Green's function formalism coupled with Gaussian broadening of discrete states for quantum transport: application to atomic and molecular wires

A Green's function formalism incorporating broadened density of states (DOS) is proposed for the calculation of electrical conductance. In cluster-molecule-cluster systems, broadened DOS of the clusters are defined as continuous DOS of electrodes and used to calculate Green's function of electrodes. This approach combined with density functional theory is applied to the electrical transmission of gold atomic wires and molecular wires consisting of benzene-1,4-dithiolate, benzene-1,4-dimethanethiolate, 4,4(')-bipyridine, hexane dithiolate, and octane dithiolate. The B3LYP, B3PW91, MPW1PW91, SVWN, and BPW91 functionals with the LANL2DZ, CEP, and SDD basis sets are employed in the calculation of conductance. The width parameter was successfully determined to reproduce the quantum unit of conductance 2e(2)/h in gold atomic wires. The combination of the B3LYP hybrid functional and the CEP-31G basis set is excellent in reproducing measured conductances of molecular wires by Tao et al. [Science 301, 1221 (2003); J. Am. Chem. Soc. 125, 16164 (2003); Nano Lett. 4, 267 (2004)].     

Kinetically and thermodynamically controlled synthesis of tetraoxa[14]metacyclophanes and hexaoxa[16]metacyclophanes

The nucleophilic aromatic substitution of 1,5-difluoro-2,4-dinitrobenzene with 2-propylresorcinol in Et₃N/CH₃CN produces a mixture of syn and anti conformers of the cyclic tetramer and the cyclic hexamer with a kinetically controlled product distribution. Moreover, the reaction in DMF was catalyzed by CsF to also produce a mixture of these cyclic oligomers. In this case, however, the C-O bond is cleaved by the fluoride ion and the cyclization reaction is reversible; therefore, in the presence of excess CsF, the thermodynamically favored product (syn-isomer of cyclic tetramer) is obtained as the major product. The structures of the two conformational isomers of cyclic tetramers were determined by X-ray crystallography.     

Catalytic application of sulfonic acid functionalized mesoporous benzene–silica with crystal-like pore wall structure in esterification

The first catalytic applications of sulfonic acid-functionalized hydrophobic mesoporous benzene–silica with lamellar pore wall structure are reported. The mesoporous benzene–silica attached with propylsulfonic groups to the crystal-like periodic pore walls exhibited the catalytic activity in the esterification of acetic acid with ethanol. The catalytic results show the higher conversion compared to the commercial Nafion-H.     

Unusual enhancement of H2 evolution by Ru on TaON photocatalyst under visible light irradiation

H2 evolution on TaON photocatalyst under visible light irradiation (420 nm < or = lambda < or = 500 nm) in an aqueous methanol solution is found to be remarkably enhanced by adding Ru as a noble-metal co-catalyst.     

Detection of a proton-transfer process by kinetic solvent isotope effects in NH(4)(+)-mediated reactions catalyzed by a hammerhead ribozyme

Hammerhead ribozymes have been considered to be metalloenzymes. However, this proposal was recently questioned by the finding that the reaction proceeds in the presence of high concentrations of monovalent ions such as NH(4)(+) ions and in the absence of any divalent metal ions. Our present analysis based on solvent isotope effects indicates that (1) a proton transfer(s) occurs only in the NH(4)(+)-mediated reaction but not in metal-ion-mediated reactions such as Mg(2+)- and Li(+)-mediated reactions, (2) the catalyst that stabilizes the 5' leaving group in the NH(4)(+)-mediated reaction is different from that in the metal-ion-mediated HH ribozyme reactions, (3) an NH(4)(+) ion seems to act as a general acid catalyst, and (4) a nucleobase alone should not be the catalyst.     

Magnetically Guided Protein Transduction by Hybrid Nanogel Chaperones with Iron Oxide Nanoparticles

Protein pharmaceuticals show great therapeutic promise, but effective intracellular delivery remains challenging. To address the need for efficient protein transduction systems, we used a magnetic nanogel chaperone (MC): a hybrid of a polysaccharide nanogel, a protein carrier with molecular chaperone‐like properties, and iron oxide nanoparticles, enabling magnetically guided delivery. The MC complexed with model proteins, such as BSA and insulin, and was not cytotoxic. Cargo proteins were delivered to the target HeLa cell cytosol using a magnetic field to promote movement of the protein complex toward the cells. Delivery was confirmed by fluorescence microscopy and flow cytometry. Delivered β‐galactosidase, inactive within the MC complex, became enzymatically active within cells to convert a prodrug. Thus, cargo proteins were released from MC complexes through exchange interactions with cytosolic proteins. The MC is a promising tool for realizing the therapeutic potential of proteins.     

Mobilities of polyatomic molecular ions in He gas

The mobilities of polyatomic molecular ions in He gas, measured at 83 and 306 K using a low-temperature drift tube, were smaller than the polarization limit K _pol. The mobilities of atomic or small molecular ions tended to show a bump at intermediate reduced field, and then approach the polarization limit at low reduced field; however, the measured mobilities of polyatomic molecular ions were different. We compared the experimental mobilities with values calculated using the MOBCAL program, and found that they agreed well.     

Criteria for Efficient Photocatalytic Water Splitting Revealed by Studying Carrier Dynamics in a Model Al-doped SrTiO3 Photocatalyst

Overall water splitting (OWS) using semiconductor photocatalysts is a promising method for solar fuel production. Achieving a high quantum efficiency is one of the most important prerequisites for photocatalysts to realize high solar-to-fuel efficiency. In a recent study (Nature 2020 , 58, 411–414), a quantum efficiency of almost 100 % has been achieved in an aluminum-doped strontium titanate (SrTiO₃ : Al) photocatalyst. Herein, using the SrTiO₃ : Al as a model photocatalyst, we reveal the criteria for efficient photocatalytic water splitting by investigating the carrier dynamics through a comprehensive photoluminescence study. It is found that the Al doping suppresses the generation of Ti³⁺ recombination centers in SrTiO₃, the surface band bending facilitates charge separation, and the in situ photo-deposited Rh/Cr₂O₃ and CoOOH co-catalysts render efficient charge extraction. By suppressing photocarrier recombination and establishing a facile charge separation and extraction mechanism, high quantum efficiency can be achieved even on photocatalysts with a very short (sub-ns) intrinsic photocarrier lifetime, challenging the belief that a long carrier lifetime is a fundamental requirement. Our findings could provide guidance on the design of OWS photocatalysts toward more efficient solar-to-fuel conversion.     

Hydrogen transfer from guest molecule to radical in adjacent hydrate-cages

Electron spin resonance measurement of gamma-ray-irradiated propane hydrates shows that the normal propyl radical withdraws hydrogen from the adjacent propane molecule through the hexagonal planes of the hydrate cage without water molecule bridging.     

Efficient utilization of nanospace of layered transition metal oxide HNbMoO6 as a strong, water-tolerant solid acid catalyst

Layered HNbMoO6 was found to function as a strong solid acid catalyst, exceeding the activity of zeolites and ion-exchange resins for Friedel-Crafts alkylation. HNbMoO6 also exhibited high catalytic activity for esterification of hydrocarboxylic acid and hydration. The catalytic performance of layered HNbMoO6 is attributed to the intercalation of reactants into the interlayer and the development of strong acidity.