Loss Of HNCO Research Articles

Fragmentation and skeletal rearrangements of 2‐arylylamino‐5‐aryl‐1,3,4‐oxadiazoles and their noncovalent complexes with cobalt cation and cyclodextrin studied by mass spectrometry

Mass spectrometric fragmentation pathways of title compounds were studied by electron ionization (EI) and electrospray ionization (ESI) as methods of ion generation. To explain the observed complex skeletal rearrangements, tandem mass spectrometry, accurate mass measurement and isotope labeling (compounds containing one 13C atom in oxadiazole ring) were used. Loss of CO, N2 and H atoms under EI conditions led to the formation of 9,10-dihydroacridine-type ions, loss of NH3 under ESI conditions yielded the 4-phenylphthalazinone-type ions and the loss of HNCO under ESI conditions produced N-arylamino-benzonitrilium ions; however, this process can be affected by the electron-donor/electron-withdrawing properties of groups substituted at the phenyl rings. The ESI was used to study the complexes of the compounds with cobalt as well as with cyclodextrin. It was found that the compounds studied tend to form inclusion complexes with cyclodextrin of stoichiometry 1:1 and complexes of different stoichiometries with cobalt, although those of stoichiometry 6:1 and 4:1 are favored and the attachment of counter ion may stabilize the complexes 3:1 and 2:1.

Differentiation of Boc‐ α,β‐ and β,α‐peptides and a pair of diastereomeric β,α‐dipeptides by positive and negative ion electrospray tandem mass spectrometry (ESI‐MS/MS)

Positive and negative ion electrospray ionization (ESI) tandem mass spectral study of a new series of hybrid peptides, viz, BocN-alpha,beta-peptides and BocN-beta,alpha-peptides, synthesized from C-linked carbo-beta3-amino acids [Caa (S)] and L-Ala has been carried out. The alpha,beta-peptides have been differentiated from beta,alpha-peptides by the collision-induced dissociation (CID) of [M + H]+ and [M - H]- ions in positive and negative ion ESI-MS respectively. The fragment ion [M + H - C(CH3)3 + H]+ formed from [M + H]+ ions by the loss of 2-methyl-prop-2-ene in alpha,beta-peptides with L-Ala at the N-terminus is insignificant or totally absent for beta,alpha-peptides which have the Caa (S) at N-terminus. The fragment ion [M - H-C(CH3)3OH - HNCO]- formed from [M - H]- of beta,alpha-peptide acids is totally absent for alpha,beta-peptide acids. This has been attributed to the absence of the beta-methylene group in alpha,beta-peptides, and the participation of the beta-methylene group in the loss of HNCO in beta,alpha-peptide acids is confirmed by the deuteration experiments. The CID of [M + H-Boc + H]+ ions of these peptides also produce characteristic fragmentation. In the CID spectra of alpha,beta-peptides, the b(n)+ ions and the resulting y(n)+ ions occur at a mass difference of 243 and 71 Da corresponding to the successive losses of Caa and L-Ala, whereas a mass difference of 71 and 243 Da is observed for beta,alpha-peptides. In contrast to the CID of protonated peptides, the CID of [M - H]- ions of the alpha,beta- and beta,alpha-peptide acids do not give b(n)- ions and show abundant z(n) (-) ions. Further, a pair of diastereomeric dipeptide esters and acids have been distinguished by the CID of [M + H]+ ions. The loss of 2-methyl-prop-2-ene is more pronounced for Boc-NH-Caa(R)-D-Ala-OCH3 (21) and Boc-NH-Caa(R)-D-Ala-OH (23) with Caa (R) at the N-terminus, whereas it is totally absent for Boc-NH-Caa (S)-D-Ala-OCH3 (22) and Boc-NH-Caa(S)-D-Ala-OH (24) peptides, which have Caa (S) at the N-terminus. Thus, on the basis of our previous and present studies, we propose that the CID of [M + H]+ ions provides a simple and useful method for distinguishing the configuration of Caa (S or R) at the N-terminus of BocN-carbo beta,alpha- and beta,beta-dipeptides.

Thermal Conversion of Guanylurea Dicyanamide into Graphitic Carbon Nitride via Prototype CNxPrecursors

Guanylurea dicyanamide, [(H2N)C(O)NHC(NH2)2][N(C⋮N)2], has been synthesized by ion exchange reaction in aqueous solution and structurally characterized by single-crystal X-ray diffraction (C2/c, a = 2249.0(5) pm, b = 483.9(1) pm, c = 1382.4(3) pm, β = 99.49(3)°, V = 1483.8(5) × 106 pm3, T = 130 K). The thermal behavior of the molecular salt has been studied by thermal analysis, temperature-programmed X-ray powder diffraction, FTIR spectroscopy, and mass spectrometry between room temperature and 823 K. The results were interpreted on a molecular level in terms of a sequence of thermally induced addition, cyclization, and elimination reactions. As a consequence, melamine (2,4,6-triamino-1,3,5-triazine) is formed with concomitant loss of HNCO. Further condensation of melamine yields the prototypic CNx precursor melem (2,6,10-triamino-s-heptazine, C6N7(NH2)3), which alongside varying amounts of directly formed CNxHy material transforms into layered CNxHy phases without significant integration of oxygen into the core framework owing to the evaporation of HNCO. Thus, further evidence can be added to melamine and its condensation product melem acting as “key intermediates” in the synthetic pathway toward graphitic CNxHy materials, whose exact constitution is still a point at issue. Due to the characteristic formation process and hydrogen content a close relationship with the polymer melon is evident. In particular, the thermal transformation of guanylurea dicyanamide clearly demonstrates that the formation of volatile compounds such as HNCO during thermal decomposition may render a large variety of previously not considered molecular compounds suitable CNx precursors despite the presence of oxygen in the starting material.

Mass spectrometric decomposition of N-arylbenzonitrilium ions

In order to determine the structure of fragment ions formed as a result of the HNCO neutral loss from protonated 1,3,4-oxadiazoles, the following compounds have been studied by electrospray ionisation (ESI) mass spectrometry: 2-(4′-methoxyphenyl)-5-phenyl-1,3,4-oxadiazole ( 1), N-(4′-methoxyphenyl)-benzamide ( 2) and 4-methoxy- N-phenyl-benzamide ( 3). Collision-induced dissociation mass spectra taken for fragment ions derived from protonated 1– 3, namely [ 1 + H HNCO] +, [ 2 + H H 2O] + ( N-4′-methoxyphenyl-benzonitrilium ion, A) and [ 3 + H H 2O] + (4-methoxy- N-phenyl-benzonitrilium ion, B) have shown that upon HNCO loss from protonated 1 formation of ion B is favored. As shown by accurate mass measurement, the methyl and CO groups are lost in the next fragmentation step.

Reactions of Urea with Cu+in the Gas Phase: An Experimental and Theoretical Study

The gas-phase reactions between Cu+ and urea have been investigated by means of mass spectrometry techniques. The primary products formed in the ion source correspond to [urea−Cu]+, [(urea)2−Cu]+, and [Cu+,C,N2,H2] complexes. The MIKE spectrum of [urea−Cu]+ complex shows several spontaneous losses, namely, NH3 and HNCO. A very weak peak corresponding to the loss of H2O is also observed, as well as a minor fragmentation of the adduct ion to yield Cu+. The structures and bonding characteristics of the different complexes involved in the urea−Cu+ potential energy surface (PES) were investigated using density functional theory (DFT) at the B3LYP level of theory and a valence triple-ζ. Attachment of Cu+ takes place preferentially at the carbonyl oxygen atom, while attachment at the amino group is 12.4 kcal/mol less exothermic. Insertion of the metal cation into the C−N bonds of the neutral is predicted to be slightly exothermic, in contrast with what was found for formamide and guanidine. The estimated urea−Cu+ binding energy (62.3 kcal/mol) is 6.0 kcal/mol greater than that of formamide. The exploration of the PES indicates that there are several reaction paths leading to the loss of ammonia yielding as product ions HNCOCu+ complexes where the metal cation is attached either to the oxygen or the nitrogen of the HNCO species. Also several reaction paths can be envisaged for the loss of HNCO, in which bisligated [HNCO−Cu−NH3]+ and [OC(NH)−Cu−NH3]+ complexes play an important role.

Pyrolysis of valine and leucine at 500°C: identification of less-volatile products using gas chromatography-Fourier transform infrared spectroscopy-mass spectrometry

The products of valine and leucine pyrolysis at 500°C under nitrogen atmosphere have been analyzed using the methods of high-performance liquid chromatography and gas-chromatography-Fourier transform infrared spectroscopy-mass spectrometry with auxiliary computer simulation of IR spectra. The amino acids do not decompose completely under the above conditions, and are recovered by 10% (Val) and 2% (Leu). Among their pyrolysis products several carboxylic acids, primary and secondary amides have been identified, as well as a number of less-volatile compounds resulting from amino acid intermolecular condensation. Major condensation pathway is the formation of cyclic dipeptides piperazine-2,5-diones with the yields of 5% for Val and 3.5% for Leu, which can further undergo thermal dehydrogenation, dealkylation, rearrangement into hydantoins, loss of HNCO, etc. The formation of small amounts of bicyclic amidines hexahydroimidazo[1,2-a]pyrazine-3,6-diones via amino acid condensation has been also observed. Pathways of their thermal decomposition also include dehydrogenation, dealkylation and loss of HNCO.

Energetics of the cyclo(Pro-Gly) cation fragmentation: a mass spectrometric study and theoretical calculations

The energetics of HNCO elimination from the cyclo(Pro–Gly) radical cation was studied by electron ionization tandem mass spectrometry, photoionization mass spectrometry and RRKM/QET modeling. The heat of formation and vibrational frequencies of the reactant were calculated by density functional theory (DFT). Homodesmotic reactions involving cyclo(Pro–Gly) were used to derive its heat of formation at 0 K as -72.0±3.0 kcal mol-1 (1 kcal=4.184 kJ). Vibrational frequencies were calculated at the B3LYP/6–31G(d) level. The critical energy for HNCO loss was determined from the experiment, by modeling, to be 1.2±0.1 eV. The heat of formation of the cyclo(Pro–Gly) radical cation and of the product ion C6H9NO+• at 0 K were determined to be 130.9±3.0 and ⩽182.8±5.0 kcal mol-1, respectively. The salient features of the potential energy profile along the reaction coordinate were probed by DFT calculations. © 1998 John Wiley & Sons, Ltd.

Role of different 5‐substituents on the mass spectrometric behaviour of uracil

AbstractThe influence of different 5‐substituents on the mass spectrometric behaviour of uracil was systematically studied by means of mass‐analysed ion kinetic energy spectrometry. By applying this technique to the molecular ions and the major primary product ions formed by loss of HNCO, the electron impact‐induced fragmentation patterns of a series of substituted uracils could be elucidated. In addition to the common decomposition processes, distinctive fragmentation routes were identified for some compounds, and a rationale for the observed behaviour is given based on the electronic properties of the substituents.

A screening method for the rapid detection of barbiturates in serum by means of tandem mass spectrometry.

A mass spectrometric screening method for barbiturates in serum was developed. Under electron impact conditions barbiturates fragment by loss of HNCO. A 'constant neutral loss' scan of 43 u provides, therefore, an indication of the presence of members of this toxicologically relevant class of compounds. Subsequent identification is possible either by 'daughter' or by 'parent ion' scans. The detection limit for propallylonal, buto- and phenobarbital was determined as better than 1 micrograms ml-1 serum.

Bifunctional even‐electron ions. V. Fragmentation behaviour of aliphatic hydroxonium ions containing an additional cyano group

AbstractThe fragmentation behaviour of a series of bifunctional hydroxonium ions C2H5C(\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + {\rm H} $\end{document})(CH2)n‐CN (n = 0‐6), a n, has been investigated by electron impact mass spectrometry. The type of interaction‐induced reactions depend strongly on the chain distance between the oxonium and the cyano moiety, but the initial step in all cases is proton transfer from the hydroxy to the cyano group. The following selective primary fragmentations have been found: loss of C  NH (HCN) from a 0, loss of CH2,  C  NH from a 1, loss of HNCO from a 2‐a 4, loss of CH3CHC  O from a 4‐a 6, and loss of CO from a3. In addition, loss of NH3 and H2O, respectively, are observed as general fragmentations, except for the lowest homologues (a 0 and a 1). Mechanistic pathways of the selective reactions have been deduced with the aid of metastable ion spectra, high resolution, deuterium labelling and comparison of metastable ion spectra with those of independently generated ions.

Mass Spectrometric Investigations of Phenylacetic Acid Derivatives, III: Fragmentations of meta‐ and para‐substituted Phenylacetamides after Electron Impact

AbstractThe electron impact induced fragmentations of m‐ and p‐substituted phenylacetamides and N,N‐dimethyl‐phenylacetamides 1–14 were investigated and compared with the o‐analogues. All m‐ and p‐substituted amides yield molecular ions with high relative intensities which do not lose their meta‐ and para‐substituents. Loss of HNCO from M+˙ is dominant in the prim, amides, whilst for the tert. amides the classical benzyl cleavage is the most favourable fragmentation pathway.

The Behavior of 1-Phenyl-2-benzimidazolinethione and 1-Phenyl-2-benzimidazolinone upon Electron Impact and Pyrolysis

The mass spectra of 1-phenyl-2-benzimidazolinethione (3) and 1-phenyl-2-benzimidazolinone (4) have been compared with their pyrolysis products and similarities have been found. In the 70 eV mass spectrum of 3, the base peak results from the loss of H•; at low ionizing voltages, this path and a competing path, loss of S, are the only ones which remain. At 650° in a stream of N2, 1-phenylbenzimidazole (8, 20%) formed from the loss of S and benzimidazo-[2,1-b]benzothiazole (5, 11%) formed by loss of H2. The major fragmentation paths in the mass spectrum of 4 are loss of CHO• and NCO•. At 950°, phenazine (6, 35%) formed by loss of CH2O, and carbazole (7, 14%) formed by loss of HNCO. In each pyrolysis, 65–70% of the starting material was recovered or accounted for.

The mass spectrometry of semicarbazones of αβ-unsaturated aldehydes and ketones, and of some related compounds

The mass spectra of a number of semicarbazones of αβ-unsaturated aldehydes and ketones, and pyrazolines have been determined. The main modes of fragmentation of the semicarbazones involving initial loss of HNCO, NH2·CO·NH2, or NH2·CO·NH· have been distinguished, and their importance related to variation in chemical structure.