Effect of substituents on spin density in benzimidazole nitronyl nitroxide radicals studied by electron spin resonance

Several novel benzimidazole‐3‐oxide‐1‐oxyl radicals with substituents at 5 and/or 6 position were synthesized. The ESR analysis of nitrogen hyperfine coupling constants (hfccs) revealed that substituents at 5 and 6‐position affect the spin density to greater extent than substituents on the phenyl ring at 2‐position. Density functional theory calculations of nitrogen hfccs were performed using several different Pople type basis sets, as well as double and triple zeta quality individual gauge for localized orbital (IGLO‐II, IGLO‐III) and electron paramagnetic resonance (EPR‐II, EPR‐II) basis sets. Experimental and theoretical hfccs are compared. Copyright © 2009 John Wiley & Sons, Ltd.     

Promoter effect of BaO on CO oxidation on PdO surfaces

The effect of bulk BaO promoter on CO oxidation activity of palladium oxide phase was studied by density functional calculations. A series of BaO(100) supported Pd(x)O(y) thin layer models were constructed, and energy profiles for CO oxidation on the films were calculated and compared with corresponding profiles for the most stable PdO bulk surfaces PdO(100) and PdO(101). The most stable of the thin films typically exhibit the same PdO(100) and PdO(101) surface planes; the PdO(100) dominates already with double layer thickness. The supporting promoter improves the CO oxidation activity of the Pd(x)O(y) phase via a direct electronic effect and introduced structural strain and corrugation. Changes in CO adsorption strength are reflected in oxidation energy barriers, and the promoting effect of even 0.3 eV can be seen locally. Easier oxygen vacancy formation may partially facilitate the reaction.     

Fluid membranes can drive linear aggregation of adsorbed spherical nanoparticles

Using computer simulations, we show that lipid membranes can mediate linear aggregation of spherical nanoparticles binding to it for a wide range of biologically relevant bending rigidities. This result is in net contrast with the isotropic aggregation of nanoparticles on fluid interfaces or the expected clustering of isotropic insertions in biological membranes. We present a phase diagram indicating where linear aggregation is expected and compute explicitly the free-energy barriers associated with linear and isotropic aggregation. Finally, we provide simple scaling arguments to explain this phenomenology.     

The effects of hydrostatic pressure and intense laser field on the linear and nonlinear optical properties of a square quantum well

In this paper, the effects of hydrostatic pressure, temperature and intense laser field on the linear and nonlinear optical processes in the conduction band of a square quantum well are numerically investigated in the effective mass approximation. The analytical expressions of optical properties are obtained by using the compact density-matrix approach. The numerical results are presented for typical square GaAs/Al_xGa_1?xAs single quantum well system. The nonlinear optical absorption and refractive index changes depending on the hydrostatic pressure and intense laser field are investigated for two different temperature values. The results show that the intense laser field, the hydrostatic pressure and the temperature have a significant effect on the optical characteristics of these structures.     

Investigation by NMR Spectroscopy and Molecular Modeling of the Conformations of Some Modified Disaccharide Antigens for Shigella Dysenteriae Type 1

Abstract

The O-polysaccharide of Shigella dysenteriae type 1 is made up of multiple repeats of the linear tetrasaccharide 3)-α-L-Rhap-(1→2)-α-D-Galp-(1→3)-α-D-GlcpNAc-(1→3)-α-L-Rhap-(1→, for which the antigenic determinant for a murine monoclonal IgM antibody is the disaccharide α-L-Rhap-(1→2)-α-D-Galp. This disaccharide and various analogs have been studied by 2D NOESY, ROESY, and TOCSY NMR spectroscopy, in conjunction with proton spin-lattice relaxation rate measurements, restrained molecular mechanics, and restrained molecular dynamics with simulated annealing. It has been found that replacement of any single hydroxyl group in the determinant by a hydrogen atom, or replacement of any single hydroxyl group in the Gal residue by a fluorine atom has little if any influence on the conformation of the resulting derivatives.

     

Effect of drying on porous silicon

The phase transition of a fluid - in particular water - confined in the pores of silicon during drying is studied. The influence of this process on surface size and porosity is discussed. Methods of air drying, supercritical drying and freeze drying are considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Averaging Results for Functional Differential Equations

Under rather general assumptions, we present some improved averaging results for functional differential equations. This is achieved with the help of nonstandard analysis and extends a similar result by the first author for a delay differential equation of a particular form.     

SAXS investigation of structure–property relationship of polypropylene/montmorillonite composites during load cycling

Polypropylene (PP) can hardly be reinforced by the layered silicate montmorillonite (MMT), but the material fatigue appears somewhat reduced. The probable reason is amplified competitive nucleation of the PP by MMT component. Utilizing small‐angle X‐ray scattering (SAXS) from synchrotron, we investigate the nanostructure evolution of the PP in straining experiments from neat PP and compatibilized composite materials. The compatibilizer is a styrene–ethylene/butylene–styrene copolymer (SEBS). Oriented injection‐molded test bars are studied. The discrete SAXS probes variations of sizes and distances among those crystalline domains that are not placed at random. Crystallite dimensions and distances are documented for modeling purposes. The nanoscopic strain is computed from the distance variation and compared with the macroscopic strain. Differences between macroscopic and nanoscopic strain are observed. They require postulating regions with statistical placement of crystallites (poorly arranged region, PAR) in addition to the SAXS‐probed well‐arranged semi‐crystalline entities (WAE). The extensibility of WAEs must be different from that of the PARs. In neat PP, the observed WAEs are well developed and stronger than the PARs. In the composites, the WAEs are made from thin and less extended crystalline domains. They are weaker than the PARs that appear reinforced. Thus, enclosing each MMT layer a PAR is formed, and the WAEs generated farther away remain imperfect. Consequently, in the composites, the narrow crystalline domains from the WAEs do not break into even smaller pieces, and the fatigue of the composites is lower than that of the neat PP. Copyright © 2013 John Wiley & Sons, Ltd.     

First Example of Schiff Bases Containing Poly(Acryl Amid) in the Synthesis and Characterization

A novel polymeric‐Schiff base derived from the condensation reaction poly(acryl amid) and indole‐3‐carboxaldehyde has been synthesized and their Co(II) and Ni(II) complexes have been prepared. Mol ratio of acrylamid group and Schiff bases group was estimated by means of height of ‐CH multiple peaks and –CH=N‐ peak in ¹H‐NMR spectrum. The studied substances were characterized by molar conductance, magnetic susceptibility, electronic and IR spectral studies. In addition, main units have been suggested with elemental analysis for these substances, and than the weight average molecular weight (M_w) has been suggested. The number average molecular weight (M_n) was determined with a vapor pressure osmometer. Polydispersity index (PDI) found to be ca 1.7 from M_w/M_n for poly‐Schiff bases and their Co(II) and Ni(II) complexes. PAA‐Schiff bases were found to have the highest thermal stablility compared to that of the Co(II) and Ni(II) complexes. The conductivities of the PAA‐Schiff bases and their complexes were measured by the four‐probe technique and were found in the range 10^?5?10^?6 S cm^?1.     

Absolute Continuity of Quasiconformal Mappings on Curves

We show that a quasiconformal mapping between two proper, locally Ahlfors Q-regular metric spaces, Q > 1, is absolutely continuous on almost every curve. We further relax the limes superior in the definition of quasiconformality to a limes inferior and verify that exceptional sets analogous to the Euclidean setting can be allowed. The authors were supported by grants from the Swiss NSF and the Academy of Finland. Part of the research was done while S.R. was visiting at the University of Bern. Received: August 2005 Accepted: January 2006