The Use of 6-Acyl-2-(Dimethylamino)Naphthalenes as Relaxation Probes of Biological Environments

Abstract

As Gregorio Weber anticipated in his seminal 1979 article, 6-acyl-2-(dimethylamino)naphthalene probes became excellent tools to study nanosecond relaxation processes of biological systems. Examples are the use of PRODAN (or DANCA) to study relaxation of specific protein matrixes, or LAURDAN (as well as PRODAN) extensively used to study the extent of water dipolar relaxation processes in biological membranes. In this chapter a novel application for this family of molecules is presented and discussed. Specifically, we show how these fluorescent probes can be used to monitor intracellular water dipolar relaxation in living cells displaying oscillatory metabolism. Our experimental results show a strong coupling between metabolism and intracellular water dynamics, challenging the view that water in the interior of cells exists mostly as a medium whose global properties are comparable to the properties of dilute solutions. The observed results can be very well interpreted in light of the association-induction hypothesis postulated by Gilbert Ling in 1962.