Ratiometric luminescent probes

Abstract

A ratiometric, luminescent Eu probe was sought for use in measuring intracellular pH, that can be excited in the range 355-405 nm. In order to achieve this, a series of 1- azathiaxanthone based chromophores has been synthesised and studied to find the best candidate to promote Eu emission. A series of 'D02A' derivatives was synthesised incorporating both the chosen chromophore (2-methyl-l-azathioxanthone) and a pH- dependent binding moiety (a tethered sulfonamide). Measurements were carried out in order to study and understand the properties of the complexes, especially the nature of the pH dependence. The protonation constants of the pendant pH 'switch' in each system were determined by luminescence titration. The influence on Eu emission of some endogenous anions and protein has also been examined by luminescence spectroscopy, along with calculations of their apparent binding constants in order to find the best candidate for measuring intracellular pH. A novel bicarbonate sensor has also been synthesised and studied incorporating a 7-(methylcarbamoylmethyl)-azathioxanthone sensitiser moiety. The luminescence properties have been thoroughly studied, and the changes in the photophysical properties and the sensitivity towards anion and protein binding rationalised. The complex displayed sensitivity towards endogenous anions and protein binding, however, a suitable calibration curve was obtained in the desired 5 - 30 mM HCO(_3) range in simulated endogenous anion mixture, using intensity ratio vs. pH plots. A series of ratiometric Eu(111)complexes has been synthesised incorporating an efficient sensitiser for measuring citrate concentrations in seminal and prostate fluid samples. Their luminescent properties were thoroughly studied using simulated prostate fluid as the background to find the best candidate for prostate adenocarcinoma detection. Preliminary studies have been undertaken to determine citrate levels in 'clinical' prostate and seminal fluid samples. Cellular uptake and localisation studies have also been undertaken with each complex revealing the complex uptake profile and the time-dependent localisation behaviour within the cell. Each complex showed no significant evidence for toxicity. Images were observed using unfixed cells, appropriate for live cell imaging applications.