Occurrence of Stilbene Glucosides in Upuna borneensis

Four new stilbene glucosides, upunosides A ( 1 ), B ( 5 ), C ( 6 ), and D ( 7 ), were isolated from the stem of Upuna borneensis (Dipterocarpaceae) together with the three known glucosides 3, 4 , and 8 . Upunoside A ( 1 ) is the first natural instance of a glucoside of a resveratrol pentamer, and its aglycone has a dibenzo‐fused bicyclo[5.3.0]octadiene and two dihydrobenzofuran moieties. The relative structure of the aglycone was determined by spectral analysis including 1D and 2D NMR experiments.     

Determination of the stereochemistry of rotenoids by1H-NMR spectroscopy in C6D6

The application of¹H-NMR spectroscopy in C₆D₆ for the determination of configurations at C_12a and C_6a in rotenoids is discussed.

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Bestimmung der Stereochemie von Rotenoiden mittels¹H-NMR-Spektroskopie in C₆D₆

Zusammenfassung Es wird die Anwendung der¹H-NMR-Spektroskopie in C₆D₆ zur Bestimmung der Konfigurationen an C_12a und C_6a in Rotenoiden diskutiert.

     

Novel biodegradable adaptive hydrogels: controlled synthesis and full characterization of the amphiphilic co-networks

Adaptive and amphiphilic poly(N,N-dimethylamino-2-ethyl methacrylate-graft-poly[epsilon-caprolactone]) co-networks (netP(DMAEMA-g-PCL)) were synthesized from a combination of controlled polymerization techniques. Firstly, PCL cross-linkers were produced by ring-opening polymerization (ROP) of epsilon-CL initiated by 1,4-butane-diol and catalyzed by tin(II) 2-ethylhexanoate ([Sn(Oct)2]), followed by the quantitative esterification reaction of terminal hydroxyl end-groups with methacrylic anhydride. Then, PCL cross-linkers were copolymerized to DMAEMA monomers by atom-transfer radical polymerization (ATRP) in THF at 60 degrees C using CuBr complexed by 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) and 2-ethyl isobutyrylbromide (EiBBr) as catalytic complex and initiator, respectively. A comprehensive study of gel formation was carried out by employing dynamic light scattering (DLS) to determine the gel point as a function of several parameters and to characterize the viscous solutions obtained before the gel point was reached. The evolution of the mean diameters was compared to a model previously developed by Fukuda and these attest to the living formation of the polymer co-network. Furthermore, we also demonstrated the reliability of ATRP for producing well-defined and homogeneous polymer co-networks by the smaller deviation from Flory's theory in terms of cross-linking density. For sake of clarity, the impact of polymerization techniques over the final structure and, therefore, properties was highlighted by comparing two samples of similar composition, but that were produced by either ATRP or thermal-initiated free-radical polymerization (FRP).     

One‐Step Preparation of Electrospun Microfibrous Polystyrene Mats Having Surface Enriched in p‐tert‐Butylcalix[4]arene Fitted with Phosphinoyl Pendant Arms

Polystyrene microfibers containing lower‐rim substituted calix[4]arene with phosphinoyl pendant arms were easily prepared in one‐step procedure by electrospinning. A specific feature of the fibers is the difference in their functionality at the surface and in the bulk. The graded structure of the fibers was shown by XPS analyses. The calix[4]arene concentration in the 3–5 nm surface layer was 50% higher than the theoretically calculated if calix[4]arene was uniformly distributed in the fibers. A six‐coordinated complex was formed between the calix[4]arene included in the fibers and Ni²⁺ ions. The distribution of phosphorus along the fibers is uniform, as evidenced by X‐ray mapping.

     

On the multi-spin magnon and spike solutions from membranes

Recently important classes of solitonic string solutions were obtained—giant magnons and single spikes. In previous study we showed the existence of giant magnon-like membrane solutions and studied their properties. In this paper we investigate classical rotating membranes representing analog of a specific class of string spiky solutions. Using the reduction to the Neumann–Rosochatius integrable system we find analog of the string single spike solutions. In contrast to the magnon-like solutions, this case is characterized with finite difference of energy and “winding number” and finite spins as well.     

Stable Aqueous Dispersion of PEGylated Nanoparticles by Polyelectrolyte Complex Formation

Stable aqueous dispersions of nanoparticles were prepared by polyelectrolyte complex formation between well‐defined poly(ethylene glycol)‐block‐poly(2‐acrylamido‐2‐methyl‐1‐propane sodium sulfonate) and poly(ethylene glycol)‐block‐poly[2‐(dimethylamino)ethyl methacrylate] diblock copolymers. Controlled synthesis of the copolymers was achieved by water‐based atom transfer radical polymerization (ATRP). The nanoparticles were characterized by a quite narrow and monomodal size distribution as evidenced by dynamic light scattering (DLS) and confirmed by atomic force microscopy (AFM) after solution casting and freeze‐drying.

     

Support size restrictions on time-frequency representations of functions on finite abelian groups

We obtain uncertainty principles for finite abelian groups that relate the cardinality of the support of a function to the cardinality of the support of its short–time Fourier transform. These uncertainty principles are based on well–established uncertainty principles for the Fourier transform. In terms of applications, the uncertainty principle for the short–time Fourier transform implies the existence of a class of equal norm tight Gabor frames that are maximally robust to erasures. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near-flat space limit of strings on AdS 4×ℂℙ3

The non-linear nature of string theory on non-trivial backgrounds, related to the AdS/CFT correspondence, force one to look for simplifications. Two such simplifications proved to be useful in studying string theory. These are the pp-wave limit, which describes point-like strings, and the so-called “near-flat space” limit which connects two different sectors of string theory—pp-wave and “giant magnons”. Recently another example of AdS/CFT duality emerged—AdS ₄/CFT ₃, which suggests duality between CS theory and superstring theory on . In this paper we study the “near-flat space” limit of strings on an background and discuss possible applications of the limiting theory. R.C. Rashkov is on leave from Department of Physics, Sofia University, Bulgaria.