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101.
Stability of hypersurfaces with constant mean curvature 总被引:12,自引:0,他引:12
102.
Barbosa M. S. da F. Costa L. Bernardes E. S. Ramakers G. van Pelt J. 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,37(1):109-115
The European Physical Journal B - The complexity of a neuronal cell shape is known to be related to its function. Specifically, among other indicators, a decreased complexity in the dendritic trees... 相似文献
103.
Macià A Borrull F Calull M Benavente F Hernández E Sanz-Nebot V Barbosa J Aguilar C 《Journal of separation science》2008,31(5):872-880
SPE coupled in-line to CE, as the strategy to enhance the concentration sensitivity in CE, has been used to enrich naproxen in tap water samples. In this study, a microcartridge containing an octadecyl silica (C18) sorbent was placed near the inlet within the separation capillary column. The optimum conditions were obtained when naproxen in an acidic aqueous solution (pH 3.5) was loaded into the capillary at 930 mbar for 30 min, and 20 mM ammonium acetate in methanol/water (70:30 v/v) was used as both an elution solution and a separation BGE. Under these conditions, the sensitivity was enhanced 1820-fold with respect to normal hydrodynamic injection, and the LOD achieved was 0.2 microg/L. To show the capability of the in-line SPE-CE method, tap water samples were analysed after a pretreatment consisting in an off-line C18-SPE procedure. The recovery of this procedure was higher than 80%. Under these conditions, naproxen could be detected at a concentration of 10 ng/L; so the potential of the procedure for the sensitive analysis of this type of drugs in water samples was demonstrated. Afterwards, these results were compared with those previously obtained for naproxen in water samples using different sample stacking techniques. 相似文献
104.
In this study, the suitability of SPE coupled on-line to CE-electrospray-MS (SPE-CE-ESI-MS) was evaluated for the analysis of neuropeptides in human plasma. First, CE-ESI-MS was investigated and a sample pretreatment based on precipitation with ACN was used for cleanup of plasma samples. The main quality parameters were determined and were consistent with those previously obtained for the analysis of standard mixtures, e.g., the LODs were of around 1 microg/mL. SPE-CE-ESI-MS employing microcartridges containing a C18 stationary phase was explored in order to decrease the LODs. A double-step sample cleanup pretreatment consisting of precipitation with ACN and ultrafiltration through 3000 Da MW cut-off membranes was needed to prevent the microcartridge saturation. Repeatability, reproducibility, linearity, and LODs of the SPE-CE-ESI-MS method and the durability of the microcartridges were studied. The LODs were markedly improved, ranging between 10 and 0.1 ng/mL depending on the peptide. 相似文献
105.
Mohammad Arif Cheema Pablo Taboada Silvia Barbosa Emilio Castro Mohammad Siddiq Víctor Mosquera 《The Journal of chemical thermodynamics》2008,40(2):298-308
Surface tension, conductivity, density, and ultrasound velocity measurements have been performed in order to determine in a systematic manner some of the aggregation properties of the phenothiazine drugs promazine and triflupromazine hydrochlorides. Both drugs are structurally related, differing in an extra CF3 group in the triflupromazine molecular structure. Surface tension data showed that the presence of an extra CF3 in the molecular structure of triflupromazine involves a higher hydrophobicity of this drug and a restriction in the number of conformations molecules can adopt due to the presence of this bulkier atomic group. This involves a larger surface area in order to accommodate triflupromazine molecules at the interface. From conductivity measurements at different temperatures, the thermodynamic quantities of the micellization process of these drugs indicate that the aggregation is a spontaneous process, mainly enthalpic, where the London-dispersion forces play an active role. Using density and ultrasound velocity measurements, apparent molar volume and adiabatic compressibility of aqueous solutions of the amphiphilic cationic drugs have been determined. Positive deviations from the Debye–Hückel limiting law of the apparent molar volume were obtained from both drugs over the whole temperature range, which provides evidence of possible pre-association at concentrations below the critical concentration. Apparent molar adiabatic compressibility of the aggregates formed by these drugs was typical of those corresponding for an aggregate formed by a stacking process. 相似文献
106.
Prazeres TJ Fedorov A Barbosa SP Martinho JM Berberan-Santos MN 《The journal of physical chemistry. A》2008,112(23):5034-5039
The S1-S0 limiting anisotropy of a widely used fluorophore, rhodamine 101, is determined with unprecedented accuracy. From time-resolved and steady-state fluorescence measurements in several solvents, it is shown that the limiting anisotropy of rhodamine 101 is for all practical purposes equal to the theoretical one-photon fundamental anisotropy value of 2/5, both in rigid and in fluid media. This fact, along with the favorable chemical and photophysical properties of rhodamine 101, point to its use as a standard for fluorescence polarization measurements. It is also shown that if the excitation pulse can be considered a delta impulse with respect to the time scale of the anisotropy decay (but not necessarily to the time scale of the intensity decay), then no deconvolution procedure is needed for anisotropy decay analysis. 相似文献
107.
S.C. Nunes V. de Zea Bermudez D. Ostrovskii P.C. Barbosa M.M. Silva M.J. Smith 《Chemical physics》2008
Fourier Transform mid-infrared and Raman spectroscopies were used to investigate the cation/polymer, cation/urea bridge, cation/anion and hydrogen bonding interactions in poly(oxyethylene) (POE)/siloxane di-ureasil networks prepared by the sol–gel route and doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Materials with compositions 200 ?n ? 5 (where n expresses the molar ratio OCH2CH2/Li+) were studied. The Li+ ions coordinate to the urea carbonyl oxygen atoms over the whole range of salt concentration considered. Bonding to the ether oxygen atoms of the POE chains occurs at n ? 40, although a significant fraction of the POE chains remain non-coordinated. In these high salt content samples, the cations interact with the anions forming contact ion pairs. “Free” ions are probably the main charge carriers at the room temperature conductivity maximum of these ormolytes. 相似文献
108.
Teixeira RR Barbosa LC Maltha CR Rocha ME Bezerra DP Costa-Lotuf LV Pessoa C Moraes MO 《Molecules (Basel, Switzerland)》2007,12(5):1101-1116
3-Benzyl-furan-2(5H)-one (2a) and 3-(4-bromobenzyl)-furan-2(5H)-one (2b) were treated with TBDMSOTf and converted into the corresponding tert-butyldimethyl-silylfuran ethers. These furans were further condensed with several aromatic aldehydes affording compounds 5-14 with general 3-benzyl-5-arylidene-furan-2(5H)-one structures in 31% to 98% yields. Such compounds are analogues of the naturally occurring nostoclide lactones, reported to present moderate cytotoxic activity. Compounds 5-14 were submitted to an in vitro bioassay against the HL-60, HCT-8, SF295 and MDA-MB-435 cancer cell lines using the MTT cytotoxicity assay. 相似文献
109.
Giménez E de Bolós C Belalcazar V Andreu D Borrás E De la Torre BG Barbosa J Segura J Pascual JA 《Analytical and bioanalytical chemistry》2007,388(7):1531-1538
Erythropoietin (EPO) is a hormone that regulates red blood cell production. Recombinant human EPO (rHuEPO) and NESP (novel
erythropoiesis stimulating protein) have been produced for therapeutic purposes and also to improve sports performance. The
primary sequences of rHuEPO and NESP differ by just five amino acids. Due to the high homology, no antibodies that are able
to discriminate between both molecules have been obtained until now. The aim of the present work was to design synthetic peptides
corresponding to the sequence that differs between EPO and NESP (87–90aa), that can then be used as immunogens to develop
specific rabbit polyclonal antibodies for selectively detecting EPO and NESP. Three peptides were synthesized: EPO (81–95),
NESP (81–95), and NESP (86–104), and these were coupled to KLH and OVA for immunization and screening purposes, respectively.
The sera obtained were tested by ELISA on synthetic peptide–OVA conjugates and purified by immunoaffinity chromatography against
the corresponding synthetic peptide. The specific purified antibodies were characterized by ELISA, SDS-PAGE, and isoelectric
focusing, followed by western blot. Antisera raised against EPO (81–95) recognized rHuEPO but not NESP. In contrast, anti-NESP
(84–106) sera gave a specific anti-NESP response only after immunoaffinity purification on a NESP (86–91) column. An efficient
strategy for generating specific antibodies against EPO and NESP can be achieved by selecting suitable synthetic peptides.
The antibodies obtained are able to differentiate between rHuEPO and NESP, and may be particularly useful for screening purposes
in both therapeutic and antidoping contexts. 相似文献
110.
Benavente F Hernández E Guzman NA Sanz-Nebot V Barbosa J 《Analytical and bioanalytical chemistry》2007,387(8):2633-2639
Several CE methodologies have been described for the analysis of rHuEPO in concentrated solutions, but the inherently limited
concentration sensitivity of CE precludes the detection of EPO at the levels found in biological fluids. In this work, we
have investigated an on-line immunoaffinity solid-phase extraction capillary electrophoresis (IA-CE) methodology for the selective
preconcentration of EPO in diluted solutions. The preliminary results obtained using a custom-made immunoaffinity sorbent
prepared from an anti-human EPO polyclonal antibody and glutaraldehyde–glass beads show the potential of this novel approach.
The summarized findings are discussed in detail as a starting point for our ongoing investigations. 相似文献