Electrospray mass and tandem mass spectrometry of homologous and isomeric singly, doubly, triply and quadruply charged cationic ruthenated meso-(phenyl)m-(meta- and para-pyridyl)n (m + n = 4) macrocyclic porphyrin complexes

✍ Scribed by Daniela M. Tomazela; Fabio C. Gozzo; Ildemar Mayer; Fábio M. Engelmann; Koiti Araki; Henrique E. Toma; Marcos N. Eberlin

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 204 KB
• Volume: 39
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/jms.699

✦ Synopsis

Abstract

Ten homologous or isomeric singly, doubly, triply and quadruply charged cationic macrocyclic complexes I–Va, b^n+^ (n = 1–4) formed by the coordination of [Ru(bipy)~2~Cl]^+^ to the pyridyl N‐atoms of a series of meso‐(phenyl)~m~‐(meta or para‐pyridyl)~n~‐porphyrins (m + n = 4) were transferred to the gas phase and structurally characterized by electrospray ionization (ESI) mass (MS) and tandem mass (MS/MS) spectrometry. Previously known to be stable in solution and in the solid state, I–Va, b^n+^ are found to constitute also a new class of stable, long‐lived multiply charged gas‐phase ions with spatially separated charge sites. Increasing intramolecular electrostatic repulsion from Ia, b^+^ to IVa, b^3+^ facilitates in‐source and tandem collision‐induced dissociation (CID). However, for the quadruply charged ions Va, b^4+^, electrostatic repulsion is alleviated mainly by ion pairing with the CF~3~SO~3~^−^ counterion forming the salt clusters [Va,b/CF~3~SO~3~]^3+^ and [Va,b/(CF~3~SO~3~)~2~]^2+^ with reduced charge states. Ion‐pairing that yields [IVa,b/CF~3~SO~3~]^2+^ is also observed as a minor ESI process for the triply charged ions IVa, b^3+^. The gaseous ions I–Va, b^n+^ (n = 2, 3 or 4) dissociate by sequential ‘charge partitioning’ with the formation of two cationic fragments by the release of [Ru(bipy)~2~Cl]^+^. The meta (a) and para (b) isomers and the positional isomers II^2+^ and III^2+^ display nearly identical ESI‐MS and ESI‐MS/MS spectra. ESI‐MS/MS of I–Va, b^n+^ shows that the Rupy(P) is, intrinsically, the weakest bond since this bond breaks preferentially upon CID. Copyright © 2004 John Wiley & Sons, Ltd.