Showing papers by "Uwe J. Meierhenrich published in 2004"

Identification of diamino acids in the Murchison meteorite

Abstract: Amino acids identified in the Murchison chondritic meteorite by molecular and isotopic analysis are thought to have been delivered to the early Earth by asteroids, comets, and interplanetary dust particles where they may have triggered the appearance of life by assisting in the synthesis of proteins via prebiotic polycondensation reactions [Oro, J. (1961) Nature 190, 389–390; Chyba, C. F. & Sagan, C. (1992) Nature 355, 125–132]. We report the identification of diamino acids in the Murchison meteorite by new enantioselective GC-MS analyses. dl-2,3-diaminopropanoic acid, dl-2,4-diaminobutanoic acid, 4,4′-diaminoisopentanoic acid, 3,3′-diaminoisobutanoic acid, and 2,3-diaminobutanoic acid were detected in the parts per billion range after chemical transformation into N,N-diethoxycarbonyl ethyl ester derivatives. The chiral diamino acids show a racemic ratio. Laboratory data indicate that diamino acids support the formation of polypeptide structures under primitive Earth conditions [Brack, A. & Orgel, L. E. (1975) Nature 256, 383–387] and suggest polycondensation reactions of diamino acids into early peptide nucleic acid material as one feasible pathway for the prebiotic evolution of DNA and RNA genomes [Joyce, G. F. (2002) Nature 418, 214–221]. The results obtained in this study favor the assumption that not only amino acids (as the required monomers of proteins) form in interstellar/circumstellar environments, but also the family of diamino monocarboxylic acids, which might have been relevant in prebiotic chemistry.

UV-photoprocessing of interstellar ice analogs: Detection of hexamethylenetetramine-based species

Abstract: The physical conditions governing the dense cloud environment are reproduced in a high vacuum experimental setup at low temperature T 12 K. The accretion and photoprocessing of ices on grain surfaces is simulated by depositing an ice layer on a cold finger, while it is irradiated by ultraviolet (UV) photons. After irradiation the sample is slowly warmed to room temperature; a residue remains, containing the most refractory products of photo- and thermal processing. In this paper we report on the analysis of the residues performed by means of gas chromatography-mass spectrometry (GC-MS). A number of new molecules based on hexamethylenetetramine (HMT, C 6 H 1 2 N 4 ), the most abundant component of the residues reported here, were detected: methyl-HMT (C 6 H 1 1 N 4 -CH 3 ), hydroxy-HMT (C 6 H 1 1 N 4 -OH), methanyl-HMT (C 6 H 1 1 N 4 -CH 2 OH), amin-aldehyd-HMT (C 6 H 1 1 N 4 -NH-CHO) and methanyl-aldehyd-HMT (C 6 H 1 1 N 4 -CHOH-CHO). To the best of our knowledge, this is the first reported synthesis of these molecules. Currently, these are the heaviest identified components of the residue. These species might also be present in the interstellar medium, given that the ice was submitted to high temperatures, of the order of 300 K, and form part of comets. Our work serves as preparation for the ESA-Rosetta mission, which plans to do in situ analysis of the composition of a comet nucleus with the COSAC instrumentation.

Photochemical concepts on the origin of biomolecular asymmetry.

Abstract: Biopolymers like DNA and proteins are strongly selective towards the chirality of their monomer units. The use of homochiral monomers is regarded as essential for the construction and function of biopolymers; the emergence of the molecular asymmetry is therefore considered as a fundamental step in Chemical Evolution. This work focuses on physicochemical mechanisms for the origin of biomolecular asymmetry. Very recently two groups, one from Allamandola at NASA Ames and the other from our Inter-European team, demonstrated simultaneously the spontaneous photoformation of a variety of chiral amino acid structures under simulated interstellar conditions. Since both groups used unpolarized light for the photoreaction the obtained amino acids turned out racemic as expected. The obtained experimental data support the assumption that tiny ice grains can furthermore play host to important asymmetric reactions when irradiated by interstellar circularly polarized ultraviolet light. It is possible that such ice grains could have become incorporated into the early cloud that formed our Solar System and ended up on Earth, assisting life to start. Several lines of evidence suggest that some of the building blocks of life were delivered to the primitive Earth via (micro-) meteoroids and/or comets. These results suggest that asymmetric interstellar photochemistry may have played a significant part in supplying Earth with some of the enantioenriched organic materials needed to trigger life. The search for the origin of biomolecular homochirality leads to a strong interest in the fields of asymmetric photochemistry with special emphasis on absolute asymmetric synthesis. We outline here the theoretical background on asymmetric interstellar ice photochemistry, summarize recent concepts and advances in the field, and discuss briefly its implications. The obtained data are crucial for the design of the enantioselective COSAC GC-MS experiment onboard the ROSETTA spacecraft to a comet to be launched in the very near future.

Spontaneous Generation of Amino Acid Structures in the Interstellar Medium

Abstract: In dense interstellar clouds dust particles accrete ice mantles. As seen in infrared (IR) observations, this ice layer consists mainly of water ice, but also of carbon and nitrogen containing molecules. We deposited a gas mixture consisting of H2O, CO2, CO, CH3OH, and NH3 onto an aluminium surface at 12 K under high vacuum, 10-7 mbar. During deposition the molecules were subjected to ultraviolet radiation with main intensity at Lyman-α. After warm-up, the refractory material was extracted from the aluminium block, hydrolysed for 24 h at 110 °C with 6 M HCl, derivatized and finally analysed by enantioselective gas chromatography coupled to a mass spectrometer. We were able to identify 16 amino acids in the room temperature products of irradiation. The results were confirmed by parallel experiments using 13C-labelled ices in order to exclude contamination. A first ‘group’ of the identified amino acids was suggested to serve as the precursors of peptides and proteins. A second ‘group’ namely the diamino carboxylic acids is assumed to contribute to the development of the first genetic material, the peptide nucleic acid PNA. Beside the two groups of amino acids, N-heterocyclic organic molecules were identified that resemble the molecular building block of biological cofactors. The obtained results support the assumption that the photochemical products could be preserved in interstellar objects, and in term be delivered to the Earth during the heavy bombardment which ended about 3.8 Gyr ago, where they triggered the appearance of live.