Wenxin Fu

Conformation-specific self-assembly of thermo-responsive poly(ethylene glycol)-b-polypeptide diblock copolymer.

Poly(ethylene glycol)-block-poly(γ-(2-methoxyethoxy)esteryl-L-glutamate) (PEG-b-poly-L-EG2Glu) was synthesized via ring-opening polymerization (ROP) of L-EG2Glu N-carboxyanhydride (NCA) using PEG-NH2 as macroinitiator. This diblock contained a thermo-responsive poly-L-EG2Glu block, which adopted primarily helical conformation in pristine aqueous solution. We found that PEG-b-poly-L-EG2Glu diblock can display two levels of self-assembly behaviors associated with hydrophobic interactions and conformation-specific reassembly, respectively. Upon temperature increase, the PEG-b-poly-L-EG2Glu diblock formed wormlike micelles, in which the poly-L-EG2Glu formed the micelle core and maintained helical conformation. However, extension of thermal annealing time drove the secondary structure transformation of the poly-L-EG2Glu block from helical conformation to β-sheet, which accounted for an assembly structure transition from wormlike micelles to nanoribbons. The critical factor was that poly-L-EG2Glu block can undergo thermo-induced hydrophobicity and conformation transformation, which offered an additional parameter to tune the nature of molecular interactions, i.e., intermolecular versus intramolecular hydrogen bonding interactions. The corresponding conformation and assembly structure changes were characterized using FTIR and electron microscopy, respectively.

Peptide hydrogels assembled from nonionic alkyl-polypeptide amphiphiles prepared by ring-opening polymerization.

Three alkyl-polypeptide (AP) amphiphiles were prepared using ring-opening polymerization of α-amino acid N-carboxyanhydride. The polypeptide segment was composed of diethylene-glycol-monomethyl-ether-functionalized poly-L-glutamate (poly-L-EG(2)Glu). These AP amphiphiles can spontaneously self-assemble into transparent hydrogels in water. These hydrogels showed shear thinning properties, and their strength can be modulated by hydrophobic alkyl tails. CryoTEM and AFM characterizations suggested that these hydrogels were formed by nanoribbons arising from intermolecular interactions between nonionic poly-L-EG(2)Glu segments.

Thermally Sensitive Self-Assembly of Glucose-Functionalized Tetrachloro-Perylene Bisimides: From Twisted Ribbons to Microplates

Chiral supramolecular structures are becoming increasingly attractive for their specific molecular arrangements, exceptional properties, and promising applications in chiral sensing and separation. However, constructing responsive chiral supramolecular structures remains a great challenge. Here, glucose-functionalized tetrachloro-perylene bisimides (GTPBIs) with thermally sensitive self-assembly behaviors are designed and synthesized. In a methanol/water mixture, GTPBIs self-assembled into twisted ribbons and microplates at 4 and 25 °C, respectively. Furthermore, the ribbon structure was metastable and could transform into microplates when the temperature was increased from 4 to 25 °C. Transmission electron microscopy (TEM) was used to track the evolution of morphology and study the assembly mechanisms of correponding nanostructures at different time intervals. The supramolecular structures were characterized with various techniques, including circular dichroism, TEM, scanning electron microscopy, atomic force microscopy, ultraviolet-visible absorption, and fluorescence spectra. This study provides insight into controlling molecular parameters and assembly conditions to construct chiral supramolecular structures.

Tailorable aqueous dispersion of single-walled carbon nanotubes using tetrachloroperylene-based bolaamphiphiles via noncovalent modification.

The enhanced dispersing capability of these bolaamphiphiles can be attributed to the large aromatic perylene core. The aqueous dispersion efficiency of single-walled carbon nanotubes (SWCNTs) is investigated by UV-vis absorption, fluorescence emission and Raman spectra, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. It is found that the tetrachloroperylene backbone moieties could interact with SWCNT via synergistic π-π and hydrophobic interactions, and the dispersing properties are closely related to the hydrophilic part of bolaamphiles. This study not only demonstrates tetrachloroperylene derivatives are able to stabilize SWCNTs, but also provides the possibility to understand the structure-property relationship between SWCNTs and tetrachloroperylene-based surfactants.

Janus Silica Hollow Spheres Prepared via Interfacial Biosilicification

A poly(ethylene glycol)-b-poly(L-lysine)-b-poly(styrene) (PEG-PLL-PS) triblock copolymer, which contains a cationic PLL block as the middle block, is synthesized via a combination of ring-opening polymerization (ROP) and atom-transfer radical polymerization (ATRP). The PEG-PLL-PS (ELS) triblock is employed as a macromolecular surfactant to form a stable oil-in-water (O/W) emulsion, which is subsequently used as the template to prepare Janus silica hollow spheres (JHS) via a one-pot biosilicification reaction. For the emulsion template, the middle PLL block assembles at the O/W interface and directs the biomimetic silica synthesis in the presence of phosphate buffer and silicic acid precursors. This biosilicification process takes place only in the intermediate layer between water and the organic interior phase, leading to the formation of silica JHSs with hydrophobic PS chains tethered to the inner surface and PEG attached to the outer surface. The three-layer JHSs, namely, PEG/silica-polylysine/PS composites, were verified by electron microscopy. Upon further breaking these JHSs into species, polymer-grafted Janus silica nanoplates (JPLs) can be obtained. Our studies provide an efficient one-step method for preparing hybrid silica Janus structures within minutes.

Surface-grafted semiconductor layer prepared by surface initiated ring-opening polymerization of L-lysine NCA derivatives.

Asymmetric and symmetric L-lysine N-carboxylic anhydrides based on perylene bisimide derivatives were successfully synthesized and grafted onto silicon wafers via surface-initiated ring-opening polymerization. The grafted n-type semiconductor film was flat and compact, and its thickness could be tuned by variation of the polymerization conditions.

Self-Assembly of Metallacages into Multidimensional Suprastructures with Tunable Emissions

Cubic metallacages were arranged into multidimensional (one-, two-, and three-dimensional) suprastructures via multistep assembly. Four new shape-controllable, hybrid metallacages with modified substituents and tunable electronic properties were prepared using dicarboxylate ligands with various substituents (sodium sulfonate, nitro, methoxyl, and amine), tetra-(4-pyridylphenyl) ethylene, and cis-(PEt3)2Pt(OTf)2. The as-prepared metallacages were used as building blocks for further assembly. Diverse suprastructures with tunable emissions (λmax from 451 to 519 nm) and various substituents (-SO3Na, -NO2, -OCH3, and -NH2) were prepared depending on the substituents and solvents used.