Dual-Color Real-Time Chemosensing of A Compartmentalized Reaction Network Involving Enzyme-Induced Membrane Permeation of Peptides.

The design of synthetic systems with interrelated reaction sequences that model incipient biological complexity is limited by physicochemical tools that allow the direct monitoring of the individual processes in real time. To mimic a simple digestion-resorption sequence, we have designed compartmentalized liposomal systems that incorporate extra- and intravesicular chemosensing ensembles. The extravesicular reporter pair consisted of cucurbit[7]uril and methylene blue to monitor the enzymatic cleavage of short enkephalin-related peptides by thermolysin through a switch-off fluorescence response ("digestion"). Because the substrate is membrane-impermeable, but the dipeptide product permeable, an uptake of the latter into the pre-formed liposomes occurred as follow-up process. The intravesicular chemosensing ensemble consisted of (i) cucurbit[8]uril, 2-anilinonaphthalene-6-sulfonic acid, and methyl viologen or (ii) cucurbit[7]uril and berberine to monitor the uptake ("resorption") of the enzymatic products through the liposomal membranes by (i) a switch-on or (ii) a switch-off fluorescence response. The dyes were designed to allow selective optical excitation and read-out of the extra- and intravesicular dyes, which allowed for a dual-color chemosensing and, therefore, a kinetic discrimination of the two sequential reactions. This article is protected by copyright. All rights reserved.