Scientists in the UK have developed new indole-based anion receptors capable of binding phosphate ions under very competitive conditions.     

Phil Gale and co-workers at the University of Southampton developed new indolylurea-based compounds to bind dihydrogen phosphate ions (H₂PO₄^-) in polar solvent mixtures.   

Phosphate anions are found in many biological systems and the environment. In nature, indole (in the form of tryptophan) is used as an anion-binding receptor in a number of biomolecules. One example of this is a sulfate binding protein which uses an indole group as part of a hydrogen bonding array to complex sulfate.  

'The design of this receptor stemmed from previous work done by us in collaboration with Markus Albrecht's group in Aachen, Germany' said Gale. 'We decided to take this work further and investigate systems based on urea but which contain two indole groups.  We found that these molecules which are very easy to make, form very stable complexes with dihydrogen phosphate,' explained Gale.

The compounds use four hydrogen bonds to bind dihydrogen phosphate. Studies conducted in DMSO with varying amounts of water showed that even in the presence of 25% water the compounds could still selectively bind H₂PO₄^-. 'That's remarkable for such a simple neutral receptor' said Gale.