Characterization of polylactides with different stereoregularity using electrospray ionization ion mobility mass...

Area of Science:

• Polymer Chemistry
• Analytical Chemistry
• Physical Chemistry

Background:

• Polylactide (PLA) stereoisomers exhibit distinct physical properties.
• Understanding gas-phase conformations is crucial for polymer characterization.

Purpose of the Study:

• To investigate the effect of stereoregularity on the gas-phase conformations of linear and cyclic polylactides (PLA).
• To correlate stereoregularity with structural differences using ion mobility mass spectrometry (IM-MS) and molecular dynamics simulations.

Main Methods:

• Electrospray ionization ion mobility mass spectrometry (ESI-IM-MS) was employed to analyze PLA ions.
• Molecular dynamics (MD) simulations were used to investigate gas-phase conformations and interactions.
• Collision cross-section (ΩD) values were measured and compared between different PLA stereoisomers.

Main Results:

• Linear poly-L-lactide (l-PLLA) showed larger collision cross-section (ΩD) values than linear poly-LD-lactide (l-PLDLA) for longer chains.
• Cyclic poly-L-lactide (c-PLLA) was more compact than cyclic poly-LD-lactide (c-PLDLA) for short chains, but exhibited larger ΩD for longer chains (>13mer).
• Differences in ΩD values were attributed to Na(+)-oxygen coordination and intramolecular hydrogen bonding, influenced by chain flexibility.

Conclusions:

• Stereoregularity critically influences the gas-phase conformations of PLA, affecting their collision cross-section values.
• The findings highlight the role of non-covalent interactions (ion-dipole and hydrogen bonding) in dictating polymer structure in the gas phase.
• Ion mobility mass spectrometry (IM-MS) is a powerful tool for characterizing polymer stereoisomers and their structural nuances.