Robust 2 nm-sized gold nanoclusters on Co3O4 for CO oxidation.

In this study, gold nanoparticles were dispersed on Co3O4 nanoplates, forming a specific Au-Co3O4 interface. Upon calcination at 300 °C in air, aberration-corrected STEM images evidenced that the gold nanoclusters (NCs) on Co3O4{111} were maintained at ca. 2.2 nm, which is similar to the size of the parent Au colloidal particles, demonstrating the stronger metal-support interaction (SMSI) on Co3O4{111}. Au/Co3O4{111} showed good catalytic activity (a full CO conversion achieved at 80 °C) and durability (over 10 hours) in CO oxidation, which was mainly due to the promotion by the surface oxygen vacancies and intrinsic defects of Co3O4{111} for activating O2 and by Au0, Auδ+, and Au+ species on the surface of gold NCs for CO activation, as evidenced by Raman and Fourier-transform infrared (FT-IR) spectroscopy analysis. Au/Co3O4 catalyzed CO oxidation obeyed the Langmuir-Hinshelwood mechanism at low temperatures.

Hydrogelation of the Short Self-Assembling Peptide I3QGK Regulated by Transglutaminase and Use for Rapid Hemostasis.

The self-assembly of short peptides is a promising route to the creation of smart biomaterials. To combine peptide self-assembly with enzymatic catalysis, we design an amphiphilic short peptide I3QGK that can self-assemble into long nanoribbons in aqueous solution. Upon addition of transglutaminase (TGase), the peptide solution undergoes a distinct sol-gel transition to form a rigid hydrogel, which shows strong shear-thinning and immediate recovery properties. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements indicate the occurrence of considerable nanofibers in addition to the original nanoribbons. Liquid chromatography and mass spectrometry analyses reveal the enzymatic formation of peptide dimers from monomers through intermolecular ε-(γ-glutamyl)lysine isopeptide bonding. The dimers rapidly self-assemble into flexible and entangled nanofibers, and the coexistence of the original nanoribbons and the newly created nanofibers is responsible for hydrogelation. Factor XIII in blood is converted by thrombin to an active TGase (Factor XIIIa) during bleeding, so the peptide solution shows a more rapid and effective hemostasis via a combination of gelling blood and promoting platelet adhesion, relative to other hemostasis methods or materials. These features of I3QGK, together with its low cytotoxicity against normal mammalian cells and noninduction of nonspecific immunogenic responses, endow it with great potential for future clinical hemostasis applications.

Tuning of peptide assembly through force balance adjustment.

Controlled self-assembly of amphiphilic tripeptides into distinct nanostructures is achieved via a controlled design of the molecular architecture. The tripeptide Ac-Phe-Phe-Lys-CONH2 (FFK), hardly soluble in water, forms long amyloid-like tubular structures with the aid of ß-sheet hydrogen bonding and aromatic π-π stacking. Substitution of phenylalanine (F) with tyrosine (Y), that is, only a subtle structural variation in adding a hydroxyl group to the phenyl ring, results in great change in molecular self-assembly behavior. When one F is substituted with Y, the resulting molecules of FYK and YFK self-assemble into long thinner fibrils with high propensity for lateral association. When both Fs are substituted with Y, the resulting YYK molecule forms spherical aggregates. Introduction of hydroxyl groups into the molecule modifies aromatic interactions and introduces hydrogen bonding. Moreover, since the driving forces for peptide self-assembly including hydrogen bonding, electrostatic repulsion, and π-π stacking have high interdependence with each other, changes in aromatic interaction induce a Domino effect and cause a shift of force balance to a new state. This leads to significant variations in self-assembly behavior.

Effects of anions on nanostructuring of cationic amphiphilic peptides.

The effects of addition of a series of stoichiometric salts on the nanostructuring of cationic amphiphilic peptides have been investigated through the combination of atomic force microscopy (AFM), circular dichroism (CD), and turbidity measurements. The results revealed that anions had more pronounced effects than cations in tuning the nanostructures formed from these peptides. Addition of ClO(3)(-), NO(3)(-), and Br(-) could stabilize the primary nanostructures (nanostacks, nanospheres, or short nanorods) formed by A(9)K and I(3)K and effectively inhibit their growth into longer nanostructures (nanorods or nanotubes). In contrast, the anions of Cl(-), SO(4)(2-), HPO(4)(2-), PO(4)(3-), and C(6)H(5)O(7)(3-) (citrate) favored the axial growth of these peptides to form long intersecting nanofibrils and led to an increase in diameter and surface roughness, as well, clearly enhancing their propensity for nanostructuring. The efficiency of different anions in promoting the growth of peptide nanoaggregates into larger ones could be ordered as ClO(3)(-) < NO(3)(-) ≤ Br(-) < Cl(-) < SO(4)(2-) < HPO(4)(2-) < PO(4)(3-) < C(6)H(5)O(7)(3-), broadly consistent with the Hofmeister anion sequence. These observations were well rationalized by considering different aspects of direct interactions of the anions with the peptide molecules.