Laser Induced Liquid Beam Research Articles

Laboratory characterization of hydrothermally processed oligopeptides in ice grains emitted by Enceladus and Europa.

The Cassini mission provided evidence for a global subsurface ocean and ongoing hydrothermal activity on Enceladus, based on results from Cassini's mass spectrometers. Laboratory simulations of hydrothermal conditions on icy moons are needed to further constrain the composition of ejected ice grains containing hydrothermally altered organic material. Here, we present results from our newly established facility to simulate the processing of ocean material within the temperature range 80-150°C and the pressure range 80-130 bar, representing conditions suggested for the water-rock interface on Enceladus. With this new facility, we investigate the hydrothermal processing of triglycine (GGG) peptide and, for the first time, analyse the extracted samples using laser-induced liquid beam ion desorption (LILBID) mass spectrometry, a laboratory analogue for impact ionization mass spectrometry of ice grains in space. We outline an approach to elucidate hydrothermally processed GGG in ice grains ejected from icy moons based on characteristic differences between GGG anion and cation mass spectra. These differences are linked to hydrothermal processing and thus provide a fingerprint of hydrothermal activity on extraterrestrial bodies. These results will serve as important guidelines for biosignatures potentially obtained by a future Enceladus mission and the SUrface Dust Analyzer (SUDA) instrument onboard Europa Clipper. This article is part of the theme issue 'Dust in the Solar System and beyond'.

Probing the Oxidation State of Ocean Worlds with SUDA: Fe (ii) and Fe (iii) in Ice Grains

Characterizing the geochemistry of Europa and Enceladus is a key step for astrobiology investigations looking for evidence of life in their subsurface oceans. Transition metals with several oxidation states, such as iron, may be tracers of the oxidation state of icy ocean moon interiors. Their detection, as well as the characterization of their oxidation states, on the moons’ (plume) ice grains would bring valuable new information about the geochemistry of both the subsurface oceans and surface processes. Impact ionization mass spectrometers such as the SUDA instrument on board Europa Clipper can analyze ice grains ejected from icy moons’ surfaces and detect ocean-derived salts therein. Here we record mass spectra analogs for SUDA using the Laser Induced Liquid Beam Ion Desorption technique for Fe2+ and Fe3+ salts (both sulfates and chlorides). We show that impact ionization mass spectrometers have the capability to detect and differentiate ferrous (Fe2+) from ferric (Fe3+) ions in both cation and anion modes owing to their tendency to form distinct ionic complexes with characteristic spectral features. Peaks bearing Fe3+, such as [Fe3+ (OH)2]+ and [Fe3+ (OH) a Cl b ]−, are particularly important to discriminate between the two oxidation states of iron in the sample. The recorded analog spectra may allow the characterization of the oxidation state of the oceans of Europa and Enceladus with implications for hydrothermal processes and potential metabolic pathways for life forms in their subsurface oceans.

Mass Spectrometric Fingerprints of Organic Compounds in NaCl-Rich Ice Grains from Europa and Enceladus

Europa and Enceladus, respective moons of Jupiter and Saturn, are prime targets in the exploration of potentially habitable extraterrestrial ocean worlds. Organic material could be incorporated from the ocean into ice grains ejected from the surface or in potential plumes and detected via spacecraft flybys with impact ionization mass spectrometers, such as the SUrface Dust Analyzer (SUDA) onboard Europa Clipper or the Cosmic Dust Analyzer (CDA) onboard the past Cassini mission. Ice grains ejected from both Europa and Enceladus are expected to contain sodium salts, specifically sodium chloride (NaCl), in varying concentrations. Consequently, it is important to understand its effects on the mass spectrometric signatures of organic material in salt-rich ice grains. Previous studies have only focused on the detection of biosignatures, such as amino acids, in salt-rich ice grains. We here perform analogue experiments using the Laser Induced Liquid Beam Ion Desorption (LILBID) technique to study how a wide variety of abiotic and potentially biotic organic molecules could be identified by SUDA-type instruments. We investigate their mass spectral characteristics and detectability at various typical NaCl concentrations expected for salt-rich ice grains and in both cation and anion modes. Results show that organics in salt-rich ice grains can still be detected because of the formation of molecular ions and sodiated and chlorinated species. However, high salt concentrations induce compound- and concentration-dependent suppression effects, depending on the chemical properties and functional groups of the analytes. Our results emphasize the need of both ion modes to detect a wide range of organics embedded in complex matrices and to discriminate between abiotic and potentially biotic species. This work complements a spectral reference library for Europa Clipper and other ocean world missions.

OLYMPIA-LILBID: A New Laboratory Setup to Calibrate Spaceborne Hypervelocity Ice Grain Detectors Using High-Resolution Mass Spectrometry

The coupling of an Orbitrap-based mass analyzer to the laser-induced liquid beam ion desorption (LILBID) technique has been investigated, with the aim to reproduce the mass spectra recorded by Cassini's Cosmic Dust Analyzer (CDA) in the vicinity of Saturn's icy moon Enceladus. LILBID setups are usually coupled with time-of-flight (TOF) mass analyzers, with a limited mass resolution (∼800 m/Δm). Thanks to the Orbitrap technology, we developed a unique analytical setup that is able to simulate hypervelocity ice grains' impact in the laboratory (at speeds in the range of 15-18 km/s) with an unprecedented high mass resolution of up to 150 000 m/Δm (at m/z 19 for a 500 ms signal duration). The results will be implemented in the LILBID database and will be useful for the calibration and future data interpretation of the Europa Clipper's SUrface Dust Analyzer (SUDA), which will characterize the habitability of Jupiter's icy moon Europa.

Complementary Mass Spectral Analysis of Isomeric O-bearing Organic Compounds and Fragmentation Differences through Analog Techniques for Spaceborne Mass Spectrometers

Mass spectrometers on board spacecraft typically use either impact ionization or electron ionization (EI) as ion sources. Understanding the similarities and differences in the spectral signatures and fragmentation patterns produced by different techniques in mass spectrometry could elucidate the composition of organic compounds. Here we present a comparison between the mass spectra obtained through laser-induced liquid beam ion desorption (LILBID; proven to simulate the impact ionization mass spectra of ice grains) and EI mass spectra of pairs of low-mass, isomeric aldehydes and ketones. Our comparison confirms that EI produces more fragmentation of carbonyl compounds, particularly aldehydes, than LILBID. We find protonated molecular ions [M+H]+ in LILBID but molecular ions [M]+ in EI spectra. From the evaluated species, LILBID generally produces oxygen-carrying fragment ions (e.g., [CHO]+ and [C2H3O]+) in the mass ranges 26–30 and 39–44 u, while in EI, most ions in these ranges correspond to hydrocarbon fragments. The LILBID spectra additionally show mostly protonated oxygen-bearing fragments [CH3O]+ and [C2H5O]+ at m/z 31 and 45, less commonly observed in EI spectra. We observe a decrease in the relative intensities of cation fragment mass lines between m/z 26 and 33 and an increase between m/z 39 and 45, with an increasing carbon number for ketones and aldehydes with LILBID and EI, respectively. Our study provides a basis for complementary compositional analysis to identify the structural properties of organic species in a space environment using different spaceborne mass spectrometers (e.g., SUrface Dust Analyzer and MAss Spectrometer for Planetary EXploration) on board NASA’s future Europa Clipper space mission.

Developing a Laser Induced Liquid Beam Ion Desorption Spectral Database as Reference for Spaceborne Mass Spectrometers

AbstractSpaceborne impact ionization mass spectrometers, such as the Cosmic Dust Analyzer on board the past Cassini spacecraft or the SUrface Dust Analyzer being built for NASA's upcoming Europa Clipper mission, are of crucial importance for the exploration of icy moons in the Solar System, such as Saturn's moon Enceladus or Jupiter's moon Europa. For the interpretation of data produced by these instruments, analogue experiments on Earth are essential. To date, thousands of laboratory mass spectra have been recorded with an analogue experiment for impact ionization mass spectrometers. Simulation of mass spectra of ice grains in space is achieved by a Laser Induced Liquid Beam Ion Desorption (LILBID) approach. The desorbed cations or anions are analyzed in a time‐of‐flight mass spectrometer. The amount of unstructured raw data is increasingly challenging to sort, process, interpret and compare with data from space. Thus far this has been achieved manually for individual mass spectra because no database containing the recorded reference spectra was available. Here we describe the development of a comprehensive, extendable database containing cation and anion mass spectra from the laboratory LILBID facility. The database is based on a Relational Database Management System with a web server interface and enables filtering of the laboratory data using a wide range of parameters. The mass spectra can be compared not only with data from past and future space missions but also mass spectral data generated by other, terrestrial, techniques. The validated and approved subset of the database is available for general public (https://lilbid-db.planet.fu-berlin.de).

Analogue spectra for impact ionization mass spectra of water ice grains obtained at different impact speeds in space.

Detecting ice grains with impact ionization mass spectrometers in space provides information about the compositions of ice grains and their sources. Depending on the impact speeds of the ice grains onto the metal target of a mass spectrometer, ionization conditions can vary substantially, resulting in changes to the appearance of the resulting mass spectra. Here we accurately reproduce mass spectra of water ice grains, recorded with the Cosmic Dust Analyzer (CDA) on board the Cassini spacecraft at typical impact speeds ranging between 4 km/s to 21 km/s, with a laboratory analogue experiment. In this Laser-Induced Liquid Beam Ion Desorption (LILBID) approach, a μm-sized liquid water beam is irradiated with a pulsed infrared laser, desorbing charged analyte and solvent aggregates and isolated ions, which are subsequently analyzed in a time-of-flight (TOF) mass spectrometer. We show that our analogue experiment can reproduce impact ionization mass spectra of ice grains obtained over a wide range of impact speeds, aiding the quantitative analyses of mass spectra from space. Spectra libraries created with the LILBID experiment will be a vital tool for inferring the composition of ice grains from mass spectra recorded by both past and future impact ionization mass spectrometers (e.g. the SUrface Dust Analyzer (SUDA) onboard NASA's Europa Clipper Mission or detectors on a future Enceladus Mission).

Liquid Beam Desorption Mass Spectrometry for the Investigation of Continuous Flow Reactions in Microfluidic Chips.

In this work, we present the combination of microfluidic chips and mass spectrometry employing laser-induced liquid beam ionization/desorption. The developed system was evaluated with respect to stable beam generation and laser parameters as well as solvent compatibility. The device was exemplarily applied to study a vinylogous Mannich reaction performed in continuous flow on chip. Fast processes can be observed with this technique which in the future could be beneficial for studying intermediates or contribute to the elucidation of reaction mechanisms.

Biochemical Analysis of the Complex between the Tetrameric Export Adapter Protein Rec of HERV-K/HML-2 and the Responsive RNA Element RcRE pck30

The RNA export adaptor protein Rec, encoded for by the human endogenous retrovirus HERV-K/HML-2 elements, binds to the Rec responsive element (RcRE) located in the 3' untranslated region of HERV-K/HML-2 transcripts. Binding allows the nucleocytoplasmic export of unspliced viral RNA, thereby overcoming host restriction. Chemical probing of the secondary structure of the RcRE corroborated the theory that the RcRE forms a complex folded structure with seven stem-loop regions. Laser-induced liquid beam ion desorption mass spectrometry revealed that Rec forms stable tetramers, which are further stabilized upon RNA binding. The RNA protein complex consists of three Rec tetramers, which bind to multiple sites on the RcRE-preferentially to purine-rich motifs-which represent several low-affinity binding sites. Mutated RcREs, with one to three purine-rich motifs deleted, were still bound and exported by Rec, indicating that the complex folded structure of the RcRE is important for Rec binding. This suggests a binding model where up to three Rec tetramers bind to the complex folded structure of the RcRE and the binding seems to be tightened by recognition of the purine-rich motifs.

The Influence of Densely Organized Maltose Shells on the Biological Properties of Poly(propylene imine) Dendrimers: New Effects Dependent on Hydrogen Bonding

Maltose-modified poly(propylene imine) (PPI) dendrimers were synthesized by reductive amination of unmodified second- to fifth-generation PPI dendrimers in the presence of excess maltose. The dendrimers were characterized by using (1)H NMR, (13)C NMR, and IR spectroscopies; laser-induced liquid beam ionization/desorption mass spectrometry; dynamic light scattering analyses; and polyelectrolyte titration. Their scaffolds have enhanced molecular rigidity and their outer spheres, at which two maltose units are bonded to the former primary amino groups on the surface, have hydrogen-bond-forming properties. Furthermore, the structural features reveal the presence of a dense shell. Experiments involving encapsulation (1-anilinonaphthalene-8-sulfonic acid) and biological properties (hemolysis and interactions with human serum albumin (HSA) and prion peptide 185-208) were performed to compare the modified with the unmodified dendrimers. These experiments gave the following results: 1) The modified dendrimers entrapped a low-molecular-weight fluorescent dye by means of a dendritic box effect, in contrast to the interfacial uptake characteristic of the unmodified PPI dendrimers. 2) Both low- and high-generation dendrimers containing maltose units showed markedly reduced toxicity. 3) The desirable features of bio-interactions depended on the generation of the dendrimer; they were retained after maltose substitution, but were now mainly governed by nonspecific hydrogen-bonding interactions involving the maltose units. The modified dendrimers interacted with HSA as strongly as the parent compounds and appeared to have potential use as antiprion agents. These improvements will initiate the development of the next platform of glycodendrimers in which apparently contrary properties can be combined, and this will enable, for example, therapeutic products such as more efficient and less toxic antiamyloid agents to be synthesized.

An intermediate step in the evolution of ATPases – a hybrid F0–V0 rotor in a bacterial Na+ F1F0 ATP synthase

The Na(+) F(1)F(0) ATP synthase operon of the anaerobic, acetogenic bacterium Acetobacterium woodii is unique because it encodes two types of c subunits, two identical 8 kDa bacterial F(0)-like c subunits (c(2) and c(3)), with two transmembrane helices, and a 18 kDa eukaryal V(0)-like (c(1)) c subunit, with four transmembrane helices but only one binding site. To determine whether both types of rotor subunits are present in the same c ring, we have isolated and studied the composition of the c ring. High-resolution atomic force microscopy of 2D crystals revealed 11 domains, each corresponding to two transmembrane helices. A projection map derived from electron micrographs, calculated to 5 A resolution, revealed that each c ring contains two concentric, slightly staggered, packed rings, each composed of 11 densities, representing 22 transmembrane helices. The inner and outer diameters of the rings, measured at the density borders, are approximately 17 and 50 A. Mass determination by laser-induced liquid beam ion desorption provided evidence that the c rings contain both types of c subunits. The stoichiometry for c(2)/c(3) : c(1) was 9 : 1. Furthermore, this stoichiometry was independent of the carbon source of the growth medium. These analyses clearly demonstrate, for the first time, an F(0)-V(0) hybrid motor in an ATP synthase.

How to make big molecules fly out of liquid water: applications, features and physics of laser assisted liquid phase dispersion mass spectrometry

Applications, features, and mechanistic details of laser assisted liquid phase dispersion mass spectrometry are highlighted and discussed. It has been used in the past to directly isolate charged molecular aggregates from the liquid phase and to determine their molecular weight employing sensitive time-of-flight mass spectrometry. The liquid matrix in this MALDI (matrix assisted laser desorption and ionization) type approach consists of a 10 microm diameter free liquid filament in vacuum (or a free droplet) which is excited with a focused infrared laser pulse tuned to match the absorption frequency of the OH-stretch vibration of bulk water near 2.8 microm. Due to these features we will refer to the approach as free liquid matrix assisted laser dispersion of ions or ionic aggregates (IR-FL-MALDI), although also LILBID ("laser induced liquid beam (bead) desorption and ionization") has been proposed early as a descriptive acronym for the technique and may be used alternatively. Low-charge-state macromolecular adducts are isolated in the gas phase from solution via a yet poorly characterized mechanism which sensitively depends upon the laser intensity and wavelength, and after the gentle liquid-to-vacuum transfer the aggregates are analyzed via time-of-flight (TOF) mass spectrometry (MS). Possible mechanisms for the isolation and charging of biomolecules directly from liquid solution are discussed in the present contribution. Recent technical advances such as minimizing the sample consumption, strategies for high throughput mass spectrometry, and coupling of liquid beam MS with HPLC will be highlighted as well. An interesting feature of IR-FL-MALDI is what we call the linear response, i.e., a surprising linearity of the gas phase mass signal on the solution concentration over many orders of magnitude for a large number of biomolecular systems as well as ions. Due to these features the approach may be regarded as a true solution probing spectroscopy, which enables elegant biokinetic studies. Several experiments in which time resolved IR-FL-MALDI-MS has recently been employed successfully are given. A particular highlight is the possibility to quantitatively detect oxidation states in solution, which clearly distinguishes the present approach from other established MS source concepts. Due to the good matrix tolerance also proteins in complex mixtures can be monitored quantitatively.

Analytical laser induced liquid beam desorption mass spectrometry of protonated amino acids and their non-covalently bound aggregates

We have used analytical laser induced liquid beam desorption in combination with high resolution mass spectrometry ( m/Δm≥ 1000) for the study of protonated amino acids (ornithine, citrulline, lysine, arginine) and their non-covalently bound complexes in the gas phase desorbed from water solutions. We report studies in which the desorption mechanism has been investigated. The results imply that biomolecule desorption at our conditions is a single step process involving laser heating of the solvent above its supercritical temperature, a rapid expansion, ion recombination and finally isolation and desorption of only a small fraction of preformed ions and charged aggregates. In addition, we report an investigation of the aqueous solution concentration and pH-dependence of the laser induced desorption of protonated species (monomers and dimers). The experimental findings suggest that the desorption process depends critically upon the proton affinity of the molecules, the concentration of other ions, and of the pH value of the solution. Therefore the ion concentrations measured in the gas phase very likely reflect solution properties (equilibrium concentrations). Arginine self-assembles large non-covalent singly protonated multimers (n = 1...8) when sampled by IR laser induced water beam desorption mass spectrometry. The structures of these aggregates may resemble those of the solid state and may be preformed in solution prior to desorption. A desorption of mixtures of amino acids in water solution enabled us to study (mixed) protonated dimers, one of the various applications of the present technique. Reasons for preferred dimerization - leading to simple cases of molecular recognition - as well as less preferred binding is discussed in terms of the number of specific H-bonds that can be established in the clusters.

Studying noncovalent protein complexes in aqueous solution with laser desorption mass spectrometry

The study of noncovalent aggregation with mass spectrometry has been largely the domain of electrospray ionization mass spectrometry (ESI-MS). In contrast, matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) has been applied to this field to a much lesser extent. The main drawback of MALDI-MS is that the sample preparation requires a crystalline matrix. This disrupts the solution environment and often leads to dissociation of noncovalent complexes. A new laser desorption method, developed in our group, promises to circumvent this shortcoming. It is called laser induced liquid beam ionization/desorption mass spectrometry (LILBID-MS). The major advantage of this new method is the use of a liquid beam in vacuum for sample preparation and as target. The beam is directly injected into the mass spectrometer, using the solvent (mostly water) as the natural matrix substance, thus allowing for a softer probe preparation and desorption. In this article we present examples for the application of this new desorption method for detecting noncovalent aggregates of proteins in aqueous solutions. Using ribonuclease S, calmodulin/melittin, and bovine pancreatic trypsin inhibitor as model systems, evidence is given that LILBID-MS is capable of desorbing intact noncovalent complexes into the gas phase. Even water bound into cavities of a protein structure can be detected. In addition, it will be shown that solution parameters (e.g. pH, temperature) have a decisive influence on the mass spectra obtained, thus confirming earlier observations that the ions detected by LILBID-MS are formed in the solution phase and are not gas phase artifacts produced by the detection process.

Detection of intact hemoglobin from aqueous solution with laser desorption mass spectrometry.

Laser induced liquid beam ionization/desorption mass spectrometry (LILBID-MS) is a new desorption method recently developed in our laboratory. This method allows ions to be desorbed directly from the liquid phase into the high-vacuum region of a mass spectrometer. This method has now been applied to the detection of noncovalent protein-protein complexes. The example given in this paper is the quartenary complex of human hemoglobin. For the first time, the intact hemoglobin could be detected by laser desorption mass spectrometry. Furthermore, evidence for the specificity of the complex is given.

Ionic clathrates from aqueous solutions detected with laser induced liquid beam ionization/desorption mass spectrometry

Clathratelike structures of the alkali metal ions M + = Li +, Na +, K + Cs +, and ammonium with water molecules have been investigated with laser induced liquid beam ionization/desorption (LILBID) mass spectrometry. The LILBID process implies the desorption of ions from a thin jet of supercooled water in high vacuum by means of an IR laser pulse. Magic numbered water clusters are observed in the cation mass spectra of K + and Cs + halides, but not for Li + and Na +. Predominant cluster sizes for K + (H 2O) n are n = 16, 20, 25, 27, and for Cs +(H 2O) n , n = 18, 20, 22, 24, 27, 29, with the highest signal intensity for n = 20. Water clusters of this size correspond to deformed dodecahedral cage structures (clathrates) with a cation in the cavity, which are known to exist in the gas phase and in the solid state. The possible occurrence of clathratelike clusters in the liquid phase is discussed in the context of the physical chemistry of electrolyte solutions and the LILBID experiment.

Laser desorption mass spectrometry on liquid beams

Laser-induced liquid beam ionization/desorption mass spectrometry (LILBID-MS) is a new and versatile laser desorption method that has recently been developed in our group. With this technique it is possible to desorb pre-formed ions directly from the liquid phase and to analyze them in a time-of-flight mass spectrometer. To achieve this, a microscopic liquid beam is injected into a high vac uum chamber and irradiated with pulses of an infrared laser beam. The ions set free are then orthogonally accelerated into the mass analyzer. Up to now, this method has only been able to analyze alcoholic solutions using a CO 2 desorption laser. In this paper we describe the successful application of this method to aqueous solutions by using an Nd:YAG pumped LiNbO3 optical parametric oscillator (OPO) which is tuned to the wavelength of bulk water. First results obtained with this new laser system are described in this report.

Examination of Condensation Products of Group 4 Alkoxides with Laser-Induced Liquid Beam Ionization/Desorption Mass Spectrometry

Oligomer formation from partially hydrolyzed Group 4 alkoxides has been monitored in solution for the first time with a new mass spectrometric technique called laser-induced liquid beam ionization/desorption (LILBID) (shown schematically). The mass spectra show continuous series of clusters from monomers up to oligomers with a mass of several thousand, and distinctive maxima in the distribution indicate preferential cluster sizes. Condensation reactions set in when at least three equivalents of water are added to the methanolic alkoxide solutions, and accordingly a shift to higher m/z is observed in the mass spectra. The oligomers thus formed are supposed to be precursors in the process of crystal growth.

Laser desorption mass spectrometry on thin liquid jets

A recently developed soft desorption method for mass spectrometry is presented, which is called Laser Induced Liquid Beam Ionization/Desorption (LILBID). Analyte ions are desorbed from a thin jet of analyte solution directly into vacuum by means of an IR laser pulse, which has been tuned to a vibrational resonance of the solvent. A comparative experiment with ammonium chloride and aniline hydrochloride shows that ion formation via proton transfer takes place in the solution. Thermally unstable compounds, as well as supra- and biomolecular complexes, can be detected intact and mass analyzed in a reflectron time-of-flight (Re-TOF) mass spectrometer. During the desorption process, noncovalent interactions and some solvation characteristics are preserved. Three examples for the capacity of LILBID are given in this short overview: (a) ion-solvent interactions with the formation of a clathrate structure Cs+(H2O)20, (b) host-guest interactions with the K+ selectivity of valinomycin, and (c) noncovalent interactions with the dimerization of gramicidin.

Copper-binding abilities of the tripeptide diglycylhistidine studied by laser-induced liquid beam ionization/desorption mass spectrometry in aqueous solution

Laser-induced liquid beam ionization/desorption (LILBID) mass spectrometry is capable of desorbing ions directly from a liquid beam into the gas phase by means of an IR laser pulse tuned to an absorption band of the solvent used. Up to now, it has been restricted to the use of alcoholic solutions owing to the limitations of the desorbing IR laser system. This paper presents the first results using an Nd:YAG–optical parametric oscillator laser system that enables us to study aqueous solutions. Using this laser system, studies on the Cu(II)-binding abilities of the tripeptide diglycylhistidine are presented. Complex formation with various concentrations of Cu(II) ions was observed in water at basic pH. The use of buffer solutions did not affect the signal intensity of the peptide-related peaks. In acidic solutions, the complex partially dissociates. The free tripeptide and the released Cu(II) can be observed in the mass spectrum. The results obtained with this method were compared with measurements undertaken with electrospray ionization mass spectrometry. © 1997 John Wiley & Sons, Ltd.