Dataset Information

Deprotonated N-(2,4-Dinitrophenyl)amino Acids Undergo Cyclization in Solution and the Gas Phase.

ABSTRACT: The collisionally activated mass spectral fragmentations of N-(2,4-dinitrophenyl)alanine and phenylalanine [M - H](-) may be gas-phase analogs of the base-catalyzed cyclization of N-(2,4-dinitrophenyl)amino acids in aqueous dioxane. This latter reaction is one source of the 2-substituted 5-nitro-1H-benzimidazole-3-oxides, which are antibacterial agents. The fragmentation of both compounds, established by tandem mass spectrometric experiments and supported by molecular modeling using DFT methods, indicate that the [M - H](-) ions dissociate via sequential eliminations of CO(2) and H(2)O to produce deprotonated benzimidazole-N-oxide derivatives. The gas-phase cyclization reactions are analogous to the base-catalyzed cyclization in solution, except that in the latter case, the reactant must be a dianion for the reaction to occur on a reasonable time scale. The cyclization of N-(2-nitrophenyl)phenylalanine, which has one less nitro group, requires a stronger base for the cyclization than the compound with a second nitro group at the 4-position. Following losses of CO(2) and H(2)O are expulsions of both neutral molecules and free radicals, the latter being examples of violations of the even-electron ion rule.

SUBMITTER: George M

PROVIDER: S-EPMC3181136 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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Publications

Deprotonated N-(2,4-Dinitrophenyl)amino Acids Undergo Cyclization in Solution and the Gas Phase.

George M M Ramesh V V Srinivas R R Giblin Daryl D Gross Michael L ML

International journal of mass spectrometry 20110901 2-3

The collisionally activated mass spectral fragmentations of N-(2,4-dinitrophenyl)alanine and phenylalanine [M - H](-) may be gas-phase analogs of the base-catalyzed cyclization of N-(2,4-dinitrophenyl)amino acids in aqueous dioxane. This latter reaction is one source of the 2-substituted 5-nitro-1H-benzimidazole-3-oxides, which are antibacterial agents. The fragmentation of both compounds, established by tandem mass spectrometric experiments and supported by molecular modeling using DFT methods, ...[more]

PMID: 21966244

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Project description:Chelation complexes of the histidine-containing tripeptides HisAlaAla, AlaHisAla, and AlaAlaHis with Ni(II) and Cu(II) having a -1 net charge are characterized in the gas phase by infrared multiple-photon dissociation (IRMPD) spectroscopy and density functional theory calculations. We address the question of whether the gas-phase complexes carry over characteristics from the corresponding condensed-phase species. We focus particularly on three aspects of their structure: (i) square-planar chelation by the deprotonated amide nitrogens around the metal ion (low-spin for the Ni case), (ii) metal-ion coordination of the imidazole side chain nitrogen, and (iii) the exceptional preference for metal-ion chelation by peptides with His in the third position from the N-terminus, as in the amino terminal Cu and Ni (ATCUN) motif. We find that square-planar binding around the metal ion, involving bonds to both deprotonated backbone nitrogens, one of the carboxylate oxygens and the N-terminal nitrogen, is the dominant binding motif for all three isomers. In contrast to the condensed-phase behavior, the dominant mode of binding for all three isomers does not involve the imidazole side chain, which is instead placed outside the coordination zone. Only for the AlaAlaHis isomer, the imidazole-bound structure is also detected as a minority population, as identified from a distinctive short-wavelength IR absorption. The observation that this conformation exists only for AlaAlaHis correlates with condensed-phase behavior at neutral-to-basic pH, in the sense that the isomer with His in the third position is exceptionally disposed to metal ion chelation by four nitrogen atoms (4N) when compared with the other isomers. These results also emphasize the divergence between the conformational stabilities in the gas phase and in solution or crystalline environments: in the gas phase, direct metal binding of the imidazole is overall less favorable than the alternative of a remote imidazole that can act as an intramolecular H-bond donor enhancing the gas-phase stability.

Dataset Information

Deprotonated N-(2,4-Dinitrophenyl)amino Acids Undergo Cyclization in Solution and the Gas Phase.

Publications

Deprotonated N-(2,4-Dinitrophenyl)amino Acids Undergo Cyclization in Solution and the Gas Phase.

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