Mass spectral measurements of complex ions MX' formed from a bicyclic-molecule (M), which comprises a macroheterocyclic crown ether and a plyoxyethylene chain linked with two thioamido groups on a diaza-3ncrown-n-ply-ether, together with an X ' ion (X=H, Li or K) are discussed. The use of fast-atodion bombardment mass spectra and particularly collision-induced dissociation and mass-analysed ion kinetic energy spectra enabled an estimate of the site of the localization of X' and the relative bond strength inside the collisionally-activated host-guest complex ion in the gas phase to be made.
Bicyclic crown ethers, or cryptands,' are known to form complexes in solution with alkali cations more easily than naturally occurring antibiotics. They also act as good hosts for some anions and neutral guests? For both monocyclic and bicyclic crown ethers it was found that the formation of host-guest complexes with ions significantly changes their secondary ~tructure.~ In contrast to the case of monocyclic crown ethers and related compounds,4 the mass spectra of macropolycyclic nitrogen-containing compounds have been described in only a few papers.'~~ It has been found that electron-impact mass spectra of cryptands can be analysed in terms of simple losses of neutral molecules? and that the main fragmentation processes occur via the migration of one or two hydrogen atoms. Similar fragmentation routes from the MH' ions of crown ethers which contain two thiourea linkages have been found!
The aim of this study was to examine the ions appearing in the gas phase in fast-atom bombardment (FAB) ionization of the compounds 1-6 (see Scheme 1) and their mixtures with LiOH and KOH using 3-nitrobenzyl alcohol (NBA) as an ionization-supporting matrix. The appearance of ions such as MLi' or MK', besides MH' ions which are formed in all instances, shows that the complexation of compounds 1-6 with Li' or K' ions can, at least partially, take place in the matrices used in these experiments. It is not intended to discuss several feasible reaction processes taking place in the matrix during FAB ionization. However, the mass spectra do show some further structurally important ions which originate not only as (ion) fragmentation products of the MH' ions, but also from the complexes existing in the matrix.
EXPERIMENTAL
Complex ions MX' (X=H, Li or K) were generated by fastatomhon bombardment ionization' of compounds 1-6 dissolved in NBA. An aliquot of 1 pmol of the appropriate base, LiOH or KOH, was added to the matrix for generation of MLi' or MK' ions. A cesium ion gun was operated to give Cs' ions of 25 keV energy. Collision-induced dissociation (CID) experiments were carried out using an AutoSpecQ tandem mass spectrometer (Fisons, VG-Analytical, Manchester, UK) with a collision cell placed between the magnetic and second electric sector. The CID massanalysed ion kinetic energy (MIKE) spectra' were obtained by scanning the voltage of the second electric sector. Nitrogen was used as collision gas at a pressure sufficient to cause a 40% attenuation of the main beam. Compounds 1-8 (Scheme 1) were obtained from the A.