jp0c10191_si_001.pdf (692.2 kB)
Switching between Proton Vacancy and Excess Proton Transfer Pathways in the Reaction between 7‑Hydroxyquinoline and Formate
journal contribution
posted on 2021-03-02, 20:05 authored by Marius-Andrei Codescu, Moritz Weiß, Martin Brehm, Oleg Kornilov, Daniel Sebastiani, Erik T. J. NibberingBifunctional or amphoteric
photoacids simultaneously present donor
(acidic) and acceptor (basic) properties making them useful tools
to analyze proton transfer reactions. In protic solvents, the proton
exchange between the acid and the base is controlled by the acidity
or basicity strength and typically occurs on two different pathways
known as protolysis and hydrolysis. We report here how the addition
of a formate base will alter the relative importance of the possible
reaction pathways of the bifunctional photoacid 7-hydroxyquinoline
(7HQ), which has been recently understood to predominantly involve
a hydroxide/methoxide transport mechanism between the basic proton-accepting
quinoline nitrogen site toward the proton-donating OH group with a
time constant of 360 ps in deuterated methanol (CD3OD).
We follow the reaction dynamics by probing the IR-active marker modes
of the different charged forms of photoexcited 7HQ, and of formic
acid (HCOOD) in CD3OD solution. A comparison of the transient
IR spectra as a function of formate concentration, and classical molecular
dynamics simulations enables us to identify distinct contributions
of “tight” (meaning “contact”) and “loose”
(i.e., “solvent-separated”) 7HQ–formate reaction
pairs in our data. Our results suggest that depending on the orientation
of the OH group with respect to the quinoline aromatic ring system,
the presence of the formate molecule in a proton relay pathway facilitates
a net proton transfer from the proton-donating OH group of 7HQ-N*
via the methanol/formate bridge toward the quinoline N site.
History
Usage metrics
Categories
Keywords
Proton Vacancy360 psmethanolformate moleculequinoline N siteproton transferHCOODformate concentrationExcess Proton Transfer PathwaysIR spectraOH groupCD 3 OD solutionreaction pathwaysprotic solventsFormate Bifunctionalproton transfer reactionsformate basebasicity strengthCD 3 ODreaction dynamicsring systemformic acidproton-donating OH groupIR-active marker modes7 HQ-Namphoteric photoacidsproton exchangeproton-accepting quinoline nitrogen...dynamics simulationsphotoexcited 7 HQ