Abstract
The mechanism of inter- and intracellular diffusional transport by vesicles in living organisms is poorly understood at the molecular scale. The diffusion of submicron and nanoparticles in dense media has been treated by numerous theoretical models. We face this problem experimentally using Mössbauer spectroscopy. On a characteristic for this method narrow time scale (≈10−7 s), the velocity distribution of 120 nm spherical Fe2O3 particles suspended in a 60% water solution of sucrose was determined by analyzing the 57Fe Mössbauer spectral line profile. The particles usually exhibit classical Brownian motion, but their main diffusion mechanism is related to infrequent (f ≈ 106 s−1) but distant (d ≈ 1 nm) translations. During such movements, the particles experience a minimal friction described by the temporal local viscosity, ηloc ≈ 28 μPa·s.
Highlights
The mobility of submicron objects in viscous media, which is a key problem in some areas of nanotechnology and the main factor responsible for inter- and intracellular transport, is poorly understood at the atomic scale
The high rate of biochemical processes in colloids has been explained by the concept of local viscosity [3], and molecular dynamics simulations have elucidated the role of the protein concentration on the lateral mobility of lipid membranes [4]
Recent developments in experimental methods have enabled the determination of the trajectories of particles composing living cells [5, 6]; the results suggest the abnormal nature of diffusion, which is frequently discussed in terms of fractional Brownian motion or continuous-time random walks (CTRWs) [8]
Summary
The mobility of submicron objects in viscous media, which is a key problem in some areas of nanotechnology and the main factor responsible for inter- and intracellular transport, is poorly understood at the atomic scale. The Einstein–Smoluchowski approach to the Brownian motion refers to free particles in an ideal gas [1, 2] but does not adequately explain the migration of massive particles. The high rate of biochemical processes in colloids has been explained by the concept of local viscosity [3], and molecular dynamics simulations have elucidated the role of the protein concentration on the lateral mobility of lipid membranes [4]. Recent developments in experimental methods have enabled the determination of the trajectories of particles composing living cells [5, 6] (for a review, see [7]); the results suggest the abnormal nature of diffusion, which is frequently discussed in terms of fractional Brownian motion or continuous-time random walks (CTRWs) [8]. Three qualitatively different types of diffusion, namely diffusion constrained by elastic force, walking confined diffusion and hop diffusion were described in [10] leading to the similar mean square displacements
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