Stokes radius
The hydrodynamic radius (also called " Stokes radius" by George Gabriel Stokes ) is the radius of a hypothetical solid sphere, in a solvent, the same diffusion properties as the particles described by the hydrodynamic radius (for example, ion, protein micelles, virus or dust particles).
The volume of a particle in solution consists of the volume of its atomic nuclei, as well as the volume of the electron clouds surrounding the solute particles solvent molecules. These can be tied to the particle ( Grotthus mechanism) due to electrostatic interactions. If it moves through the solution, so it is forced to " entrain " this solvation shell. That is, the larger the volume of the particle, the more difficult the diffusion.
With
- T is the temperature
- η the viscosity of the solvent
- D is the diffusion constant.
The hydrodynamic radius can differ considerably from the real radius of the particles; usually it is less than the effective radius of the particle.
In practice, the hydrodynamic radius of proteins and polymers is determined by
- Dynamic light scattering
- Fluorescence correlation spectroscopy,
- Electron spin resonance spectroscopy ( ESR),
- Nuclear magnetic resonance spectroscopy (NMR) or
- Measurements of fluorescence polarization.
The radius is measured to be able to make, among other things, to examine the behavior of polymers to solvents or statements about the structure of proteins.
- Atomic physics