Effects of lipid saturation on bicelle to vesicle transition of a binary phospholipid mixture: a molecular dynamics simulation study.

Controlling the transition from lipid bicelles to vesicles is essential for producing engineered vesicles. We perform coarse-grained molecular dynamics (CGMD) simulations of unsaturated/saturated lipid mixtures to clarify the effects of lipid unsaturation on vesiculation at the molecular scale. The results demonstrate that vesiculation depends on the concentration of unsaturated lipids and the degree of unsaturation. The probability of vesiculation increases linearly with the apparent unsaturated lipid concentration at a low degree of unsaturation. Higher degrees of unsaturation lead to phase segregation within the binary bicelles, reducing the probability of vesiculation. A comparison between CGMD simulations and the conventional theory of vesiculation shows that the theoretical predictions of binary lipid systems must explicitly include phase segregation effects. Furthermore, simulations with biased lipid distributions reveal that vesiculation is facilitated by the preconcentration of unsaturated lipids in the core region of the bicelle but is then temporally limited as the unsaturated lipids move to the bicelle edges. These findings advance theoretical and experimental studies on binary lipid systems and promote the development of tailor-made vesicles.

Dominant frazil ice production in the Cape Darnley polynya leading to Antarctic Bottom Water formation.

Antarctic Bottom Water (AABW) occupies the abyssal layer of the world ocean and contributes to the global overturning circulation. It originates from dense shelf water, which forms from brine rejection during sea ice production. An important region of AABW formation has been identified off the Cape Darnley polynya. However, it remains unclear why and how high ice production leads to AABW formation. Using moored acoustic measurements and a satellite microwave algorithm, we reveal that underwater frazil ice dominates in the polynya. This underwater ice formation prevents heat-insulating surface-cover ice forming, thereby enabling efficient ice production. The high ice production in the nearshore and longer residence times create high-salinity source water for the AABW. Underwater frazil ice occurs as long as strong winds continue and occasionally penetrates depths of at least 80 m. Deep-penetrating frazil ice is particularly prominent in this polynya, while it also occurs in other Antarctic coastal polynyas.

Scalable and Precise Synthesis of Armchair-Edge Graphene Nanoribbon in Metal-Organic Framework.

Graphene nanoribbons (GNRs), narrow and straight-edged stripes of graphene, attract a great deal of attention because of their excellent electronic and magnetic properties. As of yet, there is no fabrication method for GNRs to satisfy both precision at the atomic scale and scalability, which is critical for fundamental research and future technological development. Here, we report a methodology for bulk-scale synthesis of GNRs with atomic precision utilizing a metal-organic framework (MOF). The GNR was synthesized by the polymerization of perylene (PER) or its derivative within the nanochannels of the MOF. Molecular dynamics simulations showed that PER was uniaxially aligned along the nanochannels of the MOF through host-guest interactions, which allowed for regulated growth of the nanoribbons. A series of characterizations of the GNR, including NMR, UV/vis/NIR, and Raman spectroscopy measurements, confirmed the formation of the GNR with well-controlled edge structure and width.