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71.
Counterion distributions at charged flexible membranes are studied using analytical and simulation methods in both Poisson-Boltzmann and strong-coupling limits. The softer the membrane, the more smeared out the counterion-density profile becomes and counterions penetrate through the mean-membrane surface location, in agreement with anomalous scattering results. Repulsion between membrane charges enhances protrusions and induces short-scale membrane roughening. 相似文献
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Adsorption of polymers anchored to membranes 总被引:2,自引:0,他引:2
M. Breidenich R.R. Netz R. Lipowsky 《The European physical journal. E, Soft matter》2001,5(4):403-414
Polymers, which are attached to a membrane at one of their ends, exert an entropic pressure, which curves the membrane away
from the polymers. It is shown that adsorption which arises from a short-ranged potential between the polymer and the membrane
has a large influence on the curvature of the membrane, leading to a decrease of the entropically induced curvature. If one
ignores the finite size of the anchor segment, the polymer-induced curvature does not change sign and vanishes in the limit
of strong adsorption and a pure contact potential. If one includes the finite size of the anchor segment, the membrane bends
towards the polymer for sufficiently strong adsorption.
Received 20 October 2000 相似文献
76.
R.R. Netz 《The European physical journal. E, Soft matter》2001,5(2):189-205
Using a field-theoretic formalism, we calculate the static contribution to the van der Waals interaction between two dielectric
semi-infinite half-spaces in the presence of mobile salt ions. The ions can be located in the slab, in one, or in both half-spaces.
We include an excess polarizability of the salt ions, i.e., each (spherical) ion has a dielectric constant which in general is different from the surrounding medium. This leads to
a modification of the effective dielectric constant of the medium hosting the ions. This shift can be large for high salt
concentrations and therefore influences the Hamaker constant decisively. Salt ions in the slab screen the static van der Waals
interaction, as was shown by Davies and Ninham. The salt-modified van der Waals interaction also contains salt-confinement
and salt-correlation effects. This is clearly demonstrated by the fact that the interaction is non-zero even in the case when
the dielectric constant is homogeneous throughout the system, in which case salt correlations are solely responsible for the
interaction. If the salt ions are in one or both of the two half-spaces (and no ions in the slab), the van der Waals interaction
is not screened but the effective Hamaker constant approaches a universal value for large slab thickness which is different
from the value in the absence of salt ions and which is independent of the salt concentration and of the effective electrolyte
dielectric constant. If both half-spaces contain salt, the asymptotic value of the Hamaker constant for large separation between
the half-spaces is the one obtained for the interaction between two metallic half-spaces through an arbitrary dielectric medium,
which is given by A≃ - 1.20. As is explicitly demonstrated, ion enrichment or depletion at the interfaces due to image-charge effects is already
included on the one-loop level and therefore does not lead to a change of the screened van der Waals interaction as given
by Davies and Ninham. For positive and negative ions with different valencies or different excess polarizabilities, we obtain
different adsorbed surface excesses of positive and negative ions, leading to a non-vanishing surface potential, which is
computed explicitly. All of these results are obtained on the linear one-loop level. For a special case we extend the calculation
of the dispersion interaction to the two-loop level. We find the corrections to the one-loop results to be quite large for
high salt concentrations or multivalent ions.
Received 17 February 2000 相似文献
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Sani de C.R. Da Silva Dimitrios Samios P.A. Netz Dagoberto A.R. Justo A.L. De Bortoli 《Applied mathematics and computation》2008,200(2):602
The aim of this work is the numerical simulation of the formation of hydrogen-bonded base pairs between adenine, thymine, guanine and cytosine. We use a Monte Carlo diffusion simulation with geometric (molecular distances and orientation) and energetic (acceptance proportional to the Boltzmann factor) criteria. Our results show that the occurrence of the different types of base pairs is strongly influenced by base geometry. Such results can help to understand some mechanisms, which occur at processes related to mutation. 相似文献
79.
Fábio Dos Santos Grasel Tiago Charão De Oliveira Luiz Antonio Mazzini Fontoura Italo José Da Cruz Rigotti Paulo Augusto Netz 《International journal of quantum chemistry》2012,112(6):1678-1687
Amides and carbamates present an energetic barrier associated to N? C(O) bond rotation, which determines two different equilibrium geometries. In this work, the conformational equilibrium of formanilide, acetanilide, methyl and t‐butyl phenylcarbamates, and their N‐methylderivatives was studied by AM1 and B3LYP/6‐31G(d,p) calculations. The effect of aryl p‐substituents (MeO, Me, Cl, Br, CN, and NO2) was also studied. Amide barriers were found by DFT calculation between 12 and 21 kcal/mol. Carbamates, on the other hand, showed barriers between 11 and 15 kcal/mol. AM1 underestimates the energetic barriers and provides values around half those obtained by B3LYP/6‐31G(d,p) calculations. Electron withdrawing substituents on aryl group decrease the barrier. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 相似文献
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