Structure And Dynamical Behaviors Of Nano-and Bio-interface And Their Regulation

With the development of nanotechnology,the refinement of production processes and the continuous miniaturization of devices,the importance of interface has been made more prominent.The structure and properties of typical nano-and biological interfaces involve complex physical,chemical,and biological processes,thus are hot topics of molecular physical mechanics.Over the past decade or so,typical nanointerfaces such as micro-nanofluidic devices have attracted much attention due to their wide application in many research fields.The interaction of ion solution with various solid interfaces relates to many physical and chemical phenomena and processes such as corrosion,lubrication,heterogeneous catalysis,nanoparticle self-assembly and electrochemistry.Due to the diversity in structure and smooth hydrophobic surface,carbon nanostructures provide an ideal environment for studying the structure and behavior of ion solution at nano-interfaces.Liquids at the interface of nanostrucutres appear to be of many different structures and interesting properties at the nanoscale.The molecular details and inherent mechanism of interactions between water and ion solution at the nanointerface are helpful for the design of desalination membranes and biomimetic nanochannels.The typical biological interface is the most common bilayer lipid in organisms.Important processes such as signal transmission and substance transport in vivo are inseparable from the phospholipid membrane.Many synthetic nano-materials exhibit toxicity to living cells,while other nanoscale molecules can be used in targeted drug delivery and biopharmaceuticals.The exploration of the molecular behavior of flexible biological interfaces is of great significance for the design of tools for drug delivery,biological imaging,and chemical analysis,and has broad prospects in biomedicine.The findings are briefly concluded below:(1)Fast water desalination at complete salt rejection by pristine graphyne monolayers: Desalination that produces clean freshwater from seawater holds the promise of solving the global water shortage.Given their unique structure and morphological characteristics,carbon nanomaterials are expected to provide a completely different way of desalination than traditional industrial methods.The porous graphyne material has a single-layered feature and is an ideal material for desalination.Here we find by comprehensive molecular dynamics simulations and first principles modeling that pristine graphyne can desalinate seawater at an exceptionally high water permeability about two orders of magnitude higher than those for commercial state-of-the-art reverse osmosis membranes.At the same time,?-graphyne,?-graphyne and graphyne-3 can achieve a salt rejection of 100% for ions including sodium,potassium,magnesium,calcium and chloride ions.By analyzing the density distribution and the structure of water molecules in the pore area,we found that the water molecules in the pores are permeated in a single-file form.Potential of mean force from umbrella sampling showed that the high rejection of ions originates from its own unique porous structure,through which ions must overcome significantly higher energy barriers than water molecules.The results from molecular dynamics simulation indicate that graphyne filtration provides a unique approach for the future application of seawater desalination.(2)Regulation of water structure at smooth liquid/solid interface:Interfacial water is an important mediate in both nano and biological systems,and even directly regulates the structure and function of interfaces.The geometric properties and hydroaffinity of the solid surface determine the interfacial water structure.By systematic molecular dynamics simulations,we investigate the interfacial water structure with different Lennard-Jones potential parameters and different water models.Both the calculated contact angle of water droplet at hydrophobic interface and the structure of the water film relate to the selection of the water model.When transiting the surface from hydrophobic to hydrophilic,the water droplet formed by TIP4 P water model first turns into a bilayer hexagonal structure,which further turns into a single layer of irregular water film.Comparing the structures formed by commonly used empirical potential water models at hydrophilic interface,we found that the three-point water model tends to form a tetragonal structure,including a metastable tetragonal structure;while the fourand five-point models form unordered structure with both tetragonal and hexagonal rings.(3)Structure and dynamics of ion hydration shell at nanoscale dimensions: Ion solvation at nanometer scale is of fundamental importance due to its relevance to diverse biological processes such as ion transport through membrane channel proteins and technological applications such as desalination,biosensing and energy conversion.Despite much progress,a comprehensive and universal understanding of ion solvation in nanoscale spaces of various dimensions is still lacking.Here we show by molecular dynamics simulations that hydrophobic confined spaces with characteristic lengths smaller than 1.5 nm alter the hydration structure and retard the water dynamics in the first solvation shell of ions.The anomalous ion hydration stems either from structural deformation of the hydration shell due to ion-wall interactions or confinement-induced ordering of water molecule in the hydration shell.Comparison of ion solvation confined to various dimensions indicates that ions with fewer degree of freedom inhabited exhibit a stronger response to the confinement due to their higher probability to access next to the wall surfaces.These findings shed light on the design of functional nanofluidic devices,and are also helpful to understand ion-involved activities occurring in biological systems.(4)Molecular mechanism of lipid nanodisc formation by styrene maleic acid copolymers:Experimental characterization of membrane proteins often requires their solubilization.A recent approach is to use styrene maleic acid(SMA)copolymers to isolate membrane proteins in nanometersized membrane discs,so called SMA lipid particles(SMALPs).The approach has the advantage of allowing direct extraction of proteins,keeping their native lipid environment.Despite the growing popularity of using SMALPs,the molecular mechanism behind the process remains poorly understood.Here we unravel the molecular details of the nanodisc formation by using coarse-grained molecular dynamics simulation.We show how SMA copolymers can efficiently bind to the lipid bilayer interface,driven by the hydrophobic effect.Due to the concerted action of multiple adsorbed copolymers,large membrane defects appear,including small water-filled pores.The copolymers can stabilize the rim of these pores,leading to pore growth and membrane disruption.Although complete solubilization is not observed on the time scale of our simulations,additional self-assembly experiments show that small nanodiscs are the thermodynamically preferred end state.Our findings shed light on the mechanism of SMALP formation as well as on their molecular structure,and provide an important step toward the design of optimized extraction tools for membrane protein research.