Local site selectivity and conformational structures in the glycosidic bond scission of cellobiose.

School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW 2006, Australia.
The Journal of Physical Chemistry B (Impact Factor: 3.61). 08/2011; 115(36):10682-91. DOI: 10.1021/jp204199h
Source: PubMed

ABSTRACT Car-Parrinello molecular dynamics combined with metadynamics simulations were used to study the acid-catalyzed hydrolysis of cellobiose (CB) in aqueous solution. The hydrolysis was studied in two steps. Step 1 involves the proton transfer from solvent to CB and dissociation of the glycosidic bond to β-glucose and oxacarbenium ion species. Step 2 involves the formation of α-glucose from oxacarbenium and regeneration of the acid proton species. Step 1 is endothermic, while Step 2 is exothermic. The overall activation free energy of CB hydrolysis is 32.5 kcal mol(-1), and the overall reaction free energy is -5.9 kcal mol(-l), consistent with available experimental data. We observe that a stepwise mechanism generally described in the literature for Step 1 is not significantly favored relative to a concerted β-1,4' linkage dissociation process.

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