Gas-phase dissociation of ionic liquid aggregates studied by electrospray ionisation mass spectrometry and energy-variable collision induced dissociation

resumo

Positive singly charged ionic liquid aggregates [(C(n)mim)(m+1)(BF(4))(m)](+) (mim = 3-methylimidazolium; n = 2, 4, 8 and 10) and [(C(n)mim)(m+1)(A)(m)](+) (A = Cl(-), BF(4)(-), PF(6)(-), CF(3)SO(3)(-) and (CF(3)SO(2))(2)N(-)) were investigated by electrospray ionisation mass spectrometry and energy-variable collision induced dissociation. The electrospray ionisation mass spectra (ESI-MS) showed the formation of an aggregate with extra stability for m = 4 for all the ionic liquids with the exception Of [C(4)mim][CF(3)SO(3)]. ESI-MS-MS and breakdown curves of aggregate ions showed that their dissociation occurred by loss of neutral species ([C(n)mim][A])(a) with a >= 1. Variable-energy collision induced dissociation of each aggregate from m = 1 to m = 8 for all the ionic liquids studied enabled the determination of E(cm,1/2) values, whose variation with m showed that the monomers were always kinetically much more stable than the larger aggregates, independently of the nature of cation and anion. The centre-of-mass energy values correlate well with literature data on ionic volumes and interaction and hydrogen bond energies. Copyright (c) 2008 John Wiley & Sons, Ltd.

palavras-chave

SALT CLUSTER IONS; AB-INITIO; MAGIC NUMBERS; ACTIVATED DISSOCIATION; VIBRATIONAL-SPECTRA; MOLECULAR-STRUCTURE; HYDROGEN-BONDS; TEMPERATURE; SODIUM; TRAP

categoria

Biophysics; Chemistry; Spectroscopy

autores

Fernandes, AM; Coutinho, JAP; Marrucho, IM

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