, and in free bind 18 18 deformation of C18 from its free state (circular shape) to complexed state, and this can be easily recognized from the structure maps in Figure . According to the principle of thermodynamics, ∆Gbind is the most straightforward metric for determining binding capacity. The ∆Gbind data are all distinctly negative, indicating that all M + are able to stably bind to C18 at least under gas standard state, although penalty effect due to decrease in entropy evidently hinders the complexation to some extent, which is largely exhibited by the clear difference between ∆Ebind and ∆Gbind.