Ruthenium complexes with triazenide ligands bearing an N-heterocyclic moiety, and their catalytic properties in the reduction of nitroarenes.

A series of ruthenium complexes of formulae [RuCl(triazenide)(p-cymene)] have been synthesized using as ligand a triazenide monofunctionalized with an N-heterocyclic moiety. Nuclear magnetic resonance, high resolution mass spectrometry and X-ray diffraction were used to characterize the triazenide ligands and their complexes. In addition, these ruthenium complexes catalyzed the reduction of nitrobenzene to aniline in the presence of sodium borohydride and ethanol as solvent at room temperature. Notably, complex 5 was especially active in the reduction of nitroarenes substituted at the aromatic ring with electron-withdrawing or electron-donating fuctional groups affording the desired arylamines in good to excellent yields (80-100%). The role of the N-heterocyclic moiety on catalysis was explored.

Study of electrospun nanofibers loaded with Ru(ii) phenanthroline complexes as a potential material for use in dye-sensitized solar cells (DSSCs).

Dye-sensitized solar cells (DSSCs) are an increasingly attractive alternative energy source because of their low cost. Therefore, researchers have intensified efforts over the past decade to increase their energy conversion efficiency by employing new materials in each DSSC component. The present research focuses on synthesizing electrospun nanofibers as a potential new material as a counter electrode in DSSCs. Two Ru(ii) half sandwich 1,10 phenanthroline (phen) Ru-1 and 5-amino- phen Ru-2 complexes were prepared for its functionalization. As a deposition medium, poly(caprolactone) (PCL) dissolved in chloroform was used. Different Ru(ii) complex concentrations were made at 0.1% wt., 0.5% wt., and 1% wt. Thermal characterization studies using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were conducted to evaluate the behavior and weight loss of the samples with temperature variations. Fourier transform infrared spectroscopy (FTIR) measurements were taken to observe the bond interaction of the ruthenium complexes and the PCL. Finally, scanning electron microscopy (SEM) was used to structurally and morphologically evaluate the fiber distribution and porosity. These fibers have a homogeneous morphology, without bulbs, but with evident solid inlays on the surface, with fibers between ∼0.58 to 2.47 µm and percentages of porosity ∼45%. TGA and DSC thermograms show minor temperature variations that demonstrate the incorporation of the Ru(ii) complexes into the fiber. Furthermore, the melting and degradation temperature of the fibers is suitable for use in a DSSC approach. The incorporation of the ruthenium compounds into PCL fibers, along with the addition of the NH2 group into complex Ru-2, resulted in a higher current density for both anodic and cathodic peaks in Cyclic Voltammetry (CV). It is noteworthy that from I-V curves, PCL-Ru2 1% fibers demonstrated a conductivity of 0.461 µS cm-1, which is comparable to other PCL fibers carrying a higher metal load. Future studies will delve into the mechanical properties of these fibers to highlight their potential for application in this field.

Bioguided isolation of N-malonyl-(+)-tryptophan from the fruit of Pithecellobium dulce (Roxb.) Benth. that showed high activity against Hymenolepis nana.

Pithecellobium dulce is distributed in America and Asia where is widely used in traditional medicine. This study describes the bioguided fractionation of the methanol extract (ME) obtained from the P. dulce fruit that showed in vitro activity against Hymenolepis nana; Artemia salina assay was used to determine toxicity; and the purified compound was computationally analysed to obtain its absorption-distribution-metabolism-excretion-and-toxicity properties (ADMET). The ME and its fractions were more active than praziquantel (PZQ), and the purified compound was characterized as N-malonyl-(+)-tryptophan (NMT). Parasites treated with NMT showed shorter paralysis and death times (5 and 7 min) than those treated with PZQ (15 and 30 min), both used at 20 mg/mL. Toxicity and ADMET prediction results supported the slight-hazardousness and efficacy of the assayed fractions/compound. This is the first report of the antiparasitary activity of both the P. dulce ME and NMT, showing their potential to treat human H. nana infections.

Bacterial Biofilm Formation Using PCL/Curcumin Electrospun Fibers and Its Potential Use for Biotechnological Applications.

Electrospun nanofibers are used for many applications due to their large surface area, mechanical properties, and bioactivity. Bacterial biofilms are the cause of numerous problems in biomedical devices and in the food industry. On the other hand, these bacterial biofilms can produce interesting metabolites. Hence, the objective of this study is to evaluate the efficiency of poly (Ɛ- caprolactone)/Curcumin (PCL/CUR) nanofibers to promote bacterial biofilm formation. These scaffolds were characterized by scanning electron microscopy (SEM), which showed homogeneous fibers with diameters between 441-557 nm; thermogravimetric analysis and differential scanning calorimetry (TGA and DSC) demonstrated high temperature resilience with degradation temperatures over >350 °C; FTIR and 1H-NMR serve as evidence of CUR incorporation in the PCL fibers. PCL/CUR scaffolds successfully promoted the formation of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa biofilms. These results will be valuable in the study of controlled harvesting of pathogenic biofilms as well as in metabolites production for biotechnological purposes.

Novel Linezolid analogues with antiparasitic activity against Hymenolepis nana.

The stereoselective synthesis and anti- Hymenolepis nana activity of six Linezolid-type compounds, obtained by chemical modification of l-Alanine, are reported in this work. The synthetic strategy was to prepare diasteromeric N,N-dibenzylamino oxazolidinones 1 and 2, and coupling with 4-(4-bromophenyl)morpholine (3) to obtain N,N-dibenzylamino Linezolid analogues 4 and 5. A hydrogenolysis reaction over 4 and 5 resulted in amino-free Linezolid analogues 6 and 7, which were acetylated to reach diasteromeric Linezolid analogues 8 and 9. The six Linezolid analogues 4-9 show in vitro antiparasitic activity against Hymenolepis nana cestode, but not against several bacterial strains. Interestingly, compounds 6, 7 and 9 exhibit high potency, having shorter paralysis and death times after exposure (6-10 and 18-21 min, respectively), shorter than those found with antihelmintic compound Praziquantel (20 and 30 min) at 20 mg/mL. In addition, a cytocompatibility assay of 6-9 with human cells (ARPE-19 cells) demonstrate a non-cytotoxic effect at 0.4 mM. These results show the pharmacological potential of the newly reported Linezolid-type analogues as antiparasitic agents against Hymenolepis nana.

Anthocyanins of Pithecellobium dulce (Roxb.) Benth. Fruit Associated with High Antioxidant and α-Glucosidase Inhibitory Activities.

Red arils of Pithecellobium dulce fruit, commonly known as guamuchil, show high antioxidant (AOx) and α-glucosidase inhibitory (IαG) activities, which have been mainly associated with the content of unknown anthocyanins. In this study, the AOx (i.e., DPPH and ABTS as Trolox equivalents, µmol TE/g) and IαG (as half-maximal inhibitory concentration, IC50, mg/mL) activities of the anthocyanin-rich fraction (ARF) obtained from red arils were contrasted with those of the methanol extract (ME), and the main ARF anthocyanins were characterized by HPLC-DAD-ESI-MS, GC-MS and 1H-NMR. The AOx and IαG values of the ARF (DPPH = 597.8; ABTS = 884.01; IαG = 0.06) were better than those of the ME (DPPH = 41.5; ABTS = 142.3; IαG = 17.5); remarkably, the ARF IαG value was about 42 times lower than that of acarbose. The main anthocyanins in ARF were pelargonidin 3-O-glucoside and cyanidin 3-O-glucoside. Thus, the consumption of red P. dulce arils could provide health benefits for prevention/treatment of chronic degenerative diseases such as diabetes.

Synthesis, crystal structure, DFT studies and photophysical properties of a copper(I)-triphenylphosphane complex based on trans-(±)-2,4,5-tris(pyridin-2-yl)-2-imidazoline.

The possibility of using less expensive and nontoxic metals, such as copper, as substitutes for more expensive heavy metals in the synthesis of new transition-metal complexes to be used as sensitizers in dye-sensitized solar cells (DSSCs) has stimulated research in this field. The novel photoluminescent copper(I) complex bis(triphenylphosphane-κP)[trans-(±)-2,4,5-tris(pyridin-2-yl)-2-imidazoline-κ2N2,N3]copper(I) hexafluorophosphate, [CuI(C18H15N5)(C18H15P)2]PF6, has been successfully synthesized and characterized by IR and 1H NMR spectroscopy, as well as by single-crystal X-ray diffraction and thermogravimetric analysis. The complex showed interesting photophysical properties, which were studied experimentally in solution and in the solid state by UV-Vis and fluorescence spectroscopy. Density functional theory (DFT) calculations with dichloromethane as solvent reproduced reasonably well the HOMO and LUMO orbitals of the title compound.

Evolution of iridium-based molecular catalysts during water oxidation with ceric ammonium nitrate.

Organometallic iridium complexes have been reported as water oxidation catalysts (WOCs) in the presence of ceric ammonium nitrate (CAN). One challenge for all WOCs regardless of the metal used is stability. Here we provide evidence for extensive modification of many Ir-based WOCs even after exposure to only 5 or 15 equiv of Ce(IV) (whereas typically 100-10000 equiv are employed during WOC testing). We also show formation of Ir-rich nanoparticles (likely IrO(x)) even in the first 20 min of reaction, associated with a Ce matrix. A combination of UV-vis and NMR spectroscopy, scanning transmission electron microscopy, and powder X-ray diffraction is used. Even simple IrCl(3) is an excellent catalyst. Our results point to the pitfalls of studying Ir WOCs using CAN.

Imidazol-2-yl complexes of Cp*Ir as bifunctional ambident reactants.

Loss of chloride ion from imidazol-2-yl complex 4a activates the H-H bond of dihydrogen or the C-H bond of acetylene, forming an Ir(III) N-heterocyclic carbene (NHC) complex (3b or 9). Deprotonation of Ir(III) hydride 4b gives one new species, formulated as Ir(I) carbene complex 5. Protonation or alkylation of 5 occurs at the metal, returning the Ir(III) core of 6a,b. Deprotonation of cationic NHC complex 3a gives neutral imidazol-2-yl analogue 4a; as seen by X-ray diffraction, the Ir-C bond in 3a is shorter than that in 4a. These and other comparisons and interconversions of NHC complexes with an NH function and related imidazol-2-yl species expand the potential of NHC complexes by showing their bifunctional character.

Finding the proton in a key intermediate of anti-Markovnikov alkyne hydration by a bifunctional catalyst.

The secondary structure of a bifunctional catalyst positions a crucial reactive proton in the final intermediate of anti-Markovnikov alkyne hydration to give an aldehyde. NMR coupling and isotopic labeling studies elucidate the location of this proton and its involvement in hydrogen bonding.

Hydrogen-bond acceptance of bifunctional ligands in an alkyne-metal pi complex.

Experiment and theory have been used to study reactive alkyne pi complexes, intermediates in anti-Markovnikov alkyne hydration by CpRu bis(phosphine) catalysts with heterocyclic substituents. Each heterocycle accepts a hydrogen bond from an acetylene C-H, as revealed by NMR coupling constants between alkyne 13C and 1H nuclei as well as between alkyne 13C and pyridine 15N (2hJCN). Moreover, further alkyne transformations occur at temperatures from 50 to 90 degrees C below what is needed to convert a control compound without the heterocycles.