61 research outputs found

    Investigation by dielectric spectroscopy of domain motions in lysozyme: effect of solvent and binding of inhibitors

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    Interfacial characterization of mesoscopic particle suspensions by means of radiowave dielectric spectroscopy: A minireview

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    Heterogeneous systems, in particular aqueous suspensions of colloidal particles, are very complex systems characterized by a variety of dynamic processes, occurring at different length and time scales, that involve, in a very intruing manner, the structural properties of both the dispersed particles and the disperding medium. Over the last three decades, knowledge of the behavior of such systems has taken greatly advantage by dielectric spectroscopy techniques. This is due to the rapid growth of the technology that makes possible, both in the frequency domain and in the time domain, to acquire dielectric spectra in a very huge frequency interval, typically from 10-5 to 109Hz, or, correspondly, in the time interval from 10 4s to 10ps. In this paper, we will consider several typical colloidal systems, such as aqueous liposome suspensions, ionic and non-ionic micellar solutions, biological cell suspensions. We will describe how dielectric spectroscopy technique can be employed to obtain information concerning the different electrical polarization mechanisms occurring at different time scales and the way to evaluate the structural parameters governing the mesoscopic behavior of these complex systems. © 2004 Elsevier B.V. All rights reserved

    A dielectric method to investigate the interfacial composition of micellar aggregates

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    Structure ans dynamics of polymer-surfactant complexes: dielectric relaxation studies

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    The isothermal phase diagram of the system composed of water, sodium dodecyl sulfate, and hexadecyltrimethylammonium polyacrylate, PACTA, at 25°, was studied by dielec. relaxation, ionic cond., and viscosity. The polymer is not water-sol. and dissolves only in the presence of surfactant in micellarform. Dielec.relaxationspectraindicatetheoccurrenceofonerelaxationinthesurfactantsolns., above the crit. micelle concn., and of two relaxation processes in the presence of PACTA and sodium dodecyl sulfate, C12SO4Na, in micellar form. They are ascribed to free and polymer-bound micelles, resp. Data were interpreted in terms of a chem. equil. of micelles partitioned between polymer-bound and free states. The distance between micelles adsorbed on the polymer backbone is close to 40 nm and slightly changes, depending on the surfactant content. These results support the hypothesis of a necklace structure for the polymer-micelle complex. According to viscosity findings, in fact, the stiffness of the PACTA-C12SO4Na complex decreases on increasing the amt. of bound micelles

    Electrostatic interactions between a protein and oppositely charged micelles

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    Micellar solutions made of a fully fluorinated surfactant, LiPFN, form water-soluble complexes with lysozyme in a wide concentration range. Such complexes are stabilized by electrostatic and, very presumably, double-layer interactions. The mixtures were investigated by combining electrophoretic mobility, DLS, and dielectric relaxation methods. The former gives information on the surface charge density of protein-micelle complexes and indicates that the resulting adducts retain a negative charge (i.e., charge neutralization is incomplete). The double-layer thickness of proteins, micelles, and protein-micelle complexes is also connected to the dielectric relaxation frequency. Changes in particle size (inferred by DLS), charge density, and double-layer thickness are closely interrelated to each other. A model was developed to quantify such properties
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