JOURNAL OF MASS SPECTROMETRY J. Mass Spectrom. 2008; 43: 242–250 Published online 16 October 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jms.1296 Mass spectrometric study of the ionized C 60 : (g-Cyclodextrin) 2 inclusion complex by collision induced dissociation Jean-Fran ¸ cois Greisch, 1* Sam Kyritsoglou, 1 Bernard Leyh 2 and Edwin De Pauw 1 1 University of Li ` ege, Mass Spectrometry Laboratory, B4000 Li ` ege, Belgium 2 University of Li ` ege, Molecular Dynamics Laboratory, B4000 Li ` ege, Belgium Received 19 January 2007; Accepted 08 August 2007 The water soluble inclusion complex [C 60 :.g-cyclodextrin) 2 ] has been characterized using electrospray tandem mass spectrometry and collision induced dissociation. [C 60 :.g-cyclodextrin) 2 ] ions were detected in the gas phase as doubly deprotonated, doubly protonated and doubly sodiated ions. The absence of monocharged complex ions following electronebulization is a likely consequence of the dimeric nature and structural symmetry of the inclusion complex. The collision induced dissociation of positive ions led exclusively to the observation of the protonated and sodiated cyclodextrin ions as well as their fragments. In negative ion mode the closed shell anion C 60 H - was the dominant fragment detected at low collision energies whereas at higher collision energies the signal corresponding to deprotonated cyclodextrin units becomes significant. Since C 60 2- has been reported to have a nonnegligible basicity compared to C 60 and C 60 - , it is likely that the proton transfer involved in the formation of the C 60 H - anion occurs following transfer of the two electrons from the deprotonated g-cyclodextrins to the fullerene. Finally, the charge state of the inclusion complex ions is also shown to affect the interaction strengths between its subunits. The relative stabilities of the three ionic species studied in gas phase following electronebulization are as follows: [C 60 :(g-cyclodextrin) 2 + 2H] 2+ < [C 60 :(g-cyclodextrin) 2 - 2H] 2- < [C 60 :(g-cyclodextrin) 2 + 2Na] 2+ . Copyright  2007 John Wiley & Sons, Ltd. KEYWORDS: fullerene; cyclodextrin; inclusion complex; dissociation; charge transfer; mass spectrometry INTRODUCTION The negligible solubility of the [60] fullerene in polar solu- tions hinders its use in many applications. Among the strategies developed to increase water solubility of fullerenes is the inclusion of C 60 within water-soluble hosts such as cyclodextrins. 1–14 Two  -cyclodextrins ( -CyD) have been shown to form a water soluble inclusion complex with a single C 60 . The  -CyD is a macrocyclic oligosaccharide con- sisting of eight D-glucose residues, which are connected by ˛-1,4-linkage (Fig. 1). The highly flexible D-glucoses are stabilized by intramolecular hydrogen-bonds and form a cavity. This cavity, approximately of truncated conical- shape in aqueous solution as well as in solid state, is surrounded by C–H and glycosidic C–O bonds and is thus hydrophobic. 15 – 17 The formation and stability of cyclodex- trin inclusion complexes with guests of similar volume but of different shape usually results from several attractive forces whose effective contribution depends on the nature of host and guest. These forces are essentially the following: hydrophobic interactions, electrostatic interactions, hydro- gen bonding, and van der Waals interactions. 18 For guests L Correspondence to: Jean-Fran¸ cois Greisch, University of Li` ege, Mass Spectrometry Laboratory, Bat B6c, B4000 Li` ege, Belgium. E-mail: jfgreisch@ulg.ac.be uncharged and only sparingly soluble in water such as fullerenes the hydrophobic interactions significantly con- tribute to the inclusion process. The formation of an inclusion complex of  -CyD with the apolar [60]fullerene was first reported by Anders- son et al. 1 This water soluble complex of stoechiome- try 1:2 [C 60 : ⊲ -CyD⊳ 2 ] has been studied using UV-vis and IR spectroscopy, 1,2,6,9 NMR spectroscopy, 2,8,14 circular dichro¨ ısm, 8 powder X-ray diffraction, 6,14 thermogravi- metry, 6,13 fast atom bombardment (FAB) mass spectro- metry, 10 – 12 flash photolysis, and pulse radiolysis. 3–7 The initial experimental characterization of the [C 60 : ⊲ -CyD⊳ 2 ] complex was performed by Andersson et al. 1 using UV-vis spectroscopy. Using molecular modeling, Andersson et al. 1,2 also reported that the hydrophobic cavity in  -CyD was just a little too small to accommodate C 60 . Whereas in a 1 : 1 complex, the C 60 molecule would present a relatively large area towards water, in a 1 : 2 complex, the guest is perfectly enclosed by the two host molecules, which are close enough to allow for hydrogen bonding between their respective secondary hydroxyl groups, with the access to the solvent phase significantly reduced. Mass spectrometric characterization of the [C 60 : ⊲ -CyD⊳ 2 ] complex was first achieved by Andersson et al. 10 Giesa et al. 11 and Her et al. 12 using FAB on a solid ‘magic Copyright  2007 John Wiley & Sons, Ltd.