TY  - JOUR
A1  - Jeon, Jae-Hyung
A1  - Barkai, Eli
A1  - Metzler, Ralf
T1  - Noisy continuous time random walks
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - Experimental studies of the diffusion of biomolecules within biological cells are routinely confronted with multiple sources of stochasticity, whose identification renders the detailed data analysis of single molecule trajectories quite intricate. Here, we consider subdiffusive continuous time random walks that represent a seminal model for the anomalous diffusion of tracer particles in complex environments. This motion is characterized by multiple trapping events with infinite mean sojourn time. In real physical situations, however, instead of the full immobilization predicted by the continuous time random walk model, the motion of the tracer particle shows additional jiggling, for instance, due to thermal agitation of the environment. We here present and analyze in detail an extension of the continuous time random walk model. Superimposing the multiple trapping behavior with additive Gaussian noise of variable strength, we demonstrate that the resulting process exhibits a rich variety of apparent dynamic regimes. In particular, such noisy continuous time random walks may appear ergodic, while the bare continuous time random walk exhibits weak ergodicity breaking. Detailed knowledge of this behavior will be useful for the truthful physical analysis of experimentally observed subdiffusion.
Y1  - 2013
U6  - https://doi.org/10.1063/1.4816635
SN  - 0021-9606
SN  - 1089-7690
VL  - 139
IS  - 12
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Jeon, Jae-Hyung
A1  - Leijnse, Natascha
A1  - Oddershede, Lene B.
A1  - Metzler, Ralf
T1  - Anomalous diffusion and power-law relaxation of the time averaged mean squared displacement in worm-like micellar solutions
JF  - New journal of physics : the open-access journal for physics
N2  - We report the results of single tracer particle tracking by optical tweezers and video microscopy in micellar solutions. From careful analysis in terms of different stochastic models, we show that the polystyrene tracer beads of size 0.52-2.5 mu m after short-time normal diffusion turn over to perform anomalous diffusion of the form < r(2)(t)> similar or equal to t(alpha) with alpha approximate to 0.3. This free anomalous diffusion is ergodic and consistent with a description in terms of the generalized Langevin equation with a power-law memory kernel. With optical tweezers tracking, we unveil a power-law relaxation over several decades in time to the thermal plateau value under the confinement of the harmonic tweezer potential, as predicted previously (Phys. Rev. E 85 021147 (2012)). After the subdiffusive motion in the millisecond range, the motion becomes faster and turns either back to normal Brownian diffusion or to even faster superdiffusion, depending on the size of the tracer beads.
Y1  - 2013
U6  - https://doi.org/10.1088/1367-2630/15/4/045011
SN  - 1367-2630
VL  - 15
IS  - 4
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Javanainen, Matti
A1  - Hammaren, Henrik
A1  - Monticelli, Luca
A1  - Jeon, Jae-Hyung
A1  - Miettinen, Markus S.
A1  - Martinez-Seara, Hector
A1  - Metzler, Ralf
A1  - Vattulainen, Ilpo
T1  - Anomalous and normal diffusion of proteins and lipids in crowded lipid membranes
JF  - Faraday discussions
N2  - Lateral diffusion plays a crucial role in numerous processes that take place in cell membranes, yet it is quite poorly understood in native membranes characterized by, e.g., domain formation and large concentration of proteins. In this article, we use atomistic and coarse-grained simulations to consider how packing of membranes and crowding with proteins affect the lateral dynamics of lipids and membrane proteins. We find that both packing and protein crowding have a profound effect on lateral diffusion, slowing it down. Anomalous diffusion is observed to be an inherent property in both protein-free and protein-rich membranes, and the time scales of anomalous diffusion and the exponent associated with anomalous diffusion are found to strongly depend on packing and crowding. Crowding with proteins also has a striking effect on the decay rate of dynamical correlations associated with lateral single-particle motion, as the transition from anomalous to normal diffusion is found to take place at macroscopic time scales: while in protein-poor conditions normal diffusion is typically observed in hundreds of nanoseconds, in protein-rich conditions the onset of normal diffusion is tens of microseconds, and in the most crowded systems as large as milliseconds. The computational challenge which results from these time scales is not easy to deal with, not even in coarse-grained simulations. We also briefly discuss the physical limits of protein motion. Our results suggest that protein concentration is anything but constant in the plane of cell membranes. Instead, it is strongly dependent on proteins' preference for aggregation.
Y1  - 2013
U6  - https://doi.org/10.1039/c2fd20085f
SN  - 1359-6640
VL  - 161
IS  - 1
SP  - 397
EP  - 417
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  -