Thermal and sonochemical studies on the Diels-Alder cycloadditions of masked o-benzoquinones with furans: new insights into the reaction mechanism

What does a Diels-Alder cycloaddition look like? This question is here addressed in the case of the increasingly significant cycloadditions of masked o-benzoquinones (MOBs), which serve as versatile dienes for the construction of complex and functionalized structures. So first, what the mechanism is not: It is not (by and large) a classical, concerted [4 + 2] cycloaddition. Experimental evidence is now supported by sonochemical studies, which were instrumental in elucidating the pathway. Reactions with furans are accelerated and improved under sonication, even when conducted at -10 degrees C. Variation of the acoustic energy, temperature, and solvent composition allows us to optimize the yields and provide insights into the mechanism. Ultrasound does not cause sonochemical switching, as an alternative radical pathway should be ruled out. Results are consistent with a polar mechanism as claimed recently in a theoretical study. Moreover, this also does justice to a series of seminal papers, largely ignored, that gave a clue to the crucial issue of furan regioselectivity based on a nucleophilic addition. Most effects caused by ultrasonic agitation are of mechanochemical nature and suggest the existence of a perfectly stirred reactor with enhanced mass transfer.     

Development and validation method for determination of Paroxetine and its metabolites by nonaqueous capillary electrophoresis in human urine. Experimental design for evaluating the ruggedness of the method

A simple, rapid, and sensitive procedure using nonaqueous capillary electrophoresis (NACE) to measure Paroxetine (one of the mostly used antidepressants for mental diseases treatment) and three metabolites has been developed and validated. Optimum separation of paroxetine and metabolites was obtained on a 57 cm x 75 microm capillary using a nonaqueous buffer system of 9:1 methanol-acetonitrile containing 25 mM ammonium acetate and 1% acetic acid, with temperature and voltage of 25 degrees C and 15 kV, respectively, and hydrodynamic injection. Fluoxetine was used as an internal standard. Good results were obtained for different aspects including stability of the solutions, linearity, accuracy, and precision. Detection limits between 9.3 and 23.1 microg.L(-1) were obtained for paroxetine and its metabolites. A ruggedness test of the method was carried out using the Plackett-Burman fractional factorial model with a matrix of 15 experiments. This method has been used to determine paroxetine and its main metabolite B at clinically relevant levels in human urine. Prior to NACE determination, the samples were purified and enriched by means of an extraction-preconcentration step with a preconditioned C18 cartridge and eluting the compounds with methanol.     

Grafting polymerization on cellulose based textiles: A C solid state NMR characterization

Grafting of methyl methacrylate and ethyl acrylate onto cellulose chains of textiles with oxidized sites has been carried out. To this aim, carboxyl and carbonyl groups have been introduced by oxidation of the cellulose and used as photosensitive agents, allowing the formation of radical sites. The copolymerization has been started irradiating the substrate with ultraviolet light for a short time. With the grafting of acrylic monomers the mechanical strength and the thermal stability of cellulose based textiles may be improved, as well as the resistance to chemical and biological agents. The method has been successfully tested performing the grafting on a naturally aged cotton sample. It is worth to note that the grafting does not affect the aspect of the material.All samples have been characterized with ¹³C solid state NMR spectroscopy. A semi-quantitative evaluation of the grafting has been performed either studying the cross-polarization dynamic process, or by direct integration of resonances in ¹³C single pulse excitation spectra.     

Evodiamine functions as an agonist for the vanilloid receptor TRPV1

Evodiamine, a quinozole alkaloid constituent of Evodia rutaecarpa, has been reported previously to induce several responses comparable to capsaicin in animal systems. Here, we characterize evodiamine as an agonist for rat TRPV1 expressed heterologously in CHO cells. Evodiamine bound to rat TRPV1 with a Ki of 5.95 +/- 0.87 microM, as measured by inhibition of [3H] RTX binding (capsaicin, Ki = 1.8 +/- 0.3 microM). Evodiamine was a full agonist for induction of 45Ca2+ uptake, with an EC50 of 856 +/- 43 nM (capsaicin, EC50 = 45 +/- 4 nM) and was competitively antagonized by capsazepine, as revealed by a Schild plot. The pattern of cellular response, as determined by calcium imaging, was similar to that with capsaicin and yielded an EC(50) of 1.03 +/- 0.21 [micro sign]M. Molecular modeling suggested a consistent pattern of overlap between evodiamine and TRPV1 agonists. We conclude that evodiamine represents a novel class of agonists for rat TRPV1, albeit 3-19-fold less potent than capsaicin, and thus represents a new potential class of lead molecules for drug development.     

Nonaqueous capillary electrophoresis method for the analysis of gleevec and its main metabolite in human urine

The viability of nonaqueous capillary electrophoresis (NACE) was investigated for determination of gleevec and its main metabolite in human urine using a fused-silica capillary. Baseline separation of the studied solutes was obtained using a nonaqueous solution composed of 12 mM ammonium acetate and 87.6 mM acetic acid in methanol-acetonitrile (ACN) (80:20, v:v) providing analysis time shorter than 3 min. Different aspects including stability of the solutions, linearity, accuracy and precision were studied in order to validate the method in the urine matrix. Detection limits of 24 microg L(-1) for gleevec and its metabolite were obtained. A robustness test of the method was carried out using the Plackett-Burman fractional factorial model with a matrix of 15 experiments. The developed method is simple, rapid and sensitive and has been used to determine gleveec and its metabolite at clinically relevant levels in human urine. Before NACE determination, a solid-phase extraction (SPE) procedure with a C18 cartridge was necessary. Real determination of these analytes in two patient urines were done.     

Effect of introducing a cationic system into a thiol‐ene photopolymerizable formulation

Hybrid materials derived from a thiol‐ene and cationic polymerization were obtained from concomitant polymerization. The hybrid materials were cured by both photopolymerization and thermally induced polymerization. The kinetics of the photopolymerization were measured using time resolved‐IR and optical pyrometry. The nucleophilic character of the polysulfide obtained initially in the thiol‐ene polymerization inhibited the development of the cationic photoinitiated polymerization of epoxy monomers. Besides, the epoxide groups underwent a proton catalyzed addition reaction with the thiols to form new sulfides groups in the reaction mixture. It is proposed that the formed sulfides can terminate the growing polyether chains forming dormant species like trialkylsulfonium salts. These salts promote the thermal polymerization of the epoxy monomer in a post treatment, producing hard and transparent materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4829–4843, 2007     

Boundary fluxes for nonlocal diffusion

We study a nonlocal diffusion operator in a bounded smooth domain prescribing the flux through the boundary. This problem may be seen as a generalization of the usual Neumann problem for the heat equation. First, we prove existence, uniqueness and a comparison principle. Next, we study the behavior of solutions for some prescribed boundary data including blowing up ones. Finally, we look at a nonlinear flux boundary condition.     

Stability of additive mappings on large subsets

We study mappings from a group into a Banach space which are ``nearly additive' on large subsets.

     

Violating Bell's inequality beyond Cirel'son's bound

Cirel'son inequality states that the absolute value of the combination of quantum correlations appearing in the Clauser-Horne-Shimony-Holt (CHSH) inequality is bound by 2 square root of (2). It is shown that the correlations of two qubits belonging to a three-qubit system can violate the CHSH inequality beyond 2 square root of (2). Such a violation is not in conflict with Cirel'son's inequality because it is based on postselected systems. The maximum allowed violation of the CHSH inequality, 4, can be achieved using a Greenberger-Horne-Zeilinger state.     

Communication Complexity as a Principle of Quantum Mechanics

We introduce a two-party communication complexity problem in which the probability of success by using a particular strategy allows the parties to detect with certainty whether or not some forbidden communication has taken place. We show that theprobability of success is bounded by nature; any conceivable method which gives a probability of success outside these bounds is impossible. Moreover, any conceivable method to solve the problem which gives a probability success within these bounds is possible in nature. This example suggests that a suitaby chosen set of communication complexity problems could be the basis of an information-theoretic axiomatization of quantum mechanics.