Thallium-205 nuclear magnetic resonance study of the thallium(I)-gramicidin A association in trifluoroethanol.

Association of the thallous ion with gramicidin in 2,2,2-trifluoroethanol has been investigated by thallium-205 NMR spectroscopy. The data obtained suggest that the gramicidin dimer has two strong binding sites and one or more weak binding sites. Association constants for the strong binding sites were found to have the same value. From the temperature dependence of the strong binding site association constants, values for the association enthalpy and entropy of -2.13 +/- 0.12 kcal/mol and +5.45 +/- 0.04 eu, respectively, were obtained.