Light Scattering
In a controlled experiment, the scattering of light by molecules is influenced by three variables, molecular weight (MW), concentration and dn/dc, a parameter related to the index of refraction. In many circumstances, dn/dc is constant in aqueous solutions for known concentration and dn/dc, hence one can determine the sample's absolute MW from the scattering of light.

SEC-MALS (Size Exclusion Chromatography – Multi Angle Light Scattering) is a technique that uses HPLC with a size-exclusion column (separation between 10 – 150 KDa or between 10 – 1000 KDa) to separate different sizes molecules together with MALS system to measure the molecular weight of the separated molecules and a refractive index detector to measure the concentration at each measuring point. For large molecules (> 10 nm)  one can also measure the radius of gyration (Rg). 

There is also possibility to work in a batch mode (without the SEC) to measure the average molecular weight of all the solutes in a solution. In this mode one can also measure the second virial coefficient, A2, or the dn/dc of molecules in solution. A2 is a measure of the intermolecular interactions (non-ideality).

CG-MALS (Concentration Gradient – MALS) is a technique which can be used to measure self and hetero association of molecules in solution. It can determine parameters such as KD, A2 and for slow kinetics also kon and koff.it provides also the true stochiometry of the interacting molecules. In this technique, one measures the light scattering of a molecule in different concentrations. The system is fully automated with syringe-mixer.
 
For experiment design and operation of the system, please contact:
 

Hezi Sasson (tel. 03-6406211). sassonye at post.tau.ac.il