Monte Carlo study of the translocation of a polymer chain through a hole

The translocation of a polymer chain through a narrow hole in a rigid obstacle has been studied by the static Monte Carlo simulations. A modified self-avoiding walk on a cubic lattice has been used to model the polymer in an athermal solution. The entropy of the chain before, in the course, and after the translocation process has been estimated by the statistical counting method. The thermodynamic generalized forces governing the translocation have been calculated. The influence of the system geometry on the entropic barrier landscape is discussed.     

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.     

Peculiarities of the coagulation mechanism of a nanocrystalline cellulose hydrosol and a latex

Dynamic light scattering has been employed to study the coagulation kinetics of colloidal dispersion of nanocrystalline cellulose and SKS-27 ARK synthetic latex under the action of sodium chloride. It has been found that, when a system being coagulated is exposed to a mechanical action, aggregates almost cease to grow at some moment. It has been assumed that the first stage of coagulation is caused by the formation of strong contacts between primary particles and their agglomeration, while the second stage is realized via the interaction of residual hydration layers. It has been shown that, as the density of surfactant adsorption layers on the surface of latex particles is enhanced, the duration of the first stage increases, while the average hydrodynamic particle size decreases.     

Evaporation dynamics of a binary sessile droplet: Theory and comparison with experimental data on a droplet of a sulfuric-acid solution

Diffusion evaporation of a sessile binary droplet in an atmosphere of a noncondensable carrier gas has been considered. For a droplet consisting of two infinitely miscible liquids, a relation between the current values of solution concentration and volume of the droplet has been derived in an explicit form under the ideal solution approximation. It has been shown that the volume of a sessile binary droplet may, as well as the volume of a free binary droplet, vary nonmonotonically with time. The evaporation of a droplet of an aqueous sulfuric-acid solution has been considered in detail taking into account the nonideality of the solution. Time variations in the volume, base area, and contact angle have been experimentally measured for the sessile droplet of an aqueous sulfuric-acid solution on a hydrophobized substrate. The experimental data obtained at different initial humidities of water-vapor and droplet-solution concentrations have been analyzed within the theory of the stationary isothermal diffusion evaporation of a sessile binary droplet.     

Molecular ordering of a cyano compound at a displacive transition temperature: a statistical analysis based on quantum mechanics and computer simulations

A statistical analysis has been carried out to determine the configurational preference of a pair of 4-cyanophenyl 4-n-pentylbenzoate (CPPB) molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Configurational energy has been computed using the Rayleigh—Schodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at the phase transition temperature using the Maxwell—Boltzmann formula. An attempt has been made to identify the most probable configuration at the phase transition temperature. Further, the flexibility of various configurations has been studied in terms of variation of probability due to small departures from the most probable configuration. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of the molecular pair have been considered. The results are discussed in the light of experimental as well as theoretical observations. The nature of the mesophase has been correlated with the parameter introduced in this paper.     

Molecular ordering of a cyano compound at a displacive transition temperature: a statistical analysis based on quantum mechanics and computer simulations

A statistical analysis has been carried out to determine the configurational preference of a pair of 4-cyanophenyl 4- n -pentylbenzoate (CPPB) molecules with respect to translatory and orientational motions. The CNDO/2 method has been employed to evaluate the net atomic charge and atomic dipole components at each atomic centre of the molecule. Configurational energy has been computed using the Rayleigh-Schodinger perturbation method. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at the phase transition temperature using the Maxwell-Boltzmann formula. An attempt has been made to identify the most probable configuration at the phase transition temperature. Further, the flexibility of various configurations has been studied in terms of variation of probability due to small departures from the most probable configuration. On the basis of stacking, in-plane and terminal interaction energy calculations, all possible geometrical arrangements of the molecular pair have been considered. The results are discussed in the light of experimental as well as theoretical observations. The nature of the mesophase has been correlated with the parameter introduced in this paper.     

Determination of percent composition of a mixture analyzed by gas chromatography. Comparison of a helium pulsed-discharge photoionization detector with a flame ionization detector

We present the results of a study of percent composition for a mixture which has been separated by gas chromatography and analyzed using helium pulsed-discharge photoionization detection (He-PDPID) and flame ionization detection (FID). FID has long been the means by which the percent composition of a hydrocarbon mixture has been determined since it has been previously established as a "carbon counting device". However, in this study we present results which show that He-PDPID is more accurate in determining the percent composition of a hydrocarbon mixture and, because it is a universal detection method and can detect compounds that FID cannot, it is also more effective for determining the percent composition of mixtures containing organic compounds with a variety of other functional groups.     

Action of trypsin on a nucleoprotein from sturgeon gonads

A nucleoprotein has been isolated from the gonads of the Caspian sturgeon and its composition has been determined. It has been shown that it contains 55% of DNA, 2% of RNA, 36% of protamines, and about 7% of nonprotamine proteins of nonbasic nature. The nucleoprotein has been hydrolyzed with trypsin, and the amino acid compositions of some hydrolysis products have been studied. On the basis of the results obtained, the hypothesis has been put forward of a possible linkage of the DNA with the basic proteins. It has been shown that protamines react with the DNA through the basic amino acid residues located at various regions of their molecules.     

Platinum solubility of a substance designed as a model for emissions of automobile catalytic converters

Automobile catalytic converters emit nanocrystalline platinum attached to alumina particles. For investigations about the bioavailability of Pt from these particles a model substance with approx. 5% Pt on alumina has been prepared and characterized by physical methods (ESCA, XRD, TEM, DTA, TG). Measuring the platinum solubility of these samples in different solvents revealed high amounts that can be explained assuming a corrosion process. The portion of soluble platinum is dependent on the particle size distribution. For a comparative study platinum black has been used. In general the platinum determination has been carried out by electrothermal atomic absorption spectrometry (ET-AAS). The comparison of ET-AAS results with determinations by adsorptive voltammetry (formazone method) allowed to distinguish between elemental and ionic platinum; in solution samples only ionic platinum has been present. UV spectra of extracts have been used for the semi-quantitative platinum speciation in solutions.     

Platinum solubility of a substance designed as a model for emissions of automobile catalytic converters

Automobile catalytic converters emit nanocrystalline platinum attached to alumina particles. For investigations about the bioavailability of Pt from these particles a model substance with approx. 5% Pt on alumina has been prepared and characterized by physical methods (ESCA, XRD, TEM, DTA, TG). Measuring the platinum solubility of these samples in different solvents revealed high amounts that can be explained assuming a corrosion process. The portion of soluble platinum is dependent on the particle size distribution. For a comparative study platinum black has been used. In general the platinum determination has been carried out by electrothermal atomic absorption spectrometry (ET-AAS). The comparison of ET-AAS results with determinations by adsorptive voltammetry (formazone method) allowed to distinguish between elemental and ionic platinum; in solution samples only ionic platinum has been present. UV spectra of extracts have been used for the semi-quantitative platinum speciation in solutions.     

Micellar extraction of a tin complex of phenylfluorone into a cetylpyridinium chloride-based liquid phase

Optimal conditions have been found for the modification of compact liquid phases based on a cationic surfactant, cetylpyridinium chloride, with salicylic acid. On the example of the system tin-phenylfluorone we have shown the applicability of such phases to the preconcentration of multiply charged ions readily hydrolyzed metals. The influence of concentrations on the absorbance and composition of the complex has been studied; the optimal conditions of its extraction have been found. The developed spectrophotometric procedure of tin determination with phenylfluorone using micellar-extraction preconcentration has been tested for the analysis of canned vegetables and brines.     

Action of trypsin on a nucleoprotein from sturgeon gonads

A nucleoprotein has been isolated from the gonads of the Caspian sturgeon and its composition has been determined. It has been shown that it contains 55% of DNA, 2% of RNA, 36% of protamines, and about 7% of nonprotamine proteins of nonbasic nature. The nucleoprotein has been hydrolyzed with trypsin, and the amino acid compositions of some hydrolysis products have been studied. On the basis of the results obtained, the hypothesis has been put forward of a possible linkage of the DNA with the basic proteins. It has been shown that protamines react with the DNA through the basic amino acid residues located at various regions of their molecules.M. V. Lomonosov Moscow State University. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 549–553, July–August, 1979.     

Structure of a pectin homogalacturonan

A homogalacturonan has been isolated in the pure form from industrial apple pectin, and its structure has been studied by¹³C NMR spectroscopy. It has been shown that the apple pectin macromolecule consists mainly of linear macromolecules of homogalacturonan and a rhamnogalacturonan.V. I. Nikitin Institute of Chemistry, Tadzhikistan Republic Academy of Sciences, Dushanbe; and Scientific Research Institute of Blood Substitutes and Hormone Preparations, Moscow. Translated from Khimiya Prirodnykh Soedeninii, No. 1, pp. 91–96, January–February, 1993.     

Design and performance of a high resolution electrospray ion source for a magnetic sector mass spectrometer with a heated capillary inlet

The design and performance of an electrospray ion source for a high resolution magnetic sector mass spectrometer that utilizes a heated capillary has been presented. Low pressure, high sensitivity, stable electrospray, low flow rates, and low electronic noise were important factors in achieving high resolution electrospray mass spectrometry. A unit mass resolution has been achieved for biomolecules with MW > 12,000, and an accuracy of 1.4 ppm has been achieved for the average molecular weight of bovine insulin.     

Verification of a capillary model for the electroosmotic transport of a free solvent in ion-exchange membranes of different natures

It has been shown that the transport of a free solvent through ion-exchange membranes of different structural types in NaCl solutions can be calculated within the framework of the capillary model for electroosmotic transport on the basis of data on pore-radius distribution, exchange capacity, internal specific surface area, and concentration dependences of membrane electrical conductivity. The electrolyte-solution concentration range has been determined in which the convergence is observed between the data calculated in terms of the model and the results of the independent experimental determination of the numbers of water transport through the membranes. The fraction of through pores in the structure of an ion-exchange membrane has been found, and it has been shown that this fraction depends on the structural type of a polymer film alone.     

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.     

Isolation of an intermediate in the insertion of a carbodiimide into a boron-aryl bond

A 1 : 1 Lewis acid-base complex between CyN=C=NCy and PhBCl2 has been isolated and structurally characterized, heating of which in refluxing toluene results in the amidinate, [PhC{NCy}2]BCl2; the overall reaction has been modeled by DFT calculations.     

Filtration of nanoaerosols through a granular layer

Diffusion deposition of nanoparticles in model granular filters with different structures has been considered at low Reynolds numbers. On the basis of a three-dimensional flow field calculated for layers of granules, nanoparticle-collection efficiences have been determined for the granules in a wide range of the Peclet diffusion numbers. The interference of the layers has been studied, and approximation equations have been derived for calculating the pressure drop and the nanoparticle-collection efficiency.     

Model of a calorimetric sensor for medical application

A calorimetric sensor has been developed to measure surface heat dissipations in the human body. An experimental prototype has been built in order to study its performance and a simple model that represents acceptably the experimental system has been proposed.     

Ircinianin,a Novel Sesterterpene from a Marine Sponge

Ircinianin ( 2 ), a new furano-sesterterpenetertronic acid, has been isolated from a marine sponge of the genus Ircinia. Structure 2 has been established by X-ray diffraction methods.