title: Mechanism of atmospheric CO2 fixation in the cavities of a dinuclear cryptate.
abstract: Using density functional theory (DFT) methods, we have investigated two possible mechanisms for atmospheric CO(2) fixation in the cavity of the dinuclear zinc(II) octa-azacryptate, and the subsequent reaction with methanol whereby this latter reaction transforms the (essentially) chemically inert CO(2) into useful products. The first mechanism (I) was proposed by Chen et al. [Chem.-Asian J. 2007, 2, 710], and involves the attachment of one CO(2) molecule onto the hydroxyl-cryptate form, resulting in the formation of a bicarbonate-cryptate species and subsequent reaction with one methanol molecule. In addition, we suggest another mechanism that is initiated via the attachment of a methanol molecule onto one of the Zn-centers, yielding a methoxy-cryptate species. The product is used to activate a CO(2) molecule and generate a methoxycarbonate-cryptate. The energy profiles of both mechanisms were determined, and we conclude that, while both mechanisms are energetically feasible, free energy profiles suggest that the scheme proposed by Chen et al. is most likely.
authors.affiliation: The SFI Strategic Research Cluster in Solar Energy Conversion, School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: Morad M
authors.initials: MM
authors.lastname: El-Hendawy
authors.forename: Niall J
authors.initials: NJ
authors.lastname: English
authors.forename: Damian A
authors.initials: DA
authors.lastname: Mooney
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D001639:Bicarbonates / Q000737:chemistry; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000737:chemistry* / Q000302:isolation & purification*; D043844:Crown Ethers / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D011789:Quantum Theory; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry
chemical_list: D001639:Bicarbonates; D043844:Crown Ethers; D011522:Protons; D014867:Water; D002245:Carbon Dioxide; D015032:Zinc; D000432:Methanol