Formation of an Inclusion Complex of a New Transition Metal Ligand in β-Cyclodextrin

Abstract

The inclusion complex of a new transition metal ligand, 2,4,9-trithia-tricyclo[3.3.1.13,7]decane-7-carboxylic acid (2,4,9-trithia-adamantane-7-carboxylic acid, TPCOOH) in β-cyclodextrin was studied by 1H NMR, 2D NOESY NMR spectroscopy, host-induced CD spectroscopy, and tandem mass spectrometry. 1H NMR, MS–MS and NOESY data show that the TPCOOH guest forms a 1:1 inclusion complex with the host β-cyclodextrin. The NOESY experiments also show that TPCOOH is oriented in the complex with the thioketal end preferentially located at the larger opening of β-cyclodextrin. The orientation of the guest in the host molecule is also confirmed by the induced CD of the ligand, which shows a positive Cotton effect. An association constant of 660±20 M−1 was determined by 1H NMR titration for the complex at room temperature in D2O.