Brownian dynamics simulations of analytical ultracentrifugation experiments exhibiting hydrodynamic and thermodynamic non-ideality

Abstract

Hydrodynamic and thermodynamic non-ideality are important phenomena when studying concentrated and interacting systems in analytical ultracentrifugation (AUC). Here we present an extended Brownian Dynamics (BD) based algorithm which incorporates hydrodynamic and thermodynamic non-ideality. It can serve as an independent and versatile approach for the theoretical description of interparticulate interactions in AUC, as it allows tracking the trajectory of individual particles. Concentration dependencies of the sedimentation and diffusion coefficient have been implemented and validated for the extended BD model. For monodisperse systems, it is shown that profiles obtained by BD are in excellent agreement with well-established Lamm equation solvers. Moreover, important limits and restrictions of current Lamm equation based analysis methods are discussed. In particular, BD allows modeling and evaluation of AUC data of non-ideal polydisperse systems. This is relevant as most nanoparticulate systems are polydisperse in size. Here, a simulation for a polydisperse system including concentration effects is presented for the first time.

Measurement of length distribution of beta-lactoglobulin fibrils by multiwavelength analytical ultracentrifugation

“…However, as these side chains contribute only marginally to the mass of the fibrils, these minor differences in the sedimentation coefficient cannot be resolved using AUC and must therefore be neglected. Furthermore, any effects of concentration-dependent non-ideality are reduced due to the very low concentration (0.01 wt%) (Uttinger et al 2017 ). With this, we propose to establish sedimentation properties of amyloid fibrils as a representative parameter to study their functionality and effects.…”

Probing sedimentation non-ideality of particulate systems using analytical centrifugation

“…7,12 Using BD simulations, we could further demonstrate that this works well for AC experiments. 4,37 Hindrance function. Besides the Gralen coefficient, there are several other approaches to account for the reduction of the particles' sedimentation rate.…”

“…1 In this respect, centrifugation constitutes a promising technique for the experimental investigation of concentration-dependent interactions in colloidal systems. [2][3][4] The method offers the possibility to systematically investigate hydrodynamic and thermodynamic interaction parameters, which is key 2,[4][5][6][7] for the comprehensive description of mass transport phenomena beyond the limit of infinite dilution where Stokes' law prevails. [8][9][10] Sedimentation non-ideality originates from a concentration dependency of the particles' translational friction coefficient.…”

“…[8][9][10] Sedimentation non-ideality originates from a concentration dependency of the particles' translational friction coefficient. 4,7,[11][12][13][14] Firstly, the particles' sedimentation behavior is influenced by a volume flux of solvent in opposing direction, which is caused by solvent filling the space created by the sedimenting particles. 11 Furthermore, the viscosity and density of the dispersion increase with particle concentration, which leads to a further decrease in the sedimentation rate.…”

A Comprehensive Brownian Dynamics Approach for the Determination of Non-ideality Parameters from Analytical Ultracentrifugation

“…The cell is subdivided in several bins with width Δr in order to calculate local concentrations and to produce output data. This representation is taken from literature and adapted for the purpose of the illustration 1.…”