Abstract
Multi-block glucans comprising permethylated and partially methylated blocks are compounds of interest. In order to monitor their formation by transglycosylation of corresponding starting glucans, a method has been developed and applied to model compounds. This method allows determining the average length of the blocks and the progress of incorporation of methyl blocks in partially methylated sequences with a random distribution. The method, comprising liquid chromatography mass spectrometry (LC-MS) and electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MSn) measurements of two types of peralkylated glucans representing derivatives of the target compounds, is comprehensively described and discussed. ESI-MSn allows looking into the sequences of oligomeric domains. In addition, transglycosylation is followed by attenuated total reflection FTIR and NMR spectroscopy.Graphical abstract
Highlights
Originating from renewable resources, cellulose ethers are produced on a large scale by polymer analogous reactions, and they are one of the most important classes of cellulose derivatives with a wide range of applications in food, pharmaceuticals, and construction materials.In addition to the type of the substituents, physicochemical properties of cellulose ethers strongly depend on the degree of polymerization (DP), degree of substitution (DS), and distribution of substituents along the polymer chains; this, per se, points out the importance of comprehensive analysis of substitution patterns for a better understanding of structure-property relationships [1] and improvement of modification processes.Thermoreversible gelation of aqueous solutions of methylcellulose (MC) is strongly influenced by the methyl substituent pattern
Determining the average block length and monitoring the changes of the methyl profile of such products by mass spectrometry is impaired by the coincidence of the m/z peak of the permethylated component in either block
Deuteromethylation of one half produces a block copolymer product which is completely alkylated by isotopically distinct groups, i.e., Me and Me-d3
Summary
Originating from renewable resources, cellulose ethers are produced on a large scale by polymer analogous reactions, and they are one of the most important classes of cellulose derivatives with a wide range of applications in food, pharmaceuticals, and construction materials.In addition to the type of the substituents, physicochemical properties of cellulose ethers strongly depend on the degree of polymerization (DP), degree of substitution (DS), and distribution of substituents along the polymer chains; this, per se, points out the importance of comprehensive analysis of substitution patterns for a better understanding of structure-property relationships [1] and improvement of modification processes.Thermoreversible gelation of aqueous solutions of methylcellulose (MC) is strongly influenced by the methyl substituent pattern (methyl profile). Upon consumption of cyclodextrins and elongation of copolymer chains, initially formed blocks were randomized rapidly and accompanied by a slight chain degradation [16]. Another hardship of this method was that copolymerization of permethyl cyclodextrin and perbenzyl cyclodextrin did not occur due to the different reactivities of the oxocarbenium ion intermediates. In a more recent study, Rother et al [17] reported an unprecedented top-down approach for one-pot synthesis of glucan ether block copolymers by performing transglycosylation reaction (Trg) between cellulose derivatives, i.e., permethyl cellulose (per-MC) and perdeuteromethyl cellulose (per-Me-d3C) or perethyl cellulose. The timecourse study showed the randomization of blocks and the reduction of molecular weight (Mw) over the reaction time [17]
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