## 4 Discussion
While binding of hydrogen peroxide to manganese ion is a key-step in the peroxidase activity (favored for **1-4** versus **5-7**), binding of the sacrificial oxidant (CI\({}_{2}\)/HCIO/CIO\({}^{-}\)) can become the determining step in the electrolytic experiments with VA.  
Electrochemical studies at different pH provide additional insight into the equilibrium interplay between three oxidizing species, CI\({}_{2}\)/HCIO/CIO\({}^{-}\), potentially involved in the electrochemical reaction. A change in the concentration of H\({}^{+}\) or OH\({}^{-}\) shifts the equilibrium making one or another oxidising species to dominate in the media. Degradation of the lignin analogue in acidic media is mediated by the chorine formed in the anodic reaction. This process is responsible for the conversion rates at pH values below 7 in the presence or absence of complexes. The main reactions at the electrodes in acidic conditions are [50]:  
\[\text{Anode: 2 CI}^{-}\rightarrow\text{Cl}_{2}+2\text{e}^{-} \tag{1}\]  
\[\text{Cathode: 2H}_{2}\text{O}+2\text{e}^{-}\rightarrow\text{H}_{2}+2\text{OH}^{-} \tag{2}\]  
In the aqueous acidic solution, hydrolysis of chlorine generates hypochlorous acid. The equilibrium constant for chlorine to hypochlorous acid is \(4\times 10^{-4}\) while that for hypochlorous acid to hypochlorite is \(2.9\times 10^{-8}\). This means that chlorine and hypochlorous acid are the most prevalent species at acidic pH [51; 52]. In the absence of an electrocatalyst, oxidation of veratryl alcohol tends to be greater at acidic pH than at alkaline pH due to the high oxidising activity of chlorine and hypochlorous acid. At basic pH chlorine undergoes a disproportionation reaction to give chloride and hypochlorite:  
\[\mathrm{Cl_{2}+2 OH^{-}\to OCl^{-}+Cl^{-}+H_{2}O} \tag{3}\]  
Consequently, hypochlorite is the prevalent oxidising agent under alkaline conditions [53]. A proportion of the useful hypochlorite ion is lost via the diffusion-controlled cathodic reduction to chloride and anodic oxidation to chlorate [50]:  
\[\mathrm{OCl^{-}+H_{2}O+2e^{-}\to Cl^{-}+2 OH^{-}} \tag{4}\]  
As a result of these processes, the conversion ratio of veratryl alcohol to veratryl aldehyde decreases at pH 7-8.25 for the experiments carried out in the absence of a complex. Interestingly, the electrocatalytic activity of complex **1** reaches a maximum at pH 8.25, which means that reaction occurs in a chlorine-free medium with hypochlorite used as a sacrificial oxidant. The rate of degradation of the lignin model by electrochemical oxidation under these conditions is higher than in every pH media. The results obtained at pH 8.25 clearly indicate that this oxidation is mediated by complex **1**, which acts as an efficient electrocatalyst. The sum of reactions (1)-(4) represents the global process:  
\[2H_{2}O+2\;e^{-}\to H_{2}+2 OH^{-} \tag{5}\]  
The novel approach outlined above avoids the use of chlorine by simply adjusting to an alkaline pH. Ideally, photovoltaic electric current would be able to induce the oxidation of chloride into hypochlorite along with the formation of hydrogen. Any hydrogen released could be used in fuel cells to generate electricity, and this would reduce the energy consumption of the global process. The use of catalysts leads to a significant increase in the efficiency of the oxidation of the lignin model. The robustness of the catalysts makes them suitable for use in a wide range of conditions. Electrocatalytic generation of hydrogen from water is one of the potential applications of this type of complex and studies in this respect are underway. We assessed whether the catalytic behavior of this type of complex is affected by variations in the skeleton of the organic Schiff base ligand. Experiments are also ongoing with the aim of enhancing this activity by tuning the steric and electronic effects around the manganese core. Our aim is to define the appropriate choice of bulky and/or electron-withdrawing or -donating substituents to be incorporated in the Schiff bases.