Structural localisation of catalytic H2O2 oxidation sites in starch

The catalytic oxidation of potato starch by [Mn^IV₂(μ-O)₃(tmtacn)₂][H₂O](CH₃COO)₂ (Mncat, with tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) with H₂O₂, was recently introduced as a promising alternative to ubiquitous sodium hypochlorite (NaOCl). Here, we report an in-depth investigation into interactions of the catalyst with the starch granule. Pitted starches obtained by pre-treatment with high-frequency ultrasound (HFUS) were shown to result in a uniquely homogeneous oxidation. To study this further, fractionation of oxidised potato starch was done which showed a preference for the oxidation of smaller granules with a higher relative surface area. This result was corroborated by chemical surface gelatinisation of fractionated granules. These studies showed that the inside of the granules was oxidised, but that Mncat had a moderate preference for oxidation of the periphery. Together, these results allow for a better understanding of oxidation of starch by Mncat and how it differs from NaOCl oxidation making further optimisation of the process possible.