Direct observation of ground-state lactam–lactim tautomerization using temperature-jump transient 2D IR spectroscopy

• DOI: 10.1073/pnas.1303235110
• Publication Date: 2013-05-21T05:03:59Z
• Authors: Chunte Sam Peng; Carlos R. Baiz; Andrei Tokmakoff
• Keywords: Nanosecond; Temperature jump

We provide a systematic characterization of the nanosecond ground-state lactam–lactim tautomerization pyridone derivatives in aqueous solution under ambient conditions using temperature-jump transient 2D IR spectroscopy. Although electronic excited-state has been widely studied, experimental work on ground state, most relevant to chemistry and biology, is lacking. Using spectroscopy, lactam lactim tautomers 6-chloro-2-pyridone 2-chloro-4-pyridone are unambiguously identified by their unique cross-peak patterns. Monitoring correlated exponential relaxation these signals response laser temperature jump provides direct measurement kinetics. By studying temperature, concentration, solvent, pH dependence, we extract thermodynamic kinetic conclude that proceeds through two-state concerted mechanism. find intramolecular proton transfer mediated bridging water molecules reaction barrier dictated release from pyridone, as would be expected for an efficient Grothuss-type