Flexibility or rigidity of the linker between two fused proteins is an important parameter that affects the function of fusion proteins. In this study, we constructed a linker library with five elementary units based on the combination of the flexible (GGGGS) and the rigid (EAAAK) units. Molecular dynamics (MD) simulation showed that more rigid units in the linkers lead to more helical conformation and hydrogen bonds, and less distance fluctuation between the N- and C-termini of the linker. The diversity of linker flexibility of the linker library was then studied by fluorescence resonance energy transfer (FRET) of cyan fluorescent protein (CFP)-yellow fluorescent protein (YFP) fusion proteins, which showed that there is a wide range of distribution of the FRET efficiency. Dissipative particle dynamics (DPD) simulation of CFP-YFP with different linkers also gave identical results with that of FRET efficiency analysis, and we further found that the combination manner of the linker peptide had a remarkable effect on the orientation of CFP and YFP domains. Our studies demonstrated that the construction of the linker library with the widely controllable flexibility could provide appropriate linkers with the desirable characteristics to engineer the fusion proteins with the expected functions.

The ability to control the organization of anisotropic nanoparticles, such as nanorods, with high precision would greatly facilitate the fabrication of functional materials. Using a hybrid computational model, we systematically investigate the directed self-assembly of Janus nanorods, with two chemically different surface compartments, in binary polymer mixtures. Our simulations demonstrate that the energetic contributions from the surface chemistry of the Janus nanorods, the rod-rod interaction, and the spatial confinement from the polymer phases can be tailored to tune the orientation angle of the nanorods with respect to phase interface, leading to the formation of ''lying'', tilt, and ''standing'' interfacial superstructures. A detailed insight into the mechanism regarding this precise control of nanorod orientation at the interface is obtained by evaluating the rod-phase interaction energy and the entropic energy of the tethered ligands on the rods. Furthermore, since the Janus rods are localized at the interface between two polymer phases, the structural evolution of the polymer nanocomposites is dramatically curtailed. This kinetic arrest is found to depend on the surface chemistry and the aspect ratio of Janus rods. The results demonstrated in this paper offer a novel approach to achieve morphological and kinetic control in nanoscopic composites towards unique photovoltaic and mechanical properties.

The coassembly of Janus nanoparticles and block copolymers offers a unique approach to control the spatial organization of nanoparticles. Herein, using computer simulations and theoretical analysis, we explore the hierarchical structures and underlying mechanisms of the coassembly of symmetric Janus nanoparticles in asymmetric block copolymers. Our simulations constitute the first study clarifying that Janus nanoparticles with two symmetric surface moieties do not take symmetric distribution in the interfaces of asymmetric block copolymers. Rather, they take various but controllable off-center arrangements from the interfaces upon tailoring the molecular architectures of block copolymers and thereby controlling their resulted mesostructural topology. We examine the detailed mechanism of this mesostructural topology-mediated hierarchical assembly and find that the structural asymmetry of the block segments causes unconventional entropy effect at the molecular scale, and the curved interfaces can lead to topology mismatching between Janus nanoparticles and polymer interfaces at the mesoscale. Furthermore, we employ a micromechanical model to demonstrate that the deviation of the Janus nanoparticles from the interface can significantly influence the mechanical properties of the nanocomposites. These findings enrich our understanding on the thermodynamic nature of polymer nanocomposites and may suggest a novel design approach to precisely program the spatial organization of nanoparticles in polymer matrix.

Understanding entropic contributions to ordering transitions is essential for the design of self-assembling systems with tunable hierarchical structures. Herein, we report entropy-mediated precise interfacial organization of Janus nanoparticles in the flexible−semiflexible block copolymers and the resulted optical properties of this heterogeneous material by combining coarse-grained molecular dynamics and a finite difference time domain technique. We find that the stiffness of the semiflexible block can regulate the off-center distribution of symmetric Janus nanoparticles with respect to phase interfaces, featured by a roughly 35% deviation from the interface to the utmost extent. Our simulations reveal how entropic and enthalpic effects in this multiphase media contribute to the self-assembled morphologies and, in particular, can lead to novel chain stiffness-induced entropy effects that can be harnessed to tailor the interfacial organization of Janus nanoparticles in the scaffold of block copolymers. Furthermore, the combination of techniques allows us to determine how changes of the interfacial nanostructures affect the optical properties of the nanocomposite. The findings enable the applications of polymer chain stiffness in precise control over the interfacial assembly of nanoparticles in heterogeneous materials and provide guidelines for facilitating the design of photonic crystals. ■ INTRODUCTIONHierarchical control over the spatial organization of nano building blocks, such as nanoparticles, has been a major challenge in the "bottom-up" generation of technologically important materials. 1−9 Various routes to direct nanoparticles assemblies have been explored, including the use of DNA 10−13 and functional polymers. 1,14−19 Nanoparticles arrays with tunable symmetry and dimensionality can form through programmable self-assembly of tailor-made building blocks with DNA linkers. 10−13 However, large-scale fabrication of these building blocks poses a significant hurdle for many practical applications. 20 Selfassembling of block copolymers, on the other hand, offers alluring opportunities to generate exquisitely tailored materials with effective control over nanoscale-domain geometry, packing symmetry, and chemical positions, making them ideal scaffolds for directing the assembly of nanoparticles. 16,17,21−28 Of particular interest is the control of the assembly of nanoparticles at the interface between different phase domains. 29−33 Janus nanoparticles consisting of two compartments of different chemistry or polarity are ideal building blocks to generate tunable and stable interfacial nanostructures because the Janus character of these nanoparticles provides them with tailorable surface and a higher interfacial activity compared with homogeneous nanoparticles. 34 However, precise control of such interfacial nanostructures still remains a challenge because the interfacial organization of Janus nanoparticles in block copolymers is governed by an intricate balance of entropic and enthalpic interactions. 1,16,18,27...