Molecular dynamics simulation of continuous current flow through a model biological membrane channel

The conductance of sodium ions through a simplified channel-membrane system immersed in a reservoir of 1M NaCl in SPC/E water is examined by molecular dynamics simulation. An applied external potential of 1.1 V drives the ions and water through a channel of length 25 A producing a current of 19.6 pA, in reasonable agreement with experimental findings. The stream of ions and water molecules flows continuously because of the constant applied field and periodic boundary conditions. We also examine the potential profile across the simulation cell, the average density distributions of the various species in the reservoir and radially in the channel, and the ion velocity in the channel.     

Isentropic compressibilities of univalent electrolytes in methanol at 25°C

A flow densimeter and an ultrasonic sound velocimeter have been used to measure densities and isentropic compressibilities of solutions of LiBr, NaCl, NaBr, Nal, KF, KCl, KBr, Kl, RbBr, Rbl, CsF, CsBr, Ph ₄ PBr, and NaBPh ₄ in anhydrous methanol at 25°C. the latter two electrolytes were also investigated in water at 25°C. Concentrations ranged from about 0.005 m to above 0.25m, solubility permitting. Apparent molar isentropic compressibilities, K_S,, have been calculated and extrapolated to infinite dilution to obtain K _S, ^o . The K _S, ^o values in methanol are all negative, and significantly more negative than the corresponding data in water. Additional data from the literature for acetonitrile and ethanol solutions show that K _S, ^o for the alkali metal halides become more negative in direct proportion to increasing solvent isentropic compressibility. Furthermore, the dependence of K _S, ^o in ionic size also varies in proportion to solvent isentropic compressibility. An explanation of this behavior is presented.     

Inverse temperature-dependent pathway of cellulose decrystallization in trifluoroacetic acid

An unusual inverse temperature-dependent pathway was observed during cellulose decrystallization in trifluoroacetic acid (TFA). Decreasing the TFA treatment temperature accelerated the cellulose decrystallization process. It took only 100 min to completely decrystallize cellulose at 0 degrees C in TFA, a result not achieved in 48 h at 25 degrees C in the same medium. There was neither cellulose esterification nor a change of cellulose macrofibril morphology by TFA treatment at 0 degrees C. Our IR data suggest that TFA molecules are present as cyclic dimers when they penetrate into crystalline cellulose regions, transforming crystalline cellulose to amorphous cellulose. On the other hand, the rate of TFA penetration into the cellulose matrix was greatly retarded at higher temperatures where monomeric TFA prevails. At elevated temperatures, esterification of TFA monomers on the external surface of crystalline cellulose, agglomeration of cellulose macrofibrils, as well as water released from the esterification reaction, inhibit the diffusion rate of TFA into the cellulose crystalline region and decrease the TFA swelling capability.     

Die Verwendung des Cupferrons in der quantitativen Analyse

Ohne Zusammenfassung Die Zitate zu diesem Referat folgen ausnahmsweise am Schlusse des ganzen Artikels S. 66.     

Versuche zur Bestimmung von Uran mittels Cupferrons

Ohne Zusammenfassung     

A Partition Theory of Planar Animals

A dissection of an animal is a partition of its cells into blocks that are themselves animals. The n-rule allows only those dissections with the area of every block a multiple of n. If an animal with area divisible by n has no dissection allowed by the n-rule, then the animal is said to be an n-irreducible. The partition meet of all allowed dissections of a given animal is called the n-dissection residue of that animal. This paper considers only planar animals. All 2-irreducibles are found, and the problem of computing 2-dissection residues is solved. Two theorems on n-irreducibles are proved. One of them states that large n-irreducibles always arise by adding cells to smaller n-irreducibles.     

Nanotechnology and the public: Effectively communicating nanoscale science and engineering concepts

Researchers are faced with challenges when addressing the public on concepts and applications associated with nanotechnology. The goal of our work was to understand the public’s knowledge of nanotechnology in order to identify appropriate starting points for dialog. Survey results showed that people lack true understanding of concepts associated with atoms and the size of the nanoscale regime. Such gaps in understanding lead to a disappointing lack of communication between researchers and the public concerning fundamental concepts in nanoscale science and engineering. Strategies are offered on how scientists should present their research when engaging the public on nanotechnology topics. Since the time of writing, O.M. Castellini has relocated to the Department of Science and Technology, Museum of Science and Industry, 57th Street and Lake Shore Drive, Chicago, IL 60637, USA.     

Hydrogen Bonding Enhances the Electrochemical Hydrogenation of Benzaldehyde in the Aqueous Phase

The hydrogenation of benzaldehyde to benzyl alcohol on carbon‐supported metals in water, enabled by an external potential, is markedly promoted by polarization of the functional groups. The presence of polar co‐adsorbates, such as substituted phenols, enhances the hydrogenation rate of the aldehyde by two effects, that is, polarizing the carbonyl group and increasing the probability of forming a transition state for H addition. These two effects enable a hydrogenation route, in which phenol acts as a conduit for proton addition, with a higher rate than the direct proton transfer from hydronium ions. The fast hydrogenation enabled by the presence of phenol and applied potential overcompensates for the decrease in coverage of benzaldehyde caused by competitive adsorption. A higher acid strength of the co‐adsorbate increases the intensity of interactions and the rates of selective carbonyl reduction.     

Catalytic hydrogenation of glutamic acid

Technology to convert biomass into chemical building blocks provides an opportunity to displace fossil fuels and increase the economic viability of biorefineries. Coupling fermentation capability with aqueous-phase catalysis provides novel routes to monomers and chemicals, including those not accessible from petrochemical routes. Glutamic acid provides a platform to numerous compounds through thermochemical approaches including hydrogenation, cyclization, decarboxylation, and deamination. Hydrogenation of amino acids also provides access to chiral compounds with high enantiopurity. This article detals aqueous-phase hydrogenation reactions that we have developed that lead to valuable chemical intermediates from glutamic acid. In addition, ¹³C nuclear magnetic resonance and matrix-assisted laser desorption ionization mass spectral data are presented that provide a mechanistic picture of the reactions. The results show that hydrogenation of glutamic acid has unique characteristics from other amino acids and that paradigms in the literature do not hold up for this transformation.