Effect of biogenic photochromic electron acceptors on chlorophyll fluorescence

It is shown that the photophysical properties of chlorophyll a (Chl) depend on the nature and relative amounts of 2-methyl-1,4-naphthoquinone (MNQ) and nicotinamide adenine dinucleotide phosphate (NADP). Photoinduced charge separation occurs in aqueous ethanol solutions of Chl (1 × 10^?5 M) and NADP (5 × 10^?6–5 × 10^?4 M), resulting in the dynamic quenching of Chl fluorescence. Coordination interaction between Chl and NADP is established at an NADP concentration of ≥5 × 10^?4 M. The nonlinear Stern-Volmer dependence in this range is due to the input from static quenching. It is shown that the quenching of Chl fluorescence in an MNQ solution at Chl and MNQ concentrations of 1 × 10^?5 M and 6.7 × 10^?5–1 × 10^?4 M, respectively, is described by a linear dependence in the Stern-Volmer coordinates; no complex formation is observed for Chl and MNQ under these conditions, and electron transfer is of the dynamic type. Static or mixed-type energy transfer from MNQ to Chl dominates at elevated MNQ concentrations.