Preparation and structural characterisation of methoxybis(trimethylsilyl)silyl potassium and its condensation product

Depending on the conditions the reaction of tris(trimethylsilyl)methoxysilane (1) with potassium tert-butoxide either in benzene and in the presence of 18-crown-6 or in THF gives either the crown ether adduct of potassium-methoxybis(trimethylsilyl)silane (2), or 2-methoxytetrakis(trimethylsilyl)disilanyl potassium (3).     

Determination of Band Structure Parameters and the Quasi‐Particle Gap of CdSe Quantum Dots by Cyclic Voltammetry

Band structure parameters such as the conduction band edge, the valence band edge and the quasi‐particle gap of diffusing CdSe quantum dots (Q‐dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q‐dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi‐empirical pseudopotential method (SEPM)—especially in the strong size‐confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q‐dots, the difference between the quasi‐particle gap and the optical band gap gives the electron–hole Coulombic interaction energy (J_e1,h1). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.     

m-Chloroperbenzoic acid-oxchromium (VI)-mediated cleavage of 2,4,5-trisubstituted oxazoles

An array of 2-substituted-4,5-diphenyloxazoles were found to be cleaved to triacylamines and diacylamines (imides) using a reagent system composed of m-chloroperbenzoic acid (MCPBA) and 2,2′-bipyridinium chlorochromate (BPCC). The 2-alkyl-4,5-diphenyloxazoles give imides (38–60%) as the predominant cleavage product while the 2-aryl-4,5-diphenyloxazoles give triacylamines (44–71%). Two mechanisms involving intermediates such as cyclic endoperoxides or oxachromacycles were proposed. An application of the oxidative cleavage to the multi-step synthesis of (±)-phoracantholide I seco acid is detailed.     

Boric acid catalyzed convenient synthesis of 2-amino-3,5-dicarbonitrile-6-thio-pyridines in aqueous media

A one-pot three-component condensation of an aldehyde, malononitrile, and thiophenol has been achieved by conventional and ultrasound method. The reaction has been catalyzed by boric acid in aqueous medium. This protocol afforded corresponding 2-amino-3,5-dicarbonitrile-6-thio-pyridines in shorter reaction times and high yields with the green aspects by avoiding toxic catalysts and solvents.     

Chip-based high-throughput screening of herbal medicines

At present, high-throughput screening (HTS) programs in drug discovery rely mainly on compound libraries from combinational chemistry. Similarly, natural flora has been used as a prominent origin for new and potent herbal drugs. Herbal medicines have been used worldwide for thousands of years to cure many diseases. As such, herbal secondary metabolites show a remarkable structural diversity that supplements chemically synthesized compound analogs in drug discovery screening. Unfortunately, there is often a considerable deterioration in the quality of herbal drugs in such screening programs as there are time-consuming manual processes involved in the isolation of active ingredients from the highly complex mixtures of herbal plant products. The quality and quantity of herbal samples are critical for the success of HTS programs. In the recent past, there have been substantial improvements in HTS due to the miniaturization and integration of microchip (e.g., Herbochip(?), DNA chip, protein chip, cell chip, etc.)-based technologies so as to design herbal drugs that compete with synthetic drug analogs. Here we will review various technologies used for HTS of herbal medicines. Finally, we will summarize our efforts to develop a novel chip-based HTS assay to explore the antioxidant and radioprotective properties of herbal plants.     

Synthesis and Antimicrobial Activities of Novel Series of 3‐(4‐(2‐substituted thiazol‐4‐yl)phenyl)‐2‐(4‐methyl‐2‐substituted thiazol‐5‐yl)thiazolidin‐4‐one Derivatives

In the present investigation, a novel series of 3‐(4‐(2‐substituted thiazol‐4‐yl)phenyl)‐2‐(4‐methyl‐2‐substituted thiazol‐5‐yl)thiazolidin‐4‐one derivatives were synthesized by condensation of 2‐substituted‐4‐methylthiazole‐5‐carbaldehyde with 4‐(2‐substituted thiazol‐4‐yl)benzenamine followed by cyclo‐condensation with thioglycolic acid in toluene. All the newly synthesized compounds were characterized by spectral (IR, ¹H NMR, ¹³C NMR, and Mass) methods. The title compounds were screened for quantitative antibacterial activity (minimal inhibitory concentration). All compounds 7a , 7b , 7c , 7d , 7e , 7f , 7g , 7h and 8a , 8b , 8c , 8d , 8e , 8f , 8g , 8h show moderate to good antimicrobial activity, whereas compounds ( 7a , 7b , 7c , 7d , 7e , 7f , 7g , 7h ) also show moderate antifungal activity.     

Synthetic approaches to imino sugar (2R,3R,4S)-2-(hydroxymethyl)-4-methylpyrrolidine-3,4-diol from naturally occurring sugar and amino acid

Imino sugar compound 3 was prepared by two alternative routes starting from ribose and d-serine. From d-serine (3R,4R,5R)-3,4-dihydroxy-5-(hydroxymethyl)-3-methylpyrrolidin-2-one was prepared in five steps in 50% overall yield, which was further converted into (2R,3R,4S)-2-(hydroxymethyl)-4-methylpyrrolidine-3,4-diol in three steps in 23% overall yield.     

Converting poorly soluble materials into stable aqueous nanocolloids

Aqueous nanocolloids of poorly soluble materials were produced via sonicated layer-by-layer (LbL) encapsulation with polycation / polyanion shells. Synergy of simultaneous breaking powder particles with ultrasonication and coating them with polycations allowed for the production of 150-200 nm diameter polyelectrolyte coated nanoparticles with sufficient surface electrical potential for colloidal stability. This technique increases water dispersibility of low soluble materials ranging from anticancer drugs to anticorrosion agents, dyes and inorganic salts.     

An organocatalyzed facile and rapid access to α-hydroxy and α-amino phosphonates under conventional/ultrasound technique

In the present work, successful implementation of ultrasound irradiation for the rapid synthesis of α-hydroxy and α-amino phosphonates under solvent-free conditions is demonstrated. Use of a novel catalyst (i.e., camphor sulfonic acid) in combination with ultrasound technique is reported for the first time. Comparative study for the synthesis of α-hydroxy and α-amino phosphonates using conventional as well as ultrasonication method is discussed.     

Thermal and electronic charge transport in bulk nanostructured Zr0.25Hf0.75NiSn composites with full-Heusler inclusions

Bulk Zr_0.25Hf₀₇₅NiSn half-Heusler (HH) nanocomposites containing various mole fractions of full-Heusler (FH) inclusions were prepared by solid state reaction of pre-synthesized HH alloy with elemental Ni at 1073 K. The microstructures of spark plasma sintered specimens of the HH/FH nanocomposites were investigated using transmission electron microscopy and their thermoelectric properties were measured from 300 K to 775 K. The formation of coherent FH inclusions into the HH matrix arises from solid-state Ni diffusion into vacant sites of the HH structure. HH(1–y)/FH(y) composites with mole fraction of FH inclusions below the percolation threshold, y∼0.2, show increased electrical conductivity, reduced Seebeck coefficient and increased total thermal conductivity arising from gradual increase in the carrier concentration for composites. A drastic reduction (∼55%) in κ_l was observed for the composite with y=0.6 and is attributed to enhanced phonon scattering due to mass fluctuations between FH and HH, and high density of HH/FH interfaces.