## 3 Results
### Peroxidase and Electrolytical Studies  
Several water-soluble traps for radical species can be used for peroxidase assays [40]. In the present work we employed the diammonium salt of ABTS, which is commonly used with both natural peroxididases [41] and enzyme mimetics [42]. However, we recently found that photochemical processes, especially \({}^{\bullet}\)OH radical generation from H\({}_{2}\)O\({}_{2}\), can lead to erroneous results in this test [28]. The level of ABTS\({}^{\bullet+}\) can be grossly overestimated being affected by the illumination conditions and also the time at which absorbance readings are taken; many of these undesired effects can be avoided using illumination at wavelengths longer than 455 nm. Conveniently, ABTS\({}^{\bullet+}\) has several additional absorption bands at longer wavelengths including 650, 735 and 815 nm. The extent of the reaction, avoiding photochemical interferences, can be measured quantitatively at \(\lambda\) = 650 nm since \(\varepsilon\) = 12,000 M\({}^{-1}\) cm\({}^{-1}\) has been determined. When using **1-4**, the observed rates of formation of ABTS\({}^{\bullet+}\) were about 35-65% indicating a high peroxidase activity (see Table 3). On the other hand, complexes **5-7** did not show any measurable peroxidase-like activity with the UV absorbances from the ABTS\({}^{\bullet+}\) radical cation being negligible even after 60 min of illumination. VA is commonly used as a lignin model compound [43; 44]. This substrate was ideal for our experiments as complexes **1-7** do not absorb at 310 nm where the oxidised product VAH absorbs strongly (\(\varepsilon\) = 9300 M\({}^{-1}\) cm\({}^{-1}\); Figure S2) [45]. Experiments of electrochemical oxidation of VA to VAH were carried out using NaCl as electrolyte in order to increase the conductivity of water and to reduce the power dissipation. Other than improving on ionic conductivity, it was found that chloride ions could significantly reduce the adverse effect of other anions such as carbonate or sulphate. The concentration of the electrolyte has a marked influence on the cell efficiency. The addition of increasing amounts of NaCl led to higher conversion ratios of VA into VAH (Figure S3). The formation of VAH was confirmed after its isolation and characterisation by \({}^{1}\)H NMR. The \({}^{1}\)H NMR spectrum of the VAH fraction confirmed the disappearance of the CH\({}_{2}\) proton signal at 4.61 ppm from the VA precursor as well as the appearance of a new peak at 9.62 ppm from the aldehyde product (VAH, Figure S4). Temperature is another factor that leads to an increase in the conversion ratio. It was found that a significant improvement could be achieved when the experiments were carried out at 40 \({}^{\circ}\)C rather than room temperature (thermostatted 23 \({}^{\circ}\)C), although a further increase in temperature to 50 \({}^{\circ}\)C did not show any significant increase in the conversion ratio (Figure S5). The electrocatalytic studies at different pH values were mainly carried out at 40 \({}^{\circ}\)C and an NaCl concentration close to that of sea water, the most important source of water on earth and also accessible for the pulp industry. We also examined the effect of catalyst concentration on the VA conversion rate by varying a molar concentration of the catalyst against the VA concentration in the range from 0.25% to 3%. The highest conversion rates (Figure S6) were achieved when using 0.5% of the catalyst complex. The highest turnover numbers (TON), above 100 per Mn(III), were achieved using 0.25% of catalyst complex (Table 1). The use of complexes **1-7** as electrocatalysts enhanced the conversion rates for the VA oxidation to VAH at all tested driving potentials (Figure S7). The results obtained at driving potential 4 V in the presence/absence of catalysts after 2 h are represented in Figure 5 and selected data are shown in Tables 4 and 5.