High Yield Synthesis of Curcumin and Symmetric Curcuminoids: A “Click” and “Unclick” Chemistry Approach

The worldwide known and employed spice of Asian origin, turmeric, receives significant attention due to its numerous purported medicinal properties. Herein, we report an optimized synthesis of curcumin and symmetric curcuminoids of aromatic (bisdemethoxycurcumin) and heterocyclic type, with yields going from good to excellent using the cyclic difluoro-boronate derivative of acetylacetone prepared by reaction of 2,4-pentanedione with boron trifluoride in THF (ca. 95%). The subsequent cleavage of the BF₂ group is of significant importance for achieving a high overall yield in this two-step procedure. Such cleavage occurs by treatment with hydrated alumina (Al₂O₃) or silica (SiO₂) oxides, thus allowing the target heptanoids obtained in high yields as an amorphous powder to be filtered off directly from the reaction media. Furthermore, crystallization instead of chromatographic procedures provides a straightforward purification step. The ease and efficiency with which the present methodology can be applied to synthesizing the title compounds earns the terms “click” and “unclick” applied to describe particularly straightforward, efficient reactions. Furthermore, the methodology offers a simple, versatile, fast, and economical synthetic alternative for the obtention of curcumin (85% yield), bis-demethoxycurcumin (78% yield), and the symmetrical heterocyclic curcuminoids (80–92% yield), in pure form and excellent yields.     

Synergistic air electrode combining carbon nanotube tissue and fluorinated graphite material in hybrid nonaqueous aluminum batteries

Journal of Solid State Electrochemistry - In a typical Al–air battery, the air cathode functions as a deposition substrate for discharge products while allowing O2 entrance. Herein, we...     

Boundary-layer features in conservative nonlinear oscillations

Nonlinear Dynamics - This paper considers (1?+?1) dimensional conservative oscillatory systems with polynomial nonlinearities in the double limit of high amplitude...     

Aluminum electrodeposition from a non-aqueous electrolyte—a combined computational and experimental study

Electrodeposition of aluminum (Al) from an organic non-aqueous electrolyte of ethylbenzene containing aluminum bromide is demonstrated. It is offered as a simple method for the preparation of Al coatings. This work employs distinct electrochemical techniques and explores the effects of the experimental parameters on the kinetics of the process and the quality of the final coatings. The process presented here enables deposition of pure and crystalline Al at room temperature and facilitates the production of uniform Al coatings on various metallic substrates. Morphological studies establish that the growth of Al deposits follows an island mode, and thus, the most noteworthy effect of the substrate over the morphology of the deposits originates from its impact over the nucleation stage, and the density of islands. This study is complemented by theoretical modeling for the adsorption of Al atoms at the different surfaces. Corrosion evaluation determines the dissolution mechanisms of each of the studied substrates in the examined electrolyte. These findings further corroborate the claim that this electrolyte enables the reversible electrodeposition of Al.

     

Convergence Analysis of Processes with Valiant Projection Operators in Hilbert Space

Convex feasibility problems require to find a point in the intersection of a finite family of convex sets. We propose to solve such problems by performing set-enlargements and applying a new kind of projection operators called valiant projectors. A valiant projector onto a convex set implements a special relaxation strategy, proposed by Goffin in 1971, that dictates the move toward the projection according to the distance from the set. Contrary to past realizations of this strategy, our valiant projection operator implements the strategy in a continuous fashion. We study properties of valiant projectors and prove convergence of our new valiant projections method. These results include as a special case and extend the 1985 automatic relaxation method of Censor.     

A frequency-domain analysis of inexact gradient methods

Mathematical Programming - We study robustness properties of some iterative gradient-based methods for strongly convex functions, as well as for the larger class of functions with sector-bounded...     

Algorithms for the Split Variational Inequality Problem

We propose a prototypical Split Inverse Problem (SIP) and a new variational problem, called the Split Variational Inequality Problem (SVIP), which is a SIP. It entails finding a solution of one inverse problem (e.g., a Variational Inequality Problem (VIP)), the image of which under a given bounded linear transformation is a solution of another inverse problem such as a VIP. We construct iterative algorithms that solve such problems, under reasonable conditions, in Hilbert space and then discuss special cases, some of which are new even in Euclidean space.     

An interior point method with Bregman functions for the variational inequality problem with paramonotone operators

We present an algorithm for the variational inequality problem on convex sets with nonempty interior. The use of Bregman functions whose zone is the convex set allows for the generation of a sequence contained in the interior, without taking explicitly into account the constraints which define the convex set. We establish full convergence to a solution with minimal conditions upon the monotone operatorF, weaker than strong monotonicity or Lipschitz continuity, for instance, and including cases where the solution needs not be unique. We apply our algorithm to several relevant classes of convex sets, including orthants, boxes, polyhedra and balls, for which Bregman functions are presented which give rise to explicit iteration formulae, up to the determination of two scalar stepsizes, which can be found through finite search procedures. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Corresponding author.     

Stabilizer rigidity in irreducible group actions

We consider irreducible actions of locally compact product groups, and of higher rank semi-simple Lie groups. Using the intermediate factor theorems of Bader–Shalom and Nevo–Zimmer, we show that the action stabilizers, and all irreducible invariant random subgroups, are co-amenable in their normal closure. As a consequence, we derive rigidity results on irreducible actions that generalize and strengthen the results of Bader–Shalom and Stuck–Zimmer.