Phosphatidylcholine (PC) is one of the most common phospholipids and the major component of the cell membrane bilayer. Wrapping PC bilayers into hollow spherical structures results in PC vesicles, also named liposomes, which have great potentials in pharmaceutical applications. Yet the actual application of liposome is limited due to the high cost of PC. Ion pair amphiphile (IPA) is a complex composed of a pair of cationic and anionic surfactants after removing their residual counter-ions, resulting in a PC-like molecular structure. Therefore, IPA has been considered as one of the cheaper PC substitutes. In this project, we applied molecular dynamics simulations to characterize IPA bilayer properties from three different aspects: (1) examining the effects of alkyl chain lengths, (2) identifying the importance of cationic and anionic components of IPA via asymmetric chain length combinations, and (3) characterizing the effects of cholesterol additive on IPA bilayers. Simulations results showed that cationic components have greater effects on IPA bilayers in terms of both the membrane structure and the membrane elasticity. The anionic surfactants, in contrast, play more important role in the presence of cholesterol additive due the H-bonds between the their hydrophilic groups. The presented results provide valuable molecular insights into the IPA bilayer systems, which can serve as useful reference for fabricating IPA vesicles and future application designs.

self-assembly process of IPA vesicles

The fibril deposits of amyloid proteins are implicated in more than 20 human diseases, including Alzheimer’s disease, Parkinson’s disease, and type II diabetes. Yet the aggregation mechanism of amyloid fibrils remains illusive. Specifically, the amyloid fibrils of human islet amyloid polypeptide (hIAPP), or human amylin, are closely related to the development of type II diabetes. In this work, we utilized atomistic molecular dynamics combined with advanced sampling techniques to study the conformations of hIAPP monomers, oligomers, and mature fibrils and the corresponding conformational free energies. We compared the simulation data with experimental data to study the molecular mechanism of hIAPP fibril formation. We identified the aggregation mechanism of hIAPP and characterized the important intermediate species during the fibrillization process, which provides valuable insights into the future inhibitor designs. We also revealed new pathological roles of hIAPP where the aggregation of hIAPP triggers the deposition of nonamyloidogenic peptide.

We utilized molecular dynamics (MD) simulations to explore the effects of novel copolymer binder at the cathode/electrolytes interface. The radial distribution function and Li+ coordination analyses showed the interaction between Li+ and PF6- is reduced on the binder surface. The coordination around Li+ have gradually changed from EC and DEC solvent to polymer EO-segments as Li+ approaching the binder surface. Yet, the overall diffusivity of the surface bound Li+ is reduced as the surface EO-chain density increases. The combined results conclude that the addition of the EO chains can reduce the interaction between Li+ and PF6- but decrease the overall Li+ diffusivity on the binder surface. The two competing effects provide microscopic insights into the future designs of functional polymer binder.