Mapping a homopolymer onto a model fluid

We describe a linear homopolymer using a grand canonical ensemble formalism, a statistical representation that is very convenient for formal manipulations. We investigate the properties of a system where only next neighbor interactions and an external, confining, field are present and then show how a general pair interaction can be introduced perturbatively, making use of a Mayer expansion. Through a diagrammatic analysis, we shall show how constitutive equations derived for the polymeric system are equivalent to the Ornstein-Zernike and Percus-Yevick equations for a simple fluid and find the implications of such a mapping for the simple situation of Van der Waals mean field model for the fluid.     

Formation of a tris-capsule and a tris-carceplex from a cyclic six-bowl assembly

A macrocycle composed of six cavitands was assembled into a tris-capsule and a tris-carceplex, each of which encapsulates three guest molecules.     

Wetting of a drop on a sphere

In this work, the equilibrium morphology of a drop on a sphere is analyzed as a function of the contact angle and drop volume experimentally and with analytical effective interfacial energy calculations. Experimentally, a drop on a sphere geometry is realized in an oil bath by placing a water drop on a sphere coated with a dielectric, of which the radii of curvature are comparable with that of the drop. Electrowetting (EW) is used to change the contact angle of the water drop on the sphere. To validate the applicability of EW and the Lippman-Young equation on nonflat surfaces, we systematically investigate the response of the contact angle to the applied voltage (EW response) for various drop volumes and compared the results with the case of a planar surface. The effective interfacial energy of two competing morphologies, namely, the spherically symmetric "completely engulfing" and "partially engulfing" morphologies are calculated analytically. The analytical calculations are then compared to the experimental results to confirm which morphology is energetically more favored for a given contact angle and drop volume. Our findings indicate that the "partially engulfing" morphology is always the energetically more favorable morphology.     

Synthesis of a tetraazacyclotetradecadiene and a pentaazacyclotetradecatriene

Useful procedures for preparing a novel tetraazacyclotetradecadiene and a pentaazacyclotetradecatriene are reported. J. Heterocyclic Chem., 14, 1097 (1977)     

Motion of a drop on a solid surface due to a wettability gradient

The hydrodynamic force experienced by a spherical-cap drop moving on a solid surface is obtained from two approximate analytical solutions and used to predict the quasi-steady speed of the drop in a wettability gradient. One solution is based on approximation of the shape of the drop as a collection of wedges, and the other is based on lubrication theory. Also, asymptotic results from both approximations for small contact angles, as well as an asymptotic result from lubrication theory that is good when the length scale of the drop is large compared with the slip length, are given. The results for the hydrodynamic force also can be used to predict the quasi-steady speed of a drop sliding down an incline.     

两嵌段共聚高分子链通过薄膜上纳米孑孔隙输运的研究

针对两嵌段高分子链的跨膜输运过程,分别给出与不同输运次序相对戍的高分子链的自由能,进而通过求解Fokker-Planck方程并在不同条件下对平均首次通过时间进行了数值计算.计算结果表明,当共聚高分子链由良溶剂区向不良溶剂区输运时,不能发生线团一链滴转变的链首先输运总是有利于整个高分子链的输运.而在给定输运次序的情况下,化学势、线团一链滴转变、共聚链的组成以及输运速率等因素对输运时间可产生显著影响.相关研究结果可为调控实际生物高分子链的输运时间提供可能的理论线索.     

Chaperone-assisted translocation of a polymer through a nanopore

Using Langevin dynamics simulations, we investigate the dynamics of chaperone-assisted translocation of a flexible polymer through a nanopore. We find that increasing the binding energy ε between the chaperone and the chain and the chaperone concentration N(c) can greatly improve the translocation probability. Particularly, with increasing the chaperone concentration a maximum translocation probability is observed for weak binding. For a fixed chaperone concentration, the histogram of translocation time τ has a transition from a long-tailed distribution to a gaussian distribution with increasing ε. τ rapidly decreases and then almost saturates with increasing binding energy for a short chain; however, it has a minimum for longer chains at a lower chaperone concentration. We also show that τ has a minimum as a function of the chaperone concentration. For different ε, a nonuniversal dependence of τ on the chain length N is also observed. These results can be interpreted by characteristic entropic effects for flexible polymers induced by either the crowding effect from a high chaperone concentration or the intersegmental binding for the high binding energy.     

PHOTOSENSITIZING PROPERTIES OF BACTERIOCHLOROPHYLLIN a and BACTERIOCHLORIN a, TWO DERIVATIVES OF BACTERIOCHLOROPHYLL a

Abstract The photosensitizing properties of two water soluble derivatives of bacteriochlorophyll a , bacteriochlorophyllin a and bacteriochlorin a (lacking the central Mg-ion) were investigated and compared to those of hematoporphyrin derivatives. At physiological pH the oxygen consumption rate of histidine, tryptophan, dithiothreitol and guanosine upon illumination was 3 to 4 times higher when bacteriochlorin a was used as photosensitizer than when hematoporphyrin derivatives were used. Especially bacteriochlorin a proved to be an effective sensitizer for the killing of L929 cells. Because bacteriochlorin a has an absorption maximum at 765 nm in phosphate buffered saline (allowing a light penetration in tissue about ten times larger than at 630 nm) and a high molar absorption coefficient (32 000 M cm⁻¹) it has promising possibilities for the application in photodynamic therapy.     

Construction of a protein-detection system using a loop peptide library with a fluorescence label

Construction of a novel protein-detection system was carried out using a designed peptide library with fluorescent labels based on loop structures. As a basic model study, detection of alpha-amylase using fluorescent-labeled peptides derived from an active loop of tendamistat was examined. The detection methods for proteins with immobilized peptides as well as peptides in solution have been successfully established. Based on these results, a loop peptide library that has various turn sequences grafted on a stable loop structure has been constructed. Various proteins with recognition patterns corresponding, for instance, to "protein fingerprints" could be detected using an immobilized peptide library. The present results suggest that the system can be applied to the development of a peptide microarray that behaves as a protein chip.     

Processes in a Nickel-Zinc Battery with a Negative Electrode Containing a Calcium Hydroxide Additive

The influence exerted by a calcium hydroxide additive introduced into the negative electrode on the serviceability of a sealed nickel-zinc battery with a nickel oxide electrode fabricated from spherical nickel hydroxide on a foamed-nickel support was studied.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 428–432.Original Russian Text Copyright © 2005 by Arkhangel’skaya, Krasnobryzhii, Kas’yan, Loginova, Vinogradova.     

Synthesis of (+)-uniflorine a: a structural reassignment and a configurational assignment

The total synthesis of (+)-uniflorine A has allowed for the structural reassignment and the configurational assignment of the alkaloid (-)-uniflorine A from a 1,2,6,7,8-pentahydroxyindolizidine structure to (-)-(1 R,2 R,3 R,6 R,7 S,7a R)-1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine (6- epi-casuarine).     

Interaction between a disclination and a uniaxial-isotropic phase interface in a nematic liquid crystal

We consider the interaction between a disclination line of strength +/-1/2 and an interface between the uniaxial and isotropic phases of a nematic liquid crystal. We apply a recently developed set of interface conditions including a configurational force balance which generalizes the Gibbs-Thomson equation to account for the curvature elasticity of the uniaxial phase and the orientation dependence of the interfacial free-energy density. We consider a rectangular vessel containing both phases and a disclination. We formulate a relevant free-boundary problem and use numerical methods to determine equilibrium shapes of the interface. When the interfacial free-energy is constant, the shape of the interface is insensitive to whether the strength of the defect is +1/2 or -1/2 and to rotations of the director field consistent with the boundary conditions. Accounting for the dependence of the interfacial free-energy density on the angle between the interfacial unit normal field and the director field eliminates these degeneracies. In particular, when such dependence is taken into account, different solution branches are found, indicating the presence of a bifurcation. We find also that, depending on the magnitude of the anisotropic contribution to the interfacial free-energy density, the interaction between the disclination and the interface may be repulsive or attractive. When the interaction is repulsive, the disclination line positions itself at an energetically optimal distance adjacent to the interface. Otherwise, the uniaxial phase expels the disclination to the interface where a cusp forms.     

Influence of the electric field on a particle in a space with a disclination

We consider a quantum particle in a space with a linear topological defect, i.e., disclination. The effect of the uniform electric field in this space, on the particle, is shown to cause a translation of the wave function. In addition, the electric field is not found to be affected by the defect. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Electrophoresis of a rigid sphere in a Carreau fluid normal to a large charged disk

The electrophoresis of a rigid sphere in a Carreau fluid normal to a large disk is analyzed theoretically under the conditions of low surface potential and weak applied electric field. Previous analyses are extended to the case where a disk can be charged, and a more realistic electrostatic force formula is applied. We show that the qualitative behavior of a sphere depends largely on its distance from a disk, the thickness of double layer, and the nature of a fluid. In general, the presence of a disk has the effect of increasing the conventional hydrodynamic drag on a sphere, and a decrease in the thickness of the double layer surrounding a sphere has the effect of enhancing the shear-thinning effect. However, this might not be the case if a sphere is uncharged and a disk is charged, where the osmotic pressure field and the induced charge on the sphere surface can be significant. The shear-thinning effect is important only if the thickness of double layer is sufficiently thick. This result can play a significant role in practice such as in electrophoretic deposition, where the deposition electrode is charged and the fluid medium is usually of shearing-thinning nature.     

Squeezing a helium nanodroplet with a Rydberg electron

We have investigated, by means of density functional theory, the structure of a "scolium", that is, an electron circulating around a positively charged 4He nanodroplet, temporarily prevented from neutralization by the helium-electron repulsion. The positive ion core resides in the center of the nanodroplet where, as a consequence of electrostriction, a strong increase in the helium density with respect to its bulk value occurs. The electron enveloping the 4He cluster exerts an additional electrostatic pressure which further increases the local 4He density around the ion core. We argue that under such pressure, sufficiently small 4He nanodroplets may turn solid. The stability of a scolium with respect to electron-ion recombination is investigated.     

Hydrodynamic force on a microparticle approaching a wall in a nanoparticle dispersion: observation of a separation-dependent effective viscosity

Colloid probe atomic force microscopy was used to measure the hydrodynamic force exerted on a 30-μm-diameter silica particle being moved toward or away from a silica plate in aqueous dispersions of 22-nm-diameter silica nanoparticles (6 or 8 vol %). Upon comparing the measured force to predictions made using the well-known expression of Cox and Brenner (Cox, R. G.; Brenner, H. Chem. Eng. Sci.1967, 22, 1753-1777) assuming a constant viscosity equal to that of the bulk dispersion, the measured drag force was found to become significantly less than that predicted at smaller particle-plate separation distances (e.g., <500 nm). A recent theoretical paper by Bhattacharya and Blawzdziewicz (Bhattacharya, S.; Blawzdziewicz, J. J. Chem. Phys.2008, 128, 214704) predicted that in a solution of dispersed nanoparticles the effective viscosity characterizing the hydrodynamic force on the particle should vary from that of the solvent at contact to that of the bulk dispersion at large separations. By adjusting the viscosity in the Cox and Brenner expression to make the predicted hydrodynamic force match that measured (i.e., the effective viscosity), a curve showing these exact characteristics was obtained. The effective viscosity profile was not a function of particle speed, and changes in the effective viscosity extended to separation distances of as large as 2 μm (nearly 100 times the hard diameter of the nanoparticles). These results suggest that in the range of typical colloidal forces (on the order of 100 nm), the dynamics of particle motion in such systems are determined by the viscosity of the solvent and not that of the bulk dispersion.     

Cation-pi interactions of a thiocarbonyl group and a carbonyl group with a pyridinium nucleus

Attractive interactions between a thiocarbonyl group and a pyridinium nucleus, and between a carbonyl group and a pyridinium nucleus have been proven by (1)H and (13)C NMR studies, UV-vis spectral analyses, and X-ray crystallographic analyses of nicotinic amides 1 and 3, and pyridinium salts 2 and 4. Comparison of the Deltadelta values, which are the differences in the chemical shifts with reference compounds 5 or 6, showed that the absolute Deltadelta values of 2 and 4 are much larger than those of 1 and 3. In the UV-vis spectra, the n-->pi absorption of the C=S group of 2a exhibited a significant blue shift in CHCl(3). X-ray crystallographic analysis of 1-4 clearly showed that the C=S group of 2a and the C=O group of 4 are very close to the pyridinium moiety compared to the case of 1 and 3. In addition, the X-ray crystal packing structure of 2a showed the C=S group is sandwiched between two pyridinium rings. These experimental results strongly suggested the existence of attractive (C=S)...Py(+) and (C=O)...Py(+) interactions in solution and in crystal. The optimized geometries of 1 and 2 calculated at the HF/6-311G level are in good agreement with their X-ray geometries. MP2/6-311G calculations for the model systems of pyridinium salts 2 and 4 predicted that the electrostatic and induction energies are the major source of the attractive interactions. Since the larger contribution of electrostatic and induction interactions are characteristic features of cation-pi interactions, the (C=S)...Py(+) and (C=O)...Py(+) interactions would be classified as a cation-pi interaction.