High-pressure phase studies on fluid mixtures of low-volatile organic substances with supercritical carbon dioxide

Two high-pressure phase equilibrium cells working according to the analytical method in the temperature range 300 to 450 K and up to 200 MPa have been developed. In the first cell p,T,x,y equilibrium data can be determined by sampling and GC analysis. With this cell the gas-liquid phase behaviour of the ternary systems carbon dioxide + tridecane + hexadecane and carbon dioxide + tridecane + 1-hexadecanol were determined at 423.4 K and between 8 and 35 MPa. For the second apparatus a spectroscopic high-pressure cell fitted with two pairs of sapphire windows was developed. Molar absorptivities are obtained from calibration runs in the homogeneous region. Gasliquid phase equilibria in the system decane + CO₂ were investigated from 342.8 to 400.2 K and between 10 and 20 MPa; here absorption data were measured in the NIR region.     

Pseudohalogenometallverbindungen: LVIII. Reaktionen von diphenylphosphorylazid und perfluor-n-hexylsulfonylazid mit triphenylphosphan-komplexen von platin(0), rhodium(I), iridium(I), ruthenium(0), kobalt(II) und kupfer(I)

Diphenylphosphorylazide N₃P(O)(OPh)₂ reacts with Pt(PPh₃)₃, Pt(PPh₃)₂(C₂H₄), trans-RhCl(CO)(PPh₃)₂, Ru(CO)₃(PPh₃)₂, CoCl₂(PPh₃)₂ and CuCl(PPh₃)₂ to give the azido complexes Pt(PPh₃)₂(N₃)R, Pt(PPh₃)₂(N₃)₂R₂, the urylene complex RhCl(PPh₃)₂(RNCONR) and the phosphine imine complexes Ru(CO)₃(RPPh₃)₂, CoCl₂(RNPPh₃)₂, CuCl(RNPPh₃)₂, respectively, (RP(O)(OPh)₂). The oxidative addition of n-C₆F₁₃SO₂N₃ to Pt(PPh₃)₄ and Pt(PPh₃)₂(C₂H₄) affords the complexes Pt(PPh₃)₂(N₃)R and Pt(PPh₃)₂(N₃)₂R₂, respectively, (RSO₂C₆F₁₃. The compounds are characterized by elemental analysis and by their IR spectra.     

A single-fluor approach to DNA sequence determination using high performance capillary electrophoresis.

The Tabor and Richardson strategy for enzymatic chain termination sequencing of DNA using relative peak intensity has been adapted to high performance capillary gel electrophoresis with laser induced fluorescence detection. This approach to DNA sequencing involves the use of only a single fluor and results in significant reduction in the time required to determine a DNA sequence without the use of highly complicated and expensive instrumentation. We present a modification of the Tabor and Richardson approach employing two reactions, each containing complementary mixtures of only three ddNTP's in the concentration ratio 4:2:1. The DNA sequence is determined by relative peak height and by assigning the missing ddNTP to "gaps" between the peaks. The use of only three terminators/reaction simplifies the software task of differentiating between the termination types and makes more efficient use of the available dynamic range. Both complementary mixes generate complete sequence information and the two data files are combined in order to make a more confident sequence call. This process helps to eliminate errors caused by occasional non-uniform incorporation of ddNTP's or false terminations and also alleviates some of the difficulty associated with reading through compressed regions of the electropherogram.     

Sample evaporation in conventional GC split/splitless injectors. Part 1: Some quantitative estimates concerning heat consumption during evaporation

During sample evaporation in conventional vaporizing injection, the supply of heat to the evaporating liquid is a problem, first because the amounts of heat consumed are relatively large and, secondly, because the heat must be transferred to the sample within a very short time. Times available for evaporation, required amounts of heat, possible sources of heat, and the time required to transfer the heat to the sample liquid are discussed. It is shown that mixing with carrier gas contributes little heat to the evaporation process, but also that packings with glass wool have too low a heat capacity to deliver the required amount of heat to the evaporating sample. Transfer of heat from the insert wall to the sample easily requires several seconds, even if cooling of the vaporizing zone by 20° is accepted. Thus “flash evaporation” is usually impossible and most liquids must be held in the vaporizing chamber to allow full evaporation.     

Sample evaporation in conventional split/splitless GC injectors. Part 3: Retaining the liquid in the vaporizing chamber

As most sample liquids tend to pass through an empty injector insert at a speed which is too high to enable complete evaporation, movement of the liquid must be arrested before it reaches the column entrance. Stopping the liquid means deposition on to a surface; this, however, is possible only after the temperature of the surface has been cooled to (or below) the boiling point of the liquid (solvent). The performance of different means of stopping the liquid has been tested visually (by the method described in Part 2). Baffles on the wall of the injector insert had hardly any effect on evaporation: the band of liquid leaving the syringe needle performed a perfect slalorn around them. The inverted cup proved more efficient, but the best performance was obtained from a light plug of glass wool: owing to its low thermal mass, the first fibers to be met by the liquid are immediately cooled to the solvent boiling point, allowing the liquid to wet it. The sample liquid is sucked up by the glass wool, from where the sample evaporates relatively slowly, often over a period of several seconds.     

N,N-Bis(halomethyldimethylsilyl)acetamides and their reactions

N,N-Bis(halomethyldimethydimethylsilyl)acetamides, MeCON(SiMe₂CH₂X)₂, (X = Cl, Br) were prepared by transsilylation of N,O-bis(trimethylsilyl)acetamide with halomethyldimethylchlorosilane. With water and methanol, instead of the expected SiN cleavage, nucleophilic substitution of halogen took place and the products were 1-acetyl-2,2,6,6-tetramethyldisilamorpholine and N,N-bismethoxymethyldimethylsilyl)acetamide respectively. These compounds were shown by IR and ¹H NMR spectra to have the N,N-disilylacetamide structure. Thermodynamic, kinetic constants of hindered rotation around the CN bond in these compounds were determined from their temperature-variable ¹H NMR spectra. The main products of thermolysis of the silylamides are α,ω-dichloropolydimethylsiloxanes and polydimethylcyclosiloxanes.     

OXYGEN QUENCHING OF CHLOROPHYLL FLUORESCENCE IN CHLOROPLASTS

Abstract— Three phases of chlorophyll a fluorescence quenching by O₂ are observed in green plants. The effects of various inhibitors on photosynthetic partial processes in chloroplasts were investigated in attempts to (1) localize the O₂-quenching sites and (2) assess possible physiological significance of O₂-quenching. Our results localize the most sensitive (and presumably functionally important) phase to a site between plastoquinone and the photosystem I acceptor, chlorophyll (P₇₀₀), possibly plastocyanin. It is suggested that PC may transfer electrons to oxygen in addition to P₇₀₀.     

Field evaluations of the VDmax approach for substantiation of a 25 kGy sterilization dose and its application to other preselected doses

The International and European standards for radiation sterilization require evidence of the effectiveness of a minimum sterilization dose of 25 kGy but do not provide detailed guidance on how this evidence can be generated. An approach, designated VD_max, has recently been described and computer evaluated to provide safe and unambiguous substantiation of a 25 kGy sterilization dose. The approach has been further developed into a practical method, which has been subjected to field evaluations at three manufacturing facilities which produce different types of medical devices. The three facilities each used a different overall evaluation strategy: Facility A used VD_max for quarterly dose audits; Facility B compared VD_max and Method 1 in side-by-side parallel experiments; and Facility C, a new facility at start-up, used VD_max for initial substantiation of 25 kGy and subsequent quarterly dose audits. A common element at all three facilities was the use of 10 product units for irradiation in the verification dose experiment.

The field evaluations of the VD_max method were successful at all three facilities; they included many different types of medical devices/product families with a wide range of average bioburden and sample item portion values used in the verification dose experiments. Overall, around 500 verification dose experiments were performed and no failures were observed. In the side-by-side parallel experiments, the outcomes of the VD_max experiments were consistent with the outcomes observed with Method 1.

The VD_max approach has been extended to sterilization doses >25 and <25 kGy; verification doses have been derived for sterilization doses of 15, 20, 30, and 35 kGy. Widespread application of the VD_max method for doses other than 25 kGy must await controlled field evaluations and the development of appropriate specifications/standards.