Regioselective hydroxylation of 2-hydroxychalcones by dimethyldioxirane towards polymethoxylated flavonoids

The flavone nucleus is part of a large number of natural products and medicinal compounds. In this presentation the novel regioselective hydroxylation of hydroxyarenes with DMD is described. The results showed further that flavonoids with 5-hydroxy group were selectively oxyfunctionalized at the para-position C8 carbon atom by DMD. Finally, according to this methodology, the naturally occurring isosinensetin, tangeretin, sinensetin, nobiletin, natsudaidain, gardenin B, 3,3′,4′,5,6,7,8-heptamethoxyflavone, quercetin and its derivatives were synthesized.     

Computational study of the hydrolysis of degradable polysaccharide biomaterials: Substituent effects on the hydrolytic mechanism

Hyaluronic acid and its derivatives are absorbable polysaccharides which are used extensively in cosmetics and as biomaterials. Two possible mechanisms of degradation, involving an oxocarbenium ion and the corresponding radical cation, are examined by modeling of the saccharide ring and the effects of various ring substituents on the two possible mechanisms. © 1994 by John Wiley & Sons, Inc.     

Determination of multiclass pesticide residues in apple juice by gas chromatography-mass selective detection after extraction by matrix solid-phase dispersion

A multiresidue method is described for the analysis of 106 multiclass pesticides (organochlorine, organophosphate, carbamate, pyrethroid, and triazine classes) in apple juice in a single injection. The determination procedure was based on matrix solid-phase dispersion of juice on diatomaceous earth in a glass column and subsequent extraction with a mixture of hexane-dichloromethane (1 + 1) at a flow rate of 5 mL/min. The analytes were determined by capillary gas chromatography with mass spectrometric detection and confirmed by their retention times and ion ratios. The coefficients of variation for analysis of samples fortified over the range of 0.01-0.2 mg/kg were 1.62 to 18.4%, and the recoveries for all analytes were between 70 and 110%.     

Use of 1H/23Na and 1H/31P double frequency tuned birdcage coils to study in vivo carbon tetrachloride-induced hepatotoxicity in rats.

In vivo 1H and 23Na magnetic resonance imaging (MRI) and 31P magnetic resonance spectroscopy (MRS) techniques were used to study CCl4-induced acute hepatotoxicity in rats in situ. One or two hours following exposure to CCl4, a localized edematous region was detected in the liver by 1H MRI. The CCl4-induced edema was localized in a region surrounding the hepatic portal vein. With the use of a 23Na/1H double frequency tuned bird-cage imaging coil an increase in Na+ ion flux was also observed in the same region as the edematous region detected by 1H-MRI. Pretreatment with alpha-phenyl-tert-butyl nitrone (PBN), a free radical spin trap, 30 min prior to CCl4 exposure, was found to reduce the CCl4-induced edematous response in the liver observed in either 1H or 23Na-NMR images. Inhibition of the CCl4-induced edematous response in rat liver by PBN demonstrates that free radical intermediates, arising from the metabolism of CCl4, are possibly the key causal agents in the initiation of the edematous response. In addition, with the use of a 31P/1H double frequency tuned bird-cage imaging/spectroscopy coil, localized 31P spectra (ISIS) were obtained from the regions of CCl4-induced "tissue damage" observed in the 1H-MRI images. The most notable changes observed from the 31P spectra were an increase in inorganic phosphate (Pi) and a decrease in hepatocytosolic pH in the CCl4-treated rat livers in comparison to saline-treated control livers.     

Copper-mediated nucleophilic radiobromination of aryl boron precursors: Convenient preparation of a radiobrominated PARP-1 inhibitor

The copper-mediated nucleophilic radiobromination of aryl boron precursors with a radiobromide ion is a novel radiolabeling method that is efficient and robust. High radiochemical conversion (RCC) was observed using a variety of solvents, temperatures and catalysts. The reaction is also clean and is feasible for purification to obtain high chemical and radiochemical purity. This method provides a very useful route for the preparation of radiobrominated pharmaceuticals, including a radiobromine labeled PARP-1 inhibitor, and it is a valuable addition to the family of copper-mediated radiolabeling processes.     

Low voltage and high transmittance transflective blue-phase liquid crystal display with opposite polar electrodes

A single-cell-gap transflective polymer-stabilised blue-phase liquid crystal display with opposite polar pixel electrodes on an etched substrate is proposed. In the proposed structure, the space between common electrodes is adopted as transmissive region, and the space above the common electrode is adopted as reflective region. By optimising the electrode parameters of the transmissive and reflective regions, well-matched voltage-dependent transmittance and reflectance curves can be obtained. In addition, the device has good performances of low operating voltage (~3.2 V), high optical efficiency and a wide viewing angle.     

Synthesis of furo[3,2-c]coumarins via I2/TBHP-mediated reaction of 4-hydroxycoumarins with terminal alkynes

An efficient I₂/TBHP-mediated process for the formation of furo[3,2-c]coumarins from readily available materials has been developed. This process for the formation of furo[3,2-c]coumarins is quite environmental friendly and atom-economical.