Synthesis of methacrylate derivatives oligomers by dithiobenzoate‐RAFT‐mediated polymerization

Reversible addition fragmentation chain transfer (RAFT) was used to synthesize methacrylic acid oligomers and oligo(methacrylic acid)‐b‐poly(methyl methacrylate) (PMAA‐b‐PMMA) with targeted degree of polymerization ≈ 10. Characterization is by size‐exclusion chromatography (SEC) and electrospray mass‐spectrometry. SEC data are presented as hydrodynamic volume distributions (HVDs), the only proper means to present comparative and meaningful SEC data when there is no unique relationship between size and molecular weight. The RAFT agent, (4‐cyanopentanoic acid)‐4‐dithiobenzoate (CPADB), produced dithiobenzoic acid as a side product during the polymerization of methacrylate derivatives. Precipitation in diethyl ether proved to be an easy way to remove this impurity from the PMAA‐RAFT oligomers. Both unpurified and purified macro‐RAFT agent were used to prepare amphiphilic PMAA‐b‐PMMA copolymers. Diblock copolymer prepared from the purified PMAA homopolymer had a narrower HVD in comparison to those obtained from the equivalent unpurified macro‐RAFT agent. This work shows that while cyanoisopropyl‐dithiobenzoate or CPADB are good RAFT agents for methacrylate derivatives, they exhibit some instability under typical polymerization conditions, and thus when oligomers are targeted, optimal control requires checking for the degradation product and appropriate purification steps when necessary (the same effect is present for larger polymers but is unimportant). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2277–2289, 2008     

Numerical analysis and optimization of a dual-concentric-core photonic crystal fiber for broadband dispersion compensation

In this article, a novel dual-concentric-core photonic crystal fiber (DC-PCF) for dispersion compensation is presented. The proposed DC-PCF has relatively high negative dispersion over a wide wavelength range, which covers E, S, C, L and U telecommunication wavelength bands. The validity of the proposed design is carried out by employing a 2-D finite difference frequency domain method (FDFD) with perfectly matched layers (PML). By using the numerical method, the dispersion profile of the DC-PCF is optimized in terms of three air-hole diameters to achieve desirable negative dispersion. The influence of the location of ring-core, the number of air-hole rings on dispersion and loss characteristics are also studied.     

Noscapine-derived β-amino alcohols as new organocatalysts for enantioselective addition of diethylzinc to aldehydes

In this paper, synthesis of two derivatives of noscapine and their application as organocatalysts in the asymmetric addition of diethylzinc to aromatic aldehydes is reported. The first catalyst (2) was synthesized by the reduction of lactone ring of noscapine to form the corresponding diol, and the second one (3) was prepared by tert-butyl dimethyl silylation of the primary hydroxyl group of 2. Excellent yields and high ees up to 95% were obtained by using 3 as the catalyst. To the best of our knowledge, this is the first report on the application of lactone ring opened noscapinoid compounds as organocatalysts in asymmetric reactions.     

Enhancing Gauge Symmetries of Non-Abelian Supersymmetric Chern-Simons Model

In this article, we study gauge symmetries of the Non-Abelian Supersymmetric Chern-Simons model (SCS) of SU(2) group at (2+1)-dimensions in the framework of the formalism of constrained systems. Since, broken gauge symmetries in this physical system lead to the presence of nonphysical degrees of freedom, the Non-Abelian SCS model is strictly constrained to second-class constraints. Hence, by introducing some auxiliary fields and using finite order BFT method, we obtain a gauge symmetric model by converting second-class constraint to first-class ones. Ultimately, the partition function of the model is obtained in the extended phase space.     

Numerical solution of nonlinear Jaulent–Miodek and Whitham–Broer–Kaup equations

In this work we investigate the numerical solution of Jaulent–Miodek (JM) and Whitham–Broer–Kaup (WBK) equations. The proposed numerical schemes are based on the fourth-order time-stepping schemes in combination with discrete Fourier transform. We discretize the original partial differential equations (PDEs) with discrete Fourier transform in space and obtain a system of ordinary differential equations (ODEs) in Fourier space which will be solved with fourth order time-stepping methods. After transforming the equations to a system of ODEs, the linear operator in JM equation is diagonal but in WBK equation is not diagonal. However for WBK equation we can also implement the methods such as diagonal case which reduces the CPU time. Comparing numerical solutions with analytical solutions demonstrates that those methods are accurate and readily implemented.     

Pore-Scale Monitoring of Wettability Alteration by Silica Nanoparticles During Polymer Flooding to Heavy Oil in a Five-Spot Glass Micromodel

It is well known that the oil recovery is affected by wettability of porous medium; however, the role of nanoparticles on wettability alteration of medium surfaces has remained a topic of debate in the literature. Furthermore, there is a little information of the way dispersed silica nanoparticles affect the oil recovery efficiency during polymer flooding, especially, when heavy oil is used. In this study, a series of injection experiments were performed in a five-spot glass micromodel after saturation with the heavy oil. Polyacrylamide solution and dispersed silica nanoparticles in polyacrylamide (DSNP) solution were used as injected fluids. The oil recovery as well as fluid distribution in the pores and throats was measured with analysis of continuously provided pictures during the experiments. Sessile drop method was used for measuring the contact angles of the glass surface at different states of wettability after coating by heavy oil, distilled water, dispersed silica nanoparticles in water (DSNW), polyacrylamide solution, and DSNP solution. The results showed that the silica nanoparticles caused enhanced oil recovery during polymer flooding by a factor of 10%. The distribution of DSNP solution during flooding tests in pores and throats showed strong water-wetting of the medium after flooding with this solution. The results of sessile drop experiments showed that coating with heavy oil, could make an oil-wet surface. Coating with distilled water and polymer solution could partially alter the wettability of surface to water-wet and coating with DSNW and DSNP could make a strongly water-wet surface.     

Essential oil composition of Nepeta satureioides from Iran

The essential oil of Nepeta satureioides Boiss. from Iran was isolated by hydrodistillation in yield of 0.06% (w/w). The chemical composition of the essential oil was analyzed by GC and GC-MS. Forty-five compounds accounting for 97.4% of the total oil were identified. The major components were linalool (23.8%), (Z,E)-farnesol (14.7%), linalyl acetate (11.1%), β-caryophyllene (6.6%), lavandulol acetate (6.6%), caryophyllene oxide (6.4%), and (Z)-β-farnesene (3.4%). Oxygenated terpenoids were the main group of compounds. Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 144–145, March–April, 2006.     

Essential Oil Composition and Antibacterial Activity of the Leaves of <Emphasis Type="Italic">Stachys schtschegleevii</Emphasis> from Iran

The composition of the essential oil obtained by hydrodistillation from the leaves of Stachys schtschegleevii Sosn. before the flowering stage was analyzed by GC and GC-MS. Forty-five compounds representing 98.7% of the total oil were identified, of which α-pinene (36.4%), germacrene-D (18.6%), limonene (8.2%), and piperitone (6.2%) were the major constituents. Furthermore, antibacterial activity of the entire oil and its two main monoterpenes was evaluated against six Gram-positive and Gram-negative bacteria. The oil exhibited moderate activity against the tested bacteria.__________Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 138–140, March–April, 2005.     

A density functional study of N NQR parameters of imidazole derivatives and extrapolation to PfHRP2–Fe-PPIX complex

In this paper, density functional theory (DFT) was used to calculate ¹⁴N nuclear quadrupole coupling constants (NQCC), χ, and asymmetry parameters, η, for a series of imidazole derivatives: imidazole, 5-methylimidazole and histidine. These calculations were carried out with the PW91P86 method via the Gaussian 98 package. A systematic theoretical investigation of the different environmental effects on (χ, η) values of amino ¹⁴N1 and imino ¹⁴N2 of imidazole ring of these compounds, reveals that the local surrounding of nitrogen atoms play an important role in determining their χ and η values. Our calculations in solution show that adding explicit solvent molecules to the polarizable continuum model (PCM) has a strong effect on (χ, η) values, thereby indicating that for long-range effects, PCM, is not sufficient to describe the whole solvent effects. We also evaluate the influence of [Fe³⁺ (S = 1/2)] on the (χ, η) values of proximal and remote nitrogens of an axial ligand and compare with those of free ligands. The results show that Fe³⁺ has a strong effect on the (χ, η) values of proximal nitrogen unlike remote nitrogen. Finally, our results predict (χ = 1.56 MHz, η = 0.690) for proximal nitrogen and (χ = 2.75 MHz, η = 0.169) for remote nitrogen in PfHRP2–Fe³⁺-PPIX complex.     

MHD forced convection of MWCNT–Fe3O4/water hybrid nanofluid in a partially heated τ-shaped channel using LBM

Journal of Thermal Analysis and Calorimetry - Forced convection heat transfer of multi-wall carbon nanotubes–iron oxide nanoparticles/water hybrid nanofluid (MWCNT–Fe3O4/water hybrid...