Dimeric capsule vs columnar polymer: Structural factors determining the aggregation behavior of amino acid functionalized benzene-1,3,5-tricarboxamides in solution and in the solid-state

Abstract

The non-covalent aggregation of four benzene-1,3,5-tricarboxamide (BTA) derivatives formed from glycine or l-valine esters (-Me, -iPr), has been investigated in the solid-state and in chloroform solution by means of several analytical methods (NMR, FT-IR, and single crystal XRD). Two types of self-assembled structures were characterized: a dimeric capsule formed by –NH···OC- (ester) bonding and a columnar assembly with characteristic –NH···OC- (amide) bonds (alongside with monomers). In-depth solid-state studies revealed the significant role of the steric bulk of the C-terminus protecting group in supramolecular aggregation in the solid-state. Increasing the bulk of the ester group prevents the molecule from assembling into a columnar structure and instead a dimeric assembly is observed. On the other hand, it has no effect in chloroform solution, where the amino acid sidechain determines the self-assembly outcome. Our study points out the essential influence of substituent steric bulk in both positions: the alpha atom of the amino acid ester and in the ester group itself. Systematic study of these structurally similar molecules also allows identification of the moiety having the greater influence on the nature and stability of BTA aggregates in distinct phases (bulk, solution).