Gas chromatographic determination of volatile anaesthetic agents in blood. Part 1. Preparation of standard gas mixtures of volatile anaesthetic agents

A method for preparing standard gas mixtures of the volatile anaesthetics halothane, enflurane and isoflurane is described. Static mixtures of gases of known concentration can be prepared manometrically by measuring the required pressure of anaesthetic gas into a bulb and diluting to atmospheric pressure with air. Standard gas mixtures in the concentration range 0-4% V/V can be prepared with an accuracy of +/- 0.01% V/V, and the relative standard error of measurements of a single standard concentration is less than 0.8%. Significant adsorptive losses in the gas sampling valve were observed for gas standards prepared in the absence of any diluent gas. These losses were not detected for measurements of standards made up to atmospheric pressure in air. A comparison with calibration procedures currently in practice is presented.     

Conversion from a π to a σ structure on replacing oxygen by sulphur: an ESR study

The radical cations of 1,3-dioxacylohexane and 1,3-dioxacyclopentane have π-structures involving delocalisation within the [-OCH₂O-]⁺ unit with high spin-density on the CH₂ group, whilst, in complete contrast, the corresponding sulphur derivatives have a weak σ bond between the two sulphur atoms, the unpaired electron being in the σ^* orbital with negligible spin-density on the CH₂ group.     

Gas chromatographic determination of volatile anaesthetic agents in blood. Part 2. Clinical studies

A method is described for the direct determination of the volatile anaesthetics halothane and isoflurane in blood by gas chromatography with flame-ionisation detection. The method is accurate and precise and allows rapid measurements of blood levels of anaesthetic agents. Headspace concentrations of anaesthetic agents in the concentration range 0-3% V/V are determined with an accuracy of +/- 0.01% V/V. The relative standard deviation of these results is less than 4.0%. A relatively small volume of blood is required for each determination, a factor of great significance in the treatment of children. The need for separate blood calibration graphs for each patient is discussed, further emphasising the need for a rapid calibration procedure. The results from the clinical application of this method show conclusively its suitability for the management of anaesthetised subjects.     

Iron oxyhydroxide nanoparticles formed by forced hydrolysis: dependence of phase composition on solution concentration

Nanoparticles of single-phase lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) have been synthesized by forced hydrolysis of ferric nitrate with no other additives, and the particles have been characterized by XRD, FT-IR and TEM. At low Fe(NO(3))(3) concentrations the hydrolysis product is predominantly γ-FeOOH, while at high concentrations it is α-FeOOH. These particles are nanometers in size and fall within narrow particle size distributions. The dependence of the oxyhydoxide phase on ferric nitrate concentration is attributed to two thermodynamic factors, the enthalpy of formation and the surface enthalpy of hydration at the oxide-water interface (which is a function of surface area). Two potential mechanisms for the phase-specific growth are proposed that explain the solution concentration dependence of the phase formed. Three other common nanoscale particles (α-Fe(2)O(3), Fe(3)O(4) and γ-Fe(2)O(3)) have also been prepared by relatively simple thermal/chemical treatment of the γ-FeOOH nanoparticles.     

Effect of gamma irradiation on gas-ionic liquid and water-ionic liquid interfacial stability

The effect of γ-radiation on gas-ionic liquid (IL) and water-IL interfacial stability was investigated. Three phosphonium-based ILs, which vary considerably in their viscosity, conductivity and miscibility with water, were examined. The gas phase above the IL samples (headspace gas) was analyzed using gas chromatography with a mass spectrometer detector while the changes in the IL and aqueous phases were followed by conductivity measurements and Raman spectroscopy. For the gas-IL systems, the headspace samples showed trace amounts of the radiolytic decomposition products of the ILs that were small and volatile enough to become airborne. The type of cover gas, air or Ar, had no effect on the gas speciation. Negligible changes in the conductivity and the Raman spectra of the IL phase due to irradiation indicate that γ-irradiation induces negligible chemical changes in the IL phase when it is in contact with a gas phase. For the water-IL systems, the initially immiscible layers slowly developed an interfacial emulsion layer, even in the absence of radiation. This layer started at the water-IL interface and then grew downwards, eventually converting the entire IL phase to an emulsion. Gamma-irradiation accelerated the conversion of the IL phase to an emulsion. The development of the emulsion layer was accompanied by changes in the conductivity and the Raman spectra of both the IL and water phases. Based on these results, a mechanism involving the formation of micelles at, or near, the water-IL interface has been proposed to explain the development of an emulsion layer. We also suggest that radiolytic decomposition of ILs produces surfactants that can accumulate at the interface and, even at low concentrations, accelerate the emulsification process.     

From highly enantioselective catalytic reaction of 1,3-diynes with aldehydes to facile asymmetric synthesis of polycyclic compounds

(S)-1,1'-Binaphth-2-ol (BINOL) in combination with ZnEt(2), Ti(O(i)Pr)(4), and biscyclohexylamine was found to catalyze the highly enantioselective (83-95% ee) addition of various 1,3-diynes to aldehydes of diverse structures. This method provides a convenient pathway to generate a number of optically active dienediynes as the acyclic precursors to polycyclic compounds. The chiral dienediynes undergo highly chemoselective Pauson-Khand (PK) cycloaddition in benzaldehyde by using [Rh(cod)Cl](2) as the catalyst in the presence of rac-BINAP. High diastereoselectivity (up to >20:1) has also been achieved with the chiral dienediyne substrates containing a bulky substituent adjacent to the chiral center. In the presence of the Grubbs II catalyst, ring-closing enyne metathesis of the PK cycloaddition products led to the formation of the desired 5,5,7- and 5,5,8-fused tricyclic compounds. Further highly diastereoselective Diels-Alder reaction of a 5,5,7-tricyclic compound with maleic anhydride produced a 5,5,7,6-polycyclic product. The asymmetric synthesis of polycyclic compounds from optically active dienediynes has established a novel and efficient synthetic route to the structural framework of many biologically significant molecules.