isoalloxazine and 4-chlorophenol

Low-temperature absorption and Stark spectroscopy have been used to study the electronic properties of oxidized flavin mononucleotide (FMN) in old yellow enzyme (OYE) and OYE complexed with p-chlorophenol (p-Cl phenol). The low-temperature absorbance spectrum of OYE showed splittings of the blue and near-UV vibronic bands, which appears to be due to hydrogen bonding between the isoalloxazine moiety and the protein. A Stark spectroscopic analysis showed that the electronic structure of the FMN cofactor in OYE is not significantly perturbed relative to flavins in simple solvents. However, the charge-transfer band in the OYE:p-Cl phenol complex showed a large Stark effect indicative of substantial charge displacement. The magnitude and direction of this charge displacement are consistent with significant charge transfer along the charge-transfer transition dipole moment direction. In addition, the Stark spectrum of the CT band showed unexpected fine structure that could correlate with vibrational progressions in either the p-Cl phenol donor or the flavin acceptor.

Topics: Chlorophenols; Electrochemistry; Electron Transport; Energy Transfer; Flavin Mononucleotide; Flavins; Flavoproteins; Freezing; Macromolecular Substances; Models, Chemical; NADPH Dehydrogenase; Oxidation-Reduction; Spectrophotometry, Ultraviolet; Spectrum Analysis; Static Electricity