New procedure for isolation of amino acids based on selective hydrolysis of trimethylsilyl derivatives

A rapid procedure for the isolation of amino acids from physiological fluids by class separation suitable for gas chromatographic and gas chromatographic-mass spectrometric analysis is described. A physiological fluid such as plasma is adjusted to pH 2 and extracted with diethyl ether to remove organic acids and neutrals. After precipitation of proteins with trichloroacetic acid, the aqueous plasma is dried and derivatized by trimethylsilylation. Organic compounds like sugars and amino acids are rendered soluble in petroleum ether leaving inorganic salts when the soluble layer is transferred. Separation of sugars from amino acids is achieved by taking advantage of the different rates of aqueous hydrolysis of the trimethylsilyl (TMS) derivatives. Mixing the petroleum ether extract with a small volume of water results in two phases. The petroleum ether layer contains TMS-Sugar constituents of plasma and the aqueous layer contains free amino acids and amines. This procedure was used to isolate L-dopa, 3-O-methyldopa and tyrosine from human plasma in a quantitation assay using 18O-labelled amino acids and gas chromatography-mass spectrometry.     

Towards laboratory produced relativistic electron–positron pair plasmas

We review recent experimental results on the path to producing electron–positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10¹⁶ cm⁻³ and 10¹³ cm⁻³, respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 10¹⁸ cm⁻³, relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter.     

Sunna dosimeter: an integrating photoluminescent film and reader system; work in progress

A new radiation dosimeter, consisting of an optically-stimulated polymer film containing a photofluorescent sensor, can serve as a routine dosimeter and radiographic imaging medium for high-dose applications in the absorbed dose range 0.1–100 kGy. The flexible, colorless, opalescent film having a uniform thickness of 0.240 (±0.005) mm or certain other films in the thickness range 0.08–0.60 mm, are available in large batches. They can be read rapidly with a simple table-top spectrofluorimeter, excitation wavelength (λ=450 nm) and emission wavelength (λ=670 nm), giving a type A uncertainty of dose evaluation of <±5% at 95% confidence level. It supplies either single integrated dose readings or two-dimensional radiographic images with relatively high spatial resolution. The present work focuses on the following gamma-ray response characteristics of the system: inter- and intra-batch reproducibility, pre- and post-irradiation stability, and dependence of dose interpretations on absorbed dose rate and irradiation temperature.     

Solid-Phase Synthesis of Macrocyclic Systems by a Cyclorelease Strategy: Application of the Stille Coupling to a Synthesis of (S)-Zearalenone

No heteroatom required! In many solid-phase syntheses, after the release from the polymer support a heteroatom (e.g. O, S, N) remains in the substrate as a residue of a linking protecting group. With polymer-bound tin reagents cleavage and cyclization of the substrate with C–C bond formation (see picture) can now be achieved by intramolecular Stille coupling. S =substrate.     

Novel 3-hydroxylated leukotriene b4 metabolites from ethanol-treated rat hepatocytes

Coincubations of radiolabeled leukotriene B₄ (LTB₄) and ethanol with isolated rat hepatocytes led to formation of one dihydroxylated and two novel β-oxidized metabolites of LTB₄. The major radioactive peaks from reverse-phase-high performance liquid chromatography (RP-HPLC) eluted with material absorbing UV light maximally at 270 nm, with shoulders at 260 and 280 nm, indicating retention of the conjugated triene structure of the parent molecule in each metabolite structure. Following purification, catalytic reduction, and derivatization, mass spectrometric analysis revealed that all three metabolites were hydroxylated at the C-3 carbon atom based on characteristic ions at m/z 201 and 175 in the electron ionization mass spectra of the metabolites. Negative-ion electron capture mass spectrometry of the metabolites as pentafluorobenzyl (PFB) ester, trimethylsilyl ether derivatives aided structural characterizations while revealing interesting fragmentations. A ketene-containing ion appeared to result from the loss of both PFB groups (one as PFB alcohol), while a lactone alkoxide ion appeared to result following loss of PFB and bis (trimethylsilyl) ether. From these data three novel LTB₄ metabolites were suggested to be 3,20-dihydroxy-LTB₄ (3,20-diOH-LTB₄), 3-hydroxy-18-carboxy-LTB₄ (3-OH-18-COOH-LTB₄), and 3-hydroxy-16-carboxy-LTB₃ (3-OH-16-COOH-LTB₃). The significance of the almost exclusive formation of these 3-hydroxylated LTB₄ metabolites in the presence of ethanol is currently unknown, but may result from interrupted β-oxidation from the C-1 carboxyl moiety.     

Electrospray mass spectrometric analysis of 5-hydroperoxy and 5-hydroxyeicosatetraenoic acids generated by lipid peroxidation of red blood cell ghost phospholipids

Recent evidence suggests that generation of hydroxyl radicals in the presence of lipid membranes can lead to oxidation of arachidonic acid esterified to glycerophospholipids and the production of compounds isomeric to prostaglandins, thromboxanes, and leukotrienes. Liquid chromatography tandem mass spectrometry and multiple reaction monitoring were employed to quantitate the production of 5-hydroxyeicosatetraenoic acid (5-HETE), 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and 5-oxo-eicosatetraenoic acid (5-oxo-ETE) in red blood cells ghosts treated with t-butylhydroperoxide (tBuOOH). Untreated red blood cell ghosts were found to contain low, but measurable quantities of these three 5-oxygenated eicosanoids as phospholipid esters. Following treatment, there was approximately a 53- and 22. 5-fold increase in 5-HETE and 5-HPETE, respectively, and an 8. 5-fold increase in 5-oxo-ETE. The formation of these compounds was inhibited nearly 90% by the antioxidants butylated hydroxytoluene, ascorbic acid, and resveratrol providing further evidence for free radical mediated oxidation of arachidonic acid. This analytical protocol provided sufficient sensitivity for detection of these compounds in studies in which previous analysis by high-pressure liquid chromatography with UV detection failed to detect their presence. These results reveal that the biologically active eicosanoids 5-HETE, 5-HPETE, and 5-oxo-ETE are formed esterified to phospholipids following exposure of cellular membranes to reactive oxygen species and free radicals in a model system where intracellular antioxidant mechanisms were depleted.     

Enantioselective synthesis of alpha-alkyl-beta,gamma-unsaturated esters through efficient cu-catalyzed allylic alkylations

A method for enantioselective Cu-catalyzed allylic substitution between various alkylzincs and alpha,beta-unsaturated carboxylic esters that bear a gamma-phosphate is reported. These transformations afford alpha-alkyl-beta,gamma-unsaturated carbonyls with regioselectivities of 7:1 to >20:1 (S(N)2':S(N)2) and in 87-97% ee. The utility of the method is illustrated by a convergent total synthesis of topoisomerse II inhibitor (R)-elenic acid.     

Reaction of 2-trifluoromethyl-4H-3,1-benzoxazin-4-one derivatives with carboethoxymethylenetriphenylphosphorane

Treatment of a series of 2-trifluoromethyl-4H-3,1-benzoxazin-4-one derivatives 1 with carboethoxymethyl-enetriphenylphosphorane 2 yielded the phosphoranes 3 in boiling toluene solution. Thermolysis of these phosphoranes 3 gave esters 6.     

Tunable one-dimensional silver-silica nanopeapod architectures

Silica-coated silver nanowires can be chemically treated to produce a "peapod" architecture in which silver peas are embedded in silica pods. The silver "pea" dimension and interparticle spacings are controllable down to approximately 50 nm. This architecture is potentially useful for chemical sensing, plasmonic, or catalytic applications.