Galactose oxidase models: insights from 19F NMR spectroscopy.

19F labeled tripodal ligands that possess a N3O donor set (one phenol, one tertiary amine and either two pyridines or one pyridine and one quinoline) have been synthesized. The fluorine is incorporated either at the phenol O-donor (HLF and HLCF3) or at the quinoline N-donor (HLqOMe and HLqNO2). The copper(ii)-phenol complexes (2H)2+, (1H)2+, (3H)2+ and (4H)2+ as well as the corresponding copper(ii)-phenolate complexes have been characterized. X-ray diffraction reveals an increase in the oxygen-copper bond distance of more than 0.4 {\AA} upon protonation of the phenolate moiety of (4)+. Protonation is accompanied by an axial to equatorial isomerization of the quinoline group. DFT calcns. show that stretching of the Cu-O(phenol) bond, $π$-stacking interactions and rotation of the pyridine are key steps in this isomerization process. Protonation, and thus changes in the oxygen-copper bond distance induce either a decrease ((1H)2+, (2H)2+) or an increase ((3H)2+ and (4H)2+) in the copper-fluorine distance that could be monitored by 19F NMR. In the former case, a broadening of the 19F NMR signal is obsd., whereas a sharpening is obsd. in the latter case. Temp. dependent 19F NMR measurements on equimolar mixts. of the phenol and phenolate complexes of (3)+ and (4)+ reveal rate consts. for proton transfer and/or isomerization of 3000 ± 100 s-1 and 2900 ± 100 s-1, resp., at the coalescence temp. This temp. was found to be strongly affected by the phenol para-substituent as it is 226 K and ca. 330 K for (3)+ and (4)+, resp. A phenoxyl radical species ((3·)2+) could be generated and characterized for the first time by 19F NMR spectroscopy. [on SciFinder(R)]


Galactose oxidase models: insights from 19F NMR spectroscopy.
Type de publication
Article de revue
Année de publication
Dalt. Trans.
Soumis le 12 avril 2018