Conformational Properties of Comb-shaped Polyelectrolytes with Negatively Charged Backbone and Neutral Side Chains Studied by a Generic Coarse-grained Bead-and-Spring Model

A generic coarse-grained bead-and-spring model,mapped onto comb-shaped polycarboxylate-based(PCE)superplasticizers,is developed and studied by Langevin molecular dynamics simulations with implicit solvent and explicit counterions.The agreement on the radius of gyration of the PCEs with experiments shows that our model can be useful in studying the equilibrium sizes of PCEs in solution.The effects of ionic strength,side-chain number,and side-chain length on the conformational behavior of PCEs in solution are explored.Single-chain equilibrium properties,including the radius of gyration,end-to-end distance and persistenee length of the polymer backbone,shape-asphericity parameter,and the mean span dimension,are determined.It is found that with the increase of ionic strength,the equilibrium sizes of the polymers decrease only slightly,and a linear dependenew of the persistence length of backbone on the Debye screening length is found,in good agreement with the theory developed by Dobrynin.Increasing side-chain numbers and/or side-chain lengths increases not only the equilibrium sizes(radius of gyration and mean span)of the polymer as a whole,but also the persistence length of the backbone due to excluded volume interactions.

Adhesion of an Ultrasmall Nanoparticle on a Bilayer Membrane is Still Size and Shape Dependent

It has been found recently that an ultrasmall nanoparticle whose size is smaller than the thickness of a cell membrane has unique roles in biomedical applications including the development of next generation of drugs or advanced nanoscale cargo carriers.However,the effect of physical properties of an ultrasmall nanoparticle on its adhesion to a bilayer membrane,which is a key step for Nano-Bio interaction as well as the biomedical applications,is still largely unknown.By using molecular dynamics,we find that both size and shape of an ultrasmall nanoparticle strongly affect its adhesion states on a bilayer membrane(e.g.,adhesion,separation or entwined by polymer chains).Interestingly,our simulations show that with decreasing particle size,the effect of particle shape becomes even more evident for the adhesion behavior.It is indicated that the competition between nanoparticle-polymer binding and polymer chain deformation,both of which are influenced by particle size and shape,determines the final adhesion states of an ultrasmall nanoparticle.Our results are helpful for the full understanding of interaction mechanism between nanoparticles and cell membranes and the practical applications of such ultrasmall nanoparticles.