Synthesis of deuterium-labeled cryptophane-A and investigation of Xe@cryptophane complexation dynamics by 1D-EXSY-NMR experiments.

We present the synthesis of a series of deuterated cryptophanes 2-6 by a slightly modified procedure used for cryptophane-A. We show that for [Xe@cryptophane] complexes the use of variable-temperature one-dimensional 129Xe magnetization transfer (1D-EX-SY) allows the measurement of exchange rates. From these data the decomplexation activation energy Ea has been estimated to be 37.5+/-2 kJ mol(-1). The decomplexation activation enthalpy, deltaH(++) = 35.5+/-2 kJ mol(-1), and entropy, deltaS(++) = -60+/-5 J mol(-1) K(-1), have also been calculated. The calculated negative activation entropy suggests that the activated complex associated with decomplexation is conformationally more strained than the complex in its ground state.