MALDI mass spectrometry monitoring of cyclodextrin-oligolactide derivatives synthesis

Abstract

This paper aims to expand the range of matrix assisted laser desorption mass spectrometry analysis (MALDI MS) as a tool to establish the reaction kinetics for a particular case study: the synthesis of β-cyclodextrin-oligolactide (CDLA) derivatives through solution ring opening oligomerization (ROO) of d,l-lactide (LA) initiated by β-cyclodextrin (β-CD). Specifically, MALDI MS was used to estimate the molecular weight averages minute changes during the synthesis for a better understanding of the chemical process. The MALDI MS data was compared with 1H NMR for determining the DL-Lactide conversion rate and an excellent agreement level was established. The synthesis process was further studied by observing the effects of the reaction parameters with a special focus on the solvent influence. Thus, we observed that the ROO performed in dimethylformamide and N-methyl-2-pyrrolidone proceeds faster in comparison with dimethylsulfoxide due to an activation process in the LA ring opening reaction. The activation is produced by the amines resulted from the cleavage of the amide bonds in the presence of the β-CD or CDLA derivatives. The products of the degradation process were identified in the MS spectra and structurally confirmed through MS fragmentation experiments.