Electrocatalytic properties of a novel ruthenium(II) terpyridine-based complex towards CO2 reduction

The electrocatalytic properties of Ru complexes are of great technological interest given their potential application in reactions such water splitting and CO₂ reduction. In this work, a novel terpyridine-based Ru(II) complex, [RuCl(trpy)(acpy)], trpy = 2,2':6',2''-terpyridine, acpy^- = 2-pyridylacetate was synthesized and its spectroscopic, electrochemical and catalytic properties were explored in detail. In dry acetonitrile, the complex exhibits two reduction peaks at -1.95 V and -2.20 V vs. Fc/Fc⁺, attributed to consecutive 1 e^- reduction. Under CO₂ atmosphere, a catalytic wave is observed (E_onset = 2.1 V vs. Fc/Fc⁺), with CO as the main reduction product. Bulk electrolysis reveals a turnover number (TON) of 12 (k_obs = 1.5 s^-1). In the presence of 1% water, an improvement in the catalytic activity is observed (TON_CO = 21 and k_obs = 2.0 s^-1) and, additionally, formate was also detected (TON_HCOO = 7). Spectroelectrochemical experiments allowed the identification of a metallocarboxylate (Ru-COO^-) intermediate under anhydrous conditions, while in water, the partial labilization of the acpy^- ligand was observed in the course of the catalytic cycle. The experimental data was combined with DFT calculations, allowing the proposal of a catalytic cycle. The results establish important relationships between selectivity, ligand structure and reaction conditions.

Manganese(ii) Schiff-base-mediated reversible deactivation controlled radical polymerization of vinyl acetate

The manganese Schiff-base complexes were applied in the OMRP of vinyl acetate.

Ruthenium–nickel heterobimetallic complex as a bifunctional catalyst for ROMP of norbornene and ethylene polymerization

A new multifunctional Ru–Ni heterobimetallic catalyst for ROMP and ethylene polymerization.

Fragmentation Study, Dual Anti-Bactericidal and Anti-Viral Effects and Molecular Docking of Cobalt(III) Complexes

Considering our previous findings on the remarkable activity exhibited by cobalt(III) with 2-acetylpyridine-N(4)-R-thiosemicarbazone (Hatc-R) compounds against Mycobacterium tuberculosis, the present study aimed to explored new structure features of the complexes of the type [Co(atc--R)₂]Cl, where R = methyl (Me, 1) or phenyl (Ph, 2) (¹³C NMR, high-resolution mass spectrometry, LC-MS/MS, fragmentation study) together with its antibacterial and antiviral biological activities. The minimal inhibitory and minimal bactericidal concentrations (MIC and MBC) were determined, as well as the antiviral potential of the complexes on chikungunya virus (CHIKV) infection in vitro and cell viability. [Co(atc-Ph)₂]Cl revealed promising MIC and MBC values which ranged from 0.39 to 0.78 µg/mL in two strains tested and presented high potential against CHIKV by reducing viral replication by up to 80%. The results showed that the biological activity is strongly influenced by the peripheral substituent groups at the N(4) position of the atc-R^1- ligands. In addition, molecular docking analysis was performed. The relative binding energy of the docked compound with five bacteria strains was found in the range of -3.45 and -9.55 kcal/mol. Thus, this work highlights the good potential of cobalt(III) complexes and provide support for future studies on this molecule aiming at its antibacterial and antiviral therapeutic application.

Influence of the meso-substituents on the spectral features of free-base porphyrin

The role of meso-substituents on the spectral features of free-base porphyrins is explored. Meso-tetra(4-pyridyl)porphyrin is compared with meso-tetra(2-thienyl)porphyrin and meso-tetra(pentafluorophenyl)porphyrin. Our results indicate that some of the asymmetric Q-bands in the free-base porphyrin tend to become symmetric relative to the adopted meso-substituent. The results show that the outlying perturbations lead the free-base quasi-degenerated Q_x1, Q_x2, Q_y1, and Q_y2 bands to be closer in energy. Combined, absorption, fluorescence and Raman spectroscopies endorse our conclusions showing that both the frequencies and the Huang-Rhys factors associated with every vibronic progression are noticeably affected by the investigated meso-substituents. Our results confirm that the B-band is also multi-featured in agreement with what is found for the Q-bands.

Intramolecular C(sp2)–C (sp2) bond formation between phenanthroline and β-diketone thiosemicarbazones in PtII complexes: crystal structures and computational studies

[PtCl₂(phen)] reacts with β-diketone derived thiosemicarbazones leading to an intramolecular C–C coupling and formation of tetracoordinated N,N,N,S-chelates [Pt^II(phenL^R)].

Evolution of electronic and vibronic transitions in metal(II) meso-tetra(4-pyridyl)porphyrins

The changing of the electronic and vibronic states due to the insertion of Zn(II), Cu(II), Ni(II) or Co(II) ions in the meso-tetrakis(4-pyridyl)porphyrin ring center is investigated. The combination of absorption, photoluminescence, Raman and infrared spectroscopies with second-derivative-based spectral deconvolution analysis reveals that the structuration of both B- and Q-bands is very sensitive to the decorating ion. Similar to free base porphyrins, metal(II) meso-tetra(4-pyridyl)porphyrins also present their Q-band constituted of multiple electronic transitions, where the central ion plays an important role in the selection of vibration modes that mediate the vibronic transitions. Our novel results will expand and reinterpret current assignments for metal(II) meso-tetra(4-pyridyl)porphyrins vibrational modes available in the literature.

Novel insights on the vibronic transitions in free base meso-tetrapyridyl porphyrin

We present novel results on the free base 5,10,15,20-meso-tetra(pyridyl)-21H,23H-porphyrin (H₂TPyP). This molecule presents complex electronic and vibrational properties and despite the vast literature reporting the transitions observed in its absorption and fluorescence spectra, a more accurate interpretation has been kept elusive. In particular, we show that the molecule's Q-band develops into many electronic and vibronic transitions, whose the well-known "four orbital model" finds it difficult to reconcile. Using distinct spectroscopy techniques, we conclude that both Q_x- and Q_y-bands comprise, in fact, two quasi-degenerated electronic states together with their respective vibronic progressions each. The analysis of the Huang-Rhys factors and complementary time- and polarization-resolved measurements reinforce the need for the proposed Q-band multi features remodeling.

New dmso–ruthenium catalysts bearing N-heterocyclic carbene ligands for the ring-opening metathesis of norbornene

New dimethyl sulfoxide ruthenium(ii) complexes bearing aryl-substituted NHC ligands as pre-catalysts for ROMP of norbornene.

Correlation between pH and molar iron/ligand ratio during ciprofloxacin degradation by photo-Fenton process: Identification of the main transformation products

Ciprofloxacin has been determined with high frequency in studies involving environmental waters matrixes. However, no study evaluating the correlation between the initial pH and molar iron/organic ligand ratio has been published. This paper describes the degradation of the antibiotic ciprofloxacin by the photo-Fenton process using different sources of iron (Fe²⁺, Fe³⁺ and Fe³⁺-citrate and Fe³⁺-oxalate, named FeCit and FeOx, respectively) and molar iron/organic ligand ratios at initial pH values of 2.5 and 6.5. The best results at initial pH 2.5 were achieved using FeCit and FeOx at molar iron/organic ligand ratios of 1:1 and 1:3 respectively, when the ciprofloxacin concentration reached values below the quantitation limit of the HPLC after 20 min of treatment. However, at initial pH 6.5, improvements in the results (15% for FeCit, and 46% for FeOx) were achieved by increasing the molar iron/organic ligand ratios to 1:4 (FeCit) and 1:9 (FeOx), respectively. Three transformation products, (C₁₇H₁₉FN₃O₄, m/z 348; C₁₇H₂₁FN₃O₅, m/z 366; and C₁₃H₁₂FN₂O₃, m/z 263) of ciprofloxacin degradation were identified, one of them not yet being reported in the literature (C₁₇H₂₁FN₃O₅, m/z 366). Their formation and degradation was monitored and the initial steps of their formation and degradation were proposed. The results show that the piperazine ring is more susceptible to hydroxyl radical attack than the quinolone ring, which persists in the intermediates identified. Therefore, this process can be a good alternative for the treatment of this type of pollutant at near-neutral conditions.

Integrating coagulation-flocculation and UV-C or H2O2/UV-C as alternatives for pre- or complete treatment of biodiesel effluents

The feasibility of biodiesel effluent treatment combining coagulation-flocculation with a photolytic process was evaluated, being the photolytic process involving the irradiation of the effluent by UV-C, or by UV-C irradiation with simultaneous addition of H₂O₂ (H₂O₂/UV-C). The coagulation-flocculation was performed at the natural pH of the effluent (pH 2.9) using different Fe³⁺ salts (chloride, nitrate and sulfate) at different concentrations (0.25, 0.50 and 1.0 mmol L^-1) of the counterions. The best results were achieved using 0.50 mmol L^-1 Fe(NO₃)₃. Following, the degradation of the organic load and toxicity reduction of the pre-treated effluent by UV-C irradiation was evaluated. The H₂O₂/UV-C process showed to be advantageous, mainly when multiple additions of H₂O₂ were used during the course of the reaction. Additionally, the influence of the initial pH on the degradation was also evaluated. A high level of mineralization (94%) was achieved after 6 h of irradiation concomitantly with multiple additions of 2,000 mg L^-1 H₂O₂, and with the effluent at the natural pH. Thus, using coagulation-flocculation followed by the H₂O₂/UV-C process, it was possible to achieve a favourable condition for reuse of the pre-treated effluent, since, in addition to the significant reduction of the organic load, the final DBO₅ (<120 mg L^-1) and oils & fats (<50 mg L^-1) are below the limits established by the Brazilian legislation. Furthermore, a reduction of 78% of acute toxicity to V. fischeri (from 89% to 20%) was reached. The results suggest, therefore, that this process is a viable option for treatment of this kind of effluent.

Optimization of fipronil degradation by heterogeneous photocatalysis: Identification of transformation products and toxicity assessment

In this work it was studied the degradation of the insecticide fipronil (FIP) by heterogeneous photocatalysis induced by TiO₂ P25. Using chemometric methods (Factorial Design and Response Surface Methodology), it was possible to evaluate the role of interaction between pH of the reaction medium, the reaction time and concentration of TiO₂, optimizing the conditions for degradation using artificial radiation. Under the optimized conditions (79.4 mg L^-1 TiO₂ and 66.3 min of reaction time for 1.1 mg L^-1 of FIP, at pH 5.6-5.8 (natural pH of the irradiated suspension)), 90.9% of FIP degradation was achieved at a degradation rate of 1.54 × 10^-2 m² kJ^-1 in terms of accumulated UVA radiation, corresponding to a pseudo-first order rate constant of 1.34 × 10^-2 min^-1 and a half-life of 51.7 min. Under the same conditions, these assays were extended to the use of solar radiation, when the degradation rate was 14% higher, with half-life of 45 min, suggesting that in both cases FIP degradation was successful. Four by-products of FIP photocatalytic degradation could be separated, identified, and their formation and consumption followed by UHPLC-Q-TOF. Although the same intermediates have been obtained using both irradiation sources, a faster degradation of the transformation products (TPs) was observed under solar irradiation due to its expressive photonic flux covering the UVA and UVB. It is noteworthy that both the untreated effluent and the identified compounds have low toxicity with respect to V. fischeri, suggesting that the heterogeneous photocatalysis may be a good alternative for treatment of wastewaters containing FIP and its TPs, mainly when solar radiation is the source of radiation, since under this condition the power consumption during the treatment can be significantly reduced.

Degradation of Direct Red 81 mediated by Fenton reactions: multivariate optimization, effect of chloride and sulfate, and acute ecotoxicity assessment

The role of different operational parameters related to Fenton reactions (pH, concentration of Fe²⁺ and H₂O₂, and reaction time) and of Cl^- and SO ₄^- was investigated in the degradation of the azo dye Direct Red 81, expressed in terms of its decolorization. The factorial design and Pareto's charts showed that only Fe²⁺ concentration and pH influence the decolorization under the conditions evaluated. So, only these parameters were optimized using the response surface model. Under the best experimental conditions (initial pH 2.5, 11 mg L^-1 Fe²⁺, 78 mg L^-1 H₂O₂, and 20 min of reaction), 94 % of decolorization was achieved. However, even under the these conditions, but in the presence of Cl^- and SO ₄^- , a striking loss of efficiency was observed as the concentration of these ions was increased, due the formation of chloride- and sulfate-iron complexes and less reactive inorganic radicals (Cl₂^•- and SO₄^•-). The results show that the presence of Cl^- is more deleterious, since sulfate-iron complexes are more reactive towards H₂O₂, and the SO₄^•- turns out to favor the degradation. On the other hand, the  negative effect of Cl^- can be compensated by increasing the chloride concentration up to 300 mmol L^-1. In addition, although a high degradation level has been obtained by monitoring the dye absorbance and by HPLC-UV, a low mineralization occurred, being generated degradation products of higher ecotoxicity to Vibrio fischeri, showing the need of subsequent studies to identify these compounds as well as the application of additional treatments aiming the complete mineralization of the dye.

Structural characterization of Ag-doped TiO2 with enhanced photocatalytic activity

Ag-doped TiO₂ nanoparticles with different metallic content (0.5, 2.0, and 5.0% m/m) were prepared using a simple and cost-effective method based on a sol–gel technique, followed by thermal treatment.

Degradation of caffeine by photo-Fenton process: optimization of treatment conditions using experimental design

The degradation of caffeine in different kind of effluents, via photo-Fenton process, was investigated in lab-scale and in a solar pilot plant. The treatment conditions (caffeine, Fe(2+) and H(2)O(2) concentrations) were defined by experimental design. The optimized conditions for each variable, obtained using the response factor (% mineralization), were: 52.0 mg L(-1)caffeine, 10.0 mg L(-1)Fe(2+) and 42.0 mg L(-1)H(2)O(2) (replaced in kinetic experiments). Under these conditions, in ultrapure water (UW), the caffeine concentration reached the quantitation limit (0.76 mg L(-1)) after 20 min, and 78% of mineralization was obtained respectively after 120 min of reaction. Using the same conditions, the matrix influence (surface water - SW and sewage treatment plant effluent - STP) on caffeine degradation was also evaluated. The total removal of caffeine in SW was reached at the same time in UW (after 20 min), while 40 min were necessary in STP. Although lower mineralization rates were verified for high organic load, under the same operational conditions, less H(2)O(2) was necessary to mineralize the dissolved organic carbon as the initial organic load increases. A high efficiency of the photo-Fenton process was also observed in caffeine degradation by solar photocatalysis using a CPC reactor, as well as intermediates of low toxicity, demonstrating that photo-Fenton process can be a viable alternative for caffeine removal in wastewater.

Synthesis and Antitumor Evaluation of Benzopsoralen Analogues

The synthesis of five new tetracyclic benzopsoralen analogues, compounds 2-6, with 9H-xanthen-9-one or 9H-carbazole frameworks, is described. Their inhibitory effects on the growth of three human tumor cell lines (MCF-7, SF-268, and NCI-460) were evaluated, and discussed in terms of structure-activity relationship, taking into account both geometric and electronic features. Generally, the angular compounds showed significant biological activities, but the arrangement of functional groups also contributed to the overall activity.

Evaluation of nanoparticles loaded with benzopsoralen in rat peritoneal exudate cells

Psoralens are widely used for the treatment of hyperproliferative skin disease. In this work, we prepared nanoparticles (NP) containing a benzopsoralen (3-ethoxy carbonyl-2H-benzofuro[3,2-f]-1-benzopiran-2-one) by the solvent evaporation technique. We evaluated important NP parameters such as particle size, drug encapsulation efficiency, effect of the encapsulation process over the drug's photochemistry, zeta potential, external morphology, and in vitro release behavior. We also investigated the nanoparticle as a drug delivery system (DDS), as well as its target delivery to the action site, which is a very important parameter to increase the therapeutic use of psoralens and to reduce their side effects. The uptake of benzopsoralen-loaded PLGA nanoparticles by different kinds of cells found in rat peritoneal exudates was also studied. The photodamage promoted by irradiation with UV light revealed morphological characteristics of cell damage such as cytoplasmic vesiculation, mitochondrial damage, and swelling of both the granular endoplasmatic reticulum and nuclear membrane. This encapsulation method maintained the drug's properties and improved drug delivery to the target cell.

Psoralen analogues: synthesis, inhibitory activity of growth of human tumor cell lines and computational studies

Eight psoralens have been evaluated for their ability to inhibit the in vitro growth of three human tumor cell lines representing different tumor types, MCF-7 (breast cancer), NCI-H460 (non-small cell lung cancer) and SF-268 (CNS cancer). The synthesis of four new psoralens (benzofurocoumarins) is presented as well as the results of the ab initio calculations to find the parameters that relate the structure with the antitumor activity. This work provides supplementary information that could allow the development of new psoralen analogues with this type of biological activity.

Preparation of 100nm diameter unilamellar vesicles containing zinc phthalocyanine and cholesterol for use in photodynamic therapy

An efficient (89-95% yield) and low-cost procedure to prepare unilamellar vesicles was used to incorporate zinc phthalocyanine (ZnPc), a model compound used as a phototherapeutic agent in studies aiming the use of unilamellar vesicles as delivery system for photodynamic therapy (PDT). ZnPc was incorporated in the presence or absence of cholesterol (CHOL), which improved the stability of the delivery system. The net vesicles present a mean diameter around 1000 nm, whereas in the presence of CHOL, CHOL and ZnPc, or only ZnPc, a drastic reduction in its diameter, varying between 100 and 150 nm, was observed. The incorporation of only ZnPc also results in a considerable reduction in the diameter of the liposomes suggests that ZnPc, due to its high hidrophobicity, must share the same microenvironment occupied by CHOL molecules.

Paper mill wastewater detoxification by solar photocatalysis

In the WATER project the German Aerospace Center, and the Universidade Federal de Uberlândia, analyse the possibilities of treating paper mill effluents by solar photocatalysis for the paper mill of the Brazilian paper producer Votorantim Celulose e Papel, VCP, at Luiz Antônio, SP, Brazil. The degradation of the bio-polymer lignin is a vast problem in paper production. The tests have shown that treatment by the photocatalyst TiO2 and solar radiation is an ecological future oriented approach to solve this problem. The treatment of lignin containing process water by solar photocatalysis was optimised and the economics for solar treatment plants of different sizes was estimated to check the possibilities for implementing the technology in industrial processes.