Topic

# Rotational diffusion

About: Rotational diffusion is a research topic. Over the lifetime, 3117 publications have been published within this topic receiving 90161 citations.

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TL;DR: The approach promises to improve the accuracy of structures determined by NMR, and extend the size limit, and distances and angles derived from dipolar couplings in human ubiquitin are in excellent agreement with its crystal structure.

Abstract: In isotropic solution, internuclear dipolar couplings average to zero as a result of rotational diffusion. By dissolving macromolecules in a dilute aqueous nematic discotic liquid-crystalline medium containing widely spaced magnetically oriented particles, a tunable degree of solute alignment with the magnetic field can be created while retaining the high resolution and sensitivity of the regular isotropic nuclear magnetic resonance (NMR) spectrum. Dipolar couplings between1H-1H, 1H-13C,1H-15N, and 13C-13C pairs in such an oriented macromolecule no longer average to zero, and are readily measured. Distances and angles derived from dipolar couplings in human ubiquitin are in excellent agreement with its crystal structure. The approach promises to improve the accuracy of structures determined by NMR, and extend the size limit.

1,634 citations

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TL;DR: It is suggested that for a realistic situation translational diffusion should be about four times faster in relation to rotational diffusion than in the isotropic case.

Abstract: Brownian motion (diffusion) of particles in membranes occurs in a highly anisotropic environment. For such particles a translational mobility (independent of velocity) can be defined if the viscosity of the liquid embedding the membrane is taken into account. The results of a model calculation are presented. They suggest that for a realistic situation translational diffusion should be about four times faster in relation to rotational diffusion than in the isotropic case.

1,611 citations

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TL;DR: Rhodopsin undergoes rapid lateral diffusion in the disk membranes of isolated frog and mudpuppy rods, which indicates the disk membrane is highly fluid with a viscosity of ∼1P.

Abstract: Rhodopsin undergoes rapid lateral diffusion in the disk membranes of isolated frog and mudpuppy rods. The rate of lateral diffusion is consistent with the rapid rotational diffusion of rhodopsin: both indicate the disk membrane is highly fluid with a viscosity of ∼1P.

604 citations

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TL;DR: In this paper, the rotational diffusion constant of a closed cylinder rotating in a viscous medium has been calculated for length (2a) over width (2b) ratios larger than 3.5 to within a first order in b/a.

Abstract: The torque constant of a closed cylinder rotating in a viscous medium has been calculated for length (2a) over width (2b) ratios larger than 3.5 to within a first order in b/a. The analysis demonstrates how the contributions to the viscous dissipation tend to be underestimated in hydrodynamic considerations so that the geometrical values deduced from them come out too high. Experimental results for the torque on cylindrical rods and ellipsoids for a/b values from 3.5 to 30 are close to the theoretical results. For a/b>10 the difference is about 10%; for shorter molecules 20%. With the rotational diffusion constant given by 3kT (σ—γ)/8πηa3ω, where σ=log2a/b we obtain best fit with γ(σ>2)=1.57–7 (1/σ—0.28)2±0.25. Experimental data for the rotational diffusion constant of a cylindrical virus (a/b=20) in water, obtained by O'Konski and Haltner agree with this result within 10%. The length of the protein fits within 3%.

583 citations

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TL;DR: In this article, the Debye model of rotational diffusion by small angular steps is generalized to allow molecular reorientation through angular steps of arbitrarily large size, and the generalized diffusion models are found to give a rather accurate representation of molecular re-orientation in liquids and gases.

Abstract: The Debye model of rotational diffusion by small angular steps is generalized to allow molecular reorientation through angular steps of arbitrarily large size. The generalized diffusion models are found to give a rather accurate representation of molecular reorientation in liquids and gases, as observed in the infrared and Raman spectra of simple molecules. One interesting feature of both the theoretical and experimental correlation functions is that the approach to rotational equilibrium often takes the form of a damped oscillation, rather than the monotonic decay which is usually assumed.

559 citations