Direct Measurement of the Isomerization Barrier of the Isolated Retinal Chromophore

Abstract

Isomerizations of the retinal chromophore were investigated using the IMS‐IMS technique. Four different structural features of the chromophore were observed, isolated, excited collisionally, and the resulting isomer and fragment distributions were measured. By establishing the threshold activation voltages for isomerization for each of the reaction pathways, and by measuring the threshold activation voltage for fragmentation, the relative energies of the isomers as well as the energy barriers for isomerization were determined. The energy barrier for a single cis–trans isomerization is (0.64±0.05) eV, which is significantly lower than that observed for the reaction within opsin proteins.

Measurements of the stabilities of isolated retinal chromophores

“…They have also used IMS to propose a mechanism for the gas phase fragmentation of the RPSB [11] which we have later confirmed using isotope labeling mass-spectrometry [12]. Using collision induced isomerization we have determined the barrier energies for isomerization of the RPSB and have shown that the barrier energy for the biologically important isomerization is much lower in the gas phase [15]. Thus, the protein has an important role in increasing the barrier energy and regulating the rate of dark counts.…”

“…the relative energies and barrier energies for isomerizations that are detailed in appendix B. In previous work, the energy barrier for isomerization of the RPSB was extensively discussed [15]. For the case of the dimethylated RPSB the barrier energies for isomerization and fragmentation are higher than for the RPSB.…”

Photo and Collision Induced Isomerization of a Cyclic Retinal Derivative: An Ion Mobility Study

“…Parent and daughter isomer ions are separated in the second drift region. As demonstrated by Clemmer and coworkers [16,17], by monitoring CII as a function of the electric field strength, one can derive information on barrier heights for molecular rearrangements.…”

Charge, Color, and Conformation: Spectroscopy on Isomer-Selected Peptide Ions

“… 17 Comparison of the ATDs recorded after DT2 for different activation voltages ( Figure 2 a–c) allows one to probe interconversions between the different peaks. 36 , 37 After selection of peak A ( Figure 2 a), isomerization toward peak B is observed even at low excitation voltage and is amplified at high excitation voltage. After selection of peak B, the reverse process is observed, although more limited ( Figure 2 b).…”