Hydrodynamic Radius - Molecular Weight Calculator

Hydrodynamic radius estimate:

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Hydrodynamic radius estimate:

Molecular weight estimate:

Hydrodynamic radius:
Molecular weight estimate:
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This calibration assumes the density of a globular protein, please exercise caution when employing this method for other biomolecules.

What is hydrodynamic radius (Rh)?

Hydrodynamic radius (Rh), is a parameter used to describe the size of a particle or molecule in a fluid (solution), taking into account its shape, mass, and interactions with the surrounding fluid molecules. The hydrodynamic radius is defined as the radius of a hypothetical sphere that diffuses at the same rate as the particle or molecule in question, under the same conditions (
Einstein, 1905
). In-solution techniques such as flow-induced dispersion analysis (FIDA) are used to determine the hydrodynamic radius experimentally.
  • The hydrodynamic radius (Rh) is a crucial parameter in drug discovery, biotechnology, and environmental science, where the behaviour of molecules in solution is essential to their function and properties. Rh delivers information about e.g. protein stability, conformational changes, folding/unfolding, functionality (binding).

What is hydrodynamic radius used for?

What is molecular weight?

  • Molecular weight (mass) is the sum of the atomic weights of all atoms in a molecule, represented with the unit kDa. In general, larger molecules tend to have higher molecular masses than smaller molecules, but the relationship between molecular weight and size is not always straightforward. 
  • The conversion from hydrodynamic radius to molecular weight is done by running globular proteins of known mass and plotting the retention time versus the molecular weight on a double logarithmic plot as a calibration curve. Note that  this method assumes that all proteins are globular, which is not always the case. 

What is the relationship between the hydrodynamic radius and the molecular weight?

Read more in our tech note

about the relationship between hydrodynamic radius and molecular weight