Reactions of some new thienothiophene derivatives

Facile and convenient syntheses of bisdimethylthieno[2,3-b]thiophen-2,5-diyl bis(oxazole-2-amine), bis(1H-imidazol-2-amine), bis((3a)-H-indole),[1,2-a]pyrimidine), bis(1H-imidazo[1,2-b][1,2,4]triazole) and bis(9H-benzo[d]imidazo[1,2-a]imidazole) derivatives incorporating a thieno[2,3-b]thiophene moiety from the versatile and readily accessible 1,1'(3,4-dimethylthieno[2,3-b]thiophene-2,5-diyl)-bis(2-bromo-ethanone) (1) are described.     

Fast screening for presence of muddy/earthy odorants in wine and in wine must using a hyphenated gas chromatography-differential ion mobility spectrometry (GC/DMS)

Rapid, hyphenated detection techniques involving a gas chromatograph (GC) coupled to a classical time-of-flight ion mobility (IMS) spectrometer, or more recently, to a micro-machined, miniature differential ion mobility spectrometer (DMS) are quite attractive for in-situ detection of many kinds of volatile organic compounds (VOCs) of concern and notably of natural contaminants appearing in the headspaces of selected foodstuff. This work aims at a rapid detection, identification and quantification of geosmin in the headspace of grape must and of wine. Samples of white and red wines have both been analyzed with a hyphenated GC/DMS and by Solid Phase Micro-Extraction (SPME) coupled to GC/MS taken as a reference. The detection of geosmin at concentrations below the human olfactory threshold of 50 ng/L has been demonstrated.     

Analytical evaluation of three wild growing Omani medicinal plants

Three wild Omani plants, Moringa peregrina, Acacia nilotica and Rhazya stricta, were selected for the present study. Na, K and Ca contents were determined using flame photometric analysis. M. peregrina seeds (22.5 mg/g) and pods (27.7 mg/g) had higher Na contents than A. nilotica (0.33 mg/g) and R. stricta (0.30 mg/g), whereas the K and Ca contents of R. stricta were significantly higher than those of the other two plants. The protein content was lowest in R. stricta (9.8%) and highest in M peregrina seeds (21.0%). The highest total phenolic contents (TPC) were found in M. peregrina seeds (350.3 mg/g) and the lowest in A. nilotica (66.1 mg/g). The major component of M. peregrina seed oil was oleic acid (74.7%). Gas chromatographic-mass spectrometric analysis (GC-MS) revealed that octadecanal (30.9%) was the major compound in A. nilotica. The presence of various phenolics and flavonoids in M. peregrina, A. nilotica and R. stricta were confirmed by high performance liquid chromatography (HPLC).     

Preparation of a deoxynucleoside thiophosphoramidite intermediate in the synthesis of nucleoside phosphorodithioates

A general synthetic scheme for preparation of thiophosphoramidite intermediates, chloro-N,N-diisopropylaminothiomethoxyphosphine, 2, and 3′-O-deoxythymidine derivatives of N,N-diisopropylaminothiomethoxyphosphine, 4, is described. These intermediates can be used to synthesize dithiophosphate deoxyoligonucleotide analogues.     

Conformation of acetate derivatives of sugars and other cyclic alcohols. Crystal structures, NMR studies, and molecular mechanics calculations of acetates. When is the exocyclic C-O bond eclipsed?

[reaction: see text] A study of published crystal structures (of O-acetylated sugars for the most part) suggests that the exocyclic C-O bond in acetate esters of cyclic alcohols intrinsically prefers a staggered conformation, although the eclipsed conformation is only slightly less stable. When the acetate is flanked by two equatorial substituents the preferred conformation is close to eclipsed. Over 1500 C-OAc bonds have been analyzed. Diagnostic NMR criteria for torsion angles and MM3 calculations are reported and confirm these conclusions.     

Dicyclopentadienylnickel-alkyne complexes: photochemical formation and mass spectra

Irradiation of toluence or n-hexanne solutions of dicyclopentadienyldicarbonyldinickel complexes at λ ? 350 nm gives good yields of bridged dinuclear complexes (RCCR′)(CpNi)₂. Their bonding and mass spectra are discussed.     

A redetermination of the lifetime of the 4s 5s (3S1) level in Ca by high-rate electron—photon stepwise pulse excitation

The radiative lifetime of the 4s 5s (³S₁) level in Ca was measured using two-step excitation of atoms in a beam which traverses a cold-cathode Penning discharge, where, by electron impact the atoms are excited to the metastable 4s 5p (³P_{2, 1, 0}) states. Immediately thereafter, the beam is crossed with a pulse-modulated cw dye laser beam to populate the final state selectively. Using a pulse-modulation frequency of 0.5 MHz, a preliminary value of 12.4 ± 0.5 ns was obtained with a statistical error of 0.4%. The wide limits of systematic error reflect an assumed uncertainty in the excitation function and possible distortion in the fluorescence decay requiring further study.