Microemulsion polymerizations via high-frequency ultrasound irradiation

The synthesis of nanosized polymer latex particles using high-frequency ultrasound (213 kHz) has been successfully performed. The effects of surfactant type and concentration of surfactants on the rates of polymerization, latex size, and molecular weights of the polymers produced are presented.     

Induction of Columnar and Smectic Phases for Spiropyran Derivatives: Effects of Acidichromism and Photochromism

Liquid‐crystalline (LC) properties have been induced in a number of spiropyran derivatives by the addition of methanesulfonic acid. Spiropyran derivatives containing one or two gallic acid moieties with one, two, or three long alkyl chains were prepared. Acid‐induced spiro–protonated‐merocyanine isomerization induced mesomorphism for these materials. Equimolar mixtures of methanesulfonic acid and the spiropyran derivatives with one or two dodecyloxy chains exhibited smectic A phases, whereas the spiropyran derivatives containing the gallic acid moiety with three dodecyloxy chains showed hexagonal columnar phases. On the contrary, photoirradiation of the spiropyran compounds in the bulk liquid state did not lead to the induction of mesomorphism, although the merocyanine form was induced. These results suggest that these merocyanine derivatives with ionic and nonionic moieties cannot simply form nanosegregated LC structures. Complex formation of the merocyanine form with methanesulfonic acid may play a key role in the formation of LC molecular assemblies.     

Size and composition control of Pt-In nanoparticles prepared by seed-mediated growth using bimetallic seeds

A two-step method has been developed for precise size and composition control of bimetallic Pt-In nanoparticles. Very small (1.62 nm) PtIn seed nanoparticles with 1:1 metal ratio were prepared in the absence of capping agents followed by growth of Pt on their surface in the presence of oleyl amine as reducing and stabilizing agent. Nanoparticles with bulk compositions of Pt(4)In, Pt(3)In, and Pt(2)In could be synthesized with average diameter smaller than 3 nm. TEM, EDX, and XPS provided evidence for homogeneous growth without separate nucleation of pure platinum nanoparticles in the reaction solution. Pt(3)In nanoparticles were deposited onto SiO(2) surface by incipient wetness impregnation. Temperature-induced changes in the particle surface were monitored by in situ IR spectroscopy and CO adsorption. It was found that surface alloy composition of the particles could be tuned by using oxidizing or reducing atmospheres.     

High-performance liquid chromatographic assay of indomethacin in porcine plasma with applicability to human levels

A high-performance liquid chromatography (HPLC) assay is described for the determination of indomethacin in porcine plasma using acetonitrile to precipitate plasma proteins and for the one-step extraction. Calibration curves (using the internal standard method) are linear (r2 > 0.98) over the concentration range of 50.0 to 3000 ng/mL in both mobile phase and plasma. Precision, expressed as the inter- and intraday coefficient of variation (n = 5), is < 7% on the same day and < 5% between days at each plasma control sample of 300, 1000, and 3000 ng/mL, respectively. System precision, calculated as the coefficient of variation (n = 5), is < 7% at 3000 ng/mL of indomethacin, and the limit of quantitation in plasma is 50 ng/mL. The absolute recovery for both indomethacin and the internal standard (mefenamic acid) from plasma is over 97% (n = 3), and the concentrations do not deviate more than -2.9% to 2.4% from their actual values. The specificity of the method is confirmed. This technique is thus reported to be both rapid and specific. The real advantage is the small sample volume required (500 microL), which allows it to be considered for the quantitation of indomethacin in plasma from paediatric patients.     

Structural and photoluminescence investigation on the hot-wire assisted plasma enhanced chemical vapor deposition growth silicon nanowires

High density of silicon nanowires (SiNWs) were synthesized by a hot-wire assisted plasma enhanced chemical vapor deposition technique. The structural and optical properties of the as-grown SiNWs prepared at different rf power of 40 and 80 W were analyzed in this study. The SiNWs prepared at rf power of 40 W exhibited highly crystalline structure with a high crystal volume fraction, X_C of ～82% and are surrounded by a thin layer of SiO_x. The NWs show high absorption in the high energy region (E>1.8 eV) and strong photoluminescence at 1.73 to 2.05 eV (red–orange region) with a weak shoulder at 1.65 to 1.73 eV (near IR region). An increase in rf power to 80 W reduced the X_C to ～65% and led to the formation of nanocrystalline Si structures with a crystallite size of <4 nm within the SiNWs. These NWs are covered by a mixture of uncatalyzed amorphous Si layer. The SiNWs prepared at 80 W exhibited a high optical absorption ability above 99% in the broadband range between 220 and ～1500 nm and red emission between 1.65 and 1.95 eV. The interesting light absorption and photoluminescence properties from both SiNWs are discussed in the text.     

Detection of Bacterial Neutral Ceramidase in Diabetic Foot Ulcers with an Optimized Substrate and Chemoenzymatic Probes

Ceramidases (CDases) are important in controlling skin barrier integrity by regulating ceramide composition and affording downstream signal molecules. While the functions of epidermal CDases are known, roles of neutral CDases secreted by skin-residing microbes are undefined. Here, we developed a one-step fluorogenic substrate, S-B , for specific detection of bacterial CDase activity and inhibitor screening. We identified a non-hydrolyzable substrate mimic, C6 , as the best hit. Based on C6 , we designed a photoaffinity probe, JX-1 , which efficiently detects bacterial CDases. Using JX-1 , we identified endogenous low-abundance PaCDase in a P. aeruginosa monoculture and in a mixed skin bacteria culture. Harnessing both S-B and JX-1 , we found that CDase activity positively correlates with the relative abundance of P. aeruginosa and is negatively associated with wound area reduction in clinical diabetic foot ulcer patient samples. Overall, our study demonstrates that bacterial CDases are important regulators of skin ceramides and potentially play a role in wound healing.     

Confrontation of the BCF theory and computer simulation experiments with measured (R, σ) curves

A brief summary of crystal growth models – the surface diffusion model of Burton, Cabrera and Frank and computer simulation models – is given and these models are confronted with measured (R, σ) curves. It was found that the most (R, σ) curves measured so far can be fitted by BCF curves with 10⁻² ≲ σ₁ ≲ 10⁻¹ and C having an order of magnitude of 10⁻⁴ cm ≲ s⁻¹. ΔG turns out to be 12 ± 5 kcal ≲ mol⁻¹. – Some of the (R, σ) curves can be described better by a nucleus above nucleus formalism. The order of magnitude of A is 10⁻⁴ cm · s⁻¹ and 10⁻² ≲ B ≲ 10⁻¹. – It is concluded what kind of work should be done in future to check theoretical models.     

Characterization of fire retardant polymer blends by temperature resolved in-source pyrolysis mass spectrometry

The characterization of fire retardant polymer blends by temperature resolved in-source pyrolysis mass spectrometry (PYMS) is demonstrated with a few examples. Electron impact (EI) and electron capture negative ionization (ECNI) were used to identify the thermal degradation products of polymer blends containing brominated fire retardants. PYMS (EI mode) offers an analytical instrument for a fast analysis of unknown mixtures of polymers and for the presence of fire retardant additives. Under electron impact conditions, in vacuo, low-molecular weight additives like fire retardants mainly evaporate from the polymer matrix. PYMS (EI mode) has been used for the characterization of addition polymers like polystyrene and acrylonitrile-butadiene-styrene copolymer, and for condensation polymers like the polyester poly(butylene terephthalate). Applying electron capture negative ionization, at low argon pressure in the ionization chamber, a more realistic pyrolysis situation is created because the premature loss of volatile additives is suppressed. The selectivity of ECNI for electron accepting groups like bromine makes it possible to study the influence of brominated compounds on the degradation processes in the melt. This is demonstrated by our studies on polystyrene and acrylonitrile-butadiene-styrene copolymer. High-molecular weight pyrolysis products in the m/z range of 1000 - 2000 are detected for p-bromopolystyrene and for a blend of high impact polystyrene with the fire retardant system decabromodiphenyl ether/antimony(III) oxide. In addition to the formation of antimony bromides shown in earlier studies, the emission of the synergist antimony(III) oxide as a dimeric cluster (Sb₄O₆) or as a reduced Sb₄ cluster is observed under PYMS conditions.