Syntheses, Characterization, and Antioxidant Evaluation of Cu2+, Mn2+, and Fe3+ Complexes with a 14 Membered EDTA-Derived Macrocycle.

The Cu2+, Mn2+, and Fe3+ complexes of a 14 membered macrocycle were synthesized and their antioxidant capacities were evaluated against ABTS and DPPH radicals, with the objective of collecting insights into the biomimetic role of the central metal ions. The macrocycle, abbreviated as H2L14, is a derivative of EDTA cyclized with 1,4-diamine, and the moderately flexible macrocyclic frame permits the formation of [ML14·H2O] chelates with octahedral coordination geometries common among the metal ions. The metal complexes were characterized by electrospray-ionization mass spectrometry, Fourier transform infrared spectroscopy, and Raman and X-ray photoelectron spectroscopic methods, as well as thermogravimetric analysis; the octahedral coordination geometries with water coordination were optimized by DFT calculations. The antioxidant assays showed that [FeL14·H2O]+ was able to scavenge synthetic radicals with moderate capacity, whereas the other metal chelates did not show significant activity. The Raman spectrum of DPPH in solution suggests that interaction was operative between the Fe3+ chelate and the radical so as to cause scavenging capability. The nature of the central metal ions is a controlling factor for antioxidant capacity, as every metal chelate carries the same coordination geometry.

Synthesis, Characterization, and Cu(2+) Coordination Studies of a 3-Hydroxy-4-pyridinone Aza Scorpiand Derivative.

The synthesis, acid-base behavior, and Cu(2+) coordination chemistry of a new ligand (L1) consisting of an azamacrocyclic core appended with a lateral chain containing a 3-hydroxy-2-methyl-4(1H)-pyridinone group have been studied by potentiometry, cyclic voltammetry, and NMR and UV-vis spectroscopy. UV-vis and NMR studies showed that phenolate group was protonated at the highest pH values [log K = 9.72(1)]. Potentiometric studies point out the formation of Cu(2+) complexes of 1:2, 2:2, 4:3, 1:1, and 2:1 Cu(2+)/L1 stoichiometries. UV-vis analysis and electrochemical studies evidence the implication of the pyridinone moieties in the metal coordination of the 1:2 Cu(2+)/L1 complexes. L1 shows a stronger chelating ability than the reference chelating ligand deferiprone. While L1 shows no cytotoxicity in HeLa and ARPE-19 human cell lines (3.1-25.0 µg/mL), it has significant antioxidant activity, as denoted by TEAC assays at physiological pH. The addition of Cu(2+) diminishes the antioxidant activity because of its coordination to the pyridinone moiety phenolic group.

Optical Anion Receptors with Urea/Thiourea Subunits on a TentaGel Support.

Two simple chemosensors with urea (L1) and thiourea (L2) groups were synthesized and studied by different spectroscopic techniques. Both receptors can sense acetate (Ac-), dihydrogen phosphate (H2PO4 -), and fluoride (F-) anions, accompanied by changes in UV-vis and 1H NMR spectra, and an optical response is observed as a color change of the solutions due to deprotonation and hydrogen-bonding processes. Also, L1 and L2 were supported on TentaGel resins (R1 and R2), and their fluoride-sensing properties in DMSO and water solutions were studied. Interestingly, R2 can sense fluoride ions in sample solutions of 100% water.

Formulation of anomerization and protonation in d-glucosamine, based on 1H NMR.

The major anomer of non-protonated neutral d-glucosamine GlcN0 is the ß-form, while the α-anomer is dominant for protonated cationic glucosamine GlcNH+. The present work confirmed correlation between the anomerization and the protonation by simultaneous determination of signal intensity and chemical shift in pD-variation 1H NMR, and formulated the equilibrium constants between subspecies α-GlcN0, ß-GlcN0, α-GlcND+, and ß-GlcND+ to interpret the correlation. The individual anomerization constants, Kan = [ßGlcN]/[αGlcN] and KanD = [ßGlcND+]/[αGlcND+], are linked to each other through the relation KDα∙KanD = KDß∙Kan with the deuteration constants KDα and KDß of the anomers. The anomer populations are stimulated by OD- and D+ ions in the dose-response form. The acidic deuteron in α-GlcND+ is populated mostly at the nitrogen atom, whereas the population in ß-GlcND+ is comparable at nitrogen and anomeric oxygen; this difference is consistent with the basicity of the nitrogen and the anomerization process of glucosamine.

Comparative Studies of Structures and Peroxidase-like Activities of Copper(II) and Iron(III) Complexes with an EDTA-Based Phenylene-Macrocycle and Its Acyclic Analogue.

With the objective of studying the conformational and macrocyclic effects of selected metal chelates on their peroxidase activities, Cu2+ and Fe3+ complexes were synthesized with a macrocyclic derivative of ethylenediaminetetraacetic acid and o-phenylenediamine (abbreviated as edtaodH2) and its new open-chain analogue (edtabzH2). The Fe3+ complex of edtaodH2 has a peroxidase-like activity, whereas the complex of edtabzH2 does not. The X-ray study of the former shows the formation of a dimeric molecule {[Fe(edtaod)]2O} in which each metal with an octahedral coordination is overposed over the macrocyclic cavity, as a result of rigid macrocyclic frame, to form an Fe-O-Fe bridge; the exposure of the central metal to the environment facilitates the capture of oxygen to drive the biomimetic activity. The peroxidase-inactive Fe3+ complex consists of a mononuclear complex ion [Fe(edtabz)(H2O)]+, the metal ion of which is suited in a distorted pentagonal bipyramid to be protected from environmental oxygen. The copper(II) complexes, which have mononuclear structures with high thermodynamic stability compared with the iron(III) complexes, show no peroxidase activity. The steric effects play a fundamental role in the biomimetic activity.

Silver nanoparticles synthesized with Rumex hymenosepalus extracts: effective broad-spectrum microbicidal agents and cytotoxicity study.

We synthesized silver nanoparticles using Rumex hymenosepalus root extract (Rh). Nanoparticles were subjected to a purification process and final product is a composite of Rh and silver nanoparticles (AgNPsC). Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to perform a microstructure study. Additionally, two fractions (RhA and RhB) were obtained from the original extract by filtration with tetrahydrofuran (THF); both fractions were analyzed using UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and 2,2-diphenyl-1-picrylhydrazyl (DPPH); total polyphenol content was also determined. Separate inhibition tests for AgNPsC and RhA and RhB were applied to Gram-positive bacteria, Gram-negative bacteria, and yeast (Candida albicans) using the well diffusion method. Extract fractions were found to have inhibitory effects only over Gram-positive bacteria, and silver nanoparticles showed inhibitory effects over all the evaluated microorganisms. Cytotoxicity was evaluated using the tetrazolium dye (MTT) assay in mononuclear peripheral blood cells. In addition, we assessment AgNPsC in THP-1 monocyte cell line, using the cell viability estimation by trypan blue dye exclusion test (TB) and Live/Dead (LD) cell viability assays by confocal microscopy.

A ¹H NMR Investigation of the Interaction between Phenolic Acids Found in Mango (Manguifera indica cv Ataulfo) and Papaya (Carica papaya cv Maradol) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) Free Radicals.

The benefits of phenolic acids on human health are very often ascribed to their potential to counteract free radicals to provide antioxidant protection. This potential has been attributed to their acidic chemical structure, which possesses hydroxyl groups in different positions. Phenolic acids can interact between themselves and exhibit an additive, antagonistic or synergistic effect. In this paper, we used 1H NMR to analyze the interactions and mechanisms that are present in major phenolic acids found in mango (gallic, protocatechuic, chlorogenic and vanillic acids) and papaya (caffeic, ferulic and p-coumaric acids), and the DPPH radical was used to evaluate the effect of the antioxidant mixtures. The interactions were found to occur via hydrogen bonds between the -OH and -COOH groups. Moreover, the phenolic acids exhibit two types of mechanisms for the neutralization of the DPPH radical. According to the results, these two mechanisms are Hydrogen Atom Transfer (HAT) and Single Electron Transfer (SET). The ability of the phenolic acid to neutralize the DPPH radical decreases in the following order in mango: gallic > chlorogenic > protocatechuic > vanillic. Moreover, within the acids found in papaya, the order was as follows: caffeic > p-coumaric > ferulic.

Synthesis of silver nanoparticles using reducing agents obtained from natural sources (Rumex hymenosepalus extracts).

We have synthesized silver nanoparticles from silver nitrate solutions using extracts of Rumex hymenosepalus, a plant widely found in a large region in North America, as reducing agent. This plant is known to be rich in antioxidant molecules which we use as reducing agents. Silver nanoparticles grow in a single-step method, at room temperature, and with no addition of external energy. The nanoparticles have been characterized by ultraviolet-visible spectroscopy and transmission electron microscopy, as a function of the ratio of silver ions to reducing agent molecules. The nanoparticle diameters are in the range of 2 to 40 nm. High-resolution transmission electron microscopy and fast Fourier transform analysis show that two kinds of crystal structures are obtained: face-centered cubic and hexagonal.