Miguel A. Méndez-Rojas

Recent advances in planar tetracoordinate carbon chemistry

We summarize our contributions on the quest of new planar tetracoordinate carbon entities (new carbon molecules with exotic chemical structures and strange bonding schemes). We give special emphasis on the rationalization why in this type of molecules the planar configuration is favored over the tetrahedral one. We will concentrate on the latter and will show that molecules containing planar tetracoordinate carbons have a stabilizing system of delocalized π electrons, which shows similar properties as π systems in aromatic molecules.

Recent advances on technetium complexes: coordination chemistry and medical applications¶

Current literature (1990–2005) on methods for synthesizing technetium (Tc) complexes is presented. The development and design of Tc complexes for imaging of different organic tissues, of special interest for their medical applications, are also reviewed.

Direct electrosynthesis of Cu, Cd, Zn complexes of piroxicam (4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide-1,1,-dioxide) and isoxicam (4-hydroxy-2-methyl-N-(5-methyl-3-isoxazolyl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide) in nonaqueous media by in-situ generation of supporting electrolyte

Abstract The direct electrosynthesis of Cu, Cd and Zn complexes of the anti-inflammatory drugs piroxicam (4-hydroxy-2-methyl- N -(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide-1,1,-dioxide=H-pir) and isoxicam (4-hydroxy-2-methyl- N -(5-methyl-3-isoxazolyl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide=H-isox) was accomplished by electrochemical dissolution of sacrificial metallic anodes in an acetonitrile solution of the ligand. The chemical and electrochemical in-situ generation of supporting electrolyte was used as a means to obtain pure coordination compounds without the use of supporting electrolytes such as tetraalkylammonium or lithium salts in nonaqueous media. Characterization of the complexes obtained by direct synthesis and comparison with those obtained by traditional synthesis shows that a new copper–piroxicam complex was synthesized.

A helicoid ferrocene

Here, we address the problem of stabilizing a new helicoid ferrocene. Of course, to obtain a helical complex, it is essential to design suitable organic ligands. The ligands should possess the correct symmetry to match the geometrical requirement of the metal center. We propose in silico a beautiful helix that consists of one polycyclic hydrocarbon composed of 10 fused cyclopentadiene rings bound on opposite sides of an iron atom. The nature of the metal-ligand interactions between Fe(2+) and the ligand was investigated with energy decomposition analysis. Our results provide strong evidence for the viability of the hitherto unknown helicoid ferrocene as a target for synthesis.

Experimental Electron Density Study of Tetrakis-μ-(acetylsalicylate)dicopper(II): a Polymeric Structure with Cu···Cu Short Contacts

The electron density, its topological features, and the electrostatic potential of tetrakis-mu-(acetylsalicylate)dicopper(II), Cu[C(9)H(7)O(4)](2), have been derived from an accurate high-resolution diffraction experiment at 100 K. This complex exhibits a polymeric structure involving one acetyl oxygen atom as a bridge in the solid state. Only van der Waals interactions between the polymeric chains are observed. The copper cation is octahedrally coordinated with five oxygen atoms of the aspirinate ligands and one adjacent Cu with short Cu...Cu contact distances in the range of 2.6054(1) A. The Cu-O bond lengths are equal to 1.96 A except the apical one which is 2.2183(7) A. The multipole refinements were carried out using the Hansen-Coppens model coded in the MOPRO computer program. Starting from the 3d(10)4s(1) copper electron configuration, the electron density analysis and Cu d-orbital populations reveal that the observed configuration is close to being [Ar]3d(9)4s(1). As expected from the ligand field theory, the most depopulated 3d-orbital is the d(x(2)-y(2)) (1.17 e) one with lobes pointing toward the carboxylic oxygen atoms. Conversely, the d(z(2)) is the most populated orbital for a z-axis directed along the Cu...Cu bond. The atomic charges were derived from a kappa-refinement and yielded a metal net charge of +1.20(3) e. Deficits of +0.72(6) and +0.59(7) e are obtained for the acetyl carbon atoms of the aspirinate ligands, those involved in the drug activity of aspirin. Comparisons are made to the results of our previous work on the zinc-aspirinate complex.

Enhanced Antibacterial Activity of CeO2 Nanoparticles by Surfactants

Abstract CeO2 nanoparticles (NPs) were tested to assess their toxicity on Escherichia coli strain in the presence of non-ionic surfactants. The NPs were dispersed in water by sonication at different pH values and times then mixed with three different surfactants (i.e., Triton X-100, Polyvinyl Pyrrolidone (PVP) and Tween 80) with a concentration of 0.001% v/v. It was found that sonication favored dispersion of the material and produced particles having 100 nm sizes in average. The material show toxicity to E. coli at pH 7 when growth using only minimal M9 media; no toxic response was observed for bacteria growth in rich media. The toxic effect in minimal media was enhanced by adding any of the non-ionic surfactants to the media. The use of CeO2 plus surfactant decreased the minimal inhibitory concentration (MIC) value of E. coli. The highest effect was observed for addition of Tween 80, in this case MIC value was 0.150 mg mL–1 compared to 3 mg mL–1 of CeO2 alone (almost 20 times improvement). These findings suggest the importance of different substances that can interact with NPs, like surfactants, usually present in wastewater systems that may lead to undesirable unexpected toxic characteristics in materials usually considered as innocuous.

In vitro antibacterial activity of meclofenamate metal complexes with Cd(II), Pb(II), Co(II), and Cu(II). Crystal structures of [Cd(C14H10NO2Cl2)2∙(CH3OH)]n and [Cu(C14H10NO2Cl2)2(C5H5N)2].

The synthesis and characterization of five metal complexes derived from sodium meclofenamate (1) are reported: [Cd(C14H10NO2Cl2)2∙(CH3OH)]n∙nCH3OH (6), [Pb(C14H10NO2Cl2)2]n (7), [Co(C14H10NO2Cl2)]n (8), [Cu(C14H10NO2Cl2)]n (9), and [Cu(C14H10NO2Cl2)2(C5H5N)2] (10) (C14H10NO2Cl2=meclofenamate; C5H5N=pyridine). The characterization of the compounds was based on FTIR and UV-visible spectroscopy, mass spectrometry and, in the case of complexes 6 and 10, single crystal X-ray diffraction analysis. For compound 6, the structural analysis revealed a 1-D polymeric chain structure, in which pentagonal planar [Cd(RCOO)2(CH3OH)] units were linked through bridging carboxylate functions of the meclofenamate ligands. The overall coordination environment of the Cd(II) ions was seven-coordinate, since each carboxylate group exhibited a μ3-bridging coordination mode. On the other hand, for complex 10 a discrete mononuclear structure was observed, in which the six-coordinate copper(II) metal atoms were coordinated by two pyridine molecules and the carboxylate functions of two meclofenamate entities, in an anisobidentate coordination mode. The antibacterial activity of compounds 6-9 against four strains of Gram positive (Staphylococcus aureus and Bacillus subtilis) and Gram negative (Escherichia coli and Pseudomonas aeruginosa) bacteria was examined, finding that only complex 6 was active. Additionally, it was found that the Co(II) and Cu(II) complexes 8 and 9 showed peroxidase activity.

Inulin as a novel biocompatible coating: evaluation of surface affinities toward CaHPO4, α-Fe2O3, ZnO, CaHPO4@ZnO and α-Fe2O3@ZnO nanoparticles.

The introduction of biocompatible coatings onto nanoparticle surfaces can be synthetically challenging. In this work, calcium phosphate (brushite, CaHPO4⋅2H2O), iron oxide (hematite, α-Fe2O3), zinc oxide (ZnO), and CaHPO4@ZnO and α-Fe2O3@ZnO nanoparticles were synthesized and treated with the biocompatible, biodegradable, polysaccharide inulin {(2R,3S,4S,5R)-2-[[(2R,3S,4S,5R)-3,4-dihydroxy-2,5-bis(hydroxymethyl)oxolan-2-yl]oxymethyl]-5-(hydroxymethyl)oxolane-2,3,4-triol} under mild conditions. The products were fully characterized by Fourier transforms infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS), dynamic light scattering (DLS), differential thermogravimetric/differential thermal analysis (TGA/DTA), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). Surface interactions among hematite and brushite with inulin are weak, but coating the nanoparticle surface with ZnO increased the affinity toward the polysaccharide. Inulin adsorption on the nanoparticle surface was confirmed by thermal and spectroscopic analyses. The nanoparticles had diameters ranging from 50 to 80nm, with nearly spherical morphology. The nanoparticles sizes, stability and solubility in water could make them useful as components for enriched foods.

Metal Complexes Containing Natural and Artificial Radioactive Elements and Their Applications

Recent advances (during the 2007–2014 period) in the coordination and organometallic chemistry of compounds containing natural and artificially prepared radionuclides (actinides and technetium), are reviewed. Radioactive isotopes of naturally stable elements are not included for discussion in this work. Actinide and technetium complexes with O-, N-, N,O, N,S-, P-containing ligands, as well π-organometallics are discussed from the view point of their synthesis, properties, and main applications. On the basis of their properties, several mono-, bi-, tri-, tetra- or polydentate ligands have been designed for specific recognition of some particular radionuclides, and can be used in the processes of nuclear waste remediation, i.e., recycling of nuclear fuel and the separation of actinides and fission products from waste solutions or for analytical determination of actinides in solutions; actinide metal complexes are also usefulas catalysts forcoupling gaseous carbon monoxide, as well as antimicrobial and anti-fungi agents due to their biological activity. Radioactive labeling based on the short-lived metastable nuclide technetium-99m (99mTc) for biomedical use as heart, lung, kidney, bone, brain, liver or cancer imaging agents is also discussed. Finally, the promising applications of technetium labeling of nanomaterials, with potential applications as drug transport and delivery vehicles, radiotherapeutic agents or radiotracers for monitoring metabolic pathways, are also described.

Applications of nanomaterials in functional fortified dairy products: benefits and implications for human health

Abstract Nanotechnology applications in food-related fields have dramatically increased over the past few years. From nanoscale food components designed to exhibit unique functionalities to self assembled nanostructures capable of delivering flavors, drugs, or specific nutrients to the site of action, nanotechnology represents a new approach for developing added-value food products according to current consumer trends. As diseases related to nutritional deficiencies have escalated globally forcing health-conscious consumers to find efficient ways to prevent them, nanotechnology may provide a new array of tools for creating fortified or enriched products with improved digestibility and higher quality from the nutritional, sensory and functional standpoints. Arguably, dairy foods constitute the most important food category in terms of nutritional claims and occupy a significant and growing market space among functional and fortified foods. In this chapter, both the use of nanomaterials in milk by-products (cheese, yogurt, among others) and the application of emergent technologies, which may be scaled for industrial production, in dairy matrices for creating nanostructures are reviewed and discussed, stressing their potential benefits while addressing the concerns of consumers about the lack of information regarding long term use.