Showing: 10 from total: 2087 publications
71. Unexpected conversion of 4-oxo-4H-chromene-2-carboxylic acid to 2-(1,3-benzothiazol-2-yl)-4H-chromen-4-one and spiro[1,4-benzothiazine-2,2 '-chromene]-3,4 '(3 ' H,4H)-dione
Cagide, F ; Gomes, LR ; Low, JN ; Borges, F
in CHEMISTRY OF HETEROCYCLIC COMPOUNDS, 2022, ISSN: 0009-3122,  Volume: 58, 
Article,  Indexed in: crossref, scopus, wos 
Abstract 2-(1,3-Benzothiazol-2-yl)-4H-chromen-4-one and spiro[1,4-benzothiazine-2,2'-chromene]-3,4'(3'H,4H)-dione have been synthesized from 4-oxo-4H-chromene-2-carboxylic acid. The course of the reaction that usually occurs between the activated carboxylic acid and aromatic amines was changed upon the use of different reaction conditions (acidic or basic) and 2-aminobenzenethiol. As a result, new heterocyclic derivatives were obtained. Structures of the compounds have been established on the basis of spectral (1D and 2D NMR spectra) and X-ray data.

72. Rationalizing the role of electron/charge transfer in the intramolecular chemiexcitation of dioxetanone-based chemi-/bioluminescent systems
da Silva, LP ; da Silva, JE
Article,  Indexed in: crossref, scopus, wos 
Abstract The thermolysis of dioxetanones is a key process in the intramolecular chemiexcitation step of several chemi-and bioluminescent reactions. This step is generally explained with mechanisms based on either electron transfer (ET), such as the Chemically Initiated Electron-Exchange Luminescence (CIEEL) mechanism, or charge transfer (CT), such as the Charge Transfer-Initiated Luminescence (CTIL) mechanism. Here, we have used a TD-DFT approach to characterize the thermolysis and chemiexcitation steps of model dioxetanones, to rationalize the role of ET/CT in those intramolecular processes. Our results showed that ET/CT can reduce the activation barrier of the thermolysis reaction, by reducing the repulsion between the reacting fragments (ketone and CO2 moieties) that originate during peroxide bond breaking. However, in terms of singlet chemiexcitation profiles, those of non-CIEEL/CTIL-based dioxetanones appear to be more efficient than of CIEEL/CTIL-based ones. Furthermore, the ground state to singlet excited state transitions were found to be local excitations, without CT between the peroxide ring and the electron-rich moiety. So, ET/CT appear to be responsible for tuning the activation barrier of the thermolysis reaction, without playing a role in efficient singlet chemiexcitation itself.

73. Theoretical Study of the Thermolysis Reaction and Chemiexcitation of Coelenterazine Dioxetanes
Magalhaes, CM ; da Silva, JCGE ; da Silva, LP
in JOURNAL OF PHYSICAL CHEMISTRY A, 2022, ISSN: 1089-5639,  Volume: 126, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Coelenterazine and other imidazopyrazinones are important bioluminescent substrates widespread in marine species and can be found in eight phyla of luminescent organisms. Light emission from these systems is caused by the formation and subsequent thermolysis of a dioxetanone intermediate, whose decomposition allows for efficient chemiexcitation to singlet excited states. Interestingly, some studies have also reported the involvement of unexpected dioxetane intermediates in the chemiand bioluminescent reactions of Coelenterazine, albeit with little information on the underlying mechanisms of these new species. Herein, we have employed a theoretical approach based on density functional theory to study for the first time the thermolysis reaction and chemiexcitation profile of two Coelenterazine dioxetanes. We have found that the thermolysis reactions of these species are feasible but with relevant energetic differences. More importantly, we found that the singlet chemiexcitation profiles of these dioxetanes are significantly less efficient than the corresponding dioxetanones. Furthermore, we identified triplet chemiexcitation pathways for the Coelenterazine dioxetanes. Given this, the chemiexcitation of these dioxetanes should lead only to minimal luminescence. Thus, our theoretical investigation of these systems indicates that the thermolysis of these dioxetanes should only provide dark pathways for the formation of nonluminescent degradation products of the chemi- and bioluminescent reactions of Coelenterazine and other imidazopyrazinones.

74. Photocatalytic removal of pharmaceutical water pollutants by TiO2-Carbon dots nanocomposites: A review
Sendao, RMS ; da Silva, JCGE ; da Silva, LP
in CHEMOSPHERE, 2022, ISSN: 0045-6535,  Volume: 301, 
Review,  Indexed in: crossref, scopus, wos 
Abstract Pharmaceuticals are becoming increasingly more relevant water contaminants, with photocatalysts (such as TiO2) being a promising approach to remove these compounds from water. However, TiO2 has poor sunlight harvesting capacity, low photonic efficiency, and poor adsorption towards organic pollutants. One of the emerging strategies to enhance the photocatalytic performance of TiO2 is by conjugating it with fluorescent carbon dots. Herein, we performed a critical review of the development of TiO2 - carbon dots nanocomposites for the photocatalytic removal of pharmaceuticals. We found that carbon dots can improve the photocatalytic efficiency of the resulting nanocomposites, mostly due to increasing the adsorption of organic pollutants and enhancing the absorption in the visible range. However, while this approach shows significant promise, we also identified and discussed several aspects that need to be addressed before this strategy could be more widely used. We hope that this review can guide future studies aiming to the development of enhanced photocatalytic TiO2 - carbon dots nanocomposites.

75. Upconversion Emission Studies in Er3+/Yb3+ Doped/Co-Doped NaGdF4 Phosphor Particles for Intense Cathodoluminescence and Wide Temperature-Sensing Applications
Kumar, A ; Couto, H ; da Silva, JCGE
in MATERIALS, 2022, ISSN: 1996-1944,  Volume: 15, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Er3+/Yb3+ doped/co-doped NaGdF4 upconversion phosphor nanoparticles were synthesized via the thermal decomposition route of synthesis. The oc-phase crystal structure and nanostructure of these particles were confirmed using XRD and FE-SEM analysis. In the power-dependent upconversion analysis, different emission bands at 520 nm, 540 nm, and 655 nm were obtained. The sample was also examined for cathodoluminescence (CL) analysis at different filament currents of an electron beam. Through CL analysis, different emission bands of 526 nm, 550 nm, 664 nm, and 848 nm were obtained. The suitability of the present sample for temperature-sensing applications at a wide range of temperatures, from room temperature to 1173 K, was successfully demonstrated.

76. Evaluation of Different Extraction Methods on the Phenolic Profile and the Antioxidant Potential of Ceratonia siliqua L. Pods Extracts
El Mansouri, F ; Silva, JCGE ; Cacciola, F ; Asraoui, F ; Tayeq, H ; Ben Amar, YM ; Lovillo, MP ; Chouaibi, N ; Brigui, J
in MOLECULES, 2022, Volume: 27, 
Article,  Indexed in: crossref, scopus, wos 
Abstract The present work was designed to investigate the effects of different extraction processes, namely ultrasonic-assisted, supercritical fluid, microwave-assisted and Soxhlet applied to carob pods. The total phenolic quantification and the antioxidant activity were assessed by the means of rapid in vitro spectrophotometric assays; the phenolic profile was identified using ultra-high performance liquid chromatography coupled to mass spectrometry. The results revealed that the phenolic compounds and the antioxidant capacity varied significantly with the nature of the extraction process. The content of total phenolic compounds ranged from 11.55 to 34.38 mg GAE/g DW; the content of total flavonoids varied from 3.50 to 10.53 mg QE/g DW, and the content of condensed tannins fluctuated from 3.30 to 6.55 mg CE/ g DW. All extracts performed differently on antioxidant activity when determined by the DPPH assay producing a dose-dependent response, with IC50 extended from 11.33 to 6.07 mu g/mL. HPLC analysis enabled the identification of nine compounds. As a function of the studied extraction methods, the phenolic compound contents were positively correlated with antioxidant activity.

77. Efficient Removal of Eriochrome Black T Dye Using Activated Carbon of Waste Hemp (Cannabis sativa L.) Grown in Northern Morocco Enhanced by New Mathematical Models
El Mansouri, F ; Pelaz, G ; Moran, A ; Da Silva, JCGE ; Cacciola, F ; El Farissi, H ; Tayeq, H ; Zerrouk, MH ; Brigui, J
in SEPARATIONS, 2022, Volume: 9, 
Article,  Indexed in: crossref, scopus, wos 
Abstract In the present work, the adsorption behavior of Eriochrome Black T (EBT) on waste hemp activated carbon (WHAC) was examined. The surface of the WHAC was modified by H3PO4 acid treatment. The surface and structural characterization of the adsorbents was carried out using Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analysis. The effect of influential adsorption parameters (pH, contact time, dosage, and initial concentration) on the adsorption of EBT onto WHAC was examined in batch experiments; some adsorption parameters such as pH, concentration and dose were improved by new mathematical models. The adsorption behavior of EBT on the surfaces of WHAC was evaluated by applying different isotherm models (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich) to equilibrium data. The adsorption kinetics was studied by using pseudo-first-order, pseudo-second-order, Elovich and intraparticle models on the model. Adsorption followed the pseudo-second-order rate kinetics. The maximum removal of EBT was found to be 44-62.08% by WHAC at pH = 7, adsorbent dose of 10-70 mg, contact time of 3 h and initial dye concentration of 10 mg.L-1. The maximum adsorption capacities were 14.025 mg.g(-1) obtained by calculating according to the Langmuir model, while the maximum removal efficiency was obtained at 70 mg equal to 62.08% for the WHAC. The adsorption process is physical in the monolayer and multilayer.

78. Structural, Optical and Photocatalytic Properties of Mn Doped ZnO Nanoparticles Used as Photocatalysts for Azo-Dye Degradation under Visible Light
Aadnan, I ; Zegaoui, O ; El Mragui, A ; Daou, I ; Moussout, H ; da Silva, JCGE
in CATALYSTS, 2022, ISSN: 2073-4344,  Volume: 12, 
Article,  Indexed in: crossref, scopus, wos 
Abstract Doping ZnO with appropriate foreign metal and/or non-metal ions is one of the most promising ways to improve both the extension of ZnO photosensitization to the visible region and the separation of charge carriers. Herein, Mn-doped ZnO nanoparticles were synthesized using a precipitation method. The effect of the Mn amount on the physico-chemical properties of these nanomaterials was investigated using X-ray diffraction, Fourier-transform infrared spectroscopy, UV-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The photocatalytic properties of the synthesized nanomaterials were assessed through methyl orange (MO) under visible light. The obtained results showed that the structural and optical properties of the synthesized Mn-ZnO nanomaterials depended greatly on the Mn amount. It was found that the substitution of Zn2+ by Mn2+/Mn3+ within the lattice of ZnO occurred. The photocatalytic experiments revealed that the sample containing 10 wt% exhibited the best MO conversion. For this sample, the discoloration reached 96%, while the chemical oxygen demand reached 1% after 820 min of visible illumination. The enhanced photocatalytic activity was attributed to the efficient separation of charge carriers. The active species quenching experiments showed that the holes are the main active species in MO degradation under visible light in the presence of 10%Mn-ZnO.

79. Investigation of the Anticancer and Drug Combination Potential of Brominated Coelenteramines toward Breast and Prostate Cancer
Magalhaes, CM ; Gonzalez-Berdullas, P ; Pereira, M ; Duarte, D ; Vale, N ; da Silva, JCGE ; da Silva, LP
Article,  Indexed in: crossref, scopus, unpaywall, wos 
Abstract Cancer is a very challenging disease to treat, both in terms of therapeutic efficiency and harmful side effects, which continues to motivate the pursuit for novel molecules with potential anticancer activity. Herein, we have designed, synthesized, and evaluated the cytotoxicity of different brominated coelenteramines, which are metabolic products and synthesis precursors of the chemi-/bioluminescent system of marine coelenterazine. The evaluation of the anticancer potential of these molecules was carried out for both prostate and breast cancer, while also exploring their potential for use in combination therapy. Our results provided further insight into the structure-activity relationship of this type of molecule, such as their high structural specificity, as well highlighting the 4-bromophenyl moiety as essential for the anticancer activity. The obtained data also indicated that, despite their similarity, the anticancer activity displayed by both brominated coelenteramines and coelenterazines should arise from independent mechanisms of action. Finally, one of the studied coelenteramines was able to improve the profile of a known chemotherapeutic agent, even at concentrations in which its anticancer activity was not relevant. Thus, our work showed the potential of different components of marine chemi-/bioluminescent systems as novel anticancer molecules, while providing useful information for future optimizations.

80. Revisiting the Absorption Spectra of Polycyclic Aromatic Hydrocarbons over Porto (Portugal) by TD-DFT Calculations
Fernandes, GM ; Macedo, FJD ; da Silva, JCGE ; da Silva, LP
in Sustainable Chemistry, 2022, Volume: 3, 
Article,  Indexed in: crossref 
Abstract <jats:p>Brown carbon is a type of strong light-absorbing carbonaceous aerosol associated with radiative forcing. Nevertheless, the difficulty in correlating the chemical composition of brown carbon with its light absorption properties impairs the proper elucidation of its role in radiative forcing. Here, we have used a time-dependent density functional theory (TD-DFT)-based procedure to revisit the “real-world” absorption spectra of polycyclic aromatic hydrocarbons (PAHs) over the city of Porto, in Portugal, while correcting the spectra for their quantity in PM10 particulate matter. Our aim is to, by comparing these new results with those obtained previously regarding PM2.5 data, evaluate the role of different groupings of particulate matter in the light absorption of brown carbon. The results indicate that irrespective of the absorption spectra corresponding to their PM10 or PM2.5 data, the studied PAHs should contribute to radiative forcing by light absorption at UVA and (sub)visible wavelengths. However, the identity of the individual PAH species that contribute the most for the considered wavelengths can be quite different. Thus, different groupings of particulate matter appear to provide distinct contributions to light absorption and radiative forcing over the same location, even when considering the same class of molecular compounds.</jats:p>