Photo-stability of photo-cured organic coatings: Part III—Photo-degradation of organic coatings photo-cured with alkoxyacetophenone and hydroxy alkylacetophenone photo-initiators

Photo-degradation studies of polystyrene (as model) and coating resins were made with three different photo-fragmenting initiators: 2,2-dimethoxy-2-phenylacetophenone, 1-[4-(2-propyl)-phenyl]-2-hydroxy-2-methyl-propanone-1 and 1-benzoyl-1-hydroxy-cyclohexane. Addition of the initiators to a benzene solution of polystyrene gave a rapid decrease in molecular weight when the solutions were uv irradiated. The degradation rate was increased by the presence of oxygen. Irradiation of polystyrene films, containing the same initiators, showed similar effects. In addition, the polymer became partially crosslinked. Addition of a free radical scavenger decreased the degradation rate. Both photo-oxidation rate and yellowing rate were affected by the concentration and the reactivity of the radicals. Photo-oxidation during photo-curing of a coating occurs in a thin surface layer. This is due to a combination of free radicals formed by the uv irradiation and the oxygen present. Oxidation during the photo-curing of a urethane resin corresponds to more than 50% of the total surface oxidation measured with ESCA.     

The Dynamics of Marangoni-Driven Local Film Drainage between Two Drops

A study of Marangoni-driven local continuous film drainage between two drops induced by an initially nonuniform interfacial distribution of insoluble surfactant is reported. Using the lubrication approximation, a coupled system of fourth-order nonlinear partial differential equations was derived to describe the spatio-temporal evolution of the continuous film thickness and surfactant interfacial concentration. Numerical solutions of these governing equations were obtained using the Numerical Method of Lines with appropriate initial and boundary conditions. A full parametric study was undertaken to explore the effect of the viscosity ratio, background surfactant concentration, the surface Péclet number, and van der Waals interaction forces on the dynamics of the draining film for the case where surfactant is present in trace amounts. Marangoni stresses were found to cause large deformations in the liquid film: Thickening of the film at the surfactant leading edge was accompanied by rapid and severe thinning far upstream. Under certain conditions, this severe thinning leads directly to film rupture due to the influence of van der Waals forces. Time scales for rupture, promoted by Marangoni-driven local film drainage were compared with those associated with the dimpling effect, which accompanies the approach of two drops, and implications of the results of this study on drop coalescence are discussed. Copyright 2001 Academic Press.     

High-performance liquid chromatographic method for the analysis of a candidate 8-aminoquinoline antileishmanial drug using oxidative electrochemical detection

An analytical method was developed for the quantitation of a candidate antileishmanial drug, 6-methoxy-8-(6-diethylaminohexylamino)-4-methylquinoline, dihydrochloride, in canine plasma. The assay utilized internal standard technique with a structural similar 8-aminoquinoline, 6-methoxy-8-(7-diethylaminoheptylamino)-4-methylquinoline, dihydrochloride, as the internal standard. The method employs a liquid-solid extraction procedure with prepackaged silica gel columns upon which the drug and internal standard are adsorbed, then selectively washed and eluted. Reversed-phase chromatography was then employed to analyze the extracted sample by means of oxidative electrochemical detection at +0.75 V. Good accuracy and precision were obtained over the range of concentration tested (10-1500 ng/ml plasma). Analyses of plasma samples from human volunteers given the drug demonstrate the method is also suitable for analysis of human plasma samples. The entire procedure is relatively simple and requires only 1 ml of plasma.     

Curve-straightening in closed Euclidean submanifolds

The flow in the negative direction of the gradient vector field associated with the functional total squared (geodesic) curvature k ² ds is the so-called curvestraightening flow. This paper will consider spaces of closed curves in closed Euclidean submanifolds. It will define these spaces of curves as submanifolds of certain Hilbert manifolds representing all curves. The main result will then be to show the existence of a particular set of functionals defined on the entire Hilbert manifold which have the following four properties: 1. The directional derivatives of these functionals may be computed by solving an initial value problem for a system of ordinary differential equations. 2. By introducing a suitable Hilbert space basis for the Sobolev spaces used, the gradients may be effectively computed (but of course not explicitly computed, except in very special cases). 3. The gradients span the space normal to the tangent space of the space of closed curves. 4. Despite the fact that these gradients in general are not given explicitly it is nevertheless possible to compute the projection onto the tangent space to the space of closed curves. In particular we do this for the gradient of k ² ds. When all details are worked out this gives us an algorithm (which we supply) for finding critical points in the space of closed curves. It is not known if the trajectories actually always converge to critical points. If the functional is modified to include a multiple of the length so the functional becomes k ²+ds then the above convergence is known for >0. The motivating application for the curvestraightening flow is the possibility of using it to find (non-trivial) closed (periodic) geodesics. Note that if =0 then a closed geodesic is a global minimum. For any , geodesics are critical but there are also other critical points, the so-called elastic curves. The paper concludes by deriving the second variation formula for k ²+ds along closed geodesics. The quadratic functional associated with the second derivative is shown to be positive definite even for non-zero along some closed geodesics in some particular manifolds of interest.     

Solvent effects on the n-->pi* electronic transition in formaldehyde: a combined coupled cluster/molecular dynamics study

We present a study of the blueshift of the n-->pi* electronic transition in formaldehyde in aqueous solution using a combined coupled cluster/molecular mechanics model including mutual polarization effects in the Hamiltonian. In addition, we report ground and excited state dipole moments. Configurations are generated from molecular dynamics simulations with two different force fields, one with and one without an explicit polarization contribution. A statistical analysis using 1200 configurations is presented. Effects of explicit polarization contributions are found to be significant. It is found that the main difference in the effects on the excitation energies arises from the fact that the two force fields result in different liquid structures, and thus a different set of configurations is generated for the coupled cluster/molecular mechanics calculations.     

X-ray absorption spectroscopy study of the hydrogen bond network in the bulk water of aqueous solutions

We utilized X-ray absorption spectroscopy (XAS) and X-ray Raman scattering (XRS) in order to study the ion solvation effect on the bulk hydrogen bonding structure of water. The fine structures in the X-ray absorption spectra are sensitive to the local environment of the probed water molecule related to the hydrogen bond length and angles. By varying the concentration of ions, we can distinguish between contributions from water in the bulk and in the first solvation sphere. We show that the hydrogen bond network in bulk water, in terms of forming and breaking hydrogen bonds as detected by XAS/XRS, remains unchanged, and only the water molecules in the close vicinity to the ions are affected.     

High-speed synthesis of potent C2-symmetric HIV-1 protease inhibitors by in-situ aminocarbonylations

Two novel series of C2-symmetric HIV-1 protease inhibitors were synthesized by microwave-promoted, palladium-catalyzed aminocarbonylations of the o-iodo- and m-bromobenzyloxy P1/P1' substituted core structures. Molybdenum hexacarbonyl was used as a convenient solid source of carbon monoxide in these transformations. After the initial high-speed library generation, biological testing identified highly active HIV-1 protease inhibitors. Selected ortho- and meta-decorated inhibitors were subsequently resynthesized on a larger scale and retested for their affinity toward HIV-1 protease, showing micromolar to low nanomolar inhibition. The discovery of highly active inhibitors containing large phenyl amide ortho substituents in the P1/P1' positions indicates that larger groups than previously believed are tolerated in this part of the S1/S1' pocket.     

Energetic mapping of Ni catalysts by detailed kinetic modeling

Temperature-programmed desorption (TPD) of CO has been performed on supported and unsupported nickel catalysts. The unsupported Ni catalyst consists of a Ni(14 13 13) single crystal which has been studied under ultrahigh vacuum conditions. The desorption energy for CO at low CO surface coverage was found to be 119 kJ/mol, and the binding energy of C to the Ni(111) surface of the crystal was 703 kJ/mol. The supported catalysts consist of nickel supported on hydrotalcite-like compounds with three different Mg2+/Al3+ ratios. The experimental results show that for the supported Ni catalysts TPD of CO leads to desorption of both CO and CO2, with the latter being dominant. Dissociation of CO takes place, and considerable amounts of residue C are left on the surface. The residue C is removed by temperature-programmed oxidation (TPO). The results show that a low Mg2+/Al3+ ratio in the hydrotalcite precursor seems to result in more steplike sites, kinks, and defects for carbon monoxide dissociation. A detailed kinetic modeling of the TPO results based on elementary reaction steps has been conducted to give an energetic map of supported Ni catalysts. Experimental results from the ideal Ni surface fit nicely with literature values, providing useful information for identifying active sites on supported Ni catalysts.     

Ultrasound-assisted extraction and on-line LC–GC–MS for determination of polycyclic aromatic hydrocarbons (PAH) in urban dust and diesel particulate matter

A method has been developed for determination of polycyclic aromatic hydrocarbons (PAH) in particulate matter from ambient air and diesel exhaust emissions. It is reproducible and accurate and, compared with similar methods for analysis of individual PAH components in complex matrices, it is relatively fast and simple. Single PAH components can be determined in samples of particulate matter from ambient air and diesel exhaust emissions with LOD of approximately 1 pg/sample. Further, sample throughput is high, because more than 20 samples can be extracted and prepared for analysis in one working (8-h) day. The particulate matter is subjected to ultrasound-assisted extraction, a technique that is shown to extract PAH from particulate material with efficiencies fully comparable with those of Soxhlet extraction. An aliphatic/PAH-enriched fraction is obtained by solid-phase extraction before isolation, separation, and identification/quantification of PAH by on-line liquid chromatography–gas chromatography–mass spectrometry. The method was validated by analysis of US National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) 1649a, Urban Dust, and 2975, Diesel Particulate Matter. Results from the method are in good agreement with the NIST-certified PAH concentrations and with NIST reference PAH concentrations.     

Extraction of clenbuterol from calf urine using a molecularly imprinted polymer followed by quantitation by high-performance liquid chromatography with UV detection

A method for the extraction of clenbuterol from calf urine samples using a molecularly imprinted polymer (MIP) has been developed. The aim was that the final extracts from the MIP should allow quantitation of clenbuterol down to 0.5 ng/mL urine using HPLC with UV detection. The MIP was produced using brombuterol as a template and the selectivity of the MIP, for clenbuterol, was tested against a non-imprinted polymer (produced without template) and was found to be high. After loading of 5 mL diluted centrifuged urine, selective binding was established in acetonitrile-acetic acid (98:2). For further elution of interferences, 0.5 M ammonium acetate buffer pH 5 and 70% acetonitrile in water was used. Clenbuterol was eluted using 1% trifluoroacetic acid in methanol, which was evaporated and reconstituted in buffer. Results from the HPLC analyses showed that the extraction of clenbuterol using MIP is linear in the range 0.5-100 ng/mL with good precision (4.3% for 0.6 ng/mL and 2.1% for 6.0 ng/mL) and accuracy (96.7% for 0.6 ng/mL and 96.7% for 6.0 ng/mL). The recoveries were 75%. The results show that the method offers a selectivity and sensitivity that make the quantitation of 0.5 ng clenbuterol/mL urine by HPLC-UV possible and a competitive alternative to state-of-the-art routine analytical methods.