1,4-D-Glucan block copolymers: synthesis and comprehensive structural characterization

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 Electronic supplementary material The online version of this article (10.1007/s00216-020-02388-z) contains supplementary material, which is available to authorized users.


ESI-MS of 1
Nearly 3 mg of 1 was partially hydrolyzed by 1 M trifluoroacetic acid (TFA) in a 1 mL V vial for 30 min at 120 °C. Repeated co-evaporation with toluene was performed at 22 °C under a stream of nitrogen to remove the TFA and dry the sample. After dilution to 10 -4 M in LC-MS grade MeOH and filtration through a syringe PTFE membrane filter 0.45 μm, the sample was analyzed by ESI-MS in positive ion mode.
Electrospray ionization ion-trap mass spectrometry (ESI-IT-MS) was performed with an HCT Ultra ETDII (Bruker Daltonics, Bremen, Germany). The spectra were evaluated by Data Analysis 4.0 (Bruker Daltonics, Bremen, Germany). The sample was directly infused to the ESI source at a flow rate of 200 μL h−1. Nitrogen was used as dry gas (4 L/min, 300 °C) and as nebulizer gas (10 psi). Other instrumental parameters were as follows: capillary voltage -4500 V, endplate offset voltage -500 V, smart target 100,000, target mass 1000, positive ion mode. The spectrum is an average of 200 scans. Nearly 3 mg of 2 was partially hydrolyzed as explained above for 1. Thereafter, partially hydrolyzed products were labeled with m-aminobenzoic acid by reductive amination in MeOH as described in the experimental section of the manuscript. After dilution to 10 -4 M in LC-MS grade MeOH and filtration through a syringe PTFE membrane filter 0.45 μm, the sample was analyzed by ESI-MS in negative ion mode.
The spectra were evaluated by Data Analysis 4.0 (Bruker Daltonics, Bremen, Germany).
The sample was directly infused to the ESI source at a flow rate of 200 μL h −1 . Nitrogen was used as dry gas (5 L/min, 300 °C) and as nebulizer gas (10 psi). Other instrumental parameters were as follows: capillary voltage 3500 V, endplate offset voltage -500 V, smart target 100,000, target mass 1000, negative ion mode. The spectrum is an average of 150 scans.   products In order to investigate whether the scan speed plays a role in mass spectrometry analysis and subsequent average block length (BL) evaluations, each transglycosylation-a product was analyzed 6 times by ESI-MS; 3 times by the standard-enhanced mode (8100 m/z /s) and 3 times by ultra-scan mode (26000 m/z /s). Other instrumental parameters were the same and as explained below. BL of the products were evaluated based on the results at DP2 and DP3 level (Fig. S10).
The sample was directly infused to the ESI source at a flow rate of 200 μL h −1 . Nitrogen was used as dry gas (5 L/min, 300 °C) and as nebulizer gas (10 psi

A model for Me-profile of transglycosylation products over time
To obtain a model for the Me-profile of transglycosylation-b products over the reaction time based on DP5 results shown in Fig. 9 of the manuscript, the relative amounts of n(Me)/AGU of DP5 were separately plotted against the reaction time (Fig. S14).  Table S1, respectively (y is the mole percent of each n(Me)/AGU, and x is the reaction time).

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By plotting the obtained fitting curve of each n(Me)/AGU against the reaction time, the model shown in Fig. 10 of the manuscript is obtained.