Chengqian Yuan

Facile preparation of N- and O-doped hollow carbon spheres derived from poly(o-phenylenediamine) for supercapacitors

Nitrogen and oxygen doped hollow carbon spheres (HCSs) have been prepared by pyrolysis of poly(o-phenylenediamine) (PoPD) submicrospheres, which were synthesized by a facile polymerization procedure with an environmental-friendly dopant glycine. Utilizing o-phenylenediamine (oPD) and glycine as the precursors, we are also motivated by the recognition that effective heteroatom doping increases the supercapacitor performance of carbon materials. The as-prepared N- and O- doped HCSs exhibit an enlarged specific surface area (∼355 m2 g−1) and pore volume (∼0.14 cm3 g−1), and they have superior performance in supercapacitors owing to the synergies gained from effective heteroatom doping, their hollow structures, and their good mesoporosity. The reasonable capacitance performance coupled with the facile synthesis procedure suggests supercapacitor applications.

Crystalline Dipeptide Nanobelts Based on Solid–Solid Phase Transformation Self-Assembly and Their Polarization Imaging of Cells

Controlled phase transformation involving biomolecular organization to generate dynamic biomimetic self-assembly systems and functional materials is currently an appealing topic of research on molecular materials. Herein, we achieve by ultrasonic irradiation the direct solid-solid transition of bioinspired dipeptide organization from triclinic structured aggregates to xa0nanofibers and eventually to monoclinic nanobelts with strong polarized luminescence. It is suggested that the locally high temperature and pressure produced by cavitation effects cleaves the hydrophobic, π-π stacking or self-locked intramolecular interactions involved in one phase state and then rearranges the molecular packing to form another well-ordered aromatic dipeptide crystalline structure. Such a sonication-modulated solid-solid phase transition evolution is governed by distinct molecular interactions at different stages of structural organization. The resulting crystalline nanobelts are for the first time applied for polarization imaging of cells, which can be advantageous to directly inspect the uptake and fate of nanoscale delivery platforms without labeling of fluorescent dyes. This finding provides a new perspective to comprehend the dynamic evolution of biomolecular self-organization with energy supply by an external field and open up a facile and versatile approach of using anisotropic nanostructures for polarization imaging of cells and even live organisms in future.

Self-Assembled Zinc/Cystine-Based Chloroplast Mimics Capable of Photoenzymatic Reactions for Sustainable Fuel Synthesis

Prototypes of biosystems provide good blueprints for the design and creation of biomimetic systems. However, mimicking both the sophisticated natural structures and their complex biological functions still remains a great challenge. Herein, chloroplast mimics have been fabricated by one-step bioinspired amino acid mineralization and simultaneous integration of catalytically active units. Hierarchically structured crystals were obtained by the metal-ion-directed self-assembly of cystine (the oxidized dimer of the amino acid cysteine), with a porous structure and stacks of nanorods, which show similar architectural principles to chloroplasts. Porphyrins and enzymes can both be encapsulated inside the crystal during mineralization, rendering the crystal photocatalytically and enzymatically active for an efficient and sustainable synthesis of hydrogen and acetaldehyde in a coupled photoenzymatic reaction.

Charge‐Induced Secondary Structure Transformation of Amyloid‐Derived Dipeptide Assemblies from β‐Sheet to α‐Helix

Secondary structures such as α-helix and β-sheet are the major structural motifs within the three-dimensional geometry of proteins. Therefore, structure transitions from β-sheet to α-helix not only can serve as an effective strategy for the therapy of neurological diseases through the inhibition of β-sheet aggregation but also extend the application of α-helix fibrils in biomedicine. Herein, we present a charge-induced secondary structure transition of amyloid-derived dipeptide assemblies from β-sheet to α-helix. We unravel that the electrostatic (charge) repulsion between the C-terminal charges of the dipeptide molecules are responsible for the conversion of the secondary structure. This finding provides a new perspective to understanding the secondary structure formation and transformation in the supramolecular organization and life activity.

A theoretical study of weak interactions in phenylenediamine homodimer clusters

Weak intermolecular interactions in phenylenediamine dimer (pdd) clusters are studied by dispersion-corrected density functional theory (DFT) calculations. Along with the optimization of geometric structures and the calculation of interaction energies, we employ molecular electrostatic potential (MEP) mapping, natural bond orbital (NBO) analysis and quantum theory of atoms in molecule (AIM) to analyze the origin and relative energetic contributions of the weak interactions in these pdd systems. It is revealed that the most stable o-phenylenediamine dimer (opdd) cluster is dominated by N-HN hydrogen bonds, the p-phenylenediamine dimer (ppdd) cluster is largely stabilized by N-Hπ and ππ stacking interactions, while the m-phenylenediamine dimer (mpdd) cluster is mainly held by a combination of n → π*, C-Hπ and C-HN interactions. Energy decomposition analysis (EDA) of the total interaction energies of these clusters further demonstrates that the weak intermolecular interactions are associated with electrostatic and dispersion contributions. Structural spectroscopic analysis is also addressed depicting the coexistence of multiple intermolecular interactions which give rise to the spectral variation in wavenumbers of the infrared and Raman activities. Insights into the weak interactions of pdds help us to understand the molecular mechanisms involved in biochemistry and self-assembly materials.

Quantum-size-effect accommodation of gold clusters with altered fluorescence of dyes

We have synthesized monodispersed Au25 nanoclusters (NCs) stabilized with eco-friendly glutathione and report here an insight into their interactions with dye molecules. In the presence of such gold NCs, consistent fluorescence quenching was observed for all the dye molecules that we examined in this study regardless of their maximum emission wavelengths. The steady-state and time-resolved spectroscopic results demonstrate that the weakened luminance is associated with the protective ligand pertaining to a static quenching mechanism. Having expounded this issue, we further employed proper laser irradiation enabling dissociation of Au25(SG)18 so as to attain a transformation of nonplasmonic NCs into plasmonic gold nanoparticles (NPs) via photo-assisted aggregation of the dissociated gold clusters. As a result, emission enhancement for these dyes was observed, which is largely attributed to the local electromagnetic field enhancement of gold NPs. The alternation of fluorescence quenching to emission enhancement reflects an accommodation of quantum size effects upon the ligand-stabilized gold clusters.

Smart Peptide-Based Supramolecular Photodynamic Metallo-Nanodrugs Designed by Multicomponent Coordination Self-Assembly

Supramolecular photosensitizer nanodrugs that combine the flexibility of supramolecular self-assembly and the advantage of spatiotemporal, controlled drug delivery are promising for dedicated, precise, noninvasive tumor therapy. However, integrating robust blood circulation and targeted burst release in a single photosensitizer nanodrug platform that can simultaneously improve the therapeutic performance and reduce side effects is challenging. Herein, we demonstrate a multicomponent coordination self-assembly strategy that is versatile and potent for the development of photodynamic nanodrugs. Inspired by the multicomponent self-organization of polypeptides, pigments, and metal ions in metalloproteins, smart metallo-nanodrugs are constructed based on the combination and cooperation of multiple coordination, hydrophobic, and electrostatic noncovalent interactions among short peptides, photosensitizers, and metal ions. The resulting metallo-nanodrugs have uniform sizes, well-defined nanosphere structures, and high loading capacities. Most importantly, multicomponent assembled nanodrugs have robust colloidal stability and ultrasensitive responses to pH and redox stimuli. These properties prolong blood circulation, increase tumor accumulation, and enhance the photodynamic tumor therapeutic efficacy. This study offers a new strategy to harness robust, smart metallo-nanodrugs with integrated flexibility and multifunction to enhance tumor-specific delivery and therapeutic effects, highlighting opportunities to develop next-generation, smart photosensitizing nanomedicines.

Trace Water as Prominent Factor to Induce Peptide Self-Assembly: Dynamic Evolution and Governing Interactions in Ionic Liquids

The interaction between water and biomolecules including peptides is of critical importance for forming high-level architectures and triggering lifes functions. However, the bulk aqueous environment has limitations in detecting the kinetics and mechanisms of peptide self-assembly, especially relating to interactions of trace water. With ionic liquids (ILs) as a nonconventional medium, herein, it is discovered that trace amounts of water play a decisive role in triggering self-assembly of a biologically derived dipeptide. ILs provide a suitable nonaqueous environment, enabling us to mediate water content and follow the dynamic evolution of peptide self-assembly. The trace water is found to be involved in the assembly process of dipeptide, especially leading to the formation of stable noncovalent dipeptide oligomers in the early stage of nucleation, as evident by both experimental studies and theoretical simulations. The thermodynamics of the growth process is mainly governed by a synergistic effect of hydrophobic interaction and hydrogen bonds. Each step of assembly presents a different trend in thermodynamic energy. The dynamic evolution of assembly process can be efficiently mediated by changing trace water content. The decisive role of trace water in triggering and mediating self-assembly of biomolecules provides a new perspective in understanding supramolecular chemistry and molecular self-organization in biology.

Tungsten–copper clusters assembled on porous alumina for optical limiting applications

Cluster assembly materials with unique electronic and optical properties are significant for a variety of potential applications but often susceptible to intermolecular interactions which may alter the performance determined by their individual components. For the first time, here we report the assembly of a pyridine-protected tungsten–copper cluster on porous alumina, and find superior optical limiting (OL) properties retainable for multilevel clustering due to unaffected reverse saturable absorption (RSA) and constant photo-excited triplet states. Also clarified is that this transition metal W–Cu cluster bears an interesting framework structure with reasonable stability reinforced by strong donor–acceptor charge-transfer interactions.

All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry

We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ∼15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.