Zirconia-Supported Ruthenium Catalyst for Efficient Aerobic Oxidation of Alcohols to Aldehydes

We have developed the supported ruthenium catalyst (Ru­(OH)_<i>x</i>/ZrO₂) that shows highly efficient catalytic performance for the oxidation of activated, nonactivated, and heterocyclic alcohols with only 1 atm of molecular oxygen as a green oxidant. The ruthenium active site gave excellent aerobic alcohol oxidation reaction (turnover number (TON) = 63 000). The catalyst was easily recovered after the reaction and could be reused without a significant loss of its catalytic performance

Ag Shell–Au Satellite Hetero-Nanostructure for Ultra-Sensitive, Reproducible, and Homogeneous NIR SERS Activity

It is critical to create isotropic hot spots in developing a reproducible, homogeneous, and ultrasensitive SERS probe. Here, an Ag shell–Au satellite (Ag–Au SS) nanostructure composed of an Ag shell and surrounding Au nanoparticles was developed as a near-IR active SERS probe. The heterometallic shell-satellite structure based SERS probe produced intense and uniform SERS signals (SERS enhancement factor ∼1.4 × 10⁶ with 11% relative standard deviation) with high detectability (100% under current measurement condition) by 785 nm photoexcitation. This signal enhancement was independent of the laser polarizations, which reflects the isotropic feature of the SERS activity of Ag–Au SS from the three-dimensional (3D) distribution of SERS hot spots between the shell and the surrounding satellite particles. The Ag–Au SS nanostructure shows a great potential as a reproducible and quantifiable NIR SERS probe for in vivo targets

PSA Detection with Femtomolar Sensitivity and a Broad Dynamic Range Using SERS Nanoprobes and an Area-Scanning Method

Recently, surface-enhanced Raman scattering (SERS)-based immunoassays (SIA) have drawn much attention as diagnostic tools with large multiplex capacity and high sensitivity. However, several challengessuch as a low reproducibility, a time-consuming read-out process, and limited dynamic rangeremain. In this study, we report a reliable and sensitive SIA platform for prostate specific antigen (PSA) detection. Reliability and sensitivity were achieved by two approaches: (1) well-established SERS probes, so-called SERS dots that have high sensitivity (single particle detection) and little particle-to-particle variation in SERS intensity; and (2) a whole area-scanning readout method for rapid and reliable chip analysis rather than point scanning. As a feasibility test, PSA could be detected with high sensitivity (ca. 0.11 pg/mL, 3.4 fM LOD), with a wide dynamic range (0.001–1000 ng/mL). Thus, the developed platform will facilitate development of reliable immunoassays with high sensitivity and a wide dynamic range

β‑Lactoglobulin Peptide Fragments Conjugated with Caffeic Acid Displaying Dual Activities for Tyrosinase Inhibition and Antioxidant Effect

The regulation of tyrosinase activity and reactive oxygen species is of great importance for the prevention of dermatological disorders in the fields of medicine and cosmetics. Herein, we report a strategy based on solid-phase peptide chemistry for the synthesis of β-lactoglobulin peptide fragment/caffeic acid (CA) conjugates (CA-Peps) with dual activities of tyrosinase inhibition and antioxidation. The purity of the prepared conjugates, CA-MHIR, CA-HIRL, and CA-HIR, significantly increased to 99%, as acetonide-protected CA was employed in solid-phase coupling reactions on Rink amide resins. The tyrosinase inhibitory activities of all CA-Pep derivatives were higher than the activity of kojic acid, and CA-MHIR exhibited the highest tyrosinase inhibition activity (IC₅₀ = 47.9 μM). Moreover, CA-Pep derivatives displayed significantly enhanced antioxidant activities in the peroxidation of linoleic acid as compared to the pristine peptide fragments. All CA-Pep derivatives showed no cytotoxicity against B16–F1 melanoma cells

Water-Floating Giant Nanosheets from Helical Peptide Pentamers

One of the important challenges in the development of protein-mimetic materials is understanding the sequence-specific assembly behavior and dynamic folding change. Conventional strategies for constructing two-dimensional (2D) nanostructures from peptides have been limited to using β-sheet forming sequences as building blocks due to their natural tendency to form sheet-like aggregations. We have identified a peptide sequence (YFCFY) that can form dimers <i>via</i> a disulfide bridge, fold into a helix, and assemble into macroscopic flat sheets at the air/water interface. Due to the large driving force for 2D assembly and high elastic modulus of the resulting sheet, the peptide assembly induces flattening of the initially round water droplet. Additionally, we found that stabilization of the helix by dimerization is a key determinant for maintaining macroscopic flatness over a few tens of centimeters even with a uniform thickness of <10 nm. Furthermore, the ability to transfer the sheets from a water droplet to another substrate allows for multiple stacking of 2D peptide nanostructures, suggesting possible applications in biomimetic catalysis, biosensors, and 2D related electronic devices

Concave Rhombic Dodecahedral Au Nanocatalyst with Multiple High-Index Facets for CO₂ Reduction

A concave rhombic dodecahedron (RD) gold nanoparticle was synthesized by adding 4-aminothiophenol (4-ATP) during growth from seeds. This shape is enclosed by stabilized facets of various high-indexes, such as (331), (221), and (553). Because it is driven thermodynamically and stabilized by 4-ATP ligands, the concave RD maintains its structure over a few months, even after rigorous electrochemical reactions. We discussed the mechanism of the shape evolution controlled by 4-ATP and found that both the binding energy of Au–S and the aromatic geometry of 4-ATP are major determinants of Au atom deposition during growth. As a possible application, we demonstrated that the concave RD exhibits superior electrocatalytic performance for the selective conversion of CO₂ to CO in aqueous solution

Tailoring a Tyrosine-Rich Peptide into Size- and Thickness-Controllable Nanofilms

Self-assembled nanostructures of tyrosine-rich peptides have a number of potential applications such as biocatalysts, organic conducting films, and ion-selective membranes. In modulating a self-assembly process of peptides, the interfacial force is an important factor for kinetic control. Here, we present the formation of large-sized and thickness-controllable nanofilms from the YYACAYY peptide sequence (Tyr-C7mer peptide) using Langmuir–Blodgett and Langmuir–Schaefer deposition methods. The Tyr-C7mer peptide showed typical surfactant-like properties, which were demonstrated via the isotherm test (surface pressure–area) by spreading the Tyr-C7mer peptide solution onto an air/water interface. Uniform and flat peptide nanofilms were successfully fabricated and characterized. The redox activity of densely packed tyrosine moieties on the peptide nanofilm was also evaluated by assembling silver nanoparticles on the nanofilm without requiring any additives

Plasmon-Enhanced Sub-Bandgap Photocatalysis via Triplet–Triplet Annihilation Upconversion for Volatile Organic Compound Degradation

This study demonstrates the first reported photocatalytic decomposition of an indoor air pollutant, acetaldehyde, using low-energy, sub-bandgap photons harnessed through sensitized triplet–triplet annihilation (TTA) upconversion (UC). To utilize low-intensity noncoherent indoor light and maximize photocatalytic activity, we designed a plasmon-enhanced sub-bandgap photocatalyst device consisting of two main components: (1) TTA-UC rubbery polymer films containing broad-band plasmonic particles (Ag-SiO₂) to upconvert sub-bandgap photons, and (2) nanodiamond (ND)-loaded WO₃ as a visible-light photocatalyst composite. Effective decomposition of acetaldehyde was achieved using ND/WO₃ (<i>E</i>_g = 2.8 eV) coupled with TTA-UC polymer films that emit blue photons (λ_Em = 425 nm, 2.92 eV) upconverted from green photons (λ_Ex = 532 nm, 2.33 eV), which are wasted in most environmental photocatalysis. The overall photocatalytic efficiency was amplified by the broad-band surface plasmon resonance of AgNP-SiO₂ particles incorporated into the TTA-UC films

Solid-Phase Synthesis of Peptide-Conjugated Perylene Diimide Bolaamphiphile and Its Application in Photodynamic Therapy

Here, we describe a rapid and efficient synthetic method of peptide-conjugated perylene diimide (P-PDI) using solid-phase peptide synthesis (SPPS). Due to severe insolubility of perylene dianhydride (PDA) as a starting material of perylene diimide (PDI), PDA was initially conjugated with amino acids to obtain soluble PDI derivatives. Target peptides were synthesized on a 2-chlorotrityl chloride resin using the SPPS method and then conjugated with the amino acid-appended PDI. Various conditions such as loading levels, reaction times and solvents were optimized for introducing the peptides to both sides of the amino acid-appended PDI. The final P-PDI was obtained with a maximum yield of 80% in 12 h. Its singlet oxygen-derived phototoxicity on cells was confirmed, which could be applicable to photodynamic therapy

Single-Step and Rapid Growth of Silver Nanoshells as SERS-Active Nanostructures for Label-Free Detection of Pesticides

We explored a single-step approach for the rapid growth of Ag nanoshells (Ag NSs) under mild conditions. Without predeposition of seed metals, a uniform and complete layer of Ag shells was rapidly formed on silica core particles within 2 min at 25 °C via single electron transfer from octylamine to Ag⁺ ions. The size and thickness of the Ag NSs were effectively tuned by adjusting the concentration of silica nanoparticles (silica NPs) with optimal concentrations of AgNO₃ and octylamine. This unusually rapid growth of Ag NSs was attributed to a significant increase in the reduction potential of the Ag⁺ ions in ethylene glycol (EG) through the formation of an Ag/EG complex, which in turn led to their facile reduction by octylamine, even at room temperature. A substantial enhancement in the surface-enhanced Raman scattering (SERS) of the prepared Ag NSs was demonstrated. The Ag NSs were also utilized as SERS-active nanostructures for label-free detection of the pesticide thiram. The Ag NS-based SERS approach successfully detected thiram on apple peel down to the level of 38 ng/cm² in a label-free manner, which is very promising with respect to its potential use for the on-site detection of residual pesticides