Chemical Ionization Mass Spectrometry: Applications for the In Situ Measurement of Nonvolatile Organics at Ocean Worlds.

A new technique that has applications for the detection of nonvolatile organics on Ocean Worlds has been developed. Here, liquid mixtures of fatty acids (FAs) and/or amino acids (AAs) are introduced directly into a miniature quadrupole ion trap mass spectrometer (QITMS) developed at Jet Propulsion Laboratory and analyzed. Two ionization methods, electron impact and chemical ionization (EI and CI, respectively), are compared and contrasted. Further, multiple CI reagents are tested to explore their potential to "soften" ionization of FAs and AAs. Both EI and CI yield mass spectra that bear signatures of FAs or AAs; however, soft CI yields significantly cleaner mass spectra that are easier to interpret. The combination of soft CI with tandem mass spectrometry (MS/MS) has also been demonstrated for AAs, generating "fingerprint" mass spectra of fragments from protonated parent ions. To mimic potential Ocean World conditions, water is used as the primary collision gas in MS/MS experiments. This technique has the potential for the in situ analysis of molecules in the cryogenic plumes of Ocean Worlds (e.g., Enceladus) and comets with the ultimate goal of detecting potential biosignatures.

Chemical Gardens as Flow-through Reactors Simulating Natural Hydrothermal Systems.

Here we report experimental simulations of hydrothermal chimney growth using injection chemical garden methods. The versatility of this type of experiment allows for testing of various proposed ocean / hydrothermal fluid chemistries that could have driven reactions toward the origin of life in environments on the early Earth, early Mars, or even other worlds such as the icy moons of the outer planets. We show experiments that include growth of chemical garden structures under anoxic conditions simulating the early Earth, inclusion of trace components of phosphates / organics in the injection solution to incorporate them into the structure, a switch of the injection solution to introduce a secondary precipitating anion, and the measurement of membrane potentials generated by chemical gardens. Using this method, self-assembling chemical garden structures were formed that mimic the natural chimneys precipitated at submarine hydrothermal springs, and these precipitates can be used successfully as flow-through reactors by feeding through multiple successive "hydrothermal" injections.

From Chemical Gardens to Fuel Cells: Generation of Electrical Potential and Current Across Self-Assembling Iron Mineral Membranes.

We examine the electrochemical gradients that form across chemical garden membranes and investigate how self-assembling, out-of-equilibrium inorganic precipitates-mimicking in some ways those generated in far-from-equilibrium natural systems-can generate electrochemical energy. Measurements of electrical potential and current were made across membranes precipitated both by injection and solution interface methods in iron-sulfide and iron-hydroxide reaction systems. The battery-like nature of chemical gardens was demonstrated by linking multiple experiments in series which produced sufficient electrical energy to light an external light-emitting diode (LED). This work paves the way for determining relevant properties of geological precipitates that may have played a role in hydrothermal redox chemistry at the origin of life, and materials applications that utilize the electrochemical properties of self-organizing chemical systems.

The fuel cell model of abiogenesis: a new approach to origin-of-life simulations.

In this paper, we discuss how prebiotic geo-electrochemical systems can be modeled as a fuel cell and how laboratory simulations of the origin of life in general can benefit from this systems-led approach. As a specific example, the components of what we have termed the "prebiotic fuel cell" (PFC) that operates at a putative Hadean hydrothermal vent are detailed, and we used electrochemical analysis techniques and proton exchange membrane (PEM) fuel cell components to test the properties of this PFC and other geo-electrochemical systems, the results of which are reported here. The modular nature of fuel cells makes them ideal for creating geo-electrochemical reactors with which to simulate hydrothermal systems on wet rocky planets and characterize the energetic properties of the seafloor/hydrothermal interface. That electrochemical techniques should be applied to simulating the origin of life follows from the recognition of the fuel cell-like properties of prebiotic chemical systems and the earliest metabolisms. Conducting this type of laboratory simulation of the emergence of bioenergetics will not only be informative in the context of the origin of life on Earth but may help in understanding whether life might emerge in similar environments on other worlds.

Differential mobility spectrometry with nanospray ion source as a compact detector for small organics and inorganics.

Electrospray ionization (ESI) is an important tool in chemical and biochemical survey and targeted analysis in many applications. For chemical detection and identification electrospray is usually used with mass spectrometry (MS). However, for screening and monitoring of chemicals of interest in light, low power field-deployable instrumentation, an alternative detection technology with chemical selectivity would be highly useful, especially since small, lightweight, chip-based gas and liquid chromatographic technologies are being developed. Our initial list of applications requiring portable instruments includes chemical surveys on Mars, medical diagnostics based on metabolites in biological samples, and water quality analysis. In this report, we evaluate ESI-Differential Mobility Spectrometry (DMS) as a compact, low-power alternative to MS detection. Use of DMS for chemically-selective detection of ESI suffers in comparison with mass spectrometry because portable MS peak capacity is greater than that of DMS by 10X or more, but the development of light, fast chip chromatography offers compensating resolution. Standalone DMS provides the chemical selectivity familiar from DMS-MS publications, and exploits the sensitivity of ion detection. We find that sub-microliter-per-minute flows and a correctly-designed interface prepare a desolvated ion stream that enables DMS to act as an effective ion filter. Results for a several small organic biomarkers and metabolites, including citric acid, azelaic acid, n-hexanoylglycine, thymidine, and caffeine, as well as compounds such as dinitrotoluene and others, have been characterized and demonstrate selective detection. Water-quality-related halogen-containing anions, fluoride through bromate, contained in liquid samples are also isolated by DMS. A reaction-chamber interface is highlighted as most practical for portable ESI-DMS instrumentation.

Comparison of three commercial sparse-matrix crystallization screens.

Sparse-matrix sampling using commercially available crystallization screen kits has become the most popular way of determining the preliminary crystallization conditions for macromolecules. In this study, the efficiency of three commercial screening kits, Crystal Screen and Crystal Screen 2 (Hampton Research), Wizard Screens I and II (Emerald BioStructures) and Personal Structure Screens 1 and 2 (Molecular Dimensions), has been compared using a set of 19 diverse proteins. 18 proteins yielded crystals using at least one crystallization screen. Surprisingly, Crystal Screens and Personal Structure Screens showed dramatically different results, although most of the crystallization formulations are identical as listed by the manufacturers. Higher molecular weight polyethylene glycols and mixed precipitants were found to be the most effective precipitants in this study.

Lactoferrin and transferrin: functional variations on a common structural framework.

Lactoferrin shares many structural and functional features with serum transferrin, including an ability to bind iron very tightly, but reversibly, a highly-conserved three-dimensional structure, and essentially identical iron-binding sites. Nevertheless, lactoferrin has some unique properties that differentiate it: an ability to retain iron to much lower pH, a positively charged surface, and other surface features that give it additional functions. Here, we review the structural basis for these similarities and differences, including the importance of dynamics and conformational change, and specific interactions that regulate iron binding and release.

Electron transfer between cytochrome b(5) and some oxidised haemoglobins: the role of ionic strength.

We have compared experimental measurements and Brownian dynamic calculations for the reduction of oxidised adult human haemoglobin by reduced bovine cytochrome b(5) over a range of ionic strengths. Our calculations suggest that the presence of molecular electrostatic fields have a significant role to play in the formation of the electron transfer complexes. These results predict that electron transfer occurs within an ensemble of similarly weakly docked complexes, the formation of which is strongly ionic strength dependent. Application of electron tunneling analysis to the complexes allows us to predict the rates of electron transfer within each ensemble of complexes as a function of ionic strength. The outcome of this theoretical study is compared with experimental rate measurements. A comparison of the results obtained from adult and embryonic haemoglobins, at a fixed ionic strength, indicates a significant difference in the characteristics of complex formation. These data emphasise the role played by electrostatic interactions in this important physiological reaction.

A modeling study of the interaction and electron transfer between cytochrome b5 and some oxidized haemoglobins.

Using Brownian motion simulations we have studied the formation of docked complexes of reduced cytochrome b5 and oxidized haemoglobin. Our results indicate that the presence of molecular electrostatic fields has a significant role to play in the formation of these complexes. In contrast to previous modeling studies on this system, we clearly identify electron transfer within an ensemble of similarly docked complexes rather than the formation of a single complex. Docking involves a number of acidic residues surrounding the exposed haem edge of cytochrome b5 and a set of basic residues surrounding the exposed haem edge of the globins. Although amino acids from the partner globin proteins are involved to a small extent in the binding of some of the complexes, the reactivity of any particular globin is essentially independent of the nature of its partner globin chain within the haemoglobin molecule. Comparison of results from adult and embryonic haemoglobins indicates a significant difference in complex formation. Application of electron tunneling analysis to the complexes allows us to predict the rates of electron transfer within each ensemble of complexes. These data provide a theoretical insight into the important process of re-reduction of oxidized haemoglobins as well as explaining the general inability to produce crystalline forms of many docked electron transfer complexes.