Flame soot generated under controlled combustion conditions: Heterogeneous reaction of NO2 on hexane soot

We used a Combustion Aerosol Standard burner unit that affords controlled and adjustable flame conditions, and adapted it for use with liquid fuel. We prepared samples of hexane soot under different well‐defined combustion conditions, and probed the chemical properties of hexane soot by using its heterogeneous interaction with NO₂ in a Knudsen flow reactor. Soot generated under conditions of fuel to oxygen ratio near stoichiometry (λ = 0.82) produced HONO as the main product. Yields of HONO decreased for soot generated under lean conditions (λ = 0.16). Finally, NO was the principal product of the reaction for soot generated under extremely lean conditions (λ = 0.09) corresponding to the lower flammability limit. We may conclude that the combustion conditions determined surface properties gauged by the heterogeneous NO₂–soot interaction. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 620–631, 2002     

Synthesis of Biscoumarins from 4-Hydroxycoumarin and Aromatic Aldehydes—A Comparative Assessment of Percentage Yield Under Thermal and Microwave-Assisted Conditions

A convenient synthesis of various biscoumarins by condensing a series of aldehydes with 4-hydroxycoumarin under microwave irradiation is reported for the first time along with a comparative account of the syntheses under conventional conditions. The reaction times have been reduced considerably with improvement in yields in comparison to thermal conditions. The reactions have been carried out in solvent as well as under solvent-free conditions, and the adopted procedure provides an energy-and time-saving protocol.     

Precisely Designed Isopeptide Bridge‐Crosslinking Endows Artificial Hydrolases with High Stability and Catalytic Activity under Extreme Denaturing Conditions

Enzymes normally lose their activities under extreme conditions due to the dissociation of their active tertiary structure. If an enzyme could maintain its catalytic activity under non‐physiological or denaturing conditions, it might be used in more applications in the pharmaceutical and chemical industries. Recently, we reported a coiled‐coil six‐helical bundle (6HB) structure as a scaffold for designing artificial hydrolytic enzymes. Here, intermolecular isopeptide bonds were incorporated to enhance the stability and activity of such biomolecules under denaturing conditions. These isopeptide bridge‐tethered 6HB enzymes showed exceptional stability against unfolding and retained or even had increased catalytic activity for a model hydrolysis reaction under thermal and chemical denaturing conditions. Thus, isopeptide bond‐tethering represents an efficient route to construct ultrastable artificial hydrolases, with promising potential to maintain biocatalysis under extreme conditions.     

On a possible radical-cation mechanism of the biomimetic oxidation of the saturated hydrocarbon 1,3-dimethyladamantane in a Gif-type system containing a Fe2+ salt, picolinic acid, and pyridine

Based on an analysis of the ratio between the final products of the oxidation of 1,3-dimethyladamantane (1,3-DMA) with hydrogen peroxide under new catalytic conditions, an EPR-spectroscopic study of the 1,3-DMA radical cation under model radiation-chemical conditions, and the results of PM3 quantum-chemical calculations, a new mechanism was proposed for the biomimetic oxidation of the saturated hydrocarbon. This mechanism involves the intermediate formation of the 1,3-DMA radical cation, in which a tertiary C-H bond is selectively activated. Next, oxene (oxygen atom) is inserted into this C-H bond to form a tertiary alcohol. It was found that a comparison of the composition of final products in the oxidation of saturated hydrocarbons under conditions of a real chemical experiment with the structure and reactivity of their radical cations under model radiation-chemical conditions can be a methodologically new general technique for the analysis and prediction of the reactivity of saturated hydrocarbons under oxidative conditions.     

ABO2型复合氧化物上CO-NO的反应性能

以柠檬酸络合法制备了CuCrO2、CuAlO2和CuFeO2等具有铜铁矿结构的ABO2型复合氧化物,并考察了它们在氧化和还原气氛中对CO NO反应的影响. CuAlO2和CuCrO2具有好的催化活性, CuCrO2更具有相当的稳定性,经过氧化和还原条件下的CO NO反应后,体相组成仍然保持不变. CuAlO2在还原条件下,部分被还原生成了零价铜. CuFeO2的催化活性和稳定性较差,在还原气氛中催化CO NO反应过程中,样品被还原,完全转化成了Cu0和CuFe2O4.     

Redistribution of intramembrane particles of human erythrocytes induced by HVJ (Sendai virus): a prerequisite for the virus-induced cell fusion.

Aggregation of intramembrane particles of human erythrocytes was found to be induced by HVJ (Sendai virus) under conditions which lead to cell fusion. Degree of polyerythrocyte formation was compared under a variety of conditions with extent of cluster formation observed with the same preparations. Both structural changes of the membranes, ie, fusion and clustering of the particles, behaved very similarly under widely different virus-to-cell ratios and over the time course of cell fusion. Furthermore, by inclusion of high concentrations of antispectrin antibodies within the ghosts, inhibition of clustering of intramembrane particles and hindrance of virus-induced cell fusion were found to occur simultaneously. Antibodies by themselves did not induce aggregation of particles under isotonic conditions, whereas particle clustering could be induced under hypotonic conditions at antibody concentrations causing partial cross-linking of spectrin molecules. In conclusion, clustering of intramembrane particles seems to be required for virus-induced fusion of human erythrocytes.     

Direct amination of isobutylene over zeolite catalysts with various topologies and acidities

The atomically economic and green chemical reaction of direct amination of isobutylene to tertbutylamine, particularly under the relative mild reaction conditions available for future industrial use,was carried out over zeolite catalysts possessing different topological structures, from one dimensional to three dimensional pore system, and from small 8-member ring pore(MRP) to medium 10 MRP and further to large 12 MRP zeolites, to disclose the relationship between the zeolite properties/topologies and their amination performance systematically under the mild reaction conditions. It was discovered that the pore structure and the acidities of zeolite catalysts played crucial roles in the isobutylene amination process, and suitable pore diameter(larger than 0.5 nm or with large side pockets/cups in the outside surface) and a certain number of mid-strong acid sites are indispensable to catalyze the amination reaction,while too strong acid strength was not conducive to the process of isobutylene amination. Among them,zeolites with topologies of BEA, MFI, MEL, MWW and EUO exhibited good amination performance, with which the isobutylene conversion was higher than 12.61%(46.42% of the equilibrium conversion) under the studied mild reaction conditions. Due to the good amination performance and the large adjustable Si/Al_2 ratio range, ZSM-5 was selected to further study the effect of acidity on the amination performance systematically under the mild reaction conditions, and the activity-acidity relationship in the amination process was disclosed: the amination activity(isobutylene conversion) had a linear correlation with the amount of mid-strong B acidity under the studied conditions over ZSM-5 catalyst, which can provide guidance for further developing high-efficient amination catalyst under mild reaction conditions available for future industrial use.     

In vitro degradation of porous poly(l-lactide-co-glycolide)/β-tricalcium phosphate (PLGA/β-TCP) scaffolds under dynamic and static conditions

In vitro degradation of porous poly(l-lactide-co-glycolide)/β-tricalcium phosphate (PLGA/β-TCP) scaffolds was studied by incubating the samples in phosphate buffered saline (PBS) at 37 °C and pH 7.4 under dynamic loading with respect to static conditions for 12 weeks. Under dynamic conditions, acidity of PBS was alleviated by the better solution circulation, and water absorption of the scaffolds increased more than that under static conditions in the first 8 weeks. Changes in mass, height, diameter, relative molecular mass and its distribution also happened more remarkably under dynamic conditions. Moreover, obvious cracks and a larger amount of β-TCP particles were observed on the wall of the scaffolds after degradation for 12 weeks under dynamic loading. Compressive modulus and strength showed an increase from the beginning to the 10th week but were lower after then. Results showed that degradation of PLGA/β-TCP scaffolds under dynamic conditions exhibited a significantly faster rate than that under static conditions.     

ABO_2型复合氧化物上CO-NO的反应性能

以柠檬酸络合法制备了 CuCrO_2、 CuAlO_2和 CuFeO2等具有铜铁矿结构的 ABO2型复合氧化物,并考察了它们在氧化和还原气氛中对 CO- NO反应的影响 . CuAlO_2和 CuCrO_2具有好的催化活性, CuCrO_2更具有相当的稳定性,经过氧化和还原条件下的 CO- NO反应后,体相组成仍然保持不变 . CuAlO_2在还原条件下,部分被还原生成了零价铜 . CuFeO_2的催化活性和稳定性较差,在还原气氛中催化 CO- NO反应过程中,样品被还原,完全转化成了 Cu0和 CuFe2O4.     

Two‐in‐One: Inherent Anhydrous and Water‐Assisted High Proton Conduction in a 3D Metal–Organic Framework

The development of solid‐state proton‐conducting materials with high conductivity that operate under both anhydrous and humidified conditions is currently of great interest in fuel‐cell technology. A 3D metal–organic framework (MOF) with acid–base pairs in its coordination space that efficiently conducts protons under both anhydrous and humid conditions has now been developed. The anhydrous proton conductivity for this MOF is among the highest values that have been reported for MOF materials, whereas its water‐assisted proton conductivity is comparable to that of the organic polymer Nafion, which is currently used for practical applications. Unlike other MOFs, which conduct protons either under anhydrous or humid conditions, this compound should represent a considerable advance in the development of efficient solid‐state proton‐conducting materials that work under both anhydrous and humid conditions.     

Effect of high-temperature on high-performance liquid chromatography column stability and performance under temperature-programmed conditions

Six commercially available analytical (4.1 or 4.6 mm i.d.) columns were evaluated under temperature-programmed high-temperature liquid chromatography (HTLC) conditions to access their stability and performance at extreme temperatures. Seven components consisting of acidic, basic and neutral compounds were analyzed under temperature-programmed conditions and solvent gradient conditions using three different mobile phase compositions (acidic, basic and neutral). Each column was checked with a two-component test mix at various stages of the evaluation to look for signs of stationary phase collapse. Three zirconia based stationary phases studied exhibited column bleed under temperature-programmed conditions. The other three columns, a polydentate silica column, a polystyrene-divinylbenzene (PS-DVB) polymeric column, and a graphitic carbon column performed well with no evidence of stationary phase degradation. The R.S.D. for the retention times and efficiencies were less than 10% for most conditions, and not more than 15% during the course of the evaluation for each column. The polydentate silica stationary phase was temperature programmed to 100 degrees C, the PS-DVB stationary phase was temperature programmed up to 150 degrees C, and the graphitic carbon column was used with temperature programming up to 200 degrees C. Comparable peak capacities and similar retention behaviors were observed under solvent gradient and temperature-programmed conditions. Temperature programming with dynamic mobile phase preheating can replace solvent gradient analysis without a loss of peak capacity when used with 4.1 or 4.6 mm columns.     

Application of time-resolved in-situ X-ray absorption spectroscopy in solid-state chemistry

Time-resolved X-ray absorption spectroscopy (TR-XAS) possesses excellent capabilities to reveal quantitative phase composition and average valence together with the evolution of the local structure of a system under dynamic reaction conditions. The work discussed here focused on time-resolved in-situ XAS investigations aiming, first, at understanding structural evolution under dynamic conditions and, second, at revealing properties of the system studied not available from investigations under stationary conditions. Hence, not only was the local structure of a material studied under reaction conditions, but characteristic properties of the reaction, such as reaction intermediates or the kinetics of the reaction, were also elucidated. The solid–gas reactions presented here clearly demonstrate the potential of TR-XAS investigations to extend the suitability of XAS for in-situ studies in solid-state chemistry to investigations under dynamic conditions.     

Carbon surface chemical composition in para-nitrophenol adsorption determined under real oxic and anoxic conditions

A series of commercial unmodified and modified activated carbons was studied. The surface chemical composition was characterized using X-ray photoelectron spectroscopy and Boehm titration methods. Data on p-nitrophenol (pnp) adsorption isotherms determined under real oxic and anoxic conditions (at 310 K) are presented and described using bimodal Langmuir and lattice density functional theory models. The applicability of the pnp molecule for determination of surface area using adsorption from solution data is discussed. It is shown that under anoxic conditions adsorption and relative enthalpy of this process depend on the value of BET apparent surface area and DA micropore volumes. The differences between adsorption levels under both conditions increase with rise in solute equilibrium concentration. Moreover, the average difference between adsorption values under both conditions increases and next decreases with rise in the concentration of surface acidic groups. Applying quantum chemical calculations, we show that under anoxic conditions the influence of surface oxygen groups on pnp adsorption is small, whereas under oxic conditions the reverse situation is observed. Obtained theoretical results show very good correspondence to the experimental data and the origin of the relationships observed experimentally is explained and discussed.     

Modeling of the plasma sintering process at reduced pressures

Numerical simulation of the thermal behavior of sintering specimen under RF plasma conditions at reduced pressure is considered. A two-dimensional approach is adopted for describing flow, temperature, and electromagnetic fields in the reactor with appropriate boundary conditions. Slip boundary conditions are imposed for the velocity field at the sample surface and at the wall of the reactor, and corresponding jump boundary conditions are specified for the temperature field. Simple kinetic theory is employed for the calculation of the heat flux from the plasma to the specimen. The so-called capture-radiative-cascade model is adopted for ionization and recombination processes. The results indicate that ion-electron surface recombination is the dominant heat transfer mechanism to the sintering specimen under reduced pressure conditions.     

n-Butane isomerization in the gas phase and under supercritical conditions

The aromatization of n-butane under supercritical conditions on gallium-, zinc-, and platinum-modified high-silica zeolites with a modulus of 30–70 was first studied, and the experimental data were compared to the results of a study of this process in the gas phase. It was found that the operational efficiency of catalysts for n-butane conversion under supercritical conditions was much higher than that for the gas-phase reaction in terms of activity, productivity, and resistance to poisoning by condensation products. The aromatization of gaseous n-butane at 530°C and 1 atm was characterized by rapid catalyst deactivation. The selectivity for the benzene-toluene-xylene (BTX) fraction was higher than 50%. Under supercritical conditions at 430–560°C and 100–200 atm, the selectivity of formation of aromatic compounds decreased by a factor of 2, whereas the yield of C₁-C₃ cracking products increased by the above factor. On the other hand, it was found that an increase in the productivity of catalysts by a factor of 20–50 with the retention of almost 100% activity for several days of operation is an advantage of the process performed under supercritical conditions. The almost complete conversion of butane under supercritical conditions was found on promoted HZSM-5 zeolite samples. The thermogravimetric analysis of spent samples suggested a higher degree of catalyst carbonization under supercritical conditions, as compared with that in the reaction performed in the gas phase. However, the deposition of 20–30 wt % condensation products on the catalysts had no detectable effect on the high activity of the catalysts in the reaction performed under supercritical conditions.     

Synthesis of organosilicon sol-gel matrices and preparation of heterogeneous biocatalysts based on them

Hybrid organosilicon structures prepared by the sol-gel method from tetraethoxysilane, methyltriethoxysilane, and polyethylene glycol 3000 under the conditions of base catalysis were used as a matrix for immobilization of whole cells of methylotrophic yeast for developing heterogeneous biocatalysts. The influence of the precursor ratio on the time of formation of the organosilicon sol-gel structure under the conditions of base catalysis was examined. According to the IR data, the structure obtained with 50 vol % methyltriethoxysilane has the highest content of Si-O-Si bonds. Examination by scanning electron microscopy showed that microorganism cells under these conditions are centers of formation of the sol-gel structure.     

Synthesis of a novel silicon bearing linker for solid phase synthesis

A novel linker for solid phase synthesis is described, which exhibits rapid cleavage under selective, orthogonal conditions, including stability under acidic conditions. The linker incorporates a pyridyl propionate system, with a pendant β-silyl group. Rapid cleavage of the product is effected by elimination of the silyl group on treatment with fluoride. Two systems of this type have been synthesised, and the stability of the linkers has been tested under acidic and basic conditions in solution.     

Amberlite IRA900N3 as a new catalyst for the azidation of alpha,beta-unsaturated ketones under solvent-free conditions

Amberlite IRA900N3 is an excellent organocatalyst for the azidation of alpha,beta-unsaturated ketones with trimethylsilyl azide under solvent-free conditions. By avoiding the use of metallic species and of the organic reaction medium, the procedure is a green tool for the preparation of beta-azido ketones under mild conditions with yields from good to excellent. The catalyst can be recovered and re-used with no loss of its efficiency.     

Acyloin condensation of terephthaloyl chloride—a novel route to polyhydroxyketones

Acyloin condensation of terephthaloyl chloride under homogeneous conditions using a sodium naphthalene radical anion system and under heterogeneous conditions using finely dispersed molten sodium with varying ratios of sodium to organic substrate gave mainly polymeric materials that were identified as polyhydroxyketones. IR, NMR, and DTA analyses indicate that these polymers are copolymers of benzoin and benzil hitherto unknown. The yields of polymers under homogeneous conditions were higher than those obtained under heterogeneous conditions, but the molecular weight distribution was similar to those obtained with molten sodium.     

Vitamin U-bonded stationary phase in capillary ion chromatography

A vitamin U-bonded stationary phase was prepared and the retention behavior of inorganic anions was examined using ion chromatography. Inorganic anions were retained on the vitamin U-bonded stationary phase under acidic as well as neutral eluent conditions in the ion-exchange mode. The elution order of the examined anions under neutral eluent conditions was nearly the same as that observed in common ion exchange mode, while the elution order observed under acidic eluent conditions was completely different from that observed in common ion exchange mode. The retention of the analyte anions under the neutral eluent conditions was due to the sulfonium groups of the vitamin U, while protonated primary amino groups caused retention of the analyte anions with different selectivity under acidic conditions. The retention factor of the analyte anions increased with decreasing eluent concentration under both eluent conditions. The present system was applied to the determination of bromide and nitrate contained in seawater.