Synchrotron FTIR microscopy of Langmuir-Blodgett monolayers and polyelectrolyte multilayers at the solid-solid interface

Synchrotron FTIR microscopy has been used to probe the structure of model boundary lubricant layers confined at the solid-solid interface. The combination of high brightness of the IR source and a novel contact geometry that uses a hemispherical internal reflection element as the means for light delivery has enabled the detection of <2.5 nm thin monolayer lubricant layers in the solid-solid contact, in addition to allowing for spectral acquisition from specific regions of the contact. Spectra of hydration water from within a confined polyelectrolyte multilayer film have also been acquired, highlighting the altered hydrogen bonding environment within the polymer layer.     

Effects of nonionic surfactant and sodium dodecyl sulfate layers on electroacoustics of hexadecane/water emulsions

Hexadecane-in-water emulsion droplets were formed in a homogeniser in the presence of a mixture of an anionic surfactant (sodium dodecyl sulfate, SDS) and nonionic surfactants of various chain lengths [nonylphenol ethoxylate (C₉φE_N, N=100, 40 and 30) or an alcohol ethoxylate (Brij35)]. The dynamic mobility of the oil droplets was then measured using a flow-through version of an AcoustoSizer. Large changes were observed in the dynamic mobility of the particles formed with the mixed surfactants compared to particles formed with SDS alone. O'Brien's “gel layer” model was employed to interpret the data. The characteristics of the adsorbed layer appeared to be similar whether the nonionic surfactant was adsorbed concurrently with the SDS as the emulsion formed or was merely added afterwards to the emulsion established. The particle size, the charge and the molar fraction of SDS had virtually no effect. The layers formed with the nonionic surfactants decreased in thickness with decreasing molecular weight as expected. Passage through the homogeniser itself had no effect on the properties of the largest nonionic surfactant and, hence, on the adsorption layer formed with it. Received: 4 October 2000 Accepted: 16 October 2000     

The Homogeneous rate constant for the recombination of fluorine atoms with F2 as the third body

The rate constant for the homogeneous recombination of F-atoms with F₂ as the third body was found to be (3.6 ± 1.4) × 10¹⁴ cm⁶/mol²s at 300 to 320 K. The corresponding rate constants with He and Ar as third bodies were also measured.     

The thermal degradation of polysiloxanes: Part 5—Synthesis,characterisation and thermal analysis of poly(tetramethyl-p-silphenylene siloxane) and copolymers with dimethylsiloxane

Poly(tetramethyl-p-silphenylene siloxane) and a series of copolymers with dimethylsiloxane have been prepared and characterised by means of ir and nmr spectroscopy and number average molecular weight measurements. Thermal gravimetry (TG) and Thermal Volatilisation Analysis (TVA) have been used to demonstrate the relationships which exist between stability and composition.     

Radical cyclization of sugar-derived beta-(alkynyloxy)acrylates: synthesis of novel fused ethers

[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran.     

Increasing throughput and information content for in vitro drug metabolism experiments using ultra-performance liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer

The field of drug metabolism has been revolutionized by liquid chromatography/mass spectrometry (LC/MS) applications with new technologies such as triple quadrupoles, ion traps and time-of-flight (ToF) instrumentation. Over the years, these developments have often relied on the improvements to the mass spectrometer hardware and software, which has allowed users to benefit from lower levels of detection and ease-of-use. One area in which the development pace has been slower is in high-performance liquid chromatography (HPLC). In the case of metabolite identification, where there are many challenges due to the complex nature of the biological matrices and the diversity of the metabolites produced, there is a need to obtain the most accurate data possible. Reactive or toxic metabolites need to be detected and identified as early as possible in the drug discovery process, in order to reduce the very costly attrition of compounds in late-phase development. High-resolution, exact mass measurement plays a very important role in metabolite identification because it allows the elimination of false positives and the determination of non-trivial metabolites in a much faster throughput environment than any other standard current methodology available to this field. By improving the chromatographic resolution, increased peak capacity can be achieved with a reduction in the number of co-eluting species leading to superior separations. The overall enhancement in the chromatographic resolution and peak capacity is transferred into a net reduction in ion suppression leading to an improvement in the MS sensitivity. To investigate this, a number of in vitro samples were analyzed using an ultra-performance liquid chromatography (UPLC) system, with columns packed with porous 1.7 mum particles, coupled to a hybrid quadrupole time-of-flight (ToF) mass spectrometer. This technique showed very clear examples for fundamental gains in sensitivity, chromatographic resolution and speed of analysis, which are all important factors for the demands of today's HTS in discovery.     

Continuous Duality of Limits and Colimits of Topological Abelian Groups

In the category Cgp of convergence groups, the continuous dual Γ _c ( ·) is a left adjoint and takes colimits to limits in Cgp. In general, limits are not taken to colimits. In this paper we show that, if we restrict ourselves to limits of topological groups, then reduced projective limits are carried to inductive limits in Cgp. As a consequence of this we show that the inductive limit in Cgp of locally compact topological groups is reflexive if it is separated.      

Chemical defects in the highly fluorescent conjugated polymer dots

We present strong evidence for the oxidation of conjugated polymers in the formation of conjugated polymer dots (CPdots) using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Although recent studies show that folding of the polymer chain into a compact 3D structure is involved in the formation of these nanoparticles, the process by which these intrinsically hydrophobic nanoscale particles circumvent aggregation in water is still not well understood. Zeta potential results show that these dots have a negatively charged surface at neutral pH, with a zeta potential and surface charge density of approximately -40 mV and (1.39 - 1.70) × 10(-2) C/m(2), respectively. In addition, quantitative elemental analysis of CPdots indicates that oxygen composes 7-13% of these nanoparticles. The overall results support the presence of chemical defects in forming a hydrophilic surface of CPdots. As a consequence, the charged surface contributes to inhibiting the aggregation of CPdots in water, leading to colloidal stability.     

Synchrotron PEEM and ToF‐SIMS study of oxidized heterogeneous pentlandite,pyrrhotite and chalcopyrite

Synchrotron‐based photoemission electron microscopy (PEEM; probing the surface region) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS; probing the uppermost surface layer) have been used to image naturally heterogeneous samples containing chalcopyrite (CuFeS₂), pentlandite [(Ni,Fe)₉S₈] and monoclinic pyrrhotite (Fe₇S₈) both freshly polished and exposed to pH 9 KOH for 30 min. PEEM images constructed from the metal L₃ absorption edges were acquired for the freshly prepared and solution‐exposed mineral samples. These images were also used to produce near‐edge X‐ray absorption fine‐structure spectra from regions of the images, allowing the chemistry of the surface of each mineral to be interrogated, and the effect of solution exposure on the mineral surface chemistry to be determined. The PEEM results indicate that the iron in the monoclinic pyrrhotite oxidized preferentially and extensively, while the iron in the chalcopyrite and pentlandite underwent only mild oxidation. The ToF‐SIMS data gave a clearer picture of the changes happening in the uppermost surface layer, with oxidation products being observed on all three minerals, and significant polysulfide formation and copper activation being detected for pyrrhotite.