Solid-phase microextraction: investigation of the metabolism of substances that may be abused by inhalation

Purified liquefied petroleum gas (LPG), a mixture of butane, isobutane, and propane, is commonly abused by inhalation. Little is known about the mammalian metabolism of these substances. Metabolism of other hydrocarbons, including n-hexane and cyclohexane, has been studied in vitro using a range of liver preparations, with metabolites analyzed by static headspace techniques. Solid-phase microextraction (SPME) for sampling metabolites in the headspace of incubates of volatile compounds with activated rat liver microsomes is investigated. Cyclohexanol and cyclohexanone were formed from cyclohexane and 1-, 2-, and 3-hexanol and 2-hexanone from n-hexane as predicted. Secondary alcohols are found for the other compounds studied, except for propene and isobutane, together with 2-propanone and 2-butanone from propane and n-butane, respectively. Samples from three individuals who died following LPG abuse contained a range of putative n-butane metabolites: n-butanol, 2-butanol, 2,3-butanediol, 3-hydroxy-2-butanone, and 2,3-butanedione. To our knowledge, the last three compounds have not been proposed as metabolites of n-butane in man. These might be produced through similar metabolic pathways to those of n-hexane and n-heptane. The findings indicate the value of SPME for investigating the metabolism of volatile substances and for detecting and monitoring exposure to these compounds.     

UV photooxidation and photopatterning of alkanethiolate self-assembled monolayers (SAMs) on GaAs (001)

We have investigated the photooxidation of alkanethiolate self-assembled monoalyers (SAMs) adsorbed on GaAs (001) using time-of-flight secondary ion mass spectrometry. Both -CH3- and -COOH-terminated SAMs undergo photoreaction to form sulfonated species upon exposure to UV light from a 500 W Hg arc lamp (lambda = 280-440 nm) in the presence of oxygen. In contrast to SAMs adsorbed on metals, the photooxidation of octadecanethiol adsorbed on GaAs can be fit to two first-order reactions: a fast initial reaction followed by a second slower reaction ( approximately 6 times slower). For SAMs with shorter alkyl chain lengths, the photooxidation process is can be fit to a single first-order reaction. Using the optimal photooxidation time, we also demonstrate that SAMs can be successfully UV photopatterned on GaAs substrates producing sharp, well-defined patterns.     

Solvent polarity at an aqueous/alkane interface: the effect of solute identity

Resonance-enhanced second harmonic generation (SHG) has been used to probe the solvatochromic behavior of two small, aromatic chromophores adsorbed to the aqueous/cyclohexane, liquid/liquid interface. SHG spectra of p-nitrophenol (PNP) and 2,6-dimethyl-PNP (dmPNP) indicate that these two chromophores sample markedly different environments. PNP sees a polar, waterlike environment, whereas solvent polarity surrounding dmPNP is dominated by the nonpolar, organic phase. Results suggest that subtle changes in solute structure can change the distribution of solutes across an interface and thus change a solute's local solvation environment.     

Magnetic resonance and structural investigations of (monooxooctaethylchlorinato)iron(III) chloride and its bis(imidazole) complex

(Monooxooctaethylchlorinato)iron(III) chloride, (oxo-OEC)FeCl, 1, has been investigated by X-ray crystallography and by 1H NMR spectroscopy. Its bis(imidazole-d4) complex has been studied by multidimensional 1H NMR and EPR spectroscopies, and the results are compared to those for the bis(Im-d4) complex of (octaethylchlorinato)iron(III) chloride, (OEC)FeCl, 2. EPR and NMR results show that both [(oxo-OEC)Fe(Im-d4)2]Cl and [(OEC)Fe(Im-d4)2]Cl are low-spin Fe(III) complexes with (d(xy))2 (d(xz),d(yz))3 electronic ground states, both at 4.2 K (EPR spectra) and at ambient temperatures utilized for solution NMR studies. The pattern of chemical shifts of the pyrrole-CH2 and meso protons are similar, with the 8,17-carbons having the largest and the 12,13-carbons having the smallest spin densities in each case, except that [(OEC)Fe(Im-d4)2]Cl has a slightly wider range of pyrrole-CH2 chemical shifts and more resonances are observed for [(oxo-OEC)Fe(Im-d4)2]Cl due to its lower symmetry. Full proton resonance assignments for both complexes have been made from COSY, NOESY, and NOE difference experiments.     

Primer preactivation of peptidoglycan polymerases

Peptidoglycan glycosyltransferases are highly conserved bacterial enzymes that catalyze glycan strand polymerization to build the cell wall. Because the cell wall is essential for bacterial cell survival, these glycosyltransferases are potential antibiotic targets, but a detailed understanding of their mechanisms is lacking. Here we show that a synthetic peptidoglycan fragment that mimics the elongating polymer chain activates peptidoglycan glycosyltransferases by bypassing the rate-limiting initiation step.     

In situ synthesis of oligonucleotide arrays by using surface tension

This work describes the in situ synthesis of oligonucleotide arrays on glass surfaces. These arrays are composed of features defined and separated by differential surface tension (surface tension arrays). Specifically, photolithographic methods were used to create a series of spatially addressable, circular features containing an amino-terminated organosilane coupled to the glass through a siloxane linkage. Each feature is bounded by a perfluorosilanated surface. The differences in surface energies between the features and surrounding zones allow for chemical reactions to be readily localized within a defined site. The aminosilanation process was analyzed using contact angle, X-ray photoelectron spectroscopy (XPS), and time-of-flight/secondary ion mass spectroscopy (TOF-SIMS). The efficiency of phosphoramidite-based oligonucleotide synthesis on these surface tension arrays was measured by two methods. One method, termed step-yields-by-hybridization, indicates an average synthesis efficiency for all four (A,G,C,T) bases of 99.9 +/- 1.1%. Step yields measured for the individual amidite bases showed efficiencies of 98.8% (dT), 98.0% (dA), 97.0% (dC), and 97.6% (dG). The second method for determining the amidite coupling efficiencies was by capillary electrophoresis (CE) analysis. Homopolymers of dT (40- and 60mer), dA (40mer), and dC (40mer) were synthesized on an NH(4)OH labile linkage. After cleavage, the products were analyzed by CE. Synthesis efficiencies were calculated by comparison of the full-length product peak with the failure peaks. The calculated coupling efficiencies were 98.8% (dT), 96.8% (dA), and 96.7% (dC).     

Development of an improved high resolution mass spectrometry based multi-residue method for veterinary drugs in various food matrices

Multi-residue methods for veterinary drugs or pesticides in food are increasingly often based on ultra performance liquid chromatography (UPLC) coupled to high resolution mass spectrometry (HRMS). Previous available time of flight (TOF) technologies, showing resolutions up to 15,000 full width at half maximum (FWHM), were not sufficiently selective for monitoring low residue concentrations in difficult matrices (e.g. hormones in tissue or antibiotics in honey). The approach proposed in this paper is based on a single stage Orbitrap mass spectrometer operated at 50,000 FWHM. Extracts (liver and kidney) which were produced according to a validated multi-residue method (time of flight detection based) could not be analyzed by Orbitrap because of extensive signal suppression. This required the improvement of established extraction and clean-up procedures. The introduced, more extensive deproteinzation steps and dedicated instrumental settings successfully eliminated these detrimental suppression effects. The reported method, covering more than 100 different veterinary dugs, was validated according to the EU Commission Decision 2002/657/EEC. Validated matrices include muscle, kidney, liver, fish and honey. Significantly better performance parameters (e.g. linearity, reproducibility and detection limits) were obtained when comparing the new method with the older, TOF based method. These improvements are attributed to the higher resolution (50,000 versus 12,000 FWHM) and the superior mass stability of the of the Orbitrap over the previously utilized TOF instrument.     

Anionic syntheses of terminally functionalized ethylene oligomers

Synthetic procedures for preparation of terminally functionalized linear ethylene oligomers are described. The preferred synthetic method is anionic oligomerization of ethylene with n-butyllithium–tetramethylethylenediamine and electrophilic substitution of the living oligomer so-formed. Conditions and procedures for subsequent chemistry to elaborate the end groups of these oligomers are described. These procedures afford strictly linear ethylene oligomers which contain a wide variety of end groups and which range in molecular weight from 1000 to 4500 (M_n). The product oligomers were characterized spectroscopically as toluene-d₈ solutions at 110°C using multinuclear NMR, FT-IR, fluorescence, and UV-visible spectroscopies as appropriate. Alternative stepwise approaches to such oligomers are also discussed.