WATER-SOLUBLE FLUORESCENT PH SENSORS BASED ON A DIARYLACETYLENE SCAFFOLD

Abstract

Intracellular pH plays an important role in many biological processes: receptor-mediated signal transduction, enzymatic activity, cell growth and death, ion transport and homeostasis, calcium regulation, endocytosis, chemotaxis, and cell adhesion. Normal cell pH is around 7.40 and can range from 7.35-7.45 without any adverse effects. If it ranges more than 0.1-0.2 in either direction cardiopulmonary and neurologic problems can arise and in the case of extreme variations, death can result. Determination of pH in cells is of great importance and many methods exist for sensing pH; however, fluorescence is the most useful because of its nondestructive nature, high sensitivity, and specificity. We chose to use an intrinsic fluorescent probe in which the protonation site is integrated into the main chromophore. The systems were prepared by Sonogashira coupling of halopyridines with acetylenes. Protonation of the first class of pyridyl receptors synthesized occurred at a pH of 4 and was accompanied by a decrease in fluorescence. Protonation of the second class of pyridyl acceptor synthesized occurs near the pH of 5.5 and is accompanied by an increase in fluorescence intensity. Though water-soluble, model membrane transport studies show that the probes have a high affinity for non polar environments.