Fourier transform infrared spectroscopy study on order-disorder transition in Langmuir-Blodgett films of 7-(2-octadecyloxycarbonylethyl)guanine before and after recognition to cytidine

Order-disorder transitions of 9-monolayer Langmuir-Blodgett (LB) films of 7-(2-octadecyloxycarbonylethyl)guanine (ODCG) before and after recognition to cytidine were investigated by Fourier transform infrared (FTIR) spectroscopy. The different order-disorder transitions suggest that molecular recognition between ODCG and cytidine influence these two LB films on the order-disorder process of alkyl tailchain. Cleavage of the multi-hydrogen bonds was also observed by the infrared spectroscopy at elevated temperature.     

Solid polymer electrolytes X: Preparation and characterizations of polyether–siloxane,organic–inorganic,hybrid nanocomposites complexed with lithium perchlorate

Organic–inorganic hybrid nanocomposites of poly(ethylene glycol)/siloxane were obtained via the sol–gel approach. In these composites, nanometric siloxane heterogeneity was embedded into a polymer matrix with a covalent bond at the interfaces. The ²⁹Si magic-angle spinning (MAS) spectrum exhibited a high degree of condensation through the relative abundance of T⁰ [RSi(OR)₃], T¹ [RSi(OR)₂(OSi)], T² [RSi(OR)(OSi)₂], and T³ [RSi(OSi)₃] silicone nuclei. The effect of lithium salt concentration on ionic interaction, conductivity, and thermal properties of these composite electrolytes were investigated by Fourier transform infrared spectroscopy, DSC, thermogravimetric analysis, alternating current impedance, and solid-state ⁷Li MAS NMR measurements. These observations indicated that the different types of complexes by the interactions of Li⁺ and ClO ions are formed within a hybrid host, and the formation of transient crosslinks between Li⁺ ions and the ether oxygens results in an increased glass-transition temperature of the polyether segment and decomposed rate of composite electrolyte. ⁷Li MAS NMR measurements revealed the changes in line shape of lithium resonances with different LiClO₄ contents, suggesting that a significant degree of ionic association is present in the polymer-salt complexes. The behavior of ion transport in these composite electrolytes was correlated with the interactions between ions and polymer host. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1928–1937, 2004     

Preparation of free-standing nanowire arrays on conductive substrates

By combining supercritical drying technique with AAO template-assisted electrodeposition, noncollapsed, vertically aligned, and free-standing nanowire arrays on a conductive Au film have been fabricated. We also demonstrate that these free-standing nanowire arrays can be feasibly used for fabricating nanowire-based electrically driven devices.     

Asymmetric catalysis with CO2: direct synthesis of optically active propylene carbonate from racemic epoxides

This communication describes a convenient route to optically active propylene carbonate by a catalytic kinetic resolution process resulting from the coupling reaction of CO2 and racemic epoxides using simple chiral SalenCo(III)/quaternary ammonium halide catalyst systems.     

A simplified approach for evaluation of the polarity parameters for polymer using the K coefficient of the Mark-Houwink-Sakurada equation

Since two solvent polarity parameters, e.g., the Et(30) defined by Reichardt and the pi* defined by Kamlet and Taft, respectively, plotted with the K coefficient of the Mark-Houwink-Sakurada equation, presented good linear fits, this paper suggests applying the extrapolating method in the same way as the Zisman plot to obtain similar polarity parameters for polymers. In order to verify those obtained polarity parameter values for various polymers, literature-reported polarity values determined using other techniques are referenced and indicate that this paper introduced a simplified approach that can be applied to evaluate the polarity parameters for polymers. In this paper, since we observe that various polymers are of interest to present absolutely different slope tendencies, e.g., positive and negative, it is also suggested that polarity properties of polymers may be reinterpreted.     

Peralkylated-beta-cyclodextrin used as gas chromatographic stationary phase prepared by sol-gel technology for capillary column

For the first time, three peralkylated-beta-cyclodextrins (beta-CD), permethylated-beta-CD, perethylated-beta-CD and perpentylated-beta-CD, were coated onto the fused-silica capillary by sol-gel method with simplicity and rapidity. Multiple steps in conventional column preparation technology were avoided. Also, these new columns demonstrated many inherent advantages, the main being the outstanding thermal stability (up to 300 degrees C), high number of theoretical plates, excellent column-to-column and run-to-run reproducibility, and pronounced selectivity for positional isomers and enantiomers. Using n-tridecane as a test reagent (k = 4.18), an efficiency value of 3520 theoretical plates/m was obtained on a sol-gel perpentylated-beta-CD capillary column (15 m x 0.25 mm I.D.). On the basis of the results, we proposed that the peralkylated-beta-CD, which has no terminal hydroxyl group, is encapsulated in the sol-gel network and the whole matrix is chemically bonded to the surface of the fused-silica tubing.     

Classifying G-protein coupled receptors with bagging classification tree

G-protein coupled receptors (GPCRs) play a key role in different biological processes, such as regulation of growth, death and metabolism of cells. They are major therapeutic targets of numerous prescribed drugs. However, the ligand specificity of many receptors is unknown and there is little structural information available. Bioinformatics may offer one approach to bridge the gap between sequence data and functional knowledge of a receptor. In this paper, we use a bagging classification tree algorithm to predict the type of the receptor based on its amino acid composition. The prediction is performed for GPCR at the sub-family and sub-sub-family level. In a cross-validation test, we achieved an overall predictive accuracy of 91.1% for GPCR sub-family classification, and 82.4% for sub-sub-family classification. These results demonstrate the applicability of this relative simple method and its potential for improving prediction accuracy.     

Synthesis of a novel C2-symmetric thiourea and its application in the Pd-catalyzed cross-coupling reactions with arenediazonium salts under aerobic conditions

[reaction: see text] A novel thiourea-based C2-symmetric ligand was synthesized, and its application in the palladium-catalyzed Heck and Suzuki coupling reactions of arenediazonium salts was evaluated. The reactions, which were performed at room temperature, without added base, and under aerobic conditions, produced product in 4 h with good yield. The corresponding arenediazonium salts were easily generated in one step from anilines.     

Simultaneous determination of <Emphasis Type="SmallCaps">L</Emphasis>-arginine and its mono- and dimethylated metabolites in human plasma by high-performance liquid chromatography–mass spectrometry

A simple, fast, sensitive, and reproducible isocratic liquid chromatography–mass spectrometry (LC-MS) method coupled with an atmospheric pressure chemical ionization (APCI) interface for simultaneous separation and determination of L-arginine (ARG) and its methylated metabolites, N-monomethyl-L-arginine (MMA), N^G,N^G-dimethylarginine (asymmetric dimethyl arginine, ADMA), and N^G,N^G-dimethylarginine (symmetric dimethyl arginine, SDMA), in human plasma is presented. Sample pretreatment is not required other than deproteinization with 5-sulfosalicylic acid (5-SSA). Satisfactory chromatographic separation was achieved on a 2.0×150-mm Shimadzu VP-ODS column by using a mobile phase consisting of water/acetonitrile (90/10, v/v) containing 0.5% trifluoroacetic acid (TFA). Positive selective ion monitoring (SIM) mode was chosen for quantification of each analyte. The positively protonated molecular ions [M+H]⁺ of ARG, MMA, ADMA, and SDMA were monitored at m/z 175, 189, 203, and 203, respectively. L-Homoarginine was used as the internal standard (IS) for the assay. The limits of quantification (LOQs) were found to be 1.0 mol L^–1 for ARG, and 0.2 mol L^–1 for MMA, ADMA, and SDMA. The inter-assay precision and accuracy were in the range of 1.8–4.9% and –3.0–5.0%, respectively. The intra-assay precision and accuracy were in the order of 1.7–4.6 and –2.6–4.0%, respectively. The recoveries were between 90.0 and 106.6%. The levels of ARG, MMA, ADMA, and SDMA in human plasma were also determined using the developed method.