Experimental techniques for determining thermodynamic quantities of biopolymer interactions in solution

Experimental Techniques for Determining Thermodynamic Quantities of Biopolymer Interactions in Solution 

The membrane osmometer is a device for measuring the osmotic pressure, n, of a biopolymer solution separated from the pure solvent by a semi-permeable membrane (Tanford, 1961 Edmond and Ogston, 1968 Tombs and Peacocke, 1974 Edsman and Sundelof, 1987 Amur et al., 

The difference between the chemical potential of the solvent in its pure state and that in the biopolymer solution determines the osmotic pressure of the biopolymer solution  

/u ° and ju are, respectively, the chemical potentials of pure solvent and solvent at a certain concentration of biopolymer V is the molar volume of the solvent Mn=2 y/M/ is the number-averaged molar mass of the biopolymer (sum of products of mole fractions, x, and molar masses, M, over all the polymer constituent chains (/) as determined by the polymer polydispersity) (Tanford, 1961) A2, A3 and A4 are the second, third and fourth virial coefficients, respectively (in weight-scale units of cm mol g ), characterizing the two-body, three-body and four-body interactions amongst the biopolymer molecules/particles, respectively and C is the weight concentration (g ml-1) of the biopolymer. 

At small solute concentrations the second virial coefficient is the main contributor to the value of n, and so in practice the general equation (5.16) is usually restricted to just the term containing the second virial coefficient. At this level of approximation, the osmotic pressure of a ternary solution (biopolymer, + biopolymer, + solvent) may be expressed in the following simple form using the molal scale (Edmond and Ogston, 1968)  

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