Influence of the solvent in the self-assembly and binding properties of [1 + 1] tetra-imine bis-calix[4]pyrrole cages.

We report the self-assembly of shape-persistent [1 + 1] tetra-imine cages 1 based on two different tetra-α aryl-extended calix[4]pyrrole scaffolds in chlorinated solvents and in a 9 : 1 CDCl3 : CD3CN solvent mixture. We show that the use of a bis-N-oxide 4 (4,4'-dipyridyl-N,N'-dioxide) as template is not mandatory to induce the emergence of the cages but has a positive effect on the reaction yield. We use 1H NMR spectroscopy to investigate and characterize the binding properties (kinetic and thermodynamic) of the self-assembled tetra-imine cages 1 with pyridine N-oxide derivatives. The cages form kinetically and thermodynamically stable inclusion complexes with the N-oxides. For the bis-N-oxide 4, we observe the exclusive formation of 1 : 1 complexes independently of the solvent used. In contrast, the pyridine-N-oxide 5 (mono-topic guest) produces inclusion complexes displaying solvent dependent stoichiometry. The bis-N-oxide 4 is too short to bridge the gap between the two endohedral polar binding sites of 1 by establishing eight ideal hydrogen bonding interactions. Nevertheless, the bimolecular 4⊂1 complex results as energetically favored compared to the 52⊂1 ternary counterpart. The inclusion of the N-oxides, 4 and 5, in the tetra-imine cages 1 is significantly faster in chlorinated solvents (minutes) than in the 9 : 1 CDCl3 : CD3CN solvent mixture (hours). We provide an explanation for the similar energy barriers calculated for the formation of the 4⊂1 complex using the two different ternary counterparts 52⊂1 and (CD3CN)2⊂1 as precursors. We propose a mechanism for the in-out guest exchange processes experienced by the tetra-imine cages 1.

Influence of the Insertion Method of Aryl-Extended Calix[4]pyrroles into Liposomal Membranes on Their Properties as Anion Carriers.

We disclose the results of our investigations on the influence that the insertion method of aryl-extended calix[4]pyrrole into liposomal membranes exerts on their properties as anion carriers. We use the standard HPTS assay to assess the transport properties of the carriers. We show that the post-insertion of the carrier, as DMSO solution, assigns better transport activities to the "two-wall" α,α-aryl-extended calix[4]pyrrole 1 compared to the "four-wall" α,α,α,α-counterpart 2. Notably, opposite results were obtained when the carriers were pre-inserted into the liposomal membranes. We assign this difference to an improved incorporation of carrier 2 into the membrane when delivered by the pre-insertion method. On the other hand, carrier 1 shows comparable levels of transport independently of the method used for its incorporation. Thus, an accurate comparison of the chloride transport activities featured by these two carriers demands their pre-incorporation in the liposomal membranes. In contrast, using the lucigenin assay with the pre-insertion method both carriers displayed similar transport efficiencies.