Exploring the effects of additives on the molecular packing characteristic of an ion pair amphiphile bilayer by Langmuir monolayer approach and molecular dynamics simulation

  • 郭 安聰

Student thesis: Doctoral Thesis

Abstract

Physical stability of vesicle is very important for the development of catanionic vesicles as novel drug or DNA carriers To understand the stabilization mechanism for catanionic vesicles the effects of additives including double-tailed cationic surfactants dialkyldimethylammonium bromide (DXDAB) and cholesterol (CHOL) on the molecular packing characteristic of the catanionic bilayer of an ion pair amphiphile hexadecyltrimethylammonium-dodecylsulfate (HTMA-DS) were investigated The interfacial behavior of the mimic outer layers of the catanionic bilayers was explored with the Langmuir monolayer approach and infrared reflection-absorption spectroscopy (IRRAS) first The microscopic structures of the bilayers were then analyzed through molecular dynamics simulation in which a double-tailed cationic surfactant ditetradecyldimethylammonium chloride (DTDAC) was adopted as the additive For the mixed HTMA-DS/DXDAB bilayers DXDA+ would displace HTMA+ from HTMA-DS with the extent depending on the hydrocarbon chain length of DXDAB In addition the formation of triple-chained DXDA-DS could adjust the molecular packing/interaction of the bilayers thus improving the physical stability of the vesicles For the HTMA-DS/CHOL and HTMA-DS/DTDAC/CHOL bilayers the presence of CHOL could promote the bilayer condensation and enhance the order of neighboring hydrocarbon chains However CHOL-induced space in the polar region and void in the nonpolar region of the bilayers caused a conformational disorder of the hydrocarbon chains With high CHOL contents the conformational disorder effect would overwhelm the condensing effect resulting in the apparent disordering effect on the rigid bilayers Furthermore the presence of CHOL in the HTMA-DS/DTDAC bilayer would increase the distance between the charged head groups and decrease the counterion binding on the bilayer surface which could explain the CHOL-enhanced charge character of the catanionic vesicle
Date of Award2015 Jan 27
Original languageEnglish
SupervisorChien-Hsiang Chang (Supervisor)

Cite this

Exploring the effects of additives on the molecular packing characteristic of an ion pair amphiphile bilayer by Langmuir monolayer approach and molecular dynamics simulation
安聰, 郭. (Author). 2015 Jan 27

Student thesis: Doctoral Thesis