A palladium iodide-catalyzed carbonylative approach to functionalized pyrrole derivatives

A novel and convenient approach to functionalized pyrroles is presented, based on Pd-catalyzed oxidative heterocyclization-alkoxycarbonylation of readily available N-Boc-1-amino-3-yn-2-ols. Reactions were carried out in alcoholic solvents at 80-100 °C and under 20 atm (at 25 °C) of a 4:1 mixture of CO-air, in the presence of the PdI(2)-KI catalytic system (2-5 mol % of PdI(2), KI/PdI(2) molar ratio = 10). In the case of N-Boc-1-amino-3-yn-2-ols 3, bearing alkyl or aryl substituents, the carbonylation reaction led to a mixture of Boc-protected and N-unsubstituted pyrrole-3-carboxylic esters 4 and 5, respectively. This mixture could be conveniently and quantitatively converted into deprotected pyrrole-3-carboxylic esters 5 by a simple basic treatment. In the case of diastereomeric (3RS,4RS)- and (3RS,4SR)-N-Boc-3-amino-2-methyldec-5-yn-4-ol (syn-3f and anti-3f, respectively, whose relative configuration was determined by X-ray crystallographic analysis), no particular difference was observed in the reactivity of the two diastereomers between them and with respect to the diastereomeric mixture (3S,4S) + (3S,4R). Interestingly, N-Boc-2-alkynyl-1-amino-3-yn-2-ols 6, bearing an additional alkynyl substituent α to the hydroxyl group, spontaneously underwent N-deprotection under the reaction conditions and regioselective water addition to the alkynyl group at C-3 of the corresponding pyrrole-3-carboxylic ester derivative, thus directly affording highly functionalized pyrrole derivatives 7 in one step. In a similar manner, a novel functionalized dihydropyrrolizine derivative 9 was directly synthesized starting from (S)-7-(pyrrolidin-2-yl)trideca-5,8-diyn-7-ol 8.     

Bifurcation in viscoresistive MHD: the hartmann number and the reversed field pinch

A scaling approach to the simplest viscoresistive MHD model reveals that the Prandtl number acts only through the inertia term. When this term is negligible the dynamics is ruled by the Hartmann number H only. This occurs for the reversed field pinch dynamics as seen by numerical simulation of the model. When H is large the system is in a multiple helicity state. In the vicinity of H = 2500 the system displays temporal intermittency with laminar phases of quasi-single-helicity (SH) type. For lower H's two basins of SH are shown to coexist. SH regimes are of interest because of their nonchaotic magnetic field.     

Chaos healing by separatrix disappearance and quasisingle helicity states of the reversed field pinch

The resilience to chaotic perturbations of one-parameter one-degree-of-freedom Hamiltonian dynamics is shown to increase when its corresponding separatrix vanishes due to a saddle-node bifurcation. This is first highlighted for the magnetic chaos related to quasisingle helicity (QSH) states of the reversed field pinch. It provides a rationale for the confinement improvement of helical structures experimentally found for QSH plasmas; such a feature would not be expected from the classical resonance overlap picture as the separatrix disappearance occurs when the amplitude of the dominant mode increases.     

Measurements of the MHD dynamo in the quasi-single-helicity reversed-field pinch

The first experimental study of the MHD dynamo in a quasi-single-helicity (QSH) reversed-field pinch toroidal plasma is presented. In QSH plasmas, a dominant wave number appears in the velocity fluctuation spectrum. This velocity component extends throughout the plasma volume and couples with magnetic fluctuations to produce a significant MHD dynamo electric field. The narrowing of the velocity fluctuation spectrum and the single-mode character of the dynamo are features predicted by theory and computation, but only now are observed in experiment.     

Peroxiredoxin-1 from the Human Hookworm Ancylostoma ceylanicum Forms a Stable Oxidized Decamer and Is Covalently Inhibited by Conoidin A

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Stress clamp experiments on multicellular tumor spheroids

The precise role of the microenvironment on tumor growth is poorly understood. Whereas the tumor is in constant competition with the surrounding tissue, little is known about the mechanics of this interaction. Using a novel experimental procedure, we study quantitatively the effect of an applied mechanical stress on the long-term growth of a spheroid cell aggregate. We observe that a stress of 10 kPa is sufficient to drastically reduce growth by inhibition of cell proliferation mainly in the core of the spheroid. We compare the results to a simple numerical model developed to describe the role of mechanics in cancer progression.     

Angular distributions in the double ionization of noble gases by electron impact

Electron-impact double ionization of noble gases is investigated theoretically for the case of high incident energies (5 keV). An ab initio calculation is made including partial correlation in the initial state as well as in the final state. The results of the calculations are compared with those of other theories and with the first available (e, 3e) experimental data on krypton 4p ⁶.     

低能电子碰撞Ar(e, 3e)双电离实验

通过Ar(e, 3e)五重微分截面3维图的理论与实验比较发现, 在低能电子入射的情况下, 理论与实验存在较大的偏差.     

Abelian <Emphasis Type="Italic">ℓ</Emphasis>-Groups with Strong Unit and Perfect MV-Algebras

We investigate the class of abelian ℓ-groups with strong unit corresponding to perfect MV-algebras via the Γ functor, showing that this is a universal subclass of the class of all abelian ℓ-groups with strong unit and describing the formulas that axiomatize it. We further describe results for classes of abelian ℓ-groups with strong unit corresponding to local MV-algebras with finite rank.