First-transition-metal complexes containing the ligands 6-amino-6-methylperhydro-1,4-diazepine (AAZ) and a new functionalized derivative: can AAZ act as a mimetic ligand for 1,4,7-triazacyclononane?

The structure and physicochemistry of the [Ni(II)(AAZ)(2)](ClO(4))(2) (1) complex (AAZ = 6-amino-6-methylperhydro-1,4-diazepine), as a system that is able to mimic some important chelate properties of 1,4,7-triazacyclononane, are reported. The syntheses of a new unsymmetric AAZ-functionalized ligand and the structure of its first heterodinuclear Fe(III)Zn(II) complex are also presented.     

Oxidation of tertiary benzamides by 5,10,15,20-tetraphenylporphyrinatoironIII chloride-tert-butylhydroperoxide

Tertiary benzamides are oxidized by the 5,10,15,20-tetraphenylporphyrinatoiron(III) chloride-Bu'(t)OOH system at the alpha-position of the N-alkyl groups. The major products are N-acylamides, although small amounts of secondary amides, the products of dealkylation, are also formed. Plots of initial rate versus initial substrate concentration for these reactions are curved, suggesting formation of an oxidant-substrate complex. The reaction rates are almost insensitive to the substituent in the benzamide moiety, but there is a kinetic deuterium isotope effect of 5.6 for the reaction of the N,N-(CH(3))(2) and N,N-(CD(3))(2) compounds. Comparison of the reaction products from N-alkyl-N-methylbenzamides reveals that, for all compounds studied except N-cyclopropyl-N-methylbenzamide, oxidation of the alkyl group is preferred, strongly so (by a factor of ca. 8) for N-allyl-N-methylbenzamide. In contrast to microsomal oxidation, there is no steric hindrance to oxidation of an isopropyl group. Thus, we propose that these reactions proceed via hydrogen atom abstraction to form an alpha-carbon-centred radical and we attribute the observed diminished reactivity of the N-cyclopropyl group to its known reluctance to form a cyclopropyl radical. Oxidation of N-methyl-N-(2,2,3,3-tetramethylcyclopropyl)methylbenzamide provides preliminary evidence for rearrangement of an intermediate radical. While it remains unclear how these reactions proceed directly to the N-acyl products, we have established that N-hydroxymethyl, N-alkoxymethyl and N-alkylperoxymethyl intermediates are not involved.     

Suspended particles surrounded by an inhomogeneously charged permeable membrane. Solution of the Poisson-Boltzmann equation by means of the network method

The Poisson-Boltzmann equation is numerically solved for a suspended spherical particle surrounded by a permeable membrane that contains an inhomogeneous distribution of fixed charges. The calculations are carried out using the network simulation method, which makes it possible to solve the problem in the most general case, extending previous results (J.P. Hsu, Y.C. Kuo, J. Membrane Sci. 108 (1995) 107). Approximate analytical expressions for the counterion concentration and the electric potential in the membrane are also presented, together with criteria that determine their ranges of validity. The limiting case of a distribution of fixed charges in the membrane that reduces to a surface charge is also analyzed. It is shown that the solution for this case, considering a vanishingly small radius of the core, reduces to a superposition of solutions corresponding to a charged impermeable particle suspended in an electrolyte solution and to a cavity filled with a charged electrolyte solution.     

Spectroscopic characterization of polyaniline formed by using copper(II) in homogeneous and MCM-41 molecular sieve media

This work emphasizes the important role of the synthetic parameters in the structure of the polymeric material obtained in the aniline polymerization. The polymers formed by the oxidative polymerization of aniline by copper(II) ions in acidic aqueous solution, acetonitrile/water medium, and also copper(II) acetate complex encapsulated into MCM-41 molecular sieve were characterized by resonance Raman spectroscopy using three exciting laser lines and other techniques such as UV-vis, FTIR, and XANES (Nitrogen K edge). Additionally the products were investigated by thermogravimetric analysis and powder X-ray diffraction. When Cu(II) ions in acidic aqueous medium are used, emeraldine salt (ES-PANI) is formed through the usual head-to-tail polymerization mechanism, while in acetonitrile/water medium a polymer is observed having mainly phenazine-like rings, quinonediimine, and/or phenylenediamine segments in the chains, suggesting that a distinct mechanism is operating. The average molecular weights of the free polymers synthesized in water and in acetronile/water were, respectively, ca. 37 300 and 16 900 Da. The encapsulated polymer synthesized in Cu(II)-MCM-41 is a polymeric mixture of (i) ES-PANI and (ii) the polymer obtained when this metal cation was used as oxidant in acetonitrile/water medium. All the characterization data were compared to those ones obtained for standard free polyaniline and also for the encapsulated polymer into mesoporous MCM-41 formed by using persulfate in acidic aqueous medium as oxidant.     

Numerical comparison of merit function with filter criterion in inexact restoration algorithms using hard-spheres problems

Inexact Restoration methods have been introduced for solving nonlinear programming problems. Each iteration is composed of two phases. The first one reduces a measure of infeasibility, while in the second one the objective function value is reduced in a tangential approximation of the feasible set. The point obtained from the second phase is compared with the current point either by means of a merit function or by using a filter criterion. A comparative numerical study about these criteria by using a family of Hard-Spheres Problems is presented.     

Coordination of the natural ligand lapachol to iron(II): synthesis,theoretical study and antiproliferative activity

Transition Metal Chemistry - Lapachol is a natural naphthoquinone known for having a variety of biological properties, and in recent years, it has been used in the synthesis of metal complexes with...     

Peroxidase activity of new mixed‐valence cobalt complexes with ligands derived from pyridoxal

New mixed‐valence cobalt complexes with ligands derived from pyridoxal were synthesized and characterized, and their application as mimetics of the peroxidase enzyme was investigated. Single‐crystal X‐ray diffraction was used to analyze all complex structures in the solid state and their electrochemical behavior was investigated. A reactivity pattern was observed in the complex synthesis regarding the cobalt compounds from which analogous zwitterionic derivatives were obtained. The importance of these compounds lies in understanding their behavior in an oxidizing environment and evaluating whether they can activate hydrogen peroxide to oxidize phenolic compounds. In nature, enzymes called peroxidases, which efficiently oxidize phenolic compounds, trigger many reactions involving the activation of hydrogen peroxide to oxidize organic substrates. However, these enzymes present several disadvantages, including denaturation and elevated costs. Therefore, these limitations can be overcome by expanding research into the study of synthetic catalysts for the oxidation of phenolic compounds using hydrogen peroxide, which is a highly relevant field of bioinorganic chemistry.     

Silver sorption isotherms onto bentonites: Comparing mathematical models

Herein is reported the application of models on sorption isotherms for removal of silver ions from aqueous solution using 2 bentonites: SWy‐2 and BaVC‐1, low‐cost sorbents. Physicochemical attributes were determined for both materials, and sorption experiments were carried out in batch system. The pH before and after sorption decreased from 7.8 to 6.1 and 8.4 to 6.7 for SWy‐2 and BaVC‐1, respectively. Langmuir, Freundlich, Sips, Toth, Kolbe‐Corrigan, Khan, and Radke‐Prausnitiz models were applied to the data. The models showed good fit with R² above 0.999 and RMSE < 2%. The adjustable parameters indicated high affinity of silver ions to BaVC‐1 sorption sites, demonstrating high sorption capacity and thermodynamic feasibility. In general, SWy‐2 showed most heterogeneous sorption sites, while BaVC‐1 showed most homogeneous sites. Moreover, BaVC‐1 has shown larger surface area and smaller particle size, which can explain its better sorption performance as compared with SWy‐2.     

Fabrication of zinc oxide nanowires/polymer composites by two‐photon polymerization

We present an approach to fabricate ZnO nanowires/polymer composite into three‐dimensional microstructures, based on two‐photon polymerization direct laser writing, a fabrication method that allows submicrometric spatial resolution. The structural integrity of the structures was inferred by scanning electron microscopy, while the presence and distribution of ZnO nanowires was investigated by energy dispersive X‐ray, Raman spectroscopy, and X‐ray diffraction. The optical properties of the produced composite microstructures were verified by imaging the characteristic ZnO emission using a fluorescence microscope. Hence, such approach can be used to develop composite microstructures containing ZnO nanowires aiming at technological applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 333–337     

Stereoselective Synthesis of β-Hydroxy- and β-Ethoxy-δ-lactones: Model Structures for Compounds Isolated from Otoba parvifolia

Abstract: In this paper we describe a very short stereoselective synthesis of the β-ethoxylactone 13, a model structure for compounds isolated from Otoba parvifolia. The method, which also produces β-hydroxy-esters and β-hydroxy-lactones, is based on a chemo- and stereoselective Reformatsky reaction.