The field dependence of mobility in molecularly doped polymers under the conditions of nonequilibrium transport

A multiple-trapping model has been used to numerically analyze the effects of the nonequilibrium transport of holes on the field dependence of drift mobility as obtained in a time-of-flight experiment. The intrinsic field dependence has been assigned to the frequency factor in the form of the Poole-Frenkel law. Strongly dispersive transport, as well as a nonequilibrium-charge-transfer regime given by the Gaussian disorder model, has been considered. It has been established that the currently accepted approach to the analysis of the field dependence of mobility needs to be reexamined.     

An experimental study about the imbibition of aqueous solutions of low concentration of a non-adsorbable surfactant in a hydrophilic porous medium

The imbibition of aqueous solutions of Triton X-100 in calcium fluoride columns has been studied in order to determine the influence of the interfacial adsorption of the surfactant in the capillary rise of the solutions. This system has been chosen because this surfactant behaves as non-adsorbable at the surface of this solid when it is in aqueous solution. The experiments have consisted of the measurement of the increase in the weight of the porous columns caused by the capillary rise of the solutions. The analysis of the results has been made through a modified expression of Washburn's equation that takes into account that the experimental increase in the weight is caused by the imbibition as well as by the development of a liquid meniscus around the bottom base of the columns. From this analysis, it has been deduced that the surfactant concentration does not influence on the imbibition rate, it being equal to the observed for water. However, it has been also proved that the contact angle depends on the surfactant concentration, taking decreasing values as the surface tension of the solutions decreases. In order to justify these findings, a study about the influence of the interfacial adsorption on the imbibition has been carried out. By means of them, it has been proved that the absence of adsorption at the solid-liquid interface is the reason that explains both the independence of the imbibition rate from the surfactant concentration and the decrease of the contact angle. Moreover, this fact indicates that the depletion of the surfactant molecules from the advancing meniscus, which has been normally adduced as the phenomenon causing the observed behaviour, has to be ruled out as the physical cause that justifies the behaviour found from the analysis of the imbibition experiments. As a corollary, it has been also stated that only if the adsorption at the solid interfaces happened, the imbibition of aqueous solution of surfactant in hydrophilic media could be influenced by the surfactant concentration.     

Improvement of properties of silica‐filled styrene‐butadiene rubber composites through plasma surface modification of silica

The performance of plasma surface modified silica filler in styrene‐butadiene rubber (SBR) matrix has been analyzed. The conditions of plasma modification have been optimized by taking secant modulus as a standard parameter and the occurrence of the modification has been confirmed by surface area determination and Fourier transform infrared spectroscopy. The plasma‐modified surface of silica has been found to be composed of carbon–carbon double bonds and carbon–hydrogen bonds. Silane treatment also has been carried out on silica filler surface for a comparative assessment of its influence in the curing behavior and filler–rubber interaction. The cure reactions of all the rubber compounds have been found to be proceeded according to first‐order kinetics. A reduction in the cure reaction rate constant has been observed with the loading of unmodified and surface modified silica, emphasizing the cure deactivation of the matrix rubber by the silica filler. The filler dispersion, as revealed by scanning electron microscopy, has been found to be greatly improved by the plasma as well as silane treatment. The filler–rubber interaction has been found to be greatly improved by both surface treatments, but the best balance of mechanical properties has been observed with plasma surface modification only. Copyright © 2004 John Wiley & Sons, Ltd.     

pH柔性膜电极的制作与表征

采用木犀草素为pH值选择性试剂,石墨粉为导电基质,PVC为成膜材料,自制无毒无害的pH柔性膜电极(pH flexible electrode,pH/FE)。该电极有一个氧化峰,它的峰电位对2.00~9.00范围内的pH值有线性响应,并且具有弯曲度好、抗拉伸性强、溶胀性能稳定、准确度高,选择性好等性能。此电极有望作为柔性检测器件用于非平面介质表面液层pH值的测定。     

Production of macrocyclic lactones through catalytic oxidation of cyclohexanone

The aim of this work is basically centred in the improvement of the obtention of the peroxides precursors of macrocyclic lactones (C11 and C16) through the Story synthesis useful as raw materials for high performance linear polyesters. As a starting point, the yield has been increased respect to the classic synthesis using mild and intrinsically safer reactants. Concretely, a yield of 55% in triperoxide of cyclohexanone has been achieved using 35% hydrogen peroxide and phosphotungstic acid as catalyser. For this intention two factorial experimental designs, fractional and complete, have been carried out. The analytical method adequate for the reactive system studied (HPLC-UV-RI) has been chosen as well as the optimal operating conditions. A quantification of the risk on the first part of the reaction in calorimetric terms has been performed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tire-Rubber-Waste Recycling and Active Powder of Discretely Devulcanized Rubber

Key aspects of tire-rubber-waste collection, accumulation, processing, and further application have been examined. Special attention has been paid to application of ground tire rubber as a road-pavement modifier. The data on the structure and properties of tire-rubber powders obtained by different grinding techniques have been presented. It has been established that active tire-rubber powder (APDDR) fabricated by means of high-temperature shear grinding exhibits substantial advantages as compared to other rubber powders. In particular, applying these powders as modifiers has allowed to significantly improve properties of the paving bitumen and, as a result, the quality of asphalt concrete.     

An investigation of the potential uses of iodine monochloride as a titrant in thermometric titrimetry

An investigation has been made of the potential uses of iodine monochloride as a titrant in thermometric titrimetry. A series of substances, inorganic and organic, has been selected so that a range of stoichiometries and of various types of reaction products result from the oxidation. It has been found to be necessary to prevent the formation of iodine formed by oxidation of the iodide produced by the reduction of iodine monochloride. This is successfully accomplished by using mercury(II) to mask the iodide in a mercury(II)-iodide complex. However, the evolution of gaseous products tends to give curvature of the enthalpogram near the equivalence point and the method is not recommended for the determination of compounds such as thiosemicarbazide. For many other systems, iodine monochloride used in the presence of mercury(II) has analytical potential as a thermometric titrant.     

Polymerization of methyl acrylate in aqueous media

The polymerization of methyl acrylate in water and in dilute, aqueous, soap solutions, initiated by potassium peroxydisulfate, has been investigated, a dilatometric method being used to follow the conversion. It has been shown that small amounts of an anionic soap increase the rate of reaction while a cationic soap has the reverse effect. The change of molecular weight with conversion has also been examined as well as the effect of the exclusion of oxygen from the system.     

Competitive wetting of acetonitrile and dichloromethane in comparison to that of water on functionalized carbon nanotube surfaces

Differential wetting of pristine and ozonized carbon nanotubes has been studied using solvents like acetonitrile and dichloromethane in comparison to the well-known wetting behavior of water. Based on their unique structural and physical properties, functionalized CNT substrates have been used due to the fact that independent variation in molecular as well as electronic properties could be controlled by understanding the wetting of these liquids on carbon nanotubes (CNTs), both pristine as well as ozone treated. The sensitivity of the wetting behavior with respect to molecular interactions has been investigated using contact angle measurements while Raman and XPS studies unravel the differential wetting behavior. Charge-transfer between adsorbed molecules and CNTs has been identified to play a crucial role in determining the interfacial energies of these two liquids, especially in the case of acetonitrile. Ozone treatment has been observed to affect the surface properties of pristine CNTs along with a concomitant change in the wetting dynamics.     

Electrophoretic Mobility of a Polyelectrolyte Capsule

The electrophoretic motion of a polyelectrolyte capsule has been considered in a uniform electric field. The capsule carries a uniformly distributed charge and is permeable to ions of different natures. An electrolyte identical to a dispersion medium is located inside the capsule. The flow in the porous layer of the capsule has been described by the Brinkman equations taking into account the effect of electrostatic forces. The distribution of ions in the vicinity of the capsule has been determined, and its electrophoretic mobility has been found in a linear approximation. The mobility of the capsule has been studied as depending on its geometric characteristics, permeability, and charge density. In particular, a complex extremal character of variations in the mobility as depending on the solid phase fraction in the capsule has been revealed at different ratios between the thicknesses of the electrical double layer and the Brinkman filtration layer.     

Enantioselective organocatalytic alpha-fluorination of aldehydes

The first direct enantioselective catalytic alpha-fluorination of aldehydes has been accomplished. The use of enamine catalysis has provided a new organocatalytic strategy for the enantioselective fluorination of aldehydes to generate alpha-fluoro aldehydes, an important chiral synthon for medicinal agent synthesis. The use of imidazolidinone 1 as the asymmetric catalyst has been found to mediate the fluorination of a large variety of aldehyde substrates with N-fluorobenzenesulfonimide serving as the electrophilic source of fluorine. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. While catalyst quantities of 20 mol % were generally employed in this study, successful halogenation can be accomplished using catalyst loadings as low as 2.5 mol %.     

Synthesis of 1-aryl-1H-indazoles via palladium-catalyzed intramolecular amination of aryl halides

Palladium-catalyzed cyclization of arylhydrazones of 2-bromoaldehydes and 2-bromoacetophenones to give 1-aryl-1H-indazoles has been studied in detail. The cyclization of arylhydrazone of 2-bromobenzaldehydes can be performed with good to high yields using Pd(dba)2 and chelating phosphines, of which the most effective are rac-BINAP, DPEphos, and dppf, in the presence of Cs2CO3 or K3PO4 as a base. Electron-rich, bulky ligands commonly employed for intermolecular amination such as PtBu3 and o-PhC6H4PtBu2 were shown to be ineffective for cyclization and to lead instead to extensive oligomerization and tarring. The method developed is applicable for preparation of a wide scope of indazoles bearing electron-donating or electron-withdrawing substituents, among them, unprotected carboxyl, as well as various indazole heteroanalogues. The cyclization of arylhydrazones of less reactive halides such as 2-chlorobenzaldehyde, as well as 2-bromoacetophenone and bromotetralone, has been achieved. The purity of the starting hydrazone has been shown to be a critical parameter, as various impurities inhibit the cyclization.     

Infra-red and electronic absorption spectra of 2-bromopyrimidine

The electronic absorption spectrum of 2-bromopyrimidine in the u.v. region has been recorded in vapour phase and in solution phase in different solvents. Only one system has been observed in vapour phase and it has been identified as π* ← n transition. In solution phase two systems have been identified. The system on the longer wavelength side has been identified as corresponding to the one observed in vapour phase while the other one has been assigned to a π* ← π transition. The infrared spectrum of this molecule has also been recorded and analysed. Help of these i.r. data has been taken to analyse the u.v. spectrum of 2-bromopyrimidine, considering the molecule as belonging to C_2υ point group.     

Self-assembly of photonic crystals from polymer colloids

This article reviews recent developments in self-assembly of polymer colloids into colloidal crystals, a good candidate material for photonic crystals. Self-assembly strategy has developed as a facile and efficient method to fabricate colloidal crystals. Much research work has been focused on controlling the morphology and improving the quality, as well as finding applications of the colloidal crystals.     

Role of cations and confinement in asymmetric photochemistry: enantio- and diastereo-selective photocyclization of tropolone derivatives within zeolites

Asymmetric induction in photochemical reactions has been explored using the photochemistry of tropolones as a model. Three approaches have been examined: chiral inductor, chiral auxiliary and [chiral inductor + chiral auxiliary]. All three methods gave excellent asymmetric induction in zeolite and very little or zero induction in solution. Results presented on tropolones clearly illustrate the remarkable influence that a confined space studded with cations can have on asymmetric induction. Tropolone derivatives, upon irradiation undergo 4pi-electron electrocyclization to yield a bicyclic product and a rearranged product. Enantiomeric excess up to 68% has been achieved in the cyclized product. In systems where a chiral inductor has been covalently linked, diastereomeric excess as high as 88% has been achieved within a zeolite while the same system in solution gave 10%.     

Preservation mechanisms of trehalose in food and biosystems

The stability or shelf-life of food and biomaterials has always been a critical issue in the food and pharmaceutical industry. Trehalose (alpha-D-glucopyranosyl-alpha-D-glucopyranoside), a non-reducing diglucose sugar found in nature, confers to certain plant and animal cells the ability to survive dehydration for decades and to restore activity soon after rehydration. The interaction between trehalose and cell membranes or proteins, however, remains a debated subject, and a significant amount of work has been done to elucidate the mechanisms resulting in this unique behavior of preservation. This study shows how an interfacial phenomena approach has led to the use of trehalose as an excipient during freeze drying of a variety of products in the pharmaceutical industry. It also suggests opportunities as an ingredient for dried and processed food, as well as a non-toxic cryoprotectant of vaccines and organs for surgical transplants.     

Kinetics of the formation of biliverdin during the photochemical oxidation of bilirubin monitored by column liquid chromatography

In the photochemical oxidation of bilirubin, biliverdin is formed as the primary product and is further degraded. This photooxidation is especially significant in the presence of riboflavin. Column liquid chromatography was used to monitor the kinetics of this reaction. The biliverdin concentration amounts to a maximum of ca. 38% of the total loss of bilirubin in experiments in vitro. It is probable that this mechanism is also operative during phototherapy. The formation of a product of the photooxidation of biliverdin that has not yet been identified has been observed; the product behaves as a dimer. A method for the determination of biliverdin in the blood of newborn infants has been developed. It has been found that the biliverdin content increases during hyperbilirubinaemia.     

In defense of the quasimolecular ion

The term quasimolecular ion has been used to describe ions comprising a molecule and weakly bound positive or negative ion or an ion formed by the loss of a proton from a molecule. This term was used in mass spectrometry from the late 1960s after the development of chemical ionization but has been deprecated in recent terms recommendations due to what is perceived as its overly broad use. This letter argues that the term is well defined and has a long history of use in mass spectrometry and other fields and should be considered as a recommended term.     

The structure of a biosynthetic intermediate of pyrroloquinoline quinone (PQQ) and elucidation of the final step of PQQ biosynthesis

Pyrroloquinoline quinone (PQQ) is a tricyclic o-quinone, which serves as a cofactor in several enzyme-catalyzed redox reactions in certain bacteria. PQQ is also important for human health, and its role as a vitamin in mammals has recently been suggested. Although much is known about the function of enzymes that use PQQ as cofactor, relatively little is known about the biosynthesis of this coenzyme. Six gene products in Klebsiella pneumoniae (PqqA-F) are involved in PQQ biosynthesis, and PqqC has been shown to catalyze the last step in the pathway. The chemical structure of the substrate for PqqC has remained elusive and has hampered our understanding of the nature of this reaction. In this report we describe the purification and structure of the substrate as deduced by a number of spectroscopic and chemical methods. The substrate is 3a-(2-amino-2-carboxyethyl)-4,5-dioxo-4,5,6,7,8,9-hexahydroquinoline-7,9-dicarboxylic acid-a fully reduced derivative of PQQ, which has not undergone ring cyclization. These results show that PqqC catalyzes a novel reaction, which involves ring closure and an amazing eight-electron oxidation of the substrate.