NiY分子筛表面酸性影响其选择性吸附脱硫性能的机理研究

采用原位红外光谱技术,以噻吩、环己烯和苯为模型探针分子,分别考察单一烃分子在NiY分子筛上的吸附与反应行为以及噻吩与烯烃、芳烃间的竞争吸附和催化反应行为。单一探针分子吸附研究发现,NiY分子筛中与Ni物种相关的Lewis(L)酸位是噻吩的选择性吸附活性位;噻吩和环己烯在NiY分子筛中Brnsted(B)酸位上发生的质子化和低聚反应明显弱于HY分子筛。双探针分子竞争吸附研究发现,环己烯二聚体在NiY中强B酸位上的强化学吸附与噻吩存在显著的竞争吸附行为。另外,苯和噻吩在NiY上的竞争吸附现象在373K时明显减弱。由此,在选择性吸附脱硫过程中,减少吸附剂表面B酸中心可降低烯烃对噻吩的竞争吸附,另外适当提高吸附体系的温度可以有效避免芳烃对噻吩的竞争吸附。     

Application of the Study of Reactivity of Alkaline Salts of Isocyanuric Acid to the Synthesis of Mono- and Trisubstituted Isocyanurates

Reactivity of alkaline salts of isocyanuric acid has been studied. It has been established that the nucleophilic substitution is not selective because of the protonic exchanges between salts and substituted derivatives. The synthesis of mono or trisubstituted derivative is due to secondary reactions and to solvent effects. With this study, it has been possible to settle a method to prepare mono and trisubstituted derivatives of isocyanuric acid.     

Study of Self-Ignition of PVC

The self-ignition of rigid PVC has been studied under static and dynamic conditions. Only a high-temperature boundary has been found, and the self-ignition temperature in air at atmospheric pressure lies between 555 and 560°C. The effect of preliminary HC1 evolution has been investigated, and it is shown that the more the HC1 evolution, the higher the self-ignition limit. It has been impossible to make polyacetylene ignite spontaneously in the presence of HC1 in oxygen up to 900° C. This is attributed to a special role of HC1 in combustion of PVC. The rate of HC1 release was measured by a potentiometric method, and the overall activation energy of the process was found to be 9.4 kcal/mole. This low value seems to be due to the presence of oxygen. Chromatographic analysis showed CH4 and CO to be the major gaseous products of oxidation of PVC in this parametric zone.     

Precision of Flash Pyrolysis-GC-MS Analysis: Experimental Evaluation of the Sources of Variability

The present study was carried out to evaluate the precision and to identify significant sources of variability in flash pyrolysis-GC-MS experiments. The analysis of variance has been applied to the example of polyethylene pyrolysis to estimate the impact of several controlled factors: sample handling, flash pyrolysis filament ageing and calibration. It was demonstrated that to get the best precision in experimental results, it is recommended to set the operator to reduce the impact of sample handling procedure and the filament to avoid variability due to changes in filament characteristics. In comparison, filament ageing and filament calibration are shown to influence in a limited extent the experimental results.     

Effect of microwave pretreatment of coal for improvement of rheological characteristics of coal-water slurries

Indian high-ash coal contains alpha-silica components of the mineral matter. When coal is transported in the form of a slurry, alpha-silica adds to the settling properties of coal and enhances erosion of pipelines. As such any technique that will contribute to changing the characteristics of mineral matter by selective demineralization is bound to supplement the knowledge of coal slurries in the science of rheology. One such method is the use of a novel microwave technology, which changes the alpha-silica to less harmful beta-silica. Thus microwave-treated coal slurry facilitates enhanced flow characteristics and abates the erosion problem in pipeline transport as well as in coal-slurry injection furnaces. This paper reports on the rheological study of closely sized coal particles of medium-volatile, low-ash, low-moisture cleans and high-ash rejects with and without microwave treatment. Viscosity of suspensions of microwave-treated coal was found to be less than that of untreated coal, in the case of both cleans and rejects. Microwave pretreatment thus reduces the viscosity and the pumping cost and opens a new outlook for pipeline transport. An attempt has been made to quantify the improvement of rheological characteristics due to microwave pretreatment.     

Identification of a new class of nonpeptidic inhibitors of cruzain

Cruzain is the major cysteine protease of Trypanosoma cruzi, which is the causative agent of Chagas disease and is a promising target for the development of new chemotherapy. With the goal of developing potent nonpeptidic inhibitors of cruzain, the substrate activity screening (SAS) method was used to screen a library of protease substrates initially designed to target the homologous human protease cathepsin S. Structure-based design was next used to further improve substrate cleavage efficiency by introducing additional binding interactions in the S3 pocket of cruzain. The optimized substrates were then converted to inhibitors by the introduction of cysteine protease mechanism-based pharmacophores. Inhibitor 38 was determined to be reversible even though it incorporated the vinyl sulfone pharmacophore that is well documented to give irreversible cruzain inhibition for peptidic inhibitors. The previously unexplored beta-chloro vinyl sulfone pharmacophore provided mechanistic insight that led to the development of potent irreversible acyl- and aryl-oxymethyl ketone cruzain inhibitors. For these inhibitors, potency did not solely depend on leaving group p K a, with 2,3,5,6-tetrafluorophenoxymethyl ketone 54 identified as one of the most potent inhibitors with a second-order inactivation constant of 147,000 s (-1) M (-1). This inhibitor completely eradicated the T. cruzi parasite from mammalian cell cultures and consequently has the potential to lead to new chemotherapeutics for Chagas disease.     

Effects of pulses of current on the cationic electropolymerization of isobutylvinylether

The cationic electropolymerization of isobutyl vinyl ether was induced and controlled by sequences of pulses of current of various lengths and of similar or opposite polarity. A remarkable degree of control over the rate of the reaction was demonstrated for a system that is subject to “flash” polymerization by conventional chemical initiators. The mechanism is shown definitively not to correspond to the electric field effects proposed by Tanaka, Ise and Sakurada as applicable to all such electropolymerizations.     

两种含杂环的氨基萘醌化合物的合成

以2,3-二氯-1,4-萘醌为主要原料,分别与吗啡啉和糠胺在一定条件下反应生成2种含杂环的氨基萘醌类化合物。2,3-二氯-1,4-萘醌与吗啡啉及2,3-二氯-1,4-萘醌与糠胺物质的量比均为1∶2,反应温度为60℃,溶剂为乙醇。2,3-二氯-1,4-萘醌与吗啡啉反应时间为1 h,产物2-氯-3-吗啡啉基萘-1,4-二酮(a)收率为93.5%;2,3-二氯-1,4-萘醌与糠胺反应时间为4 h,产物N~2,N~3-二(2-呋喃甲基)-1,4-二((2-呋喃甲基)亚胺)-1,4-二氢化萘-2,3-二氯化铵(d)收率为46.7%。对产物进行IR、Uv、MS和H-NMR等分析表征。     

The influence of different treatments of electrostatic interactions on the thermodynamics of folding of peptides

Replica exchange molecular dynamics simulations were performed to investigate the effects of different electrostatic treatments on the structure and thermodynamics of a small beta-hairpin forming peptide. Three different electrostatic schemes were considered: regular cutoffs, generalized reaction field (GRF), and particle mesh Ewald (PME), with the peptide modeled using OPLS/AA all-atom force field with explicit TIP3P water. Both the GRF and PME methods yielded results consistent with experiment, with free energy surfaces displaying a single minimum corresponding to the native beta-hairpin structure. In contrast, use of straight cutoffs led to the population of an additional local minimum corresponding to nonhairpin conformations that compete with the formation of the native beta-hairpin at low temperatures. This extra minimum would not be apparent in conventional constant-temperature molecular dynamics simulations run for a few nanoseconds. This result points to the critical need of careful sampling of conformational space to assess the quality of different numerical treatments of long-range forces. While differences emerged in the nature of the unfolded states populated using PME and GRF approaches, simulations on the beta-hairpin forming peptide and on two additional control peptides indicate that the GRF treatment of electrostatics offers a satisfactory compromise between accuracy and computational speed for the identification of low-energy conformations. A GRF-based approach emerges as a viable means for treating larger biological systems that would be prohibitively costly to simulate using PME methods.     

Prediction of latent heat of vaporization of multicomponent mixtures

A very simple method has been developed for predicting the differential latent heat of vaporization involved in vapor-liquid equilibria of multicomponent mixtures. The technique uses the UNIFAC method for predicting activity coefficients.In order to establish this method, 88 binary systems and 13 ternary systems, both nonazeotropic and azeotropic, were tested successfully. On the basis of the 101 systems investigated, the mean overall deviation between the observed and predicted values was found to be 4.6%. Despite the fact that the majority of the systems tested were azeotropic, a consequence of the small amount of data available for the differential heats of nonazeotropic systems, the method proposed is equally applicable to nonazeotropic systems.For azeotropic mixtures, it is possible to predict the latent heat (integral or differential) by means of an analytical equation which involves only the parameters of Antoine's equation, with a mean overall deviation of 6.1%.From the differential heats obtained by the proposed method, it is possible to calculate integral heats by applying equations derived here which relate these quantities.     

Quantum-chemical investigation of the mechanism of the sulfonation of pyrrole

A detailed quantum-chemical study of the sulfonation of pyrrole with regard to the effect of the solvent (the model of overlapping spheres) on the energy characteristics of the formation of the σ-complexes produced during attack on the α-and β-positions of the heterocycle and their possible transformation paths was made by density functional theory [the B3LYP/6-31G(d) method]. The possibility of mutual transformations between the isomeric σ-complexes by α/β-migration of the SO₃ is examined. The formation of pyrrolesulfonic acids was studied for the case of the intramolecular rearrangement of the complexes. Comparison of the activation energies shows that in contrast to the gas-phase reaction the formation of the β-sulfonic acid is preferred in methylene chloride: the solvation energy of the α-isomer of the σ-complex is higher than the energy for the transition state of its rearrangement and its product, α-pyrrolesulfonic acid, leading to an increase in the kinetic barrier and to a decrease of the energy gain on the path to the formation of the latter. The opposite variation of the energy characteristics on the path to the β-isomer with regard to solvation leads to agreement between the calculated data and the experimentally observed preferred formation of the β-pyrrolesulfonic acid. Dedicated to Mikhail Grigor’evich Voronkov. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1647–1654, November, 2006.     

Study of the solid-state hydrolysis of chitosan in presence of HCl

Chemical depolymerization of chitosan was obtained in the solid state by means of gaseous HCl. This new method allowed us to simultaneously form the hydrochloric salt and saturate the hydration water with acid. The depolymerization was carried out by keeping the product at a given temperature for the desired time. The measurements of the molecular weight distributions demonstrated the ability to control the reaction and produce oligomers with chosen dimensions. This solid-state hydrolysis favors the presence of a four-fold distribution that can be related to the original morphology and crystallinity of the initial material. The effects of the hydrolysis on the crystallinity, the crystalline structure, and the supramolecular order of the obtained chitosans were also studied. Finally, the washing of the hydrolyzed products in concentrated alkaline or acidic media allowed us to eliminate the lowest DPs and thus to narrow the molecular weight distribution. In this case, the crystallinity was also increased up to values beyond 70%. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3181–3191, 1997     

Elements of the topology of the region of the existence of the metastable states of a two-component vapor

Entire regions of the metastable states for binary and single-component systems were constructed. It was established that the regions include temperature intervals from absolute zero to critical temperatures, and from vapor—condensate equilibrium to the conditions of spinodal decomposition of supersaturated vapor in the system. Algorithms for determining the regions of metastable states are presented. The data obtained on their basis are noted to coincide qualitatively with known results. Correlations found earlier are employed to calculate the critical pressures and temperatures for the binary systems in the study.     

Physicochemical studies of utilization of lead batteries

Studies in the field of utilization of spent lead batteries are analyzed. Particular attention is paid to reprocessing of active materials of the batteries, to behavior of sulfur, to reduction of lead oxide with various reductants, and to refining of secondary lead. Pyrometallurgical and hydrometallurgical technologies as well as electrochemical methods are considered.     

Synthesis of calcineurin-resistant derivatives of FK506 and selection of compensatory receptors

We used olefin metathesis to synthesize C40 derivatives of FK506 and measured their ability, when complexed to FKBP12, to inhibit calcineurin's phosphatase activity. We identified modular dimerization domains (CABs) containing segments of the calcineurin A and B polypeptides. These CABs respond to FK506 both when overexpressed in mammalian cells and in yeast or mammalian three-hybrid assays. Using chemical genetic selection, we identified compensatory mutant CABs that respond to a calcineurin-resistant FK506 derivative at concentrations well below the response threshold for CABs containing only wild-type calcineurin sequence. These reagents provide a small molecule-protein combination orthogonal to existing dimerizer systems and may be used with existing systems to increase the complexity of induced-proximity experiments. This new use of the "bump-hole" strategy protects target cells from complications arising from the inhibition of endogenous calcineurin.     

Investigation of MM-PBSA rescoring of docking poses

Target-based virtual screening is increasingly used to generate leads for targets for which high quality three-dimensional (3D) structures are available. To allow large molecular databases to be screened rapidly, a tiered scoring scheme is often employed whereby a simple scoring function is used as a fast filter of the entire database and a more rigorous and time-consuming scoring function is used to rescore the top hits to produce the final list of ranked compounds. Molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) approaches are currently thought to be quite effective at incorporating implicit solvation into the estimation of ligand binding free energies. In this paper, the ability of a high-throughput MM-PBSA rescoring function to discriminate between correct and incorrect docking poses is investigated in detail. Various initial scoring functions are used to generate docked poses for a subset of the CCDC/Astex test set and to dock one set of actives/inactives from the DUD data set. The effectiveness of each of these initial scoring functions is discussed. Overall, the ability of the MM-PBSA rescoring function to (i) regenerate the set of X-ray complexes when docking the bound conformation of the ligand, (ii) regenerate the X-ray complexes when docking conformationally expanded databases for each ligand which include "conformation decoys" of the ligand, and (iii) enrich known actives in a virtual screen for the mineralocorticoid receptor in the presence of "ligand decoys" is assessed. While a pharmacophore-based molecular docking approach, PhDock, is used to carry out the docking, the results are expected to be general to use with any docking method.     

Enthalpies of formation of lactams

Combustion calorimetry is used to measure the enthalpies of combustion and formation of azacyclooctan-2-one (I), azacyclononan-2-one (II), and azacyclotridecan-2-one (III) in the crystalline, liquid, and gaseous states. Conformational analysis is conducted, and quantum chemical calculations of the compounds’ enthalpies of formation in the gas phase for conformers corresponding to the global minima are performed. The experimental findings and published data are used to determine mutually congruent combinations of enthalpy parameters for a number of nonsubstituted lactams. The strain energies are estimated. Trends in their changes are considered for the series of cycloalkanes and lactams.     

Kinetic study of bleaching of photoinduced forms of o-methylnitrobenzothiazoles

Photochromic properties of benzothiazole derivatives containing nitro and methyl groups in the ortho positions with respect to each other were studied by flash photolysis. The rate constant of bleaching of the corresponding photoinduced nitronic acids and their anions increases as the CH₃C-CNO₂ bond becomes longer. The application of the thermodynamic approach to predict the kinetic stability of nitronic acids is limited owing to specific intramolecular interactions. The lifetime of photoinduced nitronic acid anions tends to increase with rise in the chemical shift of the methyl protons.     

Synthesis of azido-polymers of butadiene

Iodine azide adds to cyclohexene in acetonitrile or 4:1 methylene chloride/acetonitrile to give trans-1-azido-2-iodocyclohexane. In methylene chloride this reaction gives a mixture of the cis-and trans-iodoazides owing to competing radical addition. Iodine azide adds to 1-hexene in acetonitrile by an ionic mechanism to give a 3:1 mixture of the 2-azido-1-azido- and 1-azido-2-iodohexanes. Dehydroiodination of the model iodoazides proceeds smoothly with potassium t-butoxide in diethyl ether or THF in the presence of 5 mol % 18-crown-6 at room temperature, giving in the previous example a mixture of 2-azido- and trans-1-azidohexenes. Polybutadiene, carboxyterminated poly(acrylonitrile-co-butadiene), and hydroxy-terminated polybutadiene gave iodoazide derivatives with up to 96% of the theoretical maximum nitrogen content and strong azide IR absorption. High azidoiodination gave polymer with N₃/I ratios slightly higher than unity while low percent azidoiodination led to polymer with N₃/I ratios of as low as 2:3. All of the nitrogen introduced was in the form of azide function. Dehydroiodination gave polymers with vinyl azide functionality and caused loss of some of the azide groups. All the azidoiodinated polymers decomposed between 120 and 160°C. The dehydroiodinated materials were less stable, decomposing between 100 and 150°C. The temperature of initial decomposition decreased as azide content increased. Polymers with >55–60% of the theoretical maximum azide content were shock sensitive.