Binding and Saturation in Solution

The Langmuir Model Also Treats Binding and Saturation in Solution 

Put ligand molecules of type X into a solution in equilibrium with some type of particle, polymer, or surface, P. Ligands can bind the particles to form a bound complex PX, 

We want to know how 0, the fraction of binding sites on P that are filled by ligand, depends on the solution concentration of the ligand [X], 0 is the ratio (filled sites on P) / (empty + filled sites on P)  

To simplify the notation slightly, we replaced [X] by x. Equation (27.18) resembles the Langmuir Equation (27.12), but with the pressure replaced by the ligand concentration. Equation (27.18) is general, and applies whether the concentration X refers to mole fractions, molarities, molalities, or any other units. The units that you use for x determine the units of K. 

For binding in solution, the equilibrium constant K in Equation (27.18) results from both the direct ligand-surface interactions and the interactions of the ligand and surface with the solvent. 

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