Visible Light-Driven Selective Aerobic Oxidation of Benzylalcohols to Benzaldehydes by a Cu(acac)₂‑BiVO₄‑Admicelle Three-Component Heterosupramolecular Photocatalyst

A hybrid photocatalyst consisting of bis­(acetylacetonato)­copper­(II) and monoclinic sheelite bismuth­(III) vanadate (Cu­(acac)₂/<i>ms</i>-BiVO₄) has recently been shown to fulfill multiple O₂ reduction, exhibiting a high visible-light activity for the oxidation of amines without sacrificial agents (Naya et al. <i>Angew. Chem., Int. Ed</i>. <b>2014</b>, <i>53</i>, 13894.). This study shows that the addition of trimethylstearylammonium chloride (C₁₈TAC) in the reaction system drastically promote the Cu­(acac)₂/<i>ms</i>-BiVO₄-photocatalyzed oxidation of benzylalcohol analogues to the corresponding aldehydes with selectivity greater than 99% under visible-light irradiation (λ > 430 nm) at 298 K. The photocatalytic activity in the presence of C₁₈TAC is quite sensitive to the stirring conditions. Under vigorous stirring conditions (rotation speed of stirrer, <i>v</i> = 1200 rpm), the activity increases with increasing C₁₈TAC concentration (<i>C</i>_surf) to go through a maximum at <i>C</i>_surf = 0.2 mM. Under mild stirring conditions (<i>v</i> = 600 rpm), the activity significantly decreases as compared to that for the vigorous stirring system, and also, it decreases with an increase in <i>C</i>_surf at 0 < <i>C</i>_surf < 0.2 mM to reach almost constant at <i>C</i>_surf ≥ 0.2 mM. The dispersion examination of the <i>ms</i>-BiVO₄ particles in water suggested that the C₁₈TAC monolayer grows on the <i>ms</i>-BiVO₄ surface at 0 < <i>C</i>_surf < 0.2 mM to form an adsorption bilayer (or admicelle) at <i>C</i>_surf ≥ 0.2 mM. The remarkable enhancing effect by the C₁₈TAC admicelle originates from the concentration of the reaction substrate near the <i>ms</i>-BiVO₄ surface by incorporating it into the hydrophobic nanospace and the good particle dispersibitily in water due to the electrostatic repulsion between the surface charges. Also, the high selectivity can be attributed to the cooperative effect of the moderate oxidation ability of the <i>ms</i>-BiVO₄ valence band holes, the 4-electron reduction of O₂ to H₂O, and the spontaneous transport of the intermediates from the reaction field to the water phase

Two-Step Excitation-Driven Au–TiO₂–CuO Three-Component Plasmonic Photocatalyst: Selective Aerobic Oxidation of Cyclohexylamine to Cyclohexanone

The chemisorption of (acetylacetonato)­copper­(II) on gold-nanoparticle- (Au-NP-) loaded rutile TiO₂ and subsequent heating in the air at 773 K yields molecular-scale CuO clusters on the TiO₂ surface with varying CuO loading amounts (Au/TiO₂–CuO) (J. Phys. Chem. C 2013, 117, 23848−23857). The three-component Au/TiO₂–CuO plasmonic photocatalyst exhibits a high level of visible-light activity for the selective aerobic oxidation of cyclohexylamine to cyclohexanone at room temperature. The photocatalytic activity far exceeds those of the Au/TiO₂ and TiO₂–CuO two component systems. Photoelectrochemical experiments indicate that the electrons injected from Au NPs into TiO₂ by the localized surface plasmon resonance excitation are transferred to the CuO clusters through simultaneous visible-light excitation from the valence band of TiO₂ to the surface CuO-derived levels. Consequently, the high activity originates from the electron-collecting and -concentrating effects of the CuO clusters with an electrocatalytic activity for the oxygen reduction reaction

Visible-Light Activation of Strontium Titanate by the Surface Modification with Iron(III) Oxide Nanoclusters

Tris­(acetylacetonato)­iron­(III) (Fe­(acac)₃) is chemisorbed on strontium titanate (SrTiO₃) via partial ligand-exchange between the acac ligand and the surface Ti-OH group. Postheating at 773 K in the air yields extremely small iron­(III) oxide clusters on SrTiO₃ (Fe₂O₃/​SrTiO₃). The Fe₂O₃ loading amount per unit surface area of SrTiO₃ (Γ/Fe ions nm^–2) was controlled by the Fe­(acac)₃ concentration. The surface modification gives rise to visible-light activity for the oxidation of 2-naphthol used as a model water pollutant simultaneously with the UV-light activity significantly boosted. The visible-light activity is sensitive to Γ to reach a maximum at Γ ≈ 0.36. Valence band-X-ray photoelectron spectroscopy (VB-XPS) and electrochemical measurements indicated that the surface modification by the Fe₂O₃ nanoclusters (NCs) generates new vacant surface levels below the conduction band minimum of SrTiO₃, while the VB maximum level is invariant. The band energy diagram of Fe₂O₃/​SrTiO₃ suggested that the visible-light activity can be induced by the photoexcitation of the electrons in the VB of SrTiO₃ to the vacant surface levels or the bulk-to-surface interfacial electron transfer (IFET) in contrast to the visible-light-driven surface-to-bulk IFET in Fe₂O₃/​TiO₂. Eventually, the high visible-light activity of Fe₂O₃/​SrTiO₃ stems from the effective charge separation and the electrocatalytic activity of the Fe₂O₃ NCs for the oxygen reduction reaction

Reaction Mechanism of the Multiple-Electron Oxygen Reduction Reaction on the Surfaces of Gold and Platinum Nanoparticles Loaded on Titanium(IV) Oxide

Au and Pt nanoparticles with varying mean particle size and comparable loading amounts were loaded on the surface of TiO₂ (Au/TiO₂ and Pt/TiO₂, respectively). The photocatalytic activities of Au/TiO₂ and Pt/TiO₂ for the oxygen reduction reaction (ORR) in an aerated aqueous solution containing 4% ethanol were compared under ultraviolet-light irradiation at 298 K. The initial rate of H₂O₂ generation (or H₂O₂ formation rate) in the Au/TiO₂ system is much greater than that in the Pt/TiO₂ system regardless of the metal particle size. To clarify the origin for the striking difference in the activity, the photocatalytic ORR on the model slabs (M₂₈/(TiO₂)₃₂ and M₅₀/(TiO₂)₉₆, M = Au and Pt) was simulated by density functional theory (DFT) calculations taking the solvation effect into consideration. The DFT calculations clearly show that regardless of the cluster size, H₂O₂ formation more easily occurs structurally and energetically for the Au/TiO₂ system, whereas H₂O is generated with the O–O bond cleavage in the Pt/TiO₂ system

High-Throughput Manipulation of Circulating Tumor Cells Using a Multiple Single-Cell Encapsulation System with a Digital Micromirror Device

Circulating tumor cells (CTCs) are potential precursors of metastatic cancer, and genomic information obtained from CTCs have the potential to provide new insights into the biology of cancer metastasis. We previously developed a technique for single-cell manipulation based on the encapsulation of a single cell in a photopolymerized hydrogel that can be used for subsequent genetic analysis. However, this technique has limitations in terms of throughput because light irradiation must be performed on each individual cell from the confocal laser-scanning microscopy. Here, we present a high-throughput cell manipulation technique using a multiple single-cell encapsulation system with a digital micromirror device. This system enables rapid cell imaging within a microcavity array, a microfilter for the recovery of CTCs from blood samples, as well as the simultaneous encapsulation of several CTCs with hydrogels photopolymerized using a multiple light-irradiation system. Furthermore, single-cell labeling using two differently shaped hydrogels was examined to distinguish between NCI-H1975 cells and A549 cells, demonstrating the utility of the system for single-cell gene mutation analysis. In addition to CTCs, our system can be widely applied for analyses of mammalian cells and microorganisms

Manipulation of a Single Circulating Tumor Cell Using Visualization of Hydrogel Encapsulation toward Single-Cell Whole-Genome Amplification

Genetic characterization of circulating tumor cells (CTCs) could guide the choice of therapies for individual patients and also facilitate the development of new drugs. We previously developed a CTC recovery system using a microcavity array, which demonstrated highly efficient CTC recovery based on differences in cell size and deformability. However, the CTC recovery system lacked an efficient cell manipulation tool suitable for subsequent genetic analysis. Here, we resolve this issue and present a simple and rapid manipulation method for single CTCs using a photopolymerized hydrogel, polyethylene glycol diacrylate (PEGDA), which is useful for subsequent genetic analysis. First, PEGDA was introduced into the cells entrapped on the microcavity array. Then, excitation light was projected onto the target single cells for encapsulation of each CTC by confocal laser-scanning microscopy. The encapsulated single CTCs could be visualized by the naked eye and easily handled with tweezers. The single CTCs were only partially encapsulated on the PEGDA hydrogel, which allowed for sufficient whole-genome amplification and accurate genotyping. Our proposed methodology is a valuable tool for the rapid and simple manipulation of single CTCs and is expected to become widely utilized for analyses of mammalian cells and microorganisms in addition to CTCs

Microcavity Array System for Size-Based Enrichment of Circulating Tumor Cells from the Blood of Patients with Small-Cell Lung Cancer

In this study, we present a method for efficient enrichment of small-sized circulating tumor cells (CTCs) such as those found in the blood of small-cell lung cancer (SCLC) patients using a microcavity array (MCA) system. To enrich CTCs from whole blood, a microfabricated nickel filter with a rectangular MCA (10⁴ cavities/filter) was integrated with a miniaturized device, allowing for the isolation of tumor cells based on differences in size and deformability between tumor and blood cells. The shape and porosity of the MCA were optimized to efficiently capture small tumor cells on the microcavities under low flow resistance conditions, while allowing other blood cells to effectively pass through. Under optimized conditions, approximately 80% of SCLC (NCI-H69 and NCI-H82) cells spiked in 1 mL of whole blood were successfully recovered. In clinical samples, CTCs were detectable in 16 of 16 SCLC patients. In addition, the number of leukocytes captured on the rectangular MCA was significantly lower than that on the circular MCA (<i>p</i> < 0.001), suggesting that the use of the rectangular MCA diminishes a considerable number of carryover leukocytes. Therefore, our system has potential as a tool for the detection of CTCs in small cell-type tumors and detailed molecular analyses of CTCs