Catalytic properties of massive iron-subgroup metals in dichloroethane decomposition into carbon products

The formation of nanocarbon materials on massive nickel, nichrome, and some other alloys via the carbide cycle mechanism is reported using 1,2-dichloroethane decomposition as an example. The role of the physical stage of the carbide cycle is elucidated, and massive metal surface activation methods ensuring the realization of this stage are considered. The surface layer of massive nickel or some nickel alloys is most effectively activated by the action of chlorine resulting from the catalytic decomposition of 1,2-dichloroethane. It has been demonstrated by ferromagnetic resonance (FMR) spectroscopy that the activation of the massive metal surface in 1,2-dichloroethane decomposition to nanocarbon is due to the surface undergoing crystal chemical restructuring. The microstructuring of the surface yields fine Ni particles similar in size (0.2–0.3 μm) and shape, whose FMR spectra are anisotropic and have similar magnetic resonance parameters. Both chlorine-free and chlorinated hydrocarbons decompose over these particles via the carbide cycle mechanism. It is demonstrated that it is possible to design catalytic reactors packed with massive nickel or its alloy. The nanocarbon material obtained in such a reactor will not be contaminated by components of conventional catalyst supports (Al, Mg, etc.). The stable performance temperature of the catalyst will be increased, and this will allow the equilibrium outlet methane concentration to be reduced.     

Interactions of halichondrin B and eribulin with tubulin

Compounds that modulate microtubule dynamics include highly effective anticancer drugs, leading to continuing efforts to identify new agents and improve the activity of established ones. Here, we demonstrate that [(3)H]-labeled halichondrin B (HB), a complex, sponge-derived natural product, is bound to and dissociated from tubulin rapidly at one binding site per αβ-heterodimer, with an apparent K(d) of 0.31 μM. We found no HB-induced aggregation of tubulin by high-performance liquid chromatography, even following column equilibration with HB. Binding of [(3)H]HB was competitively inhibited by a newly approved clinical agent, the truncated HB analogue eribulin (apparent K(i), 0.80 μM) and noncompetitively by dolastatin 10 and vincristine (apparent K(i)'s, 0.35 and 5.4 μM, respectively). Our earlier studies demonstrated that HB inhibits nucleotide exchange on β-tubulin, and this, together with the results presented here, indicated the HB site is located on β-tubulin. Using molecular dynamics simulations, we determined complementary conformations of HB and β-tubulin that delineated in atomic detail binding interactions of HB with only β-tubulin, with no involvement of the α-subunit in the binding interaction. Moreover, the HB model served as a template for an eribulin binding model that furthered our understanding of the properties of eribulin as a drug. Overall, these results established a mechanistic basis for the antimitotic activity of the halichondrin class of compounds.     

The orientation and charge of water at the hydrophobic oil droplet-water interface

We established the charge and structure of the oil/water interface by combining ζ-potential measurements, sum frequency scattering (SFS) and molecular dynamics simulations. The SFS experiments show that the orientation of water molecules can be followed on the oil droplet/water interface. The average water orientation on a neat oil droplet/water interface is the same as the water orientation on a negatively charged interface. pH dependent experiments show, however, that there is no sign of selective adsorption of hydroxide ions. Molecular dynamics simulations, both with and without intermolecular charge transfer, show that the balance of accepting and donating hydrogen bonds is broken in the interfacial layer, leading to surface charging. This can account for the negative surface charge that is found in experiments.     

Tridentate ionic hydrogen-bonding interactions of the 5-fluorocytosine cationic dimer and other 5-fluorocytosine analogues characterized by IRMPD spectroscopy and electronic structure calculations

Ionic hydrogen-bonding interactions have been found in several clusters formed by 5-fluorocytosine (5-FC). The chloride and trimethylammonium cluster ions, along with the cationic (proton-bound) dimer have been characterized by infrared multiple-photon dissociation (IRMPD) spectroscopy and electronic structure calculations performed at the B2PLYP/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. IRMPD action spectra, in combination with calculated spectra and relative energetics, indicate that it is most probable that predominantly a single isomer exists in each experiment. For the 5-FC-trimethylammonium cluster specifically, the calculated spectrum of the lowest-energy isomer convincingly matches the experimental spectrum. Interestingly, the cationic dimer of 5-FC was found to have a single energetically relevant isomer (Cationic-IV) involving a tridentate ionic hydrogen-bonding interaction. The three sites of intermolecular ionic hydrogen bonds in this isomer interact very efficiently, leading to a significant calculated binding energy of 180 kJ/mol. The magnitude of the calculated binding energy for this species, in combination with the strong correlation between the simulated and IRMPD spectra, suggests that a tridentate-proton-bound dimer was observed predominantly in the experiments. Comparison of the calculated relative Gibbs free energies (298 K) for this species and several of the other isomers considered also supports the likelihood of the dominant protonated dimer existing as Cationic-IV.     

Intermolecular interactions in mixtures of dichroic dyes with n-alkyl-4-(4-isothiocyanatophenyl)bicyclo[2,2,2]octanes

On the basis of the polarized absorption spectra, the guest order parameter as a function of temperature for five dichroic azo dyes dissolved in four members (pentyl to octyl) of the homologous series of n-alkyl-4-(4-isothiocyanatophenyl)bicyclo[2,2,2]octanes has been evaluated. Moreover, the influence of the dichroic dye addition on the nematic-isotropic phase transition temperature has been examined. The relation between the molecular geometry of the guest, its orientation efficiency in the nematic host and the clearing temperature of the azo dye-liquid crystal mixtures has been determined. The experimental results have been compared in some detail with calculations performed on the basis of the mean field theory for binary mixtures.     

Influence of substituent length in dichroic dye molecules on the orientational properties of guest-host liquid crystal mixtures

The polarized absorption spectra of eight dichroic dyes, alkyl derivatives of 4-amino-(N-ethylnaphthalimide) dissolved in the nematic liquid crystals 5CB and 6CHBT have been measured as a function of temperature. On the basis of these spectra, the guest order parameter has been evaluated. The influence of the alkyl chain length of the dye molecule on the molecular orientation has been examined. Moreover, the nematic-isotropic transition temperatures for the dye-liquid crystal mixtures have been determined. The experimental results have been compared in some detail with calculations made on the basis of the mean field theory for binary mixtures.     

Statistical analyses of electromyographic activity in spasmodic dysphonic and normal control subjects

Heterogeneity in the quality and task sensitivity of vocal symptoms in the spasmodic dysphonia (SD) population contributes to controversy as to whether this is a single disorder or two disorders with different etiologies (neurogenic versus psychogenic). Perceptual and acoustic assessments of vocal symptoms are inadequate to resolve this controversy. However, myoelectric events are intimately proximal to the source of vocal disruption and may be informative. The present report employs statistical modeling of quantitative amplitude measures of electromyographic activity recorded from thyroarytenoid to examine neuromotor bases of vocal symptoms in SD. Consideration of perceptual ratings of the quality and task sensitivity of vocal symptoms in the context of statistical models provides support for the conclusion that the range of vocal symptoms identified as SD represents a single, neurogenic disorder.     

Coherent interactions in two-beam excite-probe absorption measurements: Phase gratings in flowing samples

As a rule, phase gratings yield no power transfer in two-beam excite-probe experiments. We show that an exception to this rule is that of ultrashort-pulse excite-probe experiments involving slow phase effects, such as thermal gratings, occurring in a moving sample medium under high-repetition-rate excitation. A symmetric coherent artifact results, and depending on the direction of the sample motion, its amplitude can be positive, negative, or zero. This artifact occurs only in multiple-pulse experiments, involving accumulated gratings, while, on the other hand, the antisymmetric artifact (described by Palfrey and Heinz) results only from single-pulse effects. We discuss these two complementary effects and present both theory and experiments.This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences Division     

On the role of vacancies in pore formation in the course of anodizing of silicon carbide

Experimental data on the preparation of stoichiometric nanoporous silicon carbide are analyzed. Theoretical calculations are performed under the assumption that nanopores are formed through the vacancy diffusion mechanism. The results obtained confirm the hypothesis that the formation of pores with a steadystate radius of several tens of nanometers in silicon carbide can be associated with the diffusion and clustering of vacancies. The experimental data indicating that the proposed mechanism of formation of nanoporous silicon carbide correlates with the existing model of formation of porous silicon carbide with a fiber structure are discussed. This correlation can be revealed by assuming that nanopores are formed at the first stage with subsequent transformation of the nanoporous structure into a fiber structure due to the dissolution of the material in an electrolyte.     

Minimal Peano curve

A Peano curve p(x) with maximum square-to-linear ratio |p(x)?p(y)|²/|x?y| equal to 5 2/3 is constructed; this ratio is smaller than that of the classical Peano-Hilbert curve, whose maximum square-to-linear ratio is 6. The curve constructed is of fractal genus 9 (i.e., it is decomposed into nine fragments that are similar to the whole curve) and of diagonal type (i.e., it intersects a square starting from one corner and ending at the opposite corner). It is proved that this curve is a unique (up to isometry) regular diagonal Peano curve of fractal genus 9 whose maximum square-to-linear ratio is less than 6. A theory is developed that allows one to find the maximum square-to-linear ratio of a regular Peano curve on the basis of computer calculations.