Removal of chloride interference in the determination of chromium by atomic absorption spectrometry with electrothermal atomization

Two mechanisms of chloride interference are described. The first arises from coordination of chloride to chromium(III), which can be prevented by addition of a masking agent such as tetraammonium—EDTA, The other is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization.     

Camptothecins and two new monoterpene glucosides from Ophiorrhiza liukiuensis

Two new monoterpene glucosides, demethylsecologanol and 3'-O-glucosylsenburiside II, were isolated from Ophiorrhiza liukiuensis (Rubiaceae) together with 23 known compounds, including camptothecins and beta-carboline-type alkaloids. Their structures were determined by spectroscopic analysis.     

Development of a Divergent Synthetic Route to the Erythrina Alkaloids: Asymmetric Syntheses of 8‐Oxo‐erythrinine,Crystamidine, 8‐Oxo‐erythraline,and Erythraline

A general synthetic methodology toward the erythrina alkaloids has been developed. Inspired by a proposed biosynthetic mechanism, the medium‐sized chiral biaryl lactam was asymmetrically transformed into the common core A–D rings by a stereospecific singlet oxygen oxidation of the phenol moiety, followed by a transannular aza‐Michael reaction to the dienone functionality. The late‐stage manipulation of the oxidation and oxygenation states of the functional groups on the peripheral moieties enabled the flexible syntheses of the erythrina alkaloids.     

Temperature–pressure shuffling outlier flooding method enhances the conformational sampling of proteins

Outlier flooding method (OFLOOD) is an efficient conformational sampling method developed by the authors. In the present study, to further enhance the conformational sampling efficiency, a set of parameters (temperatures and pressures) specified as inputs in the original OFLOOD were shuffled before restarting the short-time molecular dynamics (MD) simulations. Because of the diversity of these parameters, it was confirmed that the extended OFLOOD becomes superior to the original one in finding the folding pathways of Trp-cage. © 2019 Wiley Periodicals, Inc.     

Integrability of Hamiltonian systems and transseries expansions

This paper studies analytic Liouville-nonintegrable and C ^??-Liouville-integrable Hamiltonian systems with two degrees of freedom. We prove the property for a class of Hamiltonians more general than the one studied in Gorni and Zampieri (Differ Geom Appl 22:287?C296, 2005). We also show that a certain monodromy property of an ordinary differential equation obtained as a subsystem of a given Hamiltonian and the transseries expansion of a first integral play an important role in the analysis (cf. (4)). In the former half the analytic Liouville-nonintegrability for a class of Hamiltonians satisfying the above condition is shown. For these analytic nonintegrable Hamiltonians one cannot construct nonanalytic first integrals concretely as in Gorni and Zampieri (Differ Geom Appl 22:287?C296, 2005). In the latter half, the nonanalytic integrability from the viewpoint of a transseries expansion of a first integral is discussed. More precisely, we construct a first integral in a formal transseries expansion in a general situation. Then we show convergence of transseries or existence of the first integral being asymptotically equal to a given formal transseries solution.     

Liquid plasma crystal: Coulomb crystallization of cylindrical macroscopic grains in a gas-discharge plasma

Ordered structures formed of 300-μm-long cylindrical nylon grains with diameters of 15 and 7.5 μm are obtained. In contrast to conventional spherical monodisperse grains, which, under certain conditions, form the plasma-dust Coulomb crystal, the cylindrical grains in the plasma acquire a charge of ～7×10⁵ electrons and form a structure similar to a liquid crystal. The parameter characterizing the nonideality of the dusty component of the plasma attains 10⁶. Grains are suspended in the striation in the horizontal plane and line up in parallel with each other.     

A total synthesis of xestodecalactone a and proof of its absolute stereochemistry: interesting observations on dienophilic control with 1,3-disubstituted nonequivalent allenes

A concise total synthesis of xestodecalactone A, utilizing a Diels-Alder strategy is described. The focal Diels-Alder reaction relied on an "ynoate" dienophile to rapidly assemble the required resorcylinic acid scaffold. During this study, Diels-Alder cycloaddition reactions involving 1,3-disubstituted nonequivalent allene dienophiles were studied, and some surprising results were encountered.