Makoto Tanabe

Catalytic applications of DNA duplexes containing Ag⁺-mediated cytosine-cytosine base pairs (C-Ag⁺-C) have not been well investigated. In this study, we demonstrate a novel approach for forming highly active DNA-capped Ag nanoparticle (DNA-AgNP) catalysts for the reduction of 4-nitrophenol (4-NP) using sodium borohydride (NaBH₄). This approach is based on the in situ generation of DNA-AgNPs from DNA duplexes containing C-Ag⁺-C (DNA duplex-Ag⁺). UV-vis spectroscopic analysis suggests that the DNA duplex-Ag⁺ complex acts as an excellent catalyst precursor for 4-NP reduction with NaBH₄. Transmission electron microscopy observations of the reaction solution after the 4-NP reduction reaction using DNA duplex-Ag⁺ provided detailed experimental insights into the mechanism of the catalytic activity of DNA duplex-Ag⁺ for 4-NP reduction. In the reaction solution, DNA-AgNPs were initially formed (DNA duplex-Ag⁺ + NaBH₄ → DNA-AgNPs) and then served as water-soluble catalysts for 4-NP reduction. Notably, the catalytic properties of the DNA-AgNPs generated in situ were affected by the DNA strand length and sequence. The properties of DNA duplex-Ag⁺ may provide a new application of DNA molecules containing metallobase pairs as water-soluble catalyst precursors.

The binary oxide clusters (BOCs) composed of Cu and Bi atoms were prepared using a macromolecular dendritic template. The oxidized Cu₁₂Bi₁₆O_x exhibited the selective styrene bisperoxidation. The catalytic performance and tolerance were improved by incorporation of Bi into the CuO_x clusters.

Invited for the cover of this issue is Kimihisa Yamamoto and co‐workers at Tokyo Institute of Technology and International Christian University. The image depicts enhanced reactivity of the copper oxide subnanoparticles under low‐temperature conditions. Read the full text of the article at 10.1002/chem.202100508.

Subnanoparticles (SNPs) with sizes of approximately 1 nm are attractive for enhancing the catalytic performance of transition metals and their oxides. Such SNPs are of particular interest as redox‐active catalysts in selective oxidation reactions. However, the electronic states and oxophilicity of copper oxide SNPs are still a subject of debate in terms of their redox properties during oxidation reactions for hydrocarbons. In this work, in situ X‐ray absorption fine structure (XAFS) measurements of Cu₂₈O_x SNPs, which were prepared by using a dendritic phenylazomethine template, during temperature‐programmed reduction (TPR) with H₂ achieved lowering of the temperature (T₅₀=138 °C) reported thus far for the Cu^II→Cu^I reduction reaction because of Cu−O bond elongation in the ultrasmall copper oxide particles.

Finely size-controlled ultrasmall iron oxide particles (IOPs) on graphene nanosheets were usefully prepared by using pulsed arc plasma deposition. The IOPs are composed of a high crystallinity single γ-Fe ₂ O ₃ component without annealing.

Subnanoparticles (SNPs) with ultrasmall particle sizes (<1 nm) have potential to provide catalytic activity that is superior to that of nanoparticles. Size-controlled CunOx (n = 12, 28, and 60) materials supported on zirconia, prepared using a dendritic macromolecular reactor, exhibited increased ionicity of the Cu-O bonds with a decrease in size of the particles, which was suggested on the basis of the peak intensity in the Cu 2p3/2 region. The polarization of the Cu-O bonds in the ultrasmall copper oxides provides size-dependent catalytic activity in aerobic oxidation of aromatic hydrocarbons. The smallest Cu12Ox materials achieved an excellent large number of turnover number (TON = 40206) without any significant deactivation.

Among various approaches synthesizing metal nanoparticles and tiny clusters, a template method using dendrimers has significant advantages over other chemical approaches with respect to their synthetic precision and the scalability. A dendrimer of polydentate ligands assembles metal ions or salts into the interior allowing production of metal nanoparticles in the dendrimer. The dendrimer-encapsulated nanoparticles (DENs) exhibit unique and remarkable catalytic properties depending on the size and elemental formula. Recent advances in dendrimer chemistry even enabled the atom precise synthesis of subnanometer metal clusters that have been impossible to prepare by wet chemical methods. In addition, not only for the synthesis of metal nanoparticles and clusters, the dendrimer itself can also provide the modulation of activity and selectivity in the catalysis. In this review, we summarized the most relevant research in which the dendrimer was employed as the template, modulator, or stabilizer for nanoparticle synthesis for catalytic applications.