Sym-4,4'-disubstituted biphenyls are two-site substrates for the ligand -cyclodextrin. Since the sites are identical, the experimental binding constants for 1:1 and 1:2 complex formation are related to microscopic constants by Kn = 2Kx,x and Kn = /4, where • is the microscopic constant for binding of the first ligand, and axx is a cooperativity parameter describing interaction between the sites in 1:2 complex formation. Binding constants were measured for 8 sym-4,4'-disubstituted biphenyls with -cyclodextrin in aqueous solution at 25 °C and 0.10 M ionic strength by the solubility technique. Correlations were found of log Kn with -log S0 (where S0 is the substrate molar solubility) and of log axx with (the Hammett substituent constant), and these correlations are compared with the corresponding behavior of sym-1,4-disubstituted benzenes. Complexing of -cyclodextrin with 4,4'-dicarboxybiphenyl is highly cooperative.

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