Absorption of the green fluorescent protein chromophore anion in the gas phase studied by a combination of FTICR mass spectrometry with laser-induced photodissociation spectroscopy

The optical absorption of the green fluorescent protein chromophore anion (HBDI−) in the gas phase has been addressed by a number of experimental and theoretical studies; however, there is no consensus on its spectral characteristics yet. In this report, the intrinsic absorption of HBDI− was probed by photo-induced dissociation (“action”) spectroscopy using discrete lines of a continuous-wave (CW) laser source. The observed spectral profile of dissociation efficiency revealed a pronounced dependence on the laser irradiance. Dissociation at high irradiance is governed by multiple-photon absorption processes whose efficiency peaks between 476 and 488 nm. At very low irradiance (<0.4 mW cm−2) dissociation of gas-phase HBDI− is mostly promoted by single-photon transitions and suggests an intrinsic absorption maximum of gas-phase HBDI− <476 nm, blue-shifted compared to earlier results obtained with pulsed lasers.

Graphical abstractOptical absorption of the green fluorescent protein chromophore, HBDI−, was probed by laser photodissociation in an FTICR-MS. The photodissociation spectral profile for free HBDI− depends on the excitation power; the relevance of photodissociation data to the absorption of HBDI− is discussed.Figure optionsDownload full-size imageDownload high-quality image (138 K)Download as PowerPoint slideResearch highlights► Optical absorption of the green fluorescent protein chromophore anion (HBDI−) in the gas phase was probed by photo-induced dissociation (“action”) spectroscopy. ► A pronounced dependence on the laser irradiance was found ► Dissociation at high irradiance is governed by multiple-photon absorption processes whose efficiency peaks between 476 and 488 nm. ► At very low irradiance (<0.4 mW cm−2) dissociation of gas-phase HBDI− is mostly promoted by single-photon transitions. ► The intrinsic absorption maximum of gas-phase HBDI− <476 nm is thus suggested to be blue-shifted compared to earlier results obtained with pulsed lasers.