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INnovative chemIcal sensors for enanTioselective detectIon of chiral pOllutants

Periodic Reporting for period 1 - INITIO (INnovative chemIcal sensors for enanTioselective detectIon of chiral pOllutants)

Reporting period: 2019-01-01 to 2019-12-31

A chiral species is a single molecule or molecular assembly that cannot be superimposed with its mirror image. Chiral molecules are consequently present as two stereoisomers, called enantiomers. On a daily basis, chiral molecules are conventionally used and produced by pharmaceutical, food, agrochemical, perfume, and cosmetics industries. As a result, chiral waste becomes an extremely important issue at present. Chiral compounds can be ecologically hazardous, due to their high biological activity, creating a global pollution problem. It is of note, that enantiomers have a different impact on living organisms making it extremely important to differentiate these stereoisomers, which is extremely a difficult and challenging task and usually requires highly specific and costly instruments. Yet, the stereoisomerism of contaminants is presently not considered in detail.
In this context, the development of portable chemical sensors devices which are reliable, sensitive and rapid, capable of fast, simple and real-time in situ and on site analysis for sensing and discrimination of chiral molecules presents an attractive breakthrough target compared to existing standard instrumental methods.
However, the stereoselective detection of the chiral substances with chemical sensors is an arduous task, because, in contrast to chromatography or electrophoresis, sensors rely on a single binding event and the highly efficient discrimination of the receptor is an important prerequisite.
The main objective of the INITIO research project is the development of chemical sensors able to recognize chiral substances based on rationally designed sensing materials, with the aim of filling the existing gap between the production of enantioselective receptors and the realization of macroscopic devices. The success of the INITIO project will also open the way to a further potential application of the developed devices for chiral pollutants removal, allowing prompt remedial procedures in an unprecedented environmental “theranostic” approach.
Further prospects in this field will include not only smart and cost-effective detection of chiral pollutant but subsequent recycling and utilization of chiral waste to produce useful enantiopure intermediates and compounds to be used in chemical, pharmaceutical, agrochemical and other industries.
During the first year of the INITIO project, the following research activities have been carried out to achieve the steps necessary for the development of chiral chemical sensors:
• A first goal was the definition of synthetic protocols for the preparation of a series of chiral receptors belonging to the two typologies reported in the proposal: porphyrins and hemicucurbiturils. This synthetic effort allowed the realization of a quite wide library of different receptor structures.
An additional target of the synthetic activity has been the preparation of hybrid receptors, where both porphyrin and hemicucurbituril derivatives are linked together. Two different sets of porphyrin-hemicucurbituril and metalloporphyrin- hemicucurbituril hybrids have been prepared, where the porphyrin/hemicucrbituril ratio was 1:1 or 6:1.
• Parallel to the preparation of the molecular receptors, the second goal has been the preparation of chiral nanostructures, based on metal oxides. The aim was to use these nanostructured materials as support for the grafting of receptors. In a first system, the nanostructured oxide was formed by chiral helices of SiO2, obtained by using chiral tartrate aggregates as template. Once the hybrid helices were formed, they have been grafted with functionalized achiral porphyrinoid derivatives (porphyrins and corroles). A second tested system is represented by ZnO nanoparticles, in this case functionalized with chiral porphyrin derivatives; also in this case the chiral properties are retained in the hybrid materials.
• The binding properties towards chosen model analytes of some of the receptors developed have been studied in solution. The host-guest binding interaction between hemicucurbituril and Zn-porphyrins were studied as well, with the aim to explore their potential exploitation as bifunctional receptors.
• The crystallization and solid state structure determination of chiral hemicucurbiturils and porphyrins has been carried out, to determine the structural parameters and to understand the binding event among the receptor and the target analytes. For this reason, the same studies were performed by crystallization of the receptors in the presence of both achiral and chiral analytes, with the aim to provide information on the complexation events.
These studies now allow a better understanding of the possible mechanisms and sites of interactions between receptors and target analytes, in conditions close to that of sensing measurements.
• In the first year, we also started the optimization of the deposition protocols of the receptors onto the transducers surfaces, which are quartz crystal microbalances (QCM) for gas phase sensors and quartz transparent slides for optical transduction. The deposition step is of fundamental importance to preserve the chiral selectivity observed in solution.
• Other than the reported research activities, during the first project year different dissemination activities have been performed by the project consortium members, including the organization of a conference (Chirality), talks at conferences and publication of four scientific articles. A flyer reporting the project aims has also been published and distributed during these conferences.
• Several press releases were published as listed in the project web site.
• The Deliverables 1-27 and the Milestone 1 (related to the establishment of the project Boards) scheduled for the project first year, have been posted on the EU portal.
The INITIO project aim is to develop efficient chemical sensors able to perform chiral recognition.
To reach this goal, the main aims of the project are: a) the development of novel molecular receptors, b) integration of the receptors with different nanostructures and characterization their solid state organization, c) deposition of the structures onto transducer surfaces, d) testing and validation of the new chemical sensor devices with enantiomeric pairs of model analytes.
In the first year project important insights related to these fundamental steps have been pursued. A wide library of chiral receptors has been obtained and a series of hybrid inorganic/organic nanostructures has been investigated. The solid state organization of some receptors has also been characterized, also in the presence of target chiral analyte, in order to obtain fundamental insights on their sensing mechanism.
For the following objectives, preliminary experiments on thin layer deposition and sensing performances of some selected receptor systems have been started and they will be the target of the second part of the project.
The results obtained have been published in five articles in scientific journals, presented in International conferences and communicated in different press releases.
The success of this approach will open the way to the realization of field-capable devices, able to monitor an important class of emerging pollutants. The realization of such devices represents an important breakthrough in the monitoring of chiral pollutants.
Project presentation