β-Cyclodextrin and cucurbit[7]uril as protective encapsulation agents of the CO-releasing molecule [CpMo(CO)₃Me]

abstract

The CO releasing ability of the complex [CpMo(CO)(3)Me] (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 (t(1/2)) = 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 C-13{H-1} 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 t(1/4) for dithionite-induced CO release, and a ca. 2-fold increase in t(1/2) for photoinduced CO release.

keywords

CARBON-MONOXIDE; INCLUSION COMPLEXES; METAL-COMPLEXES; MOLYBDENUM; CHEMISTRY; TOXICITY; DELIVERY; MO; DERIVATIVES; TITANOCENE

subject category

Chemistry

authors

Monteiro, RP; Calhau, IB; Gomes, AC; Lopes, AD; Da Silva, JP; Gonçalves, IS; Pillinger, M

Groups

G1 - Porous Materials and Nanosystems

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

Rede Nacional de Ressonância Magnética Nuclear (PTNMR)

acknowledgements

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (https://doi.org/10.54499/UIDB/50011/2020), UIDP/50011/2020 (https://doi.org/10.54499/UIDP/50011/2020) & LA/P/0006/2020 (https://doi.org/10.54499/LA/P/0006/2020), financed by national funds through the FCT (FundacAo para a Ciencia e a Tecnologia)/MCTES (Ministerio da Ciencia, Tecnologia e Ensino Superior) (PIDDAC). This study received Portuguese national funds from the FCT through projects UIDB/04326/2020 (https://doi.org/10.54499/UIDB/04326/2020), UIDP/04326/2020 (https://doi.org/10.54499/UIDP/04326/2020) and LA/P/0101/2020 (https://doi.org/10.54499/LA/P/0101/2020), and from the operational programmes CRESC Algarve 2020 and COMPETE 2020 through project EMBRC.PT ALG-01-0145-FEDER-022121. R.P.M. (https://doi.org/10.54499/2020.04758.BD) and I.B.C. (https://doi.org/10.54499/2021.05953.BD) are grateful to the FCT and the European Social Fund for PhD grants. A.C.G. acknowledges the FCT/MCTES for an Assistant Researcher Position (ref. CEECIND/02128/2017) funded through the Individual Call to Scientific Employment Stimulus (https://doi.org/10.54499/CEECIND/02128/2017/CP1459/CT0039). The NMR spectrometers used in this work are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project No. 022161 (POCI-01-0145-FEDER-022161, co-financed by FEDER through COMPETE 2020, POCI and PORL, and FCT through PIDDAC).