Local NMR Relaxation of Dendrimers in the Presence of Hydrodynamic Interactions

We study the role of hydrodynamic interactions for the relaxation of segments’ orientations in dendrimers. The dynamics is considered in the Zimm framework. It is shown that inclusion of correlations between segments’ orientations plays a major role for the segments’ mobility, which reveals itself in the nuclear magnetic resonance relaxation functions. The enhancement of the reorientation dynamics of segments due to the hydrodynamic interactions is more significant for the inner segments. This effect is clearly pronounced in the reduced spectral density \(\omega J(\omega )\), maximum of which shifts to higher frequencies when the hydrodynamic interactions are taken into account.     

14-Noreudesmanes and a phenylpropane heterodimer from sea buckthorn berry inhibit Herpes simplex type 2 virus replication

Two new 14-noreudesmane sesquiterpenes, one new phenylpropane heterodimer, caulilexin C, and uvaol were isolated from the 70% MeOH extract of the fruit peel of Elaeagnus rhamnoides. The structures of the compounds were elucidated by HRESIMS and advanced NMR methods. The absolute configuration of (R)-6,9-dihydroxy-1-oxo-14-noreudesm-5,7,9-triene was determined by the TDDFT-ECD method. The new compounds, together with structurally similar naphthalenes (musizin, musizin-8-O-glucoside, torachrysone-8-O-glucoside) and 1,4-naphthoquinone (2-methylstipandrone), isolated previously from Rumex aquaticus, were investigated for their antiviral activity against Herpes simplex virus type 2 (HSV-2) using two different methods. Applying the traditional virus yield reduction test, (R)-6,9-dihydroxy-1-oxo-14-noreudesm-5,7,9-triene, 1-[3-methoxy-4-(2-methoxy-4-(1E)-propenyl-phenoxy)-phenyl]-propane-1,2-diol, and musizin caused a 2.00 log₁₀, 3.49 log₁₀, and 2.33 log₁₀ reduction of HSV-2 yield, respectively, at a concentration of 12.5?μM. 2-Hydroxy-1-methoxy-6,9-dioxo-14-noreudesm-1,3,5(10),7-tetraene exhibited an antiviral effect at concentration of 50?μM only. Similar results were obtained when the qPCR method was used to test the antiviral activity of the compounds.     

Key role of molecular kinetic energy in early stages of pentacene island growth

Organic molecular beam deposition is studied systematically at thermal and hyperthermal regimes aiming at investigating the role of molecular kinetic energy on the growth mechanism of pentacene submonolayers on SiO _x /Si. We show that the kinetic energy of the impinging molecule (E _k ) plays a crucial role in determining island structure and shape, distribution of island sizes, the crystalline quality of the first monolayer, and even the growth mode of subsequent layers. With increasing E _k , the island structure changes from fractal to nonfractal, the shape becomes more anisotropic and the island size more uniform, pointing to correlated island growth. Moreover, while 3D island growth is observed for thermal organic molecular beam deposition, supersonic molecular beam deposition gives rise to layer-by-layer growth, at least for the first two layers. When E _k ≥5.0 eV, the first monolayer is composed of large single crystalline domains which can extend over up to 10 μm, inferred from comparing atomic force micrographs of height and net transverse shear force. In these growth conditions both the high surface diffusivity and energy redistribution play a major role. We propose a mechanism where the energy dissipation occurring during the molecule–surface collision leads to the reorientation of whole islands during island coalescence, resulting in the elimination of grain boundaries.     

Ultrafast interferometric measurements of plasmonic transport in photonic crystals

We present a novel time-domain experimental approach to the study of the dynamics of surface electromagnetic wave propagation in a two-dimensional photonic crystal. A surface plasmon polariton is launched by ultrafast laser pulses and propagates into a photonic crystal, the dynamics of which are measured by an interferometric cross-correlation method. Plasmon photonic stopgaps are characterized by a single measurement. The dispersion around the stopgaps is determined with a series of angle-resolved measurements.     

The invariance principle for ϕ-mixing sequences

Summary In this paper we investigate the invariance principle for -mixing sequences, satisfying restrictions on the variances which are a weak form of stationarity. No mixing rate is assumed. For -mixing strictly stationary sequences we give a necessary and sufficient condition for the invariance principle.     

X-Ray Molecular Structure of a Red Bilin Derivative from Chlorella protothecoides. 4th communication on chlorophyll catabolism

The molecular structure of a chlorophyll a catabolite isolated from the culture medium of bleached Chlorella protothecoides cells has been determined by X-ray diffraction; the crystal structure shows a distorted helical arrangement of the pyrrole rings and consists of symmetrical dimers located at a crystallographic diad, which are stabilized by six intermolecular H-bonds.     

Application of Nanoparticles in Polymers for Electronics and Electrical Engineering

Different organophilic layered silicates and a modified hydrotalcite were used as functional nanofillers for thermoplastic and thermosetting polymers. Polyamide 6 (PA6) and poly(butylene terephthalate) silicate nanocomposites were prepared by melt compounding using a twin‐screw extruder. The morphology of the materials was investigated by transmission electron microscopy and small‐angle X‐ray scattering, and was found to be characterized by homogeneous dispersion of high aspect ratio silicate layers in the polymer matrix. The PA6 nanocomposite displayed excellent thermo‐mechanical properties at low filler loadings and improved barrier properties. Epoxy nanocomposites have also been prepared and characterized with regard to their morphology and their water vapor permeability.     

An empirical model predicting the viscosity of highly concentrated, bimodal dispersions with colloidal interactions

The relationship between particle size distribution and viscosity of concentrated dispersions is of great industrial importance, since it is the key to get high solids dispersions or suspensions. The problem is treated here experimentally as well as theoretically for the special case of strongly interacting colloidal particles. An empirical model based on a generalized Quemada equation is used to describe η as a function of volume fraction for mono- as well as multimodal dispersions. The pre-factor η˜ accounts for the shear rate dependence of η and does not affect the shape of the η vs φ curves. It is shown here for the first time that colloidal interactions do not show up in the maximum packing parameter and φ_max can be calculated from the particle size distribution without further knowledge of the interactions among the suspended particles. On the other hand, the exponent ɛ is controlled by the interactions among the particles. Starting from a limiting value of 2 for non-interacting either colloidal or non-colloidal particles, ɛ generally increases strongly with decreasing particle size. For a given particle system it then can be expressed as a function of the number average particle diameter. As a consequence, the viscosity of bimodal dispersions varies not only with the size ratio of large to small particles, but also depends on the absolute particle size going through a minimum as the size ratio increases. Furthermore, the well-known viscosity minimum for bimodal dispersions with volumetric mixing ratios of around 30/70 of small to large particles is shown to vanish if colloidal interactions contribute significantly. Received: 7 June 2000/Accepted: 12 February 2001