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Generation and Dissociation of RCOOCaCl2 and other Carboxylate-Substituted Superhalogens: CO2 Capture and Implications for Structure Analysis

Authors

  • Giovanny Rodríguez-Blanco,

    1. Department of Neurology, Laboratory of Neuro-Oncology, Erasmus Medical Center, Rotterdam (The Netherlands), Fax: (+31) 10-7044365
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  • Dr. Karl J. Jobst,

    1. Ontario Ministry of the Environment, 125 Resources Rd, Toronto, ON, M9P 3V6 (Canada)
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  • Dr. Theo M. Luider,

    1. Department of Neurology, Laboratory of Neuro-Oncology, Erasmus Medical Center, Rotterdam (The Netherlands), Fax: (+31) 10-7044365
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  • Prof. Johan K. Terlouw,

    1. Department of Chemistry and Chemical Biology, McMaster University, 1280 Main St. W., Hamilton, ON, L8S 4M1 (Canada)
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  • Dr. Peter C. Burgers

    Corresponding author
    1. Department of Neurology, Laboratory of Neuro-Oncology, Erasmus Medical Center, Rotterdam (The Netherlands), Fax: (+31) 10-7044365
    • Department of Neurology, Laboratory of Neuro-Oncology, Erasmus Medical Center, Rotterdam (The Netherlands), Fax: (+31) 10-7044365
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Abstract

Carboxylate-substituted superhalogens of the type RCOOMX2 (M=Mg, Ca, Sr, Ba, Mn, Co, Ni, Zn; X=Cl, Br) are easily accessible in the gas phase by electrospray ionisation. Their collision-induced dissociation (CID) characteristics have been probed by using ion-trap and triple-quadrupole mass analysers with particular emphasis on the behaviour of RCOOCaCl2-type ions. In the ion trap these appear to react readily with residual water to yield HOCaCl2 as the hydrolysis product. In the absence of water, a collision-induced McLafferty-type rearrangement takes over to produce HCaCl2 with the expulsion of an olefin and CO2. A brief computational analysis using the CBS-QB3 model chemistry provides a satisfactory rationale for these observations. If complexed with MX2 (M=Mg, Ca, Sr, Ba), long-chain unsaturated aliphatic carboxylate anions undergo various backbone cleavages upon collision. These lead to structure-diagnostic olefin losses because the position of the double bonds remains intact. Such cleavages are absent in the bare ion RCOO. The long-chain ions RCOOMX2 also produce the intriguing species [CO2]MX2−.. These have been characterised by CID experiments, and theory indicates that they may be viewed as a CO2 molecule captured by the salt anion MX2−.. Finally, it is shown that the CID spectra of RCOOCaCl2 ions derived from all-trans retinoic acid, a compound of current interest in biochemistry and medicine, show a unique structure-diagnostic dissociation that may greatly aid its qualitative and quantitative analysis.

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