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Biomedical subjects

G Nägele

Publications and source records attributed to G Nägele.

8 recordsLinked to original sources
PubMed2005

Diffusion and microstructural properties of solutions of charged nanosized proteins: experiment versus theory.

We have reanalyzed our former static small-angle x-ray scattering and photon correlation spectroscopy results on dense solutions of charged spherical apoferritin proteins using theories recently developed for studies of colloids. The static structure factors S(q), and the small-wave-number collective diffusion coefficient D(c) determined from those experiments are interpreted now in terms of a theoretical scheme based on a Derjaguin-Landau-Verwey-Overbeek-type continuum model of charged colloidal spheres. This scheme accounts, in an approximate way, for many-body hydrodynamic interactions. Stokesian dynamics computer simulations of the hydrodynamic function have been performed for the first time for dense charge-stabilized dispersions to assess the accuracy of the theoretical scheme. We show that the continuum model allows for a consistent description of all experimental results, and that the effective particle charge is dependent upon the protein concentration relative to the added salt concentration. In addition, we discuss the consequences of small ions dynamics for the collective protein diffusion within the framework of the coupled-mode theory.

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PubMed2001

Dynamic scaling and freezing criteria in quasi-two-dimensional dispersions.

We report on a Brownian dynamics simulation study of quasi-two-dimensional dispersions of colloidal spheres interacting by long-range electrostatic and dipolar magnetic forces. The calculated dynamic correlation functions are shown to obey dynamic scaling in terms of a characteristic relaxation time related to the mean particle distance and, due to hydrodynamic interactions, to the particle size. The dynamical freezing criterion of Löwen [Phys. Rev. E 53, R29 (1996)] is shown to be equivalent to a two-dimensional static freezing criterion.

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PubMed2001

Rotational tracer diffusion in binary colloidal sphere mixtures.

We demonstrate that tracer/host size asymmetry and electrostatic interactions strongly affect rotational self-diffusion in binary mixtures of charged colloidal tracer and host spheres. Tracer diffusion coefficients, measured with time-resolved phosphorescence anisotropy, are compared with calculations of rotational diffusion including two- and three-particle hydrodynamic interactions. We also show that the inverse dependence of the rotational diffusion coefficient on the suspension viscosity is approached only at large size ratios.

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PubMed1999

Sedimentation of Strongly and Weakly Charged Colloidal Particles: Prediction of Fractional Density Dependence.

We report on calculations of the reduced sedimentation velocity U/U0 in homogenous suspensions of strongly and weakly charged colloidal spheres as a function of particle volume fraction φ. For dilute suspensions of strongly charged spheres at low salinity, U/U0 is well represented by the parametric form 1 - pφalpha with a fractional exponent alpha = 13 and a parameter p approximately 1.8, which is essentially independent from the macroion charge Z. This nonlinear volume fraction dependence can be quantitatively understood in terms of a model of effective hard spheres with φ-dependent diameter. For weakly charged spheres in a deionized solvent, we show that the exponent alpha can be equal to 12, if an expression for U/U0 given by Petsev and Denkov (1992, J. Colloid Interface Sci. 149, 329) is employed. We further show that the range of validity of this expression is limited to very small values of φ and Z, which are probably not accessible in sedimentation experiments. The presented results might also hold for other systems such as spherical proteins or ionic micelles. Copyright 1999 Academic Press.

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PubMed1998

Optical Polydispersity and Contrast Variation Effects in Colloidal Dispersions.

We present a theoretical study on the effect of refractive index variations on static and dynamic light scattering in size-polydisperse suspensions of sterically and charge-stabilized colloidal particles with an internal optical structure (core-shell model) and size-dependent refractive indices. The equilibrium microstructure and the short-time dynamics of these optically, size-, and interaction-polydisperse systems are calculated using hypernetted chain and Percus-Yevick integral equation schemes. Our calculations show that, close to an index matching point, the scattered intensity I(k), the measurable structure factor SM(k), and the measurable hydrodynamic function HM(k) become very sensitive to the refractive index contrast with respect to the solvent. For this purpose, various definitions of index matching points are analyzed, and the strong relative enhancement of the incoherent part of the scattered intensity close to the matching points is discussed. For charge-stabilized systems we show that the anomalous behaviour of I(k) and HM(k) in the matching regime of the solvent refractive index can be well described by a simple approximative scheme, which can be easily implemented. Consequences of our study for scattering experiments aimed to determine particle sizes or structural properties of colloidal dispersions are discussed. Copyright 1998 Academic Press.

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