Removal of carbonyl sulfide and hydrogen sulfide from synthesis gas byChlorobium thiosulfatophilum

Applied Biochemistry and Biotechnology - The anaerobic, photosynthetic bacteriumChlorobium thiosulfatophilum utilizes CO2 as its carbon source and operates at the mesophilic temperature of...     

On the rational homotopy type of function spaces

The main result of this paper is the construction of a minimal model for the function space of continuous functions from a finite type, finite dimensional space to a finite type, nilpotent space in terms of minimal models for and . For the component containing the constant map, in positive dimensions. When is formal, there is a simple formula for the differential of the minimal model in terms of the differential of the minimal model for and the coproduct of . We also give a version of the main result for the space of cross sections of a fibration.

     

Integration in the GHP Formalism II: An Operator Approach for Spacetimes with Killing Vectors, with Applications to Twisting Type N Spaces

Held has proposed a coordinate- and gauge-free integration procedure within the ghp formalism built around four functionally independent zero-weighted scalars constructed from the spin coefficients and the Riemann tensor components. Unfortunately, a spacetime with Killing vectors (and hence cyclic coordinates in the metric, and in all quantities constructed from the metric) may be unable to supply the full quota of four scalars of this type. However, for such a spacetime additional scalars may be supplied by the components of the Killing vectors. As an illustration we investigate the vacuum type N spaces admitting a Killing vector and a homothetic Killing vector. In a direct manner, we reduce the problem to a pair of ordinary differential operator master equations, making use of a new zero-weighted ghp operator. In two different ways, we show how these master equations can be reduced to one real third-order operator differential equation for a complex function of a real variable—but still with the freedom to choose explicitly our fourth coordinate. It is then easy to see there is a whole class of coordinate choices where the problem reduces essentially to one real third-order differential equation for a real function of a real variable. It is also outlined how the various other differential equations, which have been derived previously in work on this problem, can be deduced from our master equations.     

Strukturelle Abwandlungen an partiell silylierten Kohlenhydraten mittels Triphenylphosphan-Azodicarbonsäureester, 5. Mitt.: Transformationen an Glykonolactonen

Reaction ofD-glucono-1,5-lactone1 with two equivalents oft-butyldimethylchlorosilane yields via a ringcontraction 2,6-bis-O-(t-BDMSi)-D-glucono-1,4-lactone2a as main product and a small amount of 5,6-bis-O-(t-BDMSi)-D-glucono-1,4-lactone2c. Under the same conditionsL-mannono-1,4-lactone3 is transformed to the derivatives 2,6-bis-O-(t-BDMSi)-L-mannono-1,4-lactone3a and 3,6-bis-O-(t-BDMSi)-L-mannono-1,4-lactone3c as the minor product. 2,6-bis-O-(t-BDMSi)-D-galactono-1,4-lactone4a and 2,6-bis-O-(t-BDMSi)-D-gulono-1,4-lactone5a are also prepared from the corresponding glyconolactones4 and5. Whereas the compounds2a, 2c, 4a and5a withAc ₂O-pyridine give the bisacetylderivatives2b, 2d, 4b and5b, 3c is converted by an accompanying migration of one silylgroup to the 5,6-bis-O-(t-BDMSi)-2,3-bis-O-acetyl-L-mannono-1,4-lactone3d. The gluconolactone derivative2a reacts easily withTPP/DEAD/HX to the 5-X-L-idono-1,4-lactone derivatives6a (X=N₃),6b (X=p-NO₂-C₆H₄COO) and6c (3-O-acetylderivative of6a). Treating6b with a second equivalentTPP/DEAD/HX leads to the unsaturated sugarlacton7b. Without an external nucleophile2a affords withTPP the mixture of 2,6-bis-O-(t-BDMSi)-3,5-carbonato-D-glucono-1,4-lactone2c, 3,5-anhydro-L-idono-1,4-lactone8 and 3,6-anhydro-D-glucono-1,4-lactone9. Analogous procedures applied to4a yield theL-altronolactonoderivatives10a, 10b and10c, the unsaturated sugarlactone11b on the one and the 3,5-carbonatogalactonolactone4c and the 2,6-bis-O-(t-BDMSi)-3-desoxy-5-ethoxycarbonyl-D-threo-hex-2-en-1,4-lactone12 on the other hand.Whereas the bis-silyletherderivative3a is transformed by the title system exclusively by an elimination process to13, the derivative5a affords withTPP/DEAD without any elimination the 3,6-anhydrosugar14. Partial desilylation of14 followed by acetylation gives the derivatives14a and14b.Structural elucidations were achieved by¹H-NMR-analysis. In some cases also CD-measurements allowed suitable correlations.

Mark, E., Zbiral, E., Brandstetter, H. H., 4. Mitt., Mh. Chem.111, 289 (1980).     

Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

A series of Ru^II polypyridyl complexes of the structural design [Ru^II(R?tpy)(NN)(CH₃CN)]²⁺ (R?tpy=2,2′:6′,2′′‐terpyridine (R=H) or 4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine (R=tBu); NN=2,2′‐bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO₂ to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron‐donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru^II(tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 3 ]²⁺; 6‐mbpy=6‐methyl‐2,2′‐bipyridine) and [Ru^II(tBu?tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 4 ]²⁺), in which the methyl group of the 6‐mbpy ligand is trans to the CH₃CN ligand, show electrocatalytic CO₂ reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH₃CN ligand dissociation, CO₂ coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.     

A phase transition from monoclinic C2 with Z′ = 1 to triclinic P1 with Z′ = 4 for the quasiracemate l‐2‐aminobutyric acid–d‐methionine (1/1)

Racemates of hydrophobic amino acids with linear side chains are known to undergo a unique series of solid‐state phase transitions that involve sliding of molecular bilayers upon heating or cooling. Recently, this behaviour was shown to extend also to quasiracemates of two different amino acids with opposite handedness [Görbitz & Karen (2015). J. Phys. Chem. B, 119 , 4975–4984]. Previous investigations are here extended to an l ‐2‐aminobutyric acid–d ‐methionine (1/1) co‐crystal, C₄H₉NO₂·C₅H₁₁NO₂S. The significant difference in size between the –CH₂CH₃ and –CH₂CH₂SCH₃ side chains leads to extensive disorder at room temperature, which is essentially resolved after a phase transition at 229 K to an unprecedented triclinic form where all four d ‐methionine molecules in the asymmetric unit have different side‐chain conformations and all three side‐chain rotamers are used for the four partner l ‐2‐aminobutyric acid molecules.     

Compressed limit sampling inspection plans for food safety

The design of attribute sampling inspection plans based on compressed or narrow limits for food safety applications is covered. Artificially compressed limits allow a significant reduction in the number of analytical tests to be carried out while maintaining the risks at predefined levels. The design of optimal sampling plans is discussed for two given points on the operating characteristic curve and especially for the zero acceptance number case. Compressed limit plans matching the attribute plans of the International Commission on Microbiological Specifications for Foods are also given. The case of unknown batch standard deviation is also discussed. Three‐class attribute plans with optimal positions for given microbiological limit M and good manufacturing practices limit m are derived. The proposed plans are illustrated through examples. R software codes to obtain sampling plans are also given. Copyright © 2016 John Wiley & Sons, Ltd.     

Conformational dynamics of tetraisopropylmethane and of tetracyclopropylmethane

Tetraisopropylmethane (1) exists in solution as a mixture of two types of conformers (D2d and S4 time-averaged symmetry) in the ratio 93:7 at -110 degrees C, interconverting with a barrier of 9.7 kcal mol-1. Molecular mechanics calculations and the multiplicity of NMR signals at low temperature allow the assignment of these conformations. The only conformation populated in tetracyclopropylmethane (2) is the same type as the minor conformation (S4 time-averaged symmetry) populated in 1. 13C NMR spectra at about -180 degrees C show that degenerate versions of this conformation interconvert with a barrier of 4.5 kcal mol-1. Molecular mechanics calculations that characterize the six possible conformational types for these molecules, and the most important interconversion pathways, are reported. Calculated and experimental barriers match satisfactorily well.     

Stereospezifische Synthese einer neuen Morphin-Teilstruktur

We describe here a synthesis of the morphine partial structures 28 and 36 , and of their enantiomers, which uses 7-methoxy-benzofurancarboxylic acid as starting material. A key intermediate in this scheme is compound 15 , which is converted, via 1,2-ketone shift, into 22 . This latter is stereospecifically reduced to the alcohol 24 and converted to the amide 25 . The diastereomer of 25 is afforded by stereospecific introduction of a ethoxycarbonyl group in 15 to yield the β-ketoester 31 , followed by Curtius degradation of the acid 32 to the acylamine 34 . An efficient method for removal of the methoxy group in methoxy-dihydro-benzofurans is presented (Scheme 9), as is the functionalization of the N-atom in 27 with concurrent complex formation between the free hydroxy group and boric-acid. The aromatization of the furan ring (Scheme 10) with DDQ gave the expected benzofuran derivative 30 .     

In Situ global method for measurement of oxygen demand and mass transfer

Two aerobic microorganisms,Saccharomycopsis lipolytica andBrevibacterium lactofermentum, have been used in a study of mass transfer and oxygen uptake from a global perspective, using a closed gas system. Oxygen concentrations in the gas and liquid were followed using oxygen electrodes; the results allowed for easy calculation of in situ oxygen transport. The cell yields on oxygen forS. lipolytica and B.lactofermentum were 1.01 and 1.53 g/g, respectively. The mass transfer coefficient was estimated as 10/h at 500 rpm for both fermentations. The advantages with this method are noticeable, since the use of model systems may be avoided, and thein situ measurements of oxygen demand assure reliable data for scale-up. Managed by Lockheed Martin Energy Research Corp. for the US Department of Energy under contract DE-AC05-96OR22464