Hydrodynamic radius

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The hydrodynamic radius of a macromolecule or colloid particle is . The macromolecule or colloid particle is a collection of subparticles. This is done most commonly for polymers; the subparticles would then be the units of the polymer. is defined by

where is the distance between subparticles and , and where the angular brackets represent an ensemble average.[1] The theoretical hydrodynamic radius was originally an estimate by John Gamble Kirkwood of the Stokes radius of a polymer, and some sources still use hydrodynamic radius as a synonym for the Stokes radius.

Note that in biophysics, hydrodynamic radius refers to the Stokes radius,[2] or commonly to the apparent Stokes radius obtained from size exclusion chromatography.[3]

The theoretical hydrodynamic radius arises in the study of the dynamic properties of polymers moving in a solvent. It is often similar in magnitude to the radius of gyration.[4]


  1. ^ J. Des Cloizeaux and G. Jannink (1990). Polymers in Solution Their Modelling and Structure. Clarendon Press. ISBN 0-19-852036-0. Chapter 10, Section 7.4, pages 415-417.
  2. ^ Harding, Stephen (1999). "Chapter 7: Protein Hydrodynamics" (PDF). Protein: A comprehensive treatise. JAI Press Inc. pp. 271–305. ISBN 1-55938-672-X.
  3. ^ Goto, Yuji; Calciano, Linda; Fink, Anthony (1990). "Acid-induced unfolding of proteins". Proc. Natl. Acad. Sci. USA. 87: 573–577. doi:10.1073/pnas.87.2.573. PMC 53307.
  4. ^ Gert R. Strobl (1996). The Physics of Polymers Concepts for Understanding Their Structures and Behavior. Springer-Verlag. ISBN 3-540-60768-4. Section 6.4 page 290.


Grosberg AY and Khokhlov AR. (1994) Statistical Physics of Macromolecules (translated by Atanov YA), AIP Press. ISBN 1-56396-071-0