Tandem ligation of multipartite peptides with cell-permeable activity

To prepare multipartite peptides with several functional cargoes including a cell-permeable sequence or transportant for intracellular delivery, tandem ligation of peptides is a convenient convergent approach with the fewest synthetic steps. It links three or four unprotected segments forming two or more regiospecific bonds consecutively without a deprotection step. This paper describes a tandem ligation strategy to prepare multipartite peptides with normal and branched architectures carrying a novel transportant peptide that is rich in arginine and proline to permit their cargoes to be translocated across membranes to affect their biological functions in cytoplasm. Our strategy consists of three ligation methods specific for amino terminal cysteine (Cys), serine/threonine (Ser/Thr), and N(alpha)-chloroacetylated amine to afford Xaa-Cys, Xaa-OPro (oxaproline) and Xaa-psiGly (pseudoglycine) at the ligation sites, respectively. Assembly of single-chain peptides from three different segments was achieved by the tandem Cys/OPro ligation to form two amide bonds, an Xaa-Cys and then an Xaa-OPro. Assembly of two- and three-chain peptides with branched architectures from four different segments was accomplished by tandem Cys/psiGly/OPro ligation. These NT-specific tandem ligation strategies were successful in generating cell-permeable multipartite peptides with one-, two-, and three-chain architectures, ranging in size from 52 to 75 residues and without the need of a protection or deprotection step. In addition, our results show that there is considerable flexibility in architectural design to obtain cell-permeable multipartite peptides containing a transportant sequence.     

Light emitting diode-based detectors Absorbance, fluorescence and spectroelectrochemical measurements in a planar flow-through cell

Light emitting diodes (LEDs) were first used for chemical analysis three decades ago. They are finally making their appearance in commercial analytical systems and dedicated detectors. LEDs are the most energy-efficient means of producing monochromatic light, and provide a concentrated small cool emitter ideal for miniature analytical devices. Although they rank behind fluorescent and halogen discharge lamps in total conversion efficiency (lm/W), new efficiency records are being set every year such that by next decade broadband (white) LED sources are not only likely in analytical instrumentation, but for general illumination. This paper begins with a review of analytical use of LEDs that has been advanced in the last decade. LED-based absorbance measurement and its use in pedagogy, titrations, in providing immunity to refractive index and turbidity effects, in field and process analysis, in capillary electrophoresis (CE), in liquid–liquid extraction systems, in film and drop-based analytical systems and with liquid core waveguides (LCWs) are discussed. LED-based fluorescence and spectroelectrochemical detection follows next. Multipurpose LED-based analytical instrumentation and special analytical applications and general applications are discussed. A listing of (mostly web-based) resources for fabricating LED-based detectors is then provided. Detector circuits and available components are considered and different modes of driving LEDs are compared. The temperature dependence of LED characteristics and strategies to ameliorate this problem are discussed.

The review and general resource material is followed with the construction details, operation and performance observed for a simple-to-fabricate multipurpose cell that allows simultaneous multiwavelength absorbance, fluorescence and spectroelectrochemical detection.     

Modulation of light absorption by optical spacer in perovskite solar cells

Lead halide perovskite solar cells with planar heterojunction configuration have recently attracted tremendous attention because of their excellent power conversion efficiencies. The modulation of optical absorption by using an optical spacer layer is a unique method to enhance the device efficiency. Here, we demonstrate the application of thin ZnO layer that act as an optical spacer that enhance the power conversion efficiency perovskite devices from 8.92% to 10.7%, which is mainly due to increment in short‐circuit current density by 16% compared to the reference solar cell. The simulation data revealed that ZnO acts as an optical spacer layer that shifts length (average) of electric field |E|² distribution from 500 nm to 750 nm wavelength is 25 nm in the perovskite layer. Which represents that exciton generation region is moved to near the hole transport layer that enhances the exciton dissociation efficiency and device efficiency.     

Impregnation of tungstophosphoric acid on poly(methacrylamide-co-methyl methacrylate) and its acid catalytic activity in TMB alkylation

A poly(methacrylamide-co-methylmethacrylate) (abbreviated PMAA-MMA) polymer support was studied for supporting a heteropolyacid (tungstophosphoric acid, H₃PW₁₂O₄₀) with its surface positively charged in the polymerization step. PMAA-MMA supports could be obtained in a porous form by eliminating template reagent molecules (benzylmalonic acid) combined with properly selected monomer (methacrylamide). The amount of amine groups in PMAA-MMA directly determined the amount of H₃PW₁₂O₄₀ impregnated, because the amine groups induced a positive charge on the PMAA-MMA surface. Finally, H₃PW₁₂O₄₀/PMAA-MMA showed better acid catalytic activities than unsupported H₃PW₁₂O₄₀ in alkylation of 1,3,5-trimethylbenzene with cyclohexene, which confirmed that PMAA-MMA supported H₃PW₁₂O₄₀ effectively.     

Influence of Fe2O3 Doping on TiO2 Electrode for Enhancement Photovoltaic Efficiency of Dye-Sensitized Solar Cells

In this work, we report for the first time the improvement of the photovoltaic characteristics of dye-sensitized solar cells (DSSCs) by doping TiO₂ with Fe₂O₃. DSSCs were fabricated using various percentages of Fe₂O₃-doped TiO₂ composite nanoparticles. The Fe₂O₃-doped DSSCs exhibited a maximum conversion efficiency of 5.76% because of the effective electron transport. DSSCs based on Fe₂O₃-doped TiO₂ films showed better photovoltaic performance than cells fabricated with only TiO₂ nanoparticles. This result was attributed to the prevention of recombination between electrons in the TiO₂ conduction band with the dye or electrolytes. A mechanism was suggested based on impedance results, which indicated improved electron transport at the interface of the TiO₂/dye/electrolyte.     

Comparison between evaporative light scattering detection and charged aerosol detection for the analysis of saikosaponins

Saikosaponins are triterpene saponins derived from the roots of Bupleurum falcatum L. (Umbelliferae), which has been traditionally used to treat fever, inflammation, liver diseases, and nephritis. It is difficult to analyze saikosaponins using HPLC-UV due to the lack of chromophores. Therefore, evaporative light scattering detection (ELSD) is used as a valuable alternative to UV detection. More recently, a charged aerosol detection (CAD) method has been developed to improve the sensitivity and reproducibility of ELSD. In this study, we compared CAD and ELSD methods in the simultaneous analysis of 10 saikosaponins, including saikosaponins-A, -B₁, -B₂, -B₃, -B₄, -C, -D, -G, -H and -I. A mixture of the 10 saikosaponins was injected into the Ascentis^® Express C18 column (100 mm × 4.6 mm, 2.7 μm) with gradient elution and detection with CAD and ELSD by splitting. We examined various factors that could affect the sensitivity of the detectors including various concentrations of additives, pH and flow rate of the mobile phase, purity of nitrogen gas and the CAD range. The sensitivity was determined based on the signal-to-noise ratio. The best sensitivity for CAD was achieved with 0.1 mM ammonium acetate at pH 4.0 in the mobile phase with a flow rate of 1.0 mL/min, and the CAD range at 100 pA, whereas that for ELSD was achieved with 0.01% acetic acid in the mobile phase with a flow rate at 0.8 mL/min. The purity of the nitrogen gas had only minor effects on the sensitivities of both detectors. Finally, the sensitivity for CAD was two to six times better than that of ELSD. Taken together, these results suggest that CAD provides a more sensitive analysis of the 10 saikosaponins than does ELSD.