title: Characterization of polylactides with different stereoregularity using electrospray ionization ion mobility mass spectrometry.
abstract: We investigated the effect of stereoregularity on the gas-phase conformations of linear and cyclic polylactides (PLA) using electrospray ionization ion mobility mass spectrometry (ESI-IM-MS) combined with molecular dynamics simulations. IM-MS analysis of PLA ions shows intriguing difference between the collision cross section (ΩD) value of poly-L-lactide (PLLA) and poly-LD-lactide (PLDLA) ions with respect to their chain architecture and stereoregularity. In the singly sodiated linear PLA (l-PLA∙Na(+)) case, both l-PLLA and l-PLDLA up to 11mer have very similar ΩD values, but the ΩD values of l-PLLA are greater than that of l-PLDLA ions for larger ions. In the case of cyclic PLA (c-PLA), c-PLLA∙Na(+) is more compact than c-PLDLA∙Na(+) for short PLA ions. However, c-PLLA exhibits larger ΩD value than c-PLDLA for PLA ions longer than 13mer. The origin of difference in the ΩD values was investigated using theoretical investigation of PLAs in the gas phase. The gas-phase conformation of PLA ions is influenced by Na(+)-oxygen coordination and the weak intramolecular hydrogen bond interaction, which are more effectively formed in more flexible chains. Therefore, the less flexible PLLA has a larger ΩD value than PLDLA. However, for short c-PLA, concomitant maximization of both Na(+)-oxygen coordination and hydrogen bond interaction is difficult due to the constricted chain freedom, which makes the ΩD value of PLAs in this range show a different trend compared with other PLA ions. Our study facilitates the understanding of correlation between stereoregularity of PLAs and their structure, providing potential utility of IM-MS to characterize stereoisomers of polymers.
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, 790-784, Korea.
authors.forename: Kihyun
authors.initials: K
authors.lastname: Kim
authors.forename: Jong Wha
authors.initials: JW
authors.lastname: Lee
authors.forename: Taihyun
authors.initials: T
authors.lastname: Chang
authors.forename: Hugh I
authors.initials: HI
authors.lastname: Kim
mesh_terms: D008958:Models, Molecular; D008968:Molecular Conformation; D011091:Polyesters / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013237:Stereoisomerism
chemical_list: D011091:Polyesters; C033616:poly(lactide)