Tandem Mass Spectrometry Characteristics of Polyester Anions and Cations Formed by Electrospray Ionization

Abstract

Electrospray ionization of polyesters composed of isophthalic acid and neopentyl glycol produces carboxylate anions in negative mode and mainly sodium ion adducts in positive mode. A tandem mass spectrometry (MS/MS) study of these ions in a quadrupole ion trap shows that the collisionally activated dissociation pathways of the anions are simpler than those of the corresponding cations. Charge-remote fragmentations predominate in both cases, but the spectra obtained in negative mode are devoid of the complicating cation exchange observed in positive mode. MS/MS of the Na(+) adducts gives rise to a greater number of fragments but not necessarily more structural information. In either positive or negative mode, polyester oligomers with different end groups fragment by similar mechanisms. The observed fragments are consistent with rearrangements initiated by the end groups. Single-stage ESI mass spectra also are more complex in positive mode because of extensive H/Na substitutions; this is also true for matrix-assisted laser desorption ionization (MALDI) mass spectra. Hence, formation and analysis of anions might be the method of choice for determining block length, end group structure and copolymer sequence, provided the polyester contains at least one carboxylic acid end group that is ionizable to anions.

Fragmentation pathways of polymer ions

“…The anion's unique CO 2 eliminations must result from charge-directed fragmentation induced by the carboxylate nucleophile; a plausible mechanism yielding an energetically favorable six-membered ring is given in Scheme 13. A combination of charge-remote and charge-induced dissociations has also been observed for deprotonated PMAA (Giordanengo et al, 2009b), deprotonated polyesters (Arnould et al, 2005), and deprotonated poly(styrene sulfonate) (Subel, 2009). Charge-remote mechanisms for CO 2 loss from the cyclic anhydride groups formed by the elimination of H 2 O from alkali metal cationized PAA.…”

“…CAD of condensation polymers mainly leads to linear fragments with the same or new end group combinations and to cyclic fragments with different repeat unit content. Linear and cyclic fragments have been designated by the acronyms l n AB and c n AB , respectively, where l and c differentiate between the linear and cyclic architecture, the subscript n gives the number of repeat units in the fragment, and the superscripted AB gives the chain ends in a linear or the combining ends in a cyclic fragment (Arnould et al, 2005).…”

“…The dissociation characteristics of polyesters depend on the structure of their constituents (Koster et al, 2000;Laine, Laitinen, & Vainiotalo, 2002;Adamus et al, 2004;Arnould et al, 2005;Rizzarelli, Puglisi, & Montaudo, 2006;Chaicharoen, 2008;Simonsick & Petkovska, 2008;Wesdemiotis, Solak, & Baker, 2009). Poly(butylene adipate), an aliphatic polyester copolymer, will be discussed in detail; such compounds have recently gained importance as biodegradable materials for the manufacture of health, consumer, and packaging products.…”

Mechanistic study of the collision-induced dissociation of sodium-cationized polylactide oligomers: A joint experimental and theoretical investigation

“…On the basis of the m/z ratio of the detected cationized oligomers, compositional pieces of information such as the number and type of monomer units but also the nature of the incorporated end-groups can be derived. Nowadays, tandem mass spectrometry (MSMS) is emerging as an essential analytical methodology when accurate structural characterization of polymers cannot be unambiguously derived from single-stage MS experiments [12]. Recent MSMS investigations were successfully used to characterize individual functional groups of new polymers, to make a clear-cut distinction between isomeric oligomers, and even to determine copolymer sequences [13].…”

Bioactive (co)oligoesters with antioxidant properties – synthesis and structural characterization at the molecular level

“…Previously, mass spectrometry was successfully applied for structural characterization at the molecular level of homopolyesters, copolyesters and their degradation products [19][20][21][22][23][24][25][26][27][28][29] . In our recent works we reported the application of ESI-MS/MS techniques for characterization at the molecular level of OHB conjugates with bioactive compounds including antioxidants used in cosmetics.…”