Structure, stability and guest affinity of tris(3-ureidobenzyl)amine capsules in solution

In non-competitive solvents, the tris(3-ureidobenzyl)amines 1a-c form dimeric assemblies in which guests such as CH(3)CN, CH(3)NO(2), CH(2)Cl(2), CH(3)I, CH(2)BrCl, CH(2)Br(2), CHCl(3) and C(6)H(6) can be encapsulated. Variable temperature (1)H and (1)H,(1)H-ROESY NMR spectroscopy, as well as pulsed-gradient spin-echo (PGSE) diffusion measurements were used to investigate the encapsulation within 1a1a (1a: tris{3-[N'-(4-butylphenyl)-ureido]benzyl}amine). Kinetic parameters for the encapsulation of CH(3)NO(2), CH(2)Cl(2) and CH(3)I, both in CDCl(3) and in [D(8)]toluene have been obtained by using magnetisation transfer methods. These data are discussed together with the thermodynamic parameters. The affinity between guest and capsule seems to be dictated mainly by the electronic, size and shape complementarity between cavity and guest. A gating mechanism for guest exchange is proposed.