Relationship between the ionic nature of some organoaluminum—transition metal catalysts and the rate of polymerization

The electrical conductivity of several trialkylaluminum and alkyl-aluminum halides was investigated in dry benzene at 25°C. within the concentration range of 10^?1–10^?3M. The equivalent conductance of the trialkylaluminum systems decreased in the following order: Al(n-C₆H₁₃)₃ > Al(n-C₁₀H₁₉)₃ > Al(n-C₄H₉)₃ > Al(i-C₄H₉)₃ > Al(n-C₃H₇)₃ > Al(C₂H₅)₃. The conductance (1/R) of a given series was also examined and found to decrease as each alkyl group was successively replaced by a chlorine atom, thus: Al(C₂H₅)₃ > Al(C₂H₅)₂Cl > Al(C₂H₅)_1.5Cl_1.5 > Al(C₂H₅)Cl₂ and Al(i-C₄H₉)₃ > Al(i-C₄H₉)₂Cl > Al(i-C₄H₉)Cl₂. The ion pair dissociation constants K were calculated and show in a qualitative manner the difference between various organoaluminum systems. The relative rate of olefin polymerization was related to the conductivity of various organoaluminum–transition metal catalyst systems used. The effect of Lewis bases such as monoglyme, diglyme, triglyme, and tetraglyme on triethylaluminum indicated that the first-mentioned base forms a 1:1 type of complex as ordinary ethers do, whereas the remaining three bases utilize only two of their available oxygen atoms to coordinate with triethylaluminum. The effect of TiCl₃ (in the presence of an ether) on the conductance was also determined.     

Characterization of a lipid-rich fraction synthesized by Streptomyces avermitilis

Isolation of the macrocyclic lactone parasiticide avermectin and other closely related natural products produced by Streptomyces avermitilis also yields a lipid-rich fraction. The latter has been characterized by techniques based on gas-liquid chromatography (GLC) and mass spectrometry (MS). Initial examination of the lipid-rich fraction by direct probe electron-impact (EI) MS and packed-column GLC showed that it consists primarily of a mixture of triglycerides possessing C14-C17 acyl groups. Further examination of this fraction by capillary column GLC-MS demonstrated that it contains low levels of C15-C17 free fatty acids, squalene and diglycerides and, as the major components, at least ten mixed acyl triglycerides (total number of acyl carbon atoms ranging from 43 to 50). Prominent among the triglycerides were a C15-C15-C16 species, a C15-C16-C16 species and a C15-C16-C17 species. Capillary-column GLC and GLC-MS of the fatty acid methyl esters resulting from transesterification demonstrated that the major triglyceride acyl groups are anteiso-C15 (12-methyltetradecanoyl), iso-C16 (14-methylpentadecanoyl), n-C16 (hexa-decanoyl) and anteiso-C17 (14-methylhexadecanoyl). Lower levels of the methyl esters of the following fatty acids were observed: iso-C14 (12-methyltridecanoic), n-C14 (tetradecanoic), iso-C15 (13-methyltetradecanoic), n-C15 (pentadecanoic), iso-C17 (15-methylhexadecanoic) and n-C17 (heptadecanoic). Little evidence was seen for either unsaturated acyl groups or acyl groups of less than 13 or more than 18 carbon atoms. Desorption chemical ionization MS (ammonia reagent gas) analysis confirmed the nature of the lipid-rich fraction, and is an attractive one-step approach for determining the molecular weights and distribution of triglycerides in a mixture.     

In situ DMSO hydration measurements of HTS compound libraries

Compounds used in high throughput screening (HTS) are typically dissolved in DMSO. These solutions are stored automation-friendly racks of wells or tubes. DMSO is hygroscopic and quickly absorbs water from the atmosphere. When present in DMSO compound solutions, water can accelerate degradation and precipitation. Understanding DMSO hydration in an HTS compound library can improve storage and screening methods by managing the impact of water on compound stability. A non-destructive, acoustic method compatible with HTS has been developed to measure water content in DMSO solutions. Performance of this acoustic method was compared with an optical technique and found to be in good agreement. The accuracy and precision of acoustic measurements was shown to be under 3% over the tested range of DMSO solutions (0% to 35% water by volume) and insensitive to the presence of HTS compounds at typical storage concentrations. Time course studies of hydration for wells in 384-well and 1536-well microplates were performed. Well geometry, fluid volume, well position and atmospheric conditions were all factors in hydration rate. High rates of hydration were seen in lower-volume fills, higher-density multi-well plates and when there was a large differential between the humidity of the lab and the water content of the DMSO. For example, a 1536-well microplate filled with 2microL of 100% DMSO exposed for one hour to a laboratory environment with approximately 40% relative humidity will absorb over 6% water by volume. Understanding DMSO hydration rates as well as the ability to reverse library hydration are important steps towards managing stability and availability of compound libraries.     

Routine analysis by high precision gas chromatography/mass selective detector/isotope ratio mass spectrometry to 0.1 parts per mil

Stable isotope methods are potentially quite useful for validating natural or enhanced mineral degradation of contaminants. For this reason, a continuous flow gas chromatograph (GC), isotope ratio mass spectrometer (IRMS) has been coupled with a quadrupole mass selective detector (MSD) to allow simultaneous mass spectral and stable carbon isotope ratio data to be obtained from a single chromatographic analysis. This allows the target contaminant and any extra-cellular degradation intermediates to be both qualified and quantified. Previously acceptable limits of precision (0.3 parts per mil) are undesirable given the small fractionation observed during aerobic degradation. To further understand the fate of organic contaminants and to gain information about the metabolic degradative pathway employed by a microorganism, routine isotopic analyses on a range of analytes have been performed. Quantities of sample producing mass-44 ion beam signal (I(44)) of 2 x 10(-10) to 1 x 10(-8) A were analysed. When the IRMS was tuned for high sensitivity, ion source nonlinearities were overcome by peak height correction from an algorithm that was produced using known isotopic standards of varying concentrations. This led to sample accuracy of <0.01 per thousand and sample precision of 0.1 per thousand. Copyright 1999 John Wiley & Sons, Ltd.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Correction of figure errors on optical surfaces by laser-induced contraction of Mo/Si multilayers

We demonstrate that laser annealing of Mo/Si multilayers can be used to make controlled modifications of the surface figure of an optical substrate on a nanometer scale. In this experiment a superpolished optical flat was exposed to single pulses from an excimer laser to produce surface depressions of widths that varied from 10 microm to 0.5 mm and of depths in the range 2-50 nm. Simulations of thermally induced contraction of the Mo/Si multilayers are in good agreement with the observed deformations and indicate that the technique can be extended to larger deformations and higher resolution.     

Strong interaction shifts and widths in light kaonic atoms

Energy shifts and line widths of X-ray transitions in kaonic atoms have been measured with an accuracy of about 10%. These data have been interpreted in terms of an optical potential. Whereas earlier approaches based on the free K⁻N scattering lengths fail to reproduce the data, a set of effective parameters consistant with all now available experiments could be derived.