Alstonia scholaris: Struktur des Indolalkaloides Narelin

Alstonia scholaris: The structure of the indole alkaloid nareline Besides the known akuammidine, picralinal, picrinine and pseudoakuammigine a new indole alkaloid called nareline (M=352) was isolated from Alstonia scholaris R. BR. , which belongs to the plant family of Apocynaceae. Its structure 2 was deduced by single crystal X-ray diffraction. 2 represents the absolute configuration. The spectroscopic data of 2 and its derivatives (Scheme 1) as well as their chemical behavior support this structure. In biogenetic sense nareline is related to the bases akuammiline ( 4 ) and picraline ( 5 ) (Scheme 2). In contrast to those the C-atom 5 is exocyclic and represents an aldehyde group which forms together with the oxygen atom of the N (4)-hydroxylamine group a cyclic half acetale. - By oxidation (CrO₃/CH₃COOH) of 2 the oxindol derivative 19 (oxonareline) is formed which contains a cyclic acetal as a partial structure element (Scheme 4).     

A turn on ESIPT probe for rapid and ratiometric fluorogenic detection of homocysteine and cysteine in water with live cell-imaging

5(Benzothiazol-2-yl)-4-hydroxyisophthalaldehyde (BHI), an intense ESIPT containing molecule in mixed media loses its properties due to resonance-assisted H-bond (RAHB) in absolute water. Due to resonance-assisted H-bond the o-aldehyde is more reactive than the other one. With addition of cysteine/homocysteine into this solution the o-aldehyde group gets transformed into thiazolidine/thiazine ring, respectively, and the phenolic proton becomes free enough for transfer to nitrogen of the benzothiazole ring in excited state, that is, the ESIPT of BHI is turned on. Thus we can detect cysteine/homocysteine in water as well as in live cells.     

Monte Carlo Simulation of Transient CSD in a Continuous Crystallizer under Stochastic Dispersion Effects

Monte Carlo simulation is a very powerful tool for simulation of transient and steady state crystal size distribution (CSD) in a continuous crystallizer under stochastic dispersion effects. In the present work, transient CSD in a continuous crystallizer has been reported when shape factor and growth rate dispersions conform to normal distribution. For the steady state run, the algorithm reported by Sen Gupta and Dutta elsewhere has been used to validate the results obtained in the present work when the steady state is reached.     

Absorption spectrometric study of charge transfer complex formation between 4-acetamidophenol (paracetamol) and a series of quinones including vitamin K3

The formation of charge transfer (CT) complexes of 4-acetamidophenol (commonly called 'paracetamol') and a series of quinones (including Vitamin K3) has been studied spectrophotometrically in ethanol medium. The vertical ionisation potential of paracetamol and the degrees of charge transfer of the complexes in their ground state has been estimated from the trends in the charge transfer bands. The oscillator and transition dipole strengths of the complexes have been determined from the CT absorption spectra at 298 K. The complexes have been found by Job's method of continuous variation to have the uncommon 2:1 (paracetamol:quinone) stoichiometry in each case. The enthalpies and entropies of formation of the complexes have been obtained by determining their formation constants at five different temperatures.     

On the symplectic structures on moduli space of stable sheaves over a K3 or abelian surface and on Hilbert scheme of points

Fix a smooth very ample curve C on a K3 or abelian surface X. Let $ \mathcal{M} $ denote the moduli space of pairs of the form (F, s), where F is a stable sheaf over X whose Hilbert polynomial coincides with that of the direct image, by the inclusion map of C in X, of a line bundle of degree d over C, and s is a nonzero section of F. Assume d to be sufficiently large such that F has a nonzero section. The pullback of the Mukai symplectic form on moduli spaces of stable sheaves over X is a holomorphic 2-form on $ \mathcal{M} $. On the other hand, $ \mathcal{M} $ has a map to a Hilbert scheme parametrizing 0-dimensional subschemes of X that sends (F, s) to the divisor, defined by s, on the curve defined by the support of F. We prove that the above 2-form on $ \mathcal{M} $ coincides with the pullback of the symplectic form on the Hilbert scheme.     

Unexpected cycloadducts from 1,3-dipolar cycloaddition of 3,4-dehydromorpholine N-oxide to N-cinnamoyl piperidines—first report of the novel formation of 2:1 cycloadducts

A series of unexpected cycloadducts along with normal cycloadducts have been isolated from the 1,3-dipolar cycloaddition of 3,4-dehydromorpholine N-oxide to piperidides of cinnamic acid and para-substituted cinnamic acids and these were analyzed by X-ray crystallography to reveal novel solid-state structures. At first, 1:1 cycloadducts were formed which underwent in situ nucleophilic attack by another reduced nitrone moiety. A plausible iminium-oxonium ion mechanism has been proposed.     

Unitary group adapted state specific multireference perturbation theory: Formulation and pilot applications

We present here a comprehensive account of the formulation and pilot applications of the second‐order perturbative analogue of the recently proposed unitary group adapted state‐specific multireference coupled cluster theory (UGA‐SSMRCC), which we call as the UGA‐SSMRPT2. We also discuss the essential similarities and differences between the UGA‐SSMRPT2 and the allied SA‐SSMRPT2. Our theory, like its parent UGA‐SSMRCC formalism, is size‐extensive. However, because of the noninvariance of the theory with respect to the transformation among the active orbitals, it requires the use of localized orbitals to ensure size‐consistency. We have demonstrated the performance of the formalism with a set of pilot applications, exploring (a) the accuracy of the potential energy surface (PES) of a set of small prototypical difficult molecules in their various low‐lying states, using natural, pseudocanonical and localized orbitals and compared the respective nonparallelity errors (NPE) and the mean average deviations (MAD) vis‐a‐vis the full CI results with the same basis; (b) the efficacy of localized active orbitals to ensure and demonstrate manifest size‐consistency with respect to fragmentation. We found that natural orbitals lead to the best overall PES, as evidenced by the NPE and MAD values. The MRMP2 results for individual states and of the MCQDPT2 for multiple states displaying avoided curve crossings are uniformly poorer as compared with the UGA‐SSMRPT2 results. The striking aspect of the size‐consistency check is the complete insensitivity of the sum of fragment energies with given fragment spin‐multiplicities, which are obtained as the asymptotic limit of super‐molecules with different coupled spins. © 2015 Wiley Periodicals, Inc.     

A convenient palladium catalyzed synthesis of symmetric biaryls, biheterocycles and biaryl chiral diamides

A series of symmetrical diamido biaryls has been synthesized in good yield by direct homocoupling of iodoarylbenzamides by palladium-catalysis. No cross product has been isolated from the reaction mixture of two different iodoarylbenzamides under similar conditions. However, only in the case of 2-iodo-N-phenylbenzamide, the intramolecularly coupled product phenanthridone has been isolated as a minor product along with the major intermolecularly coupled product. Biphenyl chiral diamides have been synthesized by this coupling method. This coupling reaction also works well with the reductive dimerization of functionalized heterocyclic compounds. Thus 6,6′-dipivaloylamino-3,3′-bipyridine and 6,6′-dimethyl-2,2′-bipyridine have been efficiently synthesized. In two cases, the X-ray crystal structures have been solved to establish the structures of symmetrical and chiral diamido biaryls and their supramolecular networks.     

Cuboctahedral symmetry in the aggregation of [60]fullerene in polar organic media

[60]fullerene is known to aggregate in water and all experimental and theoretical evidences support that the aggregates contain (C60)13 units. No chemical kinetic study of the effect of solvent polarity on the aggregation of C60 has so far been reported. Here we show by simple kinetic study of the aggregation process and by scanning electron microscopy (SEM) that when methanol is added to a solution of [60]fullerene in CCl4, spontaneous aggregation starts immediately and the aggregation numbers (n) found to be dependent on the CCl4:CH3OH ratio (v/v) of the medium. One particular ratio of the two liquids gives uniformly sized (C60)13 clusters for about 10 min. The values of n correspond to the minima of the previously reported energy calculations and in the present work, they have been shown to be a natural consequence of stacking of cuboctahedra made up of C60 molecules. A Young diagram-like method has been developed for counting the number of C60 molecules in these cuboctahedral stacks and the numbers obtained from this model and also from the present chemical kinetic and SEM studies agree very well with the "magic numbers" obtained by earlier mass spectrometric studies.