Optical limiting response by embedding copper phthalocyanine into polymer host

The multilayer film of PMMA containing mononuclear octakis(mercaptopropylisobutyl-POSS) substituted phthalocyaninato-copper (CuPc) was obtained by spin-coating on quartz substrate. The nonlinear absorption and optical limiting (OL) performance of CuPc have been described using the open-aperture Z-scan technique. The measurements were performed using collimated 4 ns pulses generated from a frequency-doubled Nd:YAG laser at 532 nm wavelength. The results indicate that CuPc/PMMA composite exhibits a much larger nonlinear absorption coefficient, a lower saturable fluence and a lower absorption cross-section ratio for optical limiting when compared to the same CuPc molecules in solution. No evidence of film fatigue or degradation was observed in the CuPc/PMMA film after numerous scans at varying laser intensity. This material is a good candidate for optical limiting applications.     

Exact Solutions for Fractional Differential-Difference Equations by (G′/G)-Expansion Method with Modified Riemann-Liouville Derivative

In this paper, the ($G′/G$)-expansion method is suggested to establish new exact solutions for fractional differential-difference equations in the sense of modified Riemann–Liouville derivative. The fractional complex transform is proposed to convert a fractional partial differential difference equation into its differential difference equation of integer order. With the aid of symbolic computation, we choose nonlinear lattice equations to illustrate the validity and advantages of the algorithm. It is shown that the proposed algorithm is effective and can be used for many other nonlinear lattice equations in mathematical physics and applied mathematics.     

An approach for computing tight numerical bounds on renewalfunctions

This method computes tight lower and upper bounds for the renewal function. It is based on Riemann-Stieltjes integration, and provides bounds for solving certain renewal equations used in the study of availability. An error analysis is given for the numerical bounds when inter-renewal time distributions are sufficiently smooth. Three examples are explored that demonstrate the accuracy of these computed numerical bounds     

A nonstandard numerical method for the modified KdV equation

A linearly implicit nonstandard finite difference method is presented for the numerical solution of modified Korteweg–de Vries equation. Local truncation error of the scheme is discussed. Numerical examples are presented to test the efficiency and accuracy of the scheme.     

Benzaldehyde lyase-catalyzed enantioselective carboligation of aromatic aldehydes with mono- and dimethoxy acetaldehyde

[reaction: see text] Benzaldehyde lyase from the Pseudomonas fluorescens catalyzes the reaction of aromatic aldehydes with methoxy and dimethoxy acetaldehyde and furnishes (R)-2-hydroxy-3-methoxy-1-arylpropan-1-one and (R)-2-hydroxy-3,3-dimethoxy-1-arylpropan-1-one in high yields and enantiomeric excess via acyloin linkage. Aromatic aldehydes and benzoins are converted into enamine-carbanion-like intermediates prior to carboligation.     

EPR study of gamma-irradiated 2-Bromo-4′-methoxyacetophenone single crystals

The gamma-irradiated single crystals of 2-Bromo-4′-methoxyaceto-phenone (2B4MA) were investigated using electron paramagnetic resonance (EPR) technique. Density-functional theory calculations were employed to investigate and identify the radicals that have been assumed to be formed upon irradiation of 2B4MA single crystals. The EPR spectra of 2B4MA were recorded at different orientations in the magnetic field at room temperature. Taking into account the chemical structure and experimental spectra of irradiated single crystal of 2B4MA, it was assumed that at least two different radicals were produced in the sample. Following this assumption, six possible radicals were modeled and EPR parameters were calculated by using the DFT, B3LYP/6-311+G(d), for the modeled radicals individually. The calculated hyperfine coupling constants and g-tensors were used as initial values for simulation studies. The three crystallographic axes on the simulated spectra were well matched with experimental spectra for the two modeled radicals. Thus, we identified the R1 type radical and R4 type radical as paramagnetic species produced in gamma-irradiated 2B4MA.     

Anhydrous proton-conducting properties of triazole-phosphonic acid copolymers: a combined study with MAS NMR

The synthesis, thermal and proton conducting properties of copolymers based on vinylphosphonic acid (VPA) and 1-vinyl-1,2,4-triazole (VTri) were investigated. The copolymers were synthesized by free-radical copolymerization of the corresponding monomers at several monomer feed ratios to obtain poly(VPA-co-VTri) copolymer electrolytes. The final structures of the copolymers were confirmed by spectroscopic methods. The composition of the low molecular weight copolymers was varied with the feed ratio of the monomers. The presence of triazole units in the copolymers suppresses the formation of phosphonic acid anhydrides up to 150 degrees C, as verified by both (31)P NMR and TGA. The observation of defined glass transition temperatures indicated that the ionic interactions do not prevent segmental relaxations of the polymer chains. In the absence of humidity, the copolymer electrolyte, poly(VPA-co-VTri), S2 (with 33% triazole content) showed proton conductivity of 10(-3) S cm(-1) at 120 degrees C, which is far higher than in imidazole based copolymers. Two different types of hydrogen-bonded protons were detected by (1)H MAS NMR in the solid copolymer systems, due to different arrangements of triazole and phosphonic acid units.     

Catalytic asymmetric nitroaldol (Henry) reaction with a zinc-Fam catalyst

Ferrocenyl-substituted aziridinylmethanol (Fam-1) was used as a catalyst with zinc for the asymmetric nitroaldol (Henry) reaction. This catalyst worked with a variety of aldehydes (aromatic, aliphatic, alpha,beta-unsaturated, and heteroaromatic) and alpha-ketoesters to give the nitroaldol product in up to 97% yield and 91% ee. The chiral ligand can be recovered and recycled without losing its activity.     

Synthesis of corrosion preventive long-chain <Emphasis Type="Italic">N</Emphasis>-alkyl-2-(phenylthio)-acetohydrazides and 2-oxo-2-phenylethyl-2-alkanoylhydrazinecarbodithioates

Long-chain N-alkyl-2-(phenylthio)acetohydrazides were synthesized via the reactions of 2-(phenylthio)acetohydrazide with long-straight-chain aldehydes and then reduction with sodium borohydride. The reactions of long-straight-chain hydrazides with carbon disulfide in alkaline media give the corresponding carbodithioate salts. Heating of potassium 2-alkanoylhydrazinecarbodithioates with phenacyl bromide do not yield cyclization and failed to give the corresponding long-chain thiazolidine-2-thiones, but gave the corresponding 2-oxo-2-phenylethyl-2-alkanoylhydrazinecarbodithioates via nucleophilic substitution reaction. In addition, the synthesized compounds were tested for their corrosion prevention capabilities in acidic or in mineral oil media. Correspondence: Ayhan Yıldırım, Department of Chemistry, Faculty of Science and Arts, Uludağ University, 16059 Bursa, Turkey.     

Efficient terpene hydroxylation catalysts based upon P450 enzymes derived from actinomycetes

The hydroxylation of alpha-ionone 1 and beta-ionone 2 to their corresponding mono-hydroxylated derivatives has been examined using a recombinant E. coli whole cell system, in which cytochromes P450 SU1 and SU2, and P450 SOY were over-expressed with their cognate ferrodoxins. Both substrates are hydroxylated with a high degree of regioselectivity and for alpha-ionone 1 the reaction is highly diastereoselective yielding the anti-isomer.