Abstract
In this work, we report the synthesis of a new bis(tris(2-aminoethyl)amine) azacryptand L with triphenyl spacers. The binding properties of its dicopper complex for aromatic dicarboxylate anions (as TBA salts) were investigated, with the aim to obtain potential building blocks for supramolecular structures like rotaxanes and pseudo-rotaxanes. As expected, UV-Vis and emission studies of [Cu2L]4+ in water/acetonitrile mixture (pH = 7) showed a high affinity for biphenyl-4,4′-dicarboxylate (dfc2−), with a binding constant of 5.46 log units, due to the best match of the anion bite with the Cu(II)-Cu(II) distance in the cage’s cavity. Compared to other similar bistren cages, the difference of the affinity of [Cu2L]4+ for the tested anions was not so pronounced: conformational changes of L seem to promote a good interaction with both long (e.g., dfc2−) and short anions (e.g., terephthalate). The good affinity of [Cu2L]4+ for these dicarboxylates, together with hydrophobic interactions within the cage’s cavity, may promote the self-assembly of a stable 1:1 complex in water mixture. These results represent a good starting point for the application of these molecular systems as building units for the design of new supramolecular architectures based on non-covalent interactions, which could be of interest in all fields related to supramolecular devices.
Highlights
More than ever, the scientific community, inspired by nature, is exploring new frontiers in the fascinating world of molecular machinery with the aim to induce and control, through specific external stimuli, the mechanical movement of single parts in a molecular/supramolecular assembly [1,2]
Rotaxanes and pseudo-rotaxanes represent an important class of supramolecular architectures: due to the combination of different kinds of interaction between the axle and the ring(s) structure, these molecular devices found a wide range of applications in different fields such as sensing, catalysis, drug delivery, and nanotechnologies [6,7,8,9]
Azacryptand L was synthesized from the tren polyamine and [1,1’:4’,1”-Terphenyl]4,4”-dicarboxaldehyde [19] using a known procedure [20]
Summary
The scientific community, inspired by nature, is exploring new frontiers in the fascinating world of molecular machinery with the aim to induce and control, through specific external stimuli, the mechanical movement of single parts in a molecular/supramolecular assembly [1,2]. Trying to achieve this challenging purpose, beautiful and functional systems controlled for example by light, changes of pH or redox processes were obtained and reported [3,4,5]. The formation of the so called “cascade” species plays synthetic step; and (3) theprocess
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