Elucidating heteroatom influence on homonuclear 4J(H,H) coupling constants by DFT/NMR approach

We report the structural dependency of long range scalar J-coupling constant across four bonds as function of the dihedral angles Φ1 and Φ3. The calculated homonuclear coupling constants ⁴J(_H,H), obtained at a density functional theory level, were measured between C(1)─X(2) and X(2)─C(3) bonds in three-term models, where C, N, O, and S were systematically used as the second atom of the alkyl structures ( 1 - 4 ). The ⁴J_(H,H) calculated values, tabulated for variation of 30° for both Φ1 and Φ3, have disclosed an unexpected detectable coupling constant (⁴J(_H,H) ≥ 1 Hz) across heteroatoms, useful to provide valuable structural information. A 2-methyl-1,3-dithiane sulfide ( 5 ) was used as a case study to prove the applicability and reliability of the calculated values to real issues. The ⁴J(_H,H) values obtained at density functional theory for the system 4 have reproduced with good accuracy an unexpected experimental ⁴J(_H2ax-H4ax) = 1.01 Hz of sulfide molecule ( 5 ), suggesting these calculated coupling constant values as a new powerful tool for the organic synthesis and stereochemical analysis.     

Isolement et identification de l'acide furfurique,nouvelle depsidone du lichen Pseudevernia furfuracea (L.) Ach

Isolation and Identification of Furfuric Acid a New Depsidone from the Lichen Pseudevernia furfuracea (L.) Ach. The structure of furfuric acid, ( 1 ), a new depsidone, isolated from the lichen Pseudevernia furfuracea (L.) Ach. has been established as 4-formyl-3,8-dihydroxy-9-(2,4-dihydroxy-5-methoxycarbonyl-3,6-dimethylbenzyl)-1,6-dimethyl-11-oxo-11H-dibenzo[b,e][1,4]dioxepin-7-carboxylic acid by spectral and chemical methods.     

Selective epoxidation of monoterpenes with H2O2 and polymer-supported methylrheniumtrioxide systems

A convenient and efficient synthesis of monoterpene epoxides by application of heterogeneous poly(4-vinylpyridine)/methyl rhenium trioxide (PVP/MTO) and polystyrene/methyl rhenium trioxide (PS/MTO) systems is described. Even highly sensitive terpenic epoxides were obtained in excellent yield. Environment friendly, easily available, and low cost H₂O₂ was used as oxidant. Catalysts were stable systems for at least five recycling experiments.     

The Einstein-Yang-Mills equations

The interaction between gravitational and gauge fields is considered. A new characterization of the Einstein-Yang-Mills equations is given. In particular, necessary and sufficient conditions which ensure the decomposition of the total Lagrangian density are established. The emphasis is on the general covariance requirements of the basic geometrical objects involved. This leads, among other things, to a better understanding of the role played by the Bianchi identity.     

Remarks on bifurcation for elliptic operators with odd nonlinearity

On estimating the eigenvalues for a class of semilinear elliptic operators, we obtain bifurcation and comparison results concerning the eigenvalues of some related linear problem.     

Adapted numerical modelling of the Belousov–Zhabotinsky reaction

Adapted numerical schemes for the integration of differential equations generating periodic wavefronts have reported benefits in terms of accuracy and stability. This work is focused on differential equations modelling chemical phenomena which are characterized by an oscillatory dynamics. The adaptation is carried out through the exponential fitting technique, which is specially suitable to follow the apriori known qualitative behavior of the solution. In particular, we have merged this strategy with the information coming from existing theoretical studies and especially the observation of time series. Numerical tests will be provided to show the effectiveness of this problem-oriented approach.     

Amyloid Polymorphism in the Protein Folding and Aggregation Energy Landscape

Protein folding involves a large number of steps and conformations in which the folding protein samples different thermodynamic states characterized by local minima. Kinetically trapped on‐ or off‐pathway intermediates are metastable folding intermediates towards the lowest absolute energy minima, which have been postulated to be the natively folded state where intramolecular interactions dominate, and the amyloid state where intermolecular interactions dominate. However, this view largely neglects the rich polymorphism found within amyloid species. We review the protein folding energy landscape in view of recent findings identifying specific transition routes among different amyloid polymorphs. Observed transitions such as twisted ribbon→crystal or helical ribbon→nanotube, and forbidden transitions such helical ribbon?crystal, are discussed and positioned within the protein folding and aggregation energy landscape. Finally, amyloid crystals are identified as the ground state of the protein folding and aggregation energy landscape.     

The Nemitskii Operator in Holder Spaces: Some Necessary and Sufficient Conditions

The Nemitskii operator in the Hölder spaces C^0, () with an open bounded subset of Rⁿ, is studied; necessary and sufficientconditions are given for boundedness, uniform continuity, anduniformly continuous differentiability on bounded sets.     

A New Water Soluble Calixarene: 5,11,17,23-tetrasulphonato-25,27-di(hydroxycarbonylmethoxy)-26, 28-dihydroxycalix[4]arene. A Thermodynamic and Spectroscopic Investigation of Its Proton and Copper(II) Complexes

A new water soluble receptor 5,11,17,23-tetrasulphonato-25,27-di(hydroxycarbonylmethoxy)-26,28-dihydroxycalix[4]arene was synthesized andcharacterized and its proton and copper(II) complexes were studied andcompared with the analogous species of the fully carboxylated ligand5,11,17,23-tetrasulphonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)calix[4]arene. H° and S° values are crucial for understanding thepeculiar acid-base properties of the ligand. EPR spectra together with theUV-VIS spectral data reveal the coordination stereochemistry of thecopper(II) species.