Cyclodextrin-Oligocaprolactone Derivatives—Synthesis and Advanced Structural Characterization by MALDI Mass Spectrometry

Abstract

Cyclodextrins have previously been proven to be active in the catalysis of cyclic ester ring-opening reactions, hypothetically in a similar way to lipase-catalyzed reactions. However, the way they act remains unclear. Here, we focus on β-cyclodextrin’s involvement in the synthesis and characterization of β-cyclodextrin-oligocaprolactone (CDCL) products obtained via the organo-catalyzed ring-opening of ε-caprolactone. Previously, bulk or supercritical carbon dioxide polymerizations has led to inhomogeneous products. Our approach consists of solution polymerization (dimethyl sulfoxide and dimethylformamide) to obtain homogeneous CDCL derivatives with four monomer units on average. Oligomerization kinetics, performed by a matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) optimized method in tandem with 1H NMR, revealed that monomer conversion occurs in two stages: first, the monomer is rapidly attached to the secondary OH groups of β-cyclodextrin and, secondly, the monomer conversion is slower with attachment to the primary OH groups. MALDI MS was further employed for the measurement of the ring-opening kinetics to establish the influence of the solvents as well as the effect of organocatalysts (4-dimethylaminopyridine and (–)-sparteine). Additionally, the mass spectrometry structural evaluation was further enhanced by fragmentation studies which confirmed the attachment of oligoesters to the cyclodextrin and the cleavage of dimethylformamide amide bonds during the ring-opening process.

Polyurethane Degradable Hydrogels Based on Cyclodextrin-Oligocaprolactone Derivatives

“…The CDCL derivatives were synthesized according to a previously published study [ 18 ]. The product characterization by MALDI MS is further discussed.…”

“…Based on the relative intensities of the MS peaks we determined the average degree of substitution of three CL units per cyclodextrin. Nuclear magnetic resonance (NMR) analysis previously described revealed a random substitution at the level of OH groups belonging to either C2, C3, or C6 o β-CD [ 18 ]. This substitution pattern of CDCL theoretically ensures the increase of the primary OH group number, which may influence the crosslinking process.…”

Matrix-Assisted Laser Desorption and Electrospray Ionization Tandem Mass Spectrometry of Microbial and Synthetic Biodegradable Polymers

“…Structural analyses of cyclodextrin–oligoester derivatives have been carried out by MALDI-MS, with the support of NMR and tandem MS [ 80 , 87 , 88 ]. Blaj et al studied the influence of different reaction conditions on the β-CD ring-opening oligomerization (ROO) of D,L-lactide by MALDI.…”

“…In a similar way, Peptu et al investigated the solution ROP of ε-caprolactone (CL) in the presence of β-CD, leading to highly water-soluble oligoCL cyclodextrin derivatives (CDCL). Secondary reactions involving the solvent used were revealed by the chemical modification of the CDCL verified using MALDI-MS and MS/MS analyses [ 88 ].…”

“…Figure 1 shows an overview of the most representative microbial and synthetic biodegradable polymers studied by MALDI and ESI-MS, and MS/MS. In the last decades, studies on fragmentation mechanisms [ 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ], structure and architecture [ 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 ], biopharmaceutical and drug delivery systems (DDS) [ 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , ...…”