Varieties Which are almost D-Affine

This paper produces several examples of varieties X for whichthe global sections functor (X,–): D_X-modD(X)-mod is exact,and makes D(X)-mod a quotient category of D_X-mod, but is notan equivalence. These varieties are quotients by finite groupactions of D-affine varieties. The torsion of (X,–) isalso described, in some cases. Here, D_x-mod denotes the categoryof quasi-coherent D_X-modules.     

Thianaphthenoyltrifluoroacetone as an analytical reagent: The keto-enol tautomerism of the 2- and 3-isomers of thianaphthenoyltrifluoroacetone

Summary The keto-enol tautomerism of the 2- and 3-isomers of thianaphthenoyltrifluoroacetone has been studied and the results explained by considering the relative negativities of the 2- and 3-position of thianaphthene. The results of the comparison of the keto-enol tautomerism of 3-thianaphthenoyltrifluoroacetone to that of 2-thenoyltrifluoroacetone in 80% benzene-20% ethanol may explain in part the greater sensitivity of the former in trace metal analysis.

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Zusammenfassung Die Keto-Enol-Tautomerie der 2- und 3-Isomeren des Thianaphthenoyltrifluoracetons wurde untersucht und mit der relativen Negativität der 2- und 3-Stellung des Thianaphtens zu erklären versucht. Der Vergleich der Keto-Enol-Tautomerie von II mit der des 2-Thenoyltrifluoracetons in BenzolÄthanol (80+20) könnte eine Erklärung für die größere Sensitivität von II bei der Spurenmetallanalyse bieten.

     

Existence of rank 3 vector bundles with given chern classes on homogeneous rational 3-folds

One proves that any rank 3 topological vector bundle on a homogeneous rational 3-fold has an algebraic structure. The proof uses extensions of ideals by rank 2 vector bundles. The paper also contains a construction of rank 3 vector bundles on 3-folds using extensions of ideals by rank 2 reflexive sheaves.     

Mass spectra of some naturally occurring stictane triterpenoids and their trimethylsilyl derivatives

The mass spectra of ten di- and tri-oxygenated stictane triterpenoids and their trimethylsilyl derivatives have been studied in detail. Gas chromatography mass spectrometry of the TMS derivatives on OV-17 and OV-101 columns provided useful separations and identifications of mixtures of stictanes triterpenoids in lichen extracts. The major fragmentations involve ring C, but specific cleavages in rings A, B and E are also observed which allow the substitution pattern of the skeleton to be readily determined. The formation of an intense [M – C₅H₁₁?]⁺ ion for 22α-OTMS stictanes appears specific to their ring E configuration.     

Pyridine ketoximes as analytical reagents. XX

Summary A solvent extraction method for the spectrophotometric determination of gold is described. The effects due to pH, time, reagent concentration and diverse ions have been evaluated. Sensitivity was increased by the use of 4-cm cells, Beer's law was obeyed and the molar absorptivity at 477 nm was 2.34×10⁴.

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Spektrophotometrische Bestimmung von Goldspuren mit 2-Pyridyl-2-thienyl-Z-ketoxim

Zusammenfassung Eine Extraktionsmethode zur spektrophotometrischen Goldbestimmung wurde beschrieben. Der Einfluß von pH, Zeit, Reagenskonzentration und verschiedenen Fremdionen wurde ermittelt. Die Empfindlichkeit wurde mittels 4-cm-Küvetten erhöht. Das Beersche Gesetz wird befolgt, die molare Extinktion bei 477 nm beträgt 2,34×10⁴.

     

Theoretical and experimental investigation of the effect of proton transfer on the (27)al MAS NMR line shapes of zeolite-adsorbate complexes: an independent measure of solid Acid strength

Assessing the degree of proton transfer from a Br?nsted acid site to one or more adsorbed bases is central to arguments regarding the strength of zeolites and other solid acids. In this regard certain solid-state NMR measurements have been fruitful; for example, some (13)C, (15)N, or (31)P resonances of adsorbed bases are sensitive to protonation, and the (1)H chemical shift of the Br?nsted site itself reflects hydrogen bonding. We modeled theoretically the structures of adsorption complexes of several bases on zeolite HZSM-5, calculated the quadrupole coupling constants (Q(cc)) and asymmetry parameters (eta) for aluminum in these complexes and then in turn simulated the central transitions of their (27)Al MAS NMR spectra. The theoretical line width decreased monotonically with the degree of proton transfer, reflecting structural relaxation around aluminum as the proton was transferred to a base. We verified this experimentally for a series of adsorbed bases by way of single-pulse MAS and triple quantum MQMAS (27)Al NMR. The combined theoretical and experimental approach described here provides a strategy by which (27)Al data can be applied to resolve disputed interpretations of proton transfer based on other evidence.     

Metallophosphites as umpolung catalysts: the enantioselective cross silyl benzoin reaction

Carbonyl polarity reversal (umpolung) has been realized employing metallophosphites as catalysts. As a result, nonenzymatic asymmetric cross silyl benzoin reactions have been achieved, giving optically active silyl ether-protected benzoin adducts. The reaction is general with respect to aryl, alkyl, and heterocyclic substrates with good to excellent yields and good to excellent enantioselectivities.     

Recent advances in micellar electrokinetic chromatography

This review contains nearly 200 reference citations, and covers advances in electrokinetic capillary chromatography based on micelles, including stabilized micelle complexes, polymeric and mixed micelles from 2003-2004. Detection strategies, analyte determinations, and applications in micellar electrokinetic capillary chromatography (MEKC) are discussed. Information regarding methods of analyte concentration, analyte specific analyses, and nonstandard micelles has been summarized in tabular form to provide a means of rapid access to information pertinent to the reader.     

Genetic screens and selections for small molecules based on a synthetic riboswitch that activates protein translation

Genetic selection provides the most powerful method to assay large libraries of biomolecules for function. However, harnessing the power of genetic selection for the detection of specific, nonendogenous small-molecule targets in vivo remains a significant challenge. The ability to genetically select for small molecules would provide a reaction-independent mechanism to clone biosynthesis genes from large DNA libraries and greatly facilitate the exploration of large libraries of mutant enzymes for improved synthetic capabilities including altered substrate specificities and enhanced regio- or stereoselectivities. While remarkable progress has been made in developing genetic methods to detect small molecules in vivo, many of these methods rely on engineering small-molecule-protein interactions which remains a difficult problem, and the potential for some of these systems to assay large libraries is limited by the low transformation efficiency and long doubling time of yeast relative to bacteria. Herein, we demonstrate that synthetic riboswitches that activate protein translation in response to a specific small molecule can be used to perform sensitive genetic screens and selections for the presence of small molecules in Escherichia coli. We further demonstrate that the exquisite molecular discrimination properties of aptamers selected in vitro translate directly into an in vivo genetic selection system. Finally, we demonstrate that a cell harboring a synthetic riboswitch with a particular ligand specificity can be selectively amplified from a million-fold larger pool of cells containing mutant riboswitches that respond to a closely related ligand, suggesting that it is possible to use genetic selection in E. coli to discover synthetic riboswitches with new ligand specificities from libraries of mutant riboswitches.     

Crystallization and dissolution temperatures of poly(vinyl alcohol) crystal lamellae

Poly(vinyl alcohol) single crystal platelets having a stepheight of approximately 100 A. were obtained by isothermal crystallization from dilute triethylene glycol solution. Material crystallized at temperature T_c redissolved in the same solvent at a higher temperature T_s. A plot of T_c versus T_s gave a straight line of slope 0.47. Extrapolation of this line to T_c = T_s gave (T_m)∞, which may be regarded as the dissolution temperature of the crystal of infinite stepheight. (T_m)∞ for this sample in triethylene glycol was 220°C. The crystalline nature of the platelets was established by electron and x-ray diffraction techniques. A total of three Bragg d spacings having the values of 3.9, 4.4, and 4.6 A. (±0.05 A.) were measured. These spacings were indexed as the (200), (101), and (101 ) reflections, respectively, of the monoclinic unit cell of Bunn. The x-ray diffractogram exhibits sharp intensities of the (101 ) and (101) reflections. The crystallinity calculated from the density of the poly(vinyl alcohol) precipitated from dilute solutions in triethylene glycol was 42%. Although the overall degree of crystalline perfection of this poly(vinyl alcohol) is low, the linear relationship between T_s and T_c and the formation of definite shaped single crystals when crystallized from dilute solution suggest that poly(vinyl alcohol) crystallizes in the same manner as other semicrystalline polymers.