ACS Special Symposium "Extraterrestrial Organic Chemistry"

¹SETI Institute, Mountain View, CA and NASA-Ames Research Center Mail Stop 245-6, Moffett Field, CA 94035-1000, mbernstein@mail.arc.nasa.gov

²U.C.Berkeley Department of Earth & Planetary Science, 301 McCone Hall, Berkeley CA 94720-4767, jenblank@seismo.berkeley.edu

It is widely accepted that many comets and meteorites fell on the Earth early in its existence and that these extraterrestrial objects were replete with organic molecules, such as amino acids, quinones, and others. Today, certain chemical coincidences between extraterrestrial and biotic compounds, such as excesses of L-amino acids, seem to indicate that some species survived to sway the trajectory of evolution on Earth. Furthermore, isotopic enrichments in cometary and meteoritic molecules imply a non-terrestrial origin. Thus, there is a (chemical) historical sequence that connects processes that occurred in the interstellar medium five billion years ago to life on Earth and perhaps elsewhere. With this symposium we hope to bring together talks pertaining to the abundance and formation of organic compounds in space, their processing en route to the surface of terrestrial planets, and subsequent terrestrial processing in order to gain a more comprehensive understanding of all aspects of exogenous delivery.

NASA-Ames Research Center, Astronomy Branch Mail Stop 245-3 Moffett Field, CA 94035 Tel: (650) 604-0324 Fax: (650) 604-6779 chiar@misty.arc.nasa.gov

Carbonaceous material in the interstellar medium (ISM) takes many forms, including aliphatic (chain-like) hydrocarbons, polycyclic aromatic (ring-like) hydrocarbons, simple alcohols and other organic molecules detectable by infrared spectroscopic techniques. The evolution of interstellar grains is believed to be a cyclic process. This cycle includes the injection of dust into the diffuse (density < 100 atoms/cm^3) intercloud medium from its formation site in the circumstellar shells of evolved stars, and the processing and destruction experienced by grains over time. New generations of star-formation regions (dense molecular clouds) form out of the swept-up combination of circumstellar dust and the recycled products from previous dense clouds. I will give an overview of the inventory of the dominant carbon-bearing molecules as a function of interstellar environment based on what we have learned from space- and ground-based infrared spectroscopic observations. I will discuss recent results concerning the nature of aliphatic hydrocarbons in the diffuse intercloud medium, and the production of aromatic carbonaceous dust around certain evolved hot stars.

Raymond and Beverly Sackler Laboratory for Astrophysics at Leiden Observatory P O Box 9513 2300 RA Leiden, The Netherlands Tel. (31) 715-275-812 Fax: (31) 715-275-819 pascale@deuterium.strw.LeidenUniv.nl

Amino acids may form by gas phase reactions in interstellar clouds, photochemical reactions in solid dust grains, or by aqueous alteration in carbonaceous meteorites. The simplest amino acid, glycine, has not been unambiguously detected in either the interstellar medium or cometary comae. Upper limits of Glycine in molecular clouds are 10^-10 relative to H₂ and <0.005 relative to H₂O in the coma of comet Hale-Bopp. However, many amino acids have been identified in carbonaceous meteorites, and they are deuterium enriched, implying an interstellar heritage. The amino acid composition of CI chondrites is strikingly different from CM chondrites, suggesting that they originate from a different type of parent body. Recent laboratory simulations indicate that amino cids are highly susceptible to UV photodestruction and have therefore limited urvivability in regions with elevated UV flux. This provides important constraints for the origin of amino acids in space and the possible exogenous delivery of such compounds to the early Earth. In this paper the current knowledge on amino acids in the interstellar medium and solar system bodies is summarized and recent laboratory studies are presented.

NASA-Ames Research Center, Exobiology Branch MS 239-4, Moffett Field, CA 94035 Tel.: (650) 604-5968 Fax: (650) 604-1088 gcooper@mail.arc.nasa.gov

Carbonaceous meteorites are relatively enriched in carbon. Much of this carbon is in the form of soluble organic compounds. Absent among the biologically important compounds reported in meteorites are polyhydroxylated compounds (polyols) including sugars, sugar alcohols, sugar acids, etc. Five-carbon sugars are central to the role of contemporary nucleic acids, DNA and RNA. Glycerol, a three-carbon sugar alcohol, is a constituent of all known biological membranes. Our analyses of Murchison and Murray meteorites show that a variety of polyhydroxylated compounds are present. The identified compounds include sugar-alcohols, sugar-acids, deoxysugar-acids, and sugar di-acids. In general the compounds follow the abiotic synthesis pattern of other meteorite classes of organic compounds: decreasing abundance with increasing carbon number within a class of compounds and many, if not all, possible isomers are present at a given carbon number.

Department of Chemistry & Biochemistry, Arizona State University Tempe AZ 85287 Tel: (480) 965-3370 Fax: (460) 956-2747 pizzar@asuchm.la.asu.edu

Carbonaceous condrites, the product of presolar and planetary abiotic processes, offer a unique record of chemical evolution. The Tagish Lake meteorite, which fell into an icy lake in the Yukon Territory in January 2000, has been classified as one of the rare CI subgroup of these chondrites. The post-impact history of this meteorite is unusual in that portions were recovered within hours of infall and frozen immediately in an airtight container. With such a collection history, samples from the meteorite may be the most pristine materials of their kind. The organic content of the meteorite has been investigated, and both its insoluble material and extractable compounds have been analyzed using LCMS separation techniques. The results will be presented and assessed in view of data already available for other carbonaceous meteorites.

¹Geophysical Laboratory, Carnegie Institution of Washington 5251 Broad Branch Rd., NW, Washington DC 20015 Tel: (202) 478-8980 Fax: (202) 478-8900 cody@gl.ciw.edu

²Department of Terrestrial Magnetism, Carnegie Insitute of Washington, 5451 Broad Branch Rd., NW, Washington DC 20015

The organic material in primitive chondritic meteorites has attracted considerable attention, not only because it retains a record of synthesis in the interstellar medium (ISM) and Solar Nebula, but also because it may have been an important component of the prebiotic organic inventory on the early Earth. The bulk of the insoluble organic matter (70-90 wt. % of the total organics) is present as a poorly characterized macromolecular material, thought to be composed of a variety of aromatic ring systems cross linked by short methylene chains, esters, sulfides and biphenyl groups. We have employed a number of solid state NMR experiments including single pulse ¹H and ¹³C (with and without ¹H decoupling), ¹⁵N and ¹³C CPMAS (with and without ¹H decoupling). In addition we have analyzed the organic residue with C-and N-XANES. The functional group information extracted from these spectroscopic data provide a basis to derive a statistically consistent molecular model for the Murchison macromolecule. Ultimately, such a model can be used as a constraint for any mechanistic scenario presented for the synthesis of the extraterrestrial macromolecular phase.

Hervé Cottin ^1,2,

Marie-Claire Gazeau ¹, Yves Bénilan¹, François Raulin ¹

¹ L.I.S.A - (Université Paris XII, Paris VII, UMR CNRS 7583) CMC - 61, Avenue du General de Gaulle, 94010 Creteil cedex, France Tel: (33) 1 45 17 15 37 Fax : (33) 1 45 17 15 64, Cottin@lisa.univ-paris12.fr

Laboratory irradiations of ice mixtures by UV photons or energetic particles to simulate the evolution of interstellar and cometary ices lead to the formation of a complex refractory material. We present and discuss results we have obtained when some of these refractory molecules are in their turn irradiated or heated. Through different processes, such as thermal- and photo-degradation, the molecules in solid phase can release volatile products, which may be different than the original icy precursors and thus act as parent molecules for extended sources in comets, and indirect pathways for the production of interstellar species. Quantitative data (quantum yields, kinetic parameters) about those processes were missing to interpret observations of comets. Now, they allow us, for instance, to address the extent to which the presence of molecules like polyoxymethylene and hexamethylenetetramine in comets is relevant as an explanation for the formaldehyde and CN radical extended sources observed in several comets.

¹ Physics Department, University of Alabama at Birmingham 310 Campbell Hall, 1300 University Blvd., Birmingham, AL 35294-1170 Tel: (205) 934-8064 Fax: (205) 934-8042 gerakines@uab.edu

Icy materials in space are subjected various forms of energy capable of inducing physical and chemical alterations, including energetic particles and ultraviolet photons. Particle irradiation and UV photolysis may be simulated in the laboratory in order to study the materials known to be present in cosmic environments. A study of the formation of organic molecules from "icy" mixtures (T ~ 20-100 K) due to both irradiation (0.8 MeV protons) and photolysis (6-10 eV) is presented here using mid-IR spectroscopy from 5000-400 cm-1 (2-25 microns). The experiments described are relevant to icy mixtures as analogs of interstellar grain mantles, comets, or icy satellites. Our mixtures contain not only H₂O, but molecules such as CO, CO₂, CH₄ and CH₃OH^- all known to exist in astrophysical ices and to play important roles in the formation and evolution of organic materials. Comparisons between irradiation and photolysis results are presented.

Jamie E. Elsila¹,

J. Seb Gillette¹, Richard N. Zare¹, Max P. Bernstein², Jason P. Dworkin², Scott A. Sandford² & Louis J Allamandola²

¹ Department of Chemistry, Stanford University,Stanford, CA 94305-5080 Tel.: (650) 723-4318 Fax: (650) 725-0259 jelsila@stanford.edu

² SETI Institute/NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035-1000

Ices on grains in interstellar dense molecular clouds contain a variety of simple molecules as well as aromatic molecules of various sizes. While in these clouds, the icy grains are photo-processed by ultraviolet light, producing more complex molecules. It has been proposed that interstellar ice photochemistry may be the source of the organic compounds seen in comet and asteroidal dust (IDPs) and carbonaceous meteorites. We will review published work on the photo-oxidation of aromatic molecules, and will present new results of UV photochemistry of aromatics in the presence of simple molecules at 12 K. Overall we find that low-temperature ice photochemistry is consistent with the molecules and deuterium enrichments seen in carbonaceous chondrites. Thus, perhaps molecules formed in the interstellar medium and delivered to the early Earth by IDPs may have had an influence on the evolution or origin of life.

Daniel J. Cziczo,

Daniel M. Murphy, David Thomson, Christopher Dobson, Barney Ellison, Adrian Tuck, & Veronica Vaida

N.O.A.A. Aeronomy Laboratory, 325 Broadway, R/AL6 Boulder, CO 80305 Tel. (303)497-3755 Fax (303)497-5373 djcziczo@al.noaa.gov

Single particle analyses of stratospheric aerosols during two NASA WB-57F missions during 1998 and 1999 have provided novel information and a means to constrain the ablation and flux of meteoritic material. Measurements in this region of the atmosphere show that approximately half of the particles contain 0.5-1.0 wt % meteoric iron by mass, requiring a total extraterrestrial influx of 11-34 Gg per year. The Na/Fe ratio in these stratospheric particles is larger and the Mg/Fe and Ca/Fe ratios smaller than in chondritic meteorites, implying the fraction of material that is ablated must lie at the low end of previous estimates. Complimentary aerosol measurements below the tropopause show that particles contain ~50% organic matter by mass, a level which cannot be explained solely by bulk solubility. These observations stimulated thought on the astrobiological implications of an inverted micelle of organic material containing meteoric components.

SURVIVABILITY OF SIMPLE BIOMOLECULES DURING EXTRA-TERRESTRIAL DELIVERY: THERMAL EFFECTS

Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Circuito Exterior C.U., A. Postal 70-543, 04510 Mexico D.F., Mexico Tel: (52) 56 22 46 74 Fax: (52) 56 16 22 33 basiuk@nuclecu.unam.mx

Whether amino acids and nucleic acid bases can be successively delivered to the Earth by the space bodies other than meteorites (i.e., comets, asteroids and interplanetary dust particles) is unclear and depends primarily on capability of the biomolecules to survive high temperatures and shock waves during atmospheric deceleration and impacts to the terrestrial surface. We focused on the effect of temperature, studying the pyrolysis of amino acids and nucleic acid bases in the interval of 400-1000 °C, in oxygen-free (N₂ or CO₂) atmosphere. The simple biomolecules exhibit rather high thermal stability: they have chances to survive to the degree of 1-10% during atmospheric entry heating of the space bodies up to 500-600 °C, even without surface protection typical for meteorites. For amino acids, we also quantified the yields of piperazine-2,5-diones (cyclic dipeptides), as well as detected other derivatives which are able to regenerate amino acids upon hydrolysis.

¹Department of Earth & Planetary Science, Grad. School of Science, University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JAPAN Tel: (81) 3-5841-4663 Fax: (81) 3-5841-8075 sugita@eps.s.u-tokyo.ac.jp

Most organic matter delivered to the Earth’s surface by large meteoritic bodies is thought to be destroyed on impact. However, the consequences of impact-destroyed organic matter are not understood well yet. In order to observe chemical reaction of reduced carbon in an impact vapor within an oxidizing atmosphere, we performed a series of impact experiments using carbon-rich projectiles, high-impedance metal targets, and N₂-O₂-Ar model atmospheres. The emission spectra of the impacts were monitored by high-speed spectrometers. The spectroscopic observation indicates that vaporized carbon readily reacts with atmospheric nitrogen and forms CN radicals, which are unstable in an oxidizing condition. This experimental result suggests that a carbon-rich meteoritic body vaporized in an oxidizing atmosphere may create a reducing local environment, which may help synthesizing organic matter from once destroyed meteoritic organic matter. Such re-synthesis of organic matter may increase the overall survivability of meteoritic organic matter significantly.

¹U.C.Berkeley Department of Earth & Planetary Science, 301 McCone Hall, Berkeley CA 94720-4767 Tel: (510) 643-0540 Fax: (510) 643-9980 jenblank@seismo.berkeley.edu

³Applied Numerical Algorithms Group, Lawrence Berkeley National Laboratory, MS 50A-1148 1 Cyclotron Road, Berkeley, CA 94720

In order to test the viability of extraterrestrial delivery of organic compounds to the Earth via a large-object impact, we performed laboratory shock experiments using a proxy comet consisting of water (or ice) and near saturation levels of amino acids. We subjected our "comet" to well-constrained, ballistic shock events generating pressures similar to those in a low-angle comet-earth collision. Post-experiment analysis using LCMS revealed that a large fraction of the initial amino acids survived the impact event and that dominant reaction products appeared to be all possible dipeptide and cyclic dipeptide pairings of the initial amino acids. We observed distinct differences in response among the amino acids to pressure and temperature and shock pulse duration. These experiments demonstrate (1) the viability of comets to transport pristine extraterrestrial organic compounds to the Earth and (2) the potential for formation of biologically important compounds using the energy released during large-scale collisions.

¹ Department of Chemistry and Biochemistry, University of California, Santa Cruz CA 95064 Tel: (831) 459-5158 Fax: (831) 459-2935 deamer@hydrogen.ucsc.edu

Amphiphilic molecules such as monocarboxylic acids up to 12 carbons long are present in carbonaceous meteorites, and have also been synthesized by Fischer-Tropsch reactions under simulated prebiotic conditions. Similar compounds are produced photochemically in simulated interstellar/precometary ices, which can then be delivered to planetary surfaces during late accretion. It is therefore likely that amphiphilic compounds were available in the early Earth environment. We tested the possibility that such compounds could self-assemble into barrier membranes required by early cellular forms of life. Under defined conditions of pH and concentration, unbranched monocarboxylic acid 8-12 carbons in length are able to assemble into vesicular bilayer membranes. Significantly, addition of small amounts of alcohols markedly stabilized the bilayers. The vesicles provided a selective permeability barrier to ionic solutes and readily encapsulated macromolecules such as DNA. We conclude that membranous vesicles produced by mixed short-chain monocarboxylic acids and alcohols are plausible models for early cell membranes.

Center for Life Detection, Jet Propulsion Laboratory, MS 183-301 4800 Oak Grove Dr., Pasadena, CA 91109 Tel: (818) 354-8014 Fax: (818) 393-4445 Gene.D.McDonald@jpl.nasa.gov

Biomarkers such as chiral amino acids are key components in the search for evidence of past or present life on Mars. In order to assess the stability of amino acid chirality on Mars, we have calculated the time to total racemization of several amino acids based on diurnal and seasonal temperature fluctuations with latitude. Because amino acid racemization is extremely sensitive to temperature, maximum temperatures at each latitude will determine overall racemization rates. We conclude that racemization will be essentially complete on Mars for most amino acids, except at polar latitudes and at depths below the surface where temperature fluctuations are damped. These results have profound implications for the design of life detection instruments for Mars, as well as for the survival of chiral biosignatures in Martian meteorites recovered on Earth.

Extra bonus photos!!

Doug Caldwell and Perry Gerakines devour fish tacos at Rubios

Bob Ferante discusses the posters

Max Bernstein and Jason Dworkin shop for conference favors