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Project Reports

• BioInspired Mimetic Cluster Synthesis: Bridging the Structure and Reactivity of Biotic and Abiotic Iron-Sulfur Motifs

  Bioinspired synthetic approaches are being utilized to bridge the gap between Fe-S minerals and highly evolved biological Fe-S metalloenzymes. Biology builds complex Fe-S clusters by first synthesizing standard Fe-S clusters and then modifying them through radical chemistry catalyzed by radical SAM enzymes. In an effort to examine hypothetical early biocatalysts, we probing simple Fe-S motifs capable of coordinating Fe-S clusters in aqueous solutions that can initiate radical chemistry.

  ROADMAP OBJECTIVES: 3.1 3.2 3.3 3.4 7.1 7.2

• Task 1.1.1 Models of the Internal Dynamics: Formation of Liquids in the Subsurface and Relationships With Cryovolcanism

  The internal and external geologic evolution of Titan was investigated so as to constrain the environment in which organic evolution has proceeded over time.

  ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2 3.3

• AIRFrame Technical Infrastructure and Visualization Software Evaluation

  We have analyzed over four thousand astrobiology articles from the scientific press, published over ten years to search for clues about their underlying connections. This information can be used to build tools and technologies that guide scientists quickly across vast, interdisciplinary libraries towards the diverse works of most relevance to them.

  ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 3.2 3.3 3.4 4.1 4.2 4.3 5.1 5.2 5.3 6.1 6.2 7.1 7.2

• Habitability of Icy Worlds

  Habitability of Icy Worlds investigates the habitability of liquid water environments in icy worlds, with a focus on what processes may give rise to life, what processes may sustain life, and what processes may deliver that life to the surface. Habitability of Icy Worlds investigation has three major objectives. Objective 1, Seafloor Processes, explores conditions that might be conducive to originating and supporting life in icy world interiors. Objective 2, Ocean Processes, investigates the formation of prebiotic cell membranes under simulated deep-ocean conditions, and Objective 3, Ice Shell Processes, investigates astrobiological aspects of ice shell evolution.

  ROADMAP OBJECTIVES: 1.1 2.1 2.2 3.1 3.2 3.3 3.4 4.1 5.1 5.3 6.1 6.2 7.1 7.2

• Ecology of Extreme Environments: Characterization of Energy Flow, Bioenergetics, and Biodiversity in Early Earth Analog Ecosystems

  The distribution of organisms and their metabolic functions on Earth is rooted, at least in part, to the numerous adaptive radiations that have resulted in the ability to occupy new ecological niches through evolutionary time. Such responses are recorded in extant organismal geographic distribution patterns (e.g., habitat range), as well as in the genetic record of organisms. The extreme variation in the geochemical composition of present day hydrothermal environments is likely to encompass many of those that were present on early Earth, when key metabolic processes are thought to have evolved. Environments such Yellowstone National Park (YNP), Wyoming harbor >12,000 geothermal features that vary widely in temperature and geochemical composition. Such environments provide a field laboratory for examining the tendency for guilds of organisms to inhabit particular ecological niches and to define the range of geochemical conditions tolerated by that functional guild (i.e., habitat range or zone of habitability). In this aim, we are examining the distribution and diversity of genes that encode for target metalloproteins in YNP environments that harbor geochemical properties that are thought to be similar to those that characterize early Earth. Using a number of newly developed computational approaches, we have been able to deduce the primary environmental parameters that constrain the distribution of a number of functional processes and which underpin their diversity. Such information is central to constraining the parameter space of environment types that are likely to have facilitated the emergence of these metal-based biocatalysts.

  ROADMAP OBJECTIVES: 3.2 3.3 3.4 4.1 4.2 5.1 5.2 5.3

• Task 1.1.2 Models of the Reaction Between Hydrocarbons and Water Ice

  Reactions between hydrocarbons and water ice was modeled to assess the possible extent of prebiotic compound formation in this context. Various environments where organics and liquids could be in contact were considered.

  ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2 3.3

• Minerals to Enzymes: The Path to CO Dehydrogenase/Acetyl – CoA Synthase

  We have through NAI Director’s discretionary initiated a project to probing the structural determinants for nickel-iron-sulfur based reversible carbon monoxide oxidation. We are probing whether we can mimic the reactivity of carbon monoxide dehydrogenase to some extent by simple organic nesting and synthesis of nickel-iron-sulfur clusters using a model system we have developed.

  ROADMAP OBJECTIVES: 3.1 3.2 3.3 3.4 7.1 7.2

• Nitrate and Nitrate Conversion to Ammonia on Iron-Sulfur Minerals

  Conversion of nitrate and nitrite may have contributed to the formation of ammonia—a key reagent in the formation of amino acids—on the prebiotic Earth. Results suggest that the presence of iron mono sulfide facilitates the conversion of nitrate and nitrite. Nitrite conversion is, however, much faster than the conversion of nitrate.

  ROADMAP OBJECTIVES: 3.1 3.2 3.3 7.1 7.2

• Paradigms for Complex Iron-Sulfur Cluster Assembly and the Origin and Evolution of Iron-Sulfur Enzymes

  We have presented seminal results in the past year that define paradigms for iron-sulfur cluster assembly in biology that are shared between several important enzymes systems. This work has allowed for the formulation of new models for the origin and evolution of iron sulfur enzymes. An evolutionary origin that involves a mineral beginning and the stepwise refinement of catalytic function in response to selective pressure.

  ROADMAP OBJECTIVES: 3.1 3.2 3.3

• Radical SAM Chemistry and Biological Ligand Accelerated Catalysis

  A number of key reactions in biological systems are catalyzed by iron-sulfur enzymes. Iron-sulfur clusters in biology have a number of features in common with iron-sulfur minerals and their derivatives. We are using iron sulfur motifs as a model system to understand how chemistry in the abiotic mineral world was incorporated into biology on a path to the origin of life. We have found that iron-sulfur motifs in biology are synthesized and modified by reactions and mechanisms that we envision minerals could have been modified on the early prebiotic Earth. The results have had a profound impact on our ability to understand a stepwise trajectory from the nonliving to the living Earth.

  ROADMAP OBJECTIVES: 3.1 3.2 3.3

• Surface Chemistry of Iron-Sulfur Minerals

  The exposure of pyrite surfaces to energetic particle beams creates an activated surface that is capable of facilitating the reduction of nitrogen molecules to ammonia. Experimental results and complementary theoretical calculations indicates that the exposure of pyrite surfaces creates anomalously reduced iron atoms. The chemical state of the surface iron atoms is somewhat similar to iron in the active center of several key enzymes. The triple bond in dinitrogen sorbed onto these reduced surface iron atoms weakens, which is a key step in the conversion to ammonia, a key reagent in the formation of amino acids on the prebiotic Earth

  ROADMAP OBJECTIVES: 3.1 3.2 3.3 7.1 7.2

• Ice Chemistry Beyond the Solar System

  The molecular inventory available on the prebiotic Earth was likely derived from both terrestrial and extraterrestrial sources. Many molecules of biological importance have their origins via chemical processing in the interstel-lar medium, the material between the stars. Polycyclic aromatic hydrocarbons (PAHs) and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block, the aromatic ben¬zene molecule, has remained elusive for decades. Formamide represents the simplest molecule contain-ing the peptide bond. Conse¬quently, the formamide molecule is of high interest as it is considered as an important precursor in the abiotic synthesis of amino acids, and thus significant to further prebiotic chemistry, in more suitable environments. Ultra-high vacuum low-temperature ice chem-istry experiments have been conducted to understand the formation pathways in the ISM for many astrobiologcally important molecules.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1 3.2 3.3 6.2 7.1

• Ice Chemistry of the Solar System

  The overall goals of this project are to understand the chemical evolution of the Solar System, in particular leading to the development of astrobiologically important molecules. This is being achieved by investigation the formation of key organic carbon-, hydrogen-, oxygen-, and nitrogen-bearing (CHON) molecules in ices of Kuiper belt objects by reproducing the space environment experimentally in a unique ultra-high vacuum surface scattering machine. During this reporting period, our team worked on six projects towards our research goal to better understand the ice-based astrochemistry of chemical synthesis for carbon-containing compounds within the solar system. The Keck Astrochemistry Laboratory was also completed during this reporting period.

  ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2 3.3 6.2 7.1