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Understanding the Dehydration Stress in Lipid Vesicles by a Combined Quartz Crystal Microbalance and Dielectric Spectroscopy Study
Journal Contribution - Journal Article
Herein, 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) vesicles are studied using a newly designed setup that combines dielectric and gravimetric (quartz crystal microbalance, QCM) measurements. This setup allows to monitor the molecular dynamics and phase transitions of lipid structures under controlled humidity and temperature conditions. The main relaxation process (R2), related to the intrinsic headgroups' dynamics, is found in all phases and reveals a systematic acceleration with increasing hydration level. In contrast, a faster relaxation mode (R1) is found exclusively in the ?liquid-crystalline,? high-temperature state, favoring water clusters located in the disordered aliphatic phase as origin. A third process (R3), being slower than the R2 mode, is attributed to a decoupled dynamics of hydration water in the hydrophilic part of the lipid bilayers occurring at higher hydration levels. In addition to molecular dynamics, both QCM and dielectric relaxation spectroscopy (DRS) measurements are demonstrated to yield consistent information on the phase behavior of the POPC samples which show a marked sensitivity to the hydration level. Moreover, contact angle measurements and atomic force microscopy confirm irreversible changes from the initial vesicles to a stacked bilayer structure upon repeated hydration-dehydration, which manifests in the hydrophobization of the surface and water reduced absorption kinetics.
Journal: Physica Status Solidi A. Applications and Materials Science
Number of pages: 9
Keywords:Materials science, Applied physics, Physics of solids, fluids and plasmas