CONFORMATIONAL INVESTIGATION OF SOME MACROBICYCLIC COMPOUNDS AND OF THEIR MONOPROTONATED CATIONS THROUGH A COMPARISON BETWEEN X-RAY CRYSTAL-STRUCTURES AND MOLECULAR-DYNAMICS SIMULATIONS

In preceding works, which have dealt with the synthesis and characteri sation of a series of macrobicyclic compounds with five donor atoms, t he unusually high basicity constants of these polyaminic cage-like mol ecules have been ascribed to the inclusion of the proton inside the ma crobicyclic cavity which results in a very efficient hydrogen-bond net work, The present paper, based on previously reported X-ray crystal st ructures regarding five-atoms bridging units and on molecular modellin g studies shows that the disposition of the five donor atoms in the mo noprotonated species is related to the protonation site. Precisely, if the protonation occurs on a bridge-head nitrogen the resulting geomet ry of the donors is a trigonal bipyramid, whereas it is square pyramid al when the proton is bound to a nitrogen belonging to a macrobicyclic chain, For what concerns the geometrical array of the donor atoms in the free amines, the favoured array seems to be the trigonal bipyramid al.