Cyclen substitution with urea-containing dendrimeric branches. Theoretical study considering the concept of collectivity.

Abstract

Equilibrium structures of novel dendrimeric compounds consisting of 1,4,7,10-tetraazacyclododecane (cyclen) mono- to tetra-substituted with four different dendrimeric branches have been studied. It has been shown using molecular dynamics (MD) that, even in the presence of the macrocycle cyclen, the most stable conformations are those with a globular shape due to close contact interactions between poly-functional branches. No collapse of cyclen occurred, making this cavity available for metal complexation. Terminal branches A=NHCOOtBu, B=OSi(Me)2tBu, C=Imidazole and D=CN have different molecular volumes in the decreasing order: B>A>C>D. This conclusion is in accord with the long range interaction energies, showing that the larger the volume the less the steric hindrance. Considering these energy values, the stability of the systems follows exactly the same tendency as observed for the molecular volume. More polar groups like A=NHCOOtBu and D=CN impart extra stability due to long range interactions between atoms separated by exactly three chemical bonds. The negative charge inside the cyclen cavity increases with the volume of the branches. Besides cyclen, urea groups located at the middle of the branches represent another independent point of negative charge for eventual interaction with small molecules. These compounds show a sum of small contributions of the functionalities in a collective fashion.