Lipids and Mass Spectrometry Application

During my PhD courses I focused attention on the applications of mass spectrometry in lipidomic studies. I applied mass spectrometry in several experimental models to try to observe differences in selected metabolites affected by a particular pathology. The first project performed in experimental model of impaird lipogenesis highlighted a cross talk between altered fatty acid synthesis and neuroactive steroid levels. The second project, mass spectrometry application allows to understand he effect of short-term diabetes on cholesterol metabolism. In the last project lipidomic pattern was investigated in experimental model of SCA38. Results obtained highlighted as elovl5 mutation affect phospholipids profile

A 1.3 cm line survey toward IRC +10216

IRC +10216 is the prototypical carbon star exhibiting an extended molecular circumstellar envelope. Its spectral properties are therefore the template for an entire class of objects. The main goal is to systematically study the $\lambda$ $\sim$1.3 cm spectral line characteristics of IRC +10216. We carried out a spectral line survey with the Effelsberg-100 m telescope toward IRC +10216. It covers the frequency range between 17.8 GHz and 26.3 GHz (K-band). In the circumstellar shell of IRC +10216, we find 78 spectral lines, among which 12 remain unidentified. The identified lines are assigned to 18 different molecules and radicals. A total of 23 lines from species known to exist in this envelope are detected for the first time outside the Solar System and there are additional 20 lines first detected in IRC +10216. The potential orgin of "U" lines is also discussed. Assuming local thermodynamic equilibrium (LTE), we then determine rotational temperatures and column densities of 17 detected molecules. Molecular abundances relative to H$_{2}$ are also estimated. A non-LTE analysis of NH$_{3}$ shows that the bulk of its emission arises from the inner envelope with a kinetic temperature of 70$\pm$20 K. Evidence for NH$_{3}$ emitting gas with higher kinetic temperature is also obtained, and potential abundance differences between various $^{13}$C-bearing isotopologues of HC$_{5}$N are evaluated. Overall, the isotopic $^{12}$C/$^{13}$C ratio is estimated to be 49$\pm$9. Finally, a comparison of detected molecules in the $\lambda$ $\sim$1.3 cm range with the dark cloud TMC-1 indicates that silicate-bearing molecules are more predominant in IRC +10216.Comment: 32 pages, 9 figures, Accepted by A&

A 1.3 cm Line Survey toward Orion KL

Orion KL has served as a benchmark for spectral line searches throughout the (sub)millimeter regime. The main goal is to systematically study spectral characteristics of Orion KL in the 1.3 cm band. We carried out a spectral line survey (17.9 GHz to 26.2 GHz) with the Effelsberg-100 m telescope towards Orion KL. We find 261 spectral lines, yielding an average line density of about 32 spectral features per GHz above 3$\sigma$. The identified lines include 164 radio recombination lines (RRLs) and 97 molecular lines. A total of 23 molecular transitions from species known to exist in Orion KL are detected for the first time in the interstellar medium. Non-metastable 15NH3 transitions are detected in Orion KL for the first time. Based on the velocity information of detected lines and the ALMA images, the spatial origins of molecular emission are constrained and discussed. A narrow feature is found in SO2 ($8_{1,7}-7_{2,6}$), possibly suggesting the presence of a maser line. Column densities and fractional abundances relative to H2 are estimated for 12 molecules with LTE methods. Rotational diagrams of non-metastable 14NH3 transitions with J=K+1 to J=K+4 yield different results; metastable 15NH3 is found to have a higher excitation temperature than non-metastable 15NH3, indicating that they may trace different regions. Elemental and isotopic abundance ratios are estimated: 12C/13C=63+-17, 14N/15N=100+-51, D/H=0.0083+-0.0045. The dispersion of the He/H ratios derived from H$\alpha$/He$\alpha$ pairs to H$\delta$/He$\delta$ pairs is very small, which is consistent with theoretical predictions that the departure coefficients bn factors for hydrogen and helium are nearly identical. Based on a non-LTE code neglecting excitation by the infrared radiation field and a likelihood analysis, we find that the denser regions have lower kinetic temperature, which favors an external heating of the Hot Core.Comment: 70 pages, 26 figures, 12 tables, accepted for publication in A&A. Figs. 1, 2, 8, 9 have been downsize

Proceedings of the Merck & Elsevier Young Chemists Symposium (MEYCS 2018)

Dear participants, welcome to the 18th edition of the Merck & Elsevier Young Chemists Symposium, formerly SAYCS and MYCS. This conference is an international scientific event organized by the Young Group of the Italian Chemical Society (SCI Giovani) with the financial support of Merck and Elsevier. This symposium is fully devoted to young researchers, such as MSc and PhD students, post-doc fellows and young researchers in companies. All the disciplines of Chemistry are covered: analytical, physical, industrial, organic, inorganic, theoretical, pharmaceutical, biological, environmental, macromolecular and electrochemistry. This year, a special emphasis will be given to chemistry from knowledge to innovation: how chemistry is increasingly present in all of the fields that are essential for human life, and how chemical fundamentals are pushing novel technologies? This year we have the exceptional number of 212 participants; we thank you for the great trust shown towards SCI Giovani, Merck and Elsevier. Enjoy the conference

Gas phase Elemental abundances in Molecular cloudS (GEMS) VI. A sulphur journey across star-forming regions: study of thioformaldehyde emission

In the context of the IRAM 30m Large Program GEMS, we present a study of thioformaldehyde in several starless cores located in star-forming filaments of Taurus, Perseus, and Orion. We investigate the influence of the environmental conditions on the abundances of these molecules in the cores, and the effect of time evolution. We have modelled the observed lines of H2CS, HDCS, and D2CS using the radiative transfer code RADEX. We have also used the chemical code Nautilus to model the evolution of these species depending on the characteristics of the starless cores. We derive column densities and abundances for all the cores. We also derive deuterium fractionation ratios, Dfrac, to determine and compare the evolutionary stage between different parts of each star-forming region. Our results indicate that the north region of the B213 filament in Taurus is more evolved than the south, while the north-eastern part of Perseus presents an earlier evolutionary stage than the south-western zone. Model results also show that Dfrac decreases with the cosmic-ray ionisation rate, while it increases with density and with the degree of sulphur depletion. In particular, we only reproduce the observations when the initial sulphur abundance in the starless cores is at least one order of magnitude lower than the solar elemental sulphur abundance. The progressive increase in HDCS/H2CS and D2CS/H2CS with time makes these ratios powerful tools for deriving the chemical evolutionary stage of starless cores. However, they cannot be used to derive the temperature of these regions, since both ratios present a similar evolution at two different temperature ranges (7-11 K and 15-19 K). Regarding chemistry, (deuterated) thioformaldehyde is mainly formed through gas-phase reactions (double-replacement and neutral-neutral displacement reactions), while surface chemistry plays an important role as a destruction mechanism.Comment: 31 pages, 26 figure

Seeds of Life in Space (SOLIS): XI. First measurement of nitrogen fractionation in shocked clumps of the L1157 protostellar outflow

Context. The isotopic ratio of nitrogen presents a wide range of values in the Solar System: from 140 in meteorites and comets to 441 in the solar wind. In star-forming systems, we observe evena higher spread of ~150-1000. The origin of these differences is still unclear. Aims. Chemical reactions in the gas phase are one of the possible processes that could modify the 14N/15N ratio. We aim to investigate if and how the passage of a shock wave in the interstellar medium, which activates a rich chemistry, can affect the relative fraction of nitrogen isotopes. Theideal place for such a study is the chemically rich outflow powered by the L1157-mm protostar, where several shocked clumps are present. Methods. We present the first measurement of the 14N/15N ratio in the two shocked clumps, B1 and B0, of the protostellar outflow L1157. The measurement is derived from the interferometeric maps of the H13CN (1-0) and the HC15N (1-0) lines obtained with the NOrthern Extended Millimeter Array (NOEMA) interferometeras part of the Seeds of Life in Space (SOLIS) programme. Results. In B1, we find that the H13CN (1-0) and HC15N (1-0) emission traces the front of the clump, that is the apex of the shocked region, where the fast jet impacts the lower velocity medium with an averaged column density of N(H13CN) ~ 7 × 1012 cm-2 and N(HC15N) 2 × 1012 cm-2. In this region, the ratio H13CN (1-0)/HC15N (1-0) is almost uniform with an average value of ~5 ± 1. The same average value isalso measured in the smaller clump B0e. Assuming the standard 12C/13C = 68, we obtain 14N/15N = 340 ± 70. This ratio is similar to those usually found with the same species in prestellar cores and protostars. We analysed the prediction of a chemical shock model for several shock conditions and we found that the nitrogen and carbon fractionations do not vary much for the first period after the shock. The observed H13CN/HC15N can be reproduced by a non-dissociative, C-type shock with pre-shock density n(H) = 105 cm-3, shock velocity Vs between 20 and 40 km s-1, and cosmic-ray ionization rate of 3 × 10-16 s-1; this agrees with previous modelling of other chemical species in L1157-B1. Conclusions. Both observations and chemical models indicate that the rich chemistry activated by the shock propagation does not affect the nitrogen isotopic ratio, which remains similar to that measured in lower temperature gas in prestellar cores and protostellar envelopes

Gas phase Elemental abundances in Molecular cloudS (GEMS) VII. Sulfur elemental abundance

Gas phase Elemental abundances in molecular CloudS (GEMS) is an IRAM 30m large program aimed at determining the elemental abundances of carbon (C), oxygen (O), nitrogen (N), and sulfur (S) in a selected set of prototypical star-forming filaments. In particular, the elemental abundance of S remains uncertain by several orders of magnitude and its determination is one of the most challenging goals of this program. We have carried out an extensive chemical modeling of the fractional abundances of CO, HCO$^+$, HCN, HNC, CS, SO, H$_2$S, OCS, and HCS$^+$ to determine the sulfur depletion toward the 244 positions in the GEMS database. These positions sample visual extinctions from A$_V$ $\sim$ 3 mag to $>$50 mag, molecular hydrogen densities ranging from a few 10$^3$~cm$^{-3}$ to 3$\times$10$^6$~cm$^{-3}$, and T$_k$ $\sim$ 10$-$35 K. Most of the positions in Taurus and Perseus are best fitted assuming early-time chemistry, t=0.1 Myr, $\zeta_{H_2}$$\sim$ (0.5$-$1)$\times$10$^{-16}$ s$^{-1}$, and [S/H]$\sim$1.5$\times$10$^{-6}$. On the contrary, most of the positions in Orion are fitted with t=1~Myr and $\zeta_{H_2}$$\sim$ 10$^{-17}$ s$^{-1}$. Moreover, $\sim$40% of the positions in Orion are best fitted assuming the undepleted sulfur abundance, [S/H]$\sim$1.5$\times$10$^{-5}$. Our results suggest that sulfur depletion depends on the environment. While the abundances of sulfur-bearing species are consistent with undepleted sulfur in Orion, a depletion factor of $\sim$20 is required to explain those observed in Taurus and Perseus. We propose that differences in the grain charge distribution in the envelopes of the studied clouds might explain these variations. The shocks associated with past and ongoing star formation could also contribute to enhance [S/H] in Orion.Comment: 22 pages, 15 figures, Astronomy and Astrophysics, in pres

Efficient Methanol Production on the Dark Side of a Prestellar Core

We present Atacama Large Millimeter/submillimeter Array maps of the starless molecular cloud core Ophiuchus/H-MM1 in the lines of deuterated ammonia (ortho-NH2D), methanol (CH3OH), and sulfur monoxide (SO). The dense core is seen in NH2D emission, whereas the CH3OH and SO distributions form a halo surrounding the core. Because methanol is formed on grain surfaces, its emission highlights regions where desorption from grains is particularly efficient. Methanol and sulfur monoxide are most abundant in a narrow zone that follows the eastern side of the core. This side is sheltered from the stronger external radiation field coming from the west. We show that photodissociation on the illuminated side can give rise to an asymmetric methanol distribution but that the stark contrast observed in H-MM1 is hard to explain without assuming enhanced desorption on the shaded side. The region of the brightest emission has a wavy structure that rolls up at one end. This is the signature of Kelvin-Helmholtz instability occurring in sheared flows. We suggest that in this zone, methanol and sulfur are released as a result of grain-grain collisions induced by shear vorticity.Peer reviewe

Gas phase Elemental abundances in Molecular cloudS (GEMS) : IV. Observational results and statistical trends

Gas phase Elemental abundances in Molecular CloudS (GEMS) is an IRAM 30 m Large Program designed to provide estimates of the S, C, N, and O depletions and gas ionization degree, X(e(-)), in a selected set of star-forming filaments of Taurus, Perseus, and Orion. Our immediate goal is to build up a complete and large database of molecular abundances that can serve as an observational basis for estimating X(e(-)) and the C, O, N, and S depletions through chemical modeling. We observed and derived the abundances of 14 species ((CO)-C-13, (CO)-O-18, HCO+, (HCO+)-C-13, (HCO+)-O-18, HCN, (HCN)-C-13, HNC, HCS+, CS, SO, (SO)-S-34, H2S, and OCS) in 244 positions, covering the A(V) similar to 3 to similar to 100 mag, n(H-2) similar to a few 10(3) to 10(6) cm(-3), and T-k similar to 10 to similar to 30 K ranges in these clouds, and avoiding protostars, HII regions, and bipolar outflows. A statistical analysis is carried out in order to identify general trends between different species and with physical parameters. Relations between molecules reveal strong linear correlations which define three different families of species: (1) (CO)-C-13 and (CO)-O-18 isotopologs; (2) (HCO+)-C-13, (HCO+)-O-18, H-13 CN, and HNC; and (3) the S-bearing molecules. The abundances of the CO isotopologs increase with the gas kinetic temperature until T-K similar to 15 K. For higher temperatures, the abundance remains constant with a scatter of a factor of similar to 3. The abundances of H-13 CO+, HC18 O+, H-13 CN, and HNC are well correlated with each other, and all of them decrease with molecular hydrogen density, following the law proportional to n(H-2)(-0.8 +/- 0.2). The abundances of S-bearing species also decrease with molecular hydrogen density at a rate of (S-bearing/H)(gas) proportional to n(H-2)(-0.6 +/- 0.1). The abundances of molecules belonging to groups 2 and 3 do not present any clear trend with gas temperature. At scales of molecular clouds, the (CO)-O-18 abundance is the quantity that better correlates with the cloud mass. We discuss the utility of the (CO)-C-13/(CO)-O-18, HCO+/(HCO+)-C-13, and H-13 CO+/(HCN)-C-13 abundance ratios as chemical diagnostics of star formation in external galaxies.Peer reviewe

Gas phase Elemental abundances in Molecular cloudS (GEMS) : III. Unlocking the CS chemistry: the CS plus O reaction

Context. Carbon monosulphide (CS) is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. However, chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. Aims. The CS+O -> CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150-400 K, but the extrapolation to lower temperatures is doubtful. Our goal is to calculate the CS+O reaction rate at temperatures Methods. We performed ab initio calculations to obtain the three lowest potential energy surfaces (PES) of the CS+O system. These PESs are used to study the reaction dynamics, using several methods (classical, quantum, and semiclassical) to eventually calculate the CS + O thermal reaction rates. In order to check the accuracy of our calculations, we compare the results of our theoretical calculations for T similar to 150-400 K with those obtained in the laboratory. Results. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150-400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, below 10(-15) cm(3) s(-1), which is consistent with the extrapolation of experimental data using the Arrhenius expression. Conclusions. We use the updated chemical network to model the sulfur chemistry in Taurus Molecular Cloud 1 (TMC 1) based on molecular abundances determined from Gas phase Elemental abundances in Molecular CloudS (GEMS) project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate, zeta(H2), along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.Peer reviewe