Vacuum-ultraviolet irradiation of pyridine:acetylene ices relevant to Titan astrochemistry.

Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are important molecules for astrochemistry and prebiotic chemistry, as their occurrence spans from interstellar molecular clouds to planetary systems. Their formation has been previously explored in gas phase experiments, but the role of solid-state chemical reactions in their formation under cryogenic conditions remains elusive. Here, we explore the formation of NPAHs through vacuum ultraviolet (VUV) irradiation of pyridine:acetylene ices in amorphous and co-crystalline phases, with the aim to simulate conditions relevant to the interstellar medium and Titan's atmosphere. Our results show that the synthesis of ethynylpyridines from VUV-irradiated pyridine:acetylene amorphous ices is achievable at 18 K. In the co-crystal phase, photolysis at 110 K leads to the formation of NPAHs such as quinolizinium+ and precursors, reflecting a dynamical system under our conditions. In contrast, irradiation at 90 K under stable conditions did not produce volatile photoproducts. These results suggest that such chemical processes can occur in Titan's atmosphere and potentially in its stratosphere, where the co-condensation of these molecules can form composite ices. Concurrently, the formation of stable co-crystals can influence the depletion rates of pyridine, which suggests that these structures can be preserved and potentially delivered to Titan's surface. Our findings provide insights into the molecular diversity and chemical evolution of organic matter on Titan, crucial for future space exploration missions, such as the Dragonfly mission, which may uncover higher-order organics derived from pyridine precursors on Titan's surface.

Simulation of Cocrystal Formation in Planetary Atmospheres: The C6H6:C2H2 Cocrystal Produced by Gas Deposition.

The formation of molecular cocrystals in condensed aerosol particles has been recently proposed as an efficient pathway for generation of complex organics in Titan's atmosphere. It follows that cocrystal precipitation may facilitate the transport of biologically important precursors to the surface to be sequestered in an organic karstic and sand environment. Recent laboratory studies on these planetary minerals have predominantly synthesized cocrystals by the controlled freezing of binary mixtures from the liquid phase, allowing for their structural and spectroscopic characterization. However, these techniques are perhaps not best representative of aerosol nucleation and growth microphysics in planetary atmospheres. Herein, we report the first synthesis of the known 1:1 C6H6:C2H2 cocrystal using vapor deposition methods onto a cryogenically cooled substrate. Subsequent transmission FTIR spectroscopy has confirmed the formation of the empirical C6H6:C2H2 cocrystal structure via the observation of diagnostic infrared spectral features. Predicted by periodic-DFT calculations, altered vibrational profiles depict a changing site symmetry of the C6H6 and C2H2 components after transition to the cocrystal unit cell geometry. The 80 K temperature of the cocrystal phase transition overlaps with the condensation curves obtained for both species in Titan's lower stratosphere, revealing that the cocrystal may act as an important environment for photo- and radio-lytic processes leading to the formation of higher order organics in Titan's atmosphere. Such solid-state astrochemistry can now be pursued in oxygen-free laboratory settings under (ultra)high vacuum using standard surface science setups.

Titan in a Test Tube: Organic Co-crystals and Implications for Titan Mineralogy.

In this Account, we highlight recent work in the developing field of mineralogy of Saturn's moon Titan, focusing on binary co-crystals of small organic molecules. Titan has a massive inventory of organic molecules on its surface that are formed via photochemistry in the atmosphere and likely processing on the surface as well. Physical processes both in the atmosphere and on the surface can lead to molecules interacting at cryogenic temperatures. Recent laboratory work has demonstrated that co-crystals between two or more molecules can form under these conditions. In the organic-rich environment of Titan, such co-crystals are naturally occurring minerals and a critical area of research to understand the physical, chemical, and possibly even biological and prebiotic processes occurring in this alien world.With a future NASA mission, Dragonfly, slated to land on Titan in the next decade, much work is needed to understand organic mineralogy in order to properly interpret the data from this and past Titan missions, such as Cassini-Huygens. By cataloging Titan minerals and their properties, we can begin to connect these behaviors to large-scale surface features observed on Titan (labyrinth terrain, lake evaporites, karst, dunes, etc.), and possible processes leading to their formation (erosion, deposition, etc.). To date, seven co-crystals (aside from clathrates and hydrates) have been experimentally reported to form under Titan-relevant conditions, with an eighth predicted by theoretical modeling. This Account will summarize the formation and properties of these cryominerals and discuss the implications for surface processes on Titan. Enhanced thermal expansion and decreased crystal size, for example, may lead to fracturing and/or more rapid erosion of co-crystal-based deposits; density changes upon co-crystal formation may also play a role in organic diagenesis and metamorphism on Titan. Some cryominerals with stability only under certain conditions may preserve the evidence of Titan's history, such as cryovolcanic activity, ethane fluvial/pluvial exposure, and outgassing of CO2 from the interior of the moon.In this Account, we will also highlight areas of future work, such as the characterization of pure molecular solids and the search for ternary (and more complex) co-crystals. We note that on Titan, organic chemistry dominates, which gives a unique opportunity for chemists to play an even more significant role in planetary science discoveries and likewise in discoveries motivated by planetary science to inform fundamental organic and physical chemistry research.

The Role of Seasonal Sediment Transport and Sintering in Shaping Titan's Landscapes: A Hypothesis.

Titan is a sedimentary world, with lakes, rivers, canyons, fans, dissected plateaux, and sand dunes. Sediments on Saturn's moon are thought to largely consist of mechanically weak organic grains, prone to rapid abrasion into dust. Yet, Titan's equatorial dunes have likely been active for 10s-100s kyr. Sustaining Titan's dunes over geologic timescales requires a mechanism that produces sand-sized particles at equatorial latitudes. We explore the hypothesis that a combination of abrasion, when grains are transported by winds or methane rivers, and sintering, when they are at rest, could produce sand grains that maintain an equilibrium size. Our model demonstrates that seasonal sediment transport may produce sand under Titan's surface conditions and could explain the latitudinal zonation of Titan's landscapes. Our findings support the hypothesis of global, source-to-sink sedimentary pathways on Titan, driven by seasons, and mediated by episodic abrasion and sintering of organic sand by rivers and winds.

Inelastic scattering dynamics of naphthalene and 2-octanone on highly oriented pyrolytic graphite.

The inelastic scattering dynamics of the isobaric molecules, naphthalene (C10H8) and 2-octanone (C8H16O), on highly oriented pyrolytic graphite (HOPG) have been investigated as part of a broader effort to inform the inlet design of a mass spectrometer for the analysis of atmospheric gases during a flyby mission through the atmosphere of a planet or moon. Molecular beam-surface scattering experiments were conducted, and the scattered products were detected with the use of a rotatable mass spectrometer detector. Continuous, supersonic beams were prepared, with average incident translational energies, ⟨Ei⟩, of 247.3 kJ mol-1 and 538.2 kJ mol-1 for naphthalene and 268.6 kJ mol-1 and 433.8 kJ mol-1 for 2-octanone. These beams were directed toward an HOPG surface, held at 530 K, at incident angles, θi, of 30°, 45°, and 70°, and scattered products were detected as functions of their translational energies and scattering angles. The scattering dynamics of both molecules are very similar and mimic the scattering of atoms and small molecules on rough surfaces, where parallel momentum is not conserved, suggesting that the dynamics are dominated by a corrugated interaction potential between the incident molecule and the surface. The effective corrugation of the molecule-surface interaction is apparently caused by the structure of the incident molecule and the consequent myriad available energy transfer pathways between the molecule and the surface during a complex collision event. In addition, the HOPG surface contributes to the corrugation of the interaction potential because it can absorb significant energy from collisions with incident molecules that have high mass and incident energy. Small differences in the scattering dynamics of the two molecules are inferred to arise from the details of the molecule-surface interaction potential, with 2-octanone exhibiting dynamics that suggest a slightly stronger interaction with the surface than naphthalene. These results add to a growing body of work on the scattering dynamics of organic molecules on HOPG, from which insight into the hypervelocity sampling and analysis of such molecules may be obtained.

Raman Signatures and Thermal Expansivity of Acetylene Clathrate Hydrate.

The vibrational signatures for the υ2 C≡C and υ1 symmetric C-H stretches of acetylene in cubic structure I clathrate, synthesized under ambient pressure, are reported for the first time. The most diagnostic features are at 1966 for υ2 and 3353 cm-1 for υ1, respectively, and are assigned to acetylene trapped in the large 51262 cages. In addition, the υ2 mode for acetylene occupying the small 512 cages is observed at 1972.5 cm-1, a red shift of 1.5 cm-1 from its gas phase frequency. Unit cell parameters and thermal expansion coefficients are determined via powder X-ray diffraction between 195 and 225 K and are found to be in good correlation with previous single crystal data at 143 K. The calculated density for acetylene clathrate is also reported, with values ranging from 0.985 g/cm3 at 195 K to 0.976 g/cm3 at 225 K. These results are relevant for spectral detection of acetylene-containing compounds on planetary bodies, as well as providing additional insights on the thermal behavior and physical properties of acetylene clathrate.

Enhancement of anion binding in lanthanide optical sensors.

In the design of molecular sensors, researchers exploit binding interactions that are usually defined in terms of topology and charge complementarity. The formation of complementary arrays of highly cooperative, noncovalent bonding networks facilitates protein-ligand binding, leading to motifs such as the "lock-and-key". Synthetic molecular sensors often employ metal complexes as key design elements as a way to construct a binding site with the desired shape and charge to achieve target selectivity. In transition metal complexes, coordination number, structure and ligand dynamics are governed primarily by a combination of inner-sphere covalent and outer-sphere noncovalent interactions. These interactions provide a rich variable space that researchers can use to tune structure, stability, and dynamics. In contrast, lanthanide(III)-ligand complex formation and ligand-exchange dynamics are dominated by reversible electrostatic and steric interactions, because the unfilled f shell is shielded by the larger, filled d shell. Luminescent lanthanides such as terbium, europium, dysprosium, and samarium display many photophysical properties that make them excellent candidates for molecular sensor applications. Complexes of lanthanide ions act as receptors that exhibit a detectable change in metal-based luminescence upon binding of an anion. In our work on sensors for detection of dipicolinate, the unique biomarker of bacterial spores, we discovered that the incorporation of an ancillary ligand (AL) can enhance binding constants of target anions to lanthanide ions by as much as two orders of magnitude. In this Account, we show that selected ALs in lanthanide/anion systems greatly improve sensor performance for medical, planetary science, and biodefense applications. We suggest that the observed anion binding enhancement could result from an AL-induced increase in positive charge at the lanthanide ion binding site. This effect depends on lanthanide polarizability, which can be established from the ionization energy of Ln(3+) → Ln(4+). These results account for the order Tb(3+) > Dy(3+) > Eu(3+) ≈ Sm(3+). As with many lanthanide properties, ranging from hydration enthalpy to vaporization energy, this AL-induced enhancement shows a large discrepancy between Tb(3+) and Eu(3+) despite their similarity in size, a phenomenon known as the "gadolinium break". This discrepancy, based on the unusual stabilities of the Eu(2+) and Tb(4+) oxidation states, results from the half-shell effect, as both of these ions have half-filled 4f-shells. The high polarizability of Tb(3+) explains the extraordinarily large increase in the binding affinity of anions for terbium compared to other lanthanides. We recommend that researchers consider this AL-induced enhancement when designing lanthanide-macrocycle optical sensors. Ancillary ligands also can reduce the impact of interfering species such as phosphate commonly found in environmental and physiological samples.

Formation of a new benzene-ethane co-crystalline structure under cryogenic conditions.

We report the first experimental finding of a solid molecular complex between benzene and ethane, two small apolar hydrocarbons, at atmospheric pressure and cryogenic temperatures. Considerable amounts of ethane are found to be incorporated inside the benzene lattice upon the addition of liquid ethane onto solid benzene at 90-150 K, resulting in formation of a distinctive co-crystalline structure that can be detected via micro-Raman spectroscopy. Two new features characteristic of these co-crystals are observed in the Raman spectra at 2873 and 1455 cm(-1), which are red-shifted by 12 cm(-1) from the υ1 (a1g) and υ11 (eg) stretching modes of liquid ethane, respectively. Analysis of benzene and ethane vibrational bands combined with quantum mechanical modeling of isolated molecular dimers reveal an interaction between the aromatic ring of benzene and the hydrogen atoms of ethane in a C-H···π fashion. The most favored configuration for the benzene-ethane dimer is the monodentate-contact structure, with a calculated interaction energy of 9.33 kJ/mol and an equilibrium bonding distance of 2.66 Å. These parameters are comparable to those for a T-shaped co-crystalline complex between benzene and acetylene that has been previously reported in the literature. These results are relevant for understanding the hydrocarbon cycle of Titan, where benzene and similar organics may act as potential hydrocarbon reservoirs due to this incorporation mechanism.

How to identify cell material in a single ice grain emitted from Enceladus or Europa.

Icy moons like Enceladus, and perhaps Europa, emit material sourced from their subsurface oceans into space via plumes of ice grains and gas. Both moons are prime targets for astrobiology investigations. Cassini measurements revealed a large compositional diversity of emitted ice grains with only 1 to 4% of Enceladus's plume ice grains containing organic material in high concentrations. Here, we report experiments simulating mass spectra of ice grains containing one bacterial cell, or fractions thereof, as encountered by advanced instruments on board future space missions to Enceladus or Europa, such as the SUrface Dust Analyzer onboard NASA's upcoming Europa Clipper mission at flyby speeds of 4 to 6 kilometers per second. Mass spectral signals characteristic of the bacteria are shown to be clearly identifiable by future missions, even if an ice grain contains much less than one cell. Our results demonstrate the advantage of analyses of individual ice grains compared to a diluted bulk sample in a heterogeneous plume.

Propyne: Determination of Physical Properties and Unit Cell Parameters under Titan-Relevant Conditions.

With its large size, dense atmosphere, methane-based hydrological-like cycle, and diverse surface features, the Saturnian moon Titan is one of the most unique of the outer Solar System satellites. Study of the photochemically produced molecules in Titan's atmosphere is critical in order to understand the mechanics of the atmosphere and, by extension, the interactions between atmosphere, surface, and subsurface water ocean. One example is propyne vapor, a photochemically produced species in Titan's upper atmosphere expected to condense in Titan's stratosphere at lower altitudes. Propyne may also be a trace species in Titan's stratospheric co-condensed ice clouds detected by the Cassini Composite InfraRed Spectrometer. Bulk structural characterization of propyne ice is currently incomplete and is lacking in published laboratory Raman spectra and X-ray diffraction data. Here, we present a laboratory characterization of propyne ice, including the first published X-ray diffraction and Raman spectroscopy results for propyne ice.

The Mapping Imaging Spectrometer for Europa (MISE).

The Mapping Imaging Spectrometer for Europa (MISE) is an infrared compositional instrument that will fly on NASA's Europa Clipper mission to the Jupiter system. MISE is designed to meet the Level-1 science requirements related to the mission's composition science objective to "understand the habitability of Europa's ocean through composition and chemistry" and to contribute to the geology science and ice shell and ocean objectives, thereby helping Europa Clipper achieve its mission goal to "explore Europa to investigate its habitability." MISE has a mass of 65 kg and uses an energy per flyby of 75.2 W-h. MISE will detect illumination from 0.8 to 5 µm with 10 nm spectral resolution, a spatial sampling of 25 m per pixel at 100 km altitude, and 300 cross-track pixels, enabling discrimination among the two principal states of water ice on Europa, identification of the main non-ice components of interest: salts, acids, and organics, and detection of trace materials as well as some thermal signatures. Furthermore, the spatial resolution and global coverage that MISE will achieve will be complemented by the higher spectral resolution of some Earth-based assets. MISE, combined with observations collected by the rest of the Europa Clipper payload, will enable significant advances in our understanding of how the large-scale structure of Europa's surface is shaped by geological processes and inform our understanding of the surface at microscale. This paper describes the planned MISE science investigations, instrument design, concept of operations, and data products.

Low-temperature microchip nonaqueous capillary electrophoresis of aliphatic primary amines: applications to Titan chemistry.

We demonstrate microchip nonaqueous capillary electrophoresis (µNACE) analysis of primary aliphatic amines (C1-C18) in ethanol down to -20 °C as a first step in adapting microfluidic protocols for in situ analysis on Titan. To our knowledge, this is the first report of a nonaqueous separation at -20 °C on-chip. Limits of detection (LODs) ranged from 1.0 nM to 2.6 nM, and we identified several primary amines ranging in length from C2 to C16 in Titan aerosol analogue (tholin) samples; new amines were also detected in a tholin sample exposed to oxygen and liquid water. This preliminary work validates the sensitivity and efficacy of microfluidic chemical analysis of complex organics with relevance to Titan aerosols and surface deposits.

Array-Based Machine Learning for Functional Group Detection in Electron Ionization Mass Spectrometry.

Mass spectrometry is a ubiquitous technique capable of complex chemical analysis. The fragmentation patterns that appear in mass spectrometry are an excellent target for artificial intelligence methods to automate and expedite the analysis of data to identify targets such as functional groups. To develop this approach, we trained models on electron ionization (a reproducible hard fragmentation technique) mass spectra so that not only the final model accuracies but also the reasoning behind model assignments could be evaluated. The convolutional neural network (CNN) models were trained on 2D images of the spectra using transfer learning of Inception V3, and the logistic regression models were trained using array-based data and Scikit Learn implementation in Python. Our training dataset consisted of 21,166 mass spectra from the United States' National Institute of Standards and Technology (NIST) Webbook. The data was used to train models to identify functional groups, both specific (e.g., amines, esters) and generalized classifications (aromatics, oxygen-containing functional groups, and nitrogen-containing functional groups). We found that the highest final accuracies on identifying new data were observed using logistic regression rather than transfer learning on CNN models. It was also determined that the mass range most beneficial for functional group analysis is 0-100 m/z. We also found success in correctly identifying functional groups of example molecules selected from both the NIST database and experimental data. Beyond functional group analysis, we also have developed a methodology to identify impactful fragments for the accurate detection of the models' targets. The results demonstrate a potential pathway for analyzing and screening substantial amounts of mass spectral data.

Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan's Surface.

Titan, Saturn's largest moon, has a plethora of organic compounds in the atmosphere and on the surface that interact with each other. Cryominerals such as co-crystals may influence the geologic processes and chemical composition of Titan's surface, which in turn informs our understanding of how Titan may have evolved, how the surface is continuing to change, and the extent of Titan's habitability. Previous works have shown that a pyridine:acetylene (1:1) co-crystal forms under specific temperatures and experimental conditions; however, this has not yet been demonstrated under Titan-relevant conditions. Our work here demonstrates that the pyridine:acetylene co-crystal is stable from 90 K, Titan's average surface temperature, up to 180 K under an atmosphere of N2. In particular, the co-crystal forms via liquid-solid interactions within minutes upon mixing of the constituents at 150 K, as evidenced by distinct, new Raman bands and band shifts. X-ray diffraction (XRD) results indicate moderate anisotropic thermal expansion (about 0.5-1.1%) along the three principal axes between 90-150 K. Additionally, the co-crystal is detectable after being exposed to liquid ethane, implying stability in a residual ethane "wetting" scenario on Titan. These results suggest that the pyridine:acetylene co-crystal could form in specific geologic contexts on Titan that allow for warm environments in which liquid pyridine could persist, and as such, this cryomineral may preserve the evidence of impact, cryovolcanism, or subsurface transport in surface materials.

Toward Detecting Biosignatures of DNA, Lipids, and Metabolic Intermediates from Bacteria in Ice Grains Emitted by Enceladus and Europa.

The reliable identification of biosignatures is key to the search for life elsewhere. On ocean worlds like Enceladus or Europa, this can be achieved by impact ionization mass spectrometers, such as the SUrface Dust Analyzer (SUDA) on board NASA's upcoming Europa Clipper mission. During spacecraft flybys, these instruments can sample ice grains formed from subsurface water and emitted by these moons. Previous laboratory analog experiments have demonstrated that SUDA-type instruments could identify amino acids, fatty acids, and peptides in ice grains and discriminate between their abiotic and biotic origins. Here, we report experiments simulating impact ionization mass spectra of ice grains containing DNA, lipids, and metabolic intermediates extracted from two bacterial cultures: Escherichia coli and Sphingopyxis alaskensis. Salty Enceladan or Europan ocean waters were simulated using matrices with different NaCl concentrations. Characteristic mass spectral signals, such as DNA nucleobases, are clearly identifiable at part-per-million-level concentrations. Mass spectra of all substances exhibit unambiguous biogenic patterns, which in some cases show significant differences between the two bacterial species. Sensitivity to the biosignatures decreases with increasing matrix salinity. The experimental parameters indicate that future impact ionization mass spectrometers will be most sensitive to the investigated biosignatures for ice grain encounter speeds of 4-6 km/s.

Exploring the Interior of Europa with the Europa Clipper.

The Galileo mission to Jupiter revealed that Europa is an ocean world. The Galileo magnetometer experiment in particular provided strong evidence for a salty subsurface ocean beneath the ice shell, likely in contact with the rocky core. Within the ice shell and ocean, a number of tectonic and geodynamic processes may operate today or have operated at some point in the past, including solid ice convection, diapirism, subsumption, and interstitial lake formation. The science objectives of the Europa Clipper mission include the characterization of Europa's interior; confirmation of the presence of a subsurface ocean; identification of constraints on the depth to this ocean, and on its salinity and thickness; and determination of processes of material exchange between the surface, ice shell, and ocean. Three broad categories of investigation are planned to interrogate different aspects of the subsurface structure and properties of the ice shell and ocean: magnetic induction, subsurface radar sounding, and tidal deformation. These investigations are supplemented by several auxiliary measurements. Alone, each of these investigations will reveal unique information. Together, the synergy between these investigations will expose the secrets of the Europan interior in unprecedented detail, an essential step in evaluating the habitability of this ocean world.

Science Objectives for Flagship-Class Mission Concepts for the Search for Evidence of Life at Enceladus.

Cassini revealed that Saturn's Moon Enceladus hosts a subsurface ocean that meets the accepted criteria for habitability with bio-essential elements and compounds, liquid water, and energy sources available in the environment. Whether these conditions are sufficiently abundant and collocated to support life remains unknown and cannot be determined from Cassini data. However, thanks to the plume of oceanic material emanating from Enceladus' south pole, a new mission to Enceladus could search for evidence of life without having to descend through kilometers of ice. In this article, we outline the science motivations for such a successor to Cassini, choosing the primary science goal to be determining whether Enceladus is inhabited and assuming a resource level equivalent to NASA's Flagship-class missions. We selected a set of potential biosignature measurements that are complementary and orthogonal to build a robust case for any life detection result. This result would be further informed by quantifications of the habitability of the environment through geochemical and geophysical investigations into the ocean and ice shell crust. This study demonstrates that Enceladus' plume offers an unparalleled opportunity for in situ exploration of an Ocean World and that the planetary science and astrobiology community is well equipped to take full advantage of it in the coming decades.

Understanding Hypervelocity Sampling of Biosignatures in Space Missions.

The atomic-scale fragmentation processes involved in molecules undergoing hypervelocity impacts (HVIs; defined as >3 km/s) are challenging to investigate via experiments and still not well understood. This is particularly relevant for the consistency of biosignals from small-molecular-weight neutral organic molecules obtained during solar system robotic missions sampling atmospheres and plumes at hypervelocities. Experimental measurements to replicate HVI effects on neutral molecules are challenging, both in terms of accelerating uncharged species and isolating the multiple transition states over very rapid timescales (<1 ps). Nonequilibrium first-principles-based simulations extend the range of what is possible with experiments. We report on high-fidelity simulations of the fragmentation of small organic biosignature molecules over the range v = 1-12 km/s, and demonstrate that the fragmentation fraction is a sensitive function of velocity, impact angle, molecular structure, impact surface material, and the presence of surrounding ice shells. Furthermore, we generate interpretable fragmentation pathways and spectra for velocity values above the fragmentation thresholds and reveal how organic molecules encased in ice grains, as would likely be the case for those in "ocean worlds," are preserved at even higher velocities than bare molecules. Our results place ideal spacecraft encounter velocities between 3 and 5 km/s for bare amino and fatty acids and within 4-6 km/s for the same species encased in ice grains and predict the onset of organic fragmentation in ice grains at >5 km/s, both consistent with recent experiments exploring HVI effects using impact-induced ionization and analysis via mass spectrometry and from the analysis of Enceladus organics in Cassini Data. From nanometer-sized ice Ih clusters, we establish that HVI energy is dissipated by ice casings through thermal resistance to the impact shock wave and that an upper fragmentation velocity limit exists at which ultimately any organic contents will be cleaved by the surrounding ice-this provides a fundamental path to characterize micrometer-sized ice grains. Altogether, these results provide quantifiable insights to bracket future instrument design and mission parameters.

Terbium-macrocycle complexes as chemical sensors: detection of an aspirin metabolite in urine using a salicylurate-specific receptor site.

Salicylurate (SU) is the major metabolite in urine of acetylsalicylic acid (aspirin) and can be used as a metric to monitor aspirin pharmacokinetics and as an indicator of appendicitis, anemia, and liver disease. Detection in urine and plasma currently requires solvent extraction or other sample handling prior to analysis. We present a simple method to quantify SU in urine via chelation to a terbium binary complex with the macrocycle 1,4,7,10-tetraazacyclododecane-1,7-bisacetate (DO2A). Binding of SU to form the [Tb(DO2A)(SU)](-) ternary complex triggers intense luminescence under UV excitation due to an absorbance-energy transfer-emission mechanism. Here we report characterization of the [Tb(DO2A)(SU)](-) ternary complex and application of this sensitized lanthanide luminescence method to quantify SU in urine samples following a low-dose aspirin regimen.

Analog Experiments for the Identification of Trace Biosignatures in Ice Grains from Extraterrestrial Ocean Worlds.

Reliable identification of biosignatures, such as amino acids, fatty acids, and peptides, on extraterrestrial ocean worlds is a key prerequisite for space missions that search for life or its emergence on these worlds. One promising approach is the use of high-performance in situ impact ionization mass spectrometers to sample water ice grains emerging from ocean-bearing moons such as Europa or Enceladus. A predecessor of such detectors, the Cosmic Dust Analyzer on board the Cassini spacecraft, has proven to be very successful in analyzing inorganic and organic ocean constituents and with that characterizing the habitability of Enceladus ocean. However, biosignatures have not been definitively identified in extraterrestrial ocean environments so far. Here, we investigate with an analog experiment the spectral appearance of amino acids, fatty acids, and peptides in water ice grains, together with their detection limits, as applicable to spaceborne mass spectrometers. We employ a laboratory-based laser induced liquid beam ion desorption technique, proven to simulate accurately the impact ionization mass spectra of water ice grains over a wide range of impact speeds. The investigated organics produce characteristic mass spectra, with molecular peaks as well as clearly identifiable, distinctive fragments. We find the detection limits of these key biosignatures to be at the µM or nM level, depending on the molecular species and instrument polarity, and infer that impact ionization mass spectrometers are most sensitive to the molecular peaks of these biosignatures at encounter velocities of 4-6 km/s.