Loss Of NH3 Research Articles

The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment

We examined the susceptibility of δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios in organic-rich sediments to pre-analysis sample treatment. Each sample was subjected to three different kinds of processing. For comparative purposes, the first measurement series (MS-1) was carried out on untreated sediment. In MS-2, the sediment was rinsed with distilled water. In MS-3, analyses were carried out on decalcified and rinsed material, in MS-4 the samples were decalcified without being subsequently washed. The sediment yielded conspicuously different results depending on the type of processing it was subjected to. Rinsing, irrespective of whether acidification was included or not, induced substantial modifications in δ<sup>15</sup>N accompanied by a pronounced loss of NH<sub>4</sub><sup>+</sup> (up to 14 wt% of the initial N-content). Molar C<sub>org</sub>/N ratios, on the other hand, were only affected by a combination of acidification and rinsing. The discrepancies are ascribed to the influence of decomposition-derived ammonium (NH<sub>4</sub><sup>+</sup>). In untreated sediment (MS-1), NH<sub>4</sub><sup>+</sup> seems to produce misleading shifts in both δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios. Presumed mechanisms involved are as follows: Firstly, nitrogen isotopes fractionate during NH<sub>4</sub><sup>+</sup>-volatilisation in the heating oven, where the sediment is put to desiccate. Secondly, NH<sub>4</sub><sup>+</sup>-ions are able to escape that fractionation when adsorbed to negatively-charged SiO<sub>2</sub>-surfaces. The adsorption capacity of SiO<sub>2</sub> increases with increasing pH of the pore water and hence with increasing carbonate content. Our findings raise serious doubts about whether untreated sediment (MS-1) can provide reliable C<sub>org</sub>/N and δ<sup>15</sup>N-records. Pre-analysis acidification plus rinsing (MS-3) seems to eliminate the deceptive influence of NH<sub>4</sub><sup>+</sup>-adsorption and -outgassing. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201100004" target="_blank">10.1002/mmng.201100004</a>

Effect of amino acid formulation and supplementation on nutrient mass balance in turkeys

Nutrient mass balances were determined for turkeys fed 4 diets in a 2 × 2 factorial design to investigate the effects of diets with 100 or 110% of NRC (1994)-recommended amino acid (AA) formulation and diets containing 2 (Lys and Met) or 3 (Lys, Met, and Thr) supplemental AA. Hybrid tom turkeys were raised and monitored in 12 rooms (3 replicates/diet; 20 toms/room at hatch, culled to 16 at 21 d and then to 12 at 28 d of age). All feed and litter entering and leaving the rooms were quantified and analyzed for nutrient content. Air emissions were measured throughout the 20-wk study. The 100% NRC diets resulted in lower cumulative loss of NH(3) (by 14%) and H(2)S (by 21%) as compared with the 110% NRC diets. Reductions corresponded to lower N and S intake. Feeding the 3 supplemental AA diets resulted in lower N excretion (by 12%) and lower cumulative loss of NH(3) (by 23%) as compared with the 2 supplemental AA diets. The NH(3) emission as a percentage of N output was not significantly influenced by dietary CP (100 vs. 110% of NRC); however, the 3 supplemental AA diets resulted in less NH(3) emitted as a percentage of N output as compared with the 2 supplemental AA diets (9.9 vs. 11.8%). Across all 4 diets, N partitioning averaged 31.4, 56.9, and11.4% for retention, excretion, and air emission, respectively. The N loss estimated from the mass balance approach (9.6%) was comparable with the measured N loss as air emission (11.9%). Partitioning of P averaged 31.9 and 68.1% for retention and excretion, respectively. Partitioning of S averaged 27.5, 72.1, and 0.5% for retention, excretion, and air emission, respectively. The results illustrated the fate of N, P, and S in a turkey production system and demonstrated the potential for reducing nutrient excretion and air emissions from turkeys through diet modification of AA.

Quantitative analysis of 15N‐labeled positional isomers of glutamine and citrulline via electrospray ionization tandem mass spectrometry of their dansyl derivatives

The enteral metabolisms of glutamine and citrulline are intertwined because, while glutamine is one of the main fuel sources for the enterocyte, citrulline is one of its products. It has been shown that the administration of (15)N-labeled glutamine results in the incorporation of the (15)N label into citrulline, but it is not clear which of the three nitrogen groups of citrulline is actually labeled. To determine the (15)N-enrichment of the positional isomers of glutamine and citrulline, a rapid liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed. The amino acids were analyzed as their dansyl derivatives. The product ion resulting from the loss of NH(3) from the omega carbon allows for the determination of the enrichment of the ureido (citrulline) or amido groups (glutamine). The protonated pyrrolidine (citrulline) or 5-oxopyrrolidine (glutamine) product ion contains the 2-N (amino group) and is used to determine its enrichment. The method described showed no ion suppression and a wide dynamic range ranging from 1.3 picomoles to 2 nanomoles for citrulline. Background samples and standards resulted in enrichments not different from those theoretically expected. The enrichment curves for the different glutamine and citrulline isotopomers were linear (R(2) > 0.998) over the range of enrichments studied. The method developed provides an additional insight into the metabolism of glutamine and citrulline tracing the precursor-product relationship between these two amino acids.

Tissue Transglutaminase-mediated Glutamine Deamidation of β-Amyloid Peptide Increases Peptide Solubility, Whereas Enzymatic Cross-linking and Peptide Fragmentation May Serve as Molecular Triggers for Rapid Peptide Aggregation

Tissue transglutaminase (TGase) has been implicated in a number of cellular processes and disease states, where the enzymatic actions of TGase may serve in both, cell survival and apoptosis. To date, the precise functional properties of TGase in cell survival or cell death mechanisms still remain elusive. TGase-mediated cross-linking has been reported to account for the formation of insoluble lesions in conformational diseases. We report here that TGase induces intramolecular cross-linking of β-amyloid peptide (Aβ), resulting in structural changes of monomeric Aβ. Using high resolution mass spectrometry (MS) of cross-linked Aβ peptides, we observed a shift in mass, which is, presumably associated with the loss of NH3 due to enzymatic transamidation activity and hence intramolecular peptide cross-linking. We have observed that a large population of Aβ monomers contained an 0.984 Da increase in mass at a glutamine residue, indicating that glutamine 15 serves as an indispensable substrate in TGase-mediated deamidation to glutamate 15. We provide strong analytical evidence on TGase-mediated Aβ peptide dimerization, through covalent intermolecular cross-linking and hence the formation of Aβ1-40 dimers. Our in depth analyses indicate that TGase-induced post-translational modifications of Aβ peptide may serve as an important seed for aggregation.

Role of 2‐oxo and 2‐thioxo modifications on the fragmentation reactions of the histidine radical cation

The fragmentation reactions of the radical cations, M(·+), of histidine, 2-oxo-histidine and 2-thioxo-histidine were examined using a combination of experiments performed on a linear ion trap and density functional theory (DFT) calculations at the UB3-LYP/6-311++G(d,p) level of theory. Low-energy collision-induced dissociation (CID) on [Cu(II)(terpy)(M)](2+) complexes, formed via electrospray ionisation, produced the radical cations in sufficient yield to examine their unimolecular chemistry via an additional stage of CID. The CID spectrum of the radical cation of histidine is dominated by loss of water with the next most abundant ion arising from the combined loss of H(2)O and CO. In contrast, the CID spectra of the radical cations of 2-oxo-histidine and 2-thioxo-histidine are dominated by the combined loss of CO(2) and NH=CH(2). The observed differences are rationalised via DFT calculations which reveal that the barrier associated with loss of CO(2) from the histidine radical cation is higher than that for loss of H(2)O. In contrast, the introduction of an oxygen or sulfur atom into the side chain of histidine results in a reversal of the order of these barrier heights, thus making CO(2) loss the preferred pathway.

Substantial Dissociation Energies for the Recently Synthesized NC-Ag-NH3 and Br-Ag-NH3 Molecules and Their Isovalent Family Members M(CN)XY3 and M(Br)XY3 (M = Cu, Ag, Au; X = N, P; Y = H, F).

Chippindale et al. have recently synthesized the unique molecules (NC)Ag(NH3) and BrAg(NH3) and shown the heavy atom skeletal structures to be linear. Here, a theoretical study is reported of 12 members each of the two isovalent series of molecules. For (NC)Ag(NH3) and BrAg(NH3), the theoretical structures agree well with those determined by X-ray crystallography. Structures for the 22 yet unknown compounds should be similarly reliable. The dissociation energies for a loss of NH3 from the two known compounds are significant (34 and 31 kcal/mol), confirming their viability. For the other systems, the ligand dissociation energies are highly variable, ranging from 9 kcal/mol (BrAg-NF3) to 44 kcal/mol (BrAu-PH3). The bond dissociation energies for the different metals follow the irregular order Au > Cu > Ag. For the XY3 ligands, the dissociation energies follow the order NH3 > PH3 > PF3 > NF3, except for the BrAu-XY3 complexes. Electronic structure insights are gained via Natural Bond Orbital (NBO) analyses.

Characterization of Nα‐Fmoc‐protected ureidopeptides by electrospray ionization tandem mass spectrometry (ESI‐MS/MS): differentiation of positional isomers

Four pairs of positional isomers of ureidopeptides, FmocNH-CH(R(1))-ϕ(NH-CO-NH)-CH(R(2))-OY and FmocNH-CH(R(2))-ϕ(NH-CO-NH)-CH(R(1))-OY (Fmoc = [(9-fluorenyl methyl)oxy]carbonyl; R(1) = H, alkyl; R(2) = alkyl, H and Y = CH(3)/H), have been characterized and differentiated by both positive and negative ion electrospray ionization (ESI) ion-trap tandem mass spectrometry (MS/MS). The major fragmentation noticed in MS/MS of all these compounds is due to --N--CH(R)--N--bond cleavage to form the characteristic N- and C-terminus fragment ions. The protonated ureidopeptide acids derived from glycine at the N-terminus form protonated (9H-fluoren-9-yl)methyl carbamate ion at m/z 240 which is absent for the corresponding esters. Another interesting fragmentation noticed in ureidopeptides derived from glycine at the N-terminus is an unusual loss of 61 units from an intermediate fragment ion FmocNH = CH(2) (+) (m/z 252). A mechanism involving an ion-neutral complex and a direct loss of NH(3) and CO(2) is proposed for this process. Whereas ureidopeptides derived from alanine, leucine and phenylalanine at the N-terminus eliminate CO(2) followed by corresponding imine to form (9H-fluoren-9-yl)methyl cation (C(14)H(11) (+)) from FmocNH = CHR(+). In addition, characteristic immonium ions are also observed. The deprotonated ureidopeptide acids dissociate differently from the protonated ureidopeptides. The [M - H](-) ions of ureidopeptide acids undergo a McLafferty-type rearrangement followed by the loss of CO(2) to form an abundant [M - H - Fmoc + H](-) which is absent for protonated ureidopeptides. Thus, the present study provides information on mass spectral characterization of ureidopeptides and distinguishes the positional isomers.

Thermal behavior of vibrational phonons and hydroxyls of muscovite in dehydroxylation: In situ high-temperature infrared spectroscopic investigations

Temperature dependencies and thermal dynamical behavior of vibrational phonons related to different bonds/motions (e.g., K-O, Si-O, and Al-O) and O-H stretching, bending, and combinations bands, as well as those of NH 4 ions, of muscovite have been investigated in detail at high temperatures using in situ infrared spectroscopy. Phonon modes of muscovite show a complex response to heating and dehydroxylation. The mode Grüneisen parameters of muscovite are largest for low-frequency bands and some bands have negative values. Approaching dehydroxylation, bands associated with K-O stretching, Al-OH bending, and Al-O vibrations exhibit significant variations, indicating modifications of local configurations related to these ions. The O-H stretching feature near 3627 cm -1 shows a change in temperature dependence of the peak position near or during dehydroxylation, and this is attributed to a dramatic loss of OH and changes in local environments. The infrared spectroscopic analyses carried out in situ or on quenched samples do not record the characteristic bands of dehydroxylation-induced H 2 O and these findings suggest that H 2 O is unlikely to be the principal diffusing species. The results suggest that de-ammoniation or loss of NH 4 in muscovite takes place at temperatures near dehydroxylation.

Isomer differentiation via collision‐induced dissociation: The case of protonated α‐, β2‐ and β3‐phenylalanines and their derivatives

A combination of electrospray ionisation (ESI), multistage and high-resolution mass spectrometry experiments is used to examine the gas-phase fragmentation reactions of the three isomeric phenylalanine derivatives, alpha-phenylalanine, beta(2)-phenylalanine and beta(3)-phenylalanine. Under collision-induced dissociation (CID) conditions, each of the protonated phenylalanine isomers fragmented differently, allowing for differentiation. For example, protonated beta(3)-phenylalanine fragments almost exclusively via the loss of NH(3), only beta(2)-phenylalanine via the loss of H(2)O, while alpha- and beta(2)-phenylalanine fragment mainly via the combined losses of H(2)O + CO. Density functional theory (DFT) calculations were performed to examine the competition between NH(3) loss and the combined losses of H(2)O and CO for each of the protonated phenylalanine isomers. Three potential NH(3) loss pathways were studied: (i) an aryl-assisted neighbouring group; (ii) 1,2 hydride migration; and (iii) neighbouring group participation by the carboxyl group. Finally, we have shown that isomer differentiation is also possible when CID is performed on the protonated methyl ester and methyl amide derivatives of alpha-, beta(2)- and beta(3)-phenylalanines.

Electrochemical incineration of diclofenac in neutral aqueous medium by anodic oxidation using Pt and boron-doped diamond anodes

The degradation of diclofenac, a common non-steroidal anti-inflammatory drug, in aqueous medium has been studied by anodic oxidation (AO) using an undivided cell with a Pt or boron-doped diamond (BDD) anode. Operating without pH regulation, AO with Pt acidifies the solution with precipitation of its protonated form, whereas using BDD, the solution becomes alkaline and only attains partial mineralization. Total incineration of low contents of the drug is feasible by AO with BDD in a neutral buffer medium of pH 6.5. Comparative treatment with Pt gives poor decontamination. The diclofenac decay always follows a pseudo first-order reaction. The increase in current for AO with BDD accelerates the degradative process, but decreases its efficiency. 2-Hydroxyphenylacetic acid, 2,5-dihydroxyphenylacetic acid, 2,6-dichloroaniline and 2,6-dichlorohydroquinone have been identified as aromatic intermediates. For AO with Pt, high amounts of malic, succinic, tartaric and oxalic acids are accumulated in the bulk and the N-derivatives produced are rapidly destroyed with loss of NH 4 + . When BDD is employed, some carboxylic acids are also accumulated in small extent, with a larger persistence of oxalic and oxamic acids. The process involves the formation of different N-derivatives that slowly release NH 4 + and NO 3 - ions. Chloride ion is lost in all cases.

XAFS investigation of [Pd(NH3)4][AuCl4]2 and its thermolysis products

Thermolysis of double complex salt [Pd(NH3)4][AuCl4]2 has been studied in helium atmosphere from ambient to 350 °C. The XAFS of Pd K and Au L3 edges and thermogravimetry measurements have been carried out to characterize the intermediates and the final product. In the temperature range 115–160 °C the complex is decomposed to form Pd(NH3)2Cl2 and AuCl4−xNx species with x ranging from 2 to 3. Subsequent heating of the intermediate up to 300 °C leads to the total loss of NH3. The Au–Cl and Au–Au bonds form the local environment of Au at the stage of decomposition while only four chlorine atoms are around Pd. At the temperature of 330 °C the Au and Pd nanoparticles as well as residues of palladium chloride are detected. The final product consists of separated Au and Pd nanoparticles.

The role of metal cation in electron-induced dissociation of tryptophan

The fragmentation of tryptophan (Trp) – metal complexes [Trp+M]+, where M = Cs, K, Na, Li and Ag, induced by 22 eV energy electrons was compared to [Trp+H]+. Additional insights were obtained through the study of collision-induced dissociation (CID) of [Trp+M]+ and through deuterium labelling. The electron-induced dissociation (EID) of [Trp+M]+ resulted in the formation of radical cations via the following pathways: (i) loss of M to form Trp+•, (ii) loss of an H atom to form [(Trp-H)+M]+•, and (iii) bond homolysis to form C2H4NO2M+•. Deuterium labelling suggests that H atom loss can occur from heteroatom and/or C–H positions. Other types of fragment ions observed include: C9H7NM+, C9H8N+, M+, C2H3NO2M+, CO2M+, C10H11N2M+, C10H9NOM+. Formation of C2H4NO2M+• and C9H7NM+ cations suggests that the metal interacts with both the backbone and aromatic side chain, thus implicating π-interactions for all M. CID of [Trp+M]+ resulted in: loss of metal cation (for M = Cs and K); successive loss of NH3 and CO as the dominant channel for M = Na, Li and Ag; formation of C2H3NO2M+. Preliminary DFT calculations were carried out on [Trp+Na]+ and [(Trp-H)+Na]+• which reveal that: the most stable conformation involves chelation by the backbone together with a \(\pi \)-interaction with the indole side chain; loss of H atom from \(\alpha \)-CH of the side chain is thermodynamically favoured over losses from other positions, with the resultant radical cation maintaining a (N, O, ring) chelated structure which is stabilized by conjugation.

Relaxation of NH(a1Δ, v = 1) in Collisions with H(2S): An Experimental and Theoretical Study

Collisions of electronically and vibrationally excited NH(a(1)Delta, v = 1) with H atoms were investigated by experimental, quantum mechanical (QM) wavepacket, and quasiclassical trajectory (QCT) methods. The NH(a(1)Delta, v = 1) total loss rate constant, corresponding to the sum of the NH vibrational relaxation, N((2)D)+H(2) formation, and electronic quenching to NH(X(3)Sigma(-)), was measured at room temperature. Most of the calculations were performed within the Born-Oppenheimer approximation, neglecting electronic quenching due to Renner-Teller coupling because QCT calculations showed that for the loss of NH(a(1)Delta, v = 1) the contribution of quenching is negligible. The QM study included Coriolis couplings, and the QCT study counted only trajectories ending close to a vibrational quantum level of the product diatom. The collisions are dominated by long-lived intermediate complexes, and QM probabilities and cross sections thus exhibit pronounced resonances. QM and QCT cross sections and rate coefficients of the various processes are in very good agreement. The measured rate constant is (9.1 +/- 3.3) x 10(-11) cm(3) s(-1), compared with (14.4 +/- 0.5) x 10(-11) and (15.6 +/- 1.6) x 10(-11) cm(3) s(-1), as obtained from QM and QCT calculations, respectively. The reason for the theoretical overestimation is unknown.

Adsorption of ammonia on graphene

We report on experimental studies ofNH3 adsorption/desorption on graphene surfaces. The study employsbottom-gated graphene field effect transistors supported onSi/SiO2 substrates.Detection of NH3 occurs through the shift of the source–drain resistance maximum (‘Dirac peak’) with the gatevoltage. The observed shift of the Dirac peak toward negative gate voltages in response toNH3 exposure is consistent with a small charge transfer (f∼0.068 ± 0.004 electrons per moleculeat pristine sites) from NH3 to graphene. The desorption kinetics involves a very rapid loss ofNH3 from the top surface and a much slower removal from the bottom surface at the interface with theSiO2 that we identify with a Fickian diffusion process.

Ammonia volatilization loss from surface applied livestock manure

Ammonia (NH3) emission from livestock manures used in agriculture reduces N uptake by crops and negatively impacts air quality. This laboratory study was conducted to evaluate NH3emission from different livestock manures applied to two soils: Candler fins sand (CFS; light-textured soil, pH 6.8 and field capacity soil water content of 70 g kg− 1) from Lake Alfred, Florida and Ogeechee loamy sand (OLS; medium-textured soil, pH 5.2 and field capacity soil water content of 140 g kg− 1) from Savannah, Georgia. Poultry litter (PL) collected from a poultry farm near Douglas, Georgia, and fresh solid separate of swine manure (SM) collected from a farm near Clinton, North Carolina were used. Each of the soil was weighed in 100 g sub samples and amended with either PL or SM at rates equivalent to either 0, 2.24, 5.60, 11.20, or 22.40 Mg ha− 1 in 1L Mason jars and incubated in the laboratory at field capacity soil water content for 19 days to monitor NH3 volatilization. Results indicated a greater NH3 loss from soils amended with SM compared to that with PL. The cumulative NH3volatilization loss over 19 days ranged from 4 to 27% and 14 to 32% of total N applied as PL and SM, respectively. Volatilization of NH3 was greater from light-textured CFS than that from medium-textured OLS. Volatilization loss increased with increasing rates of manure application. Ammonia volatilization was lower at night time than that during the day time. Differences in major factors such as soil water content, temperature, soil type and live stock manure type influenced the diurnal variation in volatilization loss of NH3 from soils. A significant portion (> 50%) of cumulative NH3 emission over 19 d occurred during the first 5–7 d following the application of livestock manures. Results of this study demonstrate that application of low rates of livestock manure (≤ 5.60 Mg ha− 1) is recommended to minimize NH3 emissions.

Removal of ammonium and phosphate from the supernatant of anaerobically digested waste activated sludge by chemical precipitation

The removal of ammonium ( NH 4 + ) and phosphate ( PO 4 3 - ) from supernatant of anaerobic digestion by magnesium ammonium phosphate (MAP) formation was studied. To be able to find out the loss of NH 4 + by its transformation to NH 3, rates of NH 4 + removal by aeration and by MAP formation combined with aeration were compared. NH 4 + removal by aeration was found to be insignificant. The kinetics of MAP formation was fast. The removal rate of NH 4 + and Mg 2+ was the smallest and the largest, respectively based on rate constants calculated. The removal of NH 4 + showed sensitivity to Mg 2+ and PO 4 3 - concentrations and controlled the purity of MAP precipitate. The removal of PO 4 3 - was found to be sensitive to mainly Mg 2+ ion. These results also indicated that as the supernatant solution became more saturated in terms of MAP forming ions, the effect of pH increase became insignificant in the removal of ions from the solution.

Forest Floor Composition and Ammonia Loss from Urea in a Loblolly Pine Plantation

Surface application of urea to pine forests may lead to ammonia (NH3) volatilization, which can reduce forest production. The objective of this study was to characterize urea reactions with the forest soil and to determine how various forest floor components interact with weather to affect NH3 loss. Three field studies were performed in a midrotation loblolly pine (Pinus taeda L.) plantation with up to three treatments in each study, where NH3 volatilization chambers were fertilized with 200 kg N ha−1 that contained either (i) intact forest floor, (ii) forest floor removed by hand raking, or (iii) forest floor burned. In a complementary laboratory study, NH3 loss was evaluated from cores comprised of: (i) mineral soil only, (ii) mineral soil + humus layer, (iii) mineral soil + humus + old needles, and (iv) mineral soil + humus + old needles + new needles. Loss of NH3 in the field was generally greatest when urea was applied to a mineral soil with no forest floor, resulting in a loss of 53 and 59% of the applied N in two 29‐d studies. Loss of NH3 was intermediate from a complete forest floor (11 and 35% loss), and rates of loss appeared to be most affected by relative humidity. Losses were least from a recently burned forest floor (6 and 7% loss), due partly to slower urea hydrolysis. Loss of NH3 in the laboratory study was also greater from the bare soil than from the complete forest floor. Retention of NH4+ in the soil layers was related to the soil pH buffering capacity below pH 7. Because the humus layer was shown to have a large pH buffering capacity to retain NH4+, these results suggest forest management that enhances humus formation should increase NH4+ sorption and decrease NH3 volatilization.

Use of diagnostic neutral losses for structural information on unknown aromatic metabolites: an experimental and theoretical study

This work presents the use of neutral losses (NL) for the identification of compounds related to the metabolism of tyrosine. The mass spectra of all the studied compounds, recorded at several collision energies, are compared. The fragmentation mechanism of protonated molecules, MH(+), is explained by combining collision-induced dissociation (CID) mass spectra and density functional theory (DFT) calculations. The results show that the first fragmentation is the elimination from MH(+) of a neutral molecule including a functional group of the linear chain. Three primary neutral losses are observed: 17 u (NH(3)), 18 u (H(2)O) and 46 u (H(2)O+CO) characterizing amino, hydroxyl and carboxylic functions on the linear chain. The presence and abundance of ions corresponding to these losses are dependent on (i) the position of the functional group on the linear chain, (ii) the initial localisation of the protonating hydrogen, and (iii) the substitution of the aromatic ring. For compounds including a functional group on the benzylic carbon atom, the investigation of the other functions requires the knowledge of secondary fragmentations. Among these secondary fragmentations we have retained the loss of NH(3) from [MH-18u](+) and the loss of ketene from [MH-17u](+). Experimentally these fragmentations are detected using losses of 35 u and 59/73 u. In other words, NL35 identifies hydroxy and amino compounds and NL 46 and/or NL59/73 identify carboxylic acids. The search for characteristic neutral losses is used for the analysis of compounds in a mixture and the analysis of biological fluid. We show that selective search of several neutral losses allows also the unambiguous differentiation of isomers and gives the opportunity to identify compounds in biological fluids.

Determination of the Rate Constant for the NH2(X2B1) + NH2(X2B1) Reaction at Low Pressure and 293 K

The rate constant for the reaction NH(2)(X(2)B(1)) + NH(2)(X(2)B(1)) --> products was measured in CF(4), N(2) and Ar carrier gases at 293 +/- 2 K over a pressure range from 2 to 10 Torr. The NH(2) radical was produced by the 193 nm photolysis of NH(3) dilute in the carrier gas. Both the loss of NH(3) and its subsequent recovery and the production of NH(2) and subsequent reaction were monitored simultaneously following the photolysis laser pulse. Both species were detected using quantitative time-resolved high-resolution absorption spectroscopy. The NH(3) molecule was monitored in the NIR using a rotation transition of the nu(1) + nu(3) first combination band near 1500 nm, and the NH(2) radical was monitored using the (1)2(21) <-- (1)3(31) rotational transition of the (0,7,0)A(2)A(1) <-- (0,0,0) X(2)B(1) band near 675 nm. The low-pressure rate constant showed a linear dependence on pressure. The slope of the pressure dependence was dominated by a recombination rate constant for NH(2) + NH(2) given by (8.0 +/- 0.5) x 10(-29), (5.7 +/- 0.7) x 10(-29), and (3.9 +/- 0.4) x 10(-29) cm(6) molecule(-2) s(-1) in CF(4), N(2), and Ar bath gases, respectively, where the uncertainties are +/-2sigma in the scatter of the measurements. The average of the three independent measurements of the sum of the disproportionation rate constants (the zero pressure rate constant) was (3.4 +/- 6) x 10(-13) cm(3) molecule(-1) s(-1), where the uncertainty is +/-2sigma in the scatter of the measurements.

Ni+Reactions with Aminoacrylonitrile, A Species of Potential Astrochemical Relevance

The reaction of aminoacrylonitrile, a species of astrochemical interest, with Ni(+)((2)D(5/2)) was investigated by means of mass spectrometry techniques and density functional theory calculations. The dominant fragmentations in the MIKE spectrum correspond to the loss of [C2,N,H3], HCN, and NH3, the loss of H2 being very minor. The structure and bonding of the different aminoacrylonitrile-Ni(+) complexes were investigated at the B3LYP/6-311G(d,p) level of theory. The same approach was employed in our survey of the corresponding potential energy surface. This survey indicates that the [C2,N,H3] neutral product can be formed either as ketenimine (CH2CNH) or acetonitrile. The formation of the latter is significantly more exothermic but involves slightly higher activation barriers; so very likely, both isomers are produced along the reaction process. The lost of HNC is not competitive with the loss of HCN, because when the former is formed the products lie higher in energy and the corresponding mechanisms involve energy barriers above the entrance channel. The loss of NH3 is associated with the formation of a complex between cyanoacetylene, HCCCN, which is very abundant in the interstellar media, and Ni(+).