Size Dependence of the Folding of Multiply Charged Sodium Cationized Polylactides Revealed by Ion Mobility Mass Spectrometry and Molecular Modelling

Abstract

Ion mobility spectrometry coupled with mass spectrometry was used to experimentally determine the three-dimensional structure of multiply charged sodium cationized polylactides (PLA). In particular, the experiments were conducted to evaluate the influence of the charge state and the size on the gas-phase conformation of cationized PLA. The measured collision cross sections were then compared to calculated values obtained by computational chemistry methods. The most striking feature was the experimental and theoretical observation of a breaking point in the quasilinear relationship between the average collision cross sections and the number of monomer units for the triply charged cations. This breaking point was theoretically demonstrated, for the doubly and triply charged cations, to be associated with a significant folding of the polymer chains around the cationizing agents. The occurrence of such breaking points could be exploited to correlate the charge state of the most intense ion series observed upon electrospray ionization with the number-average molecular mass of a polymer.

Structural Study of Analogues of Titan’s Haze by Trapped Ion Mobility Coupled with a Fourier Transform Ion Cyclotron Mass Spectrometer

“…We presume a folding effect, which was previously reported in multiple IMS-MS studies for polymers. [16][17][18] As tholins are referred to be HCNpolymers with carbon and hydrogen insertion, we could vaguely assume folding of larger tholin species can occur and will lower the isomeric diversity in terms of most compact and largest structure.…”

Correlation between the shape of the ion mobility signals and the stepwise folding process of polylactide ions

“…In the field of polymer characterization, the successful coupling of mass spectrometry (MS) with ion mobility (IM) separation provides valuable information regarding the 3D structures of polymer ions in the gas phase . The IM approach is an elegant methodology that measures the drift time of ions flying through a mobility cell pressurized with a neutral buffer gas under the influence of an electric field.…”

“…Currently, most of the IM investigations are performed by electrospray ionization (ESI)‐equipped mass spectrometers on commercially available linear polymers, such as poly(ethylene glycol) (PEG) or polyacrylates, affording a visual inspection of the evolution of the ion structures as a function of the charge state and the number of monomer units. Additionally, synthetic aliphatic polyesters such as polylactide (PLA) or poly( ε ‐caprolactone), linear, cyclic or star shaped, were also investigated by IM.…”

“…Usually, for low degrees of polymerization (DP), polymer ions adopt an extended structure in the gas phase to reduce the Coulomb repulsion between the cationizing agents . When increasing the number of monomer units, the Coulomb repulsion is attenuated by a screening effect of the monomer units permitting the charges to become closer, ultimately leading to an almost spherical (globular) structure . Once this transition is reached, any additional monomer unit will contribute to the growth of the sphere .…”

Nitroxide mediated polymerization of methacrylates at moderate temperature

“…The dominant distribution corresponds in this 40 case to doubly charged ions, which facilitates efforts to identify the range of species present. 28 As shown in Figure 4b, three distinct polymer ion compositions are detected as macroalkoxyamine species, each corresponding PMMA featuring a different end-group structure 45 (Scheme 3). From the m/z ratios, the presence of PMMA bearing (i) three V70 residues (I), (ii) two V70 and one NMMA residues (J) and (iii) two NMMA and one V70 residues (K) was identified.…”