Anisotropic rotational diffusion and transient nonlinear responses of rigid macromolecules in a strong external electric field

Nonlinear transient responses of polar polarizable particles (macromolecules) diluted in a nonpolar solvent to a sudden change in magnitude of a strong external dc field are evaluated using the anisotropic noninertial rotational diffusion model. The relaxation functions and relaxation times appropriate to the transient dynamic Kerr effect and nonlinear dielectric relaxation are calculated by solving the infinite hierarchy of differential-recurrence equations for statistical moments (ensemble averages of the Wigner D functions). The calculations involve matrix continued fractions, which ultimately yield the exact solution of the infinite hierarchy of differential-recurrence relations for the first- and second-order transient responses.     

Birefringence and dielectric relaxation decay transients and anisotropic rotational diffusion of macromolecules in a strong external electric field

The decay transient response of polar and polarizable rigid bodies (macromolecules) diluted in a nonpolar solvent after a sudden switch-off of a strong external dc field is evaluated in the context of the anisotropic noninertial rotational diffusion model. On solving the differential-recurrence equations for the statistical moments (expectation values of Wigner's D functions), the decay transients of the birefringence and dielectric relaxation are obtained. The solutions (valid for arbitrary strengths of an external electric field) are given in a closed form suitable for comparison with experiment and Brownian dynamics simulations.     

Discrepancy in the near-solute electric dipole moment calculated from the electric field

The electric dipole moment p ( r ) was computed as the integral of the permanent dipole moment of the solvent molecule μ( r ) weighted by the orientational probability distribution Ω( r ; O ) over all orientations, where O is the orientation of the solvent molecule at r . The relationship between Ω( r ; O ) and the potential of the mean torque was derived; p ( r ) is proportional to the electric field E ( r ) under the following assumptions: (1) the van der Waals (vdW) interaction is independent of the orientation of the solvent molecule at r ; (2) the solvent molecule and its electrical effect are modeled as a point dipole moment; (3) the solvent molecule at r is in a region far from the solute; and (4) μE( r ) ? k_BT, where k_B is Boltzmann's constant and T is absolute temperature. The errors caused by calculating near‐solute Ω( r ) and p ( r ) from E ( r ) are unclear. The results show that Ω( r ) is inconsistent with the value calculated from E ( r ) for water molecules in the first and second shells of solute with charge state Q = ±1 e, and a large variation in solvent molecular polarizability γ_mol(r), which appeared in the first valley of 4πr²E(r) for |Q| < 1 e. Nonetheless, p (r) is consistent with the values calculated from E (r) for |Q| ≤ 1 e. The implication is that the assumptions for calculating p ( r ) can be ignored in the calculation of the solvation free energy of biomolecules, as they pertain to protein folding and protein–protein/ligand interactions. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

Extended rotational diffusion and orientational relaxation of symmetric top molecules in a strong dc electric field: second-rank orientational correlation functions

Second-rank orientational correlation functions (pertaining to Kerr effect relaxation and Raman scattering) are obtained using the extended rotational diffusion (J-diffusion) model of symmetric top polar molecules in a strong constant external field. It is shown that the shape of the molecule noticeably affects all second-rank correlation functions and relaxation times in the rare collision limit. In the opposite limit of frequent collisions, the quantities of interest are shown to be shape independent as a consequence of vanishingly small inertial effects. An interpolation formula for the orientation relaxation times in the intermediate regime between the rare and frequent collision limits is also given.     

Quantum rigid dipole in a permanent electric field. I. Rigorous treatment

A behavior of a quantum rigid and pointlike dipole in a permanent electric field is under study. A dependence of a number of librational energy levels on the strength of the electric field is investigated on the basis of some rigorous results for the appropriate normal Jacobian matrices.     

Approximate analytic expression for the dynamic electrophoretic mobility of a spherical colloidal particle in an oscillating electric field

An approximate analytic expression is derived for the dynamic electrophoretic mobility of a spherical charged colloidal particle in an electrolyte solution in an applied oscillating electric field. This expression, which takes into account the relaxation effects, is applicable for all values of zeta potential at large kappa a (kappa a > or = ca. 30) and omega/2pi < or = ca. 10 MHz, where kappa is the Debye-Hückel parameter, a is the particle radius, and omega is the frequency of the electric field. It is shown that the obtained mobility expression is in excellent agreement with the exact numerical results of Mangelsdorf and White (J. Chem. Soc., Faraday Trans. 1992, 88, 3567).     

Superpositions of chiral states in the presence of electric dipole, magnetic dipole, and electric quadrupole interactions

This paper is a straightforward generalization of Maierle-Harris proposal regarding parity implications on the superpositions of chiral states of a molecule. It is shown that the inclusion of electric quadrupole and magnetic dipole interactions removes several of restrictions on the preparation of superpositions of mid R:L and mid R:R states of a chiral molecule. It is also found that the dephasing of mid R:L and mid R:R superpositions, due to the spontaneous emission from the chiral molecule, has opposing contributions from electric quadrupole-magnetic dipole and electric dipole interactions.     

On the rotational temperature and structure dependence of electric field deflection experiments: a case study of germanium clusters

Molecular beam electric field deflection experiments offer a probe to the structural and dielectric properties of isolated particles in the gas phase. However, their quantitative interpretation is still a formidable task. Despite the benefits of this method, the analysis of the deflection behavior is often complicated by various experimental and theoretical problems, including the amount of energy stored in internal and rotational modes of the deflected particle and the amount of structural asymmetry. In this contribution, we address these issues by discussing the experimentally observed field-induced deflection of Ge(9), Ge(10), and Ge(15) clusters in comparison to quantum mechanical and classical deflection models. Additionally, we derive simple formulas to describe how the molecular beam deflection depends on the rotational temperature and the symmetry of the particle. Based on these results, we discuss to what extend molecular beam electric field deflection experiments can be used as a tool for structure determination of isolated clusters in the gas phase.     

Biaxial order and a rotation of the minor director in the nematic phase of an organo-siloxane tetrapode by the electric field

Biaxiality in the nematic phase for a liquid crystalline tetrapode made up of organo-siloxanes mesogens is investigated using polarized infrared spectroscopy. An ordering of the minor director for the homeotropically aligned sample is found to depend on the amplitude of the in-plane electric field. On increasing the in-plane electric field, the minor director, lying initially along the rubbing direction, rotates to the direction of the applied field. The scalar order parameters of the second rank tensor are found to depend significantly on the strength of the electric field. A most significant increase is found in the nematic order parameter and in the parameter that characterizes the phase biaxiality.     

Rotational diffusion and alignment of short gold nanorods in an external electric field

We present measurements of the polarized extinction of gold nanorod suspensions exposed to an external electric field. By employing an amplitude modulated field in combination with lock-in detection we resolve changes in the optical density as low as 10(-6) in an integration time of 10 s. This sensitivity allows us to probe the partial alignment of small gold nanorods with an aspect ratio of 2.5 and a width ranging from 13 nm to 28 nm. The degree of orientation scales as the square of the electric field strength, as expected for an induced dipole moment in an external field. By varying the modulation frequency we measure the rotation diffusion constant of different samples, which are in excellent agreement with the calculated values for a short cylinder.     

Influence of varying electroosmotic flow on the effective diffusion in electric field gradient separations

Recently the use electric field gradient focusing (EFGF) to enhance focusing of proteins has been proposed and explored to provide significant improvement in separation resolution. The objective of EFGF is to focus proteins of specific electrophoretic mobilities at distinct stationary locations in a column or channel. This can be accomplished in a capillary by allowing the electric potential to vary in the streamwise direction. Because the electric field is varying, so also is the electrokinetic force exerted on the proteins and the electroosmotic velocity of the buffer solution. Due to the varying electric field, the Taylor diffusion characteristics will also vary along the column, causing a degradation of peak widths of some proteins, dependent on their equilibrium positions and local velocity distributions. The focus of this paper is an analysis that allows characterization of the local Taylor diffusion and resulting protein band peak width as a function of the local magnitude of the EOF relative to the average fluid velocity for both cylindrical and rectangular channels. In general the analysis shows that as the ratio of the local electroosmotic velocity to the average velocity deviates from unity, the effective diffusion increases significantly. The effectiveness of EFGF devices over a range of protein diffusivities, capillary diameters, flow velocities, and electric field gradient is discussed.     

Effect of anisotropic diffusion and external electric field on the rate of diffusion-controlled reactions

In this paper we investigate theoretically the effect of an external electric field on the rate constant of steady-state bulk diffusion-controlled reactions. We generalize previously derived results for isotropic diffusion in the absence of interparticle interaction [J. Chem. Phys. 87, 4622 (1987)] to the case where translational diffusion is anisotropic. A frequently occurring situation of transverse isotropy where D(x)=D(y) not equal to D(z) is considered in detail. We derive the first-order expansion for the reaction rate constant in terms of the electric field strength E, k(E)=k(0) (1+1/2epsilongamma), where gamma=k(0)/4piRD( perpendicular ), epsilon=qER/k(B)T, q is the charge, R is the contact distance, and D( perpendicular ) is the transverse diffusion coefficient. Numerical calculations show that this first-order expansion works well in the whole range of applicability of the Nernst-Einstein relation, i.e., for epsilon<1.     

An electric cyclophane: cavity control based on the rotation of a paraphenylene by redox switching

Although a free rotation around a single bond gives no mechanical output, it has let us imagine a molecular motor. A para-substituted aromatic ring can be regarded as a rotator with the para-rotation axis. When it is incorporated in a wider pi-conjugated system, a quinoidal structure is generated accompanied by oxidation on the substituted groups at the 1,4-position, and the axis is fixed. A paraphenylenediamine was selected as the nanomechanical molecular module capable of locking and releasing the free rotation using an electrode in solution. We inserted the module into a simple molecular system, cyclophane. It was clarified that the cyclophane was able to open and close its cavity in a reversible redox process repeatedly.     

Influence of the electric field on a particle in a space with a disclination

We consider a quantum particle in a space with a linear topological defect, i.e., disclination. The effect of the uniform electric field in this space, on the particle, is shown to cause a translation of the wave function. In addition, the electric field is not found to be affected by the defect. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

The interaction between an oscillating dipole and a metal surface described by a jellium model and the random phase approximation

The electric field acting on an oscillating dipole located near a metal surface is computed. The latter is described by a jellium model and the random phase approximation. The aim is ascertaining to what extent spatial dispersion and variation of the dielectric properties across the interface modify the image dipole. Implications for surface Raman and fluorescence spectroscopy are discussed.     

An electron diffusion model of the space-time distribution of radicals in a multibubble cavitation field

Conditions under which electric discharges can arise in cavitation bubbles pulsating in a multibubble cavitation field are considered. Possible electric discharge types are discussed. It is shown that, in an electric breakdown in a cavitation bubble, the probability of the formation of a streamer (all the more, a leader) or corona discharge is negligibly small. It was found that, in a cavitation bubble, the development of an electron avalanche is most probable. The basic parameters of an elementary electron avalanche are estimated.     

Numerical evaluation of matrix elements of the electric field and electric field gradient operators in a slater basis set

A method is proposed for evaluating all matrix elements of the electric field and electric field gradient operators in a Slater basis set fo systems with an arbitrary number of nuclei and geometry. These integrals are evaluated using a numerical quadrature after having modified the integrand to remove all infinities. The integration ranges are broken to avoid integrating through cusps in the integrand. With reasonable grids these procedures are adequate for numerical evaluation with an accuracy of five to six decimal places (in a.u.). Particular cases are briefly discussed.     

Quantum rigid dipole in a permanent electric field. II. Model of librational motion in liquid water and ice Ih: Preliminary results

A theoretical one-body model of librational motion in liquid water and ice Ih is proposed within the quantum mechanical treatment of a rigid and pointlike dipole in a permanent electric field and the concept of the internal electric field justified for V-structure of liquid water.