Direct in Situ Measurement of Phospholipid Hydration in an Aqueous Environment Using a Quartz Crystal Microbalance

Abstract

Hydration of phospholipid head groups is essential for stabilizing bilayer structures in an aqueous environment. Here we describe a new, easy, and rapid method that can directly and quantitatively determine phospholipid hydration in both water vapor and liquid water ; i.e., a quartz crystal microbalance is employed which enables hydration to be determined in only 1 h using just 1 μg of phospholipids under various environmental conditions. Dipalmitoylphosphatidylethanolamine (DPPE) was examined with varying temperature, KCl concentration, and phase of water, where it was found that DPPE hydration in liquid water markedly increases upon raising the temperature, even when the phospholipid is in a gel phase, being maxima1 around its phase transition temperature (63.5 °C). Furthermore, KCl addition increased DPPE hydration in a temperature-dependent manner. The method presented is demonstrated to be capable of determining phospholipid hydration under physiological conditions ; hence, it is suitable for investigating hydration phenomena involved in biological processes.