Elucidating the Fragmentation Mechanism of Protonated Lewis A Trisaccharide using MSn CID

Lewis blood group antigens are a prominent example of isomeric oligosaccharides with biological activity. Understanding the fragmentation mechanism in the gas phase is essential for their identification and assignment by mass spectrometric methods such as ESI-MS. In this work, the [M + H]+ species of Lewis A trisaccharide and Lewis A trisaccharide methyl glycoside were studied by ESI-MS with FT-ICR as mass analyzer with respect to their fragmentation mechanism. The comparison between the underivatized and the methylated species has shown that the reducing end plays a key role in this mechanism. The results of this study question the existence of Z-type fragment ions after activation of the protonated species. The main product of the fragmentation are Y-type fragment ions and a combination of Y-type fragmentation and the loss of water at the reducing end instead of Z-type fragmentation. C-type fragment ions could not be detected. MS3 measurements also reveal that each fragment ion only occurs with the participation of a mobile proton and the possibility of glycosidic bond cleavage after fragmentation has already occurred at the reducing end as B2 fragment ion.

High-temperature decomposition of amorphous and crystalline cellulose: reactive molecular simulations

We study the thermal decomposition of cellulose using molecular simulations based on the ReaxFF reactive force field. Our analysis focuses on the mechanism and kinetics of chain scission, and their sensitivity on the condensed phase environment. For this purpose, we simulate the thermal decomposition of amorphous and partially crystalline cellulose at various heating rates. We find that thermal degradation begins with depolymerization via glycosidic bond cleavage, and that the order of events corresponds to a randomly initiated chain reaction. Depolymerization is followed by ring fragmentation reactions that lead to the formation of a number of light oxygenates. Water is formed mainly in intermolecular dehydration reactions at a later stage. The reaction rate of glycosidic bond cleavage follows a sigmoidal reaction model, with an apparent activation energy of 166 ± 4 kJ/mol. Neither the condensed phase environment nor the heating programme have appreciable effects on the reactions. We make several observations that are compatible with mechanisms proposed for cellulose fast pyrolysis. However, due to the absence of anhydrosugar forming reactions, the simulations offer limited insight for conditions of industrial interest. It remains unclear whether this is a natural consequence of the reaction conditions, or a shortcoming of the force field or its parameter set. Graphic abstract

Evidence of gas-phase pyranose-to-furanose isomerization in protonated peptidoglycans

Protonated peptidoglycans isomerize prior to glycosidic bond cleavage.

NaCl-promoted phase transition and glycosidic bond cleavage under microwave heating for energy-efficient biorefinery of rice starch

NaCl promotes starch gelatinisation via selective interactions with –OH groups and assists auto-catalysed hydrolysis, reducing energy use by 70% in microwave compared to conventional heating.

Energetics of cellulose and cyclodextrin glycosidic bond cleavage

Thermochemical conversion of lignocellulosic materials for production of biofuels and renewable chemicals utilizes high temperature to thermally decompose long-chain cellulose to volatile organic compounds.