Ionic liquids make DNA rigid

Persistence length of dsDNA is known to decrease with increase in ionic concentration of the solution. In contrast to this, here we show that persistence length of dsDNA increases dramatically as a function of ionic liquid (IL) concentration. Using all atomic explicit solvent molecular dynamics simulations and theoretical models we present, for the first time, a systematic study to determine the mechanical properties of dsDNA in various hydrated ionic liquids at different concentrations. We find that dsDNA in 50 wt% ILs have lower persistence length and stretch modulus in comparison to 80 wt% ILs. We further observe that both persistence length and stretch modulus of dsDNA increase as we increase the ILs concentration. Present trend of stretch modulus and persistence length of dsDNA with ILs concentration supports the predictions of the macroscopic elastic theory, in contrast to the behavior exhibited by dsDNA in monovalent salt. Our study further suggests the preferable ILs that can be used for maintaining DNA stability during long-term storage.Comment: 16 pages, 3 figures, Supplementary Information (Accepted for publication in the Journal of Chemical Physics, AIP (USA)

Surface charge induced modifications of the structure and dynamics of mixed dipolar liquids at solid-liquid interfaces: a molecular dynamics simulation study

Molecular dynamics simulations are carried out to investigate the structural and dynamical properties of binary Stockmayer liquids near charged solid surfaces at varying surface charge density. The two solvent components differ widely in their polarity. The dipolar mixtures are formed at varying composition and the properties of the interfacial molecules are calculated in terms of several equilibrium and dynamical quantities such as the number density and polarization profiles, electrostriction at surfaces, linear and angular velocity autocorrelation functions, perpendicular (z) and parallel (x,y) components of translational diffusion tensors and rotational diffusion coefficients. The extent of selective adsorption of one species against the other at the surfaces is investigated as a function of surface charge density and composition and its effects on translational and rotational diffusion of interfacial molecules are discussed. The dynamical properties of the interfaces are also compared with those of the bulk

Structure and dynamics of mixed dipolar liquids near solid surfaces: a molecular dynamics simulation study

The structural and dynamical properties of binary Stockmayer liquids near solid surfaces are investigated by means of molecular dynamics simulations. The two solvent components differ widely in their polarity and they are mixed at varying mole fraction. The dipolar mixtures are confined between two planar solid surfaces and the properties of the interfacial molecules are calculated in terms of several equilibrium and time dependent quantities such as the number density, orientational structure, perpendicular (z) and parallel (x,y) components of translational diffusion tensors, rotational diffusion coefficients and various time correlation functions of both the species. The extent of selective adsorption of one species against the other at the surface is investigated and its effects on various dynamical properties of the interfaces are discussed. The dynamics of solvation of a newly created charge distribution near a solid surface is also studied and the results are compared with the dynamics of solvation in mixed solvent in the bulk phase. The solvation at the interface is found to occur at a much slower rate primarily because of the selective adsorption of the less polar solvent at the solid surface and redistribution of solvent molecules near the solute

Interfacial structure of a mixed dipolar liquid in contact with a charged solid surface

We develop a nonlinear theory for the calculation of interfacial structural properties of a dipolar mixture in contact with a charged solid surface. Both the molecular sizes and the dipole moments of various species can be unequal. Explicit numerical results are obtained for the interfacial structure of a binary dipolar liquid in contact with a charged surface of varying surface charge density. The dipole moments of the two species are also varied. The density profiles of both the species are found to be highly inhomogeneous and oscillatory near the solid surface. The more polar species is found to exhibit a positive electrostriction at the surface with an increasing surface electrostatic field. An opposite behavior is observed for the less polar species. The polarization profiles reveal pronounced orientational order of the solvent molecules of both the species near the charged surface. The contact polarizations of the more polar and the less polar species show, respectively, a more than linear and a less than linear increase with increasing surface charge density. The predictions of the present theory for a given set of parameter values are compared with the results of Monte Carlo simulation of the same system and a good agreement is found for the inhomogneous density and polarization profiles of both the species

Molecular dynamics simulations of simple dipolar liquids in spherical cavity: effects of confinement on structural, dielectric, and dynamical properties

The equilibrium and dynamical properties of Stockmayer liquids confined in a spherical cavity are investigated by means of molecular dynamics simulations. The simulations are carried out at varying density and cavity size. Various equilibrium and time dependent quantities such as the spatial and orientational density profiles, dielectric constants, average energies, pressures, components of translational diffusion tensors parallel and perpendicular to the cavity surface, rotational diffusion coefficients and several time correlation functions are calculated and the effects of confinement on the above properties are discussed. The density profiles are found to be highly inhomogeneous near the cavity wall, and the dielectric constant of the liquids in cavity is found to be significantly smaller than that of the bulk phases. The diffusion along the surface normal and also the dipolar orientational relaxation of solvent molecules in cavity are found to slow down because of confinement. The dynamics of solvation of a newly created charge distribution in the cavity is also studied and the results are compared with the dynamics of solvation in bulk solvent. The solvation in the cavity is found to occur at a much slower rate

Structure of a mixed dipolar liquid near a metal surface: a combined approach of weighted density and perturbative approximations

We study the interfacial structure of a mixed dipolar liquid in contact with a metal surface by using a combined approach of the weighted density and the perturbative approximations. Both the molecular size and the dipole moment of various species can be unequal. The metal surface is treated by using the jellium model. Explicit numerical results are obtained for the interfacial structure of a binary dipolar liquid in contact with a metal surface of varying electron density. The theoretical predictions are compared with the results of Monte Carlo simulations and a good agreement is found for the inhomogeneous density, mole fraction, and polarization profiles of both the species in the interfacial region

Computer simulations of dipolar liquids near charged solid surfaces: electric-field-induced modifications of structure and dynamics of interfacial solvent

The structural and dynamical properties of Stockmayer liquids near charged solid surfaces are investigated by means of molecular dynamics simulations. The inhomogeneous number density and orientational structure of dipolar molecules in the interfacial region are calculated for surfaces of varying charge density. The relaxation of perpendicular (z) and parallel (x,y) components of velocity autocorrelation functions, angular velocity autocorrelation functions, translational diffusion tensors and rotational diffusion coefficients are calculated for both interfacial and bulk solvent molecules. The dependence of these quantities on the electric field generated by surface charge density is discussed. The dynamical properties of the interfacial solvent are compared with those of the bulk. These studies reveal useful information on modifications induced by surface charge density on the structure and dynamics of interfaces

Dielectric constant of water confined in nanocavity

The dielectric constant of water confined in a nanodimensional spherical cavity is calculated by means of molecular dynamics simulations. The simulations are carried out by using two different water models: soft sticky dipole and simple point charge/extended. Three different sizes of the confining cavity are considered for each water model. For both the models, the dielectric constant of water in the cavity is found to be significantly smaller than that of bulk water. A nearly 50% decrease of the dielectric constant is observed when water is confined in a cavity of about 12 Å in diameter. In the present models, there is no electrostatic interaction between water and the cavity surface, and thus, the reduction of the dielectric constant observed in this study is purely a result of confinement

Rotational dielectric friction and molecular relaxation at metal-solvent interfaces

Dynamical properties of dipolar liquids near metal surfaces are investigated by means of molecular dynamics simulations. The dipolar molecules are characterized by the well-known Stockmayer potential (Lennard-Jones plus point dipole interaction) and the metal is treated by employing a jellium model. The metal potential is calculated self-consistently by using density functional theory. The relaxation of angular velocity autocorrelation function, time and frequency dependent rotational dielectric friction and dipole orientational correlation function are calculated for interfacial and bulk dipolar molecules. The dynamics of solvation of a newly created ion in the vicinity of metal surface is also investigated. These studies provide useful information on metal field induced modifications of dielectric friction and molecular relaxation in dipolar liquids near metal surfaces