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排序方式: 共有499条查询结果,搜索用时 31 毫秒
491.
A new cloud point extraction (CPE) method for ergotamine analysis using fluorimetric detection is described. Ergotamine from an aqueous solution was preconcentrated into a smaller surfactant-rich phase using nonionic surfactant polyoxyethylene(7.5)nonylphenylether (PONPE 7.5). Differently from the conventional CPE procedure in which the resulting surfactant-rich phase is diluted by a fluidificant before its analysis, in this method the fluorescence measurements were carried out directly onto the undiluted surfactant-rich phase. The high viscosity provided by the undiluted surfactant rich phase greatly improved the fluorescence emission of ergotamine, leading to a total enhancement factor of 1325. This spectral advantage plus the preconcentration factor achieved, contributed to the method sensitivity allowing the ergotamine determination at trace level concentration. Under optimal experimental conditions, a linear calibration curve was obtained from 3.81 × 10−7 to 1.10 μg mL−1, with detection and quantification limits of 0.11 and 0.38 pg mL−1, respectively. The accuracy and versatility of the present methodology were proved by analyzing ergotamine in real samples of different natures such as pharmaceuticals, urine and saliva. 相似文献
492.
D. Diana Paola Vargas G. Liliana Giraldo P. Juan Carlos Moreno 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1067-1072
In this study, energetic interactions between activated carbon monoliths and various liquids were evaluated by determining immersion enthalpies in C6H6, H2O and aqueous solutions of NaOH and HCl. Immersion enthalpies depend on both the surface chemistry and the interactions between specific groups, and were compared with results from volumetric titrations. Immersion enthalpies of activated carbon monoliths were between ?95.85 and ?176.5 J g?1 for C6H6 and between ?11.19 and ?68.31 J g?1 for H2O; whereas immersion enthalpies in NaOH and HCl solutions were between ?20.36 and ?82.25 J g?1 and ?18.81 and ?96.16 J g?1, respectively. In support of these results, a high level of acidic groups was found on the surface of the activated carbon monoliths by Boehm volumetric titrations, with values between 719 and 1,290 g mol?1, in agreement with the higher immersion enthalpies observed in NaOH. Correlations were established between immersion enthalpies in the liquids and the surface chemistry properties of the activated carbon monoliths determined by volumetric titrations, demonstrating that immersion enthalpy is a useful parameter for characterisation of these materials in specific liquids. 相似文献
493.
494.
Liliana Esquivel Nakao Hayashi Elena I. Kaikina 《Journal of Differential Equations》2019,266(2-3):1121-1152
We consider the inhomogeneous Dirichlet-boundary value problem for the cubic nonlinear Schrödinger equations on the half line. We present sufficient conditions of initial and boundary data which ensure asymptotic behavior of small solutions to equations by using the classical energy method and factorization techniques 相似文献
495.
Nistor MT Chiriac AP Vasile C Verestiuc L Nita LE 《Colloids and surfaces. B, Biointerfaces》2011,87(2):382-390
The study presents the preparation of a semi-synthetic hydrogel based on poly(N-isopropyl acrylamide-co-diethylene glycol diacrylate) inserted onto the collagen porous membrane. The synthesis of the hydrogels was performed through radical copolymerization of N-isopropyl acrylamide (NIPAM) with diethylene glycol diacrylate (DEGDA) also as crosslinking agent, using ammonium persulfate as initiator and N,N,N',N'-tetramethylethylene diamine as activator, and it was achieved in the presence of the collagen matrix. The prepared hydrogels were characterized by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. The swelling behaviour of the semi-interpenetrated polymer network related on the hydrogel composition, it was also evaluated. The pore sizes of the synthesized hydrogels, much larger than the typical mesh size of a conventional hydrogel, allow to consider the hybrid hydrogel based on the inserted poly(NIPAM-co-DEGDA) onto collagen fibrils as a super-porous hydrogel. 相似文献
496.
Diana Paola Vargas Liliana Giraldo Joaquín Silvestre-Albero Juan Carlos Moreno-Piraján 《Adsorption》2011,17(3):497-504
A series of activated carbon monoliths have been prepared by chemical activation of two lignocellulosic precursors, coconut
shell (CACM) and African palm stones (PACM). The incorporation of a conforming step between the impregnation with H3PO4 and the activation step allows the successful development of disc-shape monoliths without the use of a binder. Textural characterization
results using N2 adsorption at 77 K show that the effect of the activating agent highly depends on the nature of the carbon precursor used.
While chemical activation with phosphoric acid has mainly no effect when using coconut shell, a large development of both
micro- and mesoporosity is observed for African palm stones. Large concentrations of the activating agent produce the partial
shrinkage of the narrow microporous structure independently of the precursor used. Concerning the adsorption of CO2 at atmospheric pressure and 273 K, both series of activated carbon monoliths exhibit an improved adsorption behaviour with
the activation degree up to an optimum value around ∼164 mg CO2/g, for sample CACM-32, and ∼162 mg CO2/g, for sample PACM-28, the amount adsorbed decreasing thereafter. Apparently, the total amount of CO2 adsorbed under these experimental conditions is defined by the volume of narrow micropores (V
n
). 相似文献
497.
Liliana Apolinário José Guilherme Milhano Mateusz Ploskon Xiaoming Zhang 《The European Physical Journal C - Particles and Fields》2018,78(6):529
Using a novel observable that relies on the momentum difference of the two most energetic subjets within a jet \(\varDelta S_{12}\) we study the internal structure of high-energy jets simulated by several Monte Carlo event generators that implement the partonic energy-loss in a dense partonic medium. Based on inclusive jet and dijet production we demonstrate that \(\varDelta S_{12}\) is an effective tool to discriminate between different models of jet modifications over a broad kinematic range. The new quantity, while preserving the collinear and infrared safety of modern jet algorithms, it is experimentally attractive because of its inherent resilience against backgrounds of heavy-ion collisions. 相似文献
498.
Gabriel Teixeira Dinis O. Abranches Liliana P. Silva Srgio M. Vilas-Boas Simo P. Pinho Ana I. M. C. L. Ferreira Luís M. N. B. F. Santos Olga Ferreira Joo A. P. Coutinho 《Molecules (Basel, Switzerland)》2022,27(9)
The formation of deep eutectic solvents (DES) is tied to negative deviations to ideality caused by the establishment of stronger interactions in the mixture than in the pure DES precursors. This work tested thymol and menthol as hydrogen bond donors when combined with different flavonoids. Negative deviations from ideality were observed upon mixing thymol with either flavone or flavanone, two parent flavonoids that only have hydrogen bond acceptor (HBA) groups, thus forming non-ionic DES (Type V). On the other hand, the menthol systems with the same compounds generally showed positive deviations from ideality. That was also the case with the mixtures containing the more complex hydroxylated flavonoid, hesperetin, which resulted in positive deviations when mixed with either thymol or menthol. COSMO-RS successfully predicted the behavior of the solid-liquid phase diagram of the studied systems, allowing for evaluation of the impact of the different contributions to the intermolecular interactions, and proving to be a good tool for the design of DES. 相似文献
499.
Loredana Elena Nita Alexandra Croitoriu Alexandru M. Serban Maria Bercea Alina G. Rusu Alina Ghilan Maria Butnaru Liliana Mititelu-Tartau Aurica P. Chiriac 《Macromolecular bioscience》2023,23(3):2200451
Short aromatic peptide derivatives, i.e., peptides or amino acids modified with aromatic groups, such as 9-fluorenylmethoxycarbonyl (Fmoc), can self-assemble into extracellular matrix-like hydrogels due to their nanofibrillar architecture. Among different types of amino acids, lysine (Lys) and glycine (Gly) are involved in multiple physiological processes, being key factors in the proper growth of cells, carnitine production, and collagen formation. The authors have previously successfully presented the possibility of obtaining supramolecular gels based on Fmoc-Lys-Fmoc and short peptides such as Fmoc-Gly-Gly-Gly in order to use them as a substrate for cell cultures. This paper investigates how the introduction of a gelling polymer can influence the properties of the network as well as the compatibility of the resulting materials with different cell types. A series of hydrogel compositions consisting of combinations of Fmoc-Lys-Fmoc and Fmoc-Gly-Gly-Gly with Agarose and Phytagel are thus obtained. All compositions form structured gels as shown by rheological studies and scanning electron microscopy. Fourier transform infrared spectroscopy analysis evidences the formation of H-bonds between the polysaccharides and amino acids or short peptides. Moreover, all gels exhibit good cell viability on fibroblasts as demonstrated by a live-dead staining test and good in vivo biocompatibility, which highlights the great potential of these biomaterials for biomedical applications. 相似文献