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排序方式: 共有544条查询结果,搜索用时 46 毫秒
131.
This research paper presents a comparative study of two different extraction and concentration techniques to obtain representative pistachio aroma extracts: the traditional direct solvent extraction (DSE) followed by high-vacuum transfer (HVT) and the headspace solid-phase microextraction (HS-SPME). The results showed that, although both techniques provide accurate information about the aromatic composition that will be perceived by the consumer, the precision in terms of within-day repeatability and between-days repeatability (intermediate precision) of the chromatographic areas presented better values for HS-SPME than for DSE-HVT. Moreover the solvent-free HS-SPME allows the extraction of more odour-active regions, requires very little sample handling and shorter time for sampling. 相似文献
132.
Pàmies O Andersson PG Diéguez M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(48):14232-14240
This account discusses the progress made in the asymmetric hydrogenation of minimally functionalised terminal olefins as a new, alternative, sustainable and direct strategy for preparing enantioenriched hydrocarbons. It discusses the latest development in catalyst design, from the initial discovery of lanthanide catalytic precursors, through the use of transition-metal/diphosphine-iminophosphorane precursors, to the successful iridium/P,N catalytic systems. 相似文献
133.
Abd‐Elgawad Radi Xavier Muoz‐Berbel Montserrat Cortina‐Puig Jean‐Louis Marty 《Electroanalysis》2009,21(6):696-700
A novel protocol for immobilization of horseradish peroxidase (HRP) onto diazonium functionalized screen‐printed gold electrode (SPGE) has been successfully developed. This protocol involved 1) electrochemical reduction of p‐nitrophenyl diazonium salts synthesized in situ in acidic aqueous solution to graft a layer of p‐nitrophenyl on SPGE, 2) electrochemical reduction of the nitro groups to convert to amines, 3) chemical reaction with nitrous acid to transform the amine to diazonium derivative and 4) chemical coupling of the enzyme with the diazonium group to form a covalent diazo bond. The fabricated biosensor showed the direct electrochemistry of HRP and displayed electrocatalytic activity towards the reduction of hydrogen peroxide (H2O2) without any mediator. The biosensor exhibited fast amperometric response to H2O2. The catalytic current increased with increasing H2O2 concentration from 5 μM to 30 μM and the detection limit of the biosensor was 2 μM. The biosensor exhibited acceptable sensitivity, good reproducibility and long‐term stability. 相似文献
134.
Ying Wang Carole Calas‐Blanchard Montserrat Cortina‐Puig Liu Baohong Jean‐Louis Marty 《Electroanalysis》2009,21(12):1395-1400
A simple and sensitive electrochemical method for the determination of antioxidant capacity has been studied. 4‐hydroxybenzoic acid (4‐HBA) was used as a trapping agent for photogenerated .OH radicals, leading to 3,4‐dihydroxybenzoic acid (3,4‐DHBA). Square‐wave voltammetry was used to quantify the amount of 3,4‐DHBA formed from the reaction between 4‐HBA and .OH. Addition of antioxidants induced the competition between 4‐HBA and antioxidants toward .OH elimination, resulting in a decrease of the measured current. The IC50 for different standard antioxidants was calculated and expressed in Trolox equivalent antioxidant capacity (TEAC). The proposed method was successfully compared to a fluorimetric one. 相似文献
135.
Maria Jesús Sánchez-Martín José Manuel Amigo Montserrat Pujol Isabel Haro M. Asunción Alsina M. Antonia Busquets 《Analytical and bioanalytical chemistry》2009,394(4):1003-1010
The physicochemical characterization of the peptide sequence E1(145–162) corresponding to the structural protein E1 of the
hepatitis G virus was done by studying its interaction with model membranes. Small unilamellar vesicles (SUVs) of dimyristoylphosphatidylglycerol
or dimyristoylphosphatidylcholine were chosen as mimetic membranes. Peptide incorporation and location in the phospholipid
bilayer was investigated by fluorescence anisotropy with SUVs labeled with diphenylhexatriene (DPH) or trimethylammonium–DPH.
The addition of the peptide E1(145–162) showed significant changes in the anisotropy values of the probe located at the air/water
interface. These results indicate that the peptide E1(145–162) preferably interacts with the lipid surface without penetrating
inside the bilayer. A series of fluorescence experiments based on tryptophan peptide fluorescence were modeled by means of
multivariate curve resolution-alternating least squares (MCR-ALS) algorithm to further study the peptide interaction with
bilayers at different temperatures. The preliminary results obtained with MCR-ALS showed how the peptide concentration decay
is directly linked to the appearance of a new specie, which corresponds to the lipid-peptide binding. These results provide
useful information for the design of synthetic immunopeptides that can be incorporated into a liposomal system with potential
to promote a direct delivery of the membrane-incorporated immunogen to the immunocompetent cells, thus increasing the immuno
response from the host.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
136.
Several imidazo and pyrimido[1,2-a]pyrimidinones of type 1 and 2 were synthesized through intramolecular cyclization of pyrimidines 9 or pyrimidinones 10 bearing a variety of β and γ-aminoalcohols at the 2-position. Ring closure of the pyrimidinones of type 10 under Mitsunobu conditions lead to mixtures of both bicyclic regioisomers 1 and 2. Treatment of pyrimidines of type 9 with H2SO4 provided an efficient and operationally simple one-pot hydrolysis-cyclization procedure for obtaining imidazo and pyrimido[1,2-a]pyrimidinones 1 in good yields as the sole regioisomeric bicyclic product. 相似文献
137.
Flores-Moreno R Alvarez-Mendez RJ Vela A Köster AM 《Journal of computational chemistry》2006,27(9):1009-1019
A half-numeric algorithm for the evaluation of effective core potential integrals over Cartesian Gaussian functions is described. Local and semilocal integrals are separated into two-dimensional angular and one-dimensional radial integrals. The angular integrals are evaluated analytically using a general approach that has no limitation for the l-quantum number. The radial integrals are calculated by an adaptive one-dimensional numerical quadrature. For the semilocal radial part a pretabulation scheme is used. This pretabulation simplifies the handling of radial integrals, makes their calculation much faster, and allows their easy reuse for different integrals within a given shell combination. The implementation of this new algorithm is described and its performance is analyzed. 相似文献
138.
The second-order density functional approach to the partitioning of the molecular density of Cedillo, Chattaraj, and Parr (Int. J. Quantum Chem. 2000, 77, 403-407) is used, together with a local assumption for the function that projects the total density into its components, to show that the distribution function adopts a stockholders form, in terms of the local softness of the isolated fragments, and that the molecular Fukui function is distributed in the molecular fragments in the same proportion as the electronic density. 相似文献
139.
Serrano I Rodríguez M Romero I Llobet A Parella T Campelo JM Luna D Marinas JM Benet-Buchholz J 《Inorganic chemistry》2006,45(6):2644-2651
The synthesis of two Ru chloro complexes, Ru(III)Cl(3)(bpea), 1, and cis-fac-Delta-[Ru(II)Cl{(R)-(bpea)}{(S)-(BINAP)}](BF(4)), cis-fac-Delta-(R)-(S)-2, (bpea = N,N-bis(2-pyridylmethyl)ethylamine; (S)-BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl), is described. Complex 2 is characterized in solution through UV-vis, cyclic voltammetry (CV), and 1D and 2D NMR spectroscopy. X-ray diffraction analysis indicates that in the solid state it possesses the same structure as in solution, as expected for a low-spin d(6) Ru(II)-type complex. The molecular structure of cis-fac-Delta-(R)-(S)-2, consists of a nonsymmetric complex, where the Ru metal center has a significantly distorted octahedral-type coordination because of the bulkiness of the (S)-BINAP ligand. cis-fac-Delta-(R)-(S)-2 has a remarkable catalytic performance at P = 6.8 atm of H2 and T = 70 degrees C toward the hydrogenation of prochiral double bonds both from efficiency and from stereoselectivity viewpoints. As an example, prochiral olefins of technological interest such as dimethyl itaconate, methyl 2-acetamidoacrylate or methyl 2-acetamidocinnamate are catalytically hydrogenated by cis-fac-Delta-(R)-(S)-2, with conversions higher than 99.9% and ee > 99. Furthermore, cis-fac-Delta-(R)-(S)-2, also catalyzes the selective hydrogenation of beta-keto esters, although the reaction rates are lower than those found with the former substrates. 相似文献
140.
Stoian SA Vela J Smith JM Sadique AR Holland PL Münck E Bominaar EL 《Journal of the American Chemical Society》2006,128(31):10181-10192