Kinetics of thermoelectric signals under nanosecond laser heating of mercury in aqueous electrolyte solutions

Acetaldehyde oxidation to form acetic acid is enhanced by oxygen adsorbing ad-atoms to a great extent. At the same time, the oxidation is enhanced by the S_hole control by Bi, Te, Se and S ad-atoms, which do not adsorb oxygen. The number of unoccupied Pt sites isolated by these inactive ad-atoms (S_hole), which is available for reactions, is less than that required for the formation of poisoning species but equal to that required for the oxidation, resulting in the inhibition of the poison formation reaction and the enhancement of the oxidation. The same type of enhancement, that is, the enhancement both by the S_hole control by ad-atoms and by oxygen adsorbing ad-atoms, was previously found in the enhancement of formaldehyde oxidation by ad-atoms.     

Comparative determination of uranium in rock phosphates and columbite by ICP-OES,alpha &; gamma spectrometry

During this work selective separation of uranium from rock phosphate and columbite mineral was done before its quantitative estimation by using Inductively Coupled Plasma Optical Emission Spectrometery (ICP-OES). Uranium from the rock phosphate and columubite was extracted by sodium peroxide fusion followed by leaching in 2 M HNO₃. To avoid spectral interference in the estimation of uranium by ICP-OES, the selective separation of uranium from the leachate was carried out by using two different extractants, 30% Tributyl Phophates (TBP) in CCl₄ and a equi-volume mixture of Di(2-ethylhexyl) phosphoric acid (D2EHPA) & TBP in petrofin. Uranium was stripped from the organic phase by using 1 M ammonium carbonate solution. Determination of uranium by ICP-OES was done after dissolving the residue left after evaporation of ammonium carbonate solution in 4% HNO₃. The concentration of the uranium observed in the rock phosphates samples was 40–200 μg g⁻¹ whereas in columbite samples the concentration range was 100–600 μg g⁻¹. Uranium concentration evaluated by ICP-OES was complimented by gamma & alpha spectrometry. Concentration of uranium evaluated by gamma spectrometry in case of rock phosphate and coulmbite was in close agreement with the uranium content obtained by ICP-OES. Uranium determination by alpha spectrometry showed only minor deviation (1–2%) from the results obtained by ICP-OES in case of rock phosphates whereas in case of coulmbites results are off by 20–30%.     

Friedel-Crafts Polymers. 6. Friedel-Crafts Polycondensation of p-Xylylerte Dibromide with Salicylic Acid and β-Resorcyiic Acid

Polymers were prepared by condensing p-xylylene dibromide separately with salicylic acid and β-resorcylic acid in the presence of anhydrous ferric chloride in dioxane. The polymer samples_were characterized by elemental analysis, by IR spectral study, by M determined by vapor pressure osmometry, by nonaqueous conducto-metric titration in pyridine, by TGA in air, and by viscosity measurements of polymer solutions in DMF. Polymeric metal chelates of Cu²⁺, Co²⁺, Zn²⁺, Ni²⁺, and Fe³⁺ with polymer samples were prepared and characterized by elemental analysis, by IR spectral study, and by TGA in air. The chelation ion-exchange properties of the polymer samples were studied by employing the batch equilibration method.     

Synthesis and characterization of chitosan-based polyurethane elastomer dispersions

Abstract  

A number of aqueous polyurethane dispersions were synthesized by the reaction of poly(ε-caprolactone) and isophorone diisocyanate, extended with different mass ratios of chitosan and dimethylol propionic acid. Their chemical structures were characterized by using FTIR, ¹H NMR, and ¹³C NMR spectroscopy, and thermal properties were determined by TGA. Incorporation of chitosan into the polyurethane backbone improved thermal stability. The hydrophilicity of the prepared polymers was also examined by contact angle measurements. For all samples, the contact angles increased by increasing the amount of chitosan. The increased contact angle is ascribed to the decrease of the hydrophilicity of the polyurethanes, which is reduced by the increasing amount of chitosan with respect to dimethylol propionic acid chain extender.     

超细CeO2的微波辅助加热合成及其抛光性能

引言铈基抛光粉因具有发削能力强,抛光时间短、抛光精度高、操作环境清洁、比其他抛光粉的使用效果佳等优点,被人们称为抛光粉之王".     

Probing the Interaction of the Hydroxy Group at C(4) of Lactone‐Type Inhibitors with β‐Glucosidases and β‐Galactosidases

The inhibition of the β‐glucosidases from sweet almonds and from Caldocellum saccharolyticum by the 4‐amino‐4‐deoxy lactam 11 , the 4‐deoxy lactam 12 , and the corresponding imidazoles 13 and 14 was compared to the inhibition by the hydroxy analogues 1 and 3 . Substitution of the OH group at C(4) by an amino group or by hydrogen weakened the inhibition by ΔΔG_diss = + 1.9 to + 3.1 kcal/mol. Similarly, the inhibition of the β‐galactosidase from bovine liver and from E. coli by the 4‐deoxy lactam 12 and the imidazole 14 , as compared to the one by the galacto‐configured lactam 9 and imidazole 10 , is weakened by deoxygenation at C(4) (ΔΔG_diss = + 2.6 and 4.5 kcal/mol, resp.). The effect of these substitutions on the inhibition of the C. saccharolyticum β‐glucosidase is slightly stronger than the one on the sweet almonds β‐glucosidases. The effect is also stronger on the inhibition by the imidazoles than by the lactams, and depends on the flexibility of the inhibitors. The amino and deoxy lactams 11 and 12 were prepared from the galactonolactam‐derived triflate 17 by substitution with azide and hydride, respectively, followed by hydrogenation. Azidation of the galacto‐configured imidazopyridine‐derived triflate 24 and hydrogenation gave the amino‐imidazole 13 . The deoxy lactam 20 was transformed to the manno‐ and gluco‐configured deoxy‐imidazoles 29 and 30 via the thionolactam 28 . Hydrogenolytic deprotection of 30 gave the deoxy‐imidazole 14 .     

Selectin Receptors 4: Synthesis of Tetrasaccharides Sialyl Lewis A and Sialyl Lewis X Containing A Spacer Group1,2

ABSTRACT

Synthesis of two isomeric tetrasaccharides, namely Neu5Acα(2→3)Galβ(1→3)[Fucα(1→4)GlcNAcβ (sLe^a) and Neu5Acα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ (sLe^x) as 3-aminopropyl glycosides is described. Preparation of these compounds was performed by sialylation of selectively protected trisaccharides Le^a and Le^x which contain three unsubstituted OH groups at positions 2, 3 and 4 of Gal residue. Glycosylation of Le^x trisaccharide with ethylthio sialoside under promotion by NIS and TfOH in acetonitrile was effective and regio- and stereoselective to give sLe^x derivative in 81% yield. In contrast, sialylation of the Lc^a acceptor was accompanied by a variety of undesirable by-processes, namely. N-thioethylation of the GlcNAc residue, β-sialylation, and lactonisation. In order to improve the yield of sLc^a tetrasaccharide the glycosylation of Le^a acceptor by sialyl donors of ethyl and phenyl thioglycoside (promoted by NIS-TfOH or NBS-Bu₄NBr), xanthate (promotion by NIS-TfOH mixture or MeOTf) and phosphite (promoted by TMSOTf) types was also studied. Among the reactions investigated the glycosylation by phenyl thioglycoside sialoside promoted by NIS-TfOH gives the best yield (39%) of sLe^a tetrasaccharide product.     

X-ray, Raman and FTIRS studies of the microstructural evolution of zirconia particles caused by the thermal treatment

Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO₃)₂ solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 °C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO₂. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) already after a mild calcination at 500 °C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600-650 °C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM.     

The structure of granticin and of granticin B. The crystal structure of tri-O-acetyl-O-iodoacetyl-granaticins

The crystal structure of tri-O-acetyl-O-iodoacetyl-granaticin has been determined by X-ray analysis of threedimensional diffractometer intensity data. The crystals are orthorhombic, a = 17.85, b = 14.90, c = 11.26 Å, Z = 4, space group P2₁2₁2₁. The molecular structure was established by the heavy atom method and refined by full-matrix least-squares analysis. The molecular constitution and configuration is given by formula II. The chirality was determined by the use of anomalous dispersion effects.     

Extracellular oxidation of D-glucose by some members of the Enterobacteriaceae

Extracellular D-glucose oxidation by 5 enterobacterial species was studied with the purpose of selecting conditions useful for taxonomic studies. Extracellular production of gluconate from ¹⁴C-glucose by bacterial cells was evidenced by DEAE-cellulose paper chromatography. Escherichia coli oxidized glucose only when pyrroloquinoline quinone (PQQ) was added, whereas Serratia marcescens, Yersinia frederiksenii, Erwinia cypripedii and Cedecea lapagei oxidized D-glucose without added PQQ. 2-Deoxyglucose was found to be an excellent non-metabolized analogue of D-glucose in oxidation experiments. D-glucose oxidation was inhibited by KCN, p-chloromercuribenzoic acid and carbonyl cyanide m-chlorophenylhydrazone; and activated by p-benzoquinone. Iodoacetate had no action. Comparative cellulose thin-layer chromatography including 2-ketogluconate and 2,5-diketogluconate (produced by Janthinobacterium lividum) as standards, showed that gluconate was oxidized to 2-ketogluconate by S. marcescens and E. cypripedii, and 2-ketogluconate was oxidized to 2,5-diketogluconate by E. cypripedii. The diversity of D-glucose oxidation products in the Enterobacteriaceae could have some taxonomic applications.     

Consecutive captures of electrons and positrons in the positron spur by HgCl2 and halide detachment in polar solvents

In polar solvents (water, methanol and DMSO), HgCl₂ inhibits positronium formation by quasi-free electron scavenging. In methanol, this inhibition possibly leads to fast detachment of Cl^- followed by positron capture to form a bound-state, [Cl^-e⁺]. In the other solvents, the positron appears to react with the newly formed radical anion, HgCl^-₂, before Cl^- detachment can occur. The sequence of electron scavenging by HgCl₂ followed by positron capture by the newly formed anion is confirmed by examining the effect of adding competing electron scavengers to the solutions.     

Characterisation of antibodies to chloramphenicol, produced in different species by enzyme-linked immunosorbent assay and biosensor technologies

Six polyclonal antisera to chloramphenicol (CAP) were successfully raised in camels, donkeys and goats. As a comparison of sensitivity, IC₅₀ values ranged from 0.3 ng mL⁻¹ to 5.5 ng mL⁻¹ by enzyme-linked immunosorbent assay (ELISA) and from 0.7 ng mL⁻¹ to 1.7 ng mL⁻¹ by biosensor assay. The introduction of bovine milk extract improved the sensitivity of four of the antisera by ELISA and two by biosensor assay; a reduction in sensitivity of the remaining antisera ranged by a factor of 1.1-2.6. Porcine kidney extract reduced the sensitivity of all the antisera by a factor ranging from 1.1 to 7 by ELISA and a factor of 1.5 to 4 by biosensor. A low cross-reactivity with thiamphenicol (TAP) and florfenicol (FF) was displayed by antiserum G2 (1.2% and 18%, respectively) when a homologous ELISA assay format was employed. No cross-reactivity was displayed by any of the antisera when a homologous biosensor assay format was employed. Switching to a heterologous ELISA format prompted three of the antisera to display more significant cross-reactivity with TAP and FF (53% and 82%, respectively, using D1). The heterologous biosensor assay also increased the cross-reactivity of D1 for TAP and FF (56% and 129%, respectively) and of one other antiserum (G1) to a lesser degree. However, unlike the ELISA, the heterologous biosensor assay produced a substantial reduction in sensitivity (by a factor of 6 for D1).     

Substituent effect on ionisation potential in a series of related molecules: A theoretical study in a molecular orbital framework

The effect of replacing the hydrogen atoms in thioformaldehyde by halogen atoms (F, Cl) on the ionisation potential of the non-bonding electron is analysed by using the Hellman-Feynman theorem, regarding the nuclear charge of the substituent as a parameter in the many-electron Hamiltonian. The trends predicted by our theory nicely agree with the relevant ionisation potentials computed either by applying Koopmans’ theorem or by the ΔE _SCF method. For the carbonyls, avaible experimental data indicate the reliability of our prediction.     

Mass spectra of Sceletium alkaloids

The mass spectra of several naturally occuring Sceletium alkaloids, as well as several synthetic variants, have been investigated. Techniques used include high resolution mass measurements, analysis of metastable transitions by the technique of ion defocusing and specific deuterium labeling in conjunction with low resolution mass spectrometry. Characteristic major fragmentation pathways have been determined for four basic structure types studied: the cis-3a-aryl-octahydroindole ring system, exemplified by mesembrine; its 2,3-pyrido analog, Sceletium A₄; the seco series of pyridine bases, represented by tortuosamine; and the seco analog of the mesembrine-type represented by tortuosamine; and the seco analog of the mesembrine-type represented by dehydrojoubertiamine.     

Structure and mechanism formation of polyelectrolyte complex obtained from PSS/PAH system: effect of molar mixing ratio, base–acid conditions, and ionic strength

Colloidal dispersions of polyelectrolyte complexes were prepared in aqueous solutions. We have used mixtures containing the strongly charged anionic polyelectrolyte sodium polystyrene sulfonate (PSS) and the weak cationic polyelectrolyte polyallylamine hydrochloride (PAH). Both polymers have the same molecular weight. The complexes were obtained by adding drop by drop a solution of the anionic polyelectrolyte to excess cationic polyelectrolyte. In these conditions, sodium polystyrene sulfonate and polyallylamine hydrochloride self-assembled in nanometer-range complexes; the self-assembly is driven by electrostatic interactions, as well as by entropy changes due to counterion release. The electrostatic interactions were controlled in several ways: by changing the C _PSS/C _PAH concentration ratio, by modifying the pH (and thus the protonation degree of polyallylamine hydrochloride), and by adding sodium chloride (screened interactions). Dynamic light scattering experiments demonstrated that the hydrodynamics radius of the polyelectrolyte complex increases, changing from soluble to insoluble complex formation, when some physicochemical parameters are increased: the concentration ratio between polyelectrolytes, the sodium chloride concentration, and pH. Zeta potential measurements, as a function of the C _PSS/C _PAH concentration ratio, as well as of pH and ionic strength, allow us to state that the resulting particles have a structure constituted by a neutral core surrounded by a positively charged shell. The polyelectrolyte complexes have globular shapes, as observed by electron microscopy.     

Friedel-Crafts Polymers. 5. Friedel-Crafts Polycondensation of p-Xylylene Dichloride with Salicylaldehyde and o-Hydroxyacetophenone

Polymers were prepared by condensing p-xylylene dichloride (PXDC) separately with salicylaldehyde (SAL) and o-hydroxy-acetophenone (OHAC) in the presence of anhydrous ferric chloride in dioxane. The polymer samples were characterized by elemental analysis, measurement of their M by vapor pressure osmometry, by nonaqueous conductometric titration in pyridine, by IR spectral study, by TGA in air, and by viscometric study in DMF. The ion-exchange capacities of these polymeric ligands for selected metal ions were measured by the batch equilibration method and compared. Polymeric metal chelates of PXDC-SAL and PXDC-OHAC polymer samples with Cu^{2 +}, Ni²⁺, Co²⁺, Fe³ and Zn^{2 +} were prepared and characterized by elemental analyses, by IR spectral study, and by thermal analyses.     

The effect of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water

The influence of crystallinity and crosslinking on the depression of the glass transition temperature in nylon 6 by water has been investigated by dynamic mechanical methods. Radiation crosslinking by high-energy electrons was effective in preventing morphological changes during the measurement of the incremental change in heat capacity (ΔC_p) at T_g, which was performed by differential scanning calorimetry. The experimentally determined value of ΔC_p, when normalized to account for the crystalline phase, was found to deviate from a linear two-phase relation and was reduced further than would be expected based on this model. It is proposed that nylon 6 is best described by a three-phase model which consists of a crystalline domain, a wholly amorphous domain, and an “intercrystalline” region. The importance of this in explaining the relatively large depression of T_g by small quantities of water is illustrated by applying equations derived to account for the compositional dependence of T_g in polymerdiluent mixtures, based on a classical thermodynamic interpretation of the glass transition phenomenon.     

Theoretical Study on Destruction Mechanism of 2,3,7,8-TCDD by O3 and NO3

In order to improve the destruction effciency of dioxins and also for developing new dioxin control technology, the destruction mechanisms of 2,3,7,8-tetrachlorodihenzo-p-dioxin (2,3,7,8-TCDD) by O₃ and NO₃, were investigated employing quantum chemical calcula-tions. For involved reactions, the microcosmic reaction processes were analyzed and de-picted in detail based on geometry optimizations made by the B3LYP/6-31G(d) method. At the same time, the reaction activation energies were also calculated at the MP2/6-311G(d,p)//B3LYP/6-31G(d) level. Configuration analysis indicated that 2,3,7,8-TCDD could be destroyed by O₃ and NO₃ in two different ways. The destruction of 2,3,7,8-TCDD by O₃ proceeded via the addition of O₃ and the cleavage of C=C while the destruction of 2,3,7,8-TCDD by NO₃ proceeded via the substitution of chlorine by NO₃. Calculated re-sults show that, the activation energy of the destruction reaction of 2,3,7,8-TCDD by NO₃ (267.48 kJ/mol) is much larger than that of the destruction reaction of 2,3,7,8-TCDD by O₃ (51.20 kJ/mol). This indicated that the destruction of 2,3,7,8-TCDD by O₃ is much more effcient than that of 2,3,7,8-TCDD by NO₃. The reason why the activation energy for the destruction reaction of 2,3,7,8-TCDD by NO₃ is so large, is also discussed.     

Mechanism of the reaction of neutral and anionic N-nucleophiles with α-halocarbonyl compounds

N-Acylalkylation of neutral and anionic N-nucleophiles with α-halocarbonyl compounds was investigated by quantum chemical methods in terms of the density functional theory and by experimental methods for 2,3-dihydroimidazo[2,1-b]quinazolin-1(10)H-5-one, its N-anion, and simpler model structures. High reactivity of these reagents is determined primarily by stabilization of transition states (TS) by bridge bonds involving halogen or nitrogen atoms rather than by conjugation, as has been commonly accepted. Bridged TS are formed by both the substitution mechanism S _N 2 and the addition-elimination mechanism. α-Haloalkyl-substituted zwitterions, which are potential intermediates of stepwise N-acylalkylation of neutral N-nucleophiles, do not exist in the isolated state, but they are rather efficiently stabilized upon solvation. These zwitterions, as well as analogous O-anions generated from anionic N-nucleophiles, can serve as intermediates of N-acylalkylation, as was demonstrated by localization of the corresponding TS. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1150–1164, June, 2007.     

Thermodegradation kinetics of a hybrid inorganic-organic epoxy system

Lifetime of the epoxy system formed by diglycidyl ether of bisphenol A, DGEBA/4,4′-diaminediphenylmethane, DDM, modified with the silsesquioxane, glycidylisobutyl-POSS, was calculated from thermogravimetric analysis. The activation energy of the decomposition of this system was evaluated by the integral method developed by Flynn-Wall-Ozawa (E = 88.9 ± 2.1 kJ mol⁻¹) and by Coats and Redfern method (E = 85.2 ± 1.5 kJ mol⁻¹). The kinetic parameters have been used to estimate the lifetime of the system POSS/DGEBA/DDM. The obtained results by two different ways are similar.