Impact of Photon Absorption on the Electronic Properties of p-Coumaric Acid Derivatives of the Photoactive Yellow Protein Chromophore

Abstract

The changes in the electrostatic properties, between the ground and excited state, of thiomethyl p-coumaric acid (TMpCA) and its sterically hindered derivative, thiomethyl-7-hydroxy-coumarin-3-carboxylic acid (TM7HC), have been determined at 77 K using Stark spectroscopy, to better understand the origin of the photoinduced charge motion observed in these chromophores in the native photoactive yellow protein (PYP) environment. Excitation of the anionic chromophores produce changes in the permanent dipole moment (|Δμ|) of 25 (TMpCA-a) and 15 D (TM7HC-a), which are significantly larger than the |Δμ|'s measured in the neutral species: 9 (TMpCA-n) and 6 D (TM7HC-n). However, the similarity of the |Δμ|'s between the anions and the corresponding de-protonated cofactors in the native protein environment implicates the intrinsic electronic properties of the chromophore for the photoreactivity of the initially excited species in the PYP photocycle. Furthermore, the results for the neutral species suggest that, if ...