Surface friction of thermoresponsive poly(N-isopropylacrylamide) gels in water

In this paper, we report the experimental results of surface friction between thermoresponsive poly(N-isopropylacrylamide) gels in water. The static friction force was found to depend on the waiting period prior to slider movement after contact between gel surfaces, which was a result of two relaxation mechanisms: the stress decay process due to macroscopic deformation under a normal load and the microscopic conformational change in the real contact area of polymer networks. The sliding velocity and the normal load dependence of the kinetic friction force were extensively measured. The results suggested that the following two mechanisms depended on the sliding velocity: the friction force generated by direct contact of the solid-like behavior and the viscous resistance of the liquid-like behavior. The strong temperature dependence of kinetic friction was observed, which was a result of a change in the balance between hydrophobic and hydrophilic interactions. The experimental results are discussed in terms of the multi-asperity contacts between the swollen gel/gel interfaces (solid friction, depending on the waiting period) and the viscous resistance and lubricating effect between the gel/water interfaces (fluid friction, depending on the sliding velocity).     

Pyrolyzed Cobalt Corrole as a Potential Non‐Precious Catalyst for Fuel Cells

Non‐precious metal catalysts of the oxygen reduction reaction are highly favored for use in polymer electrolyte fuel cells (PEFC) because of their relatively low cost. Here, a new carbon‐black‐supported pyrolyzed Co‐corrole (py‐Co‐corrole/C) catalyst of the oxygen reduction reaction (ORR) in a PEFC cathode is demonstrated to have high catalytic performance. The py‐Co‐corrole/C at 700 °C exhibits optimized ORR activity and participates in a direct four‐electron reduction pathway for the reduction of O₂ to H₂O. The H₂‐O₂ PEFC test of py‐Co‐corrole/C in the cathode reveals a maximum power density of 275 mW cm^?2, which yields a higher performance and a lower Co loading than previous studies of Co‐based catalysts for PEFCs. The enhancement of the ORR activity of py‐Co‐corrole/C is attributable to the four‐coordinated Co‐corrole structure and the oxidation state of the central cobalt.     

Unexpected Pd-catalyzed hydrogenation of phenol to 2-cyclohexene-1-one: enhanced activity and selectivity assisted by molecular oxygen

Addition of O(2) enables the liquid-phase hydrogenation of phenol using H(2) at low temperatures under atmospheric pressure with an unexpected selectivity towards 2-cyclohexene-1-one rather than cyclohexanone. As a catalyst, as-synthesized Pd/MCM-41 including the residual templates within the mesoporous channels exhibits a prominent positive effect on the catalytic performance.     

A new synthetic strategy for catechin-class polyphenols: concise synthesis of (-)-epicatechin and its 3-O-gallate

Concise synthesis of (-)-epicatechin and its 3-O-gallate is described, illustrating efficacy of the new strategy for catechin-class polyphenols based on assembly of lithiated fluorobenzene and epoxy alcohol followed by a pyran cyclization. 1,3,5-Trifluorobenzene serves as the A-ring equivalent for functionalization and the pyran annulation.     

Catalytic reactions on neutral Rh oxide clusters more efficient than on neutral Rh clusters

Gas phase catalytic reactions involving the reduction of N(2)O and oxidation of CO were observed at the molecular level on isolated neutral rhodium clusters, Rh(n) (n = 10-28), using mass spectrometry. Sequential oxygen transfer reactions, Rh(n)O(m-1) + N(2)O → Rh(n)O(m) + N(2) (m = 1, 2, 3,…), were monitored and the rate constant for each reaction step was determined as a function of the cluster size. Oxygen extraction reactions by a CO molecule, Rh(n)O(m) + CO → Rh(n)O(m-1) + CO(2) (m = 1, 2, 3,…), were also observed when a small amount of CO was mixed with the reactant N(2)O gas. The rate constants of the oxygen extraction reactions by CO for m ≥ 4 were found to be two or three orders of magnitude higher than the rate constants for m ≤ 3, which indicates that the catalytic reaction proceeds more efficiently when the reaction cycles turn over around Rh(n)O(m) (m ≥ 4) than around bare Rh(n). Rhodium clusters operate as more efficient catalysts when they are oxidized than non- or less-oxidized rhodium clusters, which is consistent with theoretical and experimental studies on the catalytic CO oxidation reaction on a rhodium surface.     

Unified approach to catechin hetero-oligomers: first total synthesis of trimer EZ-EG-CA isolated from Ziziphus jujuba

A catechin hetero-trimer isolated from Ziziphus jujuba has been synthesized. Among three constituent monomers, (-)-epiafzelechin and (-)-epigallocatechin were prepared by de novo synthesis. Trimer formation relied on the unified approach to oligomers based on the bromo-capping and the orthogonal activation, reaching the reported structure of the natural product.     

Hetero-Diels-Alder reaction of photochemically generated α-hydroxy-o-quinodimethanes with trifluoromethyl ketones

Hetero-Diels-Alder reaction of α-hydroxy-o-quinodimethanes photochemically generated from o-tolualdehydes with trifluoromethyl ketones gave a mixture of hemiacetals and hydroxyaldehydes in fairly good yields. Their subsequent oxidation with PCC provided 1-isochromanones as formal oxidative [4+2] cycloaddition products. In contrast, similar reaction of aromatic ketones such as o-methylbenzophenone, 1-indanone, and α-tetralone gave exclusively the corresponding ketones having (trifluoromethyl)methylol groups at the o-position.