Inter-DNA attraction mediated by divalent counterions

Can nonspecifically bound divalent counterions induce attraction between DNA strands? Here, we present experimental evidence demonstrating attraction between short DNA strands mediated by Mg2+ ions. Solution small angle x-ray scattering data collected as a function of DNA concentration enable model independent extraction of the second virial coefficient. As the [Mg2+] increases, this coefficient turns from positive to negative reflecting the transition from repulsive to attractive inter-DNA interaction. This surprising observation is corroborated by independent light scattering experiments. The dependence of the observed attraction on experimental parameters including DNA length provides valuable clues to its origin.     

The inverse scattering problem and the equivalent local potential

We examine the role of the non-locality of the potential in the two-body scattering by taking the nucleon-Σ system as an example. We employ a non-local potential for the nucleon-Σ channel which has the characteristic features of the quark model and reproduces the phase shifts of widely used local potentials. We use inverse scattering methods to obtain the equivalent local potential from the non-local potential, and show that the obtained local potential has a strong short range repulsion.     

Solubility and charge inversion of complexes of DNA and basic proteins

The basic proteins, protamines and histones H1, are known to condense DNA in vivo. We examine here their ability to condense and solubilize in vitro linear DNA [and a synthetic polyanion, Poly(Styrene-Sulfonate) or PSS] at low ionic concentrations by varying the charge concentration ratio. Phase separation is observed in a very narrow range of ratios for short DNA and PSS; on both sides of this range, polydisperse and charged complexes are formed. A charge inversion is detected. For long DNA chains however, a different behavior is observed: the complexes are not soluble in excess of proteins.     

Molecular dynamics simulation of multivalent-ion mediated attraction between DNA molecules

All atom molecular dynamics simulations with explicit water were done to study the interaction between two parallel double-stranded DNA molecules in the presence of the multivalent counterions putrescine (2+), spermidine (3+), spermine (4+) and cobalt hexamine (3+). The inter-DNA interaction potential is obtained with the umbrella sampling technique. The attractive force is rationalized in terms of the formation of ion bridges, i.e., multivalent ions which are simultaneously bound to the two opposing DNA molecules. The lifetime of the ion bridges is short on the order of a few nanoseconds.     

Scaling and interaction-assisted transport in graphene with one-dimensional defects

We analyze the scattering from one-dimensional defects in intrinsic graphene. The Coulomb repulsion between electrons is found to be able to induce singularities of such scattering at zero temperature as in one-dimensional conductors. In striking contrast to electrons in one space dimension, however, repulsive interactions here can enhance transport. We present explicit calculations for the scattering from vector potentials that appear when strips of the material are under strain. There the predicted effects are exponentially large for strong scatterers.     

Nonlocal Coulomb correlations in metals close to a charge order insulator transition

The charge ordering transition induced by the nearest-neighbor Coulomb repulsion V in the 1/4-filled extended Hubbard model is investigated using cellular dynamical mean-field theory. We find a transition to a strongly renormalized charge ordered Fermi liquid at V(CO) and a metal-to-insulator transition at V(MI)>V(CO). Short range antiferromagnetism occurs concomitantly with the CO transition. Approaching the charge ordered insulator, V approximately 相似文献   

Some nucleon-nucleonS-wave potentials

A number of solvableS-wave potentials are presented which match theS-wave nucleon-nucleon phase shifts. The calculation shows that for simple, four parameter potentials there are many rather different parameter sets which yield nearly the same scattering data. We give furthermore some parameter sets which are especially suited for the low energy region. The possibility of fitting the phase shifts with an energy-dependent repulsion was examined phenomenologically. We also calculated a Scott-Moszkowski version of the potentials.     

Charge asymmetry and neutron-neutron scattering

The uncertainty in the subtraction of electromagnetic effects from S-wave proton-proton scattering potentials is studied in two models using unitarily transformed potentials. Restrictions on these models caused by theoretical, off-shell and deuteron constraints are imposed. The probable uncertainty of physical interest is found to be small. It is typically only a few parts per thousand of the one-pion exchange potential. It has relatively little effect on Coulomb displacement energies. Phenomenological charge-symmetry-breaking potentials are constructed which both fit the experimental neutron-neutron (nn) scattering length (?16.4 fm). and give roughly the needed Coulomb displacement energies. These phenomenological potentials are found to contain a short-range repulsion and a strong long-range attraction for a neutron pair. The need for experimental information on the shape and state dependence of the nn force is emphasized. These can probably be obtained from precise nn scattering measurements.     

The structure of crystallized suspensions of polystyrene spheres

We have determined the crystal structure of an ordered aqueous suspension of polystyrene spheres using Bragg scattering of laser light. At low concentrations a body-centered cubic structure is found. At higher concentrations this is found together with face-centered cubic. We believe that the ordering is due to Coulomb repulsion as in the Wigner crystal.     

Atom-surface elastic scattering with additive potential

An additive corrugated potential with linear repulsion and long range attractive well is proposed for atom-surface scattering. The computational procedure yielding the scattering probabilities (essentially linear algebra) proves to be much simpler than with other potentials. For a given shape of the corrugation function and for high values of the steepness parameter one obtains results close to those of the hard corrugated wall model, while an important enhancement of the specular intensity appears, in particular at large angles of incidence, when the steepness parameter is small.     

Quasiparticle lifetime in a two-dimensional semimetal

The quasiparticle lifetime in a two-dimensional direct band semimetal limited by inelastic Coulomb scattering has been calculated in the case where two types of charge carriers are present. It has been shown that the electron lifetime at low and high concentrations of holes is mainly determined by the electron-hole and electron-electron scattering, respectively.     

Indications of partial chiral symmetry restoration from pionic atoms

Extensive data on strong interaction effects in pionic atoms are analyzed with a density-dependent isovector scattering amplitude suggested recently by Weise to result from a density dependence of the pion decay constant. Most of the so-called ‘missing s-wave repulsion’ is removed when adopting this approach, thus indicating a partial chiral symmetry restoration in dense matter. The resulting potentials describe quite well also elastic scattering of 20 MeV pions on Ca. Further tests with elastic scattering are desirable.     

Charge inversion at high ionic strength studied by streaming currents

We report charge inversion, the sign reversal of the effective surface charge in the presence of multivalent counterions, for the biologically relevant regimes of divalent ions and mixtures of monovalent and multivalent ions. Using streaming currents, the pressure-driven transport of countercharges in the diffuse layer, we find that charge inversion occurs in rectangular silica nanochannels at high concentrations of divalent ions. Strong monovalent screening is found to cancel charge inversion, restoring the original surface charge polarity. An analytical model based on ion correlations successfully describes our observations.     

Evidence for non-DLVO hydration interactions in solutions of the protein apoferritin

We have studied molecular interactions in solutions of the protein apoferritin by static and dynamic light scattering. When plotted against the electrolyte concentration, the second osmotic virial coefficient exhibits a minimum. The ascending branch of this dependence is a manifestation of a surprisingly strong repulsion between the molecules at electrolyte concentrations about and above 0.2M, where electrostatic interactions are suppressed. We argue that the repulsion is due to the water structuring, enhanced by the accumulation of hydrophilic counterions around the apoferritin molecules, giving rise to so-called hydration forces.     

Surface plasmon model of surface enhanced Raman scattering

We present a simple model for surface enhanced Raman (SER) scattering, in which enhanced surface charge densities and fields, coupled to light through a metallic grating, are modulated by vibrating molecular potentials. The modulated charge densities produce radiation at the Stokes shifted frequency.     

Repulsion between oppositely charged surfaces in multivalent electrolytes

In answer to recent experimental force measurements between oppositely charged surfaces we here reproduce the repulsion in the presence of multivalent salt using Monte Carlo simulations within the primitive model. Our osmotic pressure curves are in good agreement with experimental results. In contrast with Poisson-Boltzmann calculations, both repulsion and charge inversion are seen in the simulations. Repulsion is observed only for conditions under which there is charge inversion at large separations. However, in these cases, the repulsion is present also at intermediate separations, where there is no charge inversion. The charge inversion is thereby not the cause of the repulsion. Instead the repulsion appears to be an effect of the large amount of excess salt in the slit. Both phenomena, however, are closely linked and a consequence of ion-ion correlations, promoted by a strong electrostatic coupling.     

Macroions in salty water with multivalent ions: giant inversion of charge

Screening of a strongly charged macroion by oppositely charged colloidal particles, micelles, or short polyelectrolytes is considered. Because of strong lateral repulsion such multivalent counterions form a strongly correlated liquid at the surface of the macroion. This liquid provides correlation-induced attraction of multivalent counterions to the macroion surface. As a result even a moderate concentration of multivalent counterions in the solution inverts the sign of the net macroion charge. We show that at high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one. This giant inversion of charge can be observed in electrophoresis.