Theoretical study of mechanism and selectivity of copper-catalyzed C-H bond amidation of indoles

Density functional theory calculations are used to study the reaction mechanism and origins of C2 selectivity in a copper(I)-catalyzed amidation of indoles. It is shown that concerted metalation-deprotonation is not able to reproduce the observed regioselectivity. Instead, an unprecedented mechanism based on a four-center reductive elimination is proposed to be responsible for the reaction outcome. This mechanism has a lower reaction barrier and is able to reproduce the experimentally observed selectivity. A possible alternative mechanism involving a Cu(II) species instead of Cu(III) is presented, but it is shown that higher energy barriers are associated with this mechanism. An important technical detail is that addition of dispersion effects to the B3LYP results is necessary to reproduce the observed selectivity, although not important for the overall mechanistic proposal.     

Effect of pretreatment of molasses and posttreatment of fermented broth in industrial production of ethanol

The aim of preclarification is to minimize sludge going to yeast separators. This purpose is partially fulfilled. However, it has been measured during the plant trial runs that preclarification does not noticeably improve fermentation. The aim of postclarification is to minimize sludge going to distillation. This purpose is well served as noted from the fact that cycle run of distillation columns using postclarification is three times longer (9–12 mo) as compared to the normal one (3–4 mo).     

Study of the influence of concentration on the time for first appearance of crystallization of polyethylene from xylene

An experiment is reported in which a simple laser light-scattering technique is used to measure the time for a critical turbidity to appear during the crystallization of polyethylene in xylene. The effect is examined over the entire range of solution concentration, and it is found that the relation between this concentration and temperature is linear for all solutions, provided that the time for turbidity to develop is arranged to be the same in all cases. In the appendix it is reasoned that similar results could have been obtained if, instead, times had been measured to a given degree of crystallinity rather than of turbidity. Departures from this linearity at low concentrations are taken as indicating multimolecular nucleation for all concentrations greater than about 1%.     

Chronocoulometric study of the electrochemistry of Prussian blue

During the electrochemical oxidation of Prussian blue (PB) to Prussian yellow (PY), an electrocatalytic oxygen production proceeds at the electrode when aqueous electrolyte solutions are used. The formed oxygen is scavenged by the PY, probably by absorption, and it is consumed during the electrochemical reduction of PY to PB by a heterogeneous chemical reaction of PB with oxygen to PY and hydrogen peroxide. Because of this catalytic regeneration of PY, it is impossible to determine the amount of low-spin iron by chronocoulometry using a potential program in which PB is first oxidized to PY and then the charge is measured to reduce PY to PB. The latter charge is biased by the electrocatalytic PY regeneration.     

Shear modulus of sintered 'house of cards'-like assemblies of crystals

A cell model of a 'house of cards'-like assembly of crystals is used for the study of the evolution of the shear modulus during sintering. The crystals are assumed to have a lozenge shape. The cell model takes different crystal-crystal contacts into account. The force needed to separate two sintered crystals is calculated using the minimum surface area (MSA) approximation. By varying the thickness, long axis, and short axis of the crystals, it is possible to make space-filing configurations which have a nonzero shear modulus at crystal volume fraction that can be as low as phi = 0.03. This is significantly lower than the volume fractions phi > 0.52 that are found in studies where the MSA approximation is applied to assemblies of spherical particles. It is found that sintering may cause a nonlinear volume fraction dependence of the shear modulus, which depends on the shape of the crystals, the type of crystal-crystal contacts, and the character of the crystal assembly. The calculated shear modulus is analyzed using the phenomenological expression (phi - phi0)beta, where phi0 represents the volume fraction at the start of sintering. The exponent beta is found to vary between 1 and 2. The interpretation of the shear modulus using a fractal model is also discussed.     

渣油悬浮床加氢水溶性催化剂预硫化研究 Ⅱ 钼酸盐硫化产物的XPS分析

通过XPS分析法对钼酸盐的硫化行为进行了考察,分别考察了四价钼物种质量分数和硫钼元素的质量分数比，发现硫化产物的表面化学组成中四价钼质量分数和硫钼元素质量分数比不成正比，证实了该产物表面钼的硫化物不完全以MoS2形式存在。未经过临氢加热的硫化产物表面的四价钼物种的质量分数显著低于经过临氢加热的样品的质量分数，说明临氢加热在钼酸盐的硫化过程中起了重要作用。氯化铵是钼酸盐硫化过程中有效的助硫化剂，当它的用量增大时，硫化产物表面四价钼的质量分数也增大。以蒽为探针，使用化学探针法测定了硫化产物在渣油加氢过程中的催化活性，发现随着氯化铵用量的增加，产物的催化活性也相应提高，印证了XPS测定结果。     

Formation of ring-shaped deposits as a result of evaporating droplets of dispersions of silver nanoparticles and study of their fine structure

Scanning electron microscopy is employed to study ring-shaped deposits formed at different time moments of evaporating droplets of silver colloidal solutions on a glass substrate. It is shown that, in addition to an external fringe, several rings are formed at intermediate stages of evaporation; these rings are, in the course of time, transformed into one dense fringe and a transition zone adjacent to its internal side. The time dependences of the height and width of the fringe are determined. It is established that an increase in the width and height of the fringe is due to the transfer of silver nanoparticles to this region, which play a key role in imparting specific structural organization to the fringe. It is noted that the height of the formed fringe may be qualitatively determined by energy dispersive X-ray microanalysis.     

Nonconservation of excitons as a mechanism of light-energy capturing

The analysis of nonstationary processes, taking place in exciton systems in consequence of the nonconservation of the number of elementary excitations, is presented and it is pointed out to a new possibility of light-energy capturing which exists in ecological systems due to the nonconservation of excitons. It is shown that, due to the nonconservation, the one-dimensional molecular chain is able to capture permanently the light energy of the order of 50 keV to 5 MeV. A part of the captured energy is expected to have a role in internal bioprocesses. It is also shown that the system is a seat where the processes of continuous creations and annihilations of pairs of excitons having opposite momenta take place with a probability of the order of 10^?4 to 10^?2. Further investigations would allow to identify biological phenomena caused by those processes.     

Optical Study of Interactions of Glass Beads ER Particles

The amount of ER effect is determined by the difference of dielectric constants of ER particles base liquid.The intensity of ER fluids can be characterized by the interaction of two particles. A double optical tweezers system suitable to study particle interaction is used to measure the particle aggregation time, and it is found that the particle aggregation time is proportional to the square of the electric field. This is the first time to directly measure the interaction of the electric dipoles of ER particles. A method is developed to use high speed CCD in measuring diffusing-wave spectroscopy (DWS), and, for the first time, the auto-correlation functions of nonegordic system of particle structure are measured to study the ER mechanism. Structure response time and force response time are obtained for glass beads ER fluid, and the time variation of characteristic decay times of system correlation functions under different electric fields is also measured. Diffusing coefficients under different fields imply that the interaction is proportional to the square of fields.     

Mechanisms of antioxidant action: Sulphur compounds as inhibitors of mechanochemical degradation of rubber

It is shown that the stability of sulphur vulcanised natural rubber to mechanodegradation (fatigue) is associated with the formation of labile oxidation products. The addition of sulphides and their oxidation products to a non-sulphur vulcanisate has a similar effect. Stress relaxation shows that the initial rate of chain scission under stress is directly related to the fatigue resistance of the vulcanisate. However, the oxidation process also produces peroxidolytic antioxidants (PD-C). It is concluded that the fatigue resistance of sulphur vulcanisates is due to a combination of facile restructurisation and an oxidation chain-breaking mechanism.     

Investigation of MM-PBSA rescoring of docking poses

Target-based virtual screening is increasingly used to generate leads for targets for which high quality three-dimensional (3D) structures are available. To allow large molecular databases to be screened rapidly, a tiered scoring scheme is often employed whereby a simple scoring function is used as a fast filter of the entire database and a more rigorous and time-consuming scoring function is used to rescore the top hits to produce the final list of ranked compounds. Molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) approaches are currently thought to be quite effective at incorporating implicit solvation into the estimation of ligand binding free energies. In this paper, the ability of a high-throughput MM-PBSA rescoring function to discriminate between correct and incorrect docking poses is investigated in detail. Various initial scoring functions are used to generate docked poses for a subset of the CCDC/Astex test set and to dock one set of actives/inactives from the DUD data set. The effectiveness of each of these initial scoring functions is discussed. Overall, the ability of the MM-PBSA rescoring function to (i) regenerate the set of X-ray complexes when docking the bound conformation of the ligand, (ii) regenerate the X-ray complexes when docking conformationally expanded databases for each ligand which include "conformation decoys" of the ligand, and (iii) enrich known actives in a virtual screen for the mineralocorticoid receptor in the presence of "ligand decoys" is assessed. While a pharmacophore-based molecular docking approach, PhDock, is used to carry out the docking, the results are expected to be general to use with any docking method.     

Dependence of the Rate of Electrodeposition of Metals at Mono- and Multielectrodes on Voltage in the Case of an Exaltation Mechanism of Mass Transport

Dependences of the rate of copper deposition on mono- and multielectrodes out of dilute solutions of acetic acid at voltages of 20–250 V are compared. It is established that the same rate of deposition in the case of a multielectrode (25 electrodes with a diameter of 0.1 mm) takes place at a voltage that is lower by 2.7 times than that in the case of a monoelectrode with a diameter of 0.5 mm and the same area. The same results are obtained during electrodeposition of cadmium and thallium. In order to explain this effect, a two-layered model of potential distribution is suggested. In accordance with this model, the resistance of electrolyte in the vicinity of a multielectrode is equal to the sum of the resistance of the layer nearest to the electrode (where it is determined by the sum of conductances to each microelectrode) and the external layer, where the potential distribution is close to hemispherical. It is shown that calculations in accordance with this model allow one to give an estimate of the effect's scale that agrees with experiment and to predict its possible limits following an increase in the number of electrodes that make up a multielectrode.     

Stability of two-dimensional growth of a packed body of proteins on a solid surface

Adsorption of proteins from the bulk is at times accompanied by a rearrangement which leads to the formation of closed packed bodies, that may or may not be crystalline. Mass transfer of protein molecules on a surface is modeled. Forced diffusion by van der Waals and electrostatic forces leads to segregation, which is eventually a different phase that is assumed to be thermodynamically favored. The net effective force in two-dimensions has been modeled approximately and shown to be much stronger and more long ranged than in the bulk: that is, under the same conditions, the protein molecules may not aggregate in the bulk they may aggregate on a surface. These forces have been used only indirectly but equivalently as an adsorption-desorption step at the interline. Eventually, a linear stability analysis of the growing body shows it to be unstable and would give rise to whiskers that are one molecule thick. This is what is observed experimentally. The conditions that give rise to the instability have been determined. The reverse case of rinsing of the protein molecules has also been studied experimentally and has been analyzed using the same mechanisms. Here it is seen that thicker inroads into the packed body cause the interline to take on a spongy appearance. It is conjectured that eventually islands will appear as seen in the experiments.     

Detection of cavities in a set of interpenetrating spheres

A general topological procedure is described that is able to detect cavities of all shapes and sizes in a system of interpenetrating spheres. The procedure is coupled to an analytic algorithm for computing surface areas and volumes, but as such, involves only logical operations and is therefore not subject to numerical imprecision. Its application to the identification of internal cavities in molecular systems is illustrated.     

Effect of solutes on the viscosity of supercritical solutions

This study shows that solutes can impart significant structure to supercritical solutions, resulting in unexpectedly high solution viscosity at pressures close to the critical value. The viscosity passes through a minimum as the pressure is increased, and this is accounted for by a solvation of the solutes leading to a decrease in solute-solute interactions. At high pressure, the solution viscosity is similar to that of the pure solvent as solvent-solvent interactions dominate. The increase in relative viscosity is modeled using a modified Dole-Jones equation, and it is shown that the change in relative viscosity is related to the volume fraction occupied by the solute. A general model is presented for simple solutes whereby the viscosity of a supercritical solution can be calculated from the molecular volume of the solute and the viscosity of the pure fluid. The higher than expected viscosity observed at low pressures is used to explain the variation of reaction rate constant with pressure.     

On the definition of the excess permittivity of a fluid mixture

It is shown that under the assumption of no intermolecular interaction, the permittivity of a homogeneous linear and isotropic fluid mixture is the sum of the individual permittivities weighted with the mole fractions of the components. For definiteness, a proof is given for gasses under standard temperature and pressure; it is, however, easy to generalize it to other conditions, as well as to liquids, as long as the assumption of no intermolecular interaction is retained. Also, although the proof is given for a binary mixture, it is a simple exercise to extend it to any multicomponent mixture.     

Antiparallel arrangement of the helices of vesicle-bound alpha-synuclein

alpha-Synuclein (alphaS) is the main component of Lewy bodies from Parkinson's disease. That alphaS binds to membranes is known, but the conformation it adopts is still unclear. Pulsed EPR on doubly spin-labeled variants of alphaS sheds light on the most likely structure. For alphaS bound to vesicles large enough to accommodate also the extended conformation, an antiparallel helix conformation is found. This suggests that the bent structure shown is the preferred conformation of alphaS on membranes.     

Application of flow field-flow fractionation for the characterization of macromolecules of biological interest: a review

An overview is given of the recent literature on (bio) analytical applications of flow field-flow fractionation (FlFFF). FlFFF is a liquid-phase separation technique that can separate macromolecules and particles according to size. The technique is increasingly used on a routine basis in a variety of application fields. In food analysis, FlFFF is applied to determine the molecular size distribution of starches and modified celluloses, or to study protein aggregation during food processing. In industrial analysis, it is applied for the characterization of polysaccharides that are used as thickeners and dispersing agents. In pharmaceutical and biomedical laboratories, FlFFF is used to monitor the refolding of recombinant proteins, to detect aggregates of antibodies, or to determine the size distribution of drug carrier particles. In environmental studies, FlFFF is used to characterize natural colloids in water streams, and especially to study trace metal distributions over colloidal particles. In this review, first a short discussion of the state of the art in instrumentation is given. Developments in the coupling of FlFFF to various detection modes are then highlighted. Finally, application studies are discussed and ordered according to the type of (bio) macromolecules or bioparticles that are fractionated.     

Kinetics of helix-coil transition in all sizes of polypeptides.

The relaxation behavior of the helix-coil transition has been investigated for all sizes of polypeptides. Unlike previously reported results, regardless of the size of polypeptides, the first-order kinetics plays a principal role in the relaxation process when a helical state is relaxed to a half-coiled state [i.e. s(f) is congruent to 1, where s(f) is the helix stability parameter at the final state]. On the other hand, when a helical state is relaxed to a coiled state [i.e., s(f) is less than 1], the zeroth-order kinetics plays a major role. In addition, the range of the validity of a kinetic version of the zipper model has been investigated. We have found that when a helical state is relaxed to a state where s(f) is less than or equal to 1, the zipper model is valid for polypeptides with chain length N satisfying the relation N is less than 1/(sigmagammaC)1/2 where sigma is the cooperativity parameter and gammaC is the coil nucleation rate parameter.