The Effects of Parent Body Processes on Amino Acids in Carbonaceous Chondrites

To investigate the effect of parent body processes on the abundance, distribution, and enantiomeric composition of amino acids in carbonaceous chondrites, the water extracts from nine different powdered Cl, CM, and CR carbonaceous chondrites were analyzed for amino acids by ultrahigh performance liquid chromatography-fluorescence detection and time-of-flight mass spectrometry (UPLC-FD/ToF-MS). Four aqueously altered type 1 carbonaceous chondrites including Orgueil (C11), Meteorite Hills (MET) 01070 (CM1), Scott Glacier (SCO) 06043 (CM1), and Grosvenor Mountains (GRO) 95577 (CR1) were analyzed using this technique for the first time. Analyses of these meteorites revealed low levels of two- to five-carbon acyclic amino alkanoic acids with concentrations ranging from -1 to 2,700 parts-per-billion (ppb). The type 1 carbonaceous chondrites have a distinct distribution of the five-carbon (C5) amino acids with much higher relative abundances of the gamma- and delta-amino acids compared to the type 2 and type 3 carbonaceous chondrites, which are dominated by a-amino acids. Much higher amino acid abundances were found in the CM2 chondrites Murchison, Lonewolf Nunataks (LON) 94102, and Lewis Cliffs (LEW) 90500, the CR2 Elephant Moraine (EET) 92042, and the CR3 Queen Alexandra Range (QUE) 99177. For example, a-aminoisobutyric acid ((alpha-AIB) and isovaline were approximately 100 to 1000 times more abundant in the type 2 and 3 chondrites compared to the more aqueously altered type 1 chondrites. Most of the chiral amino acids identified in these meteorites were racemic, indicating an extraterrestrial abiotic origin. However, non-racemic isovaline was observed in the aqueously altered carbonaceous chondrites Murchison, Orgueil, SCO 06043, and GRO 95577 with L-isovaline excesses ranging from approximately 11 to 19%, whereas the most pristine, unaltered carbonaceous chondrites analyzed in this study had no detectable L-isovaline excesses. These results are consistent with the theory that aqueous alteration played an important role in amplification of small initial left handed isovaline excesses on the parent bodies

Applications of hydrogen isotopes in the life sciences

Hydrogen isotopes are unique tools for identifying and understanding biological or chemical processes. Hydrogen isotope labeling allows for a traceless and direct incorporation of an additional mass or radioactive tag into an organic molecule with almost no change in its chemical structure, physical properties or biological activity. Using deuterium labeled isotopologues to study the unique mass spectrometric (MS)-pattern generated from mixtures of biological relevant molecules drastically simplifies analysis. Such methods are now providing unprecedented levels of insight in a wide and continuously growing range of applications in the life sciences and beyond. Tritium (3H), in particular, has seen an increased utilization, especially in pharmaceutical drug discovery. The efforts and costs required for the synthesis of labeled compounds are more than compensated for by the enhanced molecular sensitivity for analysis and high reliability of the data obtained. In this review, advances in the applications of hydrogen isotopes in the life sciences are described

Studies of prebiotic physical models towards understanding the emergence of biological homochirality

The homochirality of biological molecules is critical to the structure of biological polymers which form the structures in living organisms that allow them to exist. It is central to the fundamental mechanisms of life such as molecular recognition and the helical structure of DNA; and what is most profound is the universality of it – everywhere we look in nature, amino acids exist in the L-enantiomer and carbohydrates exist as the D-enantiomer, and that homochirality is carried forward throughout the construction of living things on the macro level. The origin of this homochirality has perplexed generations of scientists since it was first discovered by Pasteur in the 19th century and is a fundamental problem within the study of the Origin of Life. In recent years, prebiotic synthesis has leaped forward, identifying a number of not only plausible, but likely routes to the precursors of RNA, thought by some to be the first biological polymer on Earth and the root of simple living organisms. However, it has been demonstrated that for chiral RNA to polymerise, its constituent building blocks (nucleotides) must be enatio- pure, otherwise oligomerisation is inhibited. As yet, chemistry has lacked a robust explanation for how such homochirality would have arisen under prebiotic conditions when all thermodynamic rules should form both enantiomers in equal amounts. Here, we report prebiotically-plausible enantio-enrichment of nucleotide precursor molecules (aminooxazolines, oxazolidinone thiones and oxazolidinones) and related compounds, from near-racemic conditions using crystallographic approaches and applying them to new substrates. This work views the homochirality problem from a new angle and in so doing expands the crystallographic landscape of pre-biotic chemistry, opening the door to crystal engineering in Origin of Life studies

Chemical Symmetry Breaking

This book entitled “Chemical Symmetry Breaking” is a collective volume of state-of-the-art reports on unique nonlinear chemical and physical symmetry-breaking phenomena that were experimentally observed upon a thermally or photochemically induced phase transition in various organic condensed phases, such as metastable liquid crystals, crystals, amorphous solids, and colloidal polymer materials, only under nonequilibrium conditions. Each author summarizes the introductory section in simple terms but in detail for beginners in this field. We wish that many readers familiarize themselves with the general concepts and features of nonlinear and nonequilibrium (or out of equilibrium) complexity theory, which govern a variety of unique dynamic behaviors observed in chemistry, physics, life science and other fields, so that they may discover novel symmetry-breaking phenomena in their own research areas

Thermal behavior of amino acids in inorganic matrices : relevance for chemical evolution

The onset of life on Earth was preceded by an abiotic chemistry in which complex molecules were formed from simpler ones. In the presence of energy sources such as UV radiation, lightning and geothermal energy, a wide range of organic compounds probably formed on the young Earth. Stanley Miller was the first to study this scenario experimentally. He showed that amino acids were synthesized under simulated conditions of the primitive Earth?s atmosphere. Initially, it was believed that the Earth?s early atmosphere contained high concentrations of CH4, NH3, CO, and H2 and was thus strongly reducing. However, later it was assumed that the early atmosphere was redox neutral and was composed of N2, CO2, and H2O as main constituents. Isotopic data from zircons indicate that liquid water might have been present already around 4.2 billion years ago. So called banded iron formations confirm the presence of liquid water at least 3.8 billion years ago. The early geological histories of Earth and Mars were probably very similar. About 4 billion years ago, both planets had liquid water, volcanoes, and a dense atmosphere without free oxygen, and they experienced intense meteoritic and cometary impacts. Therefore, the simulation experiments described in the present thesis may also be relevant to the early Mars. Among the possible prebiotic molecules, amino acids are generally considered especially important for the origin of life. The main reason for this is that they serve as building blocks of proteins which are the pillars of metabolism in all organisms. There is practically no doubt that amino acids were present on the young Earth. They originated from endogenous and exogenous (i.e. extraterrestrial) sources. Glycine is the most abundant amino acid in carbonaceous meteorites and Miller-type experiments. In the present work, the deep black residue was studied that forms when glycine is heated at 200 °C. Similar residues have been named ?thermo-melanoid? by others. The experiments were performed under a pure nitrogen atmosphere in order to simulate the oxygen-free early atmosphere of the Earth. It was found that the formation of the thermomelanoid from neat glycine started at 160 °C and was relatively fast and complete at 200 °C. However, the residues that formed at high temperatures (250?350 °C) were different from the thermo-melanoid. The thermo-melanoid was also present in the residues obtained by heating the glycine homopeptides 2,5-diketopiperazine (DKP), diglycine, triglycine, and tetraglycine at 200 °C. In contrast, penta- and hexaglycine remained almost unreacted at this temperature. Deuterolysis experiments revealed that C=C bonds are a characteristic structural feature of the thermo-melanoid. These bonds form by an unusual condensation reaction between C=O and CH2 groups. Glycine, DKP, and diglycine were released during hydrolysis of the thermomelanoid in water at 100 °C. In these experiments, the thermo-melanoid slowly dissolved. After 10 days, for example, a mass loss of ~75 % was observed. Therefore, the thermomelanoid can be regarded as a kind of storage form of glycine and glycine oligopeptides. The lower solubility of the thermo-melanoid as compared to glycine and its homopeptides may have influenced the distribution of glycine units on the early Earth. Moreover, additional experiments have shown that the thermo-melanoid mixed with soil continuously produced a higher amount of CO2 during a six-months period than samples without the thermo-melanoid. Obviously, the thermo-melanoid was decomposed in the soil. The decomposition was probably caused by microorganisms. Therefore, one can hypothesize that the thermomelanoid could have served as nutrient for early heterotrophic (pre-)organisms. The salt concentration of the late Hadean/early Archean ocean was at least twice as high as the concentration in the present-day oceans. There are good reasons to assume that the ions were Na+, K+, Ca2+, Mg2+, and Cl?. SO4 2? and PO4 3? were possibly not present in significant concentrations as the early atmosphere of the Earth was anoxic. In relation to this, the thermal behavior of glycine was investigated in the presence of various salts. It was found that glycine changed from the initial α- to the γ-modification when it crystallized together with NaCl and NaCl?KCl mixtures. At 200 °C, the glycine that was embedded in the NaCl or NaCl?KCl salt crusts transformed into the thermo-melanoid and a small amount of DKP. Only ~5 % of unreacted glycine was left after seven days in the presence of NaCl. The results showed that the presence of these salts and the change in the modification were nearly ineffective in protecting glycine from transformation into the thermo-melanoid. In contrast to NaCl and KCl, CaCl2 formed a coordination compound with glycine, namely CaCl2(Hgly) ⋅ H2O, when solutions of CaCl2 ⋅ 2H2O and glycine were evaporated. It was found that more than 90 % of the glycine were still present in CaCl2(Hgly) ⋅ H2O after heating at 200 °C for seven days. The coordination of glycine to Ca2+ prevented the transformation of glycine into the thermo-melanoid up to 250 °C. Yusenko et al. reported that at 350 °C, small volatile N-heterocycles such as pyrroles formed from CaCl2(Hgly) ⋅ H2O. Pyrroles are the building blocks of porphyrin-type biomolecules such as cytochromes and chlorophylls. CaCl2(Hgly) ⋅ H2O was also identified in mixtures of glycine with artificial sea salt (AS) prepared from NaCl (705 mmol), KCl (15 mmol), MgCl2 ⋅ 6H2O (80 mmol), CaCl2 ⋅ 2H2O (15 mmol), and glycine (10 mmol). About 84 % of the initial glycine had survived after heating an AS?Hgly mixture for seven days at 200 °C. In contrast, neither complex formation nor change in the modification of glycine was observed in gypsum?Hgly and MgCO3?Hgly mixtures. Clay minerals are mainly produced by the weathering of volcanic rock. They are not only found on Earth, but also on Mars. A possible role of clay minerals in chemical evolution was first suggested by Bernal more than half a century ago. In the present work, the thermal behavior of glycine embedded in smectites (Ca-montmorillonite, Na-montmorillonite, and nontronite) and kaolinite was investigated. The glycine-loaded clay minerals were heated at 200 and 250 °C for two days. HPLC and MALDI?TOF/TOF MS analyses of glycine-loaded Ca-montmorillonite that had been heated at 200 °C showed the presence of unreacted glycine, DKP, and linear peptides up to decaglycine. The comparison between the smectite clay minerals revealed that glycine was best protected by Ca-montmorillonite. ~63 % of the amino acid survived in its free form at 200 °C. This was followed by Na-montmorillonite (~53 %) and nontronite (~39 %) under similar experimental conditions. These results demonstrated that smectite clay minerals protect glycine from complete decomposition and sublimation, partly by promoting its polymerization. In contrast to smectites, kaolinite has no interlayer spaces available for intercalation. Therefore, glycine is only attached to the surface of the kaolinite particles. Sublimation of glycine and newly formed DKP was observed when kaolinite mixed with glycine was heated at 200 and 250 °C. All investigated clay minerals prevented the transformation of glycine into the thermo-melanoid during thermal treatments. Various heating experiments were conducted with mixtures of glycine and volcanic rock (basaltic sand from the island of La Réunion, Indian Ocean) or Martian soil simulants (JSC Mars-1A, P-MRS, and S-MRS). Glycine and DKP were identified in the residues and sublimates after heating basaltic sand?Hgly and JSC Mars-1A?Hgly at 200 °C for two days. Additionally, the thermo-melanoid was found in the residue of basaltic sand?Hgly. JSC Mars-1A contains mainly volcanic glass. Forsterite (Mg2SiO4) was identified as the major crystalline mineral in the basaltic sand. Glycine cannot be intercalated in JSC Mars-1A and basaltic sand as they have no clay minerals. As a result, glycine in these two matrices undergoes thermal alterations similar to neat glycine. In contrast, glycine, DKP, and linear peptides from di- to hexaglycine were detected after heating a P-MRS?glycine mixture. This observation can be easily explained by the fact that P-MRS contains 70 % of clay minerals that protect the amino acid from complete decomposition and thus allow the formation of larger peptides. The S-MRS?glycine residue contained only DKP, glycine, and diglycine, obviously because the mineral matrix consisted only of rock, anhydrous iron oxides, and gypsum, but not clay minerals. These experiments again demonstrated the influence of clay minerals on the behavior of glycine when exposed to higher temperatures. Another focus of the work was on the thermal behavior of chiral amino acids intercalated in Ca-montmorillonite. The heating experiments were conducted with different L-enantiomeric excesses (ee) of alanine [L-ee = 0 (i.e. racemic), 4, 20, 50, and 100 %] under a pure nitrogen atmosphere. The residues were analyzed by GC-MS/FID after derivatization. It was found that the racemization process was fast during the first 2?3 days and thereafter slowed down considerably. After eight weeks at 200 °C, the residues still contained 17.5?25.0 % of the respective starting L-ee. Complete racemization of L-alanine was not observed even after 24 weeks of heating. It was also found that, as expected, Camontmorillonite did not have any specific preference for the formation of either the D- or L-enantiomer. Interestingly, it could be observed that L-isovaline influenced the racemization of alanine. The presence of L-isovaline increased the rate of formation of D-alanine. In addition, higher temperatures greatly accelerated the racemization. For instance, after eight weeks at 220 °C, 85 % of the initial L-ee of alanine had been lost by racemization, whereas at 120 °C only 25 % racemization was observed. These experiments made use of the fact that Ca-montmorillonite largely protects amino acids from sublimation. In contrast, neat amino acids such as alanine undergo considerable sublimation in a few hours or less, depending on the temperature. Using a racemization kinetics model, it was estimated that L-alanine can survive in Ca-montmorillonite at elevated temperatures for years. In the literature, there are several reports on enantiomeric excesses of certain amino acids in meteorites. In relation to this, experiments were performed to demonstrate the enantiomeric enrichment of amino acids by partial sublimation. After 3 and 24 hours at 200 °C, the L-ee of alanine and valine increased in the sublimation residue, whereas the L-ee of the sublimates was lower than the initial one. Thus, it seems that racemic alanine and racemic valine crystals are more volatile than enantiomerically pure crystals. It may be assumed that similar processes take place during the atmospheric entry of meteorites and in the aqueous alteration phase of asteroids. The experimental results described in the present thesis suggest that various modes of interaction of amino acids with inorganic matrices such as salt mixtures and clay minerals existed on the young Earth. These results may help to better understand some of the processes of the prebiotic chemical evolution.Dem Beginn des Lebens auf der Erde ging eine abiotische Chemie voraus, in der komplexe Moleküle aus einfacheren gebildet wurden. In Gegenwart von Energiequellen wie UVStrahlung, Blitzen und geothermaler Energie bildete sich wahrscheinlich eine breite Palette organischer Verbindungen auf der jungen Erde. Stanley Miller war der erste, der dieses Szenario experimentell erforschte. Er hat gezeigt, dass sich unter Bedingungen, die die frühe Erdatmosphäre simulierten, Aminosäuren bildeten. Anfänglich wurde angenommen, dass die frühe Atmosphäre der Erde hohe Konzentrationen an CH4, NH3, CO und H2 enthielt und daher stark reduzierend war. Später ging man jedoch davon aus, dass die frühe Atmosphäre redoxneutral und aus den Hauptbestandteilen N2, CO2 und H2O zusammengesetzt war. Isotopenmesswerte aus Zirkonen zeigen, dass flüssiges Wasser schon vor etwa 4,2 Milliarden Jahren vorhanden gewesen sein könnte. So genannte ?Banded Iron Formations? bestätigen die Anwesenheit von flüssigem Wasser seit mindestens 3,8 Milliarden Jahren. Die frühe geologische Entwicklung der Erde und des Mars verlief wahrscheinlich sehr ähnlich. Vor ungefähr 4 Milliarden Jahren besaßen beide Planeten flüssiges Wasser, Vulkane und eine dichte Atmosphäre ohne freien Sauerstoff und erlebten zahlreiche Einschläge von Meteoriten und Kometen. Daher dürften die Simulationsexperimente, die in der vorliegenden Arbeit beschrieben werden, auch für den frühen Mars relevant sein. Unter den möglichen präbiotischen Molekülen werden Aminosäuren allgemein als besonders wichtig für den Ursprung des Lebens angesehen. Dies wird hauptsächlich deshalb angenommen, weil sie als Bausteine für Proteine dienen, welche in allen Organismen die Grundlage des Stoffwechsels darstellen. Es gibt praktisch keinen Zweifel daran, dass Aminosäuren auf der jungen Erde vorhanden waren. Sie stammten aus endogenen und exogenen (d. h. außerirdischen) Quellen. Glycin ist die häufigste Aminosäure in kohligen Meteoriten und in Experimenten des Miller-Typs. In der vorliegenden Arbeit wurde der tiefschwarze Rückstand untersucht, der sich bildet, wenn Glycin auf 200 °C erhitzt wird. Ähnliche Rückstände sind von anderen als ?Thermomelanoid? bezeichnet worden. Die Versuche wurden unter reiner Stickstoffatmosphäre durchgeführt, um die sauerstofffreie frühe Atmosphäre der Erde zu simulieren. Es wurde festgestellt, dass die Bildung des Thermomelanoids aus reinem Glycin bei 160 °C beginnt und bei 200 °C verhältnismäßig schnell und vollständig ist. Die Rückstände, die sich bei hohen Temperaturen (250?350 °C) bildeten, unterschieden sich jedoch vom Thermomelanoid. Das Thermomelanoid war auch in den Rückständen vorhanden, die durch Erhitzen 200 °C erhalten wurden. Im Gegensatz dazu zeigten Penta- und Hexaglycin bei dieser Temperatur fast keine Reaktion. Deuterolyseversuche haben gezeigt, dass C=CDoppelbindungen ein charakteristisches strukturelles Merkmal des Thermomelanoids sind. Diese Bindungen bilden sich durch eine ungewöhnliche Kondensationsreaktion zwischen C=O- und CH2-Gruppen. Während der Hydrolyse des Thermomelanoids bei 100 °C in Wasser wurden Glycin, DKP und Diglycin freigesetzt. In diesen Versuchen löste sich das Thermomelanoid allmählich auf. Nach 10 Tagen wurde beispielsweise ein Masseverlust von etwa 75 % beobachtet. Daher kann das Thermomelanoid als eine Art Speicherform von Glycin und Glycin-Oligopeptiden betrachtet werden. Die geringere Löslichkeit des Thermomelanoids im Vergleich zum Glycin und seinen Homopeptiden könnte die Verteilung von Glycin-Einheiten auf der frühen Erde beeinflusst haben. Außerdem haben weitere Versuche gezeigt, dass das Thermomelanoid mit Boden vermischt in einem Zeitraum von sechs Monaten kontinuierlich eine größere Menge CO2 freisetzte als Vergleichsproben ohne das Thermomelanoid. Offensichtlich wurde das Thermomelanoid in der Erde zersetzt. Die Zersetzung wurde wahrscheinlich von Mikroorganismen verursacht. Daher kann man vermuten, dass das Thermomelanoid frühen heterotrophen (Vor-)Organismen als Nährstoff gedient haben könnte. Die Salzkonzentration des Ozeans im späten Hadaikum/frühen Archaikum war mindestens doppelt so hoch wie die Konzentration in den heutigen Ozeanen. Es gibt gute Gründe anzunehmen, dass es sich bei den Ionen um Na+, K+, Ca2+, Mg2+ und Cl? handelte. SO4 2? und PO4 3? waren möglicherweise nicht in wesentlichen Konzentrationen vorhanden, da die frühe Atmosphäre der Erde nichtoxidierend war. In Zusammenhang damit wurde das thermische Verhalten von Glycin in Anwesenheit verschiedener Salze untersucht. Es konnte festgestellt werden, dass sich Glycin von der ursprünglichen α-Modifikation in die γ-Modifikation umwandelte, wenn es gemeinsam mit NaCl oder NaCl?KCl Mischungen auskristallisierte. Bei 200 °C wandelte sich das Glycin, das in den NaCl- oder den NaCl? KCl-Salzkrusten eingebettet war, in das Thermomelanoid und wenig DKP um. In Anwesenheit von NaCl verblieben nach sieben Tagen nur etwa 5 % unreagiertes Glycin. Die Ergebnisse haben gezeigt, dass die Anwesenheit dieser Salze und die Modifikationsänderung so gut wie nicht dazu in der Lage waren, Glycin vor der Umwandlung in das Thermomelanoid zu schützen. Im Gegensatz zu NaCl und KCl bildete CaCl2 eine Koordinationsverbindung mit Glycin, nämlich CaCl2(Hgly) ⋅ H2O, wenn man Lösungen von CaCl2 ⋅ 2H2O und Glycin eintrocknen ließ. Es wurde festgestellt, dass mehr als 90 % des Glycins im CaCl2(Hgly) ⋅ H2O noch vorhanden waren, nachdem man es für sieben Tage bei 200 °C erhitzt hatte. Die Koordination des Glycins an Ca2+ verhinderte die Umwandlung der Aminosäure in das Thermomelanoid bis hinauf zu 250 °C. Yusenko et al. berichteten, dass sich aus CaCl2(Hgly) ⋅ H2O bei 350 °C kleine flüchtige N-Heterozyklen wie zum Beispiel Pyrrole bilden. Pyrrole sind die Bausteine von Biomolekülen des Porphyrin-Typs, wie zum Beispiel Cytochrome und Chlorophylle. CaCl2(Hgly) ⋅ H2O wurde auch in Mischungen von Glycin mit künstlichem Meersalz (AS) nachgewiesen, die aus NaCl (705 mmol), KCl (15 mmol), MgCl2 ⋅ 6H2O (80 mmol), CaCl2 ⋅ 2H2O (15 mmol) und Glycin (10 mmol) hergestellt wurden. Ungefähr 84 % des anfänglichen Glycins war noch vorhanden, nachdem eine AS?Hgly-Mischung für sieben Tage bei 200 °C erhitzt worden war. Im Gegensatz dazu konnten in Gips?Hgly- und MgCO3?Hgly-Mischungen weder Komplexbildung noch eine Modifikationsänderung des Glycins beobachtet werden. Tonminerale entstehen hauptsächlich beim Verwittern vulkanischen Gesteins. Man findet sie nicht nur auf der Erde, sondern auch auf dem Mars. Vor mehr als einem halben Jahrhundert wies erstmals Bernal auf eine mögliche Rolle der Tonminerale in der chemischen Evolution hin. In der vorliegenden Arbeit wurde das thermische Verhalten von Glycin nach der Einbettung in Smektite (Ca-Montmorillonit, Na-Montmorillonit und Nontronit) und Kaolinit untersucht. Die glycinbeladenen Tonminerale wurden für zwei Tage bei 200 und 250 °C erhitzt. HPLC- und MALDI-TOF/TOF-MS-Analysen von glycinbeladenem Ca- Montmorillonit, das bei 200 °C erhitzt worden war, zeigten das Vorhandensein von nicht reagiertem Glycin, DKP und linearen Peptiden bis zum Decaglycin. Der Vergleich zwischen den Smektit-Tonmineralen ließ erkennen, dass Glycin am besten durch Ca-Montmorillonit geschützt wurde. Bei 200 °C waren 63 % der Aminosäure in unveränderter Form erhalten geblieben. Dem folgten Na-Montmorillonit (~53 %) und Nontronit (~39 %) unter ähnlichen experimentellen Bedingungen. Diese Ergebnisse haben gezeigt, dass Smektit-Tonminerale das Glycin vor vollständiger Zersetzung und Sublimation schützen, teilweise indem sie seine Polymerisation begünstigen. Im Gegensatz zu den Smektiten hat Kaolinit keine Zwischenschichträume, in denen Intercalation stattfinden kann. Daher wird Glycin nur an die Oberfläche der Kaolinitpartikel angelagert. Als Kaolinit, das mit Glycin vermischt worden war, auf 200 und 250 °C erhitzt wurde, wurde die Sublimation von Glycin und neu gebildetem DKP beobachtet. Alle untersuchten Tonminerale verhinderten, dass sich das Glycin während der thermischen Behandlungen in das Thermomelanoid unwandelte. In verschiedenen Experimenten wurden Mischungen aus Glycin und Vulkangestein (Basaltsand von der Insel La Réunion, Indischer Ozean) oder simuliertem Marsboden (JSC Mars-1A, P-MRS und S-MRS) erhitzt. In den Rückständen und Sublimaten wurden Glycin und DKP identifiziert, nachdem Basaltsand?Hgly und JSC Mars-1A?Hgly für zwei Tage bei 200 °C erhitzt worden waren. Zusätzlich wurde das Thermomelanoid im Rückstand des Basaltsandes mit Hgly gefunden. JSC Mars-1A enthält hauptsächlich vulkanisches Glas. Forsterit (Mg2SiO4) wurde als das hauptsächliche kristalline Mineral im Basaltsand identifiziert. Glycin kann in JSC Mars-1A und im Basaltsand nicht intercaliert werden, da sie keine Tonminerale enthalten. Demzufolge erfährt Glycin in diesen zwei Matrizes ähnliche thermische Veränderungen wie das reine Glycin. Im Gegensatz dazu wurden nach dem Erhitzen einer P-MRS?Glycin-Mischung Glycin, DKP und lineare Peptide vom Di- bis zum Hexaglycin gefunden. Diese Beobachtung kann leicht damit erklärt werden, dass P-MRS 70 % Tonminerale enthält, die die Aminosäure vor vollständiger Zersetzung schützen und folglich die Bildung der größerer Peptide erlauben. Der S-MRS?Glycin-Rückstand enthielt nur DKP, Glycin und Diglycin, offensichtlich weil die mineralische Matrix nur aus Gesteinen, wasserfreien Eisenoxiden und Gips bestand, aber nicht aus Tonmineralen. Diese Versuche demonstrierten erneut den Einfluss von Tonmineralen auf das Verhalten von Glycin, wenn es höheren Temperaturen ausgesetzt ist. Einen weiteren Schwerpunkt der Arbeit bildete das thermische Verhalten chiraler Aminosäuren, die in Ca-Montmorillonit intercaliert waren. Die Experimente wurden mit verschiedenen L-Enantiomerenüberschüssen (ee) von Alanin [L-ee = 0 (d. h. racemisch), 4, 20, 50 und 100 %] in einer reinen Stickstoffatmosphäre durchgeführt. Nach Derivatisierung wurden die Rückstände mittels GC-MS/FID analysiert. Es wurde festgestellt, dass der Racemisierungsvorgang während der ersten 2?3 Tage schnell verlief und danach beträchtlich langsamer wurde. Nach acht Wochen bei 200 °C enthielten die Rückstände noch 17.5?25.0 % des jeweiligen Start-L-ee. Eine vollständige Racemisierung des L-Alanins konnte selbst nach 24 Wochen Erhitzen nicht beobachtet werden. Es wurde außerdem festgestellt, dass Ca- Montmorillonit, wie erwartet, weder für die Bildung des D- noch des L-Enanti

The synthesis and potential applications of asymmetric silacycles

Although the use of silicon-based reagents has undergone rapid development during the last twenty years, the application of organosilicon chemistry to asymmetric synthesis has been somewhat slower to develop. The many problems associated with the use of 'Si-centred' chiral organosilicon compounds has led to the application of 'C-centred' chiral organosilicon compounds. This work has been aimed at the synthesis and application of cyclic silicon species. Routes towards the synthesis of medium-sized rings have been investigated as a potential application of enantiomerically pure silacycles. This work has led to the discovery of an unusual tandem cycloaddition-bond fragmentation reaction of 3-(dienylacyloxy)cycloalk-2- en-l-ones, which affords a-tetralone as the principal product. Most work has been directed at the synthesis of asymmetric silacycles. Two routes have been explored. Firstly, the double asymmetric hydrosilylation of dienes, catalysts based on many transition metals were used but little evidence of hydrosilylation was observed. The second route is that of the double asymmetric hydroboration of divinylsilanes. Asymmetric stoichiometric hydroboration led to products of moderate to high enantiomeric excess, whilst rhodium-catalysed hydroboration led to high yields of the achiral syn isomer. The diastereoselectivity has been found to vary according to the length of the tether between two phosphine ligands, with maximum diastereoselectivity being observed for butanodiphosphines. NMR studies have investigated the possibility that this is related to the stability of a divinylsilane-diphosphine rhodium complex. Finally, the formation of a variety of silacycles has been attempted. Boron- redistribution of the product of hydroboration with (-)-diisopinocampheylborane has been shown to occur with retention of stereochemistry and subsequent carbonylation led to the formation of asymmetric silacyclohexanones. Oxidation of the hydroboration product led to the formation of a silyldiol species. Reactions of this silyldiol have provided the basis for encouraging preliminary attempts at the formation of other heterosilacycles

A Flexible Approach to [1]Ferrocenophanes: Metallopolymers through a New Family of Chiral Sandwich Compounds

Applying known “Ugi’s amine” chemistry and based on a literature procedure, (R,R,Sp,Sp)-2,2′-bis(α-N,N-dimethylaminoethyl)-1,1′-dibromoferrocene was prepared and the pathway was modified for a synthesis on a larger scale. Adding two more synthetic steps, amino groups were replaced with methyl groups which resulted in the planar-chiral (Sp,Sp)-1,1′-dibromo-2,2´-di(isopropyl)ferrocene (120). Starting with 120, lithium-bromine exchange using nBuLi and different solvent systems was investigated and a reliable method was developed. Salt-metathesis reaction of (Sp,Sp)-1,1'-dilithio-2,2´-di(isopropyl)ferrocene (121) and Ar′GaCl2 [Ar′ = 2-(Me2NCH2)C6H4] was performed and yielded the respective [1]ferrocenophane ([1]FCP) 122 with high conversions. This gallium-bridged [1]FCP 122 was isolated by crystallization from the reaction mixture and its molecular structure in the solid state was determined. The Differential Scanning Calorimetry (DSC) thermograph of the gallium-bridged [1]FCP 122 proved that the [1]FCP is a potential candidate for thermal ring-opening polymerization (ROP). The starting compound Ar′InCl2 was reacted with 121 and yielded a mixture of an indium-bridged [1]FCP (1261) and a [1.1]FCP (1262). Reacting the bulkier reagent (Mamx)InCl2 [Mamx = 2,4-tBu2-6-(Me2NCH2)C6H2] with 121 resulted in the selective formation of an indium-bridged [1]FCP (1251). All attempts to isolate the strained indium-bridged [1]FCP were unsuccessful as it reacted further through a spontaneous ROP under conditions of its formation. DFT (Density Functional Theory) calculations were performed to investigate the structure and reactivity of synthesized indium-bridged [1]FCPs. Moreover, the effects of different substituents on the unusual reactivity of indium-bridged [1]FCP was studied. A group of amino(dichloro)boranes with different substitutions [Et2NBCl2, iPr2NBCl2, and tBu(Me3Si)NBCl2] were reacted with 121 and its 3-pentyl substituted analog [(Sp,Sp)-1,1′-dilithio-2,2′-di(3-pentyl)ferrocene] (131). Six bora[1]ferrocenophanes were synthesized and purified with different techniques including crystallization, sublimation, and flask-to-flask condensation. While salt-metathesis reactions with Et2NBCl2 were very selective toward [1]FCPs, employing the amino(dichloro)boranes iPr2NBCl2 and tBu(Me3Si)NBCl2 resulted in formation of significant amounts of bis(boryl)ferrocenes as byproducts. A systematic study was performed, which resulted in increasing the reaction temperature and controlling the rate of addition of the amino(dichloro)boranes to increase the yield of desired [1]FCPs. Thermal ROP of selected bora[1]FCPs were performed and the resulting polymers were analyzed by Gel Permission Chromatography (GPC) and Dynamic Light Scattering (DLS). Synthesis of chiral group-14-bridged [1]FCPs were attempted by salt-metathesis reaction of 121 with tBuSnCl2 and Me2SiCl2. The respective strained [1]FCPs (140 and 141) were formed in the reaction mixture quantitatively and isolated by vacuum sublimation in good yields. The molecular structures in the solid state of both [1]FCPs were determined and it was deduced that an interaction between alkyl groups increased the strain in the molecules. Measuring DSC thermographs proved these compounds to be suitable for thermal ROP. A group of chiral phosphorus-bridged [1]FCPs (142, 143 and 144) with different groups in the bridging position (Ph, iPr, and tBu) were prepared by reacting 121 with the respective phosphorus dihalides. These compounds were stable enough to be purified by column chromatography. The molecular structures of isopropyl and phenyl substituted phosphorus-bridged [1]FCPs were determined in the solid state. Potential application of these phosphorus-bridged [1]FCPs as monodentate ligands for asymmetric catalysis will be studied in the future