We show that the charge and thermal transport measurements on ultraclean crystals of URu2Si2 reveal a number of unprecedented superconducting properties. The uniqueness is best highlighted by the peculiar field dependence of thermal conductivity including the first order transition at Hc2 with a reduction of entropy flow. This is a consequence of multi-band superconductivity with compensated electronic structure in the hidden order state of this system. We provide strong evidence for a new type of unconventional superconductivity with two distinct gaps having different nodal topology.The heavy-Fermion compound URu 2 Si 2 has mystified researchers since the superconducting state (T c = 1.5 K) is embedded within the "hidden order" phase (T h = 17.5 K) [1,2,3]. Although several exotic order parameters have been proposed for the hidden order phase [4], it is not identified yet. According to several experimental observations, most of the carriers disappear below T h resulting in a density one order of magnitude smaller than in other heavy-Fermion superconductors [5,6,7]. Superconductivity with such a low density is remarkablesince the superfluid density is very low in some way reminiscent of underdoped cuprates. Moreover, pressure studies reveal that the superconductivity coexists with the hidden order but is suppressed by antiferromagnetic ordering [8].In this Letter, using ultraclean single crystals, we report various anomalous superconducting properties in URu 2 Si 2 . We show that a peculiar electronic structure appearing below the hidden order transition provides an intriguing stage on which a new type of unconventional superconducting state appears.Single crystals of URu 2 Si 2 were grown by the Czochralski pulling method in a tetra-arc furnace. The welldefined superconducting transition was confirmed by the specific heat measurements. The thermal conductivity κ was measured using a standard four-wire steady state method along the a-axis (heat current q a). The contact resistance at low temperatures is less than 10 mΩ.We first discuss the electronic structure below T h . Figure 1 shows the temperature dependence of the resistivity ρ along the a-axis and Hall coefficient R H (solid circles) defined as R H ≡ dρxy dH at H → 0 T for H c in the tetragonal crystal structure. In zero field, ρ depends on T as ρ = ρ 0 + AT 2 below 6 K down to T c . The exceptionally low residual resistivity ρ 0 = 0.48 µΩ cm and large residual resistivity ratio RRR = 670 attest the highest crystal quality currently achievable. R H exhibits an eight-fold increase below T h and attains a T -independent value at low temperatures, associated with a strong reduction of the carrier density. Most remarkably, the magnetoresistance (MR) increases with decreasing temperature and becomes extremely large at the lowest temperatures. The inset of Fig.

In homogeneous catalyst systems, there is the persistent problem that metal aggregation and precipitation cause catalyst decomposition and considerable loss of catalytic activity. Pd black formation is a typical example. Pd catalysts are known to easily aggregate and form Pd black, although they realize a wide variety of useful reactions in organic synthesis. In order to overcome this intrinsic problem of homogeneous Pd catalysis, we explored a new class of Pd catalyst by adopting aerobic oxidation of alcohols as a probe reaction. Herein we report a new catalyst system that suppresses the Pd black formation even under air and with a high substrate to catalyst molar ratio (S/C: more than 1000) in oxidation of alcohols. The novel pyridine derivatives having a 2,3,4,5-tetraphenylphenyl substituent and its higher dendritic unit at the 3-position of the pyridine ring were found to be excellent ligands with Pd(OAc)2 in the palladium-catalyzed air (balloon) oxidation of alcohols in toluene at 80 degrees C. Comparison with structurally related pyridine ligands revealed that introduction of the 2,3,4,5-tetraphenylphenyl substituent at the 3-position of pyridine ring effectively suppresses the Pd black formation, maintaining the catalytic activity for a long time to give aldehydes or ketones as products in high yields.

Products of unfavorable chemical equilibria are not readily observed because their high energy and increased reactivity result in low concentrations. Biological macromolecules use binding forces to access unfavorable equilibria and stabilize reactive intermediates by isolating them from the medium. In a similar vein, we describe here a synthetic receptor that allows direct observation of labile tetrahedral intermediates: hemiaminals formed in the reaction of an aldehyde carbonyl group with amines. The receptor encapsulates alkyl-substituted primary amines, then orients them toward a covalently tethered aldehyde function. The hemiaminal intermediates appear at high concentration, confined from the bulk solution and observable at ambient temperature by conventional nuclear magnetic resonance spectroscopy.

A cavitand functionalized with a Kemp's triacid derivative was used to catalyze the epoxide ring-opening cyclizations of 1,5-epoxyalcohols. A deep, cylindrical cavity containing electron-rich aromatic walls and an inwardly directed carboxylic acid displayed the necessary characteristics to bind different 1,5-epoxyalcohols and initiate their cyclization reactions. The reactions inside this synthetic receptor occurred in a catalytic and regioselective manner. These results highlight that the arrangement of functionality and unique solvation provided by the structured interiors of natural enzymes can be incorporated into synthetic systems having useful physical and chemical properties.

Palladium-diamine complexes catalyzed kinetic resolution of axially chiral 2,2'-dihydroxy-1,1'-biaryls by alcoholysis of vinyl ethers. The reaction proceeded with high selectivity for various kinds of biaryls. This process is applicable to not only binaphthols but also biphenols, which have been considered to be difficult for the enantioselective synthesis by known catalytic methods.