Straight from the bottle! Wine and juice dicarboxylic acids as templates for supramolecular cage self-assembly

Programmed guest confinement via hierarchical cage to cage transformations

Taking inspiration from Nature, where (bio)molecular geometry variations are exploited to tune a large variety of functions, supramolecular chemistry has continuously developed novel systems in which, as a consequence of a specific stimulus, structural changes occur. Among the different architectures, supramolecular cages have been continuously investigated for their capability to act as functional hosts where guests can be released in a controlled fashion. In this paper, a novel methodology based on the use of phenanthrenequinone is applied to selectively change the binding properties of a tris(2-pyridylmethyl)amine TPMA-based cage. In particular, subcomponent substitution has been used to change structural cage features thus controlling the inclusion ratio of competing guests differing in size or chirality.

Chiroptical Enhancement of Chiral Dicarboxylic Acids from Confinement in a Stereodynamic Supramolecular Cage

The fundamental implications that chirality has in science and technology require continuous efforts for the development of fast, economic, and reliable quantitative methods for enantiopurity assessment. Among the different analytical approaches, chiroptical techniques in combination with supramolecular methodologies have shown promising results in terms of both costs and time analysis. In this article, a tris(2-pyridylmethyl)amines (TPMA)-based supramolecular cage is able to amplify the circular dichroism (CD) signal of a series of chiral dicarboxylic acids also in the presence of a complex mixture. This feature has been used to quantify tartaric acid in wines and to discriminate different matrixes using principal component analysis (PCA) of the raw CD data.

Picking on Carbonate: Kinetic Selectivity in the Encapsulation of Anions

Supramolecular hosts bind to inorganic anions at a fast rate and select them in proportion with thermodynamic stability of the corresponding [anion⊂host] complexes, forming in a reversible manner. In this study, we describe the action of hexapodal capsule 1 and its remarkable ability to select anions based on a large span of rates by which they enter this host. The thermodynamic affinity of 1 toward eighteen anions extends over eight orders of magnitude (0<K_a <10⁸  M^-1 ; ¹ H NMR spectroscopy). The capsule would retain CO₃ ^2- (K_a =10⁷  M^-1 ) for hours in the presence of eleven competing anions, including stronger binding SO₄ ^2- , HAsO₄ ^2- and HPO₄ ^2- (K_a =10⁷ -10⁸  M^-1 ). The observed selection resulted from 1 possessing narrow apertures (ca. 3×6 Å) comparable in size to anions (d=3.5-7.1 Å) slowing down the encapsulation to last from seconds to days. The unorthodox mode of action of 1 sets the stage for creating hosts that pick anions by their ability to access the host.

Helicity control of a perfluorinated carbon chain within a chiral supramolecular cage monitored by VCD

Confinement within supramolecular systems is the leading technology to finely tune guest functional properties. In this communication we report the synthesis of a chiral supramolecular cage able to bias the helicity of a perfluorinated carbon chain hosted within the cage. We monitor the phenomenon of chiral induction by Vibrational Circular Dichroism (VCD) experiments complemented by DFT calculations over the possible conformers.