Poly(4-vinylpyridine) catalyzed hydrolysis of methyl bromide to methanol and dimethyl ether

The hydrolysis of methyl bromide with neutral water is performed in the presence and absence of various amines in a batch reactor at different temperatures (50–125 °C). Screening of poly(4-vinylpyridine) as a potential reusable solid amine catalyst showed maximum efficiency. This significant enhancement in efficiency is due to the capture of HBr by solid PVP and remains phase-separated driving the reaction forward. The major advantage of this process is that the polymer can be easily regenerated and reused without loss of activity making it a very effective catalyst for the conversion of methyl halides to methanol and dimethyl ether.     

Syntheses and conformations of some cyclic hydroxamates. X-Ray crystal structure of 2-(p-nitrobenzoyl)tetrahydro-2H-1,2-oxazine

Alkylation of potassium p-nitrobenzohydroxamate with 1,4-dibromobutane gave 2-(p-nitrobenzoyl)tetrahydro-2H-1,2-oxazine (3). The X-ray crystal structure of 3 has been determined. The crystals are monoclinic, space group P2₁/n with a = 6.749(1), b = 7.644(1), c = 21.557(2)Å, β = 98.89(1), V = 1098.8(2)ų and Z = 4. The structure, which was refined to R = 0.039 using 1340 observed reflections, shows the oxazine and carbonyl oxygen atoms trans to each other. Alkylation of potassium benzohydroxamate with 1,3-dibromobutane gave a mixture of 3-methyl-2-benzoyloxazolidine (4) and 5-methyl-2-benzoyloxazolidine (5). The ¹H and ¹³C nmr spectra of the mixture of 4 and 5 indicates that these cyclic hydroxamates exist predominantly in the s-trans conformation.     

Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization

RAFT grafted montmorillonite (MMT) clays [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium‐MMT (PCDBAB‐MMT) and N‐(4‐((((dodecylthio)carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammo‐nium‐MMT (DCTBAB‐MMT)] of various loadings were dispersed in styrene (S) monomer and the resultant mixtures emulsified and sonicated in the presence of a hydrophobe (hexadecane) into miniemulsions. The stable miniemulsions thus obtained were polymerized to yield encapsulated polystyrene‐clay nanocomposites (PS‐CNs). The molar mass and polydispersity index (PDI) of the PS‐CNs depended on the amount of RAFT agent in the system, in accordance with the features of the RAFT process. The morphology of the PS‐CNs ranged from partially exfoliated to an intercalated morphology, depending on the percentage clay loading. The thermomechanical properties of the PS‐CNs were better than those of the neat PS polymer, and were dependent on the molar mass, PS‐CN morphology and clay loading. The similarities and differences of the PS‐CNs prepared here by miniemulsion polymerization were compared to those prepared using the same RAFT agents and polymer system by bulk polymerization (as reported by us in a previous article). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7114–7126, 2008     

Using apparent molecular weight from SEC in controlled/living polymerization and kinetics of polymerization

Apparent molecular weights from size exclusion chromatography, that is molecular weights relative to standards of a nature different to that of the polymer sample being studied, are frequently used. We use calculations corresponding to realistic cases to provide guidelines for situations when, and to what extent, apparent molecular weights (MWs) can be meaningful. In controlled polymerization, we show how, without due care, use of apparent MW, could lead to the incorrect conclusion that the reaction was not controlled, whereas the true MWs would be close to theoretical values. We show here that the quality of the eluent as a solvent for the standard and the polymer sample is a good indication of the accuracy and the significance of the apparent polydispersity index. Accurate Mark–Houwink–Sakurada parameters are of limited availability, but the data about solvent quality available in handbooks or available from static light scattering measurements. Apparent M_n is of no use in controlled polymerization if simple simulations as performed in this work do not validate their use. The determination of transfer constants by the Mayo plot can be performed using apparent M_n without introducing any significant error, contrary to apparent weight‐average molecular weight M_w or apparent ln number distribution. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 897–911, 2008     

Synthesis and characterization of synthetic polymer colloids colloidally stabilized by cationized starch oligomers

A method is developed for anchoring enzymatically degraded cationized starch as electrosteric stabilizers onto synthetic latices, using cerium(IV) to create free‐radical grafting sites on the starch. Direct anchoring of debranched starch onto a poly(methyl methacrylate) seed latex yields a latex stabilized by well‐defined oligosaccharides. Using α‐amylase to randomly cleave starch to form (1→4)‐α‐glucans, and a comonomer, N‐isopropyl acrylamide (NIPAM), whose corresponding polymer exhibits a lower critical solution temperature (LCST), creates a means to synthesize block (or graft) oligomers of oligosaccharide and synthetic polymer, which are water soluble at room temperature. Above 30 °C, they become amphiphilic and form self‐emulsifying nanoparticles (sometimes termed “frozen micelles”) from which a synthetic latex is grown after addition of methyl methacrylate, the collapsed NIPAM‐containing entities functioning as a type of in situ seed. This synthesis of stable synthetic latex particles is shown to have a high grafting efficiency. The starch fragments were characterized by ¹H solution‐state NMR before grafting, and ¹³C solid‐state cross‐polarization magic‐angle spinning (CP‐MAS) NMR was used to characterize the starch oligomers actually grafted on the final latex. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1836–1852, 2009     

Ultrafast Decay of the Excited Singlet States of Thioxanthone by Internal Conversion and Intersystem Crossing

The experimental ultrafast photophysics of thioxanthone in several aprotic organic solvents at room temperature is presented, measured using femtosecond transient absorption together with high‐level ab initio CASPT2 calculations of the singlet‐ and triplet‐state manifolds in the gas phase, including computed state minima and conical intersections, transition energies, oscillator strengths, and spin–orbit coupling terms. The initially populated singlet ππ* state is shown to decay through internal conversion and intersystem crossing processes via intermediate nπ* singlet and triplet states, respectively. Two easily accessible conical intersections explain the favorable internal conversion rates and low fluorescence quantum yields in nonpolar media. The presence of a singlet–triplet crossing near the singlet ππ* minimum and the large spin–orbit coupling terms also rationalize the high intersystem crossing rates. A phenomenological kinetic scheme is proposed that accounts for the decrease in internal conversion and intersystem crossing (i.e. the very large experimental crescendo of the fluorescence quantum yield) with the increase of solvent polarity.     

Viscosimetric detection in size-exclusion chromatography (SEC/GPC): The Goldwasser method and beyond

Size-exclusion chromatography (SEC or GPC) is the most widely used separation method to characterize polymers. The high level of complexity of most polymeric materials necessitates the use of not only concentration-sensitive detection but also structure-sensitive detection. Viscometry is usually used in conjunction with a concentration-sensitive detector and universal calibration to determine molecular weights of polymers. Goldwasser proposed to use a viscometer as a single detector to determine number-average molecular weights, M(n) (ACS Symposium Series, 521, 143). The method is particularly of interest when concentration-sensitive detection is not available, because the sample is isorefractive or not UV-absorbing, or because composition is not constant (copolymers). It has known very little applications so far. It actually does not only allow determining M(n), but also the number hydrodynamic volume distribution. This opens a wider range of applications for the Goldwasser method. Size-exclusion chromatography only yields inaccurate molecular weight distributions for some complex branched polymers. Hydrodynamic volume distributions have then a strong potential for comparative studies owing to their far higher accuracy. Our experimental tests highlight the fact that the method is highly sensitive to noise and careful optimization of the injection concentration is needed, but number distribution can be obtained as well as M(n).     

An APCI LC‐MS/MS method for routine determination of capecitabine and its metabolites in human plasma

The anticancer drug capecitabine and its metabolites [including the active metabolite 5‐fluorouracil (5‐FU)] display high pharmacokinetic inter‐patient variability. Such variability, which may lead to treatment failure or toxicity, could need drug concentration measurement to individualize dosing regimen. However, usual assay methods are often long and fastidious. A simultaneous and cost‐effective method was thus developed for the determination of the concentrations of these compounds in human plasma. Compounds were extracted via a classic liquid–liquid extraction. Chromatographic analysis was performed on a C18 reverse phase column with detection by atmosphere pressure chemical ionization LC‐MS/MS. Our method allows a good chromatographic separation of the compounds and was fully validated following Food and Drug Administration (FDA) recommendations (good selectivity, no carry‐over, linearity of the calibration curves without weighting, deviations from nominal concentrations of standard samples lower than 15%, intra‐ and inter‐assay precision and accuracy lower than 15%). Recovery and stability were also acceptable following the FDA guidelines. A matrix effect impairing the determination of 5‐FU was avoided by using a stable isotopic derivative of 5‐FU as internal standard. Interestingly, this method allows detection of TetraHydroUridine, an inhibitor of ex vivo degradation of metabolites, which is essential for the stability, the adequate conditioning of blood samples and for good laboratory practice, essential in routine determination. This method seems usable to routinely determine concentrations of capecitabine and its metabolites in blood and may be helpful in further studies aiming at performing therapeutic drug monitoring. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of high surface area TiO2/SiO2 mesostructured nanocomposite

Recently titania synthesis was reported using various structuration procedures, leading to the production of solid presenting high surface area but exhibiting moderate thermal stability. The study presents the synthesis of TiO₂/SiO₂ nanocomposites, a solid that can advantageously replace bulk titania samples as catalyst support. The silica host support used for the synthesis of the nanocomposite is a SBA-15 type silica, having a well-defined 2D hexagonal pore structure and a large pore size. The control of the impregnation media is important to obtain dispersed titania crystals into the porosity, the best results have been obtained using an impregnation in an excess of solvent. After calcination at low temperature (400 °C), nanocomposites having titania nanodomains (～2–3 nm) located inside the pores and no external aggregates visible are obtained. This nanocomposite exhibits high specific surface area (close to that of the silica host support, even with a titania loading of 55 wt.%) and a narrow pore size distribution. Surprisingly, the increase in calcination temperature up to 800 °C does not allow to detect the anatase to rutile transition. Even at 800 °C, the hexagonal mesoporous structure of the silica support is maintained, and the anatase crystal domain size is evaluated at ～10 nm, a size close to that of the silica host support porosity (8.4 nm). Comparison of their physical properties with the results presented in literature for bulk samples evidenced that these TiO₂/SiO₂ solids are promising in term of thermal stability.     

无零级衍射干扰的彩色数字全息研究

彩色数字全息研究中,用球面波为重建波及角谱衍射公式进行波前重建是一种有效的方法.然而,重建图像上通常伴有强烈的零级衍射干扰.本文通过理论分析,对波前重建过程作了重要改进.用改进后的方法进行彩色数字全息的实验研究表明,重建彩色图像的质量获得显著改善. 关键词： 彩色数字全息 波前重建 零级衍射干扰