Paper
Catalysis Science & Technology
increased 11 times with an increase in DP from 2 to 6. A
simultaneous decrease in the apparent activation energy for
hydrolysis was also observed with respect to the increase in
DP. In addition, the larger oligosaccharides showed
a
stronger affinity towards adsorption over the narrow
micropores of the carbon surface. A preference for hydrolysis
of terminal over internal glycosidic bonds was observed,
which was analogous to some enzymes in the cellulase
family. Based on these observations, we propose that the
increase in the rate of hydrolysis is caused by the reduction
in activation energy which is the result of conformational
changes in the oligosaccharide molecules when they adsorb
within the micropores of carbon.
Fig. 6 Arrhenius plots of cello-oligosaccharide (G2–G5) hydrolysis on
AC-air.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
This work was supported by the Japan Science and
Technology Agency (JST) ALCA (JPMJAL1309). AS would like to
acknowledge the funding support from the Research Fund
Program for Early Career Scientists from Hokkaido University.
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Fig.
7 Illustration showing the twisted ribbon structure of
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carbon would cause
a
conformational change in its
stable
structure.36 Cello-oligosaccharides conform to
a
twisted ribbon structure in aqueous solution.37 Upon
adsorption, this structure would untwist to accommodate
itself within the pores and to achieve adsorption of multiple
glucose units over the carbon surface (Fig. 7). This deviation
from the stable twisted form could cause a change in the
β-1,4-glycosidic bond angle, leading to reduction in activation
energy required for its cleavage.
Conclusions
We performed hydrolysis of cello-oligosaccharides with
increasing degree of polymerization in the presence of
various catalysts. Only in the presence of carbon catalysts
that the rate of hydrolysis was strongly dependent on the
degree of polymerization. The hydrolysis rate constant
Catal. Sci. Technol.
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