Synthesis and characterization of tetrakis(2,6-diethylphenyl)digermene

Tetrakis(2,6-diethylphenyl)digermene (1b) has been synthesized and its molecular structure determined: (1) the GeGe bond length is 2.213(2) Å and (2) the molecule has a twist angle of 11° about the GeGe bond and an out-of-plane bending angle of 15° at the germanium atoms.     

Novel techniques for enhancing sensitivity in static headspace extraction-gas chromatography

Static headspace extraction-gas chromatography (SHE-GC) is one of the most commonly used techniques for the analysis of volatile compounds. It is considered by most to be a mature technique and to an extent this is true: there are many users from outside the traditional chromatography research community developing and publishing SHE-GC methods and there are numerous instruments and devices for SHE-GC commercially available. However, research on new SHE-GC methods continues. In this review, several interesting new developments in SHE-GC are described using examples from the past three years’ literature. First, the fundamental theory of SHE-GC is reviewed to provide a basis and common theme for the discussion of new methods. Next, several areas of SHE-GC research are explored: new sampling configurations, analyte derivatization and ionic liquids as solvents. These are all means for enhancing partitioning of the analyte into the vapor phase, thus improving analytical sensitivity of the overall SHE-GC method. Ideally, partitioning of analytes into the vapor phase is increased while partitioning of matrix components is not, or is decreased. There are many aspects of the seemingly straightforward process in SHE-GC that require further fundamental research to extend the application range of SHE-GC and to make method development more systematic.     

Packing density of HS(CH2)(n)COOH self-assembled monolayers

Self-assembled monolayers (SAMs) of HS(CH(2))(n)COOH, n = 5, 10, 15 deposited from ethanol solution onto gold are prepared by five approaches, and their packing densities are evaluated by X-ray photoelectron spectroscopy (XPS) measurements. The five approaches are: (1) direct deposition; (2) acetic-acid-assisted deposition; (3) butyl-amine-assisted deposition; (4) displacement of a preformed HS(CH(2))(n)CH(3) (n = 5, 10, 15) SAMs; and (5) co-deposition with HS(CH(2))(n)CH(3) (n = 5, 10, 15). Packing density metrics are calculated from measurements of SAM and substrate photoemission intensities and their attenuations by two methods. In one case the attenuated photoemissions are expressed as a ratio relative to comparable measurements on an experimental HS(CH(2))(n)CH(3) model system. In the other case a new method is introduced where a calculated attenuation based on theoretical random coil and extended chain models is used as the reference to determine a packing density fraction. Packing densities are also correlated with the S2p(Au-bonded):Au4f peak area ratios and with shifts in the C1s binding energies. SAMs prepared by the direct deposition are a partial multilayer where a second molecular layer is physisorbed onto the SAM and not removable by solvent washing. The addition of acetic acid to the deposition solution disrupts dimer associations of HS(CH(2))(n)COOH in solution and at the surface of the monolayer and yields the most ordered monolayer with the highest density of -COOH groups. The addition of butyl amine results in a labile ammonium carbonate ion pair formation but results in a lower packing density in the SAM. The displacement of the preformed HS(CH(2))(n)CH(3) SAM and the co-deposition of HS(CH(2))(n)CH(3) with HS(CH(2))(n)COOH result in SAMs with little incorporation of the -COOH component.     

Adsorption behavior of hexafluorophosphate on selected bonded phases

The adsorption behavior of ammonium hexafluorophosphate was studied on four HPLC columns packed with adsorbents of different ability for dispersive interactions using frontal chromatography with LC/MS detection in negative ESI mode. Hexafluorophosphate (PF(6)(-)) adsorption isotherms were measured from acetonitrile/water and methanol/water mixtures. Increased PF(6)(-) adsorption with increased acetonitrile content was found between 0 and 15% of acetonitrile in the eluent. Further increase of the acetonitrile concentration leads to an exponential decrease of PF(6)(-) adsorption. Methanol, on the other hand, causes a steady decrease of PF(6)(-) adsorption with increased organic concentration in the mobile phase.     

Synthesis and electric field actuation of an ionic liquid polymer

Polymerizable ionic liquids and their actuation in an electric field are a combination of material and properties with unique potential to display structural and fluid dynamics above that found in small molecule ionic liquids. In an effort to blend ionic liquid nature with actuation response, we have synthesized a new ionic liquid ammonium sulfonate monomer and polymer. The liquid temperature ranges of both the monomer and polymer ionic liquid systems are quite large extending from their respective glass transitions (Tg) of -57 and -49 degrees C to decomposition at approximately 200 degrees C. Particularly remarkable is the small Tg increment that accompanies the transformation from monomer to polymer. The electrowetting behavior of the polymer and of the monomer presents an interesting contrast. This communication will encompass the polymerization, characterization, and actuation of these new ionic liquids.     

Photoreactivation of killing in Streptomyces: action spectra and kinetic studies

Abstract— An action spectrum was obtained for photoreactivation of killing (PR) of Streptomyces griseus conidia. This spectrum shows a major peak around 436 nm, originally observed by A. Kelner, and a secondary peak at 313 nm not previously reported. The rate of PR shows a strong dependence upon temperature and dose rate of the PR light at 436 nm, but this decreases to only a slight dependence upon these parameters at 313 nm. These findings suggested that PR at 436 nm in this organism is of the usual photoenzymatic type, but that PR at 313 nm might be of a different kind. A mutant (PHR-1) of S. griseus was found that shows only a narrow range of PR (roughly 310–400 nm) with a single peak at 313 nm. The PR efficiency was lower than for wild type and the PR sector not greater than one-half that of wild type. This PR shows no temperature dependence. Essentially similar behavior was observed with wild-type Streptomyces coelicolor. These findings show that at least some of the PR at 313 nm is a separable phenomenon. It is therefore unlikely to involve a mechanism identical to that at 436 nm. The nature of PR at 313 nm in Streptomyces is not known. If it is enzymatic, it is remarkable in having little or no dependence upon temperature and dose rate. Absence of photoprotection and liquid-holding recovery indicate that it is not indirect PR. Some of it (that part exhibited by S. griseus PHR-1 and S. coelicolor) might result from a direct photochemical action on DNA.     

Diastereoselective synthesis of quaternary alpha-amino acids from diketopiperazine templates

Sequential enolate alkylations of (S)-N(1)-methyl-5-methoxy-6-isopropyl-3,6-dihydropyrazin-2-one and (S)-N(1)-p-methoxybenzyl-5-methoxy-6-isopropyl-3,6-dihydropyrazin-2-one proceed with excellent levels of diastereoselectivity (>90% de) affording quaternary alpha-amino acids in high enantiomeric excess (>98% ee) after deprotection and hydrolysis.