Mechanism and kinetics of the silane decomposition in the presence of acetylene and in the presence of olefins

Kinetic data and product studies are reported for the silane pyrolysis in the presence of olefins and acetylene. The kinetics of silane loss in the presence of acetylene was found to be identical to the initial gas phase silane decomposition step (SiH₄ + M → SiH₂ + H₂ + M) when corrected for pressure fall-off effects. This result and the absence of methane or ethane from the pyrolysis of SiH₄ in the presence of 1-butene or 1-pentene demonstrate that silyl radicals and H atoms are not involved in silane-olefin or silane-acetylene reactions. Qualitative aspects and kinetic data from the SiH₄ pyrolysis in the presence of propylene are in accord with propylsilane formation via propylsilylene formed by silylene addition to propylene.     

Curve-fitting overlapped bands: quantification and improvement of curve-fitting robustness in the presence of errors in the model and in the data

Estimation of the band parameters of overlapped bands often relies on curve-fitting. It has been demonstrated that curve-fitting provides the maximum likelihood estimation of band parameters under a series of assumptions. One of these assumptions is that the curve-fitting model is correct and any error in the data is random. Under real conditions, we have to acknowledge the unavoidable presence of errors in the model and systematic errors in the data. Here, we derive an expression for the estimation of how these errors affect the quality of the parameters obtained from curve-fitting. In addition, we derive theoretical expressions to quantify the extent to which different methods can improve the curve-fitting robustness to these errors. The methods considered are: (i) deterministic and (ii) probabilistic constraints in the band parameters, (iii) curve-fitting band-narrowed data, and (iv) building a more accurate model. The theoretical expressions obtained are tested in the curve-fitting of a synthetic noisy spectrum with either baseline or band shape errors, and in the curve-fitting of the experimental infrared amide I band of the membrane protein bacteriorhodopsin.     

Synergism in the extraction of europium in the presence of alkylphosphates and sulphoxides

Synergism in the extraction of europium(III) has been investigated using a mixture of naphthoyltrifluoroacetone and synergists like trioctylphosphine-oxide (TOPO), tributylphosphate (TBP), trihexylphosphate (THP), diphenylsulphoxide (DPSO) and benzylsulphoxide (BSO). Synergism decreases in the order: TOPO < TBP ≃THP < BSO < DPSO indicating a correlation between electron density at the donor atom and extent of synergism. The equilibrium constants for adduct formation have also been evaluated.     

Analysis and assessment of the occurrence, the fate and the behavior of nanomaterials in the environment

Nanomaterials have one dimension <100 nm and possess physico-chemical properties dictated by their unusually small size, large surface area, shape and chemical composition. New properties of nanomaterials have boosted their production and industrial applications in many fields (e.g., microelectronics, catalysis, fuel cells, materials science, textiles, biotechnology and medicine). In biomedical fields, nanomaterials are of the appropriate dimensions to interact with biological matter. However, they may also have negative effects on biological systems. Nanotechnology is a major, innovative, scientific and economic growth area, but the increasing production and use of nanomaterials have led to calls for more information regarding the potential impacts that their release may have on human health and the environment.This review addresses analytical approaches for characterization and quantification of nanomaterials in the environment and recent studies on their occurrence, fate and behavior.     

Correlation Analysis of the Runoff of the Rivers and the Seisms in China

In recent hundred years the annual discharge variations of the Changjiang River (represented by the Yichang station) and the Huanghe River (represented by Shanxian and Tangnaihe, respectively) have closely related to the geographical distribution of the earthquakes coming about in China in the same year, Both the occurrence of the destructive seism or seismic swarm in the river basins and the disappearance of the shocks in the east and south of the basins are the conditions that the Changjiang and Huanghe Rivers are the high flow while that the strong earthquake of magnitude 7 or more occurred in North China is the condition for the Changjiang low flow year and that of 6 or more in the Qilian Mountains area is for the Huanghe River. In the latter part of this paper, a 2-year sample is given to explain that the conditions of the 2 rivers being high flow years are that the north-south seismic belt is active and in the meanwhile no seism occurred in South China, and those of the low flow year are that the     

Catalytic asymmetric alkylation in water in the presence of surfactants: influence of the nature of the nucleophile and the allylic acetate on the activity and enantioselectivity

Asymmetric palladium-catalyzed alkylation of 1,3-diphenyl-2-propenyl acetate with carbon and nitrogen nucleophiles occurs in water in the presence of a surfactant, a base, and Binap as the chiral ligand. Enantioselectivities up to 91% were obtained using carbon nucleophiles, and 93% using nitrogen nucleophiles, in the presence of CTHASO₄ as the surfactant. While the efficiency of the catalyst was higher in water in the presence of the surfactant in the case of carbon nucleophiles, no micellar effects were observed using the nitrogen nucleophiles. The alkylation was extended to other allylic acetates, but the efficiency as well the enantioselectivity of the coupling were lower.     

Induction by Cytodef of the biosynthesis of endogenous ethylene and cellulase and the change in the composition of the proteins in the leaf-shedding zone of the cotton plant

The influence of the defoliant Cytodef (Tsitodef) on the formation of ethylene and the activity of cellulase in the separating zone of cottonplant leaves has been investigated. It has been established that Cytodef is an inductor of a number of biochemical reactions taking place at the membrane and genetic levels and leading to leaf shedding.Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 463–466, May–June, 1995. Original article submitted October 5, 1994.     

Chemiluminescence of CaH and AIH in the reaction of the metal atoms and formaldehyde

Chemiluminescence from the reaction of calcium and aluminum with various hydrogen containing compounds in a flowing gas system and in a heat pipe oven are described. Red chemiluminescence of CaH was observed in the reaction of calcium, and weak chemiluminescence of AlH was seen in the reaction of aluminum with formaldehyde (H₂CO). It is proposed that a reaction between metal atoms and formaldehyde may be used as a source of diatomic metallic hydrides.     

Use of the salet phenomenon in the determination of sulfur and phosphorus in aqueous and organic samples

The history of the Salet phenomenon is summarized. Various experimental configurations are studied for the measurement of the S₂ and HPO emission from different sulfur and phosphorus species in low-temperature flames. Analysis of petroleum fractions for sulfur, and insecticides for phosphorus is discussed.     

Pharmacokinetics of protein-unbound linezolid in the blood and the mechanism of hepatobiliary excretion in the rat

Linezolid (Zyvox), an oxazolidinones antibiotic, was developed for the treatment of infectious diseases caused by gram-positive pathogens. To investigate the mechanism of hepatobiliary excretion of linezolid, a parallel study design used two groups; in the control group, rats received linezolid alone (3 or 10 mg/kg, i.v.). In the drug-treated groups, 10 min prior to linezolid administration, cyclosporin A (CsA; 10 mg/kg, i.v.), a P-glycoprotein (P-gp) inhibitor, was given in the rats. The microdialysis probes were implanted into the jugular vein toward right atrium and the bile duct of Sprague-Dawley rats for multiple biological fluid sampling. Separation was performed using a reversed phase C₁₈ (4.6 mm × 150 mm i.d., 5 μm) with mobile phase of acetonitrile-methanol-1% 1-octanesulfonic acid in water of 30:10:60 (v/v/v) at flow rate of 1 ml/min. The UV detection for linezolid was set at a wavelength of 260 nm. Following linezolid (10 mg/kg, i.v.) administration, the concentration of linezolid in the brain was less than the limit of quantification and the area-under the concentration curve versus time curve (AUC) of blood and bile were 1780 ± 50 and 2850 ± 276 (min μg/ml), respectively. The bile-to-blood distribution ratio was 1.6 ± 0.2 (n = 6), which was defined as AUC_bile/AUC_blood. The results demonstrated that the transportation of linezolid into bile might be mediated by active transport. However, after treatment with CsA, the linezolid AUC in bile was 3060 ± 411 (min μg/ml) which did not indicate a significant difference with linezolid alone. These results suggest that the hepatobiliary excretion of linezolid might not be regulated by P-gp transportation.     

Quantum-chemical study of the mechanism of the hydrolysis of amides in the gas phase and in aqueous solution

The MNDO, AM1, and MNDO/M methods have been used to calculate the profile of the potential energy surface for the hydrolysis of formamide in the gas phase and in aqueous solution. Estimates have been made of the changes in the energy barrier in specific acid and base catalysis, and it is shown that in the absence of proton exchange between the reacting system and the solvent the interaction of the charged reactants with a polar medium impedes the reaction.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1785–1792, August 1989.     

Theoretical studies of the structure and stability of protonated olefins in the gas phase and in solution

The calculation of carbenium and carbonium type cations resulting from the protonation of olefins with growing length and increasing chain branching was carried out by quantum chemical methods which were tested elsewhere.One result is the distinction of olefins with an equal number of alkyl substituents on both sides of the double bond and other ones with different number. In the latter case generally no bridged structures could be defined.The influence of nucleophilic solvents on the stability of the cationic structures is simulated on the basis of Klopman's solvaton model. These calculations show that solvents may change the gas phase data in a remarkable way.     

Photochromism of spirobenzopyran in the membrane of surfactant vesicle and in the cavity of cyclodextrins

Photochromic reaction of water insoluble 1,3,3-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2-indoline] (SP) was studied in water with the aid of vesicles and -cyclodextrin (-CD). In both systems, the photochromic reaction of SP was observable in spite of the low solubility of SP in water. In order to examine the microenvironment around the SP and the reaction product, photomerocyanin (MC), in those systems, the spectrum of MC was measured in various organic solvent of various polarity. Decreasing the polarity of the solvent decreased the peak absorbance and shifted the peak wavelength to the long wavelengths. When the vesicles were used, the reactant, SP, and the product, MC, were solubilized in different regions of different polarity. The reaction substrate was then supposed to have moved from the hydrophobic region of the membrane to the hydrophilic one after the photoisomerzation. The photochromic reaction of SP in the presence of -CD was slower than in the vesicles and faster than that in methanol. The polarity in the vesicular membrane and the limited rotation of the reactant in the cavity of -CD may have influenced the reaction rate. The prolonged light irradiation period resulted in a simultaneous photoreaction and polymerization, producing some unknown side reaction.     

New Aspects of the Maillard Reaction in Foods and in the Human Body

The reactions that occur during the cooking, baking, and preservation of foods of all kinds are of great importance for the production of aroma, taste, and color. However, more recently it has been shown that these reactions may be accompanied by a reduction in nutritive value and the formation of toxic compounds. For these reasons, the very complex reactions between reducing sugars and the free amino groups of amino acids or proteins, known as non-enzymatic browning or the Maillard reaction, have again caught the interest of chemists. The Maillard reaction came to be seen in a new light as it was realized that it actually occurred in the human body. As a general rule, the longer the half-life of a protein, the larger the amount of its Maillard products found, i.e., important factors are the ‘age’ or persistence of the protein in the body and the glucose concentration, particularly in diabetics. Many of the symptoms developed by diabetics resemble those of premature aging, which leads to the possibility that glucose, because of its reactivity towards proteins, is fundamentally involved in the normally slow progress of aging.     

聚氨酯/聚丙烯酸酯复合乳液的研制进展

概述聚氨酯－聚丙烯酸酯复合乳液的制备方法。特别对聚氨酯－聚丙烯酸酯复合乳液共聚法作了较为系统的介绍和讨论。     

Study on the Photodegradation of Salicylic Acid in Different Vehicles in the Absence and in the Presence of TiO2

In this work, the direct photolysis of salicylic acid, generally used as keratolytic agent in many dermatological products and as preservative in cosmetics, was investigated. The photodegradation of the acid under UVB irradiation was evaluated in different vehicles, such as water solutions at different pH, propylene glycol/water, and ethanol/water mixtures, sodium dodecyl sulphate solutions, and O/W emulsions prepared with Montanov 68 and Amphysol K as emulsifiers. The increase of pH enhanced the photodegradation of salicylic acid while the different vehicles protected the acid from the action of UVB radiations. However, the best protection was observed dissolving the acid in the lipid core of O/W emulsions, which probably removes the active from the polar environment that can promote the photolysis. The photocatalytic activity of TiO₂ on the degradation of salicylic acid also was evaluated. TiO₂ frequently is used as sunscreen in many cosmetic preparations. Salicylic acid and the pigment can be contained in the same solar formulation; hence, it can be interesting to study their interaction under UVB. TiO₂ enhanced the photodegradation of salicylic acid in all the media previously reported and its photocatalytic activity was influenced by the pH and by the components of the vehicles.     

Study of the interfacial tension in model and technical emulsions in the presence of surfactants and inorganic electrolytes

Interfacial tension in the oil/water system in the presence of various ionic surfactants and inorganic electrolytes was studied. Special features of the effect of the surfactant and oil phase natures, of the structure of their molecules, and also of the electrolytes containing ions with various radii, valences, and hydratabilities on the value of the interfacial tension were studied. The criteria and conditions of obtaining model emulsions based on paraffin hydrocarbons and technical emulsions based on vegetable oils were determined.     

Density functional computations of the energetic and spectroscopic parameters of quercetin and its radicals in the gas phase and in solvent

Quercetin and its radicals were investigated at the B3LYP density functional level with the aim of determining the energetic and spectroscopic parameters and the factors that influence their antioxidant activity in the gas phase and in aqueous solution. The results indicated that the antioxidant ability of quercetin is mainly due to the orthodiphenolic moiety but also to the presence of the C=C double bond of the pyrone ring. Differences in the stability order of the isomers of quercetins radicals were found in going from vacuum to solvent. Hyperfine coupling constants were computed to help the interpretation of the intricate ESR spectrum of quercetin.Contribution to the Jacopo Tomasi Honorary Issue     

Assessment of the indoor-to-outdoor ratio of dose rates in and around the historic objects in Bosnia and Herzegovina

Journal of Radioanalytical and Nuclear Chemistry - This paper deals with the first study of the indoor to outdoor ambient dose equivalent rates ratio measured in and around the historic objects at...     

Study of the interaction of clobazam with cyclodextrins in solution and in the solid state

Inclusion complexes of clobazam with alpha-, beta-, gamma-cyclodextrins (CyDs) and heptakis(2.6-di-O-methyl)-beta-cyclodextrin (DM-beta-CyD) in aqueous solution and in the solid phase were studied by the solubility method, infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffractometry. In addition, inclusion complex of clobazam with heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin and the solid dispersion of clobazam with methyl cellulose (MC) in a ground mixture were investigated by IR, DSC and X-ray diffractometry. It was observed that DM-beta-CyD had the highest stability constant among the four CyDs in solution. Thermal and X-ray diffraction analyses showed that clobazam molecules existed in a molecularly dispersed state in the ground mixture of CyDs. Infrared spectra showed lower frequency shifts in the case of the ground mixtures of clobazam with natural CyDs, which can be attributed to the formation of hydrogen bonds between the two carbonyl groups of clobazam and hydroxyl groups of natural CyDs. In contrast, higher frequency shifts were observed in the case of the ground mixtures of clobazam with methylated CyDs and MC and these were considered to be due to the monomolecular dispersion of clobazam in a hydrophobic environment. The mode of interaction of clobazam with DM-beta-CyD was different from that with natural CyDs in the ground mixtures. Furthermore, the crystalline inclusion complex of clobazam with DM-beta-CyD was obtained by heating of the coprecipitate in vacuo at 120 degrees C for 1 h.