6 research outputs found
Pore-blockade Times for Field-Driven Polymer Translocation
We study pore blockade times for a translocating polymer of length ,
driven by a field across the pore in three dimensions. The polymer performs
Rouse dynamics, i.e., we consider polymer dynamics in the absence of
hydrodynamical interactions. We find that the typical time the pore remains
blocked during a translocation event scales as ,
where is the Flory exponent for the polymer. In line with our
previous work, we show that this scaling behaviour stems from the polymer
dynamics at the immediate vicinity of the pore -- in particular, the memory
effects in the polymer chain tension imbalance across the pore. This result,
along with the numerical results by several other groups, violates the lower
bound suggested earlier in the literature. We discuss why
this lower bound is incorrect and show, based on conservation of energy, that
the correct lower bound for the pore-blockade time for field-driven
translocation is given by , where is the viscosity of
the medium surrounding the polymer.Comment: 14 pages, 6 figures, slightly shorter than the previous version; to
appear in J. Phys.: Cond. Ma
Probabilistic Phase Space Trajectory Description for Anomalous Polymer Dynamics
It has been recently shown that the phase space trajectories for the
anomalous dynamics of a tagged monomer of a polymer --- for single polymeric
systems such as phantom Rouse, self-avoiding Rouse, Zimm, reptation, and
translocation through a narrow pore in a membrane; as well as for
many-polymeric system such as polymer melts in the entangled regime --- is
robustly described by the Generalized Langevin Equation (GLE). Here I show that
the probability distribution of phase space trajectories for all these
classical anomalous dynamics for single polymers is that of a fractional
Brownian motion (fBm), while the dynamics for polymer melts between the
entangled regime and the eventual diffusive regime exhibits small, but
systematic deviations from that of a fBm.Comment: 8 pages, two figures, 3 eps figure files, minor changes,
supplementary material included moved to the appendix, references expanded,
to appear in J. Phys.: Condens. Matte
Amplitude and Frequency Spectrum of Thermal Fluctuations of A Translocating RNA Molecule
Using a combination of theory and computer simulations, we study the
translocation of an RNA molecule, pulled through a solid-state nanopore by an
optical tweezer, as a method to determine its secondary structure. The
resolution with which the elements of the secondary structure can be determined
is limited by thermal fluctuations. We present a detailed study of these
thermal fluctuations, including the frequency spectrum, and show that these
rule out single-nucleotide resolution under the experimental conditions which
we simulated. Two possible ways to improve this resolution are strong
stretching of the RNA with a back-pulling voltage across the membrane, and
stiffening of the translocated part of the RNA by biochemical means.Comment: Significantly expanded compared to previous version, 13 pages, 4
figures, to appear in J. Phys.: Condens. Matte
Driven polymer translocation through a nanopore: a manifestation of anomalous diffusion
We study the translocation dynamics of a polymer chain threaded through a
nanopore by an external force. By means of diverse methods (scaling arguments,
fractional calculus and Monte Carlo simulation) we show that the relevant
dynamic variable, the translocated number of segments , displays an {\em
anomalous} diffusive behavior even in the {\em presence} of an external force.
The anomalous dynamics of the translocation process is governed by the same
universal exponent , where is the Flory
exponent and - the surface exponent, which was established recently
for the case of non-driven polymer chain threading through a nanopore. A closed
analytic expression for the probability distribution function , which
follows from the relevant {\em fractional} Fokker - Planck equation, is derived
in terms of the polymer chain length and the applied drag force . It is
found that the average translocation time scales as . Also the corresponding time dependent
statistical moments, and reveal unambiguously the anomalous nature of the translocation
dynamics and permit direct measurement of in experiments. These
findings are tested and found to be in perfect agreement with extensive Monte
Carlo (MC) simulations.Comment: 6 pages, 4 figures, accepted to Europhys. Lett; some references were
supplemented; typos were correcte
Polymer translocation out of planar confinements
Polymer translocation in three dimensions out of planar confinements is studied in this paper. Three membranes are located at z = -h, z = 0 and z = h(1). These membranes are impenetrable, except for the middle one at z = 0, which has a narrow pore. A polymer with length N is initially sandwiched between the membranes placed at z = -h and z = 0 and translocates through this pore. We consider strong confinement (small h), where the polymer is essentially reduced to a two-dimensional polymer, with a radius of gyration scaling as R-g((2D)) similar to N-nu 2D; here, nu(2D) = 0.75 is the Flory exponent in two dimensions. The polymer performs Rouse dynamics. On the basis of theoretical analysis and high-precision simulation data, we show that in the unbiased case h = h(1), the dwell time tau(d) scales as N2+nu 2D, in perfect agreement with our previously published theoretical framework. For h(1) = infinity, the situation is equivalent to field-driven translocation in two dimensions. We show that in this case tau(d) scales as N-2 nu 2D, in agreement with several existing numerical results in the literature. This result violates the earlier reported lower bound N1+nu for tau(d) for field-driven translocation. We argue, on the basis of energy conservation, that the actual lower bound for tau(d) is N-2 nu and not N1+nu. Polymer translocation in such theoretically motivated geometries thus resolves some of the most fundamental issues that have been the subject of much heated debate in recent times
Anomalous dynamics of unbiased polymer translocation through a narrow pore
We consider a polymer of length N translocating through a narrow pore in the absence of external fields. The characterization of its purportedly anomalous dynamics has so far remained incomplete. We show that the polymer dynamics is anomalous up to the Rouse time tau(R) similar to N1+2 nu ., with a mean square displacement through the pore consistent with t((1+nu)/( 1+ 2 nu)), with nu approximate to 0.588 the Flory exponent. This is shown to be directly related to a decay over time of the excess monomer density near the pore as t(-(1+nu)/(1+2 nu)) exp(-t/tau(R)). Beyond the Rouse time, translocation becomes diffusive. In consequence of this, the dwell time tau(d), the time a translocating polymer typically spends within the pore, scales as N2+nu, in contrast to previous claims