title: Spin selectivity in electron transfer in photosystem I.
abstract: Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons' spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high-spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high-spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.
authors.affiliation: Department of Chemical Physics, The Weizmann Institute, Rehovot 76100 (Israel).
authors.forename: Itai
authors.initials: I
authors.lastname: Carmeli
authors.forename: Karuppannan
authors.initials: K
authors.lastname: Senthil Kumar
authors.forename: Omri
authors.initials: O
authors.lastname: Heifler
authors.forename: Chanoch
authors.initials: C
authors.lastname: Carmeli
authors.forename: Ron
authors.initials: R
authors.lastname: Naaman
mesh_terms: D004579:Electron Transport; D045331:Photosystem I Protein Complex / Q000737:chemistry*
chemical_list: D045331:Photosystem I Protein Complex
keywords: chirality; electron transfer; photosystem I; temperature-dependent charge transfer