Percorrer por autor "Silva, Luis Cunha"
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- Cyclopentadienyl vs indenyl control of thermal/photoactivated CO release in cationic molybdenum(II) dicarbonyl-ethylenediamine complexesPublication . Bruno, Sofia M.; Calhau, Isabel B.; Dias, Tiago M.; Santos, Adriana; Silva, Luis Cunha; Nolasco, Mariela M.; Goncalves, Isabel S.; Pillinger, MartynABSTRACT: Molybdenum half-sandwich carbonyl complexes continue to attract attention as potential anticancer agents and prodrugs for therapeutic use of carbon monoxide. Building on the known bioactivity and hydrolytic stability of cyclopentadienyl-based Mo fragments, we report the synthesis, structural characterization, and solution behavior of two cationic half-sandwich complexes, [(eta 5-Cp)Mo(CO)2(en)][BF4] (3) and [(eta 5-Ind)Mo(CO)2(en)][BF4] (4) (Cp = cyclopentadienyl, Ind = indenyl, en = ethylenediamine). Complex 3 is described here for the first time, while 4 was structurally characterized by single-crystal X-ray diffraction, revealing a distorted square-pyramidal geometry with cis-CO ligands and a chelating en ligand positioned beneath the indenyl ring. Both compounds are air-stable in the solid state and exhibit enhanced solubility in polar media due to their ionic nature. UV-vis stability studies under simulated physiological conditions (PBS, pH 7.4, 37 degrees C) show gradual decomposition of both complexes, accelerated by visible-light irradiation and/or the presence of air. CO-release behavior was quantified using the myoglobin assay: the allyl precursors [(eta 5-Cp')Mo(eta 3-C3H5)(CO)2] were inert, whereas complexes 3 and 4 released CO slowly, with 4 exhibiting significantly faster thermal CO liberation (t1/2 approximate to 129 min; 0.74 equiv. CO after 6 h). Complex 3 showed minimal thermal CO release but underwent enhanced and sustained photodecarbonylation under visible-light irradiation, enabling controlled CO delivery. These results identify 3 and 4 as rare examples of Mo-based CO-releasing molecules capable of slow, tunable CO release under biologically relevant conditions, with 3 displaying light-responsive behavior and 4 functioning as a spontaneous thermal CO donor.
- Enhanced borohydride oxidation kinetics with Au@MOF-808 nanocomposite electrocatalysts with ultra-low Au loadingPublication . Belhaj, Ines; Becker, J. Alexander; Viana, Alexandre M.; Gusmão, Filipe M. B.; Chaves, Miguel; Pereira, Eulália; Sljukic, Biljana; Balula, Salete S.; Silva, Luis Cunha; Santos, Diogo M. F.ABSTRACT: The highly stable metal-organic framework (MOF) composed of[Zr6O4(mu 3-OH)4(OH)6(H2O)6(BTC)2]& sdot;nH2O units (MOF-808) was modified by incorporating gold (Au) nanoparticles and functional groups to enhance electrocatalytic activity for the borohydride oxidation reaction (BOR). Three composite materials (Au@MOF-808, Au@MOF-808-NH2, and Au@MOF-808-SH) were prepared by the incorporation of Au in structurally related MOFs, MOF-808, MOF-808-NH2, and MOF-808-SH, respectively. These composite materials were evaluated as anodic electrocatalysts for BOR in alkaline media using cyclic voltammetry and chronoamperometry. Among the prepared materials, Au@MOF-808-NH2 exhibited the highest BOR activity, with an apparent activation energy of 15.3 kJ mol-1, a reaction order of 0.6, an anodic charge transfer coefficient of 0.63, and a number of exchanged electrons of 4.4. The latter was significantly below the theoretical eight-electron value, indicating the presence of alternative reaction pathways. Notably, this material achieved a high mass-specific BOR peak current of 4.23 A mu gAu-1, demonstrating outstanding electrocatalytic efficiency despite the ultralow noble metal loading. These results underscore the potential of Au@MOF-808-NH2 as a cost-effective and scalable anodic electrocatalyst for high-performance direct borohydride fuel cells.
- A Strategy to Improve Porous MOF Structural Stability for the Effective Removal of S/N Pollutants from (Bio)fuelsPublication . Silva, Dinis; Mirante, Fátima; Santos-Vieira, Isabel; Granadeiro, Carlos; Silva, Luis Cunha; Balula, Salete S.ABSTRACT: The need to mitigate environmental pollution drives the continuous quest for advanced desulfurization and denitrogenation methods in refineries. The presence of sulfur and nitrogen compounds in fossil fuels and biofuels contributes largely to atmospheric polllution. Oxidative catalysis presents a promising way for addressing these challenges, offering efficient and environmental friendly pathways. This work investigates the heterogeneous catalytic performance of the polyoxometalates, plenary Keggin PW12 structure and the derivative lacunary PW11 structure, supported on the porous MIL-100(Fe) metal-organic framework, for simultaneous oxidative desulfurization and denitrogenation. Both PW11@MIL-100(Fe) and PW12@MIL-100(Fe) catalysts demonstrated rapid and complete desulfurization within 60 min of reaction using a sustainable H2O2 oxidant. Remarkably, PW11@MIL-100(Fe) exhibited higher catalytic efficiency and demonstrated high recycle capacity. In fact, notable results were attained to remove the most noxious pollutants in (bio)fuels, offering insights for the development of effective catalytic materials with high viability for the energy industry.