Diffusion of hinged particles: An exception to the Einstein relation

Transient electric birefringence of wormlike macromolecules in electric fields of arbitrary strength: A computer simulation study

We have studied the birefringence decay of linear models of macromolecules for two different types of flexibility, the broken-rod chain and the wormlike chain, using a computer simulation of a transient electric birefringence experiment. We have paid particular attention to the influence of the intensity of the orienting field, including two orienting mechanisms, the induced dipole, and the permanent dipole. We have compared wormlike and broken-rod models of the same radius of gyration, finding that they present a different decay curve under the influence of the same intensity of the field. We have seen that these differences are due to the faster relaxation times (smaller in the wormlike chain model) and amplitudes, because, regardless of the type of flexibility, the overall size of a molecule (measured by the radius of gyration) essentially determines the longest relaxation time. We have also analyzed how the relaxation process is affected by the degree of flexibility, the orientation mechanisms, and the intensity of the field. Studying a different aspect, we have paid attention to the deformation of a molecule in a transient electric birefringence experiment as a source of information. In this work we have developed equations to characterize this deformation in terms of one of the components of the gyration tensor, if a dynamic light scattering experiment under the influence of an electric field could be performed. To develop this work we have simulated the Brownian dynamics of the different models, relaxing after the removal of an orienting external electric field of arbitrary strength. A comparison with other methods such a the rigid body treatment or the correlation analysis of Brownian trajectories has also been included. We have seen that differences between the two Brownian dynamics methods are small and that the rigid-body treatment is only an acceptable approximation to obtain the longest relaxation time.

Hydrodynamic properties of complex, rigid, biological macromolecules: theory and applications

Among the Various methods for characterizing macromolecules in solution, hydrodynamic techniques play a major role. Since the advent of the ultracentrifuge and the development of viscometric apparatus, sedimentation coefficients and intrinsic viscosities have been extensively used to learn about the size and shape of synthetic and biological polymers. More recently, refined techniques such as quasielastic light scattering, transient electric birefringence and fluorescence anisotropy decay have made it possible to obtain in a simple and rapid way quantitative information of high precision on the translational and rotational brownian dynamics of dissolved macromolecules.

Conformation of myosin in dilute solution as estimated from hydrodynamic properties

On the basis of the current knowledge of the structure and dimensions of myosin and its parts, we analyze available data on hydrodynamic properties (translational diffusion, rotational diffusion, and intrinsic viscosity) for comparison with values calculated for models with varying geometry. Special attention is paid to detecting flexibility effects in those properties. After obtaining a plausible model for subfragment S-1, we concentrate on the conformation of the rodlike parts of myosin. Although uncertainties in the experimental values do not allow a rigorous, quantitative analysis, we show how hydrodynamic data provide evidence for the flexibility of the rod at the joint of subfragment S-2 and light meromyosin.