261 research outputs found
pH-Mediated Regulation of Polymer Transport Through SiN Pores
We characterize the pH controlled polymer capture and transport thorough
silicon nitride (SiN) pores subject to protonation. A charge regulation model
able to reproduce the experimental zeta potential of SiN pores is coupled with
electrohydrodynamic polymer transport equations. The formalism can
quantitatively explain the experimentally observed non-monotonic pH dependence
of avidin conductivity in terms of the interplay between the electroosmotic and
electrophoretic drag forces on the protein. We also scrutinize the DNA
conductivity of SiN pores. We show that in the low pH regime where the
amphoteric pore is cationic, DNA-pore attraction acts as an electrostatic trap.
This provides a favorable condition for fast polymer capture and extended
translocation required for accurate polymer sequencing
Electrostatic correlations in inhomogeneous charged fluids beyond loop expansion
Electrostatic correlation effects in inhomogeneous symmetric electrolytes are
investigated within a previously developed electrostatic self-consistent (SC)
theory (R.R. Netz and H. Orland, Eur. Phys.J. E 11, 301 (2003)). To this aim,
we introduce two computational approaches that allow to solve the SC equations
beyond the loop expansion. Both approaches can handle the case of
dielectrically discontinuous boundaries where the one-loop theory is known to
fail. By comparing the theoretical results obtained from these schemes with the
results of the MC simulations that we ran for ions at neutral single dielectric
interfaces as well as with previous MC data for charged interfaces, we first
show that the weak coupling (WC) Debye-Huckel (DH) theory remains
quantitatively accurate up to the bulk ion density rhob=0.01 M, whereas the SC
theory exhibits a good quantitative accuracy up to rhob=0.2 M. Then, we derive
from the perturbative SC scheme the one-loop theory of asymmetrically
partitioned salt systems around a dielectrically homogeneous charged surface.
It is shown that correlation effects originate in these systems from a
competition between the salt screening loss at the interface driving the ions
to the bulk region, and the interfacial counterion screening excess attracting
them towards the surface. In the case of weak surface charges, the interfacial
salt screening loss is the dominant effect. As a result, correlations decrease
the MF density of both coions and counterions. With increasing surface charge,
the surface-attractive counterion screening excess starts to dominate, and
correlation effects amplify in this regime the MF density of both type of ions.
We also show that at a characteristic value of the electrostatic coupling
parameter, electrostatic correlations result in a charge inversion effect
Comment on "Nonlocal statistical field theory of dipolar particles in electrolyte solutions" by Y.A. Budkov
The article by Budkov introduces a nonlocal field-theoretic model of
solvent-explicit electrostatics. Despite giving a detailed introduction to the
early literature on the topic, the article misses out on a series of articles
that we published several years ago. Consequently, the manuscript essentially
rederives without mention several results that were derived by us for the first
time
Theory of pore-driven and end-pulled polymer translocation dynamics through a nanopore: An overview
We review recent progress on the theory of dynamics of polymer translocation
through a nanopore based on the iso-flux tension propagation (IFTP) theory. We
investigate both pore-driven translocation of flexible and a semi-flexible
polymers, and the end-pulled case of flexible chains by means of the IFTP
theory and extensive molecular dynamics (MD) simulations. The validity of the
IFTP theory can be quantified by the waiting time distributions of the monomers
which reveal the details of the dynamics of the translocation process. The IFTP
theory allows a parameter-free description of the translocation process and can
be used to derive exact analytic scaling forms in the appropriate limits,
including the influence due to the pore friction that appears as a finite-size
correction to asymptotic scaling. We show that in the case of pore-driven
semi-flexible and end-pulled polymer chains the IFTP theory must be augmented
with an explicit {\it trans} side friction term for a quantitative description
of the translocation process
Scaling theory of driven polymer translocation
We present a theoretical argument to derive a scaling law between the mean
translocation time and the chain length for driven polymer
translocation. This scaling law explicitly takes into account the pore-polymer
interactions, which appear as a correction term to asymptotic scaling and are
responsible for the dominant finite size effects in the process. By eliminating
the correction-to-scaling term we introduce a rescaled translocation time and
show, by employing both the Brownian Dynamics Tension Propagation theory
[Ikonen {\it et al.}, Phys. Rev. E {\bf 85}, 051803 (2012)] and molecular
dynamics simulations that the rescaled exponent reaches the asymptotic limit in
a range of chain lengths that is easily accessible to simulations and
experiments. The rescaling procedure can also be used to quantitatively
estimate the magnitude of the pore-polymer interaction from simulations or
experimental data. Finally, we also consider the case of driven translocation
with hydrodynamic interactions (HIs). We show that by augmenting the BDTP
theory with HIs one reaches a good agreement between the theory and previous
simulation results found in the literature. Our results suggest that the
scaling relation between and is retained even in this case.Comment: 5 pages, 4 figure
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