Browsing by Author "Calhau, Isabel B."
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- Host-guest complexes of cucurbit[8]uril and [(η5-C5H4R)Mo(CO)3CH3] (R = H, CO2CH3) for controlled release of carbon monoxidePublication . Gomes, Ana C.; Monteiro, Rodrigo P.; Calhau, Isabel B.; D. Lopes, André; Gonçalves, Isabel S.; Pillinger, MartynThe monosubstituted cyclopentadienyl half-sandwich molybdenum(II) tricarbonyl complex [(eta 5-C5H4CO2CH3) Mo(CO)3CH3] (1) and its 1:1 inclusion compound with cucurbit[8]uril (1@CB8) have been prepared and characterised by elemental and thermogravimetric analyses, powder X-ray diffraction, diffuse reflectance UV-vis, solid-state 13C{1H} MAS NMR, FT-IR, and Raman spectroscopies. The CO-releasing behaviours of 1, 1@CB8 and, for comparison, [(eta 5-C5H5)Mo(CO)3CH3] (2) and its 1:1 inclusion complex with CB8, were assessed using a deoxymyoglobin-carbonmonoxymyglobin assay. For assays performed in the dark at 37 degrees C, complex 1 undergoes thermally assisted spontaneous CO release, with ca. 0.5 equivalents of CO being released after 6 h. The half-life (t1/2) of 325 min identifies 1 as a slow releaser when compared to complex 2 bearing the unsubstituted cyclopentadienyl ligand (t1/2 = 25 min). CO release from 1 was promoted by exposure to UV light (t1/2 = 85 min), establishing the complex as a photochemically activated CO-releasing molecule (photoCORM). For 1@CB8, t1/2 for photo-assisted CO release increased to ca. 7 h, and for 2@CB8 the dark-release t1/2 increased to 165 min, showing that molecular acceptors like cucurbiturils can be used effectively as second-sphere ligands to modulate the CO release profile of CORMs.
- β-Cyclodextrin and cucurbit[7]uril as protective encapsulation agents of the CO-releasing molecule [CpMo(CO)3Me]Publication . Monteiro, Rodrigo P.; Calhau, Isabel B.; Gomes, Ana C.; D. Lopes, André; Da Silva, José Paulo; Gonçalves, Isabel P.; Pillinger, MartynThe CO releasing ability of the complex [CpMo(CO)3Me] (1) (Cp = eta 5-C5H5) has been assessed using a deoxymyoglobin-carbonmonoxymyoglobin assay. In the dark, CO release was shown to be promoted by the reducing agent sodium dithionite in a concentration-dependent manner. At lower dithionite concentrations, where dithionite-induced CO release was minimised, irradiation at 365 nm with a low-power UV lamp resulted in a strongly enhanced release of CO (half-life (t1/2) = 6.3 min), thus establishing complex 1 as a photochemically activated CO-releasing molecule. To modify the CO release behaviour of the tricarbonyl complex, the possibility of obtaining inclusion complexes between 1 and beta-cyclodextrin (beta CD) or cucurbit[7]uril (CB7) by liquid-liquid interfacial precipitation (1@beta CD(IP)), liquid antisolvent precipitation (1@CB7), and mechanochemical ball-milling (1@beta CD(BM)) was evaluated. All these methods led to the isolation of a true inclusion compound (albeit mixed with nonincluded 1 for 1@beta CD(BM)), as evidenced by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), FT-IR and FT-Raman spectroscopies, and 13C{1H} magic angle spinning (MAS) NMR. PXRD showed that 1@beta CD(IP) was microcrystalline with a channel-type crystal packing structure. High resolution mass spectrometry studies revealed the formation of aqueous phase 1 : 1 complexes between 1 and CB7. For 1@beta CD(IP) and 1@CB7, the protective effects of the hosts led to a decrease in the CO release rates with respect to nonincluded 1. beta CD had the strongest effect, with a ca. 10-fold increase in t1/4 for dithionite-induced CO release, and a ca. 2-fold increase in t1/2 for photoinduced CO release.