First Steps in the Origin of Life in the Universe

EuroConference

Sixth Trieste Conference on Chemical Evolution

Talks

REMINISCENCES PONT-à-MOUSSON- 1970 TO TRIESTE- 2000

MOHINDRA S. CHADHA

C-6, Beach House, Juhu
Mumbai- 400 049, INDIA
( e-mail:chadhams@mail.com)

The First International Conference on the Origin of Life on Earth was held
in Moscow under the auspices of the International Union of Biochemistry in
1957. This was followed by the Second Conference held at Wakulla Springs,
Florida in 1963 under the auspices of the Institute for Space Biosciences,
and the U.S. National Aeronautics and Space Administration.

As the interest in the all important subject - Chemical Evolution and Origin
of Life was growing, the Third International Conference on the Origin of
Life was convened by Rene Buvet of France and Cyril Ponnamperuma of U.S.A.
in 1970 at Pont-a-Mousson, France. Sessions were held on the synthesis of
small molecules, oligomers and polymers, photochemical processes, origin of
biological molecules, biological structures, primitive biochemistry and
biology and exobiology. Also discussed were some general and theoretical
problems related to the question of Origin of Life. Besides the father
figure in this area of scientific activity, namely Alexander Ivanovich
Oparin, several eminent scientists like I.Prigogine, M.Florkin, A.Rich,
F.Lipmann, S.W.Fox, Cyril Ponnamperuma, S.L.Miller, J.Oro, H.Baltscheffsky,
I.S.Kulaev, M.O.Dayhoff, A.A.Krasnovsky, L. Margulis and others contributed
significantly to the conference. This became the fore-runner of the
International Conferences on the Origin of Life that followed and the seed
was sown for the formation of the International Society for the Study of
the Origin of Life (ISSOL).

I was one of the fortunate ones to be a participant in the all important
Pont-a-Mousson Conference and am pleased to see some of the contributors
there viz. F.Raulin, S.L.Miller, J.Oro, M.S.Kritsky and H.Baltscheffsky to
be present at the Trieste-2000 conference also. In my personal scientific
life, my participation in all the International Conferences on the Origin of
Life and ISSOL Meetings (except for two), starting with the first one in
Barcelona in 1973( following the Pont-a-Mousson Conference) and all the six
Trieste Conferences starting with the first one in 1992 has given me a great
sense of scientific satisfaction.

For me personally, the Pont-a-Mousson conference and some of the
International Conferences on the Origin of Life and the ISSOL Meetings were
of great deal of significance as my close friend, the late Cyril
Ponnamperuma, with whom I had collaborated at Ames, NASA was a torch bearer
for many of these. The Trieste Conferences are of equal significance to me
as along with Professor Cyril Ponnamperuma, the outstanding theoretical
physicist Professor Abdus Salam, who also had his roots in the Third World,
was the co-founders of this unique series of Conferences in Trieste.
Unfortunately, they have both physically left this world and we miss them
greatly, but their spirit of enquiry and their quest to gain insights into
questions related to the Origin of Life are all pervasive. Fortunately,
Professor Chela-Flores is continuing the good work with distinction.

It is my privilege to share with you some precious moments , scientific and
social which I and on ocassions my wife, have experienced with many of the
participants of the ISSOL Meetings and Trieste Conferences. It has been a
pleasant journey during the last 30 years and I am grateful to all those who
have contributed to some of the cherished memories.

I compliment the organisers of the present conference, Profs. Julian
Chela-Flores, Tobias Owen and Francois Raulin for their untiring efforts to
put the Sixth Trieste Conference to-gether and entitle it as FIRST STEPS IN
THE ORIGIN OF LIFE IN THE UNIVERSE. While major strides have been taken in
understanding many aspects of this all important topic, but the answers are
far from complete and may continue to remain so for long. However, our quest
to find logical answers to this question will unfold many fascinating
chapters, and some of these will be presented here itself in the course of
the present conference!!

CAN DNA BASES AND AMINO ACIDS BE PRODUCED DURING STAR FORMATION?

SANDIP K. CHAKRABARTI,

SN Bose National Centre for Basic Sciences
JD Block, Sector III, Salt Lake,
Calcutta 700091, India

Abstract: The question of how life on earth was originated is a major problem in todays Astrobiology programme. We propose a model where major complex molecules, such as amino acids, urea, DNA bases etc. were originated in the interstellar clouds during the star formation phase. During collapse, the interstellar cloud temperature goes up intially very slowly (isothermal phase) and then very rapidly (adiabatic phase). Density also goes up as the collapse proceeds. Initial composition of H, N, C, O etc. slowly changes to create simple molecules such as water, ammonia, hydrogen cyanide etc. eventually creating more complex molecules. Towards the end of the collapse we find that significant amount of Adenine, Glycene, urea etc. were also formed. Since the reaction rates are generally unknown, we study many of these reactions parametrically and find that even when radiative association is included, five HCN molecules can produce sufficient adenine to contaminate during early planetary systems. It is also possible that these contaminants remain in safe custody of meteorites during the turbulent phases of the early solar system and later, during meteor storms they deposite these compounds in the earth from which complete DNA molecules were formed.

SEARCHING FOR WATER IN EXOPLANETS

C.B.COSMOVICI,
IFSI/CNR,
Rome, Italy

After the sensational discoveries made during the last 15 years in cometary research, which led to the detection of prebiotic molecules in Comets, Bioastronomy obtained in the last 5 years a second basic success after the discovery of 34 giant planets outside the Solar System.

The impact of 21 fragments of Comet Shoemaker-Levy/9 with the Jovian Atmosphere in July 1994 gave astronomers the unique opportunity to study the chemistry and physics of a planet during a catastrophic impact.

By using a 132.000 channel spectrometer coupled to the 32 m dish of the Medicina Radiotelescope, we were able during the impact of the cometary nuclei with the upper atmosphere of Jupiter not only to detect water of cometary origin at 22 GHz, but to observe for the first time in the Solar System a water MASER emission induced by a catastrophic impact (1).

Thus water MASER emission can be used as a powerful diagnostic tool for planetary search outside the Solar system, as comets are able to deliver huge amounts of water (about 50 billion tons per comet) in planetary atmospheres rising the probability of life development. Thus we started a search program at Medicina using the same multichannel spectrometer in order to cover the Doppler shifts due to exoplanetary rotation. In this contribution we'll illustrate the feasibility, the technique used and the first targets for the search within 50 Light Years.

(1) C.B.Cosmovici, S.Montebugnoli, A.Orfei, S.Pogrebenko and P.Colom, Planet.Space.Sci.,44,735,1996

ORIGIN AND PERSISTENCE OF GENETIC MATERIAL IN PREBIOTIC HABITATS. THE POSSIBLE ROLE OF NUCLEIC ACID-CLAY COMPLEXES

ENZO GALLORI

Department of Animal Biology & Genetics,
University of Florence.
Florence, Italy.

Once formed, early informational biomolecules must have been able to persist in critical conditions, like those probably present in primeval terrestrial habitats.
Recent observations on the synthesis of oligonucleotides and peptides on clay surfaces (1) have reinforced Bernal's original suggestion (2) that clay minerals played a key role in the prebiotic formation of life's polymers.
It is our belief that the formation of a close association between prebiotic genetic molecules and clay particles was a crucial step in the preservation of genetic information, allowing the genetic material to express its biological potential, i.e. to replicate and evolve.
In the present work, the molecular characteristics and biological activity of different nucleic acid molecules (DNA, RNA) adsorbed/bound on clay minerals are discussed in the light of their possible role in ancestral environments.

1) Ferris, J.P. et al. 1996 Nature 381, 59-61.
2) Bernal, J.D. The Physical Base of Life (Routledge & Kegan Paul, London, 1951).

ROBOTIC SET-UP OF A LASER DATA LINK FOR THE SAHA CRATER LUNAR RADIOASTRONOMIC AND SETI OBSERVATORY

GIANCARLO GENTA

Mechanics Dept.,
Politecnico di Torino
C. Duca degli Abruzzi 24,
10129 TORINO - Italy

ABSTRACT: One of the key issues of a radioastronomic and SETI mission in the Saha Crater is a data link which does not contribute to the radio pollution in the moon far side environment. The link must connect the radiotelescope, on the floor of the Saha crater to the radio station on Mare Smithii, 340 km away. Five different solutions, which can be implemented in the near future, have been proposed: a tether connecting the two landers, a cable shot from the radiotelescope or deposited by a rover, three laser relay stations deposited by a rover and three laser stations, mounted on small rovers landed at prescribed positions. The present paper concentrate on the last alternative, showing that three laser relay stations, landed in suitable places located not too far >from the optimal position for transmitting and receiving and then accurately positioned using walking rovers is the simplest, cheapest and safest way to establish the data link.

GENETIC CODE STRUCTURE AND EVOLUTION:
AMINOACYL-tRNA SYNTHETASES AND DINUCLEOTIDE TYPES

ROMEU CARDOSO GUIMARAES 1, CARLOS HENRIQUE COSTA MOREIRA 2

1 Dept Biologia Geral, Inst Ciencias Biologicas, Univ Federal Minas Gerais
(UFMG), 31270901 Belo Horizonte MG Brazil, TelFax +55-31-4992567,
romeucg@icb.ufmg.br
2 Dept Matematica, Inst Ciencias Exatas, UFMG, cmoreira@mat.ufmg.br

Abstract: Genetic code structure and evolution was studied through principal
dinucleotide (pDiN; 5' central -> 3' base) types of anticodon boxes.
Specificity of aminoacyl-tRNA synthetases (ARS) and tRNA pairing through
pDiN were defined mainly by anticodon central bases. These specificities
determined the matrix diagonal structure, centered on homodinucleotides
(AA:UU, GG:CC) and self-complementary dinucleotides (AU:UA, GC:CG) 8
axial boxes, with G & C cores and A & U tips, prototypes of the
homogeneous and mixed pDiN sectors and quadrants (Ho, RR:YY; Mx, RY:YR),
which were completed with the 8 non-axial boxes (Ho and Mx central
R:central Y (AG:UC, GA:CU and AC:UG, GU:CA).
Hydropathy correlation between amino acids and pDiN identified ARS
class 1 with Mx pDiN, forming a regression line, and ARS2 with Ho pDiN;
among the latter, the set of hydropathic outliers was distinguished
(GlyCC:GGPro, SerGA:CU).
Deviants from the ARS class/pDiN rule were 5 amino acids: ARS1/Ho
(LeuAG:UCGlu) and ARS2/Mx (AlaGC, ThrGU, HisUG). It is proposed that Ser
was originally octacodonic and Phe tetracodonic, the 3 hexacodonic
attributions being derived from expansion of Arg into the CU and Leu
into the AA boxes.
Simple boxes were cores and non-axial central R, complex the tips and
non-axial central Y.
Initial attributions to complex boxes remained at 1st position R,
conceding 1st position Y to new ones.
Sectors of pDiN types and ARS classes were integrated into a
nucleoproteic system via protein functions through hypercyclic dynamics.
Data on tRNA complementarity, and amino acid complexity, biosynthetic
routes and preferences for participating in protein conformations
indicated evolution from the Ho to the Mx sector, ARS2 to ARS1, and
coils and turns to extended chains.
A schema for evolution based mainly on ARS class/pDiN coherence, also
coherent with development of complexification of protein conformations,
started with the hydropathic outliers and the ARS2/Ho attributions,
typical of coils and turns. This set would be able to produce proteins
with non-specific punctuation, protein stabilizer amino acids
concentrated at the N-end and destabilizers pushed to the C-end.
Specific punctuation extended proteins and mRNAs with addition of Met,
and mRNAs with the termination codons. Translation initiation involved
the first two tRNAs, Met anticodon depicting pDiN slippage to the 1st
and central base anticodon positions, eliminating the intercalated
wobble position. Mutual interference of initiation and termination
codons and anticodons through pairing lead to deletion of tRNAs
corresponding to the termination codons.
ARS1 entered the code gradually, producing an intermediate stage where
the deviant attributions were fixed through two ARS delay processes:
ARS2 delay resulting in fixation of Leu and Glu by ARS1, and ARS1 delay
producing fixation of Ala, Thr and His by ARS2. Installation of
UCAsp,Glu and ACVal boxes were the main doors to this stage.
Final attributions were ARS1 coherent, developing specific punctuation
and the complex protein conformations, helices and sheets.

Acknowledgments:
FAPEMIG, CNPq, FAPESP, CAPES.

Romeu Cardoso Guimarães1, Carlos Henrique Costa Moreira2,1correspondence: Dept. Biologia Geral, Inst. Ciências Biológicas, Univ.
Federal Minas Gerais, 31270.901 Belo Horizonte MG - Brazil; TelFax
+55-31-499.2567, 274.4988; romeucg@icb.ufmg.br;
2Dept. Matemática, Inst.
Ciências Exatas, Univ. Federal Minas Gerais, 30123.970 Belo Horizonte MG
- Brazil; TelFax +55-31-499.5797; cmoreira@mat.ufmg.br
Abstract (June 13. 2000)

THE NUCLEOTIDE AND NUCLEOTIDE-LIKE COENZYMES
IN PRIMITIVE METABOLISM, PHOTOBIOLOGY AND EVOLUTION

Mikhail S. Kritsky

A.N. Bach Institute of Biochemistry, Russian Academy of Sciences
Leninsky Prospekt 33, Moscow, 117071 Russian Federation
Fax (+7-095) 954 2732, e-mail <inbio@glas.apc.org>

The border between RNA World and the Protein World, apparently distinct in chemical sense, acquires a blurred outline after we are starting to analyse biological functions of molecules. A group of compounds containing aromatic heterocycles accessible from chemical evolution are the example. These compounds are structurally close to nucleotides and act as coenzymes in biocatalytic reactions. Some these coenzymes, i.e. NDP-sugars, are 5'-nucleoside phosphate derivatives, and other molecules such as nicotinamide-, pterin- and flavin coenzymes bear motives similar to the RNA World structures. Moreover, NAD(P), FAD and some molybdopterins almost precisely mimic canonical dinucleotides. Their chemical closeness to RNA World is so high, that NAD and FAD are not discriminated from typical nucleoside phosphate substrates in enzymatic priming of polyribonucleotide synthesis.
Despite of their nucleotide and nucleotide-like structure, coenzymes belong functionally to Protein World, where their molecules bounded to polypeptide apoenzymes catalyse electron, proton and group transfer in biocatalytic reactions inherent in all modern organisms without exception. In organisms, besides the coenzyme function in "dark" processes, these compounds, especially pterins and flavins, are chromophores of protein photoreceptors for adaptation, behaviour and development. The photoreceptor function of these compounds is grounded on a capacity of their excited molecules to sensitise photochemical reactions. Some these reactions mimic in solution the "dark" metabolic processes requiring enzyme catalysts to proceed in organism and lead to accumulation of free energy in chemical products. The modern coenzyme photosensors are possible metabolic successors of the most primitive, likely pre-chlorophyllic, photobiological processes which were able to survive in evolution.
The present-day notion on the enzymatic capacity of RNA World has mostly arisen from the results of modern ribozymes studies. This rather limited assortment of catalytic activities will strongly expand, after diverse catalytic and photocatalytic functions manifested by nucleotide-like coenzyme molecules are added, thus making more plausible the hypothetical functional autonomy and evolutionary self-sufficiency of RNA World. Evolution towards the modern D(R)NA/Protein World, where the genetic information storage and catalytic activity are distinctly pulled apart two different molecule types, had to reject nucleotide-like coenzymes from genetic polymers as the non-perfect monomer units and to promote a selection of polypeptides capable to boost catalytic effectiveness after binding the coenzyme molecules.
Supported by Russian Foundation for Basic Research, Grant 98-04-48328a.

SIMULATED SUBMARINE HYDROTHERMAL SYSTEM: THE CASE OF EUROPA

KOICHIRO MATSUNO

Department of BioEngineering
Nagaoka University of Technology
Nagaoka 940-2188, Japan

Abstract: Hydrothermal vents in the primitive ocean on our Earth could have functioned as nature-made reactors for prebiotic synthesis. We constructed a flow reactor simulating a submarine hydrothermal system. A principal feature of our flow reactor was to facilitate to inject the hot and high-pressure solution including various reactants suddenly into the cold surrounding water and to circulate the reaction solution from the hot to the cold and back repeatedly. The simulated hydrothermal system enabled prebiotic synthesis of oligopeptides from amino acids, oligonucleotides from monomeric nucleotides, and carbonylic acids from the mixture of carbon dioxide and water. Our observation suggests that the primitive hydrothermal environments could have been competent enough to synthesize three major classes of oligomers of prebiotic significance, that is, oligopeptide, oligonucleotides and lipids. Since the major attribute of hydrothermal systems is the capacity of continuously injecting the hot solution into the cold surrounding water in a circulating manner, the likelihood of having or expecting the similar prebiotic synthesis on the watery Jovian moon, Europa should seriously be examined.

VOLCANIC LIGHTNING AND THE AVAILABILITY OF REACTIVE NITROGEN AND PHOSPHOROUS SPECIES FOR CHEMICAL EVOLUTION

RAFAEL NAVARRO-GONZÁLEZ

Laboratorio de Química de Plasmas y Estudios Planetarios
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México
Circuito exterior, Ciudad universitaria, México D.F. 04510- MEXICO

Nitrogen and phosphorous are two key elements for life. Nitrogen is present is proteins, enzymes, nucleic acids, coenzymes and energy transfer molecules whereas phosphorous is present in nucleic acids and energy transfer molecules. These two elements belong to the same chemical group in the period table. Nitrogen is believed to have been present mainly in the early Earth's atmosphere as molecular nitrogen, an inert gas under most atmospheric conditions. Phosphorous was present mainly in the lithosphere as the relatively insoluble apatite. If these two elements played a role in the origins of life, some mechanisms for making them available for chemical evolution must have operated in the early history of the Earth. Here I review a novel mechanism to fix atmospheric nitrogen and to reduce phosphate into phosphite (a soluble compound) by lightning discharges occurring inside explosive volcanic clouds.

STABILITY AND EVOLUTION OF ORGANICS IN THE MARTIAN SOIL

RICHARD RUITERKAMP

Raymond and Beverly Sackler Laboratory
for Astrophysics at Leiden Observatory
The netherlands
tel: 31 (0)71 5275812
fax: 31 (0)71 5275819
Richard.Ruiterkamp@strw.LeidenUniv.nl

The Viking landers could not detect organic matter in the top layer of the Martian soil. Moreover, exogenic delivery of organics by impact delivery of carbonatious meteorites, asteroids, interplanetary dust particles (IDPs) and comets on mars indicate an active destruction mechanism. The main destruction mechanisms for organics in the Martian upper soil layer are though to be photodissociation and oxidation.
Model studies aimed at assessing the composition of a historical atmosphere able to sustain liquid water on the Martian surface (as indicated by the surface flow patterns) predict higher CO2 pressures and of course higher temperatures.

To investigate the effects of model atmospheres, solar radiation, oxidation and thermal cycling we have proposed to perform laboratory simulations. These simulations will be performed in a closed sample chamber equipped with gas feed lines, GC-MS and a temperature controller. The chamber will be evacuated and filled with atmospheres of different composition, pressures and organic samples. An external UV source will be mounted to simulate the solar UV field. Although the solar constant for Mars is about 0.4, the flux of the UV portion of the solar radiation to reach the Martian surface is much higher than on earth. Organic samples will be selected according to their presence in meteorites, asteroids, IDPs etc. and comprise species such as aliphatic, aromatic and oxygen/nitrogen bearing hydrocarbons, amino acids, polycyclic aromatic hydrocarbons (PAHs), fullerenes, carbonaceous solids such as amorphous carbon (AC) and hydrogenated amorphous carbon (HAC), kerogens and solid bitum!
ens.

After the experiments the samples will be analyzed by GC-MS, HPLC, tof-SIMS and spectroscopic techniques by the different co-investigators. In this talk we will present an overview of the setup, proposed experiments and expected results.

MICROORGANISMS AS ANALOGUES OF EXTRATERRESTRIAL LIFE

JOSEPH SECKBACH
Hebrew University of Jerusalem, Israel.
(seckbach@cc.huji.ac.il)

Recently several new harsh habitats harboring extremophilic microorganisms have been discovered. These findings show us that the survivability and viability of microbial life are much broader than previously thought possible. The extremophiles are microbes living under severe conditions, their niches ranging at the edge temperature (hyperthermophilic living at 1100C vs. psychrophilic or freezing zones where microbes are in minus 100C). Microorganisms have been observed at both edges of the pH scales, under high pressure (in submarine zones and subterranean depths), radiation, anaerobic conditions, dryness and stress of available water. In addition, bacteria have been recovered and brought back to vitality after two and a half years on the moon's surface with conditions far away from those on Earth. Some of these extremophiles living in severe environments may serve as models for life in extraterrestrial biohabitats.
Astrobiology, the new multidisciplinary field, is concerned with several biological aspects, from Origin of Life and extremophilic environments with their microbes to the distribution and destiny of Life in the Universe (exobiology). It is accepted that life ("as we know it" [or "as we do not know it!"]) is based on carbon chemistry and on the presence of liquid water, and on temperature limits as well as other vital factors. The recent discovery by NASA scientists of (possible) ancient nanobacteria within a Martian meteorite has galvanized many scientists all over the world. If these findings will be confirmed then we will have further evidence of ancient Martial life, an idea possibly supported by the photos of the planet surface indicating that in the past history it was rich in water (and perhaps also with microbial life).
Terrestrial Life expands the envelope of habitability into realms of deep sea and land denizens: on the sea bottom (~4,333m­6,333m) thrive colonies of animals around "black smokers" vents of superheated water living in total darkness under 400­600 times the pressure of sea level; bacteria from deep basalt rocks (at a depth of more than 1,000­3,000m) have been observed living in the dark, without sunshine, or photosynthesis. Although until now the Life on other worlds has looked pretty dim, the current studies of the extremophiles have shown that the limit of life is unknown, there is still hope to find positive signs of life on or even under the surface of some celestial bodies.
At the bottom of the frozen Vostok station in Antarctica there is a liquid water lake, which presumably contain microorganisms. Several microbes have been observed during the drilling at depths of thousands meters (within the frozen soil, but still above the lake itself, which is buried beneath a 3 km icy layer). This lake may serve as a good analogue for the ocean that may lie underneath the icy layer of Europa (the Jovian satellite), one which may harbor internal warm water "oceans." Such ice microbes of terrestrial cryosphere are also excellent analogues for the types of cryobacteria that might be able to survive on comets, in the permafrost and polar caps of Mars, or on other icy moons in the universe. The wide range of microbial distribution encourages the idea that microbial life may be found in other regimes of the solar system previously considered inhospitable and devoid of life. Microbes of deep crustal rocks and submarine hydrothermal vents provide analogues for life that might exist in deep subsurface rocks on Mars, or the in high­temperature regimes of Venus, or are associated with the volcanoes of Io (volcanic moon of Jupiter).
Eukaryotes are usually not extremophiles, sometimes they may share a common thread with Archaea and Bacteria and invade extreme niches to a certain extent. Among the Life on the acid edge we will stress the natural history of some extremophilic acidophilic algae.

References:

Seckbach, J. (ed.) (1994) Evolutionary Pathways, and Enigmatic Algae: Cyanidium caldarium (Rhodophyta) and Related Cells. Kluwer Academic Publishers. Dordrecht, The Netherlands.
Seckbach, J. (ed.) (1999) Enigmatic Microorganisms and Life in Extreme Environments. Kluwer Academic Publishers. Dordrecht, The Netherlands.
Seckbach, J.(ed.) (2000) Journey to Diverse Microbial Worlds: Adaptation to Exotic Environments. Kluwer Academic Publishers. Dordrecht, The Netherlands. (in press).

ORIGINS OF LIFE IN THE UNIVERSE AND
EARLIEST PROKARYOTIC MICROORGANISMS
ON EARTH

VINOD C. TEWARI

Wadia Institute of Himalayan Geology
Dehradun- 248001, India and
The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy.

Abstract: Life must have originated in some planet of our Solar system if not on
Earth. The earliest microbes (prokaryotes) may have travelled between
Earth, Mars, Venus and Mercury when the planetary system was young. The
discovery of fossilised life forms or nannobacteria from Martian
meteorite ALH 84001 supports this hypothesis. Mars must have liquid
water and warm enough to foster life about 4.5 billion years ago. Early
evolution of life may have taken place on Mars and earliest prokaryotic
microorganisms and first stromatolites similar to the planet Earth
around 3.5 billion years might have proliferated on Mars. The life
carrying rocks landed on Earth (meteorites) blasted out of the Martian
surface. It is generally believed by scientists that life on Earth
originated from inorganic molecules in primordial soup/protocean by
complex chemical process. The first appearance of prokaryotic
microorganisms and stromatolites on Earth is not clear but carbon
isotopic and fossil evidence suggests a data between 3.85 Ga and 3.55
Ga. The Archaean oceans may have been colonized by prokaryotes and
protoeukaryotes. The prokaryotes are single celled microorganisms and
can be easily distinguished by their DNA structure which is simple and
not bounded by membrane and nucleus. The mitochondria, chromosomes and
chloroplasts are also lacking in prokaryotic cells. The transition from
prokaryotic to the first eukaryotic cell is not well documented in the
fossil records of the Earth. The eukaryotic algae from the Deoban and
Krol Group of the Himalaya, India has been recorded. There is evidence
of vegetative reproduction during Neoproterozoic. Akinetes have been
reported from Deoban cherts indicative of cell division and the
formation of thick cellular wall. Akinete germination have been
observed in which they underwent cell divisions to produce a cellular
hormogone in Deoban cells. In a new millennium, the evidences from Mars
and Europa by extensive exploration of space, Astrobiological research
is aimed to make key contributions for origins of life in the Universe.

SEARCH FOR ENANTIOMERIC EXCESS IN EXTRATERRESTRIAL SAMPLES. INTEREST FOR MARS SAMPLE RETURN.

O. VANDENABEELE-TRAMBOUZE

University of Montpellier II, UMR 5073, CC 017,
Place E. Bataillon, F- 34095 Montpellier France,
odile_trambouze@post.club-internet.fr

Amino acids are simple, stable compounds, which play a fundamental role in terrestrial life as building blocs of proteins and enzymes. Terrestrial life mainly uses 20 of them (biogenic amino acids), which are alpha-hydrogenated. In contrast, more than 70 have been identified in the Murchison meteorite, many of which bearing two alkyl groups in alpha position. A remarkable characteristic of biogenic amino acids is their homochirality: only one optical isomer (L) is present in terrestrial life, in contrast with the racemic (L=D) mixture produced by most physical and chemical amino acids production scheme.
Indications exist that physico-chemical conditions on early Mars and early Earth might have been close to each other. Life may thus have appeared on Mars 3.5-4 Gyr ago. If not, records of prebiotic chemistry could have been preserved. The low temperature and humidity on Mars since 3 Gyr provide very good conditions to preserve the amino acids and their chirality (1).
The determination of amino acids enantiomeric excess in meteorites, micrometeorites, comets is important since they may have played an important role in organic mater input on primitive planets. In the Murchison carbonaceous meteorite null or small enantiomeric excess of amino acids were found (2) and L excess determination only concerned non-biogenic amino acids, since contamination problems with biogenic amino acids did not allow reliable determination. Furthermore, biogenic amino acids can racemize upon heating. Micrometeorites represent the major fraction of the extraterrestrial input on Earth and seem to softly enter into the atmosphere : 80% of micrometeorite found on Earth are not melted. Therefore, amino acid enantiomeric excess (if existing) inside such materials may have been preserved, and their study can be useful as a reference for result interpretation on Mars samples. The surface of Mars must indeed be covered by meteoritic material (3).
The determination of amino acids enantiomeric excess in micrometeorites is rendered difficult by the risk of contamination by terrestrial biogenic amino acids and by the needed sensitivity. As a matter of fact, if amino acid abundance is the same in micrometeorites as in the Murchison meteorite, the method sensitivity must reach at least 10-13 moles/micrometeorite (considering the most abundant amino acid : one average micrometeorite = 30µg). Amino acid analysis samples as small as one micrometeorite or heterogeneous is also interesting in the scope of future analysis of very heterogeneous extraterrestrial matter, or Mars samples, which are to be expected in only small amounts.
A critical survey of classical method used in this field (gas chromatography coupled to mass spectrometry, high performance liquid chromatography (HPLC) after OPA-NAC derivatization) revealed that they are not sufficiently sensitive : for the best example, HPLC/OPA-NAC has been used on 30 micrometeorites as a whole (4). None of these two methods efficiently prevents contamination since both involve formation of unstable derivatives at the last step prior to analysis.
We recently developed Chloroethylnitrosoureas (CENU) as new derivatizing reagents for amino acids and other nucleophiles (5), for their quantitative analysis by capillary electrophoresis with laser induced fluorescence (CE-LIF) and immunoenzymatic methods (ELISA). CENUs offer new possibilities to prevent contamination since the involved derivatives are stable ; moreover their structure may be modified for optimizing the sensitivity without changing their derivatizating properties. The sensitivity obtained in CE-LIF is 100 times better than the GC-MS method that we have developed.

(1) Bada, J.L. and Mc Donald G.D. Icarus 114 (1995) 139 / (2) Cronin, J. R.; Pizzarello, S. Science 275 (1997) 951 / (3) Bland, P.A. and Smith, T.B. Icarus, 144 (2000) 21 / (4) Brinton, K. L.; Engrand, C.; Glavin, D. P.; Bada, J. L.; Maurette, M.; Orig. Life Evol. Biosphere, 28 (1998) 413 / (5) O.Vandenabeele, L. Garrelly, M. Ghelfenstein, A. Commeyras, L. Mion. J. Chromatogr. A. 795 (1998) 239 and O.Vandenabeele, L. Garrelly, A. Commeyras, L. Mion. Patent PCT/FR98/01984 16 September 1997.

PROTOPLANETARY DISCS, SOLAR SYSTEM MINOR BODIES AND ORIGIN OF LIFE.

JOSEP Mª TRIGO I RODRIGUEZ

Dept. Ciències Experimentals, Universitat Jaume I
Dept. Astronomia i Astrofísica, Universitat de València

Abstract: In the last decade, planetary science researchers have obtained significative advances on the origin and evolution of Earth. The increasing resolution and the development of new instruments (as space telescopes and adaptative optics) has provided first detailed images on protoplanetary discs and star formation regions. Moreover, in the last years, doppler spectroscopic technique have confirmed the presence of extrasolar planets. These evidences show planetary formation as a continuos and very common process in the Cosmos, indicating that our Solar System is not too special as was suggested in the past. The study of star and planetary formation in our galactic surroundings provides interesting clues on our origin. Despite this, due to interstellar distances, only Solar System minor bodies can be directly analysed in order to complete chemical and physical data on our planetary system. The direct analysis of comets and meteorites, as remnants bodies of this early period, has consequently a key role to complete this intricate puzzle. Especially remarkable would be knowing better the formation processes of comets and meteorites. For example, we don't know the origin in the Solar System of more of 99.9% of meteorites recovered because their entries in the Earth atmosphere were not registered. In this sense, photographic networks can provide interesting orbital data on meteorite origin. In 1997 the "Spanish Photographic Meteor Network" began its activities working in our country on fireballs and meteorites with the mean purpose to analyse the interplanetary matter delivery to the Earth. To quantify the degradation of cometary particles during its entry into the Earth atmosphere's is one of the most interesting research fields. The main aim of our studies is deepening into the role that comets and chondritic asteroids had in the life's origin.

EXPERIMENTAL AND THEORETICAL PHOTOCHEMICAL STUDIES OF POLYYNES AND CYANOPOLYYNES : APPLICATION TO TITAN'S ATMOSPHERE

V. VUITTON, M.-C. GAZEAU, Y. BENILAN, A. JOLLY, F. RAULIN
Laboratoire Interuniversitaire des Systèmes Atmosphériques Univ. Paris XII-CNRS UMR 7583, Créteil, France

The photochemistry that takes place in the N2/CH4 Titan's atmosphere is known to produce many organic compounds, including macromolecular organics. At the interface between gaseous and solid (aerosols) phases, lies a class of products, polyynes, made of C and H (C2nH2) and their N-C-H homologues, cyanopolyynes (HC2n+1N). To reproduce the relative abundances of C4H2 and HC3N measured at Titan's North Pole, many reactions have been included in the photochemical models of Titan's atmosphere Recently, these chemical schemes have been validated by the detection of C6H2 and HC5N in laboratory simulations. This has confirmed the importance of polyynes and cyanopolyynes in the formation of the organic aerosols of Titan's atmosphere.

But, as all photochemical models, those of Titan's are suffering from the lack of adequate experimental data. The main uncertainties concern :
kinetics data, in particular at low temperature
quantum yields of photodissociation and lifetimes of the metastable states
photolysis rates, in particular absorption cross sections at low temperature
This lack of data is particularly enhanced for polyynes and cyanopolyynes because these compounds are highly unstable in the usual pressure and temperature conditions of a laboratory and therefore are very difficult to study.

In the absence of kinetics data, the values used in the models are only estimates and this contributes to extend the uncertainties. In particular, the only kinetic rate constant of the reactions of the C2nH radicals with the other polyynes that has been measured is that of the reaction of C2H with C2H2. In all the current models, the rate constants of the C2H radicals with polyynes are all assumed to be the same but the rate constants of C2nH radicals (n>2) with acetylene are assumed to be equal to that of C2H with acetylene divided by 3n-1. The results of ab initio calculations that have been performed to extend our knowledge of these reactions will be presented.
The quantum yields of dissociation and production of metastable triplets states are another parameters that present large uncertainties. For example, the quantum yield of dissociation of acetylene is low at all its absorption wavelengths and therefore a metastable triplet state is supposed to be formed. If the radiative lifetime of this state is long enough, its reactions could compete in the low stratosphere with the ones which involve C2H to form higher polyynes. The same phenomenon is observed for C4H2, for which the reaction of the metastable state favour the formation of aromatic products. To include this process in the photochemical models, it is necessary to know the lifetimes of these triplet states which are not available at the moment. A new LASER experiment developed to measure such data will be presented.
The absorption cross section of a molecule depends on the physical conditions such as temperature and pressure. As it is very difficult to reproduce in a laboratory the cold conditions of Titan's atmosphere, it is necessary to extrapolate the data obtained at 300 K and 1 atm, using theoretical calculations. For simple molecules as C2H2,which has a structured spectrum, it is possible to build a synthetic spectrum in which temperature and resolution are parameters. These spectra and consequently the subsequent absorption cross sections, made available in spectroscopic databases, could then be included in photochemical models or used to interpret the UV observations. For the highly unstable compounds that are very difficult to synthesise, ab initio calculations are once again very useful to predict their spectroscopic characteristics. Thus, as the position and the intensities of the bands of the acetylene and the first polyynes (C2nH2, n from 1 to 4) are known, they have been used to extend the data to longer carbon chains. This has also been done for the cyanopolyynes HC2n+1N. The corresponding results will be presented.