Fast thermal desorption spectroscopy study of H/D isotopic exchange reaction in polycrystalline ice near its melting point

Using fast thermal desorption spectroscopy, a novel technique developed in our laboratory, we investigated the kinetics of HD isotopic exchange in 3 microm thick polycrystalline H2O ice films containing D2O layers at thicknesses ranging from 10 to 300 nm at a temperature of -2.0+/-1.5 degrees C. According to our results over the duration of a typical fast thermal desorption experiment (3-4 ms), the isotopic exchange is confined to a 50+/-10 nm wide reaction zone located at the boundary between polycrystalline H2O and D2O ice. Combining these data with a theoretical analysis of the diffusion in polycrystalline medium, we establish the range of possible values for water self-diffusion coefficients and the grain boundary widths characteristic of our ice samples. Our analysis shows that for the grain boundary width on the order of a few nanometers, the diffusivity of D2O along the grain boundaries must be at least two orders of magnitude lower than that in bulk water at the same temperature. Based on these results, we argue that, in the limit of low concentrations of impurities, polycrystalline ice does not undergo grain boundary premelting at temperatures up to -2 degrees C.     

Representation of a class of locally convex (M)-lattices

We prove a representation theorem for Hausdorff locally convex (M)-lattices which are Dedekind σ-complete, and whose topologies are order σ-continuous and monotonically complete. These turn out to be the weighted spaces c₀(T, H), defined in the paper for T ≠ and H ^T₊. We also characterize the dual of c₀(T, H), as the space l¹ (T, H) defined in the last section. The known representation (on c₀(T)) of Banach (M)-lattices with order continuous norm follows as a particular case. We obtain these results by first proving a new general isomorphism theorem, which seems to be of independent interest. Our notion of “monotonic topological completeness” is weaker than the usual completeness and seems to be very convenient in the framework of topological ordered vector spaces.     

Characteristics of polyurethane-based sustained release membranes for drug delivery

This paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications.      

Superacidic low-temperature cyclization of terpenols and their acetates

The superacidic low-temperature cyclization of terpenols and their acetates by fluorosulfonic acid represents a highly efficient chemo- and structurally selective and stereospecific process. Homoallylic alcohols (-isomers of cycloterpenols) are the products of cyclization of terpenols; the configuration of the hydroxymethyl group in the products is predetermined by the configuration of the allylic double bond in aliphatic or partially cyclized precursors. The cyclization of terpenyl acetates yields monoacetates of fully cyclized diastereomeric primary-tertiary -diols. Their stereochemistry also depends on the configuration of the allylic double bond in the starting substrates.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2494–2506, December, 1995.     

Superacidic cyclization of higher terpenoid acids and their esters

The superacidic cyclization of aliphatic and partially cyclized C₁₅–C₂₅ terpenoid acids and their esters proceeds structure-selectively and stereospecifically, affording -isomers of completely cyclized epimeric ,-unsaturated acids or esters; the configuration of their carboxylic or ester groups is predetermined by the configuration of the double bond conjugated with the carboxyl or ester groups in the starting compounds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2507–2513, December, 1995.     

New and automated MS<Superscript>n</Superscript> approaches for top-down identification of modified proteins

An automated top-down approach including data-dependent MS(3) experiment for protein identification/characterization is described. A mixture of wild-type yeast proteins has been separated on-line using reverse-phase liquid chromatography and introduced into a hybrid linear ion trap (LTQ) Fourier transform ion cylclotron resonance (FTICR) mass spectrometer, where the most abundant molecular ions were automatically isolated and fragmented. The MS(2) spectra were interpreted by an automated algorithm and the resulting fragment mass values were uploaded to the ProSight PTM search engine to identify three yeast proteins, two of which were found to be modified. Subsequent MS(3) analyses pinpointed the location of these modifications. In addition, data-dependent MS(3) experiments were performed on standard proteins and wild-type yeast proteins using the stand alone linear trap mass spectrometer. Initially, the most abundant molecular ions underwent collisionally activated dissociation, followed by data-dependent dissociation of only those MS(2) fragment ions for which a charge state could be automatically determined. The resulting spectra were processed to identify amino acid sequence tags in a robust fashion. New hybrid search modes utilized the MS(3) sequence tag and the absolute mass values of the MS(2) fragment ions to collectively provide unambiguous identification of the standard and wild-type yeast proteins from custom databases harboring a large number of post-translational modifications populated in a combinatorial fashion.     

Investigation of the products of the ozonolysis of larixol

On the ozonization of larixol in methanol followed by treatment with ammonium chloride, the main reaction products were 15,16,20-trisnorlabd-6-ene-8,13-dione and 6-hydroxy-8,13;8,14-diepoxy-15,20-bisnorlabd-14-one. When ozonization was performed in methanol in the presence of dimethyl sulfide or in methylene chloride in the presence of pyridine, 6,14-dihydroxy-8,13;8,14-diepoxy-15,20-bisnorlabdane and 6-hydroxy-14,50,20-trisnorlabd-8,13-dione predominated in the reaction products.Institute of Chemistry of the MSSR Academy of Sciences, Kishinev, and Institute of Organic Chemistry of the Bashkir Branch of the USSR Academy of Sciences, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 577–584, September–October, 1986.     

Transition events fluctuations in jump markovian dynamics. A general approach to Šolc's problem

We introduce a new formalism for computing the moments of transition events for nonhomogeneous Markov jump processes. Our method is applied directly to the master equation and does not involve the use of diffusion approximation. The general theory is applied to produce exact expressions for means and dispersions. For time homogeneous Markov processes with a finite number of connected states we are able to prove that both means and dispersions asymptotically increase linearly in time.     

Raman analysis of oxide cladded silicon core nanowires grown with solid silicon feed stock

Solid–liquid–solid (SLS) combined with Vapor-liquid–solid (VLS) growth mechanism has been used for synthesizing Core-clad silicon nanowires (SiNWs) by thermal annealing onto two different catalyst substrates (Au/Si and Ni/Ti/Si). It provides a novel method to synthesize SiNWs which is cost-effective, large-area-compatible and may give a higher degree of control of the end product, facilitated by the simple experimental process for further device applications. The first-order Raman peaks of the SiNWs were found to shift and to broaden asymmetrically in comparison to the c-Si Raman peak. Using a phonon confinement model, the average diameter of the wires can be estimated from the Raman spectra but are consistently lower than the diameters measured using high-resolution transmission electron microscopy. We interpret this as due to the confining contribution of the oxide clad. Due to the simplicity of the method, it could be adapted in industry for large scale synthesis of SiNWs with oxide clad for device fabrication, e.g., surround-gate field effect transistors.