Engineering Light-Mediated Bistable Azobenzene Switches Bearing Urea d-Aminoglucose Units for Chiral Discrimination of Carboxylates

Abstract

The symmetrical molecular receptors 1a and 1b consisting of a photochemically addressable azobenzene tether functionalized with urea hydrogen-bonding groups and d-carbohydrates as chiral selectors were developed to achieve control over the chiral recognition of α-amino acid-derived carboxylates. The photo- and thermally interconvertible planar E-1 and concaved Z-1 were found to exhibit different affinities, selectivities, and binding modes toward these biologically important anions in a highly polar medium (DMSO + 0.5% H2O). Binding affinity for the same enantiomerically pure guest was up to 3 times higher for E-1 than for Z-1 (cf. parameter β). In addition, the rate of thermal Z → E isomerization was found to depend on the chiral binding ability of Z-1, i.e., more strongly bound carboxylate enantiomer as well as higher enantiomer concentration caused faster relaxation to E-1.

Photoswitchable Carbohydrate‐Based Macrocyclic Azobenzene: Synthesis, Chiroptical Switching, and Multistimuli‐Responsive Self‐Assembly

“…Macrocycles containing one to several azobenzenes have been designed, synthesized, and investigated for light‐induced chirality transfers, ion complexation, multistate switches, optical storage devices, photoswitchable phase transition in liquid crystals and crystals, or as artificial molecular machines and molecular actuators. Photoresponsive glycosides have recently been developed for light‐controlled carbohydrate–protein interactions, cell adhesion, chiral discrimination, or as photosensitive protein cross‐linkers, surfactants, and gelators . Supramolecular gels represent remarkable functional soft nanomaterials with potential applications ranging from (bio)catalysis, chemosensors, drug delivery, cosmetics to optoelectronics, shape‐memory, and display devices .…”

“…Of particular interest for supramolecular constructs are “smart gels”, that is, gels whose properties can be controlled reversibly or irreversibly by external stimuli like chemical, photon, electron, temperature, or mechanical stress . Design and synthesis of photoswitchable carbohydrate‐based macrocycles should be very interesting for spatiotemporally controlling various chemical, structural, and biological properties of sugar‐based macrocyclic compounds by light . After preliminary design and molecular mechanics (MM2) calculations, we envisioned the synthesis of carbohydrate‐based macrocyclic azobenzene 1 bearing one 2,2′‐carboxymethoxyazobenzene moiety on the 4,6‐position of phenyl thio‐α‐ d ‐mannopyranoside (Scheme ).…”

Configurational Selection in Azobenzene‐Based Supramolecular Systems Through Dual‐Stimuli Processes

“…Interestingly, Z ‐ 15 a binds benzoate 4.5 times stronger than Z ‐ 15 b (first association constant) while no difference in the affinity for the anion was observed between Z ‐ and E ‐ 15 a . In a subsequent work by the same authors, these concepts were applied to the chiral recognition of α‐amino acid carboxylates using symmetrical receptors 16 a , b , exposing D ‐carbohydrate termini as chiral selectors. The E and Z isomers of 16 display different binding modes ( i.e ., 1 : 2 and 1 : 1, respectively) and different affinities ( E > Z ) towards the phenylalanine and tryptophan anions, while the enantioselective discrimination of the two amino acids was moderate.…”

Synthesis and Photochromic Properties of Azobenzene‐Derived Glycomacrolactones

“…Photochromism has attracted increasing interest of carbohydrate community to develop photoswitchable glycoconjugates for light‐controlled carbohydrate‐lectin interactions, intracellular target recognition, cell adhesion, chiral discrimination, photoregulation of enzyme activity and protein conformation, or as photoresponsive surfactants, hydrogelators, organogelators, liquid crystals, as well as water‐compatible molecular logic gate. Azobenzene,, spiropyran, and diarylethene have been used as photochromic moiety in these glycoconjugates, with the azobenzene being the most employed one, probably due to its small size, its excellent photostability and the large changes in molecular size, conformation and dipole moment between E and Z isomers.…”