Counterion-controlled spectral tuning of the protonated Schiff-base retinal

Yoni Toker, Jeppe Langeland, Elisabeth Gruber, Christina Kjær, Steen Brøndsted Nielsen, Lars H. Andersen, Veniamin A. Borin, Igor Schapiro

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


Color vision is based on the ability of different opsin proteins to tune the absorption band of their chromophore, the retinal protonated Schiff base (RPSB). Two main mechanisms proposed for this tunability are geometric and electrostatic. Here we probe the latter effect experimentally and by a quantum chemical calculation of the absorption by an isolated complex containing the retinal chromophore and molecules with a strong dipole moment. Betaine complexation causes an anomalously large blue shift. The shift provides direct evidence that the strong charge-transfer character of the electronic transition is the cause of the opsin shift, and shows that the electric field of the counterion is responsible for the color tuning, which allows absorption of light in the blue region of the visible spectrum by opsin proteins.

Original languageAmerican English
Article number043428
JournalPhysical Review A
Issue number4
StatePublished - 23 Oct 2018

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© 2018 American Physical Society.


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