Joule-Thomson inversion curve prediction by using equation of state

In this paper five equations of state are tested for checking their ability to predict the Joule-Thomson inversion curve.These five equations of state are:Mohsennia-Modarres-Mansoori(MMM),Ji-Lemp(JL),modified Soave-Redlich-Kwang(SRK)equation of state by Graboski(MSRK1),modified SRK equation of state by Peneloux and Rauzy(MSRK2),and modified Peng-Robinson (PR)equation of state by Rauzy(PRmr).The investigated equations of state give good prediction of the low-temperature branch of the inversion curve,except for MMM equation of state.The high-temperature branch and the peak of the inversion curve have been observed,in general,to be sensitive to the applied equation of state.The values of the maximum inversion temperature and maximum inversion pressure are calculated for each component used in this work.     

High-throughput screening of enzyme libraries: thiolactonases evolved by fluorescence-activated sorting of single cells in emulsion compartments

Single bacterial cells, each expressing a different library variant, were compartmentalized in aqueous droplets of water-in-oil (w/o) emulsions, thus maintaining a linkage between a plasmid-borne gene, the encoded enzyme variant, and the fluorescent product this enzyme may generate. Conversion into a double, water-in-oil-in-water (w/o/w) emulsion enabled the sorting of these compartments by FACS, as well as the isolation of living bacteria cells and their enzyme-coding genes. We demonstrate the directed evolution of new enzyme variants by screening >10(7) serum paraoxonase (PON1) mutants, to yield 100-fold improvements in thiolactonase activity. In vitro compartmentalization (IVC) of single cells, each carrying >10(4) enzyme molecules, in a volume of <10 femtoliter (fl), enabled detection and selection despite the fast, spontaneous hydrolysis of the substrate, the very low initial thiolactonase activity of PON1, and the use of difusable fluorescent products.     

Diverse redox-active molecules bearing O-, S-, or Se-terminated tethers for attachment to silicon in studies of molecular information storage

A molecular approach to information storage employs redox-active molecules tethered to an electroactive surface. Attachment of the molecules to electroactive surfaces requires control over the nature of the tether (linker and surface attachment group). We have synthesized a collection of redox-active molecules bearing different linkers and surface anchor groups in free or protected form (hydroxy, mercapto, S-acetylthio, and Se-acetylseleno) for attachment to surfaces such as silicon, germanium, and gold. The molecules exhibit a number of cationic oxidation states, including one (ferrocene), two [zinc(II)porphyrin], three [cobalt(II)porphyrin], or four (lanthanide triple-decker sandwich compound). Electrochemical studies of monolayers of a variety of the redox-active molecules attached to Si(100) electrodes indicate that molecules exhibit a regular mode of attachment (via a Si-X bond, X = O, S, or Se), relatively homogeneous surface organization, and robust reversible electrochemical behavior. The acetyl protecting group undergoes cleavage during the surface deposition process, enabling attachment to silicon via thio or seleno groups without handling free thiols or selenols.     

Polarographic microdetermination of sulphur in organic compounds after oxygen flask combustion

Summary Three polarographic micro-methods are described for the determination of sulphur in organic compounds after oxygen-flask combustion. The products are converted into sulphuric acid by oxidation with hydrogen peroxide, the excess of which is expelled through boiling. The methods are based upon allowing the sulphuric acid to react with an excess of barium iodate or bromate, then recording polarographically the cathodic reduction wave of the iodate or bromate ion. The bromate methods are superior to the iodate method being simpler and more rapid, and the results are correct to within ca. ±0.5%.

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Zusammenfassung Drei polarographische Mikromethoden zur Bestimmung von Schwefel in organischen Verbindungen nach deren Verbrennung im Sauerstoffkolben wurden beschrieben. Die Verbrennungsprodukte werden durch Oxydation mit Wasserstoffperoxid in Schwefelsäure umgesetzt. Der Überschuß des Oxydationsmittels wird durch Kochen zerstört. Die Schwefelsäure läßt man mit überschüssigem Bariumjodat oder -bromat reagieren und mißt dann polarographisch die kathodische Reduktionswelle des Jodats oder Bromats. Die Bromatmethode ist der Jodatmethode überlegen, da sie einfacher und rascher zu Resultaten führt, die innerhalb ±0,5% korrekt sind.

     

Novel aromatic polyimides derived from benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA)

Benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA) is introduced as a monomer for the synthesis of a series of novel polyimides with enhanced high thermal stability. Polyimides derived from BBTDA and aromatic diamines showed high glass transition (T_g>296 °C) and degradation (T₅>455 °C) temperatures, and were soluble in organic solvents (i.e. N-methyl pyrrolidone (NMP), N,N^′-dimethylformamide (DMF), N,N^′-dimethylacetamide (DMAc)). The polymerization yielded high-molecular-weight polyimides with inherent viscosities ranging from 1.75 to 2.14 dl/g. The polymers were characterized by IR and elemental analysis.     

Structural Elucidation of {[(CH3)2SnCl2·H2O]2·18-crown-6} n and its Hydrogen Bonding in Solution by HMBC Spectroscopy

Behavior of {[(CH₃)₂SnCl₂·H₂O]₂·18-crown-6}_n in solution have been investigated by HMBC NMR. The results show that coordination of water to tin containing species and its hydrogen bonding to crown ether remains intact in non-coordinating solvent in contrast to coordinating solvent. H-NMR reveals that the chemical shift of water in complex varies by solvent of crystallization.     

Efficient and practical Ag-catalyzed cycloadditions between arylimines and the Danishefsky diene

An efficient Ag-catalyzed method for asymmetric addition of the Danishefsky diene to various aryl imines to afford cycloadducts in > or =89% ee and > or =85% isolated yield is reported. Reactions are effected with 0.1-1 mol % catalyst (4 degrees C), and the chiral ligand is readily prepared from commercially available materials, including the inexpensive i-Leu. These catalytic asymmetric cycloadditions can be carried out without the use of solvent or with undistilled THF in air. A first generation supported chiral catalyst that effectively promotes the cycloaddition reaction and can be recycled (five cycles) is described.     

Hydrodynamics of a bounded vertical film with nonlinear surface properties

The drainage of a thin liquid film with an insoluble monolayer down a vertical wall is studied. Lubrication theory is used to develop a model where the film is pinned at the top with a given thickness and the film drains into a bath at the bottom. A nonlinear equation of state is used for the surface tension and the surface viscosity is a nonlinear function of the surfactant concentration; these are appropriate for some aqueous systems. The three partial differential equations are solved via discretization in space and then the resulting differential algebraic system is solved. Results are described for a wide range of parameters, and the conditions under which the free surface is immobilized are discussed.     

Separation of peptides and proteins by capillary electrophoresis using acidic buffers containing tetraalkylammonium cations and cyclodextrins

A method for improving separations of peptides and other positively charged species in capillary zone electrophoresis with untreated capillaries using acidic buffers containing tetraalkylammonium cations is described. Tetramethylammonium and tetrabutylammonium cations dynamically modify the capillary surface, leading to a reversal in the direction of the electroosmotic flow. As a result, the adsorption of positively charged peptides and proteins is minimized, and resolution and peak capacity are improved as the migration of cationic analytes is counterbalanced by the electroosmotic flow. The combining effect of reversing electroosmotic flow and cyclodextrin inclusion complexation on separations of closely related peptides and a protein mixture, as well as tryptic digest of hemoglobin is demonstrated.     

Quantitative reaction cascades of ninhydrin in the solid state

Crystalline ninhydrin (1) undergoes waste-free solid-state cascade reactions with dimedone, L-proline, three o-phenylenediamines, o-mercaptoaniline, two ureas, three thioureas, and methyl 3-aminocrotonate. The yields are quantitative and give pure crystalline products without workup just by milling stoichiometric mixtures of the crystalline reagents. The structures of the new and the previously obtained products with lower yields from solutions are established or confirmed by spectroscopic data and density functional calculations at the B3LYP/6-31G* level. The success of 3- and 4-cascade reactions in the crystal without melting is unusual and of unmatched atom economy. They are mechanistically investigated with atomic force microscopy techniques (AFM) on six different faces of 1 when o-phenylenediamine was the reagent (substitution, elimination, cyclization, elimination) and interpreted on the basis of known crystal structure data. Strict correlations to the crystal packings are observed. The characteristic surface features grow to microm heights in some cases at distances of 0.5 mm from the contact edge of the reacting crystals. The waste-free and easy syntheses of highly functionalized (C=O; O-H; C=N) heterocycles or of a tetraketone are also of interest for synthetic use.