2015/04/10 09:20
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文献名: Structural, morphological and optical properties of Bi NPs obtained by laser ablation and their selective detection of L-cysteine 作者: Ramon Gabriel Teixeira Rosaa, Celso de Araujo Duartea , Wido Herwig Schreinera, Ney Pereira Mattoso Filhoa, Arandi Ginane Bezerra Jr.b, Andersson Barisonc, Fernanda Maria Marins Ocamposc a Departamento de Física, Universidade Federal do Paraná Centro Politécnico, CP 19044, 81531-990 Curitiba (PR), Brazil b Departamento Acadêmico de Física, Universidade Tecnológica Federal do Paraná, 80230-901 Curitiba (PR), Brazil c Departamento de Química, Universidade Federal do Paraná Centro Politécnico, CP 19081, 81531-990 Curitiba (PR), Brazil 摘要:In the present work we show the results of the investigation of the properties of bismuth nanoparticles (NPs) obtained by the laser ablation in water. The samples were characterized by various techniques: UV/vis spectroscopy, dynamic light scattering, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, nuclear magnetic resonance and zeta potential. The NPs were metallic and surface oxidated, exhibiting absorption peak at 257 nm due to the surface plasmon resonance. The interaction between the NPs and various amino acids was studied and revealed a selective sensibility to cysteine on a range of concentration from 80 to 720 μM, which we attribute to a dimerization of cysteine to cystine probably complexed to the nanoparticle surface by electrostatic interactions, leading to the modification of the NP absorption spectrum. 关键词:Bismuth; Nanoparticles; Laser ablation; Cysteine
2015/04/16
Study of Protein Hydrodynamics with Light Scatter-ing: Size and Charge of Lysozyme
Proteins are not only important nutrient source for human society, but also play a crucial role in devising various protein-based therapies for many terminal diseases [1]. Therapeutic proteins are usually administrated by the parenteral route. Their dosage form needs to be formulated either as a solution, a suspension or a reconstituted solid dosage form. Therefore, for protein therapeutic products development, protein hydrodynamic behavior in solutions or suspensions is proven to be much more relevant than its isolated and denatured characteristics revealed via advanced microscopy tech-niques. This can be manifested as either protein size monitoring for QC purposes of its purification processes or their charge property control for optimized formulation stability. The critical requirements for these applications often include, but not limited to, non-invasive (in-situ) nature of measurement techniques, easy-of-use and rapidness of tests. Laser light scattering techniques satisfy these require-ments and provide vital access to the hydrodynamic characteris-tics of biological macromolecules in their native application envi-ronments [2]. Their diffusive displacement (“Brownian” motion) can be quantified as diffusion coefficient with a dynamic light scattering measurement. In turn, their hydrodynamic radius can be calculated. When placed under an electric filed, the charged proteins undergo a uniform translational movement, the so-called electrophoretic motion or electrophoresis. It results in a Doppler phase/frequency shift of the light signal scattered from the moving proteins, which can be quantitatively evaluated with a carefully designed electrophoretic light scattering experiment. From the measured phase/frequency shift, the charge status of proteins can be extracted.
2015/03/12
The Structure-Function Relationship of PAMAM Dendrimers as Robust Oil Dispersants
PAMAM dendrimers have recently been investigated as efficient and biocompatible oil dispersants utilizing their encapsulation capacity; however, their high cationic charge density has been shown to be cytotoxic. It is therefore imperative to mitigate cationic charge-induced toxicity and understand the effects of such changes. Presented here is a synergistic experimental and computational approach to examine the effects of varying terminal surface charge on the capacity of dendrimers to disperse model liner, polycyclic aromatic, and hybrid hydrocarbons. Uncharged dendrimers collapse by forming intra-molecular hydrogen bonds, which reduce the hosting capability. On the other hand, changing the surface charges from positive to negative greatly shifts the pKa of tertiary amines of the PAMAM dendrimer interior. As a result, the negatively charged dendrimers have a significant percentage of tertiary amines protonated, ~30%. This unexpected change in interior protonation state cause electrostatic interactions with the anionic terminal groups, leading to contraction and a marked decrease in hydrocarbon hosting capacity. The present work highlights the robust nature of dendrimer oil dispersion and also illuminates potentially unintended or unanticipated effects of varying dendrimer surface chemistry on their encapsulation or hosting efficacy, which is important for their environmental, industrial, and biomedical applications.
2015/03/12
Interfacial silica nanoparticles stabilize cocontinuous polymer blends
We investigated the formation of cocontinuous structures in polymer blends. These polymeric bijels (bicontinuous interfacially jammed emulsion gels) were composed of polystyrene oligomer, polybutene and fluorescent hydrophobic silica nanoparticles. A micron-sized cocontinuous morphology was stabilized by a monolayer of silica nanoparticles at the interface. Real-time observation of coalescence dynamics in co-continuous polymer blends stabilized by interfacial particles was for the first time achieved via laser scanning confocal microscopy. We demonstrated that suppression of coalescence arises from coverage of interfaces by nanoparticles. Furthermore, by combining confocal microscopy with rheology, we correlated the rheological response of a cocontinuous structure with its morphology change. We found that the rheological behavior can be attributed to competition between interface shrinkage and particle network formation. In addition, we showed that a particle scaffold is maintained even after the remixing of two polymer phases above the spinodal point. Finally, we also discussed differences between the shear response of the particle-stabilized cocontinuous structure and normal colloidal gels: the former one is more fragile than the latter under shear.
2015/03/12