Research Articles (Chemistry)

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Browsing Research Articles (Chemistry) by Subject "Chemistry"

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    Optimized CO2 capture of the zeolitic imidazolate framework ZIF‑8 modified by solvent-assisted ligand exchange
    (American Chemical Society, 2021) Abraha, Yuel W.; Tsai, Chih-Wei; Niemantsverdriet, J. W. Hans; Langner, Ernst H. G.
    Zeolitic imidazolate frameworks, like ZIF-8 and related structures, have shown great potential for the capture of carbon dioxide. Modifying their structure by exchanging part of the constituent organic ligands is a proven method for enhancing the capacity to absorb CO2. In this work, we performed solvent-assisted ligand exchange (SALE) on nanosized ZIF-8 (nZIF-8) with a series of functionalized imidazole derivatives (exchange percentages, after 24 h): 2-bromoimidazole (19%), 2-chloroimidazole (29%), 2-trifluoromethylbenzimidazole (4%), 2-mercaptobenzimidazole (4%), and 2-nitroimidazole (54%). The sodalite topology and porosity of nZIF-8 were maintained with all SALE modifications. Low-pressure CO2 adsorption of nZIF-8 (38.5 cm3 g–1) at STP was appreciably enhanced with all mixed-linker SALE products. Using halogenated (−Cl, −Br, and −CF3) imidazole derivatives in a 24 h SALE treatment resulted in increases between 11 and 22% in CO2 adsorption, while the thiol (−SH)- and nitro (−NO2)-functionalized SALE products led to 32 and 100% increases in CO2 uptakes, respectively. These CO2 uptakes were further optimized by varying the SALE treatment time. The SHbIm- and NO2Im-exchanged SALE products of nZIF-8 show 87 and 98 cm3 g–1 of CO2 uptakes after 60 and 120 h of SALE, respectively. These are record high CO2 adsorptions for all reported ZIF derivatives at low-pressure conditions.
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    Substitution reactivity and structural variability induced by tryptamine on the biomimetic rhenium tricarbonyl complex
    (Royal Society of Chemistry, 2021) Jacobs, Frederick J. F.; Venter, Gertruida J. S.; Fourie, Eleanor; Kroon, Robin E.; Brink, Alice
    A series of seven fac-[Re(CO)3(5Me-Sal-Trypt)(L)] complexes containing tryptamine on the N,O 5-methylsalicylidene bidentate ligand backbone and where L is MeOH, Py, Imi, DMAP, PPh3 coordinated to the 6th position have been studied, including the formation of a dinuclear Re2 cluster. The crystallographic solid state structures show marked similarity in structural tendency, in particular the rigidity of the Re core and the hydrogen bond interactions similar to those found in protein structures. The rates of formation and stability of the complexes were evaluated by rapid time-resolved stopped-flow techniques and the methanol substitution reaction indicates the significant activation induced by the use of the N,O salicylidene bidentate ligand as manifested by the second-order rate constants for the entering nucleophiles. Both linear and limiting kinetics were observed and a systematic evaluation of the kinetics is reported clearly indicating an interchange type of intimate mechanism for the methanol substitution. The anticancer activity of compounds 1–7 was tested on HeLa cells and it was found that all compounds showed similar cytotoxicity where solubility allowed. IC50-values between ca. 11 and 22 mM indicate that some cytotoxicity resides most likely on the salicylidene–tryptamine ligand. The photoluminescence of the seven complexes is similar in maximum emission wavelength with little variation despite the broad range of ligands coordinated to the 6th position on the metal centre.