A macromolecule, interpenetrating molecular structure of a type designated rotaxane able to selectively recognize iodide from other halides (bromide and chloride) in water was reported in Nature Chemistry by Victor Felix and Igor Marques, CICECO researchers (University of Aveiro), in partnership with the researchers Paul Beer, Matthew Langton and Sean Robinson of the University of Oxford, receiving the honors of being the major highlight in the front cover. The CICECO team researched the mechanism of recognition of these halides using molecular simulation methodology. The resulting theoretical results were fundamental to the understanding of the complementary experimental data.

Over the last decade, molecular modeling group led by Victor Felix, Professor from the Chemistry Department, researcher from CICECO and the Autonomous Section of Health Sciences, has actively collaborated with the group led by Paul Beer, professor at the University of Oxford in the development of so-called macrocycles and interpenetrated molecules (designated Rotaxanes or Catenanes) able to selectively capture anions in organic solvents or aqueous mixtures of organic solvents. The recognition of anions in water it is not a trivial process and need to consider several variables simultaneously, such as solubility of the receptor, pH and / or competitiveness of water molecules to the receptor recognition sites due to formation of hydrogen bonds.

The rotaxane reported in the article "Halogen bonding in water results in enhanced anion in recognition and acyclic rotaxane hosts" comprises a macrocycle which surrounds the axis of a dumbbell-shaped structure forming a three dimensional cavity capable of selectively recognizing iodide in water through cooperative halogen and hydrogen bonds (see video below, where the hydrogen bond between the anion and the macrocycle are represented by dashed lines in yellow, while the connections between the halogen anion and the dumbbell by purple dashed lines). This achievement represents an important milestone for the development of supramolecular chemistry and, in particular, the collaboration between these two research groups.

In parallel to the investigation of halogen bonds, molecular modeling group has paid particular attention to the design and computational research libraries of small molecules for transport of anions across cell membrane, since the deregulation of chloride transport across the membrane mobile is associated with the development of several diseases, including cystic fibrosis.

A halogen bond is the result of electrostatic interaction between a chemical structure donor of electrons and another receptor. Very recently, these not covalent interactions have earned the scientific community attention, given its application in various areas such as catalysis, design and molecular recognition, transport across the cell membrane, structural biology and medicinal chemistry.

These theoretical studies are performed in cell membranes models using high-performance computing means (GPU) and dedicated software.

In this context, the work reported in the December issue of Nature Chemistry also opens new perspectives for the rational development of anion transporters.