Internal flow in polymer solution droplets deposited on a lyophobic surface during a receding process

When a polymer solution droplet is deposited on a lyophobic surface, the contact line is moved back to some degree and subsequently pinned. An experimental setup is constructed to investigate not only the receding process but also an internal flow of polystyrene-acetophenone and -anisole solutions. As a result, the time variation of the evaporation rate per unit area during receding does not strongly depend on the initial solute concentration. The average solute concentration at the pinning of the contact line increases as the initial solute concentration increases. A convective circulation flow that is upward at the axis of symmetry is observed. This flow pattern is different from those of pure liquids such as water, acetone, benzene, and so forth, which have been previously reported. Furthermore, the observed flow is enhanced as the initial solute concentration increases, contrary to an increase in the fluid viscosity. To resolve these discrepancies, the mechanism of the flow is numerically investigated using a hemispherical droplet model considering the density and surface tension distributions. The numerical results demonstrate that the circulation flow that is experimentally observed is actually caused. It is also found that the solutal Rayleigh effect initially induces the internal flow, and subsequently the solutal Marangoni effect dominates the flow. Both effects are enhanced as the initial concentration increases because of the evaporative mass balance at the free surface.     

Unique catalysis of gold nanoparticles in the chemoselective hydrogenolysis with H2: cooperative effect between small gold nanoparticles and a basic support

Gold nanoparticles on hydrotalcite act as a heterogeneous catalyst for the chemoselective hydrogenolysis of various allylic carbonates to the corresponding terminal alkenes using H(2) as a clean reductant. The combination of gold nanoparticles and basic supports elicited significantly unique and selective catalysis in the hydrogenolysis.     

Cuspidans A and B, two new stilbenoids from the bark of Gnetum cuspidatum

Cuspidan A (1), a new stilbene sestermer consisting of a resveratrol, an oxyresveratrol, and a 3,5-dihydroxyphenylmethanol constituent units and cuspidan B (2), a new tri-cyclic stilbene monomer were isolated from the bark of Gnetum cuspidatum. The structures and configurations of 1 and 2 were elucidated on the basis of 2D-NMR correlations.     

Development of High Performance Heterogeneous Catalysts for Selective Cleavage of C−O and C−C Bonds of Biomass‐Derived Oxygenates

The environmental impact of CO₂ emissions via the use of fossil resources as chemical feedstock and fuels has stimulated research to utilize renewable biomass feedstock. The biogenic compounds such as polyols are highly oxygenated and their valorization requires the new methods to control the oxygen to carbon ratio of the chemicals. The catalytic cleavage of C?O bonds and C?C bonds is promising methods, but the conventional catalyst systems encounter the difficulty to obtain the high yields of the desired products. This review describes our recent development of the high performance heterogeneous catalysts for the valorization of the biogenic chemicals such as glycerol, furfural, and levulinic acid via selective cleavage of C?O bonds and C?C bonds in the liquid‐phase. Selective C?O bond cleavage by hydrogenolysis enables production of various diols useful as engineering plastics, antifreeze, and cosmetics in high yields. The success of the selective C?C bond scission of levulinic acid can be applied to a wide range of the biogenic oxygenates such as carboxylic acids, esters, lactones, and primary alcohols, in which the selective C?C bond scission at adjacent to the oxygen functional groups are achieved. Furthermore, valorization of glycerol by selective acetylation and acetalization, and of levulinic acid by hydrogenation is described. Our catalysts show excellent performance compared to the reported catalysts in the aforementioned valorization.     

Dehydrogenative Synthesis of 2,2′‐Bipyridyls through Regioselective Pyridine Dimerization

2,2′‐Bipyridyls have been utilized as indispensable ligands in metal‐catalyzed reactions. The most streamlined approach for the synthesis of 2,2′‐bipyridyls is the dehydrogenative dimerization of unfunctionalized pyridine. Herein, we report on the palladium‐catalyzed dehydrogenative synthesis of 2,2′‐bipyridyl derivatives. The Pd catalysis effectively works with an Ag^I salt as the oxidant in the presence of pivalic acid. A variety of pyridines regioselectively react at the C2‐positions. This dimerization method is applicable for challenging substrates such as sterically hindered 3‐substituted pyridines, where the pyridines regioselectively react at the C2‐position. This reaction enables the concise synthesis of twisted 3,3′‐disubstituted‐2,2′‐bipyridyls as an underdeveloped class of ligands.     

Measurement of A zz of pd radiative capture at E d = 196 MeV

In our previous measurement of pd radiative capture at E _d = 137 and 196?MeV, we found an interesting fact that the measured tensor analyzing powers show the relation A _xx ≈ A _yy , although calculated A _xx and A _yy are apparently different, A _xx ≠ A _yy . The measured A _yy agrees fairly well with the 3N calculations, and the measured A _xx largely disagrees with calculated A _xx . Similar experiments on pd capture have been made at KVI at nearly the same energies of 130–180?MeV. The KVI data also support A _xx ≈ A _yy relation, but absolute values of A _xx and A _yy at KVI are about half of RCNP data. Therefore, we made a new experiment of pd capture at E _d = 196?MeV. A _zz was measured in three different ways, and data analysis is in progress. Preliminary data seem to support our previous data.     

EXCIMER FORMATION OF N-(I-PYRENESULFONYL)-DIPALMITOYL-L-α- PHOSPHATIDYLETHANOLAMINE AT THE LIPID-WATER INTERFACE OF FAT CELL PLASMA MEMBRANES

Abstract— The mechanism of excimer formation of N-(l-pyrenesulfonyl)-dipalmitoyl-L-α-phosphatidylethanolamine incorporated into fat cell plasma membranes was studied by means of steady-state and pulse fluorometry. It was found that the pyrenesulfonyl group at the lipid-water interface of the membrane formed an appreciable amount of ground-state dimers and that the excimer of the pyrenesulfonyl group was formed through two different processes: (i) the collisional interaction of an excited monomer with a ground-state monomer, and (ii) the direct excitation of a ground-state dimer (approximate ratio of the two processes, 1:1). Analysis of fluorescence decay curves revealed that the detailed mechanism of excimer formation by process (i) is essentially similar to the mechanism established for the reaction in organic solvents but not to that in a highly viscous medium such as the hydrocarbon core of the membrane.     

Pressure control of enantiodifferentiating polar addition of 1,1-diphenylpropene sensitized by chiral naphthalenecarboxylates

Effects of pressure on the enantiodifferentiating methanol addition to 1,1-diphenylpropene (1) sensitized by chiral naphthalenedicarboxylates (3 and 4) were investigated over 0.1-400 MPa. The logarithm of enantiomeric excess (ee) of photoadduct, i.e. 1,1-diphenyl-2-methoxypropane (2), was a linear function of both pressure (P) and temperature (T); further, the product chirality was switched by P in some cases. From the slope of P- ln(k(R)/k(S)) plot, the differential activation volume (Delta DeltaV(double dagger)) was determined for the first time for bimolecular asymmetric photoreactions. The Delta DeltaV(double dagger) values obtained are mostly larger than those obtained for relevant unimolecular photoreactions, and are a critical function of the nature of the chiral auxiliary and solvent, indicating conformation changes of the intervening diastereomeric exciplex or transition state in different solvents. Indeed, fluorescence spectral examinations of the sensitizer and exciplex under high pressure revealed the existence of exciplexes of variable energy and structure, which may rationalize the different Delta DeltaV(double dagger) and product ee obtained. A three-dimensional diagram, correlating the ee with P and T, was constructed from the pressure dependence data at different T, from which we may propose an idea of the multidimensional control of asymmetric reaction by the combined use of the entropy-related environmental factors.