Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA（ss DNA）tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows： i） when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii）for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii） when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.

Molecular dynamics simulation of diffusion of nanoparticles in mucus

The rapid diffusion of nanoparticles （NPs） through mucus layer is critical for efficient transportation of NPs-loaded drug delivery system. To understand how the physical and surface properties of NPs affect their diffusion in mucus, we have developed a coarse-grained molecular dynamics model to study the diffusion of NPs in modeled mucus layer. Both steric obstruction and hydrodynamic interaction are included in the model capable of capturing the key characteristics of NPs＇ diffusion in mucus. The results show that both particle size and surface properties significantly affect the diffusivities of NPs in mucus. Furthermore, we find rodlike NPs can gain a higher diffusivity than spherical NPs with the same hydrodynamic diameter. In addition, the disturbed environment can enhance the diffusivity of NPs. Our findings can be utilized to design mucus penetrating NPs for targeted drug delivery system.

Toward Rational and Modular Molecular Design in Soft Matter Engineering

This essay discusses some preliminary thoughts on the development of a rational and modular approach for molecular design in soft matter engineering and proposes ideas of structural and functional synthons for advanced functional materials. It echoes the Materials Genome Initiative by practicing a tentative retro-functional analysis （RFA） scheme. The importance of hierarchical structures in transferring and amplifying molecular functions into macroscopic properties is recognized and emphasized. According to the role of molecular segments in final materials, there are two types of building blocks： structural synthon and functional synthon. Guided by a specific structure for a desired function, these synthons can be modularly combined in various ways to construct molecular scaffolds. Detailed molecular structures are then deduced, designed and synthesized precisely and modularly. While the assembled structure and property may deviate from the original design, the study may allow further refinement of the molecular design toward the target function, The strategy has been used in the development of soft fullerene materials and other giant molecules. There are a few aspects that are not yet well addressed： （1） function and structure are not fully decoupled and （2） the assembled hierarchical structures are sensitive to secondary interactions and molecular geometries across different length scales. Nevertheless, the RFA approach provides a starting point and an alternative thinking pathway by provoking creativity with considerations from both chemistry and physics. This is particularly useful for engineering soft matters with supramolecular lattice formation, as in giant molecules, where the synthons are relatively independent of each other.

Giant molecules:where chemistry,physics,and bio-science meet

This feature article focuses on the recent development of giant molecules,which has emerged at the interface among chemistry,physics,and bio-science.Their molecular designs are inspired by natural polymers like proteins and are modularly constructed from molecular nanoparticle building blocks via sequential "click" chemistry.Most important molecular parameters such as topology,composition,and molecular weight can be precisely controlled.Their hierarchical assembly reveals many features reminiscent of both small molecules and proteins yet unusual for conventional synthetic polymers.These features are summarized and compared along with synthetic polymers and proteins.Specifically,examples are given in each category of giant molecules to illustrate the characteristics of their hierarchical assembly across different length,time and energy scales.The idea of "artificial domain" is presented in analogy to the structural domains in proteins.By doing so,we aim to develop a rational and modular approach toward functional materials.The factors that dominate the materials functions are discussed with respect to the precision and dynamics of the assembly.The complexity of structure-function relationship is acknowledged,which suggests that there is still a long way to go toward the convergence of synthetic polymers and biopolymers.