ESI MS/MS Study of Calix[4]arene Derivatives and their Metal Complexes

The peptidocalixarenes 1-3 bearing tryptophan, phenylglycine and leucil units at the lower rim and their complexes with alkali-metal (Li+, Na+, K+, Rb+, Cs+) and selected lanthanide cations (La3+, Ce3+, EU3+, Yb3+) were analyzed by ESI MS. The influences of the solvent (acetonitrile, methanol, addition of formic acid or sodium acetate) and the calixarene:cation molar ratio on signal intensities were investigated. Comprehensive MS/MS analyses were performed of all singly and doubly charged ions of 1-3 and their complexes, and fragmentation pathways were proposed. An inductive cleavage was observed during dissociation of protonated ions, while the presence of alkali-metal or lanthanide cations caused homolytic cleavage and formation of radical cations. The results of MS analysis were in accordance with those obtained by other techniques (spectrophotometric, potentiometric, and conductometric titrations). The MS/MS experiments could be used as fast and sensitive method for prediction of relative stabilities of calixarene complexes with metal ions. (doi: 10.5562/cca2125)