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Isomerization of Isolated Retinal Chromophore


  Lihi Musbat  ,  Dilger J. M.  ,  Nihamkin M.  ,  Fuller D. R.  ,  El-Baba T. J.  ,  Sarkar S.  ,  Kronik L.  ,  Hirshfeld A.  ,  Friedman N.  ,  Sheves M.  ,  Clemmer D. E.  ,  Toker Y.  
 Department of Physics, Institute for Nanotechnology, Bar-Ilan University
Spectrum Warfare Systems Department, NSWC Crane Division, Crane, Indiana, USA
Department of Physics, Institute for Nanotechnology, Bar-Ilan University
Department of Chemistry, Indiana University Bloomington, Indiana, USA
Department of Chemistry, Indiana University Bloomington, Indiana, USA
Departement of Materials and Interfaces, Weizmann Institute of Science
Departement of Materials and Interfaces, Weizmann Institute of Science
Departement of Organic Chemistry, Weizmann Institute of Science
Departement of Organic Chemistry, Weizmann Institute of Science
Departement of Organic Chemistry, Weizmann Institute of Science
Department of Chemistry, Indiana University Bloomington, Indiana, USA
Department of Physics, Institute for Nanotechnology, Bar-Ilan University

One of the main challenges of modern science is to measure structure and structural changes (isomerization) of biological molecules. Recent developments in the field of ion mobility spectroscopy allow us to isolate specific structures of a given molecule, and experimentally determine the relative energies of different isomers and the energy barrier for isomerizations in the gas phase. One of the most fascinating isomerization in nature is that of the Retinal Protonated Schiff-base (RPSB) chromophore. The isomerization of this molecule after photon absorption is the first step in every known form of animal vision and has intriguing properties: it is very efficient, specific and ultrafast (occurs in less than 200 fs). In order to understand what makes the RPSB isomerization so unique, we measured the energy barrier for each isomerization channel, with ion mobility spectroscopy method, and compare them to RPSB derivatives. We observe that the barrier height for isomerization is much smaller than within the protein. We find that small changes to the structure of the chromophore have a great effect on its ground-state energetics, and in particular that the methyl group in the C13 position plays a crucial role.