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Multistate Multiconfiguration Quantum Chemical Computation of the Two-Photon Absorption Spectra of Bovine Rhodopsin
Samira Gholami1, Laura Pedraza-González2, Xuchun Yang1
1Department of Chemistry , Bowling Green State University , Bowling Green , Ohio 43403 , United States.
Humans can perceive infrared light through two-photon absorption (TPA) in the retina. Our study supports this, showing TPA allows rod photoreceptors to detect light around 950 nm.
Area of Science:
- Biophysics
- Photochemistry
- Vision Science
Background:
- Recent advancements reveal human perception of infrared (IR) light.
- This phenomenon is hypothesized to involve two-photon absorption (TPA) in retinal photoreceptors.
- Specifically, TPA may excite rhodopsin (Rh), the dim-light rod photoreceptor, to states normally reached by one-photon absorption (OPA).
Purpose of the Study:
- To computationally investigate the two-photon absorption (TPA) spectrum of bovine rhodopsin (Rh).
- To model human photoreceptors and understand the mechanism of infrared light detection.
- To elucidate the role of TPA in enabling vision under IR illumination.
Main Methods:
- Employed quantum mechanics/molecular mechanics (QM/MM) calculations.
- Utilized extended multiconfiguration quasi-degenerate perturbation theory (XMC-QDPT).
- Simulated the TPA spectrum of bovine rhodopsin as a model system.
Main Results:
- The simulated TPA spectrum of rhodopsin exhibits an intense S0 → S1 transition.
- Significant S0 → S2 and S0 → S3 transitions were observed in the TPA spectrum.
- The relative intensities of these higher-energy transitions were notably enhanced compared to the one-photon absorption (OPA) spectrum.
Conclusions:
- Infrared light around 950 nm can be perceived by rod photoreceptors via TPA.
- This provides strong support for the two-photon absorption mechanism underlying IR perception.
- Rhodopsin can also detect red light (approx. 680 nm) if TPA leads to S2 state population.
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