Influence of hydrodynamic coupling on the electric linear dichroism of DNA fragments

In the present work, we study the effect of translational-rotational hydrodynamic coupling on the stationary electric linear dichroism of DNA fragments. The theoretical resolution of the problem has, so far, been dealt with analytic methods valid only in the limit of low electric fields. In this work, we apply numerical methods that allow us to study the problem and also consider electric fields of arbitrary strength. We use the bent rod molecules model to describe DNA fragments with physical properties characterized by their electric charge, electric polarizability tensor, rotational diffusion tensor, and translation-rotation coupling diffusion tensor. The necessary orientational distribution function to calculate electric dichroism is obtained by solving the Fokker-Planck equation through the finite difference method. We analyze the different contributions due to electric polarizability and translational-rotational coupling to the electric dichroism.     

Influence of hydrodynamic coupling on the density dependence of quasi-one-dimensional diffusion

The effect on the short time one particle diffusion coefficient of hydrodynamic interaction between pairs of colloid particles, and between colloid particles and the walls of a quasi-one-dimensional cylindrical channel, are calculated using the method of reflections. The nonzero size of the colloid particle is accounted for in the analysis, and the theoretical predictions are compared with the experimental data of Lin, Cui, Lee, and Yu for the short time one particle diffusion coefficient of colloids in a square open channel [Europhys. Lett. 57, 724 (2002)].     

Some aspects of vibronic coupling in circular dichroism

After a review of the quantum mechanical formulation of vibrational-electronic coupling, the adiabatic approximations for ordinary absorption dipole strength and circular dichroic absorption rotatory strength are presented and interpreted. The expressions include the effect of two vibrational quantum changes coupled to electronic excitation in addition to the more familiar concept of coupling by a one quantum change. A polarizability theory of vibronically coupled rotatory strength is presented which is comparable to the polarizability theory of rotatory strength without regard to vibration.     

Oxidation of fullerene mixtures obtained by the electric arc evaporation of graphite rods

A mixture of stable derivatives of fullerenes containing ether/diketone functional groups, some of which are water-soluble, were obtained during the destruction of fullerenes upon annealing in air. The results were confirmed by IR and UV spectroscopy.     

The effect of wettability on drop attachment to glass rods

The coalescence of droplets in fibrous filters depends on many parameters such as wettability, filter depth, flow velocity, and filter materials. The objective of this work is to determine the effect of the wettability on the coalescence mechanism. Experimental results from tests on coated glass rods are presented. Three different silanes are deposited on the glass rod surfaces to change the surface wettability. Flow of water-in-oil emulsion past the glass rods is observed. When the rod surface is wetting the dispersed phase coats the rod. When the surface is nonwetting the drops do not stick easily to the surface and do not coat it but slide around to the downstream side, where they are dragged off the rod. Such behavior is important in understanding the performance of coalescing filter media.     

Diffusion of spheres in isotropic and nematic networks of rods: electrostatic interactions and hydrodynamic screening

Translational diffusion of a small charged tracer sphere in isotropic and nematic suspensions of long and thin charged rods is investigated as a function of ionic strength and rod concentration. A theory for the diffusive properties of a small sphere is developed, where both (screened) hydrodynamic interactions and charge interactions between the tracer sphere and the rod network are analyzed. Hydrodynamic interactions are formulated in terms of the hydrodynamic screening length. As yet, there are no independent theoretical predictions for the hydrodynamic screening length for rod networks. Experimental tracer-diffusion data are presented for various ionic strengths as a function of the rod concentration, both in the isotropic and nematic states. Orientational order parameters are measured for the same ionic strengths as a function of the rod concentration. The hydrodynamic screening length is determined from these experimental data and scaling relations obtained from the above mentioned theory. For the isotropic networks, a master curve is found for the hydrodynamic screening length as a function of the rod concentration. For the nematic networks the screening length turns out to be a very sensitive function of the orientational order parameter.     

Vibronic coupling effect on the paramagnetism of deoxygenated hemoglobin

A square pyramidal iron(II) complex coupled with a β₁ vibrational mode is considered as a model for deoxyhemoglobin. The calculations performed on this model show that the introduction of the vibronic coupling may allow a strong reduction of the rhombic splitting and account for the different magnetic moment in phosphate-free and phosphate-bound deoxyhemoglobin.     

The effect of nanoparticle nonuniformity on the ratio of gyration and hydrodynamic radiuses

The ratio of the radius of gyration, obtained by static light scattering, and the hydrodynamic radius, obtained by dynamic light scattering, are routine experimental techniques for the assessment of nanoparticle shape. The potential effect of particle nonuniformity is mostly not considered. In this communication, we demonstrate that, even with medium particle nonuniformities, it is advisable to apply appropriate corrections. The values of the correction factors are offered in a diagram for various particle shapes, and two types of particle-size distributions and their widths.     

The effect of hydrodynamic interactions on the dynamics of DNA translocation through pores

In this work, we investigate the effect of hydrodynamic interactions on the dynamics of DNA translocation through micropores. We simulate DNA as a bead-spring chain and use a lattice Boltzmann method to simulate the flow field that arises from the motion of the molecule. We investigate the free-draining entrance of DNA to the pore by diffusion and find that, consistent with experiments, molecules have a higher probability of entering the pore from one end. We then consider the electric-field driven translocation of 21-210 microm DNA with and without hydrodynamic interactions. Consistent with experiments, we study translocation events that are much shorter than the relaxation time of DNA. We find that the effect of hydrodynamic interactions on this process is to cause different regions of a molecule, other than the ones pulled by voltage or chain connectivity into the pore, to move toward the pore. We quantify this effect and show that it is smaller than the difference in the translocation dynamics of chains that arises from different initial configurations of the molecules. A power-law scaling of translocation time with chain length is observed, with exponents of 1.28+/-0.03 and 1.31+/-0.03 in simulations with and without hydrodynamic interactions, respectively. Our results are in good agreement with recent translocation experiments conducted in small pores and show that, for the regime considered in this work, hydrodynamic interactions play a minor role in the relation of the translocation time to chain length. For fast translocation processes, the effect of hydrodynamic interactions is local and the main factor determining the dynamics of DNA is the initial configuration of the molecules.     

Is perfection ever attainable? Strong coupling effects in the Perfect Echo

The Perfect Echo sequence, originally proposed in the late 1980s, has recently been popularised with many applications in the field of small-molecule proton NMR spectroscopy. The Perfect Echo refocuses all homonuclear J-couplings for AX spin systems and refocuses magnetization in-phase for more complex weakly coupled spin systems, albeit with some intensity reduction. In contrast to suggestions in previous publications, spectra acquired in our laboratory showed that the Perfect Echo caused intensity distortions in strongly coupled systems where the chemical shift difference between the coupled spins was not large compared to the J-coupling. This paper reports experimental observations and theoretical analysis of strongly coupled spins to confirm the distortions are real and that they originate principally from transfer of magnetization caused by the final inversion pulse of the Perfect Echo. The intensity changes are not large, but because of them, identifications of coupling partners based on resonance intensities (“roofing”) can no longer be relied on when the Perfect Echo is used. However, theory and experiment confirm that adding an orthogonal excitation pulse at the end of the Perfect Echo greatly reduces the distortions.     

Unprecedented metal template effect on the coupling of dithiafulvene moieties

Coordination of two dithiafulvenyldiphenylphosphines on a Mo(CO)(4) fragment allows a carbon-carbon bond formation upon oxidation, leading to a novel type of metallacycle substituted by a redox active vinylogous tetrathiafulvalene.     

Chiral-achiral molecular coupling: The effect on the chiral partner

Pair coupling between a chiral molecule and an achiral molecule can induce weak circular dichroism in the achiral partner, as is well known in induced circular dichroism. Here the effect of the same coupling on the chiral partner is analyzed. The effect is an increase or decrease in the rotatory strength that may be detectable under conditions where the effect is enhanced by a near-resonance.     

The effect of covalency on the spin—orbit coupling constant

It is shown that the spin—orbit coupling constant, ζ, for a series of 3d transition metal ions may be satisfactorily evaluated using approximate double-zeta SCF functions. The radial distance dependence of ζ has been calculated, and the results indicate that the reduction of ζ below the free-ion value on complex formation should be dominantly to symmetry restricted covalency, rather than to central field effects.