Photophysical properties and semiempirical calculations of perylene-3,4,9,10-tetracarboxylic tetramethylester (PTME)

The spectral behavior and fluorescence quantum yield of perylene-3,4,9,10-tetracarboxylic tetramethylester (PTME) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity. The dye exhibits high fluorescence quantum yield and high photostable. Crystalline solid of PTME gives excimer-like emission at 530 nm. The laser activity of PTME has been investigated. The dye solution in N,N-dimethylformamide (DMF) gives laser emission around 480 nm upon excitation by 337.1 nm nitrogen laser pulse. The excitation energy transfer from 7-dimethylamino-4-methylcoumarine (DMC) to PTME has also has been studied and the value of energy transfer rate constant, k(ET), and critical transfer distance, R(0) indicate a F?rster-type mechanism. The photodecomposition of PTME in chloromethane solvents has been also studied. We applied semiempirical MO calculations using (PM3 and ZINDO-CI) calculations to explain the geometric and electronic behaviors of the PTME molecule in both ground and excited states and make a correlation with the experimental observations.     

Oscillating Poiseuille flow in photo‐aligned liquid crystal cells

We present an experimental study of thin liquid crystal (LC) layers under the action of a harmonically varied pressure gradient. Optical measurements were performed to register the linear oscillations of a nematic director related to homeotropic and homeoplanar (hybrid) initial states. In the latter case one of the inner surfaces of the rectangular channels was treated by ultraviolet light to provide a relatively weak planar anchoring. The optical response of hybrid and homeotropic LC cells under an oscillating pressure gradient was investigated in relation to on the amplitude and frequency of the pressure gradient. A hydrodynamic model is developed taking into account the LC polar anchoring strength and the surface viscosity responsible for a fast LC surface dynamics. Our estimates show that the thickness of the boundary layer corresponding to the surface viscosity does not exceed 10^?6 m, and further experiments are needed with thinner LC cells and higher frequency oscillations to achieve a more precise value. An oscillating Poiseuille flow in the hybrid cell was found to be useful for characterizing elastic and viscous properties of a weakly anchoring LC surface layer in a fast surface dynamic process.     

Electrocatalytical properties presented by Cu/Ni alloy modified electrodes toward the oxidation of glucose

This paper concerns the deposition of metal alloys formed by nickel and copper on electrode surface aiming at the development of electrocatalytic systems. Such alloys were formed on platinum electrodes by direct reduction of Ni²⁺ and Cu²⁺ sulfate salts in different proportions in a simple and straightforward electrochemical treatment. After the deposition, the conversion to the electrocatalytic oxide form was done in alkaline solutions by cyclic voltammograms. The experimental parameters, such as deposition time and the proportion of copper and nickel in the synthetic solution, were investigated toward the catalytic oxidation of glucose. The materials were characterized by electrochemical experiments, infrared and Raman spectroscopies, and X-ray diffraction, showing that the material is not a simple mixture of nickel and copper oxides. The modified electrodes showed remarkable electrocatalytic properties, indicating an interesting application in the sensor and fuel cell development.     

Impact of strain induced by polymer curing in benzocyclobutene embedded semiconductor nanostructures

Polymers such as benzocyclobutene are commonly used as embedding materials for semiconductor nanostructures. During the curing process of the polymer up to 250 °C, a significant impact of strain can be induced on the embedded semiconductor material due to different thermal expansion coefficients. This strain has been revealed by X‐ray diffraction in free‐standing GaAs nanowires grown on a silicon substrate, embedded in a polymer matrix. It will be shown that this strain is released during the X‐ray irradiation if additionally an external static electric field is applied.

     

Opposed steric constraints in human DNA polymerase beta and E. coli DNA polymerase I

DNA polymerase selectivity is crucial for the survival of any living species, yet varies significantly among different DNA polymerases. Errors within DNA polymerase-catalyzed DNA synthesis result from the insertion of noncanonical nucleotides and extension of misaligned DNA substrates. The substrate binding characteristics among DNA polymerases are believed to vary in properties such as shape and tightness of the binding pocket, which might account for the observed differences in fidelity. Here, we employed 4'-alkylated nucleotides and primer strands bearing 4'-alkylated nucleotides at the 3'-terminal position as steric probes to investigate differential active site properties of human DNA polymerase beta (Pol beta) and the 3'-->5'-exonuclease-deficient Klenow fragment of E. coli DNA polymerase I (KF(exo-)). Transient kinetic measurements indicate that both enzymes vary significantly in active site tightness at both positions. While small 4'-methyl and -ethyl modifications of the nucleoside triphosphate perturb Pol beta catalysis, extension of modified primer strands is only marginally affected. Just the opposite was observed for KF(exo-). Here, incorporation of the modified nucleotides is only slightly reduced, whereas size augmentation of the 3'-terminal nucleotide in the primer reduces the catalytic efficiency by more than 7000- and 260,000-fold, respectively. NMR studies support the notion that the observed effects derive from enzyme substrate interactions rather than inherent properties of the modified substrates. These findings are consistent with the observed differential capability of the investigated DNA polymerases in fidelity such as processing misaligned DNA substrates. The results presented provide direct evidence for the involvement of varied steric effects among different DNA polymerases on their fidelity.     

Synthesis and characterization of supermacroporous cryogel with immobilized p-aminobenzenesulfonamide as affinity ligand for the purification of lactoperoxidase from whey

This study proposed the development of a monolithic supermacroporous affinity column for direct capture of lactoperoxidase, a glycoprotein present in milk, whey, and colostrum, with several applications due to its wide antimicrobial activity. A poly(acrylamide)-based cryogel was produced by radical co-polymerization of monomers in frozen aqueous solution and activated with p-aminobenzenesulfonamide as a ligand for specific interaction with the lactoperoxidase. The axial liquid dispersion coefficients at different liquid flow rates were determined by measuring residence time distributions using the tracer pulse-response method. The axial dispersion coefficient was low and the height equivalent to theoretical plate was not dependent on the flow velocity. The adsorptive capacity of affinity cryogel was studied as a function of flow velocity and the best condition was 0.9 cm/min. The response surface methodology was applied to optimize the capture of the enzyme, as a function of pH and salt concentration. Higher purification factor value was found at a salt concentration of 80 mmol/L and pH of 8.0 (p < 0.05). There was no influence of the variables under study on the yield (p > 0.05). The results indicated that affinity cryogel is a promising chromatography support for the use in high-throughput one-step purification of lactoperoxidase from whey.     

3-Aza-8,10-dioxa-bicyclo[5.2.1]decane (9-exo BTKa) carboxylic acid as a new reverse turn inducer: synthesis and conformational analysis of a model peptide

Dipeptide isostere 5, belonging to the class of 9-exo BTKa, was synthesised starting from R,R-tartaric acid and 4-nitro-1-(3-nitrophenyl)butan-1-one. The nine-membered lactam showed interesting structural features and was inserted in a 5-residue model peptide. The conformational properties of this modified peptide have been studied by NMR and molecular modelling, indicating that compound 5 acted as a reverse turn inducer.     

Chemistry of the silica surface: reaction with phosphorus pentachloride

Solid-state 31P and 29Si NMR experiments, with Magic-Angle Spinning (MAS), were used to elucidate the chemistry that occurs when silica gel is treated with phosphorus pentachloride. A low-loading regime (in which the molar ratio of initial PCl5 to surface silanols sites is <1) and a high-loading regime (in which this ratio is approximately 1) were examined. For each regime, the results for limited and intentional exposure to moisture are presented. The occurrence of phosphorus bridging between two adjacent silanols sites is observed. Bridging structures based on Si-O-P-O-P-O-Si linkages are also indicated.     

Production of Lactic Acid from Sucrose: Strain Selection, Fermentation, and Kinetic Modeling

Lactic acid is an important product arising from the anaerobic fermentation of sugars. It is used in the pharmaceutical, cosmetic, chemical, and food industries as well as for biodegradable polymer and green solvent production. In this work, several bacterial strains were isolated from industrial ethanol fermentation, and the most efficient strain for lactic acid production was selected. The fermentation was conducted in a batch system under anaerobic conditions for 50 h at a temperature of 34 °C, a pH value of 5.0, and an initial sucrose concentration of 12 g/L using diluted sugarcane molasses. Throughout the process, pulses of molasses were added in order to avoid the cell growth inhibition due to high sugar concentration as well as increased lactic acid concentrations. At the end of the fermentation, about 90% of sucrose was consumed to produce lactic acid and cells. A kinetic model has been developed to simulate the batch lactic acid fermentation results. The data obtained from the fermentation were used for determining the kinetic parameters of the model. The developed model for lactic acid production, growth cell, and sugar consumption simulates the experimental data well.