Photolysis of (Me2Si)6 in argon matrices doped with high concentrations (ca. 20%) of N2O or C2H4O: formation of (Me2SiO)6

Irradiation using a low pressure mercury lamp (λ=ca. 250 nm) of argon matrices containing ca. 1% (Me₂Si)₆ and ca. 20% ethylene oxide (C₂H₄O) or nitrous oxide (N₂O) for a period of ca. 20 h leads to the formation of the cyclic compound (Me₂SiO)₆. This has a 12-membered ring with alternating Si and O atoms. It is identified by comparison of its infrared spectrum with a spectrum of an authentic sample. The reaction appears to proceed by stepwise insertion of O atoms into Si---Si bonds.     

A short and stereospecific synthesis of (±)-α-lycorane

(±)-α-Lycorane (4) has been synthesized stereospecifically in five steps from commercially available 3,4-(methylenedioxy)phenylacetonitrile (7). The key step involves an intramolecular unstabilized iminium ylide-olefin [3+2] cyclo addition reaction 6 → 9.     

Capillary GC on 50 micrometer I.D. Columns coated with thick films. Theory and selected practical results

The chromatographic performance of 50 μm internal diameter (i.d.) fused silica columns coated with up to 2 μm films of immobilized SE-54 (methyl phenyl (5%) silicone) is evaluated under gas chromatographic conditions. The influence of pressure drop on the plate height is discussed. In comparison to thick film 250–530 μm i.d. columns, much higher efficiencies and faster analyses are obtained. Practical examples, performed on a standard GC instrument, illustrate the features of thick film 50 μm i.d. columns.     

Patient risk in anesthesia: Probabilistic risk analysis and management improvements

In this paper, we present a pilot study in which we use probabilistic risk analysis (PRA) to assess patient risk in anesthesia and its human factor component. We then identify and evaluate the benefits of several risk reduction policies. We focus on healthy patients, in modern hospitals, and on cases where the anesthetist is a trained medical doctor. When an accident occurs for such patients, it is often because an error was made by the anesthesiologist, either triggering the event that initiated the accident sequence, or failing to take timely corrective measures. We present first a dynamic PRA model of anesthesia accidents. Our data include published results of the Australian Incident Monitoring Study as well as expert opinions. We link the probabilities of the different types of accidents to the state of the anesthesiologist characterized both in terms of alertness and competence. We consider different management factors that affect the state of the anesthesiologist, we identify several risk reduction policies, and we compute the corresponding risk reduction benefits based on the PRA model. We conclude that periodic recertification of all anesthesiologists, the use of anesthesia simulators in training, and closer supervision of residents could reduce substantially the patient risk.     

Rapid method development for chiral separation in drug discovery using sample pooling and supercritical fluid chromatography-mass spectrometry

A novel strategy for rapid chiral method development has been implemented using sample pooling and supercritical fluid chromatography-mass spectrometry (SFC-MS) on four chiral stationary phases, namely Chiralpak AD and AS, and Chiralcel OJ and OD, and eight different modifier concentrations (5 to 40% methanol-0.2% isopropylamine). The screening is performed under an outlet pressure of 110 bar at 35 degrees C, and at a flow-rate of 2.5 ml/min for the initial 20 min and then ramped up to 4 ml/min and held for 4.5 min to elute all solutes from the column. The entire process is fully automated from injection to data processing, and operates unattended for 15 h overnight to obtain optimal chiral separation for multiple compounds. A unique feature of using SFC-MS to monitor chiral synthesis is the negligible interferences from achiral impurities. In addition, with SFC-MS, enantiomeric excess can be determined with much lower detection limits than UV and much shorter analysis times compared to normal-phase/reversed-phase liquid chromatography.     

On the capillary gas chromatographic separation of enantiomers of N-trifluoroacetyl-O-alkyl esters of selected amino acids on 2,3-di-O-pentyl-6-O-acyl cyclodextrins

In this work, the separation of enantiomers of N-TFA-O-alkyl amino acids on the 2,3-di-O-pentyl-6-O-acyl alpha-, beta- and gamma-cyclodextrin stationary phases has been studied. The influence of structure differences in the alkyl substituents bonded to the stereogenic carbon atom (R1), as well as in the ester group (R2) of the selected amino acid derivatives, and the selectivity of modified alpha-, beta- and gamma-cyclodextrin phases in gas chromatographic separation of derivatized amino acid enantiomers was studied in detail. A model set of N-TFA-alkyl esters of four amino acids was separated on five columns. The separation of enantiomers was evaluated in terms of the interactions of the alkyl substituents bonded to the stereogenic carbon (R1) and/or the ester group (R2) of the N-TFA-O-alkyl amino acid derivatives as well as the nature of the 3-O-acyl group in the 2,6-di-O-pentyl-3-O-acyl alpha-, beta- and gamma-cyclodextrins. It was shown that the variation in the enantiomeric separation with temperature and the retention order of enantiomers on a given cyclodextrin capillary column depends both on the nature of the bonded R1 and R2 alkyl groups. It was found that the temperature dependencies of selectivity factors, ln alpha on 1/T, were mostly non-linear. The thermodynamic data [delta(deltaS) and [delta(deltaH)] which characterize the chiral recognition were used to gain more insight into the mechanistic aspects of enantio separation of the N-TFA-O-alkyl amino acid derivatives on 2,6-di-O-pentyl-3-O-acyl-alpha-, beta- and gamma-cyclodextrins.