German Edition: DOI: 10.1002/ange.201501678 Selectivity at Surfaces International Edition: DOI: 10.1002/anie.201501678 Chiral Selective Chemistry Induced by Natural Selection of Spin- Polarized Electrons** Richard A. Rosenberg,* Debabrata Mishra, and Ron Naaman Abstract: The search to understand the origin of homochirality in nature has been ongoing since the time of Pasteur. Previous work has shown that DNA can act as a spin filter for low- energy electrons and that spin-polarized secondary electrons produced by X-ray irradiation of a magnetic substrate can induce chiral selective chemistry. In the present work it is demonstrated that secondary electrons from a substrate that are transmitted through a chiral overlayer cause enantiomeric selective chemistry in an adsorbed adlayer. We determine the quantum yields (QYs) for dissociation of (R)- or (S)-epichlor- ohydrin adsorbed on a chiral self-assembled layer of DNA on gold and on bare gold (for control). The results show that there is a significant difference in the QYs between the two enantiomers when adsorbed on DNA, but none when they are adsorbed on bare Au. We propose that the effect results from natural spin filtering effects cause by the chiral mono- layer. Most biomolecules can be synthesized in two different mirror-image (chiral) shapes, namely two enantiomers. The enantiomers are recognized by their ability to rotate the polarization of linear polarized light either to the left ( l) or to the right ( d). In bioorganisms, sugars are always D and amino acids are always l. How this enantiomeric preference originated remains a mystery. Investigations into possible avenues of prebiotic chiral selectivity have been pursued since the time of Pasteur, and much of the effort in this area has been summarized in a number of reviews. [1] So-called determinate mechanisms presuppose that interaction of a chiral physical force with relevant organic molecules led to an enantiomeric excess (ee). Many investigations in this area have been devoted to pathways that involve preferential destruction of a particular isomer in an initially racemic mixture (equal quantities of both enantiomers), through the interactions of chiral particles such as circularly polarized UV radiation [2] or longitudinally spin-polarized electrons. [3] It has been shown that low-energy (0–10 eV) spin- polarized secondary electrons, produced by irradiation of a magnetic substrate, can induce chiral-selective chemistry in an adsorbed adlayer. [4] Additional work has demonstrated that organized, double-stranded (ds) DNA, adsorbed on a gold substrate, acts as a natural spin filter for initially unpolarized, low-energy (0–1.2 eV) electrons, resulting in net polarizations as high as 60 %. [5] This selectivity arises from the tendency of the electrons moving in a left- or right-handed chiral potential to have their spin orientations aligned parallel or antiparallel to their velocity. [6] Experiment and theory indicates that this spin filtering effect should be effective for higher energy (E < 15 eV) electrons as well. [7] In the present study, we probe whether low-energy secondary electrons, produced by X-ray irradiation of a gold substrate, and transferred through the chiral monolayer, induce enantio- meric selective chemistry in an adsorbed adlayer. To test this, (R)- or (S)-epichlorohydrin (C 3 H 5 ClO, Epi) was adsorbed on a self-assembled monolayer of 70 base-pair- long dsDNA (Figure 1). The secondary electron-induced reaction was monitored by following changes in the Cl 2p X-ray photoelectron spectroscopy (XPS) spectra. By kinetic modeling of the reaction, quantum yields (QYs) were determined. For (S)-Epi, the QY was about 16 % greater than for the R enantiomer, while the QYs were the same for the two enantiomers when they were adsorbed on bare Au. Figure 2 presents XPS spectra of both bare Au and Au/ dsDNA samples taken before and after dosing with Epi. Figure 1. Diagram showing how the secondary electrons produced by X-ray irradiation become spin-polarized, with their spins aligned antiparallel to their velocity, and induce chiral selective chemistry in adsorbed (R)- or (S)- epichlorohdydrin. [*] Dr. R. A. Rosenberg Advanced Photon Source, Argonne National Laboratory 9700 S. Cass Avenue, Argonne, IL 60439 (USA) E-mail: rar@aps.anl.gov Dr. D. Mishra, Prof. R. Naaman Department of Chemical Physics, Weizmann Institute Rehovot 76100 (Israel) [**] We would like to thank Omicron for the loan of the Argus electron energy analyzer and Dr. Reuben Gann and Prof. Thom Orlando for experimental help. The work performed at the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under contract No. DE- AC02-06CH11357. R.N. and D.M. acknowledge the support from the ARC-Adv grant. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201501678. Angewandte Chemie 7295 Angew. Chem. Int. Ed. 2015, 54, 7295 –7298 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim