrolyte) suggest that the polarity of the medium plays a key role in the determination of the reversible potential. Reduction processes involving very highly charged [alpha-S2W18O62](8-/9-/10-) species are strongly influenced by the purity of the medium.     

Two generalizable routes to terminal carbido complexes

Desulfurization of the thiocarbonyl ligand in square pyramidal [Ru(CS)Cl2(PCy3)2] (1-S) via sulfur atom abstraction using [Mo(H)(eta2-Me2CNAr)(N[i-Pr]Ar)2] forms [Ru(C)Cl2(PCy3)2] (1) cleanly over several hours in benzene; isolated yield is 55%. Complex 1 is also formed in 87% isolated yield upon reaction of [Ru(CHR)(PCy3)2Cl2] (R = p-C6H4Me, 2; Ph, 3) with vinyl acetate in dichloromethane. Complex 1-S is re-formed quantitatively from 1 upon treatment with elemental sulfur in CH2Cl2, but is prepared most conveniently by treatment of crude [Ru(CS)Cl2(PPh3)2(OH2)] with excess PCy3 in toluene. Nearly quantitative conversion of 1 to [Ru(CO)Cl2(PCy3)2] (1-O) occurs upon addition of dimethyldioxirane solution in acetone to 1 dissolved in CH2Cl2 at ca. -90 degrees C.     

Chemistry of sulfonyl isocyanates and sulfonyl isothiocyanates. IX. Routes to substituted oxazolidin-2-ones and oxazolidine-2-thiones

4-Chlorobenzenesulfonyl isocyanate (I) reacted with 2-chloroethanol and 1-chloro-2-propanol to give, respectively, 2-chloroethyl 4-chlorobenzenesulfonyl carbamate (III) and 1-chloro-2-propyl 4-chlorobenzenesulfonyl carbamate (VI). The carbamates III and VI cyclized under the influence of pyridine to afford, respectively, 3-(4-chlorobenzenesulfonyl)oxazolidin-2-one (IV) and 3-(4-chlorobenzenesulfonyl)-5-methyloxazolidin-2-one (VII). The oxazolidin-2-ones were stable toward hydrochloric acid but hydrolyzed in 2M sodium hydroxide solution to N-(2-hydroxyethyl)-4-chlorobenzenesulfonamide (V) and N-(2-hydroxy-1-propyl)-4-chlorobenzene-sulfonamide (VIII), respectively. 4-Toluenesulfonyl isothiocyanate (II) reacted with 2-chloroethanol to give 2-chloroethyl 4-chlorobenzenesulfonyl thiocarbamate (IX), which was converted by pyridine to 3-(4-toluenesulfonyl)oxazolidine-2-thione (X).