Establishing a Proper HA Oxidative Degradation System

FIGURE 3 Time dependences of dynamic viscosity values of the HA solution in the presence of 1.0 pM CuCl plus ascorbate at concentrations 10 (1), 50 (2), or 100 (3) pM. 

Note 1 It is a well known fact that AscH donates a hydrogen atom (H or H+ + e ) yielding the resonance stabilized tricarbonyl ascorbate free radical. Since the latter has a pAT value of 0.86, it is not protonated and thus in aqueous solution it will be present as Asc [13]. 

As the cuprous ions are unstable, namely they can quickly undergo a dispropor-tional reaction Cu(I) + Cu(I) Cu(0) + Cu(ll), they are charge stabilized by an excess of the present ascorbate as follows AscH + Cu(I) [AscH - Cu(I)]. This reaction intermediate participates in the next bielectron reduction of the dioxygen molecule (0 = 0) 

In summary, we could express the following final/net reaction  

Yet the conditions of the flow chart should be taken into account Since within the reaction system there is a real ascorbate excess, the nascent hydroxyl radicals are continually quenched and due to these facts the EPR spectrometer monitors exclusively the ascorbyl radicals. 

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