Hydrolysis of p-Nitrophenyl Esters Promoted by Semi-fluorinated Quaternary Ammonium Polymer Latexes and Films

Semifluorinated polymer latexes were prepared by emulsion polymerization of 2.5-25% of a fluoroalkyl methacrylate, 25% chloromethylstyrene, 1% styrylmethyl(trimethyl)ammonium chloride, and the remainder 2-ethylhexyl methacrylate under surfactant-free conditions. The chloromethylstyrene units were converted to quaternary ammonium ions with trimethylamine. In aqueous dispersions at particle concentrations of less than 1 mg mL-1 the quaternary ammonium ion latexes promoted hydrolyses of p-nitrophenyl hexanoate (PNPH) in pH 9.4 borate buffer and of diethyl p-nitrophenyl phosphate (Paraoxon) in 0.1 M NaOH at 30 oC with half-lives of less than 10 minutes. Thin 0.7-2 μm films of the latexes on glass promoted fast hydrolysis of Paraoxon but not of PNPH under the same conditions. Even after annealing the quaternary ammonium ion polymer films at temperatures well above their glass transition temperatures, AFM images of the film surfaces had textures of particles. Contact angle measurements of the annealed films against water and against hexadecane showed that the surfaces were not highly fluorinated

Autoxidation of tetralin in water catalysed by cobalt(ii)-pyridine complexes bound to polymer colloids

Cobalt(ii)-pyridine complexes bound to 60 nm diameter latex copolymers of styrene, divinylbenzene, and either acrylic or methacrylic acid catalyse autoxidation of tetralin in water faster than cobalt(ii)-pyridine complexes in aqueous solution or cobalt(ii) acetate in acetic acid.Peer reviewedChemistr

Survey of alkyl methacrylate latexes as aqueous catalytic media

Cationic polymer latexes serve as catalytic media for the hydrolysis of p-nitrophenyl esters by providing a more lipophilic environment into which these compounds can partition from the aqueous phase. The latex quaternary ammonium ions attract high local concentrations of reactive or catalytic anions into the water-swollen particles. We synthesized 32 different methacrylate and styrene latexes via a parallel synthetic route and tested their activities for the hydrolysis of p-nitrophenyl hexanoate. The most active latex is a copolymer of 75% 2-ethylhexyl methacrylate and 25% vinylbenzyl chloride that was quaternized with tributylamine. The rate of hydrolysis at 30 °C is 17 times faster using 0.6 mg mL-1 of latex in pH 9.4 borate buffer relative to control experiments that lacked polymer latex. Analysis of the kinetics shows that the latex activities depend primarily on the latex/water partition coefficients of p-nitrophenyl hexanoate. The latexes also promote the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate (6-NBIC) in aqueous media, and 0.6 mg mL-1 of the latex from 75% 2-ethylhexyl methacrylate and 25% vinylbenzyl chloride quaternized with tributylamine gave an observed rate constant 10 400 times that in water alone. The rate accelerations of 6-NBIC decarboxylation are due to both favorable partitioning into the latex and faster intraparticle rate constants.Peer reviewedChemistr

A photometric and astrometric investigation of the brown dwarfs in Blanco 1

We present the results of a photometric and astrometric study of the low mass stellar and substellar population of the young open cluster Blanco 1. We have exploited J band data, obtained recently with the Wide Field Camera (WFCAM) on the United Kingdom InfraRed Telescope (UKIRT), and 10 year old I and z band optical imaging from CFH12k and Canada France Hawaii Telescope (CFHT), to identify 44 candidate low mass stellar and substellar members, in an area of 2 sq. degrees, on the basis of their colours and proper motions. This sample includes five sources which are newly discovered. We also confirm the lowest mass candidate member of Blanco 1 unearthed so far (29MJup). We determine the cluster mass function to have a slope of alpha=+0.93, assuming it to have a power law form. This is high, but nearly consistent with previous studies of the cluster (to within the errors), and also that of its much better studied northern hemisphere analogue, the Pleiades.Comment: 8 Pages, 5 Figures, 2 Tables and 1 Appendix. Accepted for publication in MNRA

Quantum Flux from a Moving Spherical Mirror

We calculate the flux from a spherical mirror which is expanding or contracting with nearly uniform acceleration. We find that the flux at an exterior point (which could in principle be a functional of the mirror's past history) is actually found to be a local function, depending on the first and second time derivatives of acceleration at the retarded time.Comment: 13 pages, 2 figures, RevTex, submitted to Phys. Rev.

XANES and EXAFS study of a platinum phthalocyanine

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) studies on [octa(2-ethylhexyloxy)phthalocyaninato]platinum [PtL] as a film at room temperature suggest that the structure consists of non-planar, concave discotic molecules packed perpendicular to the stacking axis.Peer reviewedChemistr

Giant two-phonon Raman scattering from nanoscale NbC precipitates in Nb

High purity niobium (Nb), subjected to the processing methods used in the fabrication of superconducting RF cavities, displays micron-sized surface patches containing excess carbon. High-resolution transmission electron microscopy and electron energy-loss spectroscopy measurements are presented which reveal the presence of nanoscale NbC coherent precipitates in such regions. Raman backscatter spectroscopy on similar surface regions exhibit spectra consistent with the literature results on bulk NbC but with significantly enhanced two-phonon scattering. The unprecedented strength and sharpness of the two-phonon signal has prompted a theoretical analysis, using density functional theory (DFT), of phonon modes in NbC for two different interface models of the coherent precipitate. One model leads to overall compressive strain and a comparison to ab-initio calculations of phonon dispersion curves under uniform compression of the NbC shows that the measured two-phonon peaks are linked directly to phonon anomalies arising from strong electron-phonon interaction. Another model of the extended interface between Nb and NbC, studied by DFT, gives insight into the frequency shifts of the acoustic and optical mode density of states measured by first order Raman. The exact origin of the stronger two-phonon response is not known at present but it suggests the possibility of enhanced electron-phonon coupling in transition metal carbides under strain found either in the bulk NbC inclusions or at their interfaces with Nb metal. Preliminary tunneling studies using a point contact method show some energy gaps larger than expected for bulk NbC.Comment: Phys. Rev. B, accepte

Post-COVID-19 condition and persisting symptoms in English schoolchildren: repeated surveys to March 2022

BACKGROUND: Both post-COVID-19 condition (long COVID) and the presence of persisting symptoms that do not meet formal definitions of post-COVID-19-condition may adversely affect quality of life and function. However, their prevalence among children and young people in England is unclear. METHODS: We used data from repeated surveys in a large cohort of English schoolchildren from the COVID-19 Schools Infection Survey (SIS) for the school year 2021/22 to describe the weighted prevalence of post-COVID-19-condition and compare persisting symptoms between individuals with a positive SARS-CoV-2 test and those with neither a positive test history nor suspected infection. RESULTS: Among 7797 children from 173 schools, 1.8% of primary school pupils (aged 4 to 11 years), 4.5% of secondary school pupils in years 7-11 (aged 11 to 16 years) and 6.9% of those in years 12-13 (aged 16 to 18 years) met a definition of post-COVID-19 condition in March 2022. Specific persisting symptoms such as anxiety or difficulty concentrating were frequently reported regardless of prior infection status and increased with age: 48.0% of primary school pupils, 52.9% of secondary school pupils in years 7-11 and 79.5% in years 12-13 reporting at least one symptom lasting more than 12 weeks. Persisting loss of smell and taste, cardiovascular and some systemic symptoms were more frequently reported by those with a previous positive test. CONCLUSIONS: We showed that ongoing symptoms were frequently reported by English schoolchildren regardless of SARS-CoV-2 test results and some specific symptoms such as loss of smell and taste were more prevalent in those with a positive test history. Our study emphasises the wide-ranging impacts of the COVID-19 pandemic on the health and wellbeing of children and young people

Western Diet-Fed, Aortic-Banded Ossabaw Swine: A Preclinical Model of Cardio-Metabolic Heart Failure.

The development of new treatments for heart failure lack animal models that encompass the increasingly heterogeneous disease profile of this patient population. This report provides evidence supporting the hypothesis that Western Diet-fed, aortic-banded Ossabaw swine display an integrated physiological, morphological, and genetic phenotype evocative of cardio-metabolic heart failure. This new preclinical animal model displays a distinctive constellation of findings that are conceivably useful to extending the understanding of how pre-existing cardio-metabolic syndrome can contribute to developing HF

Long-ranged attraction between charged polystyrene spheres at aqueous interfaces

We report an optical and atomic force microscopic study of interactions between charged polystyrene spheres at a water-air interface. Optical observations of bonded particle clusters and formation of circular chainlike structures at the interface demonstrate that the interaction potential is of dipole origin. Atomic force microscope phase images show patchy domains on the colloidal surface, indicating that the surface charge distribution is not uniform as is commonly believed. Such surface heterogeneity introduces inplane dipoles, leading to an attraction at short interparticle distances.Peer reviewedChemistr