Monomeric metal aqua complexes in the interlayer space of montmorillonites as strong Lewis acid catalysts for heterogeneous carbon-carbon bond-forming reactions

Montmorillonite-enwrapped copper and scandium catalysts (Cu(2+)- and Sc(3+)-monts) were easily prepared by treating Na(+)-mont with the aqueous solution of the copper nitrate and scandium triflate, respectively. The resulting Cu(2+)- and Sc(3+)-monts showed outstanding catalytic activities for a variety of carbon-carbon bond-forming reactions, such as the Michael reaction, the Sakurai-Hosomi allylation, and the Diels-Alder reaction, under solvent-free or aqueous conditions. The remarkable activity of the mont catalysts is attributable to the negatively charged silicate layers that are capable of stabilizing metal cations. Furthermore, these catalysts were reusable without any appreciable loss in activity and selectivity. The Cu(2+)-mont-catalyzed Michael reaction proceeds via a ternary complex in which both the 1,3-dicarbonyl compound and the enone are coordinated to a Lewis acid Cu(2+) center.     

Truncated microsupport and holomorphic solutions of D-modules

We study the truncated microsupport SS_k of sheaves on a real manifold. Applying our results to the case of , the complex of holomorphic solutions of a coherent -module , we show that SS_k(F) is completely determined by the characteristic variety of . As an application, we obtain an extension theorem for the sections of H^j(F), j<d, defined on an open subset whose boundary is non-characteristic outside of a complex analytic subvariety of codimension d. We also give a characterization of the perversity for -constructible sheaves in terms of their truncated microsupports.     

Elastic response of single DNA molecules exhibits a reentrant collapsing transition

We measured the elastic response of single DNA molecules at various concentrations of the trivalent cation, spermidine. When added spermidine caused the DNA to collapse, the force-extension curves showed either plateaus or stick-release patterns depending on the concentration. The periodic stick-release response determines a characteristic length, which may reflect toroidal supercoiling. At high concentrations of spermidine, we observed the reelongation of single molecules of collapsed DNA. Thus condensation occurs between lower and upper critical concentrations, verifying that the transition is reentrant as theoretically predicted.     

Nitration of 2'-deoxyguanosine by a NO/O2 gas mixture: identification and characterization of N2-nitro-2'-deoxyguanosine

[reaction: see text] A gas mixture of NO and O(2) was bubbled into 2'-deoxyguanosine solution at neutral pH and 37 degrees C. A novel nitrated nucleoside was generated in the reaction mixture in addition to 8-nitroguanine, 8-nitroxanthine, 2'-deoxyxanthosine, xanthine, and guanine. The novel nucleoside was identified as N(2)-nitro-2'-deoxyguanosine by spectrometric data.     

Nd-isotopic composition of Phanerozoic sediments in the Inner Zone of Southwest Japan Arc: implications on provenance characteristics and contribution to formation of mature island arc system

The Nd-isotopic data on sedimentary and metamorphic rocks of SW Japan Arc allow their discrimination into five different depleted mantle (Tdm) model age clusters, 2.6-2.45 Ga, 2.3-2.05 Ga, 1.9-1.55 Ga, 1.45-1.25 Ga, 1.2-0.85 Ga. The 2.6-2.45 Ga and 1.9-1.55 Ga model ages are also coincident with U-Pb inherited zircon ages of the above two epochs as well as the major magmatic activity in the Sino-Korean Craton (SKC). The 2.3-2.05 Ga model ages can be considered as the initial formation ages for the precursors of sedimentary rocks. The Nd-isotopic data suggest that the Hida Belt was most likely formed as a part of the SKC. The mantle underlying the Ryoke Belt had continental lithospheric signature during Triassic-Jurassic period. The 1.9-1.55 Ga model ages, especially 1.8 Ga~, can be associated with the formation of this belt. The source material for the sedimentary rocks occurring in the accretionary terrane of northeastern areas in the SW Japan Arc was probably in and around the SKC of the Ryoke Belt itself. The sedimentary rocks occurring in southwestern areas of the Arc were mainly composed of materials derived from a relatively younger source (1.45-0.85 Ga).     

Bovine serum albumin-mediated enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylate

Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxyalate (AC) was performed at 25 degrees C in aqueous buffer solution (pH 7) in the presence of bovine-serum albumin (BSA) to afford four [4 + 4] cyclodimers, i.e., anti- and syn-head-to-tail (HT) (1 and 2) and anti- and syn-head-to-head (HH) dimers (3 and 4), of which only 2 and 3 are chiral. We found that (1) BSA possesses four sets of binding sites for AC of different affinities, stoichiometries, and chiral environment for photoreaction, which bind 1, 3, 2, and 3 AC molecules with binding constants of 5.3 x 107, 1.3 x 105, 1.4 x 104, and 3.0 x 103 M-1, respectively, (2) the regioselectivity of photodimerization is switched from HT to HH by adding BSA (the HH/HT ratio varies from 0.28 to 4.3), (3) BSA-mediated photodimerization of AC affords optically active products 2 and 3 of up to 29% and 41% ee, respectively. It is emphasized that the selective excitation of bound substrate, utilizing the spectral shift upon complexation with BSA, is not a prerequisite for efficient photochirogenesis using biomolecules.     

Synthesis, structure, and reactivity of a eta(3)-1-hydroxyallyl complex: protonation of an alpha,beta-unsaturated carbonyl compound bound to palladium(0) and platinum(0)

The direct addition of a proton to a carbonyl oxygen in an eta2-enone complex of palladium and platinum led to the quantitative formation of eta3-1-hydroxyallyl complexes of palladium and platinum, of which X-ray diffraction analysis showed typical eta3-allyl structure.     

Diastereoselective photocycloaddition of axially chiral monothiosuccinimides to 1,1-diphenylethylene

Photolysis of axially chiral monothiosuccinimides in the presence of diphenylethylene gave spirothietanes effectively, where the cycloaddition took place diastereoselectively by way of the steric effect of the ortho-substituent on the phenyl ring.