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21.
Martí MP Pino J Boqué R Busto O Guasch J 《Analytical and bioanalytical chemistry》2005,382(2):440-443
The aromatic composition of sugar cane spirits and, in general, of alcoholic beverages, is mainly influenced by the ageing process in wood barrels. There are several factors that affect the quality of the final aged product, but the time of the storage in the barrel is perhaps the most important one. Ageing time must therefore be controlled in order to detect counterfeits; however, this parameter is very difficult to control and, at present, there is no analytical method available to determine it. We propose a quantitative method for determining the ageing time of sugar cane spirits in oak barrels by using an electronic nose based on coupling directly a headspace sampler to a mass spectrometer (HS-MS), and multivariate calibration. The method developed is simple and provides, in 5 min, the ageing time of spirits with an accuracy of about 1 month. 相似文献
22.
Various high levels of theory have been applied to the characterization of two higher lying biradicaloid metastable singlet states of peroxynitrous acid. A singlet minimum (cis-2) was located that had an elongated O-O distance (2.17 A) and was only 12.2 kcal/mol [UB3LYP/6-311+G(3df,2p)+ZPVE] higher in energy than its ground-state precursor. A trans-metastable singlet (trans-2) was 10.9 kcal/mol higher in energy than ground-state HO-ONO. CASSCF(12,10)/6-311+G(d,p) calculations predict the optimized geometries of these cis- and trans-metastable singlets to be close to those obtained with DFT. Optimization of cis- and trans-2 within the COSMO solvent model suggests that both exist as energy minima in polar media. Both cis- and trans-2 exist as hydrogen bonded complexes with several water molecules. These collective data suggest that solvated forms of cis-2.3H(2)O and trans-2.3H(2)O represent the elusive higher lying biradicaloid minima that were recently (J. Am. Chem. Soc. 2003, 125, 16204) advocated as the metastable forms of peroxynitrous acid (HOONO). The involvement of metastable trans-2 in the gas phase oxidation of methane and isobutane is firmly established to take place on the unrestricted [UB3LYP/6-311+G(d,p)] potential energy surface (PES) with classical activations barriers for the hydrogen abstraction step that are 15.7 and 5.9 kcal/mol lower than the corresponding activation energies for producing products methanol and tert-butyl alcohol formed on the restricted PES. The oxidation of dimethyl sulfide and dimethyl selenide, two-electron oxidations, proceeds by an S(N)2-like attack of the heteroatom lone pair on the O-O bond of ground-state peroxynitrous acid. No involvement of metastable forms of HO-ONO was discernible. 相似文献
23.
Triolo A Russina O Hardacre C Nieuwenhuyzen M Gonzalez MA Grimm H 《The journal of physical chemistry. B》2005,109(46):22061-22066
A detailed investigation on the nature of the relaxation processes occurring in a typical room temperature ionic liquid (RTIL), namely, 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim][PF(6)]), is reported. The study was conducted using both elastic and inelastic neutron scattering over a wide temperature range from 10 to 400 K, accessing the dynamic features of both the liquid and glassy amorphous states. In this study, the inelastic fixed energy scan technique has been applied for the first time to this class of materials. Using this technique, the existence of two relaxation processes below the glass transition and a further diffusive process occurring above the glass-liquid transition are observed. The low temperature processes are associated with methyl group rotation and butyl chain relaxation in the glassy state and have been modeled in terms of two Debye-like, Arrhenius activated processes. The high temperature process has been modeled in terms of a Kohlraush-Williams-Watts relaxation, with a distinct Vogel-Fulcher-Tamman temperature dependence. These results provide novel information that will be useful in rationalizing the observed structural and dynamical behavior of RTILs in the amorphous state. 相似文献
24.
Lebedeva OV Kim BS Vinogradova OI 《Langmuir : the ACS journal of surfaces and colloids》2004,20(24):10685-10690
By using a combination of atomic force and confocal microscopy, we explore the deformation properties of multilayer microcapsules filled with a solution of strong polyelectrolyte. Encapsulation of polyelectrolyte was performed by regulation of the multilayer shell permeability in water-acetone solutions. The "filled"capsules prepared by this method were found to be stiffer than "hollow" ones, which reflects the contribution of the excess osmotic pressure to the capsule stiffness. The force-deformation curves contain three distinct regimes of reversible, partially reversible, and irreversible deformations depending on the degree of compression. The analysis of the shape of compressed capsules and of the inner polyelectrolyte spacial distribution allowed one to relate the deformation regimes to the permeability of the multilayer shells for water and inner polyelectrolyte at different stage of compression. 相似文献
25.
Kassi S Macko P Naumenko O Campargue A 《Physical chemistry chemical physics : PCCP》2005,7(12):2460-2467
The absorption spectrum of natural water vapour around 750 nm has been recorded with a typical sensitivity of 3 x 10(-10) cm(-1) using a cw cavity ring down spectroscopy set up based on a Ti:sapphire laser. The 13 312.4-13 377.7 cm(-1) spectral interval was chosen as it corresponds to the region where water dimer absorption was recently measured (K. Pfeisticker et al., Science, 2003, 300, 2078-2080). The line parameters (wavenumber and intensity) of a total of 286 lines of water vapor were measured by a one by one fit of the lines to a Voigt profile. For the main water isotopologue, 276 lines were measured with line intensities as weak as 5 x 10(-29) cm molecule(-1)i.e. about 50 times smaller than the weakest H(2)16O line intensities included in the 2004 edition of the HITRAN database. On the basis of the predictions of Schwenke and Partridge, all but 16 lines could be assigned to different isotopologues of water (H(2)16O, H(2)18O, and HD16O) present in natural abundance in the sample. A total of 272 energy levels of H(2)16O were determined and rovibrationally assigned to 18 upper vibrational states. Half of them had not been reported previously. The importance of the additional absorbance resulting from the observation of many new weak lines is discussed in relation to the detection of water dimer absorption and compared to the absorbance predicted by Schwenke and Partridge. The quality of the line parameters of water monomer is shown to be of crucial importance to identify the absorbance of the water dimer in the considered region. 相似文献
26.
Lead is extracted from urine with ammonium pyrrolidien dithiocrbamate into methyl isobutyl ketone, and 20 μl of the extract is injected into a water carrier stream in a flow-injection/atomic absorption system. The procedure is simple, quick, accurate and reproducible. Recoveries are 96–105%. The mean urine lead contents of 20 unexposed and 20 printing-press lead exposed workers was found to be 39.0 ± 8.3 and 71.7 ± 26.3 μg Pb l?1, respectively. 相似文献
27.
Synthesis and characterization of nanoparticulate MnS within the pores of mesoporous silica 总被引:1,自引:0,他引:1
Louse Barry Mark Copley Justin D. Holmes David J. Otway Olga Kazakova Michael A. Morris 《Journal of solid state chemistry》2007,180(12):3443-3449
Mesoporous silica was loaded with nanoparticulate MnS via a simple post-synthesis treatment. The mesoporous material that still contained surfactant was passivated to prevent MnS formation at the surface. The surfactant was extracted and a novel manganese ethylxanthate was used to impregnate the pore network. This precursor thermally decomposes to yield MnS particles that are smaller or equal to the pore size. The particles exhibit all three common polymorphs. The passivation treatment is most effective at lower loadings because at the highest loadings (SiO2:MnS molar ratio of 6:1) large particles (>50 nm) form at the exterior of the mesoporous particles. The integrity of the mesoporous network is maintained through the preparation and high order is maintained. The MnS particles exhibit unexpected ferromagnetism at low temperatures. Strong luminescence of these samples is observed and this suggests that they may have a range of important application areas. 相似文献
28.
Serganov A Yuan YR Pikovskaya O Polonskaia A Malinina L Phan AT Hobartner C Micura R Breaker RR Patel DJ 《Chemistry & biology》2004,11(12):1729-1741
Metabolite-sensing mRNAs, or "riboswitches," specifically interact with small ligands and direct expression of the genes involved in their metabolism. Riboswitches contain sensing "aptamer" modules, capable of ligand-induced structural changes, and downstream regions, harboring expression-controlling elements. We report the crystal structures of the add A-riboswitch and xpt G-riboswitch aptamer modules that distinguish between bound adenine and guanine with exquisite specificity and modulate expression of two different sets of genes. The riboswitches form tuning fork-like architectures, in which the prongs are held in parallel through hairpin loop interactions, and the internal bubble zippers up to form the purine binding pocket. The bound purines are held by hydrogen bonding interactions involving conserved nucleotides along their entire periphery. Recognition specificity is associated with Watson-Crick pairing of the encapsulated adenine and guanine ligands with uridine and cytosine, respectively. 相似文献
29.
Perišić-Janjić Nada U. Ž. Jovanović Bratislav Janjić Natasa J. Rajković Olga S. Antonović Dušan G. 《平面色谱法杂志一现代薄层色谱法》2003,16(6):425-432
JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of nine newly synthesized s-tri-azines has been studied by thin-layer chromatography on C18/UV254... 相似文献
30.
The UV-absorption, fluorescence excitation and emission spectra of the alkaloids eudistomin N (6-bromo-nor-harmane) and eudistomin O (8-bromo-nor-harmane) were described. In order to perform a comparative analysis, we also studied other bromo-beta-carbolines and the corresponding non-substituted-carboline. Thus, 6-bromo-, 8-bromo-, 6,8-dibromo-, 3,6-dibromo- and 3,6,8-tribromo-derivatives of nor-harmane, harmane and harmine were studied. These studies were performed in EtOH and in EtOH + 1% perchloric acid solutions (pa). Furthermore, fluorescence quantum yields (phi(f)) in acetonitrile and acetonitrile + 1% perchloric acid solutions at 298 K were measured. The HOMO and LUMO energy, the positions (lambda(max)) and oscillator strength (f) of the (1)S(1) <--(1)S(0) band for all the neutral and protonated beta-carbolines studied was calculated and compared with the experimental data. The pK(a) values in aqueous solution for eudistomin N and O (6-bromo- and 8-bromo-nor-harmane), for 6-bromo-, 8-bromo- and 6,8-dibromo-harmane, and for 6-bromo- and 8-bromo-harmine were spectrophotometrically measured (pK((a)(H(2)O))) . The change of the acid-base character of these compounds on going from the ground state (pK(a)) to the first electronic excited singlet state (pK(a)(*)) as DeltapK(a) = pK(a)(*)-pK(a) = 0.625 Deltanu /T, in ethanol solution at 298 K were calculated (DeltapK(a(EtOH))). Proton affinities (PA) for all the compounds studied defined as minus the enthalpy change of the reaction M+H(+)--> MH(+) (gas state) were calculated. Basicity relative to pyridine (DeltaH(rPy)) defined as the enthalpy change of the isodesmic reaction MH(+) + Py--> M + PyH(+) (gas state) was also calculated. The effect of bromine as substituent on the properties of the beta-carboline moiety in nor-harmane, harmane and harmine is discussed. 相似文献