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Highly efficient and reusable CNT supported iron(II) catalyst for microwave assisted alcohol oxidation

Publication . Martins, Luisa; Ribeiro, A. P. C.; Carabineiro, S. A. C.; Figueiredo, J. L.; Pombeiro, Armando

The highly efficient eco-friendly synthesis of ketones (yields over 99%) from secondary alcohols is achieved by combination of [FeCl2{eta(3)-HC(pz)(3)}] (pz = pyrazol-1-yl) supported on functionalized multi-walled carbon nanotubes and microwave irradiation, in a solvent-free medium. The carbon homoscorpionate iron(II) complex is the first one of this class to be used as catalyst for the oxidation of alcohols.

2016Journal article

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Ball milling as an effective method to prepare magnetically recoverable heterometallic catalysts for alcohol oxidation

Publication . Fontolan, Emmanuele; Alegria, Elisabete; Da Costa Ribeiro, Ana Paula; Kopylovich, Maximilian; Bertani, Roberta; Pombeiro, Armando

Heterometallic double Fe2O3–CoCl2, CoCl2–V2O5, MoO3–V2O5, and triple CuO–Fe2O3–CoCl2 3d metal dispersed systems were easily prepared by ball milling at room temperature and characterized by scanning electron microscopy (SEM), field emission gun scanning electron microscopy (FEGSEM), energydispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). They catalyze the microwave-assisted solvent-free heterogeneous oxidation of 1-phenylethanol to acetophenone with tert-butyl hydroperoxide (t-BuOOH) as oxidant, used as a model reaction. In most of the heterometallic systems a significant improvement in the catalytic activity was observed in comparison to homometallic ones. For the tested catalytic systems and experimental conditions, the CuO–Fe2O3–CoCl2 and Fe2O3–CoCl2 systems exhibit the highest activity with maximum 78% yield and TON 39 after 1 h. The possibility of magnetic recovery of the catalysts was demonstrated for the Fe2O3–CoCl2 (3:1) system.

2017-01-30Journal article

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Elementary and efficient catalyst process for the Knoevenagel condensation of araldehydes with arylmethylidene malononitrile

Publication . Jlassi, Raja; Da Costa Ribeiro, Ana Paula; Tiago, Gonçalo; Wang, Jiawei; Krawczyk, Marta S.; Martins, Luisa; Naili, Houcine; Pombeiro, Armando; Rekik, Walid

A comparative study of the Knoevenagel condensation of an aromatic aldehyde with an active methylene compound (e.g., malononitrile or ethyl cyanoacetate), using solvent free grindstone conditions and microwave irradiation is reported. Our solvent free approaches led these reactions to proceed faster, more cleanly and in higher yields. Moreover, they also allowed the use of nitrobenzaldehydes, which failed to yield the desired products under traditional and water based approaches. Thus, an efficient procedure for the Knoevenagel condensation of aryl and heteroaromatic aldehydes with malononitrile. using the complex [CdNa2(mu-L-2)](n)center dot 6.34H(2)O or commercial CdO as catalyst under solvent-free and very mild conditions has been developed. (C) 2017 Elsevier B.V. All rights reserved.

2018-02-24Journal article

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Supported C-Scorpionate Vanadium(IV) Complexes as Reusable Catalysts for Xylene Oxidation

Publication . Wang, Jiawei; Martins, Luisa; Da Costa Ribeiro, Ana Paula; Carabineiro, Sonia Alexandra Correia; Figueiredo, José L.; Pombeiro, Armando

C-Scorpionate vanadium(IV) [VOxCl3-x{k(3)-RC(pz)(3)}] [pz = pyrazol-1-yl; x=0, R = SO3 (1); x = 1, R= CH2OH (2) or CH2OSO2Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V-scorpionate catalysts used so far for the neat oxidation of o-, m- or p-xylene, with TBHP (70% aqueous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably, a p-toluic acid yield of 43% (73% selectivity, TON = 1.34 V 10(3)) was obtained with 2@CNT in a simple microwave-assisted mild oxidation procedure, using a very low catalyst charge (3.2 x 10(-2) mol% vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of a greener and more sustainable process for oxidation of xylenes. Moreover, reuse of catalysts with preservation of their activity was found for up to six consecutive cycles. The effects of reaction parameters, such as reaction time, temperature, amount of catalyst or type of heating source, on the performance of the above catalytic systems are reported and discussed.

2017-10Journal article

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Evaluation of cell toxicity and DNA and protein binding of green synthesized silver nanoparticles

Publication . Da Costa Ribeiro, Ana Paula; Anbu, S; Alegria, Elisabete; Fernandes, Alexandra; Baptista, Pedro; Mendes, Rita; Matias, A. S.; Mendes, M.; Guedes Da Silva, M. Fátima C.; Pombeiro, Armando

Silver nanoparticles (AgNPs) were prepared by GREEN chemistry relying on the reduction of AgNO3 by phytochemicals present in black tea extract. AgNPs were fully characterized by transmission electron microscopy (TEM), ultraviolet-visible spectroscopy ((UV-vis)), X-ray diffraction (XRD) and energy dispersive absorption spectroscopy (EDS). The synthesized AgNPs induced a decrease of the cell viability in a dose-dependent manner with a low IC50 (0.5 +/- 0.1 mu M) for an ovarian carcinoma cell line (A2780) compared to primary human fibroblasts (IC50 5.0 +/- 0.1 mu M). The DNA binding capability of CT (calf thymus) DNA was investigated using electronic absorption and fluorescence spectroscopies, circular dichroism and viscosity titration methods. Additionally, the AgNPs strongly quench the intrinsic fluorescence of BSA, as determined by synchronous fluorescence spectra.

2018-05Journal article

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