Biomimetic monolayer films of monogalactosyldiacylglycerol incorporating plastoquinone.

Photosynthetic organisms use light to convert the inorganic matter in organic one. Photosynthetic process consists on several steps, and one of them involves plastoquinone (PQ) that acts as electron and proton shuttle between photosystem II and cytochrome. We prepared membranes that mimic the characteristics and composition of natural photosynthetic membranes and we characterized them using several techniques in order to obtain both the PQ molecules disposition in the membrane and their electrochemical behavior. The selected lipid was monogalactosyldiacylglycerol (MGDG) that represents the 50% of the lipid content of the thylakoid membrane. Both MGDG and PQ, and the MGDG:PQ mixtures have been studied using surface pressure-area isotherms and the presence of PQ alters the physical state and compactness of the MGDG matrix. Langmuir-Blodgett (LB) films have been obtained by transferring a monolayer that mimics half of the bilayer of a biological membrane. The AFM topographical characterization of the monolayers on mica indicates the presence of differentiated domains, corresponding to different physical states linked to the influence of the PQ content. Moreover, the electrochemical behavior of the monolayers has been studied when transferred on ITO, observing one main electrochemical process that is due to the diving position of PQ molecules in the lipid matrix.