New paths of cyanogenesis from enzymatic-promoted cleavage of ß-cyanoglucosides are suggested by a mixed DFT/QTAIM approach.

ABSTRACT

Cyanogenesis is an enzyme-promoted cleavage of ß-cyanoglucosides; the release of hydrogen cyanide is believed to produce food poisoning by consumption of certain crops as Cassava (Manihot esculenta Crantz). The production of hydrogen cyanide by some disruption of the plant wall is related to the content of two ß-cyanoglucosides (linamarin and lotaustralin) which are stored within the tuber. Some features about the mechanistic bases of these transformations have been published; nevertheless, there are still questions about the exact mechanism, such as the feasibility of a difference in the kinetics of cyanogenesis between both cyanoglucosides. In this work, we have performed a theoretical analysis using DFT and QTAIM theoretical frameworks to propose a feasible mechanism of the observed first step of the enzyme-catalyzed rupture of these glucosides; our results led us to explain the observed difference between linamarin and lotaustralin. Meanwhile, DFT studies suggest that there are no differences between local reactivity indexes of both glucosides; QTAIM topological analysis suggests two important intramolecular interactions which we found to fix the glucoside in such a way that suggests the linamarin as a more reactive system towards a nucleophilic attack, thus explaining the readiness to liberate hydrogen cyanide.