Dynamic Nuclear Polarization with a Rigid Biradical

A new polarizing agent with superior performance in dynamic nuclear polarization experiments is introduced, and utilizes two TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl) moieties connected through a rigid spiro tether (see structure). The observed NMR signal intensities were enhanced by a factor of 1.4 compared to those of TOTAPOL, a previously described TEMPO‐based biradical with a flexible tether.

     

Pre-concentration of phenolic compounds in water samples by novel liquid–liquid microextraction and determination by gas chromatography–mass spectrometry

Pre-concentration and determination of 8 phenolic compounds in water samples has been achieved by in situ derivatization and using a new liquid–liquid microextraction coupled GC–MS system. Microextraction efficiency factors have been investigated and optimized: 9 μL 1-undecanol microdrop exposed for 15 min floated on surface of a 10 mL water sample at 55 °C, stirred at 1200 rpm, low pH level and saturated salt conditions. Chromatographic problems associated with free phenols have been overcome by simultaneous in situ derivatization utilizing 40 μL of acetic anhydride and 0.5% (w/v) K₂CO₃. Under the selected conditions, pre-concentration factor of 235–1174, limit of detection of 0.005–0.68 μg/L (S/N = 3) and linearity range of 0.02–300 μg/L have been obtained. A reasonable repeatability (RSD ≤ 10.4%, n = 5) with satisfactory linearity (0.9995 ≥ r² ≥ 0.9975) of results illustrated a good performance of the present method. The relative recovery of different natural water samples was higher than 84%.     

Tame Supercuspidal Representations of GL(n) Distinguished by a Unitary Group

This paper analyzes the space Hom_H(, 1), where is an irreducible, tame supercuspidal representation of GL(n) over a p-adic field and H is a unitary group in n variables contained in GL(n). It is shown that this space of linear forms has dimension at most one. The representations which admit nonzero H-invariant linear forms are characterized in several ways, for example, as the irreducible, tame supercuspidal representations which are quadratic base change lifts.Research supported in part by NSA grant #MDA904-99-1-0065.Research supported in part by NSERC     

Molecular diversity of Artocarpus champeden (Moraceae): A species endemic to Indonesia

A summary of results obtained in the study of natural products isolated from a Moraceae species Artocarpus champeden is presented. The various classes of 3-prenylflavonoids isolated and the biogenetical correlation between the metabolites are discussed. Some of the flavonoids exhibited strong cytotoxicity against murine leukemia P388 cell lines, suggesting that flavonoids derived from moraceous plants represent a plausible unexplored resource of novel antitumor leads.     

Study of the mechanism of direct laser desorption/ionisation for some small organic molecules (M < 400 Daltons)

Aspects of direct laser desorption/ionisation have been studied for three molecules, aminotriazole (positive ion), dinoterb and ioxynil (negative ion). The samples are deposited on metallic substrates, and a nitrogen laser is used for desorption/ionisation; ion yields are measured with a time-of-flight mass spectrometer. Previous work had shown that ion yields can strongly vary from one substrate to another, and that this variation does not reflect the (calculated) metal surface temperatures. New results obtained in this work indicate that the desorption/ionisation mechanism is linked to the physical state of the substrate surface. Copyright 1999 John Wiley & Sons, Ltd.     

Spin trapping of superoxide in the presence of beta-cyclodextrins

The trapping of superoxide anion with DMPO and DEPMPO has been carried out in the presence of a methylated beta-cyclodextrin, Me-beta-CD; inclusion of the spin adducts in the cavity of Me-beta-CD resulted in a seven-fold increase of their half-life (t1/2 = 96 min for DEPMPO-superoxide spin adduct) and in their protection towards glutathione peroxidase (Gpx) and also ascrobate anion in the case of DEPMPO.     

Resolution of crystalline ribonuclease by paper electrophoresis

1. Crystalline ribonuclease samples obtained from different commercial sources in addition to one prepared in the laboratory were resolved into their components, RNases I, II, III and IV, by a new two-dimensional electrophoretic technique 2. RNase I and RNase II liberated more uridyhc acid and cytidylic acid from yeast nbonucleic acid, and demonstrated a greater enzymic activity on undine-2', 3'-phosphate and cytidine-2',3'-phosphate, than either RNase III or RNase IV RNase III and RNaso IV liberated more adenylic acid and guanylic acid from yeast ribonucleic acid, and showed a greater enzymic activity on adenosine-2',3'-phosphate and guanosine-2', 3 '-phosphate than cither RNase I and RNase II 3. The degree of heterogeneity of the RNase samples studied revealed the age of the preparation 4. It is thus demonstrated, that certain of the activities of “crystalline nbonucleasc” reside in four different protein entities, and some activity toward punne nucleotidc esters existed in two of the four protein entities