Light-Triggered Transformation of Molecular Baskets into Organic Nanoparticles

Abstract

Discovering novel and functional photoresponsive materials is of interest for improving controlled release of molecules and scavenging toxic compounds for cleaning our environment or designing chemosensors. In this study, we report on the photoinduced decarboxylation of basket 1^6- , containing three glutamic acids at its rim. This concave compound is, in an aqueous environment (30 mm phosphate buffer at pH 7.0), monomeric (¹ H NMR DOSY, DLS) with glutamic acid residues randomly oriented about its rim (¹ H NMR and MM-OPLS3). The irradiation (300 nm) of 1^6- leads to the exclusive removal of its α-carboxylates to give amphiphilic 2^3- possessing γ-carboxylates. The photochemical transformation is a consecutive reaction with mono- and bis-decarboxylated products observed with ¹ H NMR spectroscopy and ESI mass spectrometry. Amphiphilic 2^3- is a preorganized molecule (MM-OPLS3) that, in water, aggregates into organic nanoparticles (ca. 50-200 nm in diameter; DLS, TEM and cryo-TEM) having a critical aggregation concentration of 12 μm (UV/Vis). As the transition of monomeric 1^6- into nanoparticulate 2^3- is triggered with light, we reasoned that stimuli-responsive formation of the soft material lends itself to nanotechnology applications such as controlled release or scavenging of targeted compounds.

Keywords: cavitands; molecular recognition; organic nanoparticles; photoresponsive system; self-assembly.