The Dynamics of Water Molecules Confined in the Interior of DMPC Phospholipid Reverse Micelle

摘要

6.1 Introduction Amphiphilic molecules like surfactants and lipids exhibit a variety of phases in aqueous environment. They undergo self-association under specific conditions to form aggregates such as vesicles, bilayers, micelles, etc. [1-5]. The geometrical form of these aggregates is a consequence of a delicate balance between two opposing forces. The attractive tail-tail hydrophobic interaction is the driving force for the aggregation of surfactant molecules, whereas the electrostatic repulsion between the head group sets a lower limit on the size that an aggregate can attain. A typical micelle is spherical with the hydrophilic "head" regions in contact with surrounding environment, sequestering the hydrophobic single-tail regions in the micelle center. Micelles have been the subject of intense interest for several decades, both from a fundamental physical chemistry point of view and because of their widespread applications in detergent, cosmetic, pharmaceutical, and food industries. In some nonpolar solvents can be formed the spherical aggregates of amphipathic molecules with the hydrophobic part of each molecule pointing outward. These aggregates are called reverse micelles because of the reverse of the situation in normal micelles. Reverse micelles have recently garnered significant attention as model systems to explore the effects of confinement [6-9]. Confined environments occur naturally in many biologically important systems as well as a range of physically interesting materials such as porous glasses. The beauty of the reverse micelle is that it is easily created, shows substantial stability, and provides a well-characterized nanoscale pool for a range of chemistries. In recent years, the molecular dynamics (MD) computer simulation method has become a popular way to study micelles [5, 9-31], because of its ability to simulate phenomena at the atomic scale on very short time periods. In this work we have used MD technique to detailed study of the dynamics