Determination of the Kinetics of the Back Reaction of Photosystem Ii in the Presence of 3–(3,4‐dichlorphenyl)‐1,1‐dimethylurea From Luminescence Measurements

Abstract

Abstract— An alternative method to that used by Mar and Roy (1974) for the determination of the kinetics of the back reaction of photosystem II from the luminescence decay curve in the presence of 3–(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) has been suggested. The new theory relies upon two hypotheses: the well‐known recombination hypothesis of luminescence and the assumption that the luminescence yield in the seconds region is given by the variable part of the live fluorescence yield. The second hypothesis was introduced since assuming a constant luminescence yield results in kinetic data that are not consistent with measurements of the kinetics of the back reaction by the restoration of the area over the fluorescence rise curve. The dependence of the live fluorescence yield from the concentration of closed PS II traps was assumed to be represented by Delosme's expression originally derived for the rise curve of the fluorescence yield in the presence of DCMU. The theory is based on the fact that then the partial and total light sums of luminescence are simple functions of the concentration of the primary electron acceptor Q‐ of PS II. Thus, after integrating the luminescence decay curve the theory permits a convenient evaluation of the kinetics of the back reaction [Q‐](t) in terms of the partial and total light sum. This method was applied in order to determine the kinetics of the back reaction in Chlorella fusca in the presence of DCMU. It is shown that the kinetics of deactivation of the S, state can be described using the expression for the kinetics of the back reaction derived by Mar and Roy. As an alternative explanation, a biphasic first order decay of S2 is proposed.

A library of copper-peptide/peptidomimetic complexes to explore the effect of ligand framework modification on electrocatalytic water oxidation

“…For these compounds, the CuL4 centers have an overall charge of 0, indicating two deprotonated amide nitrogen ligands and two uncharged nitrogen ligands, as expected for a high pH solution 29 . The g values are also consistent with established g values of Cu II in an N4 ligand environment 22 (Table ST 3…”