Cosmic-ray and UV induced processes within mixed ices and at formamide : mineral interfaces

1. JPL NAI Titan Kickoff Meeting, July 8, 2009 Cosmic-ray and UV induced processes within mixed ices and at formamide : mineral interfaces T. M. Orlando, G. Grieves, M. Dawley, H. Barks, N. Hud, and Ernesto Di Mauro JPL NAI-Titan as a Prebiotic Chemical System Image from NASA Website

2. We are interested in cosmic ray, solar-photon and impact induced surface chemistry. I Cosmic ray (i.e. low-energy electron) interactions with ice. II. Reactive scattering with trapped methane. Formation of CO, CO2, HCOOH, etc. III. Reactive scattering with PAHs, Tholins and graphite to form sugar precursors. IV. The importance of another bio-solvent – formamide (NH2COH). Nulceobase formation on mineral surfaces. A plausible route to RNA? Surfaces chemistry can mean aerosol surfaces as well as Titan’s surface. Figure from 2008 JPL-NAI proposal

3. Simulating Titan’s atmospheric aerosol surface chemistry. Orlando Research Group UHV-Surface Science “ideal” conditions - Metal oxides and mineral surfaces Mineral/surfaces reactions under Low-temp/higher pressure conditions

4. Xe 355 nm 118 nm w1 3w1 w1 w1 Generating Vacuum Ultraviolet (VUV) Photons – Third Harmonic Generation P3 ω= N2 | χ(3 ω)|2 P ω3 F(b,Δk, L) P: laser density N: number density of Xenon χ: linear susceptibility ω: input angular frequency F: phase matching function b: confocal beam parameter Δk: wave-vector mismatch L: length of medium • VUV photons can be used to generate aerosols and in sensitive detection of desorbed products using-SPI*: • High sensitivity • High ionization efficiency • Little or no fragmentation 355 nm 355 nm 118 nm 85 nm * Ediristinghe, P.D.; et al.Anal. Chem. 2004, 4267-70

5. Laser based methods for multidimensional MS analysis of complex hydrocarbon mixtures • Analyzing complex hydrocarbon mixtures using two-step laser desorption and photoionization. • Couple this to 2-D GC methods

6. UHV system to simulate cosmic ray bombardment • Ice surfaces produced under ultrahigh vacuum (2x10-10 torr) • Surface cooled by closed cycle helium refrigerator and heated resistively for TPD • Surface is irradiated with 1-100 eV electrons from pulsed electron gun • Electron induced production and • desorption of products measured with • TOF, REMPI-TOF and QMS. • Also equipped with an FTIR (during and post irradiation).

7. Post-Irradiation TPD: D2O with CH4 dosed in pores 100 eV 200 nA 2 hours rastered • CH4 at 16 amu shows low temperature desorption and release during pore collapse • N2 (from background) and CO at mass 28 also released from pores • CO2 is retained until the ice overlayer desorbs at 190 K – forms only at the interfaces Grieves and Orlando manuscript in prep.

8. C3H3-6+ H+ HCCO+ HCCO+ H2+ CH3+ H3CCO+ H2O+ (HCCH)H+ HCO+ HOCO+ C5H5-9+ x10 C4H5-9+ Measuring ion yields from PAH’s, tholins or graphitic inclusions/substrates? Polyunsaturated fragments are produced which resemble graphite step-edge plus oxidized functional groups. This is with less than 1ML of water present. Oxidation is very facile.

9. What about oxidants from PAH’s, tholins or graphitic inclusions/substrates? Tholins/Ice mixture - Black Pure Tholins - Blue IR reflectance spectra of tholins (Sample from Mark Smith, UA).) A two-tier system – VUV induced formation of aerosols. Analyzing deposited material-IR reflectance, FTIR, Auger, Raman Can deposit micron sized “grains” TPD of NH3 and HCN.

10. Can formamide reactions occur during impact events? • Speculation – • Perhaps formamide chemistry was important during impact events? • High temperature excursions could have occurred. (Calculations on longevity of impact oases on Titan: 103-104 yrs. (O’Brien, Lorenz, and Lunine, Icarus 173, (2005) 243 • NH3 may be needed with limited amount of water. • . Figure from 2008 JPL-NAI proposal

11. This component of Theme 3 will address: • the VUV and low-energy electron induced formation of organic aerosols via gas-phase photochemical and low-energy electron induced nucleation processes. • the uptake, “dissolution” and oxidation of these organic aerosols by condensed ices and simulated cosmic ray bombardment. • laser desorption, single-photon mass spectrometry analysis of complex organic mixtures produced by photochemical deposition. • silicate, phosphate mineral reactions with HCN, nitriles and possibly formamide which may lead to polymer and nucleobase formation. Tholin work in collaboration with T. McCord and M. Smith Visit us at http://web.chemistry.gatech.edu/~orlando/epicslab/

12. 5 guanine 3 adenine formamide 4 hypoxanthine Effects of mineral catalysts and The presence of radiation. (UV light)? 1 purine Heating formamide produces only purine unless minerals are present D, hn 2 allopurinol • Mineral catalyst required to produce anything but purine • Nonspecific product distributions reduces requirement for particular minerals • Synergistic with mineral catalysts, UV light further enhances synthesis rather than purely degradation. UV light expands product diversity 130 oC for 48 hours

13. Scheme 1. Route to formation of adenine from formamide. After thermal degradation of formamide into HCN and water. Reactions proceed via HCN polymerization and are enhanced by mineral catalysts. Spiking with DAMN accelerates both the thermal and nonthermal routes to adenine formation but the UV photochemical route results in significantly higher yields. Testing the chemistry • Time series measurement of the production of adenine from UV irradiated formamide at 130 oC. • Triangles represent adenine from neat formamide irradiation (magnified twenty times), while diamonds are for the same experiment spiked with 10 mg DAMN in 4 mL. • The dashed-line with diamonds represents no UV.

14. Post irradiation TPD after electron irradiation of methane in H2O18 ice: Production of CO218 H2O18 post irradiation • No mass coincidence for CO2, CO218 • We observe all the following masses • 44 = CO2 • 45 - HOCO • 46 = O16CO18 • 48 = CO218 CO2 is formed due to reactions with CO and hot/mobile O as well as via HCO and OH. The yield above 190 K is likely a surface/interface reaction

15. Post irradiation TPD after electron irradiation of methane in H2O18 ice: Production of CO18 Use O18 labeled water to distinguish between background N2 (mass 28) and stimulated production of CO (mass 28) CO18 (mass 30) pore collapse • Unirradiated sample releases some mass 30 (NO or HCOOH contaminant) during sublimation. • Irradiated mixture releases mass 30 (primarily CO18) during pore collapse

16. An example of electron-stimulated removal of edge-sites and defects from epitaxial graphene and graphene-oxide The H+ yield is very high for both surfaces There are high mass hydrocarbons from both substrates. There are O-containing Fragments from the graphene oxide. The total cross section for hydrogen removal is ~10 -19 cm2 Incident electron energy - 50 eV HCO+ HCCO+ C2Hx+ C3Hx+ C4Hx+ C5Hx+

17. 100 eV 200 nA 2 hours Rastered over 1 cm2 ~ 1015 e- /cm2 total dose Post Irradiation TPD: D2O D2O + CH4 (pores) unirradiated D2O + CH4 (pores) irradiated Grieves, Orlando, Blake manuscript in prep.

18. Biological building blocks for RNA and DNA from Formamide? Na3PO4 cytosine purine • Formamide provides plausible routes to nucleobase formation, nucleoside phosphorylation and nucleic acid polymerization. • Saladino and Di Mauro laboratories have demonstrated purine formation from formamide in the presence of mineral catalysts. Review: Chemistry and Biodiversity Vol. 4, 694 (2007) Hureaulite cytosine mg product per g formamide guanine Ludlamite purine formylglycine adenine uracil formamide Turquoise allopurinol cytosine hypoxanthine formylglycine