UV photolysis of quinoline in interstellar ice analogs

available online at http://meteoritics.org 785 © The Meteoritical Society, 2006. Printed in USA. UV photolysis of quinoline in interstellar ice analogs Jamie E. ELSILA1*, Matthew R. HAMMOND2, Max P. BERNSTEIN1, Scott A. SANDFORD1, and Richard N. ZARE2 1NASA Ames Research Center, MS 245-6, Moffett Field, California 94035–1000, USA 2Department of Chemistry, Stanford University, Stanford, California 94305–5080, USA *Corresponding author. E-mail: [email protected] (Received 16 November 2005; revision accepted 03 February 2006) Abstract–The polycyclic aromatic nitrogen heterocycle (PANH) quinoline (C9H7N) was frozen at 20 K in interstellar ice analogs containing either pure water or water mixed with methanol or methane and exposed to ultraviolet (UV) radiation. Upon warming, the photolysis products were analyzed by high-performance liquid chromatography and nanoscale liquid chromatography-electrospray ionization mass spectrometry. A suite of hydroxyquinolines, which were formed by the addition of oxygen atoms to quinoline, was observed as the primary product in all the ices. Quinoline N oxide was not formed, but five hydroxyquinoline isomers were produced with no clear dominance of one isomer. Reduction products, formed by hydrogen atom addition, were also created. Ices created at 20 K with H2O: quinoline ratios of 10:1 to 100:1 showed similar product distributions to those at 122 K, with no apparent temperature or concentration dependence. Increasing the UV dose led to a decrease in overall yield, indicating that quinoline and its products may be photo-destroyed. Methylquinolines were formed upon photolysis of the methanoland methane-containing ices. In addition, possible methoxyquinolines or quinoline methylene alcohols were formed in the methanolcontaining ice, while methylhydroxyquinolines were created in the methane-containing ice. This work indicates that oxidation of PANHs could occur in icy extraterrestrial environments and suggests that a search for such compounds in carbonaceous meteorites could illuminate the possible link between interstellar ice chemistry and meteoritic organics. Given the importance of oxidized and alkylated PANHs to biochemistry, the formation and delivery of such molecules to the early Earth may have played a role in the origin and evolution of life.The polycyclic aromatic nitrogen heterocycle (PANH) quinoline (C9H7N) was frozen at 20 K in interstellar ice analogs containing either pure water or water mixed with methanol or methane and exposed to ultraviolet (UV) radiation. Upon warming, the photolysis products were analyzed by high-performance liquid chromatography and nanoscale liquid chromatography-electrospray ionization mass spectrometry. A suite of hydroxyquinolines, which were formed by the addition of oxygen atoms to quinoline, was observed as the primary product in all the ices. Quinoline N oxide was not formed, but five hydroxyquinoline isomers were produced with no clear dominance of one isomer. Reduction products, formed by hydrogen atom addition, were also created. Ices created at 20 K with H2O: quinoline ratios of 10:1 to 100:1 showed similar product distributions to those at 122 K, with no apparent temperature or concentration dependence. Increasing the UV dose led to a decrease in overall yield, indicating that quinoline and its products may be photo-destroyed. Methylquinolines were formed upon photolysis of the methanoland methane-containing ices. In addition, possible methoxyquinolines or quinoline methylene alcohols were formed in the methanolcontaining ice, while methylhydroxyquinolines were created in the methane-containing ice. This work indicates that oxidation of PANHs could occur in icy extraterrestrial environments and suggests that a search for such compounds in carbonaceous meteorites could illuminate the possible link between interstellar ice chemistry and meteoritic organics. Given the importance of oxidized and alkylated PANHs to biochemistry, the formation and delivery of such molecules to the early Earth may have played a role in the origin and evolution of life.