Stereoselective Total Synthesis of Xestodecalactone C

A simple and highly efficient stereoselective total synthesis of xestodecalactone C ( IIb ), a polyketide natural product, was achieved (Scheme 2). The synthesis involved Keck's asymmetric allylation, a iodine‐induced electrophilic cyclization, and an intramolecular Friedel–Crafts acylation as key steps.     

Gas–solid interaction force from direct numerical simulation (DNS) of binary systems with extreme diameter ratios

Fluid-particle systems as commonly encountered in chemical, metallurgical and petroleum industries are mostly polydisperse in nature. However, the relations used to describe fluid-particle interactions are originally derived from monodisperse systems, with ad hoc modifications to account for polydispersity. In previous work it was shown that for bidisperse systems with moderate diameter ratios of 1:2 to 1:4, this approach leads to discrepancies, and a correction factor is needed. In this work we demonstrate...     

The first total synthesis of neohelmanticins A–D,amino derivatives of the 1,2-dihydroxypropane core and biological evaluation

A concise total synthesis of neohelmanticins A–D has been accomplished in 15 steps starting from commercially available gallic acid. Swern oxidation conditions, a Grignard reaction, Sharpless kinetic resolution, and regioselective ring opening of an epoxide with lithium aluminum hydride (LAH) are the key features to install the basic core, dihydroxy phenyl propane 2. One hydroxyl group of this core was esterified with tiglic acid followed by the oxidation and esterification with corresponding acids to yield neohelmanticins A–D.     

Comment on: “Universal relation between spectroscopic constants”

Kaur and Mahajan [1] have claimed to derive a universal relation InG = 1.91578(±0.09727) + 0.97111(±0.03809) In Δ between the Sutherland parameter Δ(=ω _er _e ² /2D_e) and the dimensionless parameterG(= 8ω _ex_e/B_e) for the ground as well as excited electronic states of diatomic molecules. Validity of this relation is checked and we find that the relation is not correct. Next, we checked the validity of the relation Δ = 2.2r_e for the alkali group diatomic molecules. This relation is also found not to be correct.     

Self-assembly of heterobimetallic neutral macrocycles incorporating ferrocene spacer groups: spectroelectrochemical analysis of the double two-electron oxidation of a molecular rectangle

Two Pt(4)-Fe(2) mixed-metal neutral assemblies, 4 and 5, incorporating four bis(triethylphosphine)platinum(II) centers, two flexible bridging 1,1'-ferrocenedicarboxylates, and two rigid 2,9-phenanthrenediyl (4) or 1,8-anthracenediyl (5) bridges, have been synthesized. X-ray characterization of 4 and 5 reveals the formation of discrete and highly symmetrical heterobimetallic neutral species possessing a rhomboidal and rectangular shape, respectively. The rectangular molecules, 5, could be reversibly oxidized in two two-electron steps, separated by 0.21 V. Spectroelectrochemistry in the UV-vis-NIR region confirms the ferrocene groups as primary oxidation sites; however, the intermediate 5(2+) is EPR silent even at 4 K due to enhanced EPR relaxation involving the oxidizable 1,8-anthracenediyl linkers.     

Nitric oxide (NO) production inhibitory constituents of Tabebuia avellanedae from Brazil

From the water extract of Brazilian Tabebuia avellanedae, two new iridoids (1, 2) and a new phenylethanoid glycoside (3) have been isolated together with twelve known compounds (4-15). Their structures were determined based on the spectroscopic data. The isolated compounds inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-activated macrophage-like J774.1 cells. Compounds 1, 3, 10, 11, and 12 showed inhibitory activities more potent (IC50, 13.8-26.1 microg/ml) than a positive control N(G)-monomethyl-L-arginine (L-NMMA; IC50, 27.4 microg/ml).     

Characteristic Function of a Pure Commuting Contractive Tuple

A theorem of Sz.-Nagy and Foias [9] shows that the characteristic function of a completely non-unitary contraction T is a complete unitary invariant for T. In this note we extend this theorem to the case of a pure commuting contractive tuple using a natural generalization of the characteristic function to an operator-valued analytic function defined on the open unit ball of This function is related to the curvature invariant introduced by Arveson [3].     

Direct observation of the ... 4+-to-2+ ... [corrected] gamma transition in 8Be

Electromagnetic transition rates provide an important test for nuclear structure models. The nucleus 8Be exhibits a pronounced alpha-cluster structure and is a building block for more complex cluster nuclei. Here we report on the first observation of the gamma transition between the 4(+) and 2(+) states of 8Be in the 4He+4He reaction. The measured on-resonance cross section of 165+/-54 nb leads to a B(E2) of25+/-8e(2) fm(4), in good agreement with alpha-cluster models and sophisticated ab initio structure calculations.     

Scaling behavior of the Portevin-Le Chatelier effect in an Al-2.5%Mg alloy

The scaling behavior of the Portevin-Le Chatelier (PLC) effect was studied by deforming an Al-2.5%Mg alloy for a wide range of strain rates. To reveal the exact scaling nature, the time series data of true stress versus time, obtained during deformation, were analyzed by two complementary methods: the finite variance scaling method and the diffusion entropy analysis. From these analyses we could establish that, in the entire span of strain rates, the PLC effect showed the Levy-walk property.