Electrocatalytic activity in sensing of nitrite by films produced by electropolymerization of [Fe(Br-ph-tpy)₂]²⁺

<p>Nitrite is a preservative agent broadly used in the food industry. Its excessive consumption can cause several diseases including cancer. Thus, the development of sensors for nitrite is indispensable for strict nitrite level control in industrialized products and consequently for human welfare. Herein, is presented a study of the modification of electrodes by electropolymerization of [Fe(Br-ph-tpy)₂](PF₆)₂ and its use as electroactive films in sensing of nitrite. The films were characterized by cyclic voltammetry, electrochemical quartz crystal microbalance, atomic-force microscopy and they were employed in electroanalytical experiments. The film obtained by electropolymerization exhibited some fibers dispersed on the substrate, reflecting the formation polymers on the surface of the electrode. The electrodes were further improved by drop casting a film of the complex on a glass carbon electrode, and then performing the electropolymerization of the complex. An increase in stability and a 41% enhancement of the electrocatalytical response for nitrite ions have been observed, in comparison with the bare electrode.</p

Photocatalytic Activity of Reduced Graphene Oxide–Gold Nanoparticle Nanomaterials: Interaction with Asphaltene and Conversion of a Model Compound

Asphaltenes are residual materials from the oil industry and are usually converted, after exhaustive distillation, into coke and asphalt. However, conversion of asphaltenes into more valuable raw materials, for instance, by photocatalytic cracking using suitable catalysts, would be a better, more economic option. To explore this idea, we combined the electronic and chemical properties of asphaltene and graphene derivatives with the plasmonic nature of gold nanoparticles. For this purpose, a hybrid material was generated <i>in situ</i>, containing reduced graphene oxide and gold nanoparticles (RGO@AuNP). Evaluation of the interaction between the hybrid material and asphaltenes by hyperspectral dark-field optical microscopy indicated the occurrence of charge transfer between the two species. Using 9-anthraldehyde (9-ATA) as a model compound for asphaltene, photocatalytic experiments performed with RGO@AuNP at room temperature, under visible light irradiation, revealed the formation of cyclic endoperoxides, which undergo further reactions, resulting in their cleavage, with 90% yield for the 9-ATA degradation

Electrostatic bending and outer-sphere intervalence transfer in a flexible ligand-bridged ruthenium(III)-iron(II) complex

<p>In the mixed-valence complex [Ru^III(NH₃)₅(μ-dpypn)Fe^II(CN)₅] with the flexible bridging ligand 1,3-di(4-pyridyl)propane (dpypn), electrostatic interactions between the {Ru(NH₃)₅}³⁺ and {Fe(CN)₅}³⁻ moieties drive a strong bending of dpypn and approximation of the Ru^III and Fe^II centers, from which the enhanced electronic coupling between metal ions produces an intense intervalence-transfer absorption in the near-infrared region. Density functional theory calculations corroborate both the electrostatic bending in this heterobinuclear complex and a linear geometry in the homobinuclear counterparts [Ru(NH₃)₅(μ-dpypn)Ru(NH₃)₅]⁵⁺ and [Fe(CN)₅(μ-dpypn)Fe(CN)₅]⁵⁻, for which no evidence of electronic coupling was found because of the separation between metal centers. Furthermore, the heterobinuclear species formed an inclusion complex with β-cyclodextrin where the imposed linear geometry prevents significant electronic coupling and intervalence charge transfer between the Ru^III and Fe^II centers.</p

Surface Enhanced Raman Spectroelectrochemistry of a μ‑Oxo Triruthenium Acetate Cluster: An Experimental and Theoretical Approach

Surface enhanced Raman spectroelectrochemistry (SERS) spectroelectrochemistry provides a very sensitive technique to investigate the vibrational characteristics of coordination compounds and their particular behavior under the influence of plasmonic surfaces, concomitant with the exploitation of their redox properties and electronic spectra. The results, however, depend upon the mechanisms involved in the intensification of Raman spectra associated with the electromagnetic, resonance Raman and charge-transfer excitation at the Fermi levels. By probing the model complex [(Ru₃O)­(CH₃COO)₆­(4,4′-bipy)₃]<i>ⁿ</i> (<i>n</i> = 1, 0, −1) adsorbed onto rough gold electrode surfaces, contrasting SERS profiles were obtained at several successive redox potentials and oxidation states, which enables a critical discussion on the role of the complex interaction with the gold surface, and the influence of the specific electronic bands in the triruthenium acetate cluster. Density functional theory (DFT) and time-dependent DFT calculations were carried out for the complex bound to an Au₂₀ cluster to show the participation of active lowest unoccupied molecular orbital levels centered on the gold atoms. The corresponding charge-transfer band was predicted around 1200 nm, which supports a charge-transfer interpretation for the SERS response observed at λ_exc = 1064 nm. The selective enhancement of the vibrational modes was discussed based on the Raman theoretical calculations

Green Processing of Strategic Elements Based on Magnetic Nanohydrometallurgy

<div><p>Magnetic nanohydrometallurgy (NHM) is a new process based on engineered superparamagnetic nanoparticles capable of performing as complexing agents for extracting and recovering strategic metals from mineral sources and urban wastes, as well as for removing hazardous elements from contaminated water. Its principles and application are reviewed in this paper. Typical examples involving copper, silver and mercury processing are here discussed, including the exploitation of a novel nanotechnological strategy for capturing and fractionating rare earth elements.</p></div

Superparamagnetic Maghemite-Based CdTe Quantum Dots as Efficient Hybrid Nanoprobes for Water-Bath Magnetic Particle Inspection

Fluorescent water-based cadmium telluride quantum dots (QDs) and citrate-functionalized maghemite nanoparticles (MghNPs) were synthesized and assembled together (MghNPs@QDs) through electrostatic interactions by using cetyltrimethylammonium bromide (CTAB) as a linker and steric spacer to minimize the Förster resonance energy transfer (FRET) restriction. A whole family of hybrid and multifunctional nanoparticles has been successfully obtained, exhibiting good performance in nondestructive water-bath magnetic particle inspection (MPI) assays

Non-innocent behavior of 1-(2′-pyridylazo)-2-naphtholate coordinated to polypyridine ruthenium(II) complexes

<div><p>The study of non-innocent redox behavior of ligands is important for the development of new catalysts and to comprehend the function of bioinorganic molecules in biochemical processes. In this work, we present a description of the non-innocent behavior of 1-(2′-pyridylazo)-2-naphtholate (pan) coordinated to ruthenium complexes. The synthesis and characterization of a series of [Ru(pan)(PPh₃)(L)]PF₆ complexes [where L = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (dmbpy), and 1,10-phenanthroline (phen)] are presented. UV–vis analyses of the studied ruthenium complexes show intense absorptions from intraligand <i>π</i>–<i>π</i>* and metal-to-ligand charge-transfer transitions bands in the visible region. This observation shows a significant contribution of the pan ligand in all electronic transitions and is the indicative of non-innocent behavior. Theoretical calculations were carried out to support the UV–vis spectral assignments. Non-innocent behavior of pan was observed and confirmed using the electrochemical parameter <i>E</i>_L(L) and by electrochemical studies. The pan ligand is non-innocent and can be modulated by donor and acceptor character of the other ligands present in the coordination sphere of the complex.</p></div

Unusual Photooxidation of S‑Bonded Mercaptopyridine in a Mixed Ligand Ruthenium(II) Complex with Terpyridine and Bipyridine Ligands

An unusual photooxidation of a coordinated 4-mercaptopyridine (<i>S</i>pyH) ligand in the [Ru­(Hmctpy)­(dmbpy)­(κ<i>S</i>-SpyH)]²⁺complex (Hmctpy = 4′-carboxy-2,2′;6′,2″-terpyridine, dmbpy = 4,4′-dimethyl-2,2′-bipyridine) takes place under visible and UV irradiation, in aerated acetonitrile. The [Ru­(mctpy)­(dmbpy)­(κ<i>S</i>-SO₂py)] sulfinato product has been characterized by a variety of methods, including X-ray diffraction which supports the presence of the Ru-κ<i>S-S</i>pyH isomer in the starting complex. The photooxidation of the 4-mercaptopyridine ligand enhances the back-bonding interactions in the complex by means of the strongly acceptor 4-pyridinesulfinato-SO₂py species, increasing the redox potential of the Ru­(III)/Ru­(II) couple significantly from 1.23 to 1.62 V. It also led to pronounced changes in the electronic and NMR spectra of the complexes, corroborated by DFT and ZINDO-S calculations. A possible mechanism based on referenced data of photooxidation has been proposed, which involves the formation of a reactive oxygen species and intermediate endoperoxide species, yielding a very stable Ru-sulfinato product. This novel species exhibits stronger luminescence (Φ_<i>f</i> = 0.004) than the starting complex under UV excitation

Unveiling the Structure of Polytetraruthenated Nickel Porphyrin by Raman Spectroelectrochemistry

The structure of polytetraruthenated nickel porphyrin was unveiled for the first time by electrochemistry, Raman spectroelectrochemistry, and a hydroxyl radical trapping assay. The electrocatalytic active material, precipitated on the electrode surface after successive cycling of [NiTPyP­{Ru­(bipy)₂Cl}₄]⁴⁺ species in strong aqueous alkaline solution (pH 13), was found to be a peroxo-bridged coordination polymer. The electropolymerization process involves hydroxyl radicals (as confirmed by the characteristic set of DMPO/^•OH adduct EPR peaks) as reaction intermediates, electrocatalytically generated in the 0.80–1.10 V range, that induce the formation of Ni–O–O–Ni coordination polymers, as evidenced by Raman spectroelectrochemistry and molecular modeling studies. The film growth is halted above 1.10 V due to the formation of oxygen gas bubbles