Unequivocal 13C NMR assignment of cyclohexadienyl rings in bromotyrosine‐derived metabolites from marine sponges

Bromotyrosine‐derived compounds are commonly isolated from Verongida sponges and are a major class of marine natural products. Here we report on the unequivocal ¹³C NMR assignment of the brominated carbons at positions C‐2 and C‐4 of the cyclohexadiene ring, two carbons whose resonances are often incorrectly assigned. Interpretation of HMBC data acquired for a series of known bromotyrosine analogues, which included ianthesine E (1), aerothionin (2), 11‐hydroxyaerothionin (3), and 11,19‐dideoxyfistularin‐3 (4), allowed us to unequivocally assign the carbons in question, C‐2 and C‐4, through the observance of unique HMBC correlations from the C‐1 hydroxyl proton. Here we present the complete 2D NMR data sets recorded in DMSO‐d₆ for 2–4 that were used to confirm the assignment and establish the working model. Using this model, a survey of the literature revealed that many members of this structure class had been wrongly assigned. This paper serves to reassign those compounds whose ¹³C NMR assignment at positions C‐2 and C‐4 of the cyclohexadiene ring should be reversed. Copyright © 2012 John Wiley & Sons, Ltd.     

Kinetic relations and the propagation of phase boundaries in solids

This paper treats the dynamics of phase transformations in elastic bars. The specific issue studied is the compatibility of the field equations and jump conditions of the one-dimensional theory of such bars with two additional constitutive requirements: a kinetic relation controlling the rate at which the phase transition takes place and a nucleation criterion for the initiation of the phase transition. A special elastic material with a piecewise-linear, non-monotonic stress-strain relation is considered, and the Riemann problem for this material is analyzed. For a large class of initial data, it is found that the kinetic relation and the nucleation criterion together single out a unique solution to this problem from among the infinitely many solutions that satisfy the entropy jump condition at all strain discontinuities.     

Equilibrium shocks in plane deformations of incompressible elastic materials

This paper is concerned with piecewise smooth plane deformations in an isotropic, incompressible elastic material. An explicit necessary and sufficient condition for the existence of piecewise homogeneous equilibrium states is established, and the set of all such states is precisely characterized. A particularly simple expression is derived for the driving traction on a surface of discontinuity in the deformation gradient.     

Void collapse in an elastic solid

Radial deformations of an infinite medium surrounding a traction-free spherical cavity are considered. The body is composed of an isotropic, incompressible elastic material and is subjected to a uniform pressure at infinity. The possibility of void collapse (i.e. the void radius becoming zero at a finite value of the applied stress) is examined. This does not occur in all materials. The class of materials that do exhibit this phenomenon is determined, and for such materials, an explicit expression for the value of the applied pressure at which collapse occurs is derived. The stability of the deformation and the influence of a finite outer radius are also considered. The results are illustrated for a particular class of power-law materials. In certain respects, the present results for void collapse are complementary to Ball (1982)'s results for cavitation in an incompressible elastic material.Some brief observations on void collapse in compressible materials are made. The collapse of a void under non-symmetric conditions is also discussed by utilizing a solution obtained by Varley and Cumberbatch (1977, 1980).The results reported here were obtained in the course of an investigation supported in part by the U.S. Army Research Office.     

Non-elliptic elastic materials and the modeling of dissipative mechanical behavior: an example

In the context of a special problem, this paper investigates the possibility of modeling dissipative mechanical response in solids on the basis of the equilibrium theory of finite elasticity for materials that may lose ellipticity at large strains. Quasi-static motions for such materials are in general dissipative if the associated equilibrium fields involve discontinuous displacement gradients. For the problem treated, consideration of such deformations is shown to lead naturally to an internal variable formalism similar to those used to describe macroscopic plastic behavior arising from microstructural effects. For quasi-static motions which are maximally dissipative in a specified sense, this formalism leads to a mechanical response which resembles that associated with the pseudo-elastic effect in shape-memory alloys.     

Modeling Large-deformation-induced Microflow in Soft Biological Tissues

The homogenization approach to multiscale modeling of soft biological tissues is presented. The homogenized model describes the relationship between the macroscopic hereditary creep behavior and the microflow in a fluid-saturated dual-porous medium at the microscopic level. The micromodel is based on Biot’s system for quasistatic deformation processes, modified for the updated Lagrangian formulation to account for coupling the fluid diffusion through a porous solid undergoing large deformation. Its microstructure is constituted by fluid-filled inclusions embedded in the porous matrix. The tangential stiffness coefficients and the retardation stress for the macromodel are derived for a time-stepping algorithm. Numerical examples are discussed, showing the strong potential of the model for simulations of deformation-driven physiological processes at the microscopic scale.     

A green,multicomponent, regio- and stereo-selective 1,3-dipolar cycloaddition of azides and azomethine ylides generated in situ with bifunctional dipolarophiles using PEG-400

A series of novel dispiropyrrolidine-linked 1,2,3-triazole derivatives have been prepared by one-pot, four-component protocol that employed 5-arylidene-3-(prop-2-ynyl)thiazolidine-2,4-dione, isatin, sarcosine and substituted azides using Cu(I) generated in situ as catalyst in PEG-400 as a highly efficient and green media. This is the first report of a four-component reaction involving a classical Huisgen reaction, in which the two dipolar moieties (substituted azides and in situ generated azomethine ylides) react with acetylenic and olefinic dipolarophiles, respectively. The 1,3-dipolar cycloaddition proceeds in a highly regio- and stereo-selective manner. This methodology can be an ideal tool for the preparation of biologically important five-membered heterocyclic compounds in one pot.     

Computational homogenization and nonlinear effects in heterogeneous fluid saturated porous media

For the two-scale modelling of deforming fluid-saturated porous structure we apply the asymptotic homogenization approach to the fluid-structure interaction problem involving linear elastic porous skeleton and the Newtonian compressible fluid. The sensitivity analysis of effective coefficients depending on the geometrical configuration is used to introduce a weakly nonlinear formulation which enables to capture influences of the deformation on the material properties. The paper is devoted to the comparison of the linear and the weakly nonlinear models (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microwave‐Mediated Debromination of vicinal‐Dibromides

Debromination of vicinal‐dibromides to E‐alkenes is reported using inorganic solid supports (silica gel or acidic alumina) under microwave irradiation.     

A new green approach for the synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthene-11-one derivatives using task specific acidic ionic liquid[NMP]H_2PO_4

12-Aryl-8,9,10,12-tetrahydrobenzo[a]xanthene-11-one derivatives were synthesized by a convenient and environmentally benign procedure involving multicomponent condensation reactions of substituted aromatic aldehydes with 2,7-dihydroxynaphthalene/2-naphthols/2,6-dihydroxynaphthlene and cyclic 1,3-dicarbonyl compounds in task specific acidic ionic liquid[NMP]H_2PO_4 at 80 ℃.This protocol has proved to be efficient in terms of good yields,operational simplicity,easy workup,recyclability of reaction medium/catalyst,and short reaction time.