| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS+EN-TuA |
| Session: | Photocatalysis, Photochemistry, and Chirality at Surfaces |
| Presenter: | Richard Rosenberg, Argonne National Laboratory |
| Authors: | R.A. Rosenberg, Argonne National Laboratory D. Mishra, Weizmann Institute of Science, Israel R. Naaman, Weizmann Institute of Science, Israel |
| Correspondent: | Click to Email |
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 bio-organisms, 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. Many investigations in this area have been devoted to pathways that involve preferential destruction of a particular isomer in an initially racemic (equal quantities of both enantiomers) mixture, through the interactions of chiral particles such as circularly polarized UV radiation or longitudinally spin polarized electrons. 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.[1] 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 produced by UV irradiation of the substrate, resulting in net polarizations as high as 60%.[2] Experiment and theory indicates that this spin filtering effect should be effective for higher energy (E < 15 eV) electrons as well.[3] In the present study, we probe if low energy secondary electrons, produced by x-ray irradiation of a gold substrate, and transferred through the chiral monolayer, induce enantiomeric selective chemistry in an adsorbed adlayer. To test this, (R)- or (S)-epichloroydrin (C3H5ClO, Epi) was adsorbed on a self-assembled monolayer of 70 base pair long dsDNA. The secondary electron-induced reaction was monitored by following changes in the Cl 2p x-ray photoelectron spectroscopy spectra. By kinetic modeling of the reaction, quantum yields (QYs) were determined. For S-Epi the QY was ~16 % greater than for the (R) enantiomer, while the QYs were the same for the two enantiomers when they were adsorbed on bare Au.
[1] R. A. Rosenberg, M. Abu Haija, P. J. Ryan, Phys. Rev. Lett. 2008, 101, 178301.
[2] a) B. Gohler, V. Hamelbeck, T. Z. Markus, M. Kettner, G. F. Hanne, Z. Vager, R. Naaman, H. Zacharias, Science 2011, 331, 894-897; b) S. G. Ray, S. S. Daube, G. Leitus, Z. Vager, R. Naaman, Phys. Rev. Lett. 2006, 96, 036101.
[3] R. A. Rosenberg, J. M. Symonds, V. Kalyanaraman, T. Markus, T. M. Orlando, R. Naaman, E. A. Medina, F. A. López, V. Mujica, J. Phys. Chem. C 2013, 117, 22307-22313.