期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 110, 期 23, 页码 9243-9248出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1303235110
关键词
keto-enol tautomerism; multidimensional; time-resolved spectroscopy; ultrafast
资金
- National Science Foundation [CHE-1212557]
- Massachusetts Institute of Technology (MIT) Center for Environmental Health Sciences [National Institutes of Health (NIH) Center Grant] [P30-ES002109]
- MIT Laser Biomedical Research Center (NIH Center Grant) [P41-EB015871]
- Agilent Technologies
- Ruth L. Kirschstein National Research Service Award [F32GM105104]
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1212557] Funding Source: National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1414486] Funding Source: National Science Foundation
We provide a systematic characterization of the nanosecond ground-state lactam-lactim tautomerization of pyridone derivatives in aqueous solution under ambient conditions using temperature-jump transient 2D IR spectroscopy. Although electronic excited-state tautomerization has been widely studied, experimental work on the ground electronic state, most relevant to chemistry and biology, is lacking. Using 2D IR spectroscopy, lactam and lactim tautomers of 6-chloro-2-pyridone and 2-chloro-4-pyridone are unambiguously identified by their unique cross-peak patterns. Monitoring the correlated exponential relaxation of these signals in response to a laser temperature jump provides a direct measurement of the nanosecond tautomerization kinetics. By studying the temperature, concentration, solvent, and pH dependence, we extract a thermodynamic and kinetic characterization and conclude that the tautomerization proceeds through a two-state concerted mechanism. We find that the intramolecular proton transfer is mediated by bridging water molecules and the reaction barrier is dictated by the release of a proton from pyridone, as would be expected for an efficient Grothuss-type proton transfer mechanism.
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