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A New Halo-Imidazolums and Halo-Triazoliums Halogen-Bonding Receptors for Anion Recognition and Sensing

Final Report Summary - CIGACP (A New Halo-Imidazolums and Halo-Triazoliums Halogen-Bonding Receptors for Anion Recognition and Sensing)

The field of anion recognition chemistry has expanded enormously during the past few decades, inspired in large part by the realization of the many fundamental roles that the negatively charged species play in a range of chemical, biological, medical and environmental processes. Although many research groups are working in the design of new anion receptors, their success in the developing of anion receptor is still very low compared with the cation recognition.
It is clear that the researchers need to focuses their effort in other direction and explore new and innovative solutions for detections of anion. Obviously the target interaction must be stronger and more directional than the hydrogen bonding, the better and more used interaction knows to date. One exciting alternative could be the utilization of the halogen bonding in the design of new anion sensors. To date, almost all the investigations on halogen bonding have been conducted in the solid state where the non-covalent interaction has been imaginatively exploited in the crystal engineering of magnetic, conducting and liquid crystalline materials. In contrast halogen bonding in the solution phase is still in its infancy, which is surprising given its potentially powerful analogy to ubiquitous hydrogen bonding. Taking this into account, this project aims to provide quantitative information about the behaviour of the halogen bonding in solution compared with the traditional hydrogen bonding.
During the course of the of the project we have synthesized a big number of new halo-imidazolium ans halo triazolium receptors bearing fluorescent or electrochemical signalling units and therefore studied their potential as fluorescent or electrochemical chemosensor for anion recognition in solution through combinations. In order to do a comparative study between the halogen bonding interaction with the traditional hydrogen bonding, the analogous hydrogen bonding receptor and the mixed hydrogen an halogen bonding receptors were also synthesized and studied. Aditionally, hydrogen bonding interactions C+sp3-H•••A- were also studied by the synthesis of new trimethyl imidazolium based receptors.
Some of the most relevant finding obtained during the course of this project are the following:
1.-) The incorporation of halogen atoms in fluorescent chemosensors has proved to be an important tool in the design of turn-on fluorescent receptors due to the halogen atoms induce the fluorescence quenching in the free receptors.
2.-) The association constant values of the halogen-bonding receptors for anions are larger than the hydrogen-bonding counterpart in very polar or protic solvent, while the strength the halogen- and hydrogen bonding interaction in non polar organic solvent are very similar.
3.-) Some of the Bromo-imidazolium based receptors behave as a chemodosimeter toward HP2O73- anion, through its transformation into the corresponding bisimidazolone after debromination by the action of the basic anion. Interestingly this behaviour was not observed in the Hydrogen bonding analogue. This fact is a new and simple methodology of the synthesis of imidazolone rings.
4.-) Two different mechanism in the HP2O73- recognition were observed in some triazolium receptor where the triazolium ring can act as the traditional hydrogen bond donnor but also by Anion-pi interactions.
5.-) The utilization of the 2,3,5-trimethyl imidazoliums as anion binding, demonstrated its ability to recognize anion in new fluorescent receptor.
Taking into account the lack of knowledge on halogen bonding in solution this project have provided quantitative data regarding the donor ability of a wide range of new halogen bonding receptors. Additionally this project has demonstrated some important differences between halogen and hydrogen bonding interactions.
Taking into account the interest of the scientific community about all related with the halogen bonding interaction in solution the results of this interdisciplinary research project which have been published in prestigious internationally renowned scientific journals and presented at international conferences have extend the state of the art and greatly contribute to European scientific excellence and competition. In addition, commercially exploitable results could be patented and exploited in a close future.