GEOCHRONOLOGY, GEOCHEMISTRY, AND TECTONIC CHARACTERIZATION OF QUATERNARY LARGE-VOLUME TRAVERTINE DEPOSITS IN THE SOUTHWESTERN UNITED STATES AND THEIR IMPLICATIONS FOR CO2 SEQUESTRATION

Travertines are freshwater carbonates that precipitate from carbonic groundwater due to the degassing of CO2. Travertine deposits are often situated along faults that serve as conduits for CO2-charged groundwater and their geochemistry often records mixing of deeply-derived fluids and volatiles with shallow meteoric water. Travertines are surface expressions of dynamic mantle processes related to the tectonic setting. This dissertation includes four chapters that focus on different aspects of travertine formation and their scientific value. They are excellent, although underestimated, diagnostic tools for climatology, hydrology, tectonics, geochemistry, geomicrobiology, and they can inform carbon sequestration models. Quaternary Large-volume travertine deposits in New Mexico and Arizona occur in an extensional tectonic stress regime on the southeastern Colorado Plateau and along the Rio Grande rift. They accumulated above fault systems during episodes of high hydraulic head in confined aquifers, increased regional volcanic activity, and high input of mantle-derived volatiles such as CO2 and He. Stable isotope and trace element geochemistry of travertines is controlled by groundwater geochemistry as well as the degassing of CO2. The geochemical composition allows for distinguishing different travertine facies and evaluating past groundwater flow. The travertine deposits in New Mexico are interpreted to be extinct CO2 fields due to the large volumes that accumulated and in analogy to the travertine deposits in Arizona that are associated with an active CO2-gas field. Travertines are natural analogues for CO2 leakage along fault systems that bypassed regional cap rocks and they provide important insight into the migration of CO2 from a reservoir to the surface. The volume of travertine can be used to infer the integrated CO2 leakage along a fault system over geologic time. This leakage is estimated as: (1) CO2 that becomes fixed in CaCO3/travertine (tons of carbon converted into tons of carbonate), (2) the amount of CO2 that degassed into the atmosphere (twice the amount of (1), based on reaction stoichiometry), (3) dissolved CO2 that is carried away with the water discharging from a spring (based on modern spring discharge and dissolved carbon content), and (4) CO2 that escapes through the soil (based on modern soil flux measurements). Better understanding of integrated CO2 leakage and fault-related seal bypass is needed to design CO2 sequestration sites to effectively store anthropogenic CO2 in the subsurface

Optical manipulation of sphingolipid biosynthesis using photoswitchable ceramides

Ceramides are central intermediates of sphingolipid metabolism that also function as potent messengers in stress signaling and apoptosis. Progress in understanding how ceramides execute their biological roles is hampered by a lack of methods to manipulate their cellular levels and metabolic fate with appropriate spatiotemporal precision. Here, we report on clickable, azobenzene-containing ceramides, caCers, as photoswitchable metabolic substrates to exert optical control over sphingolipid production in cells. Combining atomic force microscopy on model bilayers with metabolic tracing studies in cells, we demonstrate that light-induced alterations in the lateral packing of caCers lead to marked differences in their metabolic conversion by sphingomyelin synthase and glucosylceramide synthase. These changes in metabolic rates are instant and reversible over several cycles of photoswitching. Our findings disclose new opportunities to probe the causal roles of ceramides and their metabolic derivatives in a wide array of sphingolipid-dependent cellular processes with the spatiotemporal precision of light

X-ray-Induced Reversible Switching of an Azobenzene Derivative Adsorbed on Bi(111)

We report on the adsorption of a submonolayer of di-m-cyanoazobenzene (DMC) on Bi(111) and on the reversible switching of these molecules induced by resonant X-ray illumination. DMC adsorbs in at least two configurations, the flat trans and the nonflat cis isomer. We find that in 0.8 monolayers at least 26% of the molecules change their configuration at 110 K by excitation of the N1s → LUMO transition at the azo group, and by a thermally induced back reaction at 120 K. Nonresonant excitation with X-ray light does not induce any reversible changes

Synthesis of Tetrahydro-1,2-oxazines and Pyrrolidines via Cycloadditions of Donor-Acceptor Cyclobutanes and Nitrosoarenes

During efforts to expand the scope of Lewis-acid-catalyzed [4+2] cycloaddition between donor–acceptor cyclobutanes and nitrosoarenes, an unexpected formation of pyrrolidine products was discovered when 50 mol-% of MgI2 was used as a Lewis acid. It was also observed that the electronics of the nitrosoarene and judicious selection of the Lewis acid catalyst have a profound effect on the regioselectivity of the reaction

420,000 year assessment of fault leakage rates shows geological carbon storage is secure

Carbon capture and storage (CCS) technology is routinely cited as a cost effective tool for climate change mitigation. CCS can directly reduce industrial CO2 emissions and is essential for the retention of CO2 extracted from the atmosphere. To be effective as a climate change mitigation tool, CO2 must be securely retained for 10,000 years (10 ka) with a leakage rate of below 0.01% per year of the total amount of CO2 injected. Migration of CO2 back to the atmosphere via leakage through geological faults is a potential high impact risk to CO2 storage integrity. Here, we calculate for the first time natural leakage rates from a 420 ka paleo-record of CO2 leakage above a naturally occurring, faulted, CO2 reservoir in Arizona, USA. Surface travertine (CaCO3) deposits provide evidence of vertical CO2 leakage linked to known faults. U-Th dating of travertine deposits shows leakage varies along a single fault and that individual seeps have lifespans of up to 200 ka. Whilst the total volumes of CO2 required to form the travertine deposits are high, time-averaged leakage equates to a linear rate of less than 0.01%/yr. Hence, even this natural geological storage site, which would be deemed to be of too high risk to be selected for engineered geologic storage, is adequate to store CO2 for climate mitigation purposes

Photoswitchable Amino Acids – Synthesis, Photochromism and Incorporation into Peptidic Grb2-SH2 Antagonists

Der Einbau photoschaltbarer Elemente in Biomoleküle ermöglicht die Modulation ihrer Konformation und damit auch ihrer Aktivität durch Bestrahlung mit Licht. Im Fokus der vorliegenden Arbeit stand die Entwicklung photoschaltbarer Phosphopeptide, die als Antagonisten der Grb2-SH2 Domäne fungieren. Zur Modulation der Struktur und Funktion solcher Peptide wurden in dieser Arbeit neue photochrome ω-Aminosäuren auf Azobenzolbasis entwickelt. Es konnte ein Verfahren zur effizienten Synthese elektronenarmer aromatischer Nitrosoverbindungen mit Oxon als Oxidans in einem zweiphasigen Lösungsmittelsystem entwickelt werden, mit dessen Hilfe eine Vielzahl unterschiedlich substituierter Azobenzole in guten Ausbeuten zugänglich sind. Des weiteren konnte die Verwendung von Selendioxid als Katalysator zur wasserstoffperoxidvermittelten Oxidation aromatischer Amine gezeigt werden. In diesem Fall ließ sich die Produktselektivität über die Wahl des Lösungsmittels steuern. In einem thematisch abgegrenzten Teil wurden substituierte Azobenzole zur Untersuchung von molekularen Schaltvorgängen an Oberflächen aufgebaut und hinsichtlich ihrer photochromen Eigenschaften mittels UV/Vis- und 1H-NMR-Spektroskopie untersucht. Auf der Grundlage der hierbei gewonnenen Erkenntnisse konnten neue azobenzolbasierte ω-Aminosäuren mit verbesserter thermischer Stabilität entwickelt werden, die ebenfalls hinsichtlich ihrer photochromen Eigenschaften charakterisiert wurden. Es konnte eine Gleichung zur Abschätzung der thermischen Halbwertszeit dieser Verbindungen bei 30 °C in Dimethylsulfoxid anhand ihres Absorptionsmaximums gefunden werden. Die Anwendbarkeit dieser neuen Aminosäuren in der Festphasenpeptidsynthese konnte erfolgreich anhand der Synthese zyklischer Phosphopeptide gezeigt werden. Untersuchungen der photochemischen Eigenschaften eines zyklischen Peptides mittels UV/Vis- und 1H-NMR-Spektroskopie zeigten die Übertragung des Schaltvorganges auf das Peptidrückgrat.Reversible control of the conformation and the activity of biomolecules by light can be achieved through the incorporation of photoswitches. The goal of the present work was the development of photochromic phosphopeptides acting as antagonists of the Grb2-SH2 domain. For this purpose new azobenzene-based ω-amino acids were synthesized. A simple, high-yielding synthesis of nitrosoarenes using oxone was developed providing access to a range of substituted azobenzenes. Furthermore, selenium dioxide was shown to be suitable for the catalytic oxidation of anilines by hydrogen peroxide. Another part of this work focussed on the synthesis of azobenzenes for the investigation of elementary processes in molecular switches at surfaces. The photochromic properties of these switches were investigated by means of UV/Vis and 1H-NMR spectroscopy. Based on the results obtained, new photochromic ω-amino acids with improved thermal stability were developed. A linear relationship could be established between the thermal half-decay time of the photoswitches and their wavelength of maximum absorbance. The application of these new amino acids in solid phase peptide synthesis was successfully demonstrated by the synthesis of cyclic phosphopeptides. Investigation by means of UV/Vis and 1H-NMR spectroscopy indicated a transfer of the isomerization process from the switch to the peptide backbone

Efficient Preparation of Nitrosoarenes for the Synthesis of Azobenzenes^†

Reaction conditions are described for the oxidation of anilines furnishing nitrosoarenes and the synthesis of unsymmetrically substituted azobenzenes. In a comparative study, the catalytic oxidation of methyl 4-aminobenzoate by hydrogen peroxide was investigated, and SeO2 proved to be superior or equal to methyl trioxorhenium (MTO) and Na2WO4, respectively. Nevertheless, the application of the inexpensive, environmentally friendly, Oxone in a biphasic system proved to be more efficient, and a variety of useful nitrosoarenes for the synthesis of azo compounds were prepared in high yield and purity on a large scale

Efficient Preparation of Nitrosoarenes for the Synthesis of Azobenzenes^†

Reaction conditions are described for the oxidation of anilines furnishing nitrosoarenes and the synthesis of unsymmetrically substituted azobenzenes. In a comparative study, the catalytic oxidation of methyl 4-aminobenzoate by hydrogen peroxide was investigated, and SeO2 proved to be superior or equal to methyl trioxorhenium (MTO) and Na2WO4, respectively. Nevertheless, the application of the inexpensive, environmentally friendly, Oxone in a biphasic system proved to be more efficient, and a variety of useful nitrosoarenes for the synthesis of azo compounds were prepared in high yield and purity on a large scale