Rational redesign of Candida antarctica lipase B for the ring opening polymerization of D,D-lactide

Based on molecular modelling, the enzyme Candida antarctica lipase B was redesigned as a catalyst for the ring opening polymerization of D,D-lactide. Two mutants with 90-fold increased activity as compared to the wild-type enzyme were created. In a preparative synthesis of poly(D,D-lactide) the mutants greatly improved the rate and the degree of polymerization.     

The use of umbelliferone in the synthesis of new heterocyclic compounds

New coumarin derivatives, namely 7-[(5-amino-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one, 5-[(2-oxo-2H-chromen-7-yloxy)methyl]-1,3,4-thiadiazol-2(3H)-one, 2-[2-(2-oxo-2H-chromen-7-yloxy)acetyl]-N-phenylhydrazinecarbothioamide, 7-[(5-(phenylamino)-1,3,4-thiadiazol-2-yl)methoxy]-2H-chromen-2-one and 7-[(5-mercapto-4-phenyl-4H-1,2,4-triazol-3-yl)methoxy]-2H-chromen-2-one were prepared starting from the natural compound umbelliferone. The newly synthesized compounds were characterized by elemental analysis and spectral studies (IR, 1H-NMR and 13C-NMR).     

Interactions of the N3 dye with the iodide redox shuttle: quantum chemical mechanistic studies of the dye regeneration in the dye-sensitized solar cell

The iodide/triiodide redox couple plays a unique role in the dye-sensitized solar cell (DSSC). It is a necessary and unique part of every highly efficient DSSC published to date; alternative redox couples do not perform nearly as well. Hence, a detailed molecular-level understanding of its function is desirable. A density-functional theory (DFT) study has been carried out on the kinetic and thermodynamic aspects of the dye regeneration mechanism involving the iodide/triiodide redox couple and the prototypical N3 dye in the DSSC. The intermediate complexes between the oxidized dye and iodide have been identified. These are outer-sphere complexes of the general formula [dye(+)···I(-)]. Solvent effects are seen to play a critical role in the thermodynamics, whereas relativistic spin-orbit effects are less important. Both the kinetic and thermodynamic data reveal that the formation of complexes between [dye(+)···I(-)] and I(-) is the rate limiting step for the overall dye regeneration process. The regeneration of the neutral dye proceeds with the liberation of I; processes involving atomic iodine or I(-) are inferior, both from thermodynamic and kinetic considerations. The overall dye regeneration reaction is an exothermic process.     

On the stability of the solitary waves to the rotation Benjamin‐Ono equation

In this paper, we study several aspects of solitary wave solutions of the rotation Benjamin‐Ono equation. By solving a minimization problem on the line, we construct a family of even travelling waves ψ_c,γ. We then prove the uniqueness of even ground states associated with large speed and their orbital stability. Note that this improves the results in Esfahani and Levandosky, where only the stability of the set of ground states is proven.     

Design of fiber Bragg grating-based Fabry–Perot sensor for simultaneous measurement of humidity and temperature

A new sensor for simultaneous measurement of humidity and temperature is proposed. The sensor consists of Fabry–Perot cavity formed by two identical uniform fiber Bragg gratings. To make the cavity serves as humidity sensor, moisture sensitive polymer, which is polyimide, is coated on the FBG and on the cavity with different thickness. When the sensor is exposed to the relative humidity change, the polyimide will expand and stretch the fiber and induces strain on the FBG and on the cavity. The induced strain alters the grating period, cavity length and effective refractive index of fiber. The simulation results show that the humidity sensitivity and thermal sensitivity are 1.92 pm/%RH and 8.87 pm/°C, respectively, for polyimide coating thickness of 10 μm on the FBG and 15 μm on the cavity.     

Effect of NH4I and I2 concentration on agar gel polymer electrolyte properties for a dye-sensitized solar cell

Gel polymer electrolytes were prepared using agar polymer host, NH₄I, and I₂ salts. The sample of agar paste with 1.0 M of NH₄I and 0.2 μM of I₂ exhibits the highest conductivity and lowest viscosity values at room temperature of (2.64?±?0.19)?×?10^?3?S?cm^?1 and 1.17?±?0.29 Pa?s, respectively. All of the gel polymer electrolytes display Arrhenian behavior, and the optimum agar paste gave the lowest activation energy of 0.25 eV. It also had a good physical appearance compared with the other samples. This gel polymer electrolyte had a good potential and was applicable to a role as electrolyte in ITO-ZnO (N719 dye)/agar paste?+?1.0 M NH₄I?+?0.2 μM I₂/Au-Pd-ITO dye-sensitized solar cell.     

On the interplay between inertial and viscoelastic effects for the flow in weakly modulated channels

The flow inside a spatially modulated channel is examined for viscoelastic fluids of the Oldroyd‐B type. The lower wall is flat and the upper wall is sinusoidally modulated. The modulation amplitude is assumed to be small. Thus, a regular perturbation expansion of the flow field coupled to a variable‐step finite‐difference scheme is used to solve the problem. Convergence and accuracy assessment against earlier experimental results indicate that there is a significant range of validity of the perturbation approach. The influences of wall geometry, inertia and viscoelasticity on the flow kinematics and stresses are investigated systematically. In particular, the interplay between the flow and fluid parameters effects on the conditions for the onset of backflow, number of vortices, their size and location is revealed. The distance between the flow separation and reattachment locations identifies the vortex size. Non‐monotonic dependence of the vortex size on elasticity is reported. The critical conditions for the onset of negative elasticity effects on vortex size are identified. The critical Reynolds number for the onset of backflow initially decreases then levels off or even increases as elasticity increases. For highly elastic fluid and large enough Reynolds number, more than one vortex appear near the lower wall. Copyright © 2005 John Wiley & Sons, Ltd.     

Spectral Properties of Bifunctional Schiff Bases, [Bis (X-Phenyl)-Ethane Diimine]

Electronic spectra of five (Bis(X-phenyl)-Ethane diimine] compounds I-V, have been investigated in various organic solvents and aqueous buffer solutions of varying pH's. The observed visible band is assigned to intramolecular CT transition. Furthermore, it is deduced that structure of the o-hydroxy derivative is not entirely planar. The acid dissociation constant values of the hydroxy derivatives have been determined and are discussed.     

Convergence Dynamics of Delayed Hopfield-Type Neural Networks Under Almost Periodic Stimuli

Convergence dynamics of Hopfield-type neural networks subjected to almost periodic external stimuli are investigated. In this article, we assume that the network parameters vary almost periodically with time and we incorporate variable delays in the processing part of the network architectures. By employing Halanay inequalities, we obtain delay independent sufficient conditions for the networks to converge exponentially toward encoded patterns associated with the external stimuli. The networks are guaranteed to have exponentially hetero-associative stable encoding of the external stimuli.     

Microchip electrophoresis for specific gene detection of the pathogenic bacteria V. cholerae by circle-to-circle amplification.

We have developed a new method for a fast and precise analysis of circle-to-circle amplification (C2CA) product for specific gene detection by microchip electrophoresis. In this method, we have added a new enzymatic step to the C2CA reaction, which could be carried out isothermally at 37 degrees C. Compared to the original single-stranded DNA, the double-stranded DNA that is produced by this enzymatic reaction is more reliable for analysis by microchip electrophoresis. C2CA product was detected within 55 s with high reproducibility by this method which was successfully applied to the detection of 10-ng genomic DNA of the pathogenic bacteria Vibrio. cholerae within 110 s. Purification was found to be an indispensable step for the analysis of the C2CA product of genomic DNA samples.