Evidence for a vibrational phase-dependent isotope effect on the photochemistry of vision

Abstract

Vibronic coupling is key to efficient energy flow in molecular systems and a critical component of most mechanisms invoking quantum effects in biological processes. Despite increasing evidence for coherent coupling of electronic states being mediated by vibrational motion, it is not clear how and to what degree properties associated with vibrational coherence such as phase and coupling of atomic motion can impact the efficiency of light-induced processes under natural, incoherent illumination. Here, we show that deuteration of the H-C=C-H double-bond of the 11-cis retinal chromophore in the visual pigment rhodopsin significantly and unexpectedly alters the photoisomerization yield while inducing smaller changes in the ultrafast isomerization dynamics assignable to known isotope effects. Combination of these results with non-adiabatic molecular dynamics simulations reveals a vibrational phase-dependent isotope effect that we suggest is an intrinsic attribute of vibronically coherent photochemical processes.

OpenMolcas: From Source Code to Insight

“…In a recent study of the photoisomerization in rhodopsin, the new feature helped to reveal a new type of kinetic isotope effect. 232 In this specific case, the hydrogen atoms of the 11-cis isomerizing double bond were replaced by deuterium in three different ways: at both hydrogens, and at the hydrogen at either the 11 or 12 position ( fig. 9).…”

Coherent exciton-vibrational dynamics and energy transfer in conjugated organics

“…While the initial reports had attributed the observed dynamics to unexpectedly long-lasting electronic coherences, later investigations linked it to the interplay between both electronic and vibrational degrees of freedom 13 , 14 and it was broadly hypothesized that oscillatory evolution of delocalized electronic wavefunctions can improve transport of energy and charge carriers for light-harvesting, lighting, and other optoelectronic applications 1 , 3 , 8 , 15 , 16 . The change in thinking towards more complex interaction between vibrations and electronic coherences was particularly prevalent in the realm of photobiology 17 , where commonly employed models treat vibrations as quantum degrees of freedom 18 – 23 .…”

Synthesis of 9-CD3-9-cis-retinal cofactor of isorhodopsin

“…23,24 Isotopically labeled retinoids are also useful in studies employing neutron diffraction 25–27 and vibrational spectroscopy. 28,29 To our knowledge, this is the first report on the preparation of this labeled molecule.…”