Significance: The role of the electron spin in chemistry and biology has been receiving much attention because of a plausible relation to electromagnetic field effects on living organisms. Part of the difficulty in studying the subject arises from the lack of a physical model that can rationalize these phenomena. Recently the chiral-induced spin selectivity effect was observed in electron transmission through organic molecules. The question is to what extent the effect takes place in proteins. In the present study, we probed bacteriorhodopsin embedded in its native membrane environment. We observed clear evidence for spin-dependent electron transmission through this system. The results point to the possibility that the effect may play a role in electron transfer in biological systems.

We have measured the room temperature magnetization in Al-substituted magnesium oxide, Mg(Al)O nanoparticles with Al fractions of up to 5 at. %. All samples, including undoped MgO nanoparticles, exhibit weak room temperature ferromagnetism, with the saturation magnetization reaching a maximum of 0.023 emu/g at 2 at. % of Al. X-ray photoelectron spectroscopy identifies the presence of oxygen vacancies in both doped and undoped MgO nanoparticles, with the vacancy concentration increasing upon vacuum annealing of Mg(Al)O, resulting in two-fold enhancement of the saturation magnetization for 2 at. % Al-doped MgO. Our results suggest that the oxygen vacancies are largely responsible for the weak room temperature ferromagnetism in MgO.

The role of the electron spin in chemistry and biology has received much attention recently owing to to the possible electromagnetic field effects on living organisms and the prospect of using molecules in the emerging field of spintronics. Recently the chiral-induced spin selectivity effect was observed by electron transmission through organic molecules. In the present study, we demonstrated the ability to control the spin filtering of electrons by light transmitted through purple membranes containing bacteriorhodopsin (bR) and its D96N mutant. The spin-dependent electrochemical cyclic voltammetry (CV) and chronoamperometric measurements were performed with the membranes deposited on nickel substrates. High spin-dependent electron transmission through the membranes was observed; however, after the samples were illuminated by 532 nm light, the spin filtering in the D96N mutant was dramatically reduced whereas the light did not have any effect on the wild-type bR. Beyond demonstrating spin-dependent electron transmission, this work also provides an interesting insight into the relationship between the structure of proteins and spin filtering by conducting electrons.