Shape-controlled fabrication of polypyrrole microstructures by replicating organic crystals through electrostatic interactions

Polypyrrole (PPy) microstructures with diverse shapes were synthesized in an aqueous inorganic salt medium including organic crystals and pyrrole (Py). A series of sulfobenzoic acid salt forms with various cations (K⁺, Na⁺, Li⁺, NH₄⁺) in different positions (para, meta, ortho) of the sulfonate group on the benzene ring were used to form organic crystals as sacrificial templates. Using these crystals, we produced five different shapes of PPy microstructures (hexagonal microplates, curled nanofibers, lozenge-shaped microplates, rigid rods, parallelogram microplates), which replicated the shapes of the organic crystal templates through electrostatic interaction between the anionic crystal surfaces and the cationic PPy chains. In contrast, PPy that was polymerized without crystals showed bulky agglomerates of 200-500 nm size. The electrical properties were dictated by the molecular structures of the organic salt molecules used. While the highest conductivity (200.3 Scm⁻¹) was observed in PPy using crystals of para-linked 4-sulfobenzoic acid monopotassium salt, the lowest conductivity (0.8 Scm⁻¹) was observed in PPy prepared in the presence of crystals of ortho-linked 2-sulfobenzoic acid monoammonium salt.     

Effects of annealing on performances of 1.3-μm InAs-InGaAs-GaAs quantum dot electroabsorption modulators

In this work, we investigated the effects of quantum dot (QD) annealing (as-grown, 600°C-annealed, and 750°C-annealed) on the preliminary performances of 1.3-μm InAs-InGaAs-GaAs quantum dot electroabsorption modulators (QD-EAMs). Both extinction ratio and insertion loss were found to vary inversely with the annealing temperature. Most importantly, the 3-dB response of the 750°C-annealed lumped-element QD-EAM was found to be 1.6 GHz at zero reverse bias voltage - the lowest reverse bias voltage reported. We believe that this work will be beneficial to researchers working on on-chip integration of QD-EAMs with other devices since energy consumption will be an important consideration.     

Carotenoids and Their Geometry Isomers in Selected Tropical Fruits

This study determined the carotenoids content in cherry tomato, pink guava, and red grapefruit pulps and juices. Cherry tomato pulp exhibited the highest β-carotene content whereas pink guava pulp had the highest lycopene content. However, β-carotene and lycopene contents in the studied fruit juices were lower than their pulps in the same sample portion. Interestingly, six to twelve cis-isomers of carotenoids were identified in the fruit pulps and juices studied. A higher number of trace amounts of cis-carotenoids was found in fruit pulps as compared to juices. Therefore, consumption of whole fruit is recommended as the studied fruit juices have lower carotenoids content.     

Purification and enzymatic properties of the extracellular and constitutive chitosanase produced by Bacillus subtilis RKY3

BACKGROUND: Purification and enzymatic properties of a chitosanase from Bacillus subtilis RKY3 have been investigated to produce a chitooligosaccharide. The enzyme reported was extracellular and constitutive, which was purified by two sequential steps including ammonium sulfate precipitation and ion exchange chromatography. RESULTS: Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis of the purified chitosanase revealed one single band corresponding to a molecular weight of around 24 kDa. The highest chitosanase activity was found to be at pH 6.0 and at 60 °C. Although the mercaptide forming agents such as Hg²⁺ (10 mmol L^?1) and p‐hydroxymercuribenzoic acid (1 mmol L^?1, 10 mmol L^?1) significantly or totally inhibited the enzyme activity, its activity was enhanced by the presence of 10 mmol L^?1 Mn²⁺. The enzyme showed activity for hydrolysis of soluble chitosan and glycol chitosan, but colloidal chitin, carboxymethyl cellulose, crystalline cellulose, and soluble starch were not hydrolyzed. The analysis of chitosan hydrolysis by thin‐layer chromatography and viscosity variation revealed that the purified enzyme should be endosplitting‐type chitosanase. CONCLUSION: The chitosanase produced by Bacillus subtilis RKY3 was a novel chitosanlytic enzyme with relatively low molecular weight, which is a versatile enzyme for chitosan hydrolysis because it could hydrolyze soluble chitosan into a biofunctional oligosaccharide at a high level. Copyright © 2011 Society of Chemical Industry     

A mathematical study on a unified variational principle with two constrained parameters

In this paper, a parameterized variational principle based on a mixed functional obtained by a linear combination of the total potential energy functional, the modified Hellinger-Reissner functional, and the Hu-Washizu functional with two constrained parameters is proposed, and the mathematical characteristics of the variational equation of the principle are investigated for the analysis of boundary value problems in linear elasticity. It is first proved that the Euler-Lagrange equations of the variational equation is identical to the governing equations for the given problem. Then existence of the unique solution of the variational equation is systematically proved by showing that the energy bilinear form is weakly-coercive. As an application, the stress/strain smoothing can be obtained as a form of mixed FEM based on the variational equation.     

Cytotoxic Petrosiacetylenes from the Marine Sponge Petrosia sp.

A novel petrosiacetylene analog (petrosiacetylene E) has been isolated from the Korean marine sponge Petrosia sp., along with petrosiacetylene A, B and C. Their structures were elucidated on the basis of spectroscopic methods and the stereochemistry of the new compound was determined by using the modified Mosher’s method. Petrosiacetylene E showed higher cytotoxicity against five human cancer cell lines than petrosiacetylene A and B, presumably due to the additional hydroxy group located at C-16.