Artificial Neural Networks Coupled with MALDI-TOF MS Serum Fingerprinting To Classify and Diagnose Pathological Pain Subtypes in Preclinical Models.

Pathological pain subtypes can be classified as either neuropathic pain, caused by a somatosensory nervous system lesion or disease, or nociplastic pain, which develops without evidence of somatosensory system damage. Since there is no gold standard for the diagnosis of pathological pain subtypes, the proper classification of individual patients is currently an unmet challenge for clinicians. While the determination of specific biomarkers for each condition by current biochemical techniques is a complex task, the use of multimolecular techniques, such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), combined with artificial intelligence allows specific fingerprints for pathological pain-subtypes to be obtained, which may be useful for diagnosis. We analyzed whether the information provided by the mass spectra of serum samples of four experimental models of neuropathic and nociplastic pain combined with their functional pain outcomes could enable pathological pain subtype classification by artificial neural networks. As a result, a simple and innovative clinical decision support method has been developed that combines MALDI-TOF MS serum spectra and pain evaluation with its subsequent data analysis by artificial neural networks and allows the identification and classification of pathological pain subtypes in experimental models with a high level of specificity.

Detection of SARS-CoV-2 Infection in Human Nasopharyngeal Samples by Combining MALDI-TOF MS and Artificial Intelligence.

The high infectivity of SARS-CoV-2 makes it essential to develop a rapid and accurate diagnostic test so that carriers can be isolated at an early stage. Viral RNA in nasopharyngeal samples by RT-PCR is currently considered the reference method although it is not recognized as a strong gold standard due to certain drawbacks. Here we develop a methodology combining the analysis of from human nasopharyngeal (NP) samples by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with the use of machine learning (ML). A total of 236 NP samples collected in two different viral transport media were analyzed with minimal sample preparation and the subsequent mass spectra data was used to build different ML models with two different techniques. The best model showed high performance in terms of accuracy, sensitivity and specificity, in all cases reaching values higher than 90%. Our results suggest that the analysis of NP samples by MALDI-TOF MS and ML is a simple, safe, fast and economic diagnostic test for COVID-19.

Laser ablation synthesis of metal-doped gold clusters from composites of gold nanoparticles with metal organic frameworks.

Metal-doped gold clusters, mainly cages, are receiving rapidly increasing attention due to their tunable catalytic properties. Their synthesis is mostly based on complex procedures, including several steps. In this work, via adsorption of gold nanoparticles (AuNPs) from aqueous solution to MOF (metal organic frameworks) of M = Co, Cu, Ni, and Zn with various linkers the {AuNPs, MOF} composites were prepared. These composites were used for laser ablation synthesis (LAS) using a common mass spectrometer. Several series of positively and negatively charged AumMn+/- clusters were observed in mass spectra and their stoichiometry (m = 1-35, n = 1-5) was determined. For each dopant (Co, Cu, Ni, and Zn) ~ 50 different clusters were identified in positive, as well as in negative ion modes. About 100 of these clusters were proposed to be endohedral metal-doped gold cages (for m > 12). The developed approach represents a simple procedure for generating metal-doped gold clusters or endohedral metal-doped gold cages materials with potential applications in medicine and/or electronics.

Rapid discrimination of multiple myeloma patients by artificial neural networks coupled with mass spectrometry of peripheral blood plasma.

Multiple myeloma (MM) is a highly heterogeneous disease of malignant plasma cells. Diagnosis and monitoring of MM patients is based on bone marrow biopsies and detection of abnormal immunoglobulin in serum and/or urine. However, biopsies have a single-site bias; thus, new diagnostic tests and early detection strategies are needed. Matrix-Assisted Laser Desorption/Ionization Time-of Flight Mass Spectrometry (MALDI-TOF MS) is a powerful method that found its applications in clinical diagnostics. Artificial intelligence approaches, such as Artificial Neural Networks (ANNs), can handle non-linear data and provide prediction and classification of variables in multidimensional datasets. In this study, we used MALDI-TOF MS to acquire low mass profiles of peripheral blood plasma obtained from MM patients and healthy donors. Informative patterns in mass spectra served as inputs for ANN that specifically predicted MM samples with high sensitivity (100%), specificity (95%) and accuracy (98%). Thus, mass spectrometry coupled with ANN can provide a minimally invasive approach for MM diagnostics.

Laser ablation synthesis of arsenic-phosphide Asm Pn clusters from As-P mixtures. Laser desorption ionisation with quadrupole ion trap time-of-flight mass spectrometry: The mass spectrometer as a synthesizer.

RATIONALE: Only a few arsenic phosphides are known. A high potential for the generation of new compounds is offered by Laser Ablation Synthesis (LAS) and when Laser Desorption Ionization (LDI) is coupled with simultaneous Time-Of-Flight Mass Spectrometry (TOFMS), immediate identification of the clusters can be achieved. METHODS: LAS was used for the generation of arsenic phosphides via laser ablation of phosphorus-arsenic mixtures while quadrupole ion trap time-of-flight mass spectrometry (QIT-TOFMS) was used to acquire the mass spectra. RESULTS: Many new Asm Pn± clusters (479 binary and 369 mono-elemental) not yet described in the literature were generated in the gas phase and their stoichiometry determined. The likely structures for some of the observed clusters arbitrary selected (20) were computed by density functional theory (DFT) optimization. CONCLUSIONS: LAS is an advantageous approach for the generation of new Asm Pn clusters, while mass spectrometry was found to be an efficient technique for the determination of cluster stoichiometry. The results achieved might inspire the synthesis of new materials.

Intact Cell Mass Spectrometry as a Quality Control Tool for Revealing Minute Phenotypic Changes of Cultured Human Embryonic Stem Cells.

The stability of in vitro cell cultures is an important issue for any clinical, bio-industrial, or pharmacological use. Embryonic stem cells are pluripotent; consequently, they possess the ability to differentiate into all three germ layers and are inherently prone to respond to differentiation stimuli. However, long-term culture inevitably yields clones that are best adapted to the culture conditions, passaging regimes, or differentiation sensitivity. This cellular plasticity is a major obstacle in the development of bio-industrial or clinical-grade cultures. At present, the quality control of cell cultures is limited by the lack of reliable (epi)genetic or molecular markers or by the focus on a particular type of instability such as karyotype abnormalities or adverse phenotypic traits. Therefore, there is an ongoing need for robust, feasible, and sensitive methods of determining or confirming cell status and for revealing potential divergences from the optimal state. We modeled both intrinsic and extrinsic changes in human embryonic stem cell (hESC) states using different experimental strategies and addressed the changes in cell status by intact cell mass spectrometry fingerprinting. The analysis of spectral fingerprints by methods routinely used in analytical chemistry clearly distinguished the morphologically and biochemically similar populations of hESCs and provided a biomarker-independent tool for the quality control of cell culture. Stem Cells Translational Medicine 2018;7:109-114.

Clusters of Monoisotopic Elements for Calibration in (TOF) Mass Spectrometry.

Precise calibration in TOF MS requires suitable and reliable standards, which are not always available for high masses. We evaluated inorganic clusters of the monoisotopic elements gold and phosphorus (Au n+/Au n- and P n+/P n-) as an alternative to peptides or proteins for the external and internal calibration of mass spectra in various experimental and instrumental scenarios. Monoisotopic gold or phosphorus clusters can be easily generated in situ from suitable precursors by laser desorption/ionization (LDI) or matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Their use offers numerous advantages, including simplicity of preparation, biological inertness, and exact mass determination even at lower mass resolution. We used citrate-stabilized gold nanoparticles to generate gold calibration clusters, and red phosphorus powder to generate phosphorus clusters. Both elements can be added to samples to perform internal calibration up to mass-to-charge (m/z) 10-15,000 without significantly interfering with the analyte. We demonstrated the use of the gold and phosphorous clusters in the MS analysis of complex biological samples, including microbial standards and total extracts of mouse embryonic fibroblasts. We believe that clusters of monoisotopic elements could be used as generally applicable calibrants for complex biological samples. Graphical Abstract ᅟ.

Laser Ablation Synthesis of Gold Selenides by using a Mass Spectrometer as a Synthesizer: Laser Desorption Ionization Time-of-Flight Mass Spectrometry.

Methods for the rapid construction of new chemical motifs have the potential to accelerate the development of nanoscience. The synthesis of new chemical entities by laser ablation has been systematically demonstrated by using mixtures of gold and selenium. The compounds generated are detected by time-of-flight mass spectrometry and, for selected compounds, the structure is investigated by using density functional theory optimization. In total, 67 new gold selenide clusters have been synthesized, demonstrating an unsuspected richness in gold chemistry. Chemical species generated in the gas phase might inspire new routes for the synthesis of novel compounds in the solid state.

Laser desorption time-of-flight mass spectrometry of atomic switch memory Ge2Sb2Te5 bulk materials and its thin films.

RATIONALE: Although the structure of atomic switch Ge2Sb2Te5 (GST) thin films is well established, the composition of the clusters formed in the plasma plume during pulsed-laser deposition (PLD) is not known. Laser Desorption Ionization Time-of-Flight Mass Spectrometry (LDI-TOF MS) is an effective method for the generation and study of clusters formed by laser ablation of various solids and thus for determining their structural fragments. METHODS: LDI of bulk or PLD-deposited GST thin layers and of various precursors (Ge, Sb, Te, and Ge-Te or Sb-Te mixtures) using a nitrogen laser (337 nm) was applied while the mass spectra were recorded in positive and negative ion modes using a TOF mass spectrometer equipped with a reflectron while the stoichiometry of the clusters formed was determined via isotopic envelope analysis. RESULTS: The singly negatively or positively charged clusters identified from the LDI of GST were Ge, Ge2, GeTe, Ge2Te, Ten (n = 1-3), GeTe2, Ge2Te2, GeTe3, SbTe2, Sb2Te, GeSbTe2, Sb3Te and the low abundance ternary GeSbTe3, while the LDI of germanium telluride yielded Gem Ten (+) clusters (m = 1-3, n = 1-3). Several minor Ge-H clusters were also observed for pure germanium and for germanium telluride. Sbn clusters (n = 1-3) and the formation of binary TeSb, TeSb2 and TeSb3 clusters were detected when Sb2Te3 was examined. CONCLUSIONS: This is the first report that elucidates the stoichiometry of Gem Sbn Tep clusters formed in plasma when bulk or nano-layers of GST material are ablated. The clusters were found to be fragments of the original structure. The results might facilitate the development of PLD technology for this memory phase-change material.

Laser ablation synthesis of new gold arsenides using nano-gold and arsenic as precursors. Laser desorption ionisation time-of-flight mass spectrometry and spectrophotometry.

RATIONALE: Currently, a limited number of gold arsenides have been described, some of which have important industrial applications, Laser ablation synthesis (LAS) has been employed in an attempt to generate some novel gold arsenide compounds. METHODS: LAS of gold arsenides was performed using nano-gold (NG) and arsenic as precursors. The clusters formed during laser desorption ionisation (LDI) were analysed by mass spectrometry using a quadrupole ion trap and reflectron time-of-flight analyser to determine the stoichiometry. UV/VIS spectrophotometry was used to follow possible hydrothermal synthesis of gold arsenides. RESULTS: LAS of NG yielded singly charged gold clusters Aum (+(-)) (m = 1-35). LAS of bulk arsenic and nano-arsenic produced Asn (+(-)) clusters with n = 2-10 and n = 2-20, respectively. Laser ablation of Au-As nano-composites or NG-As mixtures generated Aum (+(-)) (m = 1-12), Asn (+(-)) (n = 3-4), and several series of Aum Asn (+(-)) (m = 1-60, n = 1-18) clusters. Over 450 species of gold arsenide clusters and 212 mixed chlorinated Aum Asn Clx clusters were detected and their stoichiometry determined. CONCLUSIONS: Many new gold arsenides were synthesised via LAS for the first time with Au-As composites and NG-As mixtures of different Au:As ratios using mass spectrometry to determine cluster stoichiometry. The resolved stoichiometry of Aum Asn clusters determined in this study could accelerate the development of advanced Au-As nano-materials.

Laser ablation synthesis of new gold carbides. From gold-diamond nano-composite as a precursor to gold-doped diamonds. Time-of-flight mass spectrometric study.

RATIONALE: Gold carbides can be produced via laser ablation synthesis (LAS) from mixtures of nano-gold (NG) and various carbonaceous materials. The nano-composite of nano-gold (NG) and nano-diamond (ND) might represent a promising precursor for the generation of new gold carbides. METHODS: Time-of-flight mass spectrometry (TOF MS), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) were used. The stoichiometry of clusters was determined via modelling of the isotopic patterns and MS(n) analysis. RESULTS: A simple procedure for the preparation of ND-NG nano-composite was developed using NG and ND. The formation of AuCn(+) (n = 1-11, 18), Au2Cn(+) (n = 1-16) and Au3Cn(+) (n = 1-10) clusters during LAS of the nano-composite was proved. Structures of gold carbides are proposed and discussed. Diamonds-containing AumCn(+) (m = 1-3, n = 10, 14, 18, 22) clusters might be not carbides but endohedral supramolecular complexes Aum@Cn(+) i.e., 'gold-doped' diamonds. CONCLUSIONS: TOF MS was shown to be a useful technique for following the formation of gold carbides in the gas phase. Clusters and 'gold-doped' diamonds generated might inspire synthesis of new Au-C materials with hardly predictable, unusual properties.

Laser ablation synthesis of new gold tellurides using tellurium and nanogold as precursors. Laser desorption ionisation time-of-flight mass spectrometry.

RATIONALE: Only a few gold tellurides are known. However, Laser Ablation Synthesis (LAS) using Laser Desorption Ionisation (LDI) time-of-flight mass spectrometry (TOF MS) has high potential for the generation of new compounds. METHODS: LDI of nanogold-Te conjugate using a nitrogen laser 337 nm was applied while the mass spectra were recorded in positive and negative ion modes using a quadrupole ion trap-TOF mass spectrometer equipped with a reflectron. Diffuse coplanar surface barrier discharge was applied for the plasma treatment of glass and silicon surfaces. RESULTS: A form of nanogold-Te conjugate was prepared and found suitable for LAS of gold tellurides. Several new Au(m)Te(n) (m = 1-11; n = 1-4) clusters were identified. An excess of nanogold and chloride or an excess of auric acid caused the formation of mixed Au(m)Te(n)Cl(x) clusters. The nanogold-Te conjugate can be deposited from an aqueous suspension onto glass while the deposition is strongly enhanced if the surface is modified by plasma. CONCLUSIONS: LDI of nanogold-Te conjugate is a suitable procedure for the generation of new gold telluride clusters. Treatment of borosilicate glass with a diffuse coplanar surface barrier discharge strongly enhances the deposition of gold tellurides on glass while limited adsorption on a silicon surface was observed.

Laser ablation synthesis of new gold phosphides using red phosphorus and nanogold as precursors. Laser desorption ionisation time-of-flight mass spectrometry.

Gold phosphides show unique optical or semiconductor properties and there are extensive high technology applications, e.g. in laser diodes, etc. In spite of the various AuP structures known, the search for new materials is wide. Laser ablation synthesis is a promising screening and synthetic method. Generation of gold phosphides via laser ablation of red phosphorus and nanogold mixtures was studied using laser desorption ionisation time-of-flight mass spectrometry (LDI TOFMS). Gold clusters Au(m)(+) (m = 1 to ~35) were observed with a difference of one gold atom and their intensities were in decreasing order with respect to m. For P(n)(+) (n = 2 to ~111) clusters, the intensities of odd-numbered phosphorus clusters are much higher than those for even-numbered phosphorus clusters. During ablation of P-nanogold mixtures, clusters Au(m)(+) (m = 1-12), P(n)(+) (n = 2-7, 9, 11, 13-33, 35-95 (odd numbers)), AuP(n)(+) (n = 1, 2-88 (even numbers)), Au(2)P(n)(+) (n = 1-7, 14-16, 21-51 (odd numbers)), Au(3)P(n)(+) (n = 1-6, 8, 9, 14), Au(4)P(n)(+) (n = 1-9, 14-16), Au(5)P(n)(+) (n = 1-6, 14, 16), Au(6)P(n)(+) (n = 1-6), Au(7)P(n)(+) (n = 1-7), Au(8)P(n)(+) (n = 1-6, 8), Au(9)P(n)(+) (n = 1-10), Au(10)P(n)(+) (n = 1-8, 15), Au(11)P(n)(+) (n = 1-6), and Au(12)P(n)(+) (n = 1, 2, 4) were detected in positive ion mode. In negative ion mode, Au(m)(-) (m = 1-5), P(n)(-) (n = 2, 3, 5-11, 13-19, 21-35, 39, 41, 47, 49, 55 (odd numbers)), AuP(n)(-) (n = 4-6, 8-26, 30-36 (even numbers), 48), Au(2)P(n)(-) (n = 2-5, 8, 11, 13, 15, 17), A(3) P(n)(-) (n = 6-11, 32), Au(4)P(n)(-) (n = 1, 2, 4, 6, 10), Au(6)P(5)(-), and Au(7)P(8)(-) clusters were observed. In both modes, phosphorus-rich Au(m)P(n) clusters prevailed. The first experimental evidence for formation of AuP(60) and gold-covered phosphorus Au(12)P(n) (n = 1, 2, 4) clusters is given. The new gold phosphides generated might inspire synthesis of new Au-P materials with specific properties.

Cluster analysis and artificial neural networks multivariate classification of onion varieties.

Eight cultivars of different colored onions (white, golden, and red) were evaluated for fresh bulbs cultivated and grown under the same environmental and agronomical conditions. Cluster analysis and principal component analysis, based on different flavonoids, total phenols, and pungency, data showed that the onions were not clustered according to variety (genetic similarity degree), whereas the color was the variable with the highest influence, ranging between 50 and 70%. Artificial neural networks were applied to study the possibility of discriminating among onion varieties. Characterization of the onion according to variety and procedence of the seeds was around 95-100%. Samples belonging to the Carrizal Alto procedence had an incorrect classification for 25% of the data.

Mass spectrometry and UV-VIS spectrophotometry of ruthenium(II) [RuClCp(mPTA)2](OSO2CF3)2 complex in solution.

Ruthenium(II) complexes are of great interest as a new class of cancerostatics with advantages over classical platinum compounds including lower toxicity. The stability of the [RuClCp(mPTA)2](OSO2CF3)2 complex (I) (Cp cyclopentadienyl, mPTA N-methyl 1,3,5-triaza-7-phosphaadamantane) in aqueous solution was studied using spectrophotometry, matrix-assisted laser desorption/ionization (MALDI) and laser desorption/ionization (LDI) time-of-flight (TOF) mass spectrometry (MS). Spectrophotometry proves that at least three different reactions take place in water. Dissolution of I leads to fast coordination of water molecules to the Ru(II) cation and then slow hydrolysis and ligand exchange of chloride and mPTA with water, hydroxide or with trifluoromethane sulfonate itself. Via MALDI and LDI of the hydrolyzed solutions the formation of singly positively charged ions of general formula RuCl(p)(Cp)(q)(mPTA)(r)(H2O)(s)(OH)(t) (p = 0-1, q = 0-1, r = 0-2, s = 0-5, t = 0-2) and of some fragment ions was shown. The stoichiometry was determined by analyzing the isotopic envelopes and computer modelling. The [RuClCp(mPTA)2](OSO2CF3)2 complex can be stabilized in dilute hydrochloric acid or in neutral 0.15 M isotonic sodium chloride solution.

Laser ablation of AgSbS(2) and cluster analysis by time-of-flight mass spectrometry.

Thin films of AgSbS(2) are important for phase-change memory applications. This solid is deposited by various techniques, such as metal organic chemical vapour deposition or laser ablation deposition, and the structure of AgSbS(2)(s), as either amorphous or crystalline, is already well characterized. The pulsed laser ablation deposition (PLD) of solid AgSbS(2) is also used as a manufacturing process. However, the processes in plasma have not been well studied. We have studied the laser ablation of synthesized AgSbS(2)(s) using a nitrogen laser of 337 nm and the clusters formed in the laser plume were identified. The ablation leads to the formation of various single charged ternary Ag(p)Sb(q)S(r) clusters. Negatively charged AgSbS(4) (-), AgSb(2)S(3) (-), AgSb(2)S(4) (-), AgSb(2)S(5) (-) and positively charged ternary AgSbS(+), AgSb(2)S(+), AgSb(2)S(2) (+), AgSb(2)S(3) (+) clusters were identified. The formation of several singly charged Ag(+), Ag(2) (-), Ag(3) (-), Sb(3) (+), Sb(3) (-), S(8) (+) ions and binary Ag(p)S(r) clusters such as AgSb(2) (-), Ag(3)S(-), SbS(r) (-) (r = 1-5), Sb(2)S(-), Sb(2)S(2) (-), Sb(3)S(r) (-) (r = 1-4) and AgS(2) (+), SbS(+), SbS(2) (+), Sb(2)S(+), Sb(2)S(2) (+), Sb(3)S(r) (+) (r = 1-4), AgSb(2) (+) was also observed. The stoichiometry of the clusters was determined via isotopic envelope analysis and computer modeling. The relation of the composition of the clusters to the crystal structure of AgSbS(2) is discussed.

Mass spectrometry of nanodiamonds.

Detonation nanodiamonds (NDs) were studied by time-of-flight mass spectrometry (TOF MS). The formation of singly charged carbon clusters, C(n) (+), with groups of clusters at n = 1-35, n approximately 160-400 and clusters with n approximately 8000 was observed. On applying either high laser energy or ultrasound, the position and intensity of the maxima change and a new group of clusters at n approximately 70-80 is formed. High carbon clusters consist of an even number of carbons while the percentage of odd-numbered clusters is quite low (< or =5-10%). On increasing the laser energy, the maximum of ionization (at n approximately 200 carbons) is shifted towards the lower m/z values. It is suggested that this is mainly due to the disaggregation of the original NDs. However, the partial destruction of NDs is also possible. The carbon clusters (n approximately 2-35) are partially hydrogenated and the average value of the hydrogenation was 10-30%. Trace impurities in NDs like Li, B, Fe, and others were detected at high laser energy. Several matrices for ionizing NDs were examined and NDs themselves can also be used as a matrix for the ionization of various organic compounds. When NDs were used as a matrix for gold nanoparticles, the formation of various gold carbides Au(m)C(n) was detected and their stoichiometry was determined. It was demonstrated that TOF MS can be used advantageously to analyze NDs, characterize their size distribution, aggregation, presence of trace impurities and surface chemistry.

Characterization of humic substances of different origin by means of mass spectrometry and neural networks.

Mass spectrometry fingerprinting of humic acids extracted from different soils has been carried out using laser desorption/ionization mass spectrometry (LDI-TOF MS). LDI-TOF MS provides characteristic mass spectra fingerprints for the humic acids of different origin. The information given in the fingerprints was evaluated for natural grouping trends in the samples by neural networks computing tools, such as self-organizing feature map (SOFM). This approach is efficient for recognizing patterns in the humic acids samples independently of their characteristic variability; variability characterizing natural products such as humic substances. The use of multi-layer perceptron artificial neural networks gave a successful classification of the samples.

Laser desorption/ionization and laser ablation synthesis of new selenium oxide compounds from selenium(IV) dioxide.

Laser desorption/ionization (LDI) and/or laser ablation (LA) of selenium dioxide crystals or its mixtures with sodium peroxide were studied using a commercial matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometer. It was found that LDI and LA of selenium (IV) dioxide not only ionizes SeO(2), but also leads to the formation of several positively and negatively singly charged species: SeO(n) (+) (n = 0-2), Se(2) (+), SeO(n) (-) (n = 0-4), Se(2)O(n) (-) (n = 3-7), Se(3)O(n) (-) (n = 4-9), Se(4)O(n) (-) (n = 8-10). A rather high yield of selenium species in the positive ion mode, Se(m) (+) (m = 1-8) and Se(m)OH(+) (m = 3-7), was obtained by using the MALDI approach while the species detected in the negative ion mode, SeO(n) (-) (n = 0-4), Se(2)O(n) (-) (n = 3-7), Se(3)O(n) (-) (n = 4-9), and Se(4)O(n) (-) (n = 9, 10), were the same as those observed during LDI/LA of selenium dioxide. The addition of sodium peroxide to selenium dioxide with the aim of enhancing its oxidation and thus increasing the production of SeO(4) product resulted in extensive cationization of the species with sodium or potassium. The following positively and negatively charged species were identified: Se(+), Se(2) (+), Se(2)OH(+), Se(2)ONa(+), SeO(n) (-) (n = 0-3), and Se(2)O(n) (-) (n = 0, 1, 4). Also observed in mass spectra of such mixtures, various mixed sodium and/or potassium adducts with selenium oxide species, e.g. Se(2)O(4)K(2)Na(-), were identified. In all, 26 totally new species, Se(2)O(n) (-) (n = 3-6), Se(3)O(n) (-) (n = 4-9), Se(4)O(n) (-) (n = 8-10), Se(4)O(11)H(5) (-), Se(4)O(12)H(3) (-), Se(2)O(4)Na(-), Se(2)O(5)HNa(-), Se(2)O(5)HNa(2) (-), Se(3)O(6)K(2)Na(-), Se(3)O(6)K(2)Na(2) (-), Se(2)ONa(+), and Se(m)OH(+) (m = 3-7), were described for the first time. Also, for the first time, the formation of selenium(IV) diperoxide, O-O-Se-O-O or O(2)SeO(2), is described. The stoichiometries of the compounds generated were confirmed using isotopic pattern modeling.

Laser ablation synthesis of selenium superoxide anion SeO4- via selenium trioxide photolysis. Time-of-flight mass spectrometry and ab initio calculations.

Laser desorption/ionisation and laser ablation of solid selenium trioxide, as well as the gas-phase behaviour of selenium trioxide, were studied. Selenium trioxide undergoes photochemical decomposition and, from the mass spectra obtained by laser desorption/ionisation time-of-flight mass spectrometry (LDI-TOF-MS), the following species were identified: O-, O2-, O3-, SeO-, SeO2-, SeO3-, SeO4-, Se2O7-, Se3O11-, and Se4O14-. Formation of the selenium superoxide SeO4- anion is described in this work for the first time. In addition, low-abundance selenium species such as Se2O8H2-, Se3O11H-, and Se4O15H2- were also detected. The stoichiometry of all ions was confirmed via isotopic pattern modeling and/or post-source decay (PSD) analysis. Photolysis of selenium trioxide leads partly to ozone formation. It was found that the most likely mechanisms of selenium superoxide formation are oxidation of selenium trioxide with ozone and/or reactive oxygen radicals, or photolysis of selenium trioxide tetramer (SeO3)4. Therefore, ab initio calculations were performed to support the mass spectrometric evidence and to suggest probable geometries for selenium superoxide anion SeO4- and diselenium superoxide anion Se2O7-, as well as to provide insight into and/or predict possible formation pathways. It has been found that both cyclic and non-cyclic peroxide structures of SeO4- and Se2O7- ions are possible. In addition, the SeO4 structure was also calculated guided by thermodynamic considerations using Gaussian-2 methodology, and the inferred stability of the SeO4 neutral molecule was supported by ab initio calculations.