Constructive generation of very hard 3-colorability instances

Graph colorability (COL), is a typical constraint satisfaction problem to which phase transition phenomena (PTs), are important in the computational complexity of combinatorial search algorithms. PTs are significant and subtle because, in the PT region, extraordinarily hard problem instances are found, which may require exponential-order computational time to solve. To clarify PT mechanism, many studies have been undertaken to produce very hard instances, many of which were based on generate-and-test approaches. We propose a rather systematic or constructive algorithm that repeats the embedding of 4-critical graphs to arbitrarily generate large extraordinarily hard 3-colorability instances. We demonstrated experimentally that the computational cost to solve our generated instances is of an exponential order of the number of vertices by using a few actual coloring algorithms and constraint satisfaction algorithms.     

Stereospecific Transformations of Chiral Compounds Using Anchimeric Assistance of Arylthio and Arylseleno Group

A new chiral pool method is developed starting from readily available chiral oxiranes, the key step being the substitution reaction through the anchimeric assistance of the arylthio and arylseleno group. The overall transformation is the introduction of nucleopiles into the chiral carbon of the oxiranes with retention of the configuration.     

Prevention of Racemization of the Chiral Carbon in the Episelenonium ION Intermediate: Steric Protection and Electron-Withdrawing Effect

To prevent the racemization of the chiral carbon in the episelenonium ion intermediate bearing an aryl group on the selenium atom, both the bulky substituent(s) on the ortho position(s) of the aryl group and electron-with-drawing substituent(s) in the aryl group are found to play an important role.     

Fluorous tag method for the simultaneous synthesis of different kinds of glycolipids

A mixture of saccharide primers with partially fluorinated tails, 2-(perfluorooctyl)ethyl 4′-O-(β-d-galactopyranosyl)-β-d-glucopyranoside (Lac H2F8) and 6-(perfluorohexyl)hexyl 2′-acetamido-2′-deoxy-β-d-glucopyranoside (GN H6H6), were introduced to animal cells. The oligosaccharide of Lac H2F8 was elongated by cellular enzymes and gave a GM3-type oligosaccharide. On the other hand, GN H6F6 was galactosylated to afford a lactosamine derivative that was further sialylated. This research confirmed that simultaneous glycosylation processes took place for Lac H2F8 and GN H6F6 primers and that the presence of one did not prevent the glycosylation of the other from proceeding. Each primer was recognized independently and elongated sequentially by cellular enzymes. Significantly, the synthesis of glycolipids from a mixture of these artificial scaffolds did not prevent the synthesis of glycolipids from the natural precursor. The glycosyl transferases recognized both precursors resulting to simultaneous synthesis of glycolipids.     

Plate-shaped non-contact ultrasonic transporter using flexural vibration

We developed a plate-shaped non-contact transporter based on ultrasonic vibration, exploiting a phenomenon that a plate can be statically levitated at the place where its gravity and the acoustic radiation force are balanced. In the experiment, four piezoelectric zirconate titanate elements were attached to aluminum plates, on which lattice flexural vibration was excited at 22.3 kHz. The vibrating plates were connected to a loading plate via flexible posts that can minimize the influence of the flexure induced by heavy loads. The distribution of the vibration displacement on the plate was predicted through finite-element analysis to find the appropriate positions of the posts. The maximum levitation height of this transporter was 256 μm with no load. When two vibrating plates were connected to a loading plate, the maximum transportable load was 4.0 kgf.     

DFT calculations for aerobic oxidation of alcohols over neutral Au6 cluster

Lately, it was found that the Au nanoclusters stabilised by poly(N-vinyl-2-pyrrolidone) [PVP; (C₆H₉ON)_n], abbreviated to Au:PVP, can oxidise p-hydroxybenzyl alcohol selectively into the corresponding aldehyde in water without degradation. This observation indicates that Au cluster can exhibit high catalytic activity without any metal oxide supports. From previous works, it was found that the anionic Au clusters played an important role for the activation of oxygen molecule on the Au clusters. However, the catalytic activity of neutral Au clusters for the aerobic oxidation reaction of alcohol is not still investigated in detail. In order to examine the catalytic activity of neutral Au clusters, the aerobic oxidation of p-hydroxybenzyl alcohol to the corresponding aldehyde catalysed by Au₆ has been investigated quantum chemically using density functional theory with the PBE0 functional. Possible reaction pathways are investigated taking account of full structure relaxation of the model systems. From the calculation results, it was found that the formations of both a hydroperoxyl anion and a hydride were the important steps for the aerobic oxidation of p-hydroxybenzyl alcohol over Au₆ cluster.     

2H Natural-abundance MAS NMR spectroscopy: an alternative approach to obtain 1H chemical shifts in solids

(2)H NMR was examined as an approach to determine (1)H chemical shifts in solids. For high-resolution observation, the line width due to (2)H quadrupole interaction and chemical-shift anisotropy was removed by magic-angle spinning and that due to (1)H-(2)H dipolar interactions by (1)H decoupling. Further, we showed that the sensitivity can be enhanced by applying (1)H to (2)H cross polarization and by adding spinning-sideband spectra. These make it possible to obtain (2)H natural-abundance MAS spectra revealing highly resolved (2)H signals. The second-order quadrupole effects of (2)H are also examined.     

Chiral Brønsted acid-catalyzed inverse electron-demand aza Diels-Alder reaction

Inverse electron-demand aza Diels-Alder reaction of aldimine with enol ethers proceeded under the influence of a phosphoric acid diester, derived from (R)-BINOL, to give tetrahydroquinoline derivatives with excellent enantioselectivity.     

Scandium-catalyzed carbon-carbon bond formations using alpha-organosulfanyl and organoselanyl-alpha-fluoroacetic acid derivatives

The scandium-catalyzed reactions of alpha-organosulfanyl and organoselanyl-alpha-fluoroacetates 1-2, acetamides 3-4 and acetonitrile 5 with soft nucleophiles proceeded to give the products 6a-b, 7a-c, 8a-c, 9a-e in good to high yields. We also successfully performed the scandium-catalyzed intramolecular cyclization reactions and obtained the unique 5-methylene-2-oxotetrahydropyrans 16-17.