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Structural Examination of Non-Covalent Supramolecular Architectures by ESI-MS

presented by

Christoph Schalley
The Scripps Research Institute

April 14, 1999

The Scripps Research Institute, W.M. Keck Foundation Amphitheater


Background:

Christoph Schalley was born in 1968 in Krefeld, Germany. After studying chemistry in Freiburg and Berlin, he joined the mass spectrometry lab of Prof. Dr. Helmut Schwarz at the Technical University in Berlin in 1993. Here, Christoph worked on the metal-mediated activation of CC and CH bonds, on the development of neutralization-reionization mass spectrometric methods, and on combined experimental and theoretical studies of spin-forbidden reactions. In 1997, he finished his Ph.D. thesis on the gas-phase ion chemistry of peroxides. Currently, he is working as a postdoctoral fellow of the Deutsche Akademie der Naturforscher Leopoldina in the group of Prof. Julius Rebek at the Scripps Research Institute. Although he planned to focus on synthetic supramolecular chemistry, he got stuck with mass spectrometry? his old love? and is now studying non-covalent complexes.

Abstract:

Hydrogen-bonded, self-assembling cap-sules derived from the reversible assembly of self-complementary monomers are characterized by electrospray ionization mass spectrometry. Ion labeling is achieved through the encapsulation of ammonium ions as guest molecules. Evidence for the capsular gas-phase ion structure of these host-guest complexes is provided by a three-step mass spectrometric approach: (i) The correct composition of the aggregates is determined from isotope pattern analysis and the encapsulation of labeled guest ions. (ii) Heterodimer/heterotetramer formation and destruction of the capsules by competitive solvents provide evidence for the hydrogen-bonded nature of the ions. (iii) Collision (source-CID) experiments and the observation of a distinct selectivity for the encapsulation of ammonium ions with sizes and shapes congruent with the capsule cavity strongly support the assignment of a capsular structure with an ionic guest inside the cavity. This protocol is applied to capsules with different hydrogen-bonding patterns. Larger dumbbell-shaped aggregates containing two and three charged guests are observed. Although a quantitative analysis of the mass spectrometric data is not feasible, the results qualitatively parallel previous findings from NMR experiments with neutral and ionic guests in solution.

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