Showing papers on "Hexane published in 1993"

X-ray crystal structure of gamma -chymotrypsin in hexane

Abstract: Crystals of gamma-chymotrypsin grown in aqueous solution were soaked in n-hexane, and the structures of both the soaked and the native crystals were determined to 2.2-A resolution. Seven hexane molecules and 130 water molecules were found in the hexane-soaked crystals. Two of the seven hexane molecules are found near the active site, and the rest are close to hydrophobic regions on or near the surface of the enzyme. In the hexane structure, water molecules that were not observed in the native structure form a clathrate around one of the hexane molecules. Only 97 water molecules were found in the native structure. The temperature factors for atoms in the hexane environment are lower than those in the aqueous environment. There are significant changes between the two structures in the side chains of both polar and neutral residues, particularly in the vicinity of the hexane molecules. These changes have perturbed the hydrogen-bonding patterns. The electron density for the peptide bound in the active site has been dramatically altered in hexane and appears to be tetrahedral at the carbon that is covalently bound to Ser 195. The crystalline enzyme retains its active conformation in the nonpolar medium and can catalyze both hydrolysis and synthesis reactions in hexane.

Side-chain order in poly(3-alkylthiophenes)

Abstract: The structures of unoriented films of poly(3-alkylthiophenes) were studied by X-ray diffraction, IR spectroscopy, and organic vapor sorption. Side-chain crystallization takes place in these films when the alkyl groups contain 12 or more carbon atoms. The disordering of the side chain upon melting results in a large increase in the amount of hexane vapor absorbed by poly(3-tetradecylthiophene) (PTDT) when the temperature is raised to above the melting point. The effective distance of side-chain overlap, an measured by hexane as the diffusional probe, is estimated to be 6.7 A along the α-axis

cis-Stilbene photochemistry: solvent dependence of the initial dynamics and quantum yields

Abstract: Photochemical quantum yields for the formation of Trans-stilbene and 4a,4b-dihydrophenanthrene from cis-stilbene have been measured in cyclohexane, hexane, acetonitrile, and methanol solvents. Degassed cis-stilbene samples at 27 o C were irradiated at 280 nm, and the formation of photoproducts was monitored by absorption spectroscopy. The quantum yield for formation of dihydrophenanthrene is two to three times greater in the nonpolar solvents than in the polar ones (15-19% vs 5-8%), while a slight solvent dependence of the yield of trans-stilbene is observed (35-39%in the polar solvents vs 32-35% in the hydrocarbons)

Three extraction methods for determination of lipids in fish meal: Evaluation of a hexane/isopropanol method as an alternative to chloroform-based methods

Abstract: Three different extraction methods were compared for the determination of lipids in both oxidised and antioxidant-stabilised brown fish meal. The three methods under investigation were those of Smith-Ambrose-Knobl using chloroform/methanol/water, Bligh and Dyer also using chloroform/methanol/water but monophasic, and Hara and Radin using hexane/isopropanol. The fat content, determined gravimetrically, was significantly lower (P < 0.05) when hexane/isopropanol was used for lipid extraction from both oxidised and antioxidant-stabilised fish meal, than when either of the chloroform systems was used. Determination of lipid classes in the lipid extracts using silica gel thin-layer chromatography on Chromarods-SIII, with flame ionisation detection by latroscan, suggested that the lower lipid recovery by the hexane/isopropanol method may be due to a less effective extraction of the more polar lipid classes. including oxidation products, present in brown fish meal.

Molecular dynamics studies of the melting of butane and hexane monolayers adsorbed on the basal‐plane surface of graphite

Abstract: The effect of molecular steric properties on the melting of quasi‐two‐dimensional solids is investigated by comparing results of molecular dynamics simulations of the melting of butane and hexane monolayers adsorbed on the basal‐plane surface of graphite. These molecules differ only in their length, being members of the n‐alkane series [CH3(CH2)n−2CH3] where n=4 for butane and n=6 for hexane. The simulations employ a skeletal model, which does not include the hydrogen atoms explicitly, to represent the intermolecular and molecule–substrate interactions. Nearest‐neighbor intramolecular bonds are fixed in length, but the molecular flexibility is preserved by allowing the bend and dihedral torsion angles to vary. The simulations show a qualitatively different melting behavior for the butane and hexane monolayers consistent with neutron and x‐ray scattering experiments. The melting of the low‐temperature herringbone (HB) phase of the butane monolayer is abrupt and characterized by a simultaneous breakdown of ...

Vapor pressures of binary mixtures of hexane + 1-butanol, + 2-butanol, + 2-methyl-1-propanol, or + 2-methyl-2-propanol at 298. 15 K

Abstract: Previous papers from this laboratory reported measurements of excess enthalpies, excess volumes, vapor pressures, and dipole moments for mixtures containing an alkanol. The authors have now begun a systematic study of the properties of mixtures containing isomeric butanols. While many studies of the thermodynamic properties of 1-butanol have been published, only a few systematic investigations have been carried out for mixtures containing isomeric butanols. The total vapor pressures of binary mixtures of hexane + 1-butanol, + 2-butanol, + 2-methyl-1-propanol, or + 2-methyl-2-propanol were measured by a static method at 298.15 K. Vapor-phase compositions, activity coefficients, and excess molar Gibbs energies were calculated by Barker's method.

Solubility of anthracene in binary alkane + 1-propanol and alkane + 1-butanol solvent mixtures

Abstract: Article on the solubility of anthracene in binary alkane + 1-propanol and alkane + 1-butanol solvent mixtures.

Modification of metabolism and neurotoxicity of hexane by co-exposure of toluene.

Abstract: The effects of co-exposure of hexane and toluene were investigated in field surveys and animal experiments. One field survey suggested that increase of hexane content in adhesives might have caused an outbreak of polyneuropathy in a vinyl sandal manufacture in Japan. The animal experiments proved that co-exposure of hexane and toluene decrease hexane neurotoxicity and urinary excretion of hexane metabolites in rats. The results also suggested that toluene might inhibit metabolism of hexane. Another recent field survey indicated that the ratio of urinary 2,5-hexanedione to hexane exposure in the workers co-exposed to hexane and toluene decreased in parallel with in more crease of toluene concentration. The results indicated that urinary excretion of 2,5-hexanedione could be depressed by co-exposure of toluene even in the workers exposed to relatively low concentrations. These above-mentioned results suggest that co-exposure of hexane and toluene could inhibit hexane metabolism and decrease hexane neurotoxicity in both experimental animals and workers. Although metabolism of hexane could be easily modified by toluene or other solvents and might not be a good indicator for hexane exposure in mixed exposure, urinary 2,5-hexanedione might be a good indicator for neurotoxicity of hexane even in mixed exposure.

Adsorption isotherms of sesame oil in a concentrated miscella system

Abstract: The adsorption of peroxides, unsaturated carbonyls, free fatty acids and carotenoids from unrefined sesame oil on vegetable carbon (5%, w/w) in a miscella system was studied. Three different solvent conditions (hexane/ethanol, 100:0, 95:5 and 75:25, vol/vol), combined in a factorial design with five levels of solvent (0, 10, 20, 30 and 40%, w/w), were used to develop the miscella. Equilibrium adsorption was not achieved during the 100 min of adsorption, mainly because the oil components were involved in oxidation reactions during the adsorption process. However, for a given solvent concentration, adsorption of the oil components showed a significant linear regression on their respective initial concentration in the miscella (Ci). Peroxides and carbonyls showed, at all solvent levels investigated, an affinity for the carbon more independent of their Ci than free fatty acids and carotenoids. In general, at the same Ci, a higher adsorption was achieved as solvent concentration increased. The results indicated that free fatty acid adsorption may depend on competitive adsorption based on molecule hydrophobicity. However, in spite of the higher hydrophobicity of carotenoids, compared with free fatty acids, they might not be competing for the same adsorbing sites. Ethanol showed a prooxidant effect that increased peroxide production during adsorption but did not affect the reaction involved in carbonyl production.

Hydrocarbon conversion catalyst for producing high quality gasoline and C3 and C4 olefins

Abstract: A hydrocarbon conversion catalyst for converting petroleum distillates of different boiling ranges, residue oils, and crude oils, especially the heavy hydrocarbons containing high nickel, into high quality gasoline and C3 and C4 olefins. The catalyst of the invention comprises three zeolitic active components consisting of a rare-earth-containing pentasil type high silica zeolite ZRP, a REY zeolite, and a high silica Y zeolite, in a total content of 10-40 wt % based on the total weight of the catalyst, and the remainder synthetic matrix or semi-synthetic matrix comprising 10-40 wt % silica and/or alumina binder. In the total amount of the active components, zeolite ZRP, REY, and the high silica Y are 3-50, 12-75, and 12-75 wt % respectively. The zeolite ZRP used in the catalyst is characterized in an anhydrous chemical composition of the formula 0.01-0.30 RE2 O3.0.4-1.0 Na2 O.Al2 O3.20-60 SiO2 , a specific X- ray diffraction pattern, a higher adsorption capacity ratio of normal hexane to cyclohexane, and a rare earth ingredient which originates from a rare earth containing faujasite used as seed in the synthesis of the zeolite.

Vapor-liquid equilibria of mixtures of propane and isomeric hexanes

Abstract: Vapor-liquid equilibrium data ertending to critical pressures are reported for mixtures of propane with each of the hexane isomers, n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane. Dew-bubble curves for five different compositions are tabulated for each of the five mixtures. The data in pressure, temperature, and density are successfully correlated by the Leung-Griffiths model as modified by Moldover, Rainwater, and co-workers. The coexistence surfaces are all quite similar with only subtle differences due to the different shapes of the isomeric hexane molecules

Solvent sensitivity of the wavenumber characterising the carbonyl stretching vibration of N-cyclohexyl-2-pyrrolidinone dissolved in pure liquids and in mixtures formed by hexane and deuteriotrichloromethane at 298.2 K

Abstract: The dependence of (CO) on solvent for N-cyclohexyl-2-pyrrolidinone (NCP) as solute in 18 pure solvents can be described using a two-parameter equation based on the Taft–Kamlet π*(dipolarity/polarisability) and α proton donor parameters In alcoholic solvents two bands are recorded, the band at the lower wavenumber following the correlation When CDCl3 is added to a solution of NCP in hexane, (CO) shifts to lower wavenumbers but over a range of mixture compositions two bands are also observed characteristic of the carbonyl group in NCP The origin of these bands is discussed in terms of two types of hydrogen bonding together with their individual dependences on mixture composition Comparisons are drawn with the solvent sensitivities of (CO) for propanone, cyclohexanone and dimethylacetamide

Solid catalysts treated with anions: XXI. Zirconia-supported chromium catalyst for dehydrocyclization of hexane to benzene

Abstract: A dehydrogenation catalyst for alkanes was obtained by immersing Zr(OH)4 in 0.05M (NH4)2CrO4, followed by calcination in air at 600–800°C and reduction at 550°C (0.5 wt.-% Cr). This catalyst converted hexane into benzene with a selectivity of up to 89% under pulse conditions, and the yield of benzene at 550° C was steady up to 6 h with 76% selectivity in a flow system at atmospheric pressure. HfO2 was also effective as a support, but Al2O3, SiO2, TiO2, and SnO2 were not. Measurements of ESR and XPS showed the ZrO2 catalyst to be CrIII-CrIV, created by reduction of CrO42−/ZrO2.

Solubility of Pyrene in Binary Alkane + 1-Propanol and Alkane + 2-Propanol Solvent Mixtures

Abstract: Article on the solubility of pyrene in binary alkane + 1-propanol and alkane + 2-propanol solvent mixtures.

TRANSLATIONAL MOBILITY OF n-BUTANE AND n-HEXANE IN ZSM-5 MEASURED BY QUASI-ELASTIC NEUTRON SCATTERING

Abstract: The translational and rotational dynamics of n-butane and n-hexane adsorbed in ZSM-5 have been studied by quasi-elastic neutron scattering. The self-diffusion coefficients, mean jump lengths and activation energies for diffusion are derived and compared with the results obtained by other techniques. A relationship is observed between the diffusion coefficient measured by neutron scattering and the carbon number of a series of n-alkanes (methane, ethane, propane, butane and hexane). The alkanes are found to reside mainly in the pore segments rather than in the channel intersections. The activation energy for self-diffusion is similar for all the alkanes of the series, ≈ 5 kJ mol-1.

Interaction of benzene and n-hexane molecules with OH-groups of various acid strengths in NaHZSM-5 zeolite

Abstract: The 3609 cm−1 OH-groups in NaHZSM-5 zeolites are heterogeneous, 5 kinds of OH-groups being found. Benzene is more strongly bonded to more acidic hydroxyls and n-hexane to less acidic hydroxyls.

The essential oil of Scaligeria lazica Boiss.

Abstract: The water-distilled essential oil of Scaligeria lazica, an endemic species in Turkey, was determined by GC and GC/MS. Thirty-six constituents representing 92% of the oil were identified with (E)-anethole (49.67%) as the major component. In the hexane extract of the aqueous distillate from which the oil was separated, 2-hydroxy-5-methoxy-benzaldehyde (21.51%) and phenylacetaldehyde (14.40%) were found to be the major components.

The heat of oxidation of 1,2-di-n-butylhydrazine to azo-n-butane

Abstract: 1,2-Di-n-butylhydrazine in hexane solution has been oxidized to azo-n-butane with oxygen and Pd/C catalyst and with red mercuric oxide. Both methods led to the same calculated heat of hydrogenation (ΔH H ) of the azo group in hexane, -16.4±0.3 kcal/mol. This value is 10.6 kcal/mol less exothermic than the ΔH H of carbon-carbon double bonds

Interrelationships among C6F10 valence isomers

Abstract: Thermal and photochemical interconversions among the three valence isomers perfluoro-1,5-hexadiene (1), perfluorobicyclo[2.2.0]hexane(2), and perfluorobicyclo[2.1.1]hexane (3) have been explored. At 250 o C 1 and 2 existin eguilibrium with K 1→2 =1.1, but at higher temperatures irreversible isomerization to 3 becomes rapid. This chemistry contrasts sharply with the behavior of the corresponding hydrocarbons, where the diene is lowest in free energy. Mercury-sensitized photolysis of diene 1 yields 3 and 2 in ratios of 3-4:1. The cleanness of both the thermal and the photochemistry, together with thermodynamics favorable to cyclization, bode well for synthesizing new bicyclic and polycyclic fluorocarbons from other unsaturated precursors

Production of carbon cluster c60

Abstract: PURPOSE:To obtain a carbon cluster C60 of improved purity by separating carbon cluster C60 through liquid column chromatography from a carbon cluster mixture obtained by extracting soot in an exhaust gas from an internal combustion engine with an aromatic hydrocarbon. CONSTITUTION:A fuel such as gasoline is burned in the cylinder of an internal combustion engine and soot is collected from the exhaust gas from an exhaust vent. The soot is then extracted with an aromatic hydrocarbon such as benzene using a Soxhlet extractor to obtain a carbon cluster mixture whose content is 0.1-5wt.% in the soot. On subjecting the mixture to mass spectroscopy, carbon cluster (hereafter, referred to as fullerene) C60 and fullerene C70 can be recognized at mass/charge of 720 and 840, respectively. The mixture is then developed with e.g. hexane using liquid column chromatography packed with neutral Al2O3 as absorbent to obtain a hexane solution of fullerene C60 followed by evaporating the hexane, thus obtaining the objective high-purity fullerene C60.

Separation of hexane from vinyl acetate by azeotropic distillation

Abstract: Hexane cannot be separated from vinyl acetate by conventional distillation or rectification because of the minimum boiling azeotrope. Hexane can be readily separated from vinyl acetate by using azeotropic distillation. Typical examples of effective agents are acetone, acetonitrile or methyl t-butyl ether.