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One metal is enough: a nickel complex reduces nitrate anions to nitrogen gas.

ABSTRACT: A stepwise reduction sequence from nitrate to dinitrogen gas at a single nickel center was discovered. A PNP nickel scaffold (PNP^- = N[2-P ⁱ Pr₂-4-Me-C₆H₃]₂) emerged as a universal platform for the deoxygenation of NO _x substrates. In these reactions carbon monoxide acts as the oxygen acceptor and forms CO₂ to provide the necessary chemical driving force. Whereas the first two oxygens are removed from the Ni-nitrate and Ni-nitrite complexes with CO, the deoxygenation of NO requires a disproportionation reaction with another NO molecule to form NO₂ and N₂O. The final deoxygenation of nitrous oxide is accomplished by the Ni-NO complex and generates N₂ and Ni-NO₂ in a relatively slow, but clean reaction. This sequence of reactions is the first example of the complete denitrification of nitrate at a single metal-site and suggests a new paradigm of connecting CO and NO _x as an effective reaction pair for NO _x removal.

SUBMITTER: Gwak J

PROVIDER: S-EPMC6510316 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

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One metal is enough: a nickel complex reduces nitrate anions to nitrogen gas.

Gwak Jinseong J Ahn Seihwan S Baik Mu-Hyun MH Lee Yunho Y

Chemical science 20190409 18

A stepwise reduction sequence from nitrate to dinitrogen gas at a single nickel center was discovered. A PNP nickel scaffold (PNP- = N[2-P i Pr2-4-Me-C6H3]2) emerged as a universal platform for the deoxygenation of NO x substrates. In these reactions carbon monoxide acts as the oxygen acceptor and forms CO2 to provide the necessary chemical driving force. Whereas the first two oxygens are remove ...[more]

PMID: 31160953

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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.

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One metal is enough: a nickel complex reduces nitrate anions to nitrogen gas.

Publications

One metal is enough: a nickel complex reduces nitrate anions to nitrogen gas.

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