A convenient and versatile synthesis of Laurdan-like fluorescent membrane probes: characterization of their fluorescence properties
Abstract
It is now well established that biomembranes show a high degree of lateral organization, with the coexistence of lipid domains showing increased order within a fluid phase. Environment-sensitive fluorescent probes such as Laurdan have played an important role in the study of membrane lipids properties. However, it has been shown that, despite its interesting spectroscopic features, including efficient two-photon excitation in the visible range, Laurdan can be difficult to use for investigating cellular membranes and its capacity to accurately document membrane properties has been challenged. We present here a simple and versatile two-step synthetic scheme that readily leads to Laurdan analogs differing by their polar head. We prepared a small library in order to evaluate the influence of the polar headgroup on the probe's ability to monitor membrane properties. The spectroscopic properties of the probes dissolved in different organic solvents or inserted into liposomes made of synthetic as well as natural phospholipids at different temperatures are described. Comparison of the fluorescence properties of existing Laurdan and C-Laurdan with the newly synthesized fluorescent probes indicates that the structure of the electron-donating amino group is a key parameter for the development of better-performing probes, especially in membranes containing negatively charged phospholipids.