Acid hydrolysis of carboxymethylcellulose of low degree of substitution

Cotton cellulose was swollen in a sodium hydroxide solution and carboxymethylated by a two-bath method for different periods of time for each process. The kinetics of acid hydrolysis and the crystallinity of the swollen and carboxymethylated samples were measured. The proportion of broken bonds, rate constants for hydrolysis, and permeability of cellulose to hydrolyzing agents were calculated. The susceptibility of glycosidic linkages to acid hydrolysis was improved by carboxymethylation more than by swelling in alkali. The increased accessibility of carboxymethylcellulose to acid was regarded as a consequence of increased intra-and intercrystalline swelling and of the glycosidic bonds' weakness caused by the electron-attracting carboxymethyl group on the C-6 position.     

Chemical modification of the surface of a sulfonated membrane by formation of a sulfonamide bond

This paper describes a novel approach for the surface modification of a cation-exchange membrane, bearing sulfonate groups, by a cationic layer. The modification procedure involved the chlorosulfonation of the sulfonate groups of the base membrane with thionyl chloride, followed by a reaction with a diamine to yield a sulfonamide bond and a terminal amine. The latter could be quaternized by reaction with methyl iodide or protonated by soaking in acidic media. The membranes were characterized in detail by attenuated total reflectance Fourier transform infrared and X-ray photoelectron spectroscopies as well as elemental analysis to confirm that the above reactions occurred. The selectivity of these membranes toward the electrochemically assisted transport of protons versus Zn2+ metallic cations was determined during an electrodialysis in a two-compartment electrochemical cell. The data indicate a significant decrease of the transport of the metallic cations following modification of the membrane with the cationic layer. The later allows for the transport of protons from the catholyte to the anolyte compartment with much improved selectivity since the divalent cations are excluded from the membrane due to the electrostatic barrier of the cationic layer.     

Study of the mechanism of formation of transparent polyacrylonitrile

The kinetics of bulk polymerization of acrylonitrile, leading to a transparent polymer, was studied. The reaction was followed by a dilatometer specially designed for high degrees of conversion and for continuous supply of monomer during the reaction. The last stages of polymerization were followed by density determinations. It was found that the kinetic scheme did not show any irregularities, and that the major condition for obtaining a transparent polymer is a continuous supply of monomer to fill up the gaps formed by the contraction during the polymerization process.     

Thermocrystallization flow of nonfreezing water films on the surface of capillaries

The rates of mass transfer under the influence of a temperature gradient between the menisci of ice in a thin quartz capillary are measured. The mass transfer rate is determined by the diffusion of vapor and by the flow of a nonfrozen polymolecular adsorption film over the capillary surface. It is shown that the flow of the film is attributable neither to the thermoosmotic nor to the thermocapillary flow. The flow rate of a nonfrozen film is well described by a thermocrystallization transfer equation derived earlier, the thermocrystallization transfer being controlled by the water-ice phase transition heat.     

The Kinetics of Thermal Decomposition of Polymers

The rate equations for the thermal decomposition of a polymer by a random scission reaction followed by evaporation of low molecular weight species are solved using a different approach to that used by previous workers. The results obtained are in agreement with their conclusions.     

Prediction of chemical structure of aromatic hydrocarbons by pattern recognition of spectral lines obtained by fluorescence spectrometry in a supersonic jet

A technique based on pattern recognition of data obtained by supersonic jet spectrometry is employed for the prediction of chemical structure. The degree of similarity is evaluated quantitatively by calculating a cross correlation factor between sample and reference molecules. A probability density function is determined by fitting the data to a specified equation. The functional group and its position are also predicted by a similar technique. The pattern recognition provides a method for prediction of the chemical structure and is applicable to samples that have not been examined by supersonic jet spectrometry.     

Application of constant rate thermal analysis (CRTA) to the synthesis of silicon nitride by carbothermal reduction of silica

The carbothermal reduction of silica under flowing nitrogen at a pressure of 1 atm has been followed by means of a CO IR detector attached to the gas output of a high temperature tubular furnace. The control of the reaction temperature is carried out by interfacing the analogical output of the IR detector to a controller that allows to monitor the sample temperature in such a way that the concentration of CO generated in the reaction is maintained constant at a value previously selected by the user. The reaction rate at a particular concentration of CO can be fixed by properly selecting the flow rate of the reactive gas. The influence of the reaction rate and the CO concentration on both the reaction temperature and the structure of the final product of the reaction are analysed.     

Synthesis and conformational analysis of 17alpha,21-cyclo-22-unsaturated analogues of calcitriol

Six new calcitriol analogues, conformationally restricted at their side chain by the introduction of both a cyclopropane ring at C17-C20 and a double or triple bond at C22, were synthesized using the Wittig-Horner approach to construct the triene system. The six CD-ring and side-chain bearing fragments were prepared from ketone 14 by a divergent route to generate both series of epimers at C20, followed by stereoselective cyclopropanation. The (E)-alkenyl side chain was synthesized by means of a Wittig reaction. The alkynyl side chain was prepared by Corey-Fuchs homologation, followed by alkylation. The (Z)-alkenyl side chain was prepared from the previous alkyne by partial hydrogenation. The 20-epi analogues bind more strongly to VDR than the corresponding analogues with the C20 natural stereochemistry. These results can be reasoned by conformational analysis and hydrophobic interactions with the VDR ligand-binding domain.     

Polymerization of cyclic derivatives of uracil and thymine

Cyclic derivatives of uracil and thymine were synthesized from their corresponding 1-(2′-chloroethyl) derivatives by dehydrochlorination. These compounds were found to undergo a variety of reactions, giving many valuable derivatives of uracil and thymine. The cyclic derivatives, as monomers, were polymerized with a cationic initiator by a unique ring-opening process. The polymerization proceeded by ring opening with isomerization of the pyrimidine ring to give a polymer in which pyrimidine rings were connected with ethylene between N-1 and N-3 or O-4 in the pyrimidine ring. The structure of these polymers was determined by nuclear magnetic resonance (NMR), ultraviolet (UV), infrared (IR), and mass spectra. The structure was affected by polymerization temperature.     

Anionic Polymerization of Methyl Methacrylate in the Presence of Piperidine

Anionic polymerization of methyl methacrylate (MMA) initiated by lithium tert-butoxide (t-BuOLi) was investigated in different mixtures of benzene and piperidine. The latter compound activates the associated alkoxide, as evidenced by the observed increase in the rate of polymerization, proportional to piperidine concentration and also by the lowering of the overall kinetic order of the polymerization reaction with respect to initial monomer concentration. However, at higher piperidine concentration the rate of the polymer growth significantly decreases after a short period of time; a probable reason for this retardation or termination effect is the decay of active growth centers by a termination reaction with the methacrylate carbonyl group. The molecular weight of the polymer is significantly lowered by even a small addition of piperidine as a result of increased initiator efficiency that leads to a higher absolute concentration of active centers and approaches the theoretical limit given by the stoichiometric ratio of monomer and initiator concentrations. The microstructure of the product is affected by the presence of the polar solvent to a considerably lesser degree than in the case of classical alkylmetal initiators. The isotacticity slowly decreases with piperidine concentration over the whole investigated range. The high stability of the complex active center of growth formed by the alkoxide initiator and also the gradual change in the character of the ionic pair at the end of the growing polymer chain are responsible for the relatively small changes of the microstructure.     

Analysis of precision of activation analysis method

The precision of an activation analysis method prescribes the estimation of the precision of a single analytical result. The adequacy of these estimates to account for the observed variation between duplicate results from the analysis of different samples and materials, is tested by the statistic T, which is shown to be approximated by a chi-squared distribution. Application of this test to the results of determinations of manganese in human serum by a method of established precision, led to the detection of airborne pollution of the serum during the sampling process. The subsequent improvement in sampling conditions was shown to give not only increased precision, but also improved accuracy of the results.     

A formal total synthesis of the salicylihalamides

The synthesis of the macrolactone 23 is described. The synthesis features a diastereoselective hydroboration of the chiral alkene 17 followed by a Suzuki cross-coupling reaction with the benzoate 5. The resulting seco acid 21 was converted to the macrolactone 23 by a Mitsunobu lactonization using immobilized triphenylphosphine. The stereogenic centers in the alkene 17 were established by a Noyori reduction of the beta-keto ester 8 and an Evans aldol reaction. The synthesis illustrates the conversion of a syn aldol product to the corresponding anti product by inversion of the methyl-bearing center.     

Influence of the morphology of samples in the pyrolysis of PVC

PVC was used as a model substance to study the dependence of thermal measurement data on the preparation and morphological characteristics of samples The PVC treated was a commercially available suspension polymer, Ongrovil S 155, produced by the Borsodi Vegyi Kombinát. The whole thermal process was followed by TG and DTG measurements in air and argon atmospheres by means of a Du Pont 990 Thermoanalyzer. Evolved-gas analysis was performed with a home-made apparatus. Pyrolysis gas chromatography was accomplished using a Hamilton type pyrolyzer and a Carlo Erba Chromatograph furnished with a flame ionization detector. The investigations showed benzene and other components to be evolved from the initial polymer and an alteration depending on the morphological characteristics of the samples. This was suggested to be due to the different mechanisms of thermal degradation of the PVC.     

Synthesis of oxa-bridged analogues of farnesyltransferase inhibitor RPR 115135

Two synthetic routes to new oxygen-bridged analogues of farnesyltransferase inhibitors are described that follow either a [3 + 2]/[4 + 2] or a [4 + 2]/[3 + 2] sequence of reactions. The first approach has been achieved by reacting the in situ generated phenylisobenzofuran (PIBF) 4 with pyrroline 5a and has led stereoselectively to racemic 18, which was transformed in a few steps into the target molecule 2. The second pathway relies on a key intermediate 6, obtained either by condensation of PIBF with methyl acrylate, followed by a deprotonation/selenation and an oxidation/elimination sequence, or by cycloaddition between PIBF and alpha-phenylselenoacrylate 11, followed by the same oxidation/elimination sequence. The reaction of 6 with amino dipole 7 gives diastereoselective access to pyrrolidine 25, a precursor of the second target 3, an epimer of 2.     

Investigation of the origin of archaeological glass artefacts by means of pattern recognition

The origin of medieval glass artefacts is studied by using a supervised learning technique, which is shown to be helpful when samples cannot be identified by typical design and appearance. A set of seventy pieces of glass was analyzed for ten trace elements by optical emission spectrography. The data matrix of 33 known objects from five origins was evaluated by multivariate variance and discriminant analysis in a training step. The extracted non-elementary discriminant functions were used to classify the 37 unidentified samples. The classification result is discussed in terms of its cultural/historical information content.     

An insight into the process of tablet formation of microcrystalline cellulose

The present paper aims to show whether the shrinking of the microcrystalline cellulose (MCC) tablets can be derived from underlying processes and whether these processes can be visualized on a nanoscale level. Tableting of MCC was performed on an instrumented eccentric tableting machine to a maximum relative density (ρ_rel,max) of 0.90 of the tablets. The apparent density of the tablets was analyzed by helium pycnometry after tableting. The breaking surface of a MCC tablet was analyzed directly after tableting continuously by video in an environmental scanning electron microscope (ESEM) at constant humidity. Further the breaking surface was analyzed by transmission electron microscopy (TEM) after freeze fracturing. The results show that firstly apparent density by helium pycnometry increases after tableting and that secondly inside the tablet the fiber strength decreased while also the gaps between the fibers increased as was visualized by ESEM. Further the results by TEM indicate that the decrease in fiber strength is caused by a parallel orientation of the MCC microcrystals which is induced by a mechanical activation due to tableting. In conclusion the measured shrinking MCC tablets after tableting is caused by processes on a nanoscale level.     

Analysis of precision of activation-analysis methods

The precision of an activation-analysis method prescribes the estimation of the precision of a single analytical result. The adequacy of these estimates to account for the observed variation between duplicate results from the analysis of different samples and materials, is tested by the statistic T, which is shown to be approximated by a chi(2) distribution. Application of this test to the results of determinations of manganese in human serum by a method of established precision, led to the detection of airborne pollution of the serum during the sampling process. The subsequent improvement in sampling conditions was shown to give not only increased precision, but also improved accuracy of the results.     

Formation and plasmonic response of self-assembled layers of colloidal gold nanorods and branched gold nanoparticles

The plasmonic properties of self-assembled layers of rod- and branched-shaped gold nanoparticles were investigated using optical techniques. Nanoparticles were synthesized by a surfactant-guided, seed-mediated growth method. The layers were obtained by gradual assembly of nanoparticles at the interface between a polar and a nonpolar solvent and were transferred to a glass slide. Polarization and angle-dependent extinction measurements showed that the layers made of gold nanorods were governed by an effective medium response. The response of the layers made by branched gold particles was characterized by random light scattering. Microscopic mapping of the spatial mode structure demonstrates a uniform optical response of the nanoparticle layers down to a submicrometer length scale.     

Study of cryostructurization of polymer systems

The influence of freezing of a reaction mass on the properties of the resulting covalently cross-linked gels is exemplified by a system composed of a solution of chitosan in aqueous acetic acid and glutaric dialdehyde serving as a cross-linking agent. The freezing is shown to lead to a noticeable decrease of critical concentration of gelation as compared with the reactions of polymeric chain cross-linking in ordinary conditions. Consideration is given to some properties of three-dimensional networks obtained by cryostructurization.     

Immobilization of ultra-thin layer of monoclonal antibody on glass surface

When preparing an affinity column and a biosensor, it is desirable to immobilize a unimolecular layer of pure protein on a matrix. In this work, we tried to immobilize a monoclonal antibody on a surface of a glass test-tube as a model, to confirm the stability of this ultra-thin layer by an enzyme immunoassay, and to estimate the thickness of the layer on a slide glass by Fourier transform infrared reflection spectrometry. A new test-tube was washed and dried. The tube was filled with 5% 3-aminopropyltriethoxysilane. The 3-aminopropylsilylated surface was treated with glutaraldehyde and 5.6.10(-2) mg/ml solution of a normal mouse monoclonal antibody. The Schiff base between glutaraldehyde and the antibody was further reduced with 7.9.10(-3)% NaBH4. The tube was washed with 0.05% Tween 20 to block non-specific binding. The antibody immobilized on the surface was measured by an enzyme immunoassay based on a reaction of anti-mouse immunoglobulin G labelled with alkaline phosphatase, with which p-nitrophenol was produced from p-nitrophenylphosphate as a substrate. Meanwhile, various amounts of the antibody were immobilized on slide glasses in the same manner. The antibody on each surface was measured by Fourier transform infrared reflection spectrometry. The antibody immobilized under the final conditions was detectable by the enzyme immunoassay, and stable at 4 degrees C for ten days. The antibody on the slide glass was a unimolecular layer, as judged from the Fourier transform infrared spectra referred to -CONH- band semiquantitatively. Thus, we found the optimal conditions for immobilizing an ultra-thin layer of the monoclonal antibody on the glass surface.(ABSTRACT TRUNCATED AT 250 WORDS)