Invited
Spectral tuning and isomerizations of the retinal chromophore

The retinal protonated Schiff base (RPSB) chromophore is the photon detector used in every known form of animal vision. We have recently measured the blue shift in absroption band by the RPSB induced by an external electric field. This was achieved by measuring the absorption band of the RPSB complexated with N.N.N. trimethylglycine, a molecule with an extremely large dipole moment (11.9 D). The anomalosly large blue shift we observe provides direct evidence for the charge transfer character of the electronic transition in the RPSB and proves that the electrostatic effect from the counter-ion is the dominant tuning mechanism in opsin proteins enabling us to see blue colors.

We will also discuss gas phase studies of RPSB isomerizations, which were conducted using ion mobility spectroscopy, and show that slight changes to the structure of the RPSB, while not effecting is absorption band, can have dramatic effects on its isomerization dynamics.

References

1. “Counterion-controlled spectral tuning of the protonated Schiff-base retinal” Yoni Toker, Jeppe Langeland, Elisabeth Gruber, Christina Kjr, Steen Brndsted Nielsen, and Lars H. Andersen, Veniamin A. Borin and Igor Schapiro, Phys. Rev. A. 98 (2018), 043428.
2. “Measurement of the stabilities of isolated retinal chromophores” L. Musbat, M. Nihamkin, Y. Toker, J. M. Dilger, D. R. Fuller, T. J. El-Baba, D. E. Clemmer, S. Sarkar, L. Kronik, A. Hirshfeld, N. Friedman, and M. Sheves, Phys. Rev. E 95 (2017), 012406.
3. “Direct Measurement of the Isomerization Barrier of the Isolated Retinal Chromophore”, J. Dilger, L. Musbat, M. Sheves, A. B. Bochenkova, D. E. Clemmer, Y. Toker, Ang. Chemie Int. Ed. 127 (2015), 4830-4834.