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Generation and Dissociation of RCOOCaCl 2 − and other Carboxylate‐Substituted Superhalogens: CO 2 Capture and Implications for Structure Analysis
Author(s) -
RodríguezBlanco Giovanny,
Jobst Karl J.,
Luider Theo M.,
Terlouw Johan K.,
Burgers Peter C.
Publication year - 2013
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201300161
Subject(s) - carboxylate , chemistry , dissociation (chemistry) , mass spectrometry , collision induced dissociation , ion , molecule , crystallography , electrospray ionization , mass spectrum , analytical chemistry (journal) , tandem mass spectrometry , stereochemistry , organic chemistry , chromatography
Carboxylate‐substituted superhalogens of the type RCOOMX 2 − (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 RCOOCaCl 2 − ‐type ions. In the ion trap these appear to react readily with residual water to yield HOCaCl 2 − as the hydrolysis product. In the absence of water, a collision‐induced McLafferty‐type rearrangement takes over to produce HCaCl 2 − with the expulsion of an olefin and CO 2 . A brief computational analysis using the CBS‐QB3 model chemistry provides a satisfactory rationale for these observations. If complexed with MX 2 (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 RCOOMX 2 − also produce the intriguing species [CO 2 ]MX 2 −. . These have been characterised by CID experiments, and theory indicates that they may be viewed as a CO 2 molecule captured by the salt anion MX 2 −. . Finally, it is shown that the CID spectra of RCOOCaCl 2 − 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.