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排序方式: 共有633条查询结果,搜索用时 15 毫秒
611.
Burrows HD Tapia MJ Silva CL Pais AA Fonseca SM Pina J de Melo JS Wang Y Marques EF Knaapila M Monkman AP Garamus VM Pradhan S Scherf U 《The journal of physical chemistry. B》2007,111(17):4401-4410
Understanding factors responsible for the fluorescence behavior of conjugated polyelectrolytes and modulation of their behavior are important for their application as functional materials. The interaction between the anionic poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl}copolymer (PBS-PFP) and cationic gemini surfactants alpha,omega-(CmH2m+1N+(CH3)2)2(CH2)s(Br-)2 (m-s-m; m=12, s=2, 3, 5, 6, 10, and 12) has been studied experimentally in aqueous solution. These surfactants are chosen to see whether molecular recognition and self-assembly occurs between the oppositely charged conjugated polyelectrolyte and gemini surfactant when the spacer length on the surfactant is similar to the intercharge separation on the polymer. Without surfactants, PBS-PFP exists as aggregates. These are broken up upon addition of gemini surfactants. However, as anticipated, the behavior strongly depends upon spacer length (s). Fluorescence measurements show three surfactant concentration regimes: At low concentrations (<2x10(-6) M) quenching occurs and is most marked with the small spacer 12-2-12; at intermediate concentrations (approximately 2x10(-6)-10(-3) M), fluorescence intensity is constant, with a 12-carbon spacer 12-12-12 showing the strongest fluorescence; above the critical micelle concentration (CMC; approximately 10(-3) M) increases in emission intensity are seen in all cases and are largest with the intermediate spacers 12-5-12 and 12-6-12, where the spacer length most closely matches the distance between monomer units on the polymer. With longer spacer length surfactants, surface tension measurements for concentrations below the CMC reveal the presence of polymer-surfactant aggregates at the air-water interface, possibly reflecting increased hydrophobicity. Above the CMC, small-angle neutron scattering experiments for the 12-6-12 system show the presence of spherical aggregates, both for the pure surfactant and for polyelectrolyte/gemini mixtures. Molecular dynamics simulations help rationalize these observations and show that there is a very fine balance between electrostatic and hydrophobic interactions. With the shortest spacer 12-2-12, Coulombic interactions are dominant, while for the longest spacer 12-12-12 the driving force involves hydrophobic interactions. Qualitatively, with the intermediate 12-5-12 and 12-6-12 systems, the optimum balance is observed between Coulombic and hydrophobic interactions, explaining their strong fluorescence enhancement. 相似文献
612.
Full‐Spectrum Photonic Pigments with Non‐iridescent Structural Colors through Colloidal Assembly 下载免费PDF全文
Dr. Jin‐Gyu Park Prof. Shin‐Hyun Kim Sofia Magkiriadou Tae Min Choi Dr. Young‐Seok Kim Prof. Vinothan N. Manoharan 《Angewandte Chemie (International ed. in English)》2014,53(11):2899-2903
Structurally colored materials could potentially replace dyes and pigments in many applications, but it is challenging to fabricate structural colors that mimic the appearance of absorbing pigments. We demonstrate the microfluidic fabrication of “photonic pigments” consisting of microcapsules containing dense amorphous packings of core–shell colloidal particles. These microcapsules show non‐iridescent structural colors that are independent of viewing angle, a critical requirement for applications such as displays or coatings. We show that the design of the microcapsules facilitates the suppression of incoherent and multiple scattering, enabling the fabrication of photonic pigments with colors spanning the visible spectrum. Our findings should provide new insights into the design and synthesis of materials with structural colors. 相似文献
613.
Olive pomace, the solid by-product derived from olive oil production consists of a high concentration of bioactive compounds with antioxidant activity, such as phenolic compounds, and their recovery by applying innovative techniques is a great opportunity and challenge for the olive oil industry. This study aimed to point out a new approach for the integrated valorization of olive pomace by extracting the phenolic compounds and protecting them by encapsulation or incorporation in nanoemulsions. Innovative assisted extraction methods were evaluated such as microwave (MAE), homogenization (HAE), ultrasound (UAE), and high hydrostatic pressure (HHPAE) using various solvent systems including ethanol, methanol, and natural deep eutectic solvents (NADESs). The best extraction efficiency of phenolic compounds was achieved by using NADES as extraction solvent and in particular the mixture choline chloride-caffeic acid (CCA) and choline chloride-lactic acid (CLA); by HAE at 60 °C/12,000 rpm and UAE at 60 °C, the total phenolic content (TPC) of extracts was 34.08 mg gallic acid (GA)/g dw and 20.14 mg GA/g dw for CCA, and by MAE at 60 °C and HHPAE at 600 MPa/10 min, the TPC was 29.57 mg GA/g dw and 25.96 mg GA/g dw for CLA. HAE proved to be the best method for the extraction of phenolic compounds from olive pomace. Microencapsulation and nanoemulsion formulations were also reviewed for the protection of the phenolic compounds extracted from olive pomace. Both encapsulation techniques exhibited satisfactory results in terms of encapsulation stability. Thus, they can be proposed as an excellent technique to incorporate phenolic compounds into food products in order to enhance both their antioxidative stability and nutritional value. 相似文献
614.
Luísa Ramos M Justino LL Branco A Duarte CM Abreu PE Fonseca SM Burrows HD 《Dalton transactions (Cambridge, England : 2003)》2011,40(44):11732-11741
Multinuclear ((1)H, (13)C) magnetic resonance spectroscopy, DFT calculations and luminescence techniques have been used to study 8-hydroxyquinoline-5-sulfonate (8-HQS) and its complexes with Zn(ii), in aqueous solution. The study combines the high sensitivity of luminescence techniques, the selectivity of multinuclear NMR spectroscopy with the structural details accessible through DFT calculations, and aims to obtain a detailed understanding of the complexation between the Zn(2+) ion and 8-HQS. In addition to a complete assignment of the (1)H and (13)C NMR signals of 8-HQS, a full speciation study has been performed. Over the concentration region studied, Zn(2+) metal ion forms only one significant complex species with 8-HQS in aqueous solution in the pH range 6-8. Job's method shows that this species has a 1:2 (metal:ligand) stoichiometry. The geometry around the metal centre, according to structural optimization using DFT calculations, is suggested to be square bipyramidal, with two coordinated water molecules mutually trans, and the remaining positions occupied by the donor groups of the two coordinated 8-HQS ligands. On binding to Zn(ii), 8-HQS shows a marked fluorescence compared with the weakly-luminescent free ligand. In addition, as previously noted, there are marked changes in the absorption spectra, which support the use of 8-HQS as a sensitive fluorescent sensor to detect Zn(2+) metal ion in surface waters, biological fluids, etc. Based on results of the structural studies, suggestions are made of ways for enhancing fluorescence sensitivity. 相似文献
615.
Patrizia Daniele Sofia Giuffrè Antonino Maugeri Fabio Raciti 《Journal of Optimization Theory and Applications》2014,162(3):718-734
This paper is concerned with the problem of strong duality between an infinite dimensional convex optimization problem with cone and equality constraints and its Lagrange dual. A necessary and sufficient condition and sufficient conditions, really new, in order that the strong duality holds true are given. As an application, the existence of the Lagrange multiplier associated with the obstacle problem and to an elastic–plastic torsion problem, more general than the ones previously considered, is stated together with a characterization of the elastic–plastic torsion problem. This application is the main result of the paper. It is worth remarking that the usual conditions based on the interior, on the core, on the intrinsic core or on the strong quasi-relative interior cannot be used because they require the nonemptiness of the interior (and of the above mentioned generalized interior concepts) of the ordering cone, which is usually empty. 相似文献
616.
Sofia Nascimento dos Santos Sara Rhaissa Rezende dos Reis Suyene Rocha Pinto Cristal Cerqueira-Coutinho Fiammetta Nigro Thereza Christina Barja-Fidalgo Nathalia Martins Alexandre Pinheiro Heitor Affonso Paula Neto Ralph Santos-Oliveira 《Journal of nanoparticle research》2017,19(10):345
Despite advancements in treatment of infectious diseases, opportunistic pathogens continue to pose a worldwide threat. Identifying a source of infection/inflammation is often challenging which highlights the need of improved diagnostic agents. Using a model of local S. aureus infection, here we evaluated the potential of betamethasone or dexamethasone loaded in poly (lactic acid) nanoparticles and radiolabeled with 99mTc to detect an infection/inflammation site in vivo. A betamethasone and dexamethasone nanoparticles (NPs) with 200 and 220 nm in size, respectively, were created with a 98% 99mTc radiolabeling efficiency. When injected in infected mice, betamethasone NPs presented a higher accumulation in the infected hind paw in comparison with dexamethasone NPs. Our results suggest that this nanosystem may be a valid nanoradiopharmaceutical for the detection of inflammation/infection foci in vivo. 相似文献
617.
Yuri V. Mironov Alexander V. Virovets Sofia B. Artemkina Vladimir E. Fedorov 《Angewandte Chemie (International ed. in English)》1998,37(18):2507-2509
Diffusion of aqueous solutions of K4[Re4Te4(CN)12] and CuCl2 in the opposite direction through silica gel gives rise to the new polymer-like compound 1 . This complex has a layered structure built from the interconnected cubane-like cluster cations [Cu4(μ3-OH)4]4+ and the cluster anions [Re4Te4(CN)12]4− (see picture). 相似文献
618.
Martín-Calvo A García-Pérez E García-Sánchez A Bueno-Pérez R Hamad S Calero S 《Physical chemistry chemical physics : PCCP》2011,13(23):11165-11174
We have used interatomic potential-based simulations to study the removal of carbon tetrachloride from air at 298 K, using Cu-BTC metal organic framework. We have developed new sets of Lennard-Jones parameters that accurately describe the vapour-liquid equilibrium curves of carbon tetrachloride and the main components from air (oxygen, nitrogen, and argon). Using these parameters we performed Monte Carlo simulations for the following systems: (a) single component adsorption of carbon tetrachloride, oxygen, nitrogen, and argon molecules, (b) binary Ar/CCl(4), O(2)/CCl(4), and N(2)/CCl(4) mixtures with bulk gas compositions 99?:?1 and 99.9?:?0.1, (c) ternary O(2)/N(2)/Ar mixtures with both, equimolar and 21?:?78?:?1 bulk gas composition, (d) quaternary mixture formed by 0.1% of CCl(4) pollutant, 20.979% O(2), 77.922% N(2), and 0.999% Ar, and (e) five-component mixtures corresponding to 0.1% of CCl(4) pollutant in air with relative humidity ranging from 0 to 100%. The carbon tetrachloride adsorption selectivity and the self-diffusivity and preferential sitting of the different molecules in the structure are studied for all the systems. 相似文献
619.
620.
John S. Fossey Francois D'Hooge Jean M. H. van den Elsen Marta P. Pereira Morais Sofia I. Pascu Steven D. Bull Frank Marken A. Toby A. Jenkins Yun‐Bao Jiang Tony D. James 《Chemical record (New York, N.Y.)》2012,12(5):464-478
Synthetic receptors for diols that incorporate boronic acid motifs have been developed as new sensors and separation tools. Utilizing the reversible interactions of diols with boronic acids to form boronic esters under new binding regimes has provided new hydrogel constructs that have found use as dye‐displacement sensors and electrophoretic separation tools; similarly, molecular boronic‐acid‐containing chemosensors were constructed that offer applications in the sensing of diols. This review provides a somewhat‐personal perspective of developments in boronic‐acid‐mediated sensing and separation, placed in the context of the seminal works of others in the area, as well as offering a concise summary of the contributions of the co‐authors in the area. DOI 10.1002/tcr.201200006 相似文献