Thermal behavior of astrophysical amorphous molecular ices.

Ice is a major component of astrophysical environments - from interstellar molecular clouds through protoplanetary disks to evolved solar systems. Ice and complex organic matter coexist in these environments as well, and it is thought primordial ice brought the molecules of life to Earth four billion years ago, which could have kickstarted the origin of life on Earth. To understand the journey of ice and organics from their origins to becoming a part of evolved planetary systems, it is important to complement high spatial and spectral resolution telescopes such as JWST with laboratory experimental studies that provide deeper insight into the processes that occur in these astrophysical environments. Our laboratory studies are aimed at providing this knowledge. In this article we present simultaneous mass spectrometric and infrared spectroscopic investigation on how molecular ice mixtures behave at different temperatures and how this information is critical to interpret observational data from protoplanetary disks as well as comets. We find that amorphous to crystalline water ice transformation is the most critical phenomenon that differentiates between outgassing of trapped volatiles such as CO2vs. outgassing of pure molecular ice domains of the same in a mixed molecular ice. Crystalline water ice is found to trap only a small fraction of other volatiles (<5%), indicating ice grain composition in astrophysical and planetary environments must be different depending on whether the ice is in amorphous phase or transformed into crystalline phase, even if the crystalline ice undergoes radiation-induced amorphization subsequently. Crystallization of water ice is a key differentiator for many ices in astronomical environments as well as in our Solar System.

Testing Abiotic Reduction of NAD+ Directly Mediated by Iron/Sulfur Minerals.

Life emerged in a geochemical context, possibly in the midst of mineral substrates. However, it is not known to what extent minerals and dissolved inorganic ions could have facilitated the evolution of biochemical reactions. Herein, we have experimentally shown that iron sulfide minerals can act as electron transfer agents for the reduction of the ubiquitous biological protein cofactor nicotinamide adenine dinucleotide (NAD+) under anaerobic prebiotic conditions, observing the NAD+/NADH redox transition by using ultraviolet-visible spectroscopy and 1H nuclear magnetic resonance. This reaction was mediated with iron sulfide minerals, which were likely abundant on early Earth in seafloor and hydrothermal settings; and the NAD+/NADH redox reaction occurred in the absence of UV light, peptide ligand(s), or dissolved mediators. To better understand this reaction, thermodynamic modeling was also performed. The ability of an iron sulfide mineral to transfer electrons to a biochemical cofactor that is found in every living cell demonstrates how geologic materials could have played a direct role in the evolution of certain cofactor-driven metabolic pathways.

Extraction and Separation of Chiral Amino Acids for Life Detection on Ocean Worlds Without Using Organic Solvents or Derivatization.

In situ instrumentation that can detect amino acids at parts-per-billion concentration levels and distinguish an enantiomeric excess of either d- or l-amino acids is vital for future robotic life-detection missions to promising targets in our solar system. In this article, a novel chiral amino acid analysis method is described, which reduces the risk of organic contamination and spurious signals from by-products by avoiding organic solvents and organic additives. Online solid-phase extraction, chiral liquid chromatography, and mass spectrometry were used for automated analysis of amino acids from solid and aqueous environmental samples. Carbonated water (pH ∼3, ∼5 wt % CO2 achieved at 6 MPa) was used as the extraction solvent for solid samples at 150°C and as the mobile phase at ambient temperature for chiral chromatographic separation. Of 18 enantiomeric amino acids, 5 enantiomeric pairs were separated with a chromatographic resolution >1.5 and 12 pairs with a resolution >0.7. The median lower limit of detection of amino acids was 2.5 µg/L, with the lowest experimentally verified as low as 0.25 µg/L. Samples from a geyser site (Great Fountain Geyser) and a geothermal spring site (Lemon Spring) in Yellowstone National Park were analyzed to demonstrate the viability of the method for future in situ missions to Ocean Worlds.

Online supercritical fluid extraction and chromatography of biomarkers analysis in aqueous samples for in situ planetary applications.

Sensitive and robust in situ chemical analysis of organic biomarkers is essential in the endeavor of finding chemical signatures of life either extinct or extant on our solar system bodies such as Europa, Enceladus, or Titan. Development of new analytical instruments and accompanying methodologies are needed, especially those that are compatible with unknown and diverse samples potentially found on solar system targets and that avoid complexities involved with other wet chemistry techniques (desalting, derivatization and contamination issues, etc.). In this study, we demonstrate that online supercritical fluid extraction and supercritical fluid chromatography with water-saturated CO2 can extract and separate nonpolar analytes of astrobiological interest, such as free fatty acids, polycyclic aromatic hydrocarbons, and polycyclic aromatic compounds containing nitrogen or sulfur. Silica was used as a support material to immobilize aqueous samples during extraction. A C18 stationary phase with an embedded polar functional group and efficient end-capping in combination with water in the mobile phase allowed efficient separation of both free fatty acids and basic compounds. The total analysis time was 30 min, including extraction, equilibration, and separation. Detection was performed with a UV detector and a quadrupole mass spectrometer equipped with electrospray ionization. The method was validated in terms of lower detection limits (0.02-40 µg/L), precision (repeatability 3-13%), relative standard deviation (RSD), intermediate precision 4-26% (RSD), trueness (bias ranging from - 48 to 9%), and retention time shifts (< 2% RSD) for 16 analytes in sample matrices with sodium chloride and magnesium sulfate that may be present in ocean worlds such as Europa or Enceladus. Graphical Abstract.

Macromolecular organic compounds from the depths of Enceladus.

Saturn's moon Enceladus harbours a global water ocean 1 , which lies under an ice crust and above a rocky core 2 . Through warm cracks in the crust 3 a cryo-volcanic plume ejects ice grains and vapour into space4-7 that contain materials originating from the ocean8,9. Hydrothermal activity is suspected to occur deep inside the porous core10-12, powered by tidal dissipation 13 . So far, only simple organic compounds with molecular masses mostly below 50 atomic mass units have been observed in plume material6,14,15. Here we report observations of emitted ice grains containing concentrated and complex macromolecular organic material with molecular masses above 200 atomic mass units. The data constrain the macromolecular structure of organics detected in the ice grains and suggest the presence of a thin organic-rich film on top of the oceanic water table, where organic nucleation cores generated by the bursting of bubbles allow the probing of Enceladus' organic inventory in enhanced concentrations.

Plume composition and evolution in multicomponent ices using resonant two-step laser ablation and ionization mass spectrometry.

The composition and evolution of plumes generated in a resonant infrared (IR) laser desorption of low-temperature ices is investigated via a recently developed two-step laser desorption and ionization mass spectrometry (2S-LAIMS) technique where a neutral plume is ejected by an IR laser pulse and ionized by a UV laser pulse for analysis via time-of-flight mass spectrometry. By varying the delay between the lasers, we can construct a complete time-resolved model of the ejected plume components. We found that water ices containing mixtures of polar and nonpolar analytes displayed complex mass spectral profiles that varied as the plume evolved. In these samples, the low-volatility polar analytes and clusters were restricted to the early part of the plume, whereas volatile or nonpolar analytes were spread throughout the plume. The distributions of low-volatility polar species, clusters, and impurities from the copper substrate were well-represented by single Maxwell-like distributions centered at high velocities (600-800 m s(-1)), while nonpolar, volatile species contained two distinct components, indicating both ablation and thermal desorption processes. Characterization of plume distributions can therefore provide new insight into an analyte's chemical identity and can aid in assignment of otherwise ambiguous signals in the mass spectra.

Continuous spectroscopic measurements of photo-stimulated release of molecules by nanomachines in a single living cell.

The first continuous, real-time spectroscopic monitoring of a photo-driven cargo delivery event from a mesoporous silica-based nanocarrier inside a single living cell is reported. By chemically attaching azobenzene molecules inside the 3 nm pore channels of mesoporous silica nanoparticles (∼70 nm diameter), the escape of the cargo molecule [propidium iodide (PI)] from the pore is prevented in the dark but is facilitated by the light-driven isomerization motion. Real-time spectroscopic measurements of a single cell uncover intermediate processes that occur during this intracellular delivery event, from nanomachine activation to the release of PI into the cytosol and to PI's eventual intercalation with nuclear DNA. Changes in PI's fluorescence intensity and the hypsochromic shift of the band maxima are used to identify the local environment of the fluorophore that is being observed in the cell. The ability to precisely initiate a chemical event inside an individual cell and continuously monitor the subsequent biological responses will enhance our understanding of intracellular process upon drug, protein and nucleic acid delivery.

Excited state kinetics in crystalline solids: self-quenching in nanocrystals of 4,4'-disubstituted benzophenone triplets occurs by a reductive quenching mechanism.

We report an efficient triplet state self-quenching mechanism in crystals of eight benzophenones, which included the parent structure (1), six 4,4'-disubstituted compounds with NH(2) (2), NMe(2) (3), OH (4), OMe (5), COOH (6), and COOMe (7), and benzophenone-3,3',4,4'-tetracarboxylic dianhydride (8). Self-quenching effects were determined by measuring their triplet-triplet lifetimes and spectra using femtosecond and nanosecond transient absorption measurements with nanocrystalline suspensions. When possible, triplet lifetimes were confirmed by measuring the phosphorescence lifetimes and with the help of diffusion-limited quenching with iodide ions. We were surprised to discover that the triplet lifetimes of substituted benzophenones in crystals vary over 9 orders of magnitude from ca. 62 ps to 1 ms. In contrast to nanocrystalline suspensions, the lifetimes in solution only vary over 3 orders of magnitude (1-1000 µs). Analysis of the rate constants of quenching show that the more electron-rich benzophenones are the most efficiently deactivated such that there is an excellent correlation, ρ = -2.85, between the triplet quenching rate constants and the Hammet σ(+) values for the 4,4' substituents. Several crystal structures indicate the existence of near-neighbor arrangements that deviate from the proposed ideal for "n-type" quenching, suggesting that charge transfer quenching is mediated by a relatively loose arrangement.

Role of Fe doping in tuning the band gap of TiO2 for the photo-oxidation-induced cytotoxicity paradigm.

UV-light-induced electron-hole (e(-)/h(+)) pair generation with free radical production in TiO(2)-based nanoparticles is a major conceptual paradigm for biological injury. However, to date, this hypothesis has been difficult to experimentally verify due to the high energy of UV light that is intrinsically highly toxic to biological systems. Here, a versatile flame spray pyrolysis (FSP) synthetic process has been exploited to synthesize a library of iron-doped (0-10 wt%) TiO(2) nanoparticles. These particles have been tested for photoactivation-mediated cytotoxicity using near-visible light exposure. The reduction in TiO(2) band gap energy with incremental levels of Fe loading maintained the nanoparticle crystalline structure in spite of homogeneous Fe distribution (demonstrated by XRD, HRTEM, SAED, EFTEM, and EELS). Photochemical studies showed that band gap energy was reciprocally tuned proportional to the Fe content. The photo-oxidation capability of Fe-doped TiO(2) was found to increase during near-visible light exposure. Use of a macrophage cell line to evaluate cytotoxic and ROS production showed increased oxidant injury and cell death in parallel with a decrease in band gap energy. These findings demonstrate the importance of band gap energy in the phototoxic response of the cell to TiO(2) nanoparticles and reflect the potential of this material to generate adverse effects in humans and the environment during high-intensity light exposure.

Multiple photochemical reaction pathways in a Ni(II) coordination compound.

The gas-phase photofragmentation of the mixed-ligand coordination compound trans-bis(trifluoroacetato)bis(N,N'-dimethylethylenediamine)nickel(II) (Ni(tfa)2(dmen)2) detected via time-of-flight mass spectrometry is reported. In contrast to most gas-phase studies of metal-containing compounds where fragmentation of weak metal-ligand bonds dominates, the data here show that the dmen ligands fragment while still coordinated to nickel. The manner in which these ligands fragment is highly specific, leading to mono- and diimine species that remain coordinated to nickel. Uncoordinated mono- and diimine species and various small dmen fragments are also observed with high intensities in the low mass region of the spectra. NiF+, a fragment that is formed by fluorine abstraction, is always observed, even though no Ni-F bonds exist in the starting material.