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Query: CAS:142-82-5 (heptane)
 3,094 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Seventeen pure aerobic microbial isolates were obtained from soil samples of three regions of Antarctica: Casey Station, Dewart Island and Terra Nova Bay. Most of them were gram positive coryneform bacteria. Isolates were tested for their ability to grow on mineral salt agar plates supplemented with one of the following model n-alkanes or aromatic hydrocarbons: hexane, heptane, paraffin, benzene, toluene, naphthalene and kerosene. Cell hydrophobicity, the ability to produce anionic glycolipids and extracellular emulsifying activity were also determined and assessed on the basis of growth of soil isolates on hydrocarbons. This study revealed degraders with broader abilities to grow on both types of hydrocarbons, good production of glycolipids and emulsifying activity. On this basis, a mixed culture of strains is proposed, which may find application for bioremediation at temperate temperature of soil environments polluted with different hydrocarbons.
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PMID:Potential for biodegradation of hydrocarbons by microorganisms isolated from Antarctic soils. 1501 68

A method of effective application of normal-phase high-performance liquid chromatography (NP-HPLC) with ultraviolet diode array detection (DAD) and refractive index detection (RID) for the determination of class composition of gasoline and its components, i.e. for the determination of content of alkenes, aromatic and saturated hydrocarbons in gasoline meeting modern quality standards, has been developed. An aminopropyl-bonded silica stationary phase was used along with n-hexane or n-heptane as the mobile phase. A DAD signal integrated over the 207-240 nm range was used to determine alkenes. This eliminates the necessity of separating alkenes from saturates, because the latter do not absorb UV radiation above 200 nm. The content of aromatic hydrocarbons is determined by means of a refractive index detector. Calibration was based on hydrocarbon type composition determined by the fluorescent indicator adsorption method, ASTM D1319. The results obtained by the developed method were found to be consistent with those obtained by fluorescent indicator adsorption or by a multidimensional GC method (PIONA) (ASTM D5443). The method can be applied to gasoline meeting recent quality standards, irrespective of refining technology used in the production of gasoline components, including gasoline with various contents of oxygenates. The developed method cannot be used to determine the hydrocarbon type composition of gasoline that contains as a component the so-called pyrocondensate, i.e. the fraction with a boiling point up to 220 degrees C, obtained through thermal pyrolysis of distillation residues of crude oil or coal and, consequently, does not meet the quality standards. The paper includes the procedure for identification of this type of gasoline.
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PMID:Application of high-performance liquid chromatography with ultraviolet diode array detection and refractive index detection to the determination of class composition and to the analysis of gasoline. 1503 52

Carbon-carbon spin-spin coupling constants were calculated at the SOPPA level for a series of seven classical spiroalkanes, spiro[2.2]pentane, spiro[2.3]hexane, spiro[2.4]heptane, spiro[2.5]octane, spiro[3.3]heptane, spiro[4.4]nonane and spiro[5.5]undecane, with special focus upon couplings involving and/or across spiro carbons. Many interesting structural trends were investigated originating in specific geometries and unusual bonding environments at the spiro carbon.
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PMID:Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 7--spiroalkanes. 1513 43

Sulphuric acid impregnated silica was used for the lipid free extraction of polychlorinated biphenyls from fat containing food and feed matrices using pressurized liquid extraction on a Dionex ASE300, with 34 mL cells. Data were compared to a previous publication where extractions had been performed on a Dionex ASE200, with 33 mL cells. Four different fat/fat retainer ratios (FFRs) were tested (0.100, 0.075, 0.050 and 0.025) at 50 and 100 degrees C using n-pentane, n-hexane or n-heptane as extraction solvent. The best results were obtained with a FFR of 0.025 when applying a temperature of 100 degrees C. Both n-pentane and n-heptane were capable of replacing n-hexane as extraction solvent. A flush volume of 60% was sufficient as suggested in US Environmental Protection Agency Method 3545. The applicability of the method was demonstrated for naturally contaminated fish meal as well as various spiked and certified materials.
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PMID:Selective pressurized liquid extraction of polychlorinated biphenyls from fat-containing food and feed samples influence of cell dimensions, solvent type, temperature and flush volume. 1523 May 21

We studied the effect of segmented solvent molecules on the free energy of transfer of small molecules from water into alkanes (hexane, heptane, octane, decane, dodecane, tetradecane, and hexadecane). For these alkanes we measured partition coefficients of benzene, 3-methylindole (3MI), 2,3,4,6-tetrachlorophenol (TeCP), and 2,4,6-tribromophenol (TriBP) at 3, 11, 20, 33 [corrected], and 47 degrees C. For 3MI, TeCP, and TriBP the dependence of free energy of transfer on length of alkane chains was found to be very different from that for benzene. In contrast to benzene, the energy of transfer for 3MI, TeCP, and TriBP was independent of the number of carbons in alkanes. To interpret data, we used the classic Flory-Huggins (FH) theory of concentrated polymer solutions for the alkane phase. For benzene, the measured dependence of energy of transfer on the number of carbons in alkanes agreed well with predictions based on FH model in which the size of alkane segments was obtained from the ratio of molar volumes of alkanes and the solute. We show that for benzene, the energy of transfer can be divided into two components, one called environmental swap energy (ESE), and one representing the contribution of configurational entropy of alkane chains. For 3MI, TeCP, and TriBP the contribution of configurational entropy was not measurable even though the magnitude of the effect predicted from the FH model for short chain alkanes was as much as 20 times greater than experimental uncertainties. From the temperature dependence of ESE we obtained enthalpy and entropy of transfer for benzene, 3MI, TeCP, and TriBP. Experimental results are discussed in terms of a thermodynamic cycle considering creation of cavity, insertion of solute, and activation of solute-medium attractive interactions. Our results suggest that correcting experimental free energy of transfer by Flory-Huggins configurational entropy term is not generally appropriate and cannot be applied indiscriminately.
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PMID:Environmental swap energy and role of configurational entropy in transfer of small molecules from water into alkanes. 1526 64

Solid-fluid and solid-solid phase equilibrium for binary mixtures of hard sphere chains modeling n-hexane, n-heptane, and n-octane has been calculated using Monte Carlo computer simulations. Thermodynamic integration was used to calculate the Gibbs free energy and chemical potentials in the solid and fluid phases from pure component reference values. A multiple stage free energy perturbation method was used to calculate the composition derivative of the Gibbs free energy. Equation of state and free energy data for the fluid phase indicate ideal solution behavior. Nonideality is much more significant in the solid phase with only partial solubility of shorter chains in the longer chains and essentially no solubility at the other end of the composition range. The miscibility decreases with increasing chain length difference between the components. For the model of n-hexane/n-octane mixtures solid--solid phase separation has been observed directly in some of the simulations, with the components segregating between the layers of the solid structure. The behavior is similar to that seen in some binary n-alkane mixtures with longer chain lengths but comparable chain length ratios between the components. Such phase separation, although indicated thermodynamically, is not seen directly in the simulations of the n-heptane/n-octane mixture due to the difference in the pure component crystal structures.
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PMID:Solid-fluid and solid-solid phase equilibrium in a model of n-alkane mixtures. 1526 45

It has been known that halophilic bacteria often show natural resistance to antibiotics, dyes, and toxic metal ions, but the mechanism and regulation of this resistance have remained unexplained. We have addressed this question by identifying the gene responsible for multidrug resistance. A spontaneous ofloxacin-resistant mutant derived from the moderately halophilic bacterium Chromohalobacter sp. strain 160 showed a two- to fourfold increased resistance to structurally diverse compounds, such as tetracycline, cefsulodin, chloramphenicol, and ethidium bromide (EtBr), and tolerance to organic solvents, e.g., hexane and heptane. The mutant produced an elevated level of the 58-kDa outer membrane protein. This mutant (160R) accumulated about one-third the level of EtBr that the parent cells did. An uncoupler, carbonyl cyanide m-chlorophenylhydrazone, caused a severalfold increase in the intracellular accumulation of EtBr, with the wild-type and mutant cells accumulating nearly equal amounts. The hrdC gene encoding the 58-kDa outer membrane protein has been cloned. Disruption of this gene rendered the cells hypersusceptible to antibiotics and EtBr and led to a high level of accumulation of intracellular EtBr. The primary structure of HrdC has a weak similarity to that of Escherichia coli TolC. Interestingly, both drug resistance and the expression of HrdC were markedly increased in the presence of a high salt concentration in the growth medium, but this was not observed in hrdC-disrupted cells. These results indicate that HrdC is the outer membrane component of the putative efflux pump assembly and that it plays a major role in the observed induction of drug resistance by salt in this bacterium.
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PMID:Salt-inducible multidrug efflux pump protein in the moderately halophilic bacterium Chromohalobacter sp. 1529 69

The kinetic analysis of the adsorption of two carotenoids (i.e., ethyl ester of beta-apo-8'-carotenoic acid and beta-carotene, all trans-isomers) from n-hexane solutions at the oil/water interface is presented for several carotenoid concentrations in the oil phase. A new kinetic approach is developed and it addresses the diffusion adsorption associated with a reversible interfacial reaction, which describes the reorientation of surfactant molecules between two conformations. This approach leads to a general analytical expression that contains four physical parameters and describes with high accuracy the experimental dynamic interfacial tensions for the two carotenoids, which independently adsorb from n-hexane phase to the n-hexane/water interface. The calculations give the characteristic times for the carotenoid adsorption at the oil/water interface in terms of diffusion relaxation and kinetic relaxation times. The results explain the long time effects on the adsorption of these carotenoids at the oil/water interface. The data are in substantial agreement with the molecular structure of these carotenoids and with the earlier data recorded for cholesterol adsorption at the n-heptane/water interface. Based on these findings, we propose a molecular mechanism for the interfacial transformation of carotenoid molecules at a hydrophobic/hydrophilic interface.
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PMID:Adsorption kinetics of some carotenoids at the oil/water interface. 1534 17

A rapid, sensitive and novel narrow-bore liquid chromatography-mass spectrometric method was developed and fully validated for the quantification of citalopram in human plasma. The analyte and internal standard (imipramine) were extracted by liquid-liquid extraction with a mixture of hexane-heptane-isopropanol (88:10:2, v/v/v). The use of a Hypersil BDS C(8) micro-bore column (250 mm x 2.1 mm i.d.; 3.5 microm particle size), results in substantial reduction in solvent consumption. The mobile phase consisted of 10 mM ammonium formate-formic acid (pH 4.5) and acetonitrile (30:70, v/v), pumped at a flow rate of 0.15 ml min(-1). The analytes were detected after positive electrospray ionization using the selected ion-monitoring mode of the species at m/z 325 for citalopram and m/z 281 for imipramine. The method had a chromatographic run time of 10.0 min and a linear calibration curve over the range 0.50-250 ng ml(-1) (r(2) > 0.996). The limit of quantitation was 0.50 ng ml(-1). Accuracy and precision were below the acceptance limits of 15%.
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PMID:Liquid chromatography-positive ion electrospray mass spectrometry method for the quantification of citalopram in human plasma. 1538 Jul 20

The reversible encapsulation of a series of normal alkane guests in a cylindrical host was studied by NMR methods. For small hydrocarbons such as n-pentane or n-hexane, two guests enter the host, and they move freely within. With n-heptane no encapsulation takes place. For longer alkanes such as n-decane, a single guest enters and the aromatic walls of the host are seen to twist to avoid empty spaces and increase favorable interactions with the hydrocarbon. The best guest (n-undecane) adopts a conformation with minimal gauche interactions. The longest alkane accommodated, n-tetradecane, adopts a helical conformation to fit in the cavity, a shape that maximizes CH/pi interactions with the aromatic walls of the receptor. These reciprocal conformational changes are discussed in terms of optimal host/guest interactions.
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PMID:Helical folding of alkanes in a self-assembled, cylindrical capsule. 1547 7


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