Inherently Chiral Artificial Membranes as Key Components in Chiral Potentiometric Sensors

Chiral membranes are important tools for enantiomer discrimination or/and separation in a broad range of applications, especially concerning preparative separations in the pharmaceutic field. Many chiral membranes are of natural origin (e.g. polysaccharides, polyaminoacid derivatives), or based on natural chiral components while less common so far are membranes based on synthetic chiral components (e.g. calixarenes or crown ethers). However, synthetic chiral membranes have interesting intrinsic features, like wide range of molecular designs and functional properties, equal availability of both enantiomers, and easy synthesis scalability. Among analytical applications of chiral membranes, a potentially interesting one concerns implementation as key components in chiral potentiometric sensors. Concerning design of synthetic membranes, different stereogenic elements can be considered to endow them with chirality, the most common ones being localized stereocenters, but it was observed that much better enantioselection performances can be obtained by implementation of the “inherent chirality” strategy. [1-2] In this frame we have discovered that the electrooligomerization, in acetonitrile as solvent, for 108 deposition cycles, on an ITO electrode support, of our “inherently chiral” benchmark monomer, leads to self-standing racemic or enantiopure membranes. These ones were obtained by simply peeling off the solid deposit from the ITO immersed in water after the electrodeposition in acetonitrile. We have then characterized inherently chiral membranes with different techniques (e.g FTIR, HR LDI, scanning electron microscopy, BET for surface area and pore size distribution, CD spectra to check that chirality was fully transferred from the monomer to the oligomer films, and atomic force microscopy) comparing the racemic vs enantiopure deposit properties. We have decided to implement enantiopure inherently chiral membranes in a “ion-selective like” set-up in order to study their enantiorecognition capability (as depicted in the Figure). First of all we have verified the potential difference was read correctly through the membrane to allow correct determinations of transmembrane potentials. After that we have tested enantiopure membranes in the presence of chiral charged species (in all configurations for both membranes and internal/external electrode solutions) for determining their enantioselective capability [3]. Preliminary results are very promising and encourage us to perform the scaling up of the membrane electrosynthesis to be used for industrial scopes and to extend the study to other probe useful in the analytical and pharmaceutical field. References: [1] S. Arnaboldi, M. Magni, P. R. Mussini, Curr. Op. in Electrochemistry 8 (2018) 60-72. [2] S. Arnaboldi, S. Grecchi, M. Magni, P.R. Mussini, Curr. Op. in Electrochemistry 7 (2018) 188-199. [3] S. Arnaboldi, D. Vigo, M. Longhi, F. Orsini, S. Riva, S. Grecchi, E. Giacovelli, V. Guglielmi, R. Cirilli, G. Longhi, G. Mazzeo, T. Benincori, P. R. Mussini, Chem Electrochem, DOI: 10.1002/celc.201900779 (2019).