Microwave Thermolysis Vi : A Rapid and General Method for Dethioacetalization Using “Clayan” in Dry Media

A variety of thioacetals, dithiolanes and dithianes are deprotected into their carbonyl compounds using clay supported ammonium nitrate “Clayan” under microwave irradiation. The present method avoids the use of toxic oxidants and excess of solvent.     

On the dynamics of moving single bubble sonoluminescence

It is well known that the primary Bjerknes force is the origin of the trapping of sonoluminescing bubble in the sound field in liquid. In the present Letter, the quantitative investigation of the behavior of hydrodynamic force on the moving sonoluminescing (SL) bubble introduces the new role of stabilizing the trajectory motion of the bubble for primary Bjerknes force. Using a complete force balanced radial-translational dynamics, it is analytically discussed that by increasing the bubble distance from the antinode of the sound field the increase of the magnitude of inward Bjerknes force, controls the size of the domain of the bubble trajectory. At this time the wake produced by the rapid variation of the bubble's relative translational velocity to the surrounding liquid, changes the bubble direction of motion through the effect of history force. The required momentum for accelerating the SL bubble around the central antinode is produced by the added mass force at the bubble collapse. It is revealed in a re-examination of the coupled radial-translational dynamics for a trapping bubble that because of the bubble lower translational acceleration caused due to the lower added mass force and the bubble attraction towards the acoustic antinodes in presence of inward Bjerknes force, the small bubble will be trapped at the antinode of the sound field.     

Nonisothermal crystallization and melting behavior of the copolymer derived from p-dioxanone and poly(ethylene glycol)

Nonisothermal crystallization and melting behaviors of poly(p-dioxanone)(PPDO)-b-poly(ethylene glycol)(PEG) with mole ratios of 80:20 and 30:70, has been studied by differential scanning calorimeter using various cooling rates. Crystallization behavior of each crystallizable segments of the copolymer was compared with the corresponding segment of homopolymer. For a given composition, the crystallization process began at higher temperature when the slower scanning rates were used. The kinetics of the PPDO segments and the PEG segments in the copolymers under nonisothermal crystallization conditions were analyzed by Ozawa equation and also the crystallization results of the copolymer segments were compared with the corresponding homopolymers. The results showed that the Ozawa equation fails to describe the whole crystallization process of the copolymer segments along with PPDO homopolymer, but describes the crystallization behavior of the PEG homopolymer. Crystallization activation energy and absolute crystallinity values were estimated from the cooling scans (using Kissinger’s method) and fusion endotherms of the subsequent heating scans, respectively.     

Preparation and studies of electrical properties of cobalt substituted Li-Zn ferrites by sol-gel auto combustion method

A series of Co substituted lithium zinc ferrite powders with different content of Co (0.00 to 0.1 in steps of 0.02) were prepared by a novel sol-gel auto combustion process using citric acid. Their spinel structure was confirmed by XRD. The variation in lattice parameter and density with cobalt concentration was studied which showed an increasing trend. A decreasing pattern was observed in variation of porosity with increasing Co. Room temperature dielectric constant and resistivity were studied as a function of composition at 10 KHz. The room temperature dielectric constant decreases with successive addition of Co²⁺ in the series. The observed variation in dielectric constant has been explained on the basis of space charge polarization and Koops two layer model. Resistivity is observed to increase with increasing concentration and the observed variation in resistivity has been explained by Verwey hopping mechanism.     

Multinuclear oxo-bridged manganese complexes with a bulky substituted benzoate ligand: novel species obtained by using steric control

A sterically hindered carboxylate ligand is used to synthesize the first transition metal complex containing both bis-mu-oxo and bis-mu-carboxylato groups, [Mn2(mu-O)2(mu-ArtolCO2)2(bpy)2]+. However, methyl substitution on the chelating bipyridine ligand results in the formation of a strikingly different and novel hexanuclear species, [Mn6(mu-O)4(mu3-O)4(mu-ArtolCO2)2(dmb)6]4+. Steric interactions between the bridging carboxylates and chelating pyridine-based ligands determine the nuclearity of the complexes formed.     

Toward synthetic models for high oxidation state forms of the photosystem II active site metal cluster: the first tetranuclear manganese cluster containing a [Mn4(mu-O)5]6+ core

The first tetrameric high valent manganese complex consisting of a MnIV4(mu-O)5 bridged core, [Mn4(mu-O)5(dmb)4(dmbO)2](ClO4)4, [symbol: see text] was isolated via dimanganese (III,IV) and (IV,IV) intermediates in presence of the oxidant tert-butyl hydroperoxide and was characterized by X-ray crystallography, electrochemistry, infrared, UV-visible, 1H NMR, and mass spectroscopy; the structure found differs greatly from a proposal for the putative Mn4O5 aggregate found in Photosystem II.     

Solvodynamic Properties of Sodium Polystyrenesulfo-nate in Methanol-Water Mixed Solvent Media in Absence and in the Presence of a Salt Using Viscometric Method

Linear extrapolation of the reduced viscosity values of uncharged polymer solutions as the concentration approaches zero constitutes the basis for the traditional method for the determination of the intrinsic viscosities of polymer solutions. While this method works well for uncharged polymer solutions, it fails completely for polyelectrolyte solutions especially in absence and also in presence of small amount of an added electrolyte. A very convenient method has recently been proposed by Wolf (Wolf, Macromol. Rapid Commun. 2007, 28, 164) to determine the intrinsic viscosities of polyelectrolyte solutions on the basis of the laws of phenomenological thermodynamics applied to the viscosity of polymer solutions. In spite of the success and the convenience of this method, this has so far been applied to a limited number of polyelectrolyte systems by the Wolf group alone (Wolf, Macromol. Rapid Commun. 2007, 28, 164; Eckelt et al., Macromolecules 2008, 41, 912; Badiger et al., Macromol. Chem. Phys. 2008 , 209, 2087; Ghimici et al., J. Phys. Chem.B. 2009, 113, 8020). In order to improve the situation, we have measured the viscosities of an anionic polyelectrolyte, sodium polystyrenesulfonate, in methanol-water mixed solvent media both in absence and in the presence of an electrolyte, sodium chloride. The results show that the experimental data fit well with the Wolf model and thus allow the calculation of intrinsic viscosities, which provide important insight about the dependence of the polyion conformation on solvent composition as well as on the concentration of the added electrolyte. This new evaluation method, thus, proves to be very useful to a better understanding of the rheological behaviour of the polyelectrolyte system investigated.     

Molecular Simulations and Drug Discovery of Adenosine Receptors

G protein-coupled receptors (GPCRs) represent the largest family of human membrane proteins. Four subtypes of adenosine receptors (ARs), the A₁AR, A_2AAR, A_2BAR and A₃AR, each with a unique pharmacological profile and distribution within the tissues in the human body, mediate many physiological functions and serve as critical drug targets for treating numerous human diseases including cancer, neuropathic pain, cardiac ischemia, stroke and diabetes. The A₁AR and A₃AR preferentially couple to the G_i/o proteins, while the A_2AAR and A_2BAR prefer coupling to the G_s proteins. Adenosine receptors were the first subclass of GPCRs that had experimental structures determined in complex with distinct G proteins. Here, we will review recent studies in molecular simulations and computer-aided drug discovery of the adenosine receptors and also highlight their future research opportunities.     

Biodegradable electrospun mat: Novel block copolymer of poly (p‐dioxanone‐co‐L‐lactide)‐block‐poly(ethylene glycol)

Ultrafine fibers of a laboratory‐synthesized new biodegradable poly(p‐dioxanone‐co‐L ‐lactide)‐block‐poly(ethylene glycol) copolymer were electrospun from solution and collected as a nonwoven mat. The structure and morphology of the electrospun membrane were investigated by scanning electron microscopy, differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and a mercury porosimeter. Solutions of the copolymer, ranging in the lactide fraction from 60 to 80 mol % in copolymer composition, were readily electrospun at room temperature from solutions up to 20 wt % in methylene chloride. We demonstrate the ability to control the fiber diameter of the copolymer as a function of solution concentration with dimethylformamide as a cosolvent. DSC and WAXD results showed the relatively poor crystallinity of the electrospun copolymer fiber. Electrospun copolymer membrane was applied for the hydrolytic degradation in phosphate buffer solution (pH = 7.5) at 37 °C. Preliminary results of the hydrolytic degradation demonstrated the degradation rate of the electrospun membrane was slower than that of the corresponding copolymers of cast film. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1955–1964, 2003