Pyridinium-based receptors

Ghosh K, Sarkar AR, Patra A (2009) Pyridinium amide-based simple synthetic receptor for selective recognition of dihydrogenphosphate. Tetrahedron Lett 50 6557-6561... 

The anion templated syntheses by Beer afforded receptors 60-62 by reacting the chloride salt of the starting pyridinium precursor with an appropriately chosen 1,3-diamidobenzene derivative. Based on 1H NMR spectroscopic titrations carried out in acetone-d6, the structure Cl 60 was found to form with a 1 1 stoichiometry and with an association constant of 2400 M-1. 

The Bronsted acid/base pair pyridinium/pyridine is unusual because redox potentials are available for both partners in an accessible range [35]. This allows detailed anticipation of the sensory behaviour of systems containing pyridine receptors. (49), whose fluorescence properties have received some attention before [113], is a member of a family of PET sensors for protons whose excitation and emission wavelengths spread over a substantial fraction of the accessible optical spectrum without compromising sensory action [114]. 

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