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7. Optimizing Antimicrobial Efficacy: Investigating the Impact of Zinc Oxide Nanoparticle Shape and Size.

Author

Mendes, Ana Rita, Granadeiro, Carlos M., Leite, Andreia, Pereira, Eulália, Teixeira, Paula, and Poças, Fátima

Subjects
*NANOPARTICLE size, *ENERGY dispersive X-ray spectroscopy, *ESCHERICHIA coli, *FOURIER transform infrared spectroscopy, *ELECTRON paramagnetic resonance, *ZINC oxide
Abstract

Zinc oxide nanoparticles (ZnO NPs) have been investigated due to their distinct properties, variety of structures and sizes, and mainly for their antimicrobial activity. They have received a positive safety evaluation from the European Food Safety Authority (EFSA) for packaging applications as transparent ultraviolet (UV) light absorbers based on the absence of significant migration of zinc oxide in particulate form. ZnO NPs with different morphologies (spherical, flower, and sheet) have been synthesized via different sol–gel methods and extensively characterized by several solid-state techniques, namely vibrational spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), Fourier Transform Infrared Spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV-VIS), electron paramagnetic resonance (EPR), and nitrogen adsorption–desorption isotherms. The ZnO NPs were assessed for their antibacterial activity against Escherichia coli (gram-negative bacteria) and Staphylococcus aureus (gram-positive bacteria) to study the influence of morphology and size on efficacy. ZnO NPs with different morphologies and sizes demonstrated antimicrobial activity against both bacteria. The highest microbial cell reduction rate (7–8 log CFU mL−1 for E. coli and 6–7 log CFU mL−1 for S. aureus) was obtained for the sheet- and spherical-shaped NPs as a result of the high specific surface area. In fact, the higher surface areas of the sheet- and spherical-shaped nanoparticles (18.5 and 13.4 m2 g−1, respectively), compared to the flower-shaped NPs (5.3 m2g−1), seem to promote more efficient bacterial cell reduction. The spherical-shaped particles were also smaller (31 nm) compared with the flower-shaped (233 × 249 nm) ones. The flower ZnO NP resulted in a 4–5 log CFU mL−1 reduction for E. coli and 3–4 log CFU mL−1 reduction for S. aureus. The lower apparent antibacterial activity of the flower-shaped could be associated with either the lack of defects on the particle core or the shape shielding effect. Compared to S. aureus, E. coli seems to be less resistant to ZnO NPs, which may be explained by the characteristics of its cell membrane. With simple synthesis techniques, which do not allow the size and shape of the nanoparticles to be controlled simultaneously, it is a challenge to elucidate the effect of each of these two parameters on antibacterial performance. [ABSTRACT FROM AUTHOR]

Published
2024
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32. Lanthanopolyoxometalate-Silica Core/Shell Nanoparticles as Potential MRI Contrast Agents

Author

Carvalho, Rui F.S. (author), Pereira, Giovannia A.L. (author), Rocha, João (author), Castro, M. Margarida C.A. (author), Granadeiro, Carlos M. (author), Nogueira, Helena I.S. (author), Peters, J.A. (author), Geraldes, Carlos F.G.C. (author), Carvalho, Rui F.S. (author), Pereira, Giovannia A.L. (author), Rocha, João (author), Castro, M. Margarida C.A. (author), Granadeiro, Carlos M. (author), Nogueira, Helena I.S. (author), Peters, J.A. (author), and Geraldes, Carlos F.G.C. (author)

Abstract

The NMR relaxivities of the decatungstolanthanoate core-shell nanoparticles, prepared by encapsulating [Ln(W5O18)2]9− polyoxometalates (LnPOM) within amorphous silica shells (K9[Ln(W5O18)2]@SiO2), were studied along the Ln series. The relaxivity of GdPOM is slightly higher than for Gd-DTPA due to second-sphere relaxation effects, but the values for the other paramagnetic LnPOMs are much smaller due to the short T1e values of their Ln3+-ions. The NPs have core-shell spherical structures, with LnPOM-containing cores with 9.5–28 nm diameters, and 4.0–11.0 nm thick amorphous silica shells. In water suspensions, the NPs have negative zeta potentials (−32.5 to −40.0 mV) and time-dependent hydrodynamic diameters (31–195 nm) reflecting the formation of aggregates. The relaxivities of GdPOM@SiO2 NPs suspensions (r1=10.97 (mM Gd)−1 s−1, r2=12.02 (mM Gd)−1 s−1, 0.47 T, 25 °C) are considerably larger than for the GdPOM solutions, indicating that their silica shell is significantly porous to water. This increase is limited by the agglomeration of the complexes in the NPs core, limiting their access to water to those at the core surface. Replacing half of the Gd3+ ions by Eu3+ decreases the NPs r1 and r2 relaxivities at 0.47 T to 20 % and 35 % of their initial values, which are still considerable, but does not affect the efficient luminescence properties of the Eu3+ centers. This indicates that the mixed NPs have potential as dual modality MRI/optical imaging contrast agents., Accepted Author Manuscript, BT/Biocatalysis

Published
2021
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34. Oxidative desulfurization strategies using Keggin-type polyoxometalate catalysts: Biphasic versus solvent-free systems

Author

Fundação para a Ciência e a Tecnologia (Portugal), Ministério da Ciência, Tecnologia e Ensino Superior (Portugal), Ribeiro, Susana O., Granadeiro, Carlos M., Almeida, Pedro L., Pires, João, Capel Sánchez, María del Carmen, Campos Martín, José Miguel, Gago, Sandra, de Castro, Baltazar, Balula, Salete S., Fundação para a Ciência e a Tecnologia (Portugal), Ministério da Ciência, Tecnologia e Ensino Superior (Portugal), Ribeiro, Susana O., Granadeiro, Carlos M., Almeida, Pedro L., Pires, João, Capel Sánchez, María del Carmen, Campos Martín, José Miguel, Gago, Sandra, de Castro, Baltazar, and Balula, Salete S.

Abstract

[EN] Strategic polyoxometalate Keggin-type structural modification was performed to increase the oxidative catalytic performance to desulfurize model and real diesels. The most active lacunar structure [PWO] (PW) showed to complete desulfurize a simulated diesel after 60 min at 70 °C. Its application as homogeneous catalyst using a biphasic system 1:1 diesel/acetonitrile needed to use an excess of oxidant (ratio HO/S = 8). The immobilization of the PW on amine-functionalized SBA-15 supports originated two heterogeneous catalysts PW@aptesSBA-15 and PW@tbaSBA-15. The best results were attained with the PW@aptesSBA-15 catalyst showing identical oxidative desulfurization performance as the homogeneous analogue. As advantage, this heterogeneous catalyst promotes the complete desulfurization of simulated diesel using a solvent-free system, i.e. without the need of acetonitrile use. On the other hand, the same desulfurization efficiency could be achieved using half the amount of oxidant (HO/S = 4). The oxidative desulfurization of the real diesel achieved a remarkable 83.4% of efficiency after just 2 h. The recycling capacity of PW@aptesSBA-15 catalyst was confirmed for eight consecutive cycles using the biphasic and the solvent-free systems. Its stability investigation demonstrates to be higher under the solvent-free system than the biphasic system, without practically any occurrence of PW leaching in the first case. On the other hand, the Venturello peroxocomplex [PO{W(O)} ], recognized as active intermediate in the homogeneous biphasic system, was not identified in the heterogeneous catalytic systems.

Published
2019

35. Mesoporous Silica vs. Organosilica Composites to Desulfurize Diesel

Author

Fundação para a Ciência e a Tecnologia (Portugal), Ministério da Ciência, Tecnologia e Ensino Superior (Portugal), Portuguese Nuclear Magnetic Resonance Network, Ribeiro, Susana O., Granadeiro, Carlos M., Corvo, Marta C., Pires, João, Campos Martín, José Miguel, Castro, Baltazar de, Balula, Salete S., Fundação para a Ciência e a Tecnologia (Portugal), Ministério da Ciência, Tecnologia e Ensino Superior (Portugal), Portuguese Nuclear Magnetic Resonance Network, Ribeiro, Susana O., Granadeiro, Carlos M., Corvo, Marta C., Pires, João, Campos Martín, José Miguel, Castro, Baltazar de, and Balula, Salete S.

Abstract

[EN] The monolacunary Keggin-type [PWO] (PW) heteropolyanion was immobilized on porous framework of mesoporous silicas, namely SBA-15 and an ethylene-bridged periodic mesoporous organosilica (PMOE). The supports were functionalized with a cationic group (N-trimethoxysilypropyl-N, N, N-trimethylammonium, TMA) for the successful anchoring of the anionic polyoxometalate. The PW@TMA-SBA-15 and PW@TMA-PMOE composites were evaluated as heterogeneous catalysts in the oxidative desulfurization of a model diesel. The PW@TMA-SBA-15 catalyst showed a remarkable desulfurization performance by reaching ultra-low sulfur levels (<10 ppm) after only 60 min using either a biphasic extractive and catalytic oxidative desulfurization (ECODS) system (1:1 MeCN/diesel) or a solvent-free catalytic oxidative desulfurization (CODS) system. Furthermore, the mesoporous silica composite was able to be recycled for six consecutive cycles without any apparent loss of activity. The promising results have led to the application of the catalyst in the desulfurization of an untreated real diesel supplied by CEPSA (1,335 ppm S) using the biphasic system. The system has proved to be a highly efficient process by reaching desulfurization values higher than 90% for real diesel during three consecutive cycles.

Published
2019

40. Multifunctionality in Two Families of Dinuclear Lanthanide(III) Complexes with a Tridentate Schiff-Base Ligand

Author

Anastasiadis, Nikolaos C., primary, Granadeiro, Carlos M., additional, Mayans, Julia, additional, Raptopoulou, Catherine P., additional, Bekiari, Vlasoula, additional, Cunha-Silva, Luís, additional, Psycharis, Vassilis, additional, Escuer, Albert, additional, Balula, Salete S., additional, Konidaris, Konstantis F., additional, and Perlepes, Spyros P., additional

Published
2019
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46. SiW11Fe@MIL-101(Cr) Composite: A Novel and Versatile Electrocatalyst

Author

Fernandes, Diana M., primary, Granadeiro, Carlos M., additional, Paes de Sousa, Patrícia M., additional, Grazina, Raquel, additional, Moura, José J. G., additional, Silva, Patrícia, additional, Almeida Paz, Filipe A., additional, Cunha-Silva, Luís, additional, Balula, Salete S., additional, and Freire, Cristina, additional

Published
2014
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