The diffusion coefficient of a molecule is a much more reliable guide to the aparent molecular weight and tertiary structure than NMR relaxation time or line width measurements, especially in absence of resonance assignments. The Stokes-Einstein relation relates the Diffusion coefficient, D, of a particle to its molecular shape via a friction coeficient f

Factors affecting the diffusion coefficient:

• Molecular shape
  
• Molecular size
  
• Solvent viscosity
  
• Solution properties as salt concentration, pH, temperature ...