Stereo-differentiation in the excited state behaviour of naphthalene-thymine dyads

Using two diastereomeric dyads containing naphthalene and thymine units, significant chiral discrimination has been found in the photophysical processes involving the naphthalene excited states: singlet deactivation by hydrogen bonding molecules, singlet-singlet energy transfer from thymine and triplet decay.     

Highly diastereoselective formation of C2-symmetric bis-thioglycoside Pd(II) complexes: the role of the exo anomeric effect

Treatment of several C(2) symmetric bis-thioglycosides with Pd(CH(3)CN)(2)Cl(2) always leads to a single diastereomeric Pd(II) complex as a consequence of the exo-anomeric effect.     

The influence of CHx coating on the optical properties of porous silicon

In this work, we report a study on the influence of CH_x thickness layer on optical properties of CH_x/PS/Si structures. The hydrocarbon groups were deposited by plasma of methane–argon mixture.The properties of these structures are investigated by photoluminescence (PL), reflection and spectral response measurements from where a different behavior depending on CH_x layer thickness has been observed.The entire total reflection spectrum is modulated by Fabry–Pérot fringes that are a result of thin film interference. As the CH_x layer thickness increases, the amplitude of the interferences decreases and a positive shift of the maximum peak is observed.The PL spectra from CH_x/PS samples with two CH_x layer thicknesses show more intense luminescence than that observed from PS sample and the existence of an optimum thickness CH_x that gives the maximum PL intensity. The spectral response spectra show the presence of an intense peak at 450 nm. Finally, the results point out the importance of CH_x coating in optoelectronic applications.     

Electronic structure of ScN, YN, LaN and GdN superlattices

Using the plane wave version of the full potential linear muffin-tin orbital (FPLMTO) method, which enables an accurate treatment of the interstitial regions, the electronic properties of ScN, YN, LaN and GdN rocksalt/rocksalt superlattices are calculated. It is found that apart from YN/ScN, all the other superlattices have negative bandgaps. However, it is shown that these systems can be semiconductors if a correction is made to the local density approximation (LDA).     

Volumetric,Ultrasonic and Viscosimetric Studies for the Binary Mixture (1, 4-Dioxane + Water) at T = (295.15, 298.15, 301.15, 304.15, 307.15, 310.15 and 313.15) K

Journal of Solution Chemistry - Density, speed of sound and viscosity data for the binary mixtures (1,4-dioxane (1)?+?water (2)), were measured over the whole composition range at...     

pH‐Sensitive methacrylic acid–methyl methacrylate copolymer Eudragit L100 and dimethylaminoethyl methacrylate,butyl methacrylate,and methyl methacrylate tri‐copolymer Eudragit E100

Poly (methyl methacrylate) derivatives such as Eudragit are largely used for drug encapsulation and in controlled oral drug delivery. With special focusing on those applications, solubilization and precipitation conditions of two pH‐sensitive Eudragit polymers, namely, L100 and E100, were investigated via systematic studies. Effects of various physicochemical parameters such as pH, polymer concentration, salinity, buffer concentration, and incubation time on the solubilization and precipitation of these polymers were investigated. In addition, pH titration of both polymers was reported. Considering both macroscopic and quantitative aspects such as the final mean particle size, size distribution, morphology, and the zeta potential, it was established that the different precited parameters could not be dissociated and exert a synergic action on the solubilization and precipitation of both polymers. Titration curves revealed two equivalences that helped estimating carboxylic content of Eudragit L100 (6 mmol/g) and ammonium content of Eudragit E100 (4 mmol/g). In this study, the solubilization and the precipitation domains were for the first time clearly established by considering the above‐mentioned parameters. Moreover, it was found that Eudragit L100 and E100 cannot be considered as classic polyelectrolytes; in fact, solubilization and precipitation domains were not affected by ionic strength.     

Boron‐functionalized poly(3‐hydroxybutyrate)s from hydroboration of poly(allyl‐β‐hydroxyalkanoate)s: Synthesis and insights into the microstructure

The controlled ring‐opening polymerization of racemic allyl‐β‐butyrolactone (rac‐BL^allyl) in toluene or in bulk, catalyzed by the discrete β‐diiminate zinc amido [(BDI^iPr)Zn(N(SiMe₃)₂)] ( 1 ) or {amino‐methoxy‐bis(phenolate)}yttrium amido [(ONOO^tBu)Y(N(SiHMe₂)₂)(THF)] ( 2 ) complexes, in association with an alcohol, gave poly(β‐hydroxyalkanoate)s (PHAs) with allylic side chains. These PHAs^allyl exhibit either a slightly isotactic‐enriched (P_m = 0.61) or highly syndiotactic‐enriched (P_r = 0.82) backbone structure, respectively, with high molar mass (M _n up to 21,100 g mol^?1) and narrow molar mass distribution values (1.05 < M _w/M _n < 1.28), as evidenced by detailed ¹³C NMR and size exclusion chromatography analyses. Postpolymerization rhodium‐catalyzed hydroboration of the resulting PHAs^allyl with pinacolborane quantitatively afforded the corresponding PHAs^boron. Introduction of boron into the pendant chains did not alter neither the structure of the polymer backbone nor the macromolecular features (M _n, M _w/M _n, and stereoregularity). However, differential scanning calorimetry analyses revealed a significant increase of the glass transition temperature on modifying the allyl for the boron function in these PHAs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011