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 (Eonset = 2.1 V vs. Fc/Fc+), with CO as the main reduction product. Bulk electrolysis reveals a turnover number (TON) of 12 (kobs = 1.5 s-1). In the presence of 1% water, an improvement in the catalytic activity is observed (TONCO = 21 and kobs = 2.0 s-1) and, additionally, formate was also detected (TONHCOO = 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.

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-R1- 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.

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

[PtCl2(phen)] reacts with thiosemicarbazones derived from ß-diketones (H2LR) leading to an intramolecular C-C coupling between phen and the ketone upon formation of tetradentate N,N,N,S chelates [PtII(LRphen)]. The reactions proceed via bidentate coordination of the doubly deprotonated (LR)2- followed by an intra-nucleophilic attack and consecutive C-C bond formation.

In vitro leishmanicidal activity and theoretical insights into biological action of ruthenium(II) organometallic complexes containing anti-inflammatories.

Leishmaniasis, a neglected tropical disease caused by protozoans of the genus Leishmania, kills around 20-30 thousand people in Africa, Asia, and Latin America annually and, despite its potential lethality, it can be treated and eventually cured. However, the current treatments are limited owing to severe side effects and resistance development by some Leishmania. These factors make it urgent to develop new leishmanicidal drugs. In the present study, three ruthenium(II) organometallic complexes containing as ligands the commercially available anti-inflammatories diclofenac (dic), ibuprofen (ibu), and naproxen (nap) were synthesized, characterized, and subjected to in vitro leishmanicidal activity. The in vitro cytotoxicity assays against Leishmania (L.) amazonensis and Leishmania (L.) infantum promastigotes have shown that complexes [RuCl(dic)(η6-p-cymene)] (1) and [RuCl(nap)(η6-p-cymene)] (3) were active against both Leishmania species. Complex [RuCl(ibu)(η6-p-cymene)] (2) has exhibited no activity. The IC50 values for the two active complexes were respectively 7.42 and 23.55 µM, for L. (L.) amazonensis, and 8.57 and 42.25 µM, for L. (L.) infantum. Based on the toxicological results and computational analysis, we proposed a correlation between the complexes and their activity. Our results suggest both complexation to ruthenium(II) and ligands structure are key elements to leishmanicidal activity.

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.

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 spectroscopic characterization of two tetrasubstituted cationic porphyrin derivatives.

An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by (1)H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed.

Photoinactivation of different human tumor cell lines and sheep red blood cells in vitro by liposome-bound Zn(II) Phthalocyanine: Effects of cholesterol.

The in vitro photoinactivation of human tumor cell lines and sheep red blood cells (SRBC) by Zinc (II) Phthalocyanine (ZnPc) was investigated using unilamellar liposome (LUV) as delivery system, in the presence and absence of cholesterol (CHOL) in the formulation. The presence of CHOL improves the stability of the system showing to be essential for the photodynamic action of ZnPc. LUVs prepared without CHOL did not present any antiproliferative effects neither induced significant photohaemolysis. The presence of ZnPc in the culture medium caused total cell growth inhibition (TGI) only at concentrations higher than 250 micromol dm(-3). For ZnPc in LUV/CHOL (mass ratio=3:1), the mean TGI values for almost all studied cells were around 80 micromol dm(-3), and 14 micromol dm(-3) for human ovarian carcinoma (NIH: OVCAR-3) cells. The cytoplasmic components of OVCAR-3 and SRBC when irradiated in presence of ZnPc in LUV/CHOL were completely destroyed, culminating in cell swelling, lysis and death by necrosis.

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.

Preparation of 100 nm 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.

Theoretical and experimental studies on the adsorption of aromatic compounds onto cellulose.

The adsorption of several aromatic compounds over microcrystalline cellulose was studied by molecular modeling and experimentally using gas chromatography. Experimental adsorption enthalpies were obtained from an equation based on Clausius-Clapeyron formalism and the temperature dependence of retention volume at infinite dilution. Four different cellulose surfaces (three crystalline (110, 100, and 010) and one amorphous) were modeled. Overall strong agreement was observed between the experimental and theoretical work with 84% of the adsorbate-cellulose systems having differences between measured and predicted values of less than 20%. Based on both calculated and experimental data, a morphology for the microcrystalline cellulose as a weighted combination of the four surfaces was proposed: 39% (110), 28% (100), 10% (010), and 23% amorphous. By adopting this distribution, differences between experimental and weighted average predicted adsorption energies were 10% or less for 14 out of 17 compounds; a maximum of 15% was observed for guaiacol. Experimental results for monosubstituted aromatic compounds revealed that adsorption enthalpies are related to the hydrophilic/hydrophobic character of the substituent groups: 3.5 kJ mol(-1) for a methyl group, 15.7 kJ mol(-1) for a double bond, 21.0 kJ mol(-1) for a methoxyl group, 22.8 kJ mol(-1) for a carbonyl group, and 27.6 kJ mol(-1) for a hydroxyl group. These tendencies were confirmed by modeling, except for the aldehyde carbonyl group, where an overestimation of 10.8 kJ mol(-1) was observed. Analysis of experimental and predicted adsorption enthalpies of multisubstituted aromatic compounds suggests that the efficiency of their interaction with cellulose depends on a compromise between the roughness of the cellulose surface and their conformational adaptability.