Bovine serum albumin (BSA) is a common protein used in biophysical studies. Its molecular weight is \( 65 \mathrm{kD} \) and its diffusivity in water at \( 20^{\circ} \mathrm{C} \) is about \( 6 \times 10^{-7} \mathrm{~cm}^{2} / \mathrm{s} \) (depending weakly on \( \mathrm{pH} \) and ionic strength, which affects its folding). What is its hydrodynamic radius in nanometers (nm)?

Answer should be around 4.5 nm but using the Einstein Stokes Eqn I'm not getting anything close to that.