1H NMR and computational study of the conformations in solution of one host/guest complex formed with an usnic acid tweezer and 2,4,7-trinitro-9-fluorenone (TNF)

Abstract : In a host-guest model formed by a molecular tweezer 4, bearing two usnic acid units, and TNF, the TNF protons chemical shifts are measured at various temperatures. With the help of a computational study, the geometries of complexation of this host-guest system are identified and their TNF protons chemical shifts calculated. Data analysis led to conclude that in solution two types of conformations are present: the “lateral” one (similar to the structure found in the solid state) and the “longitudinal” one in which the TNF is less engaged inside the host. The proportion of the latter increases with decreasing temperatures