Gas Phase Ion Chemistry

Ammonia is a key alkaline species, playing an important role by neutralizing atmospheric acidity and inorganic secondary aerosol production. On the other hand, the NH3/NH4+ increases the acidity and eutrophication in natural ecosystems, being NH3 classified as toxic atmospheric pollutant. The present study aims to give a better comprehension of the nitrogen content species distribution in fine and coarse particulate matter (PM2.5 and PM2.5–10) and to quantify ammonia vehicular emissions from an urban vehicular tunnel experiment in the metropolitan area of São Paulo (MASP). MASP is the largest megacity in South America, with over 20 million inhabitants spread over 2000 km2 of urbanized area, which faces serious environmental problems. The PM2.5 and PM2.5–10 median mass concentrations were 44.5 and 66.6 μg m−3, respectively, during weekdays. In the PM2.5, sulfate showed the highest concentration, 3.27 ± 1.76 μg m−3, followed by ammonium, 1.14 ± 0.71 μg m−3, and nitrate,
0.80 ± 0.52 μg m−3. Likewise, the dominance (30 % of total PM2.5) of solid species, mainly the ammonium salts, NH4HSO4, (NH4)2SO4, and NH4NO3, resulted from simulation of inorganic species. The ISORROPIA simulation was relevant to show the importance of environment conditions for the ammonium phase distribution (solid/aqueous),
which was solely aqueous at outside and almost entirely solid at inside tunnel. Regarding gaseous ammonia concentrations, the value measured inside the tunnel (46.5 ± 17.5 μg m−3) was 3-fold higher than that outside (15.2 ± 11.3 μg m−3). The NH3 vehicular emission factor
(EF) estimated by carbon balance for urban tunnel was 44 ± 22 mg km−1. From this EF value and considering the MASP traffic characteristics, it was possible to estimate more than 7 Gg NH3 year−1 emissions that along with NOx are likely to cause rather serious problems to natural ecosystems in the region.

A one-step enzymatic reaction for improving the collision-induced dissociation (CID)-based tandem mass spectrometry (MS/MS) analysis of phosphorylated peptides in an ion trap is presented. Carboxypeptidase-B (CBP-B) was used to selectively remove C-terminal arginine or lysine residues from phosphorylated tryptic/Lys-C peptides prior to their MS/MS analysis by CID with a Paul-type ion trap. Removal of this basic C-terminal residue served to limit the extent of gas-phase neutral loss of phosphoric acid (H 3 PO 4 ), favoring the formation of diagnostic b and y ions as determined by an increase in both the number and relative intensities of the sequence-specific product ions. Such differential fragmentation is particularly valuable when the H 3 PO 4 elimination is so predominant that localizing the phosphorylation site on the peptide sequence is hindered. Improvement in the quality of tandem mass spectral data generated by CID upon CBP-B treatment resulted in greater confidence both in assignment of the phosphopeptide primary sequence and for pinpointing the site of phosphorylation. Higher Mascot ion scores were also generated, combined with lower expectation values and higher delta scores for improved confidence in site assignment; Ascore values also improved. These results are rationalized in accordance with the accepted mechanisms for the elimination of H 3 PO 4 upon low energy CID and insights into the factors dictating the observed dissociation pathways are presented. We anticipate this approach will be of utility in the MS analysis of phosphorylated peptides, especially when alternative electron-driven fragmentation techniques are not available.

Packed columns are an important part of the broad selection of mass and heat transfer equipment. Nowadays, the use of packed columns is increasing, which is because of its lower pressure drop, higher capacity and higher mass transfer in comparison to tray columns. The experiential tests and the hypothetical analysis display that the chemical dehumidification of air by hygroscopic salt solutions confirms the stable reduction in humidity ratio, which is appropriate for uses to air conditioning or drying processes The mass transfer factors in the pulse were found to correspond nearly to the factors that would be achieved in the distributed bubble flow regime In the present study, parameters that affect column performance, such as, fluid retention and gas-phase mass transfer coefficient in a humidification column using random packing in towers with 0.1 m and 0.2 m diameters and 1m height, were measured Air velocity was 1.32 to 3.92 m3 per hour and liquid velocity was 10 to 70 m3 per hour. In this research, the Nakajima model was used to calculate the effective area. Thereafter, experimental values for gas-phase mass transfer coefficients were compared to Zech, Shi, Grouff, Shulman, Billet and Ondamodels The mean relative errors of these models with the present study’s experimental findings were 7%, 15%, 29%, 21%, 45% and 195%. Findings showed that by decreasing the column diameter, the gas-phase mass transfer coefficient (Kg.ae) also increases Further, the obtained retention values showed that retention in the column with a 0.1 m diameter was higher than the column with a 0.2 m column.

Density functional calculations 22 a b s t r a c t S-nitrosation of cysteine plays an important role in storage and transport of NO, a key signaling molecule in vivo. An approach to detect this modification in the bare, charged amino acid is presented, based on IR multiple photon dissociation (IRMPD) spectroscopy. Protonated and deprotonated S-nitrosocysteine ions, [SNOCys+H] + and [SNOCys−H] − , have been obtained by electrospray ionization and assayed for IR activity in either the 1000-1900 cm −1 or the 3000-3600 cm −1 wavenumber range. The so-obtained IRMPD spectra display characteristic features ascribed to the presence of the S-nitrosation motif, which are missing in the corresponding IRMPD spectra of the native cysteine ions, [Cys+H] + and [Cys−H] − . In particular, the NO stretching mode is unambiguously identified by the red shift observed for the 15 N-labelled species. The interpretation of the IRMPD spectra is supported by density functional theory calculations of the optimized geometries, relative energies and IR spectra of [SNOCys+H] + and [SNO-Cys−H] − . Both sampled ions comprise a thermally averaged population of conformers contributing to the experimental IRMPD spectra. This notion is supported by the agreement between the convoluted IR spectra of the several conformers, and the recorded IRMPD spectrum. The gathered evidence points to a characteristic NO stretching mode that emerges as a pronounced feature at 1460-1490 cm −1 in the IRMPD spectrum of [SNOCys−H] − , namely in a region where [Cys−H] − displays no IRMPD activity. Conversely, the NO stretching vibration of [SNOCys+H] + is enclosed in a wide absorption including the C O stretching mode at 1780 cm −1 . The [SNOCys−H] − negative ions are thus a promising benchmark in a search for S-nitrosation features using IRMPD spectroscopy. contribution infra-red multiple photon dissociation (IRMPD) spec-35 troscopy, based on the use of an IR radiation source of high 36 power and wide tunability combined with tandem mass spectrom-37 etry, has been exploited to gain insight into the structural and 38 spectroscopic features of ions derived from SNOCys. The ions deliv-39 ered into the gas phase by electrospray ionization are either the 40 protonated molecule, [SNOCys+H] + , or the deprotonated species 41 [SNOCysNO−H] − . The high degree of in-depth information that can 42 be gained by IRMPD spectroscopy of the ionic species obtained 43 from the natural amino acids is well illustrated in several recent 44 papers and review articles [10-27]. In particular, a notable effort 45 has been devoted to ascertain the conditions favoring zwitterionic 46 structures and to unambiguously characterize them. The sample 47 ions obtained by protonation or deprotonation of native cysteine 48 ([Cys+H] + and [Cys−H] − , respectively) have been already assayed 49 by IRMPD spectroscopy in the 600-1800 cm −1 IR range and the 50 experimental spectra have been discussed in association with the 51 calculated IR spectra of the most stable conformers in two landmark 52 papers [28,29]. The deprotonated cysteine ion has been probed as 53 model ion in view of the current interest about the structure of 54 ions formed by electrospray ionization (ESI) [30-33]. Whether they 55 G Model MASPEC 14739 1-7 2 F. Lanucara et al. / International Journal of Mass Spectrometry xxx (2012) xxx-xxx retain their former structure in solution or rather adopt the one 56 thermodynamically favored in the gas phase is a topic of active 57 investigation and debate. The deprotonated cysteine ion displays 58 an experimental IRMPD spectrum consistent with a carboxylate 59 structure (deprotonation on the COOH group) although the thio-60 late structure (deprotonation on the SH group) is calculated to be 61 lower in energy [30,34,35]. 62 [Cys+H] + and [Cys−H] − ions are now re-examined as refer-63 ence species to aid in identifying distinctive signatures for the 64 nitrosation feature in the IRMPD spectra of [SNOCys+H] + and [SNO-65 Cys−H] − . 66 2. Experimental details 67 2.1. Materials 68 l-Cysteine hydrochloride, NaNO 2 , Na 15 NO 2 and all the solvents 69 used in this work were research grade products from commercial 70 sources (Sigma-Aldrich s.r.l. Milan, Italy) and were used without 71 any further purification. S-nitrosocysteine was obtained from the 72 reaction of l-cysteine (2 mM) and NaNO 2 or Na 15 NO 2 (2 mM) in 73 H 2 O:CH 3 CN 1:1 (2 ml) at 37 • C, by adding H 2 SO 4 (98%) to the reac-74 tion mixture to pH 1.5, followed by a 1 in 100 dilution in H 2 O:CH 3 CN 75 1:1. An alternative method has also been assayed, allowing l-76 cysteine (20 mM in H 2 O:CH 3 CN) to react with NO (1 bar) after 77 purging the solution and the flask repeatedly with Ar. UV-vis spec-78 troscopy has been used to confirm the formation and stability of 79 S-nitrosocysteine by monitoring the presence of the band at 543 nm 80 assigned to an n → * charge-transfer transition. Soon after prepa-81 ration of the compound (which occurs on mixing), diluted solutions 82 (about 7 M) for ESI-MS experiments were prepared. ESI-MS anal-83 ysis shows the protonated molecule [SNOCys+H] + at m/z 151, the 84 protonated disulfide (protonated cystine) at m/z 241 and the cys-85 teine radical cation at m/z 121. The deprotonated amino acids are 86 generated by ESI of 0.1 mM solutions in H 2 O:CH 3 CN 1:1 by the 87 addition of NH 3 to assist deprotonation. 88 2.2. IRMPD experiments 89 IRMPD experiments on the protonated and deprotonated forms 90 of S-nitrosocysteine and cysteine have been performed in two spec-91 tral regions, namely 1000-2000 cm −1 and 3200-3600 cm −1 , using 92 two different IR radiation sources, the free electron laser (FEL) at 93 the Centre Laser Infrarouge d'Orsay (CLIO) facility and an Opti-94 cal Parametric Oscillator/Amplifier (OPO/OPA) laser system at the 95 Università di Roma "La Sapienza", respectively. The FEL radiation 96 G Model MASPEC 14739 1-7 F. Lanucara et al. / International Journal of Mass Spectrometry xxx (2012) xxx-xxx 7 significant IRMPD activity in a relatively wide region between 1313 438 and 1647 cm −1 , namely the frequency positions of the symmet-439 ric and asymmetric −CO 2 − stretching modes. It is in this blank 440 interval that [SNOCys−H] − ions display a remarkable, 15 N-isotope-441 sensitive band. The band is assigned to the NO stretching vibration 442 and stands out as a notable signature for S-nitrosation. A similar, 443 clearcut piece of information cannot be gained from IRMPD spec-444 troscopy of the positively charged [SNOCys+H] + ion. For this species 445 the informative NO stretching mode is active at a frequency close to 446 the C O stretching resonance, yielding a broad, unresolved absorp-447 tion. Indeed, a (partial) separation of the two modes is revealed 448 only in the spectrum of the 15 N-labelled [S 15 NOCys+H] + ion, which 449 allowed to identify the distinct presence and activity of the two 450 modes. 451 The unambiguous identification of the nitrosation feature in 452 the IRMPD spectrum of deprotonated S-nitrosocysteine provides 453 a characteristic signature of this modification. In a similar way, 454 characteristic IRMPD signatures have been identified for the phos-455 phorylation of amino acids and peptides [60-62], for the nitration 456 of tyrosine [38] and for the sulfide to sulfoxide oxidation in methi-457 onine and related compounds [63]. 458 Acknowledgements 459 Financial support was provided by the Italian Ministero 460 dell'Istruzione, dell'Università e della Ricerca and by the European 461 Community's Seventh Framework Programme (FP7/2007-2013, 462 under grant agreement no. 226716) which provided also travel 463 funding to F.L., M.E.C. and B.C. for access to the European multi-user 464 facility CLIO. The skilful assistance of the CLIO team under the direc-465 tion of J.M. Ortega and of Joel Lemaire, in charge of the beamline, is 466 gratefully acknowledged. 467 Appendix A. Supplementary data 468 Supplementary data associated with this article can be found, in 469 the online version, at http://dx.