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Stabilization of 4H hexagonal phase in gold nanoribbons.

ABSTRACT: Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.

SUBMITTER: Fan Z

PROVIDER: S-EPMC4525209 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature

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Stabilization of 4H hexagonal phase in gold nanoribbons.

Fan Zhanxi Z Bosman Michel M Huang Xiao X Huang Ding D Yu Yi Y Ong Khuong P KP Akimov Yuriy A YA Wu Lin L Li Bing B Wu Jumiati J Huang Ying Y Liu Qing Q Png Ching Eng CE Gan Chee Lip CL Yang Peidong P Zhang Hua H

Nature communications 20150728

Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption o ...[more]

PMID: 26216712

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Project description:Cholesterol is a major component of many lipid-based drug delivery systems, including cationic lipid nanoparticles. Despite its critical role in the drug release stage, the underlying molecular mechanism by which cholesterol assists in endosomal escape remains unclear. An efficient drug release from the endosome requires endosomal disruption. This disruption is believed to involve a lamellar-to-inverted hexagonal (Lα-HII) phase transition upon fusion of the lipid nanoparticle with the endosomal membrane. We used molecular dynamics simulations to study the structural properties of HII systems composed of an anionic lipid distearoyl phosphatidylserine (DSPS), an ionizable cationic lipid (KC2H), and cholesterol for several hydration levels and molar ratios. This system corresponds to the lipid mixtures in the hypothesized HII structure formed upon fusion and is of interest for the rational design of ionizable cationic lipids, including KC2, for an optimal drug release. Simulations suggest a geometry- and symmetry-driven lipid sorting and cholesterol-DSPS co-location around the water cores. Cholesterol preferentially co-locates with negatively charged saturated DSPS lipids at interstitial angles. The observed cholesterol-DSPS co-location results in an overall increase in the DSPS acyl chains' order parameters, which we propose to assist in stabilizing the HII phase by stretching the DSPS acyl chains for filling the voids formed by three adjacent lipid tubules. Furthermore, a systematic increase in the cholesterol concentration increased the lattice plane spacing and the water core radius but decreased the undulations along the lipid tubule axis. We propose that cholesterol and the degree of saturation/polyunsaturation of the lipid acyl chains, and not the lipid charge, are the main contributors in facilitating the Lα-HII phase transition and stabilizing/destabilizing the formed HII phase, whereas the positive charge of the ionizable cationic lipid promotes the LNP-endosomal membrane adhesion and assists in initiating the fusion process at the local contact area. We also propose that the effect of cholesterol on the HII structure and curvature is the main underlying reason for the well-documented HII stabilization and destabilization at low and high molar concentrations of cholesterol, respectively.

Dataset Information

Stabilization of 4H hexagonal phase in gold nanoribbons.

Publications

Stabilization of 4H hexagonal phase in gold nanoribbons.

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