An electrospray ionization tandem mass spectrometric study of p ‐ tert ‐butylcalix[6]arene complexation with ammonium hydroxide, and ammonium and sodium ions

The formation of complexes involving p ‐ tert ‐butylcalix[6]arene with neutral and charged species has been investigated by tandem mass spectrometry combined with electrospray ionization. Complexes of p ‐ tert ‐butylcalix[6]arene with NH   4 +ions were observed in the ratios 1:1, 2:1, and 3:1, together with the complexes of p ‐ tert ‐butylcalix[6]arene with NH 4 OH and Na + ions in the ratios 1:1:1, 2:1:1, and 3:1:1. A single 1:1 complex of p ‐ tert ‐butylcalix[6]arene with Na + ions was observed. In addition, a doubly charged complex of p ‐ tert ‐butylcalix[6]arene with NH 4 OH, Na + , and NH   4 +ions in the ratio 6:1:1:1 was observed. The identity of each complex was determined by mass analysis of product ions formed by the application of a declustering potential over the range 20–220 V and by observation of product ion mass spectra wherein the collision energy was varied from 5 to 50 eV. Fragmentation of the complexes is characterized by the facile loss of the ammonia molecule, sodium and ammonium ions, loss of neutral p ‐ tert ‐butylcalix[6]arene, and successive neutral losses of C 4 H 8 from the six tert ‐butyl groups in each p ‐ tert ‐butylcalix[6]arene molecule. Copyright © 2008 John Wiley & Sons, Ltd.