What's the difference between Rg & Rh?

The radius of gyration (R_g), classically measured by monitoring the angular dependence of the sample scattering intensity in a static light scattering experiment, is defined as the mass weighted average distance from the center of mass to each mass element in a macromolecule.

The hydrodynamic radius (R_h), measured using the dynamic light scattering technique, is representative of the size of a hard sphere that diffuses at the same rate as the macromolecule being measured.

Theoretically derived molecular shape dependent relationships between Rg and Rh exist, including those listed below (Schmitz, S. K. "An Introduction To Dynamic Light Scattering By Macromolecules", Academic Press, New York, 1990).

R_g = 0.774 R_h (spheres)

R_g = 0.816 R_h (coils)

R_g = 1.732 R_h (cylinders)

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