Biomimetic monolayer films of monogalactosyldiacylglycerol incorporating ubiquinone

Abstract

Ubiquinone and plastoquinone are two of the main electron and proton shuttle molecules in biological systems, and monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the thylakoid membrane of chloroplasts. Saturated MGDG, ubiquinone-10 (UQ) and MGDG:UQ mixed monolayers at the air/water interface have been studied using Surface Pressure-Area isotherms and Brewster Angle Microscopy. Moreover, the transferred Langmuir-Blodgett films have been observed by Atomic Force Microscopy. The results show that MGDG:UQ mixtures present more fluid phase than pure MGDG indicating a higher order degree for the later. It is also observed an important influence of UQ on the MGDG matrix before UQ collapse pressure and a low influence after this event, due to UQ expulsion from the MGDG matrix. This expulsion leads to a similar remaining UQ content for all the tested mixtures, indicating a limiting content of this molecule in the MGDG matrix at high surface pressures. The thermodynamic studies confirm the stability of the MGDG:UQ mixtures at low surface pressures, although presenting a non-ideal behaviour. Results point to consider UQ as a good candidate for studies of artificial photosynthesis.

Electrochemistry of LB films of mixed MGDG:UQ on ITO

“…1), the AFM results reported in our previous work [31] and the electrochemical discussion presented in the previous section. The description of the UQ positons in the MGDG monolayer will be made using the model proposed by Söderhäll and Laaksonen [52].…”

“…The AFM studies of the LB films of pure MGDG and MGDG:UQ mixtures on mica reported in [31] indicated that the MGDG and the MGDG:UQ mixtures with low UQ content, both at low surface pressure, present similar covered area by the LC state, whereas the MGDG:UQ 5:1 ratio presents a markedly lower covered area by this LC state. These observations indicate that UQ is present in both physical states (LE and LC) in the MGDG:UQ mixtures.…”

“…The main results about the surface pressure-area, π-A, isotherms and thermodynamic processing of mixed films of MGDG and UQ have been presented previously [31]. Table 1 summarizes some of the characteristic values of these isotherms.…”

“…In this work the electrochemistry of mixed films of MGDG and UQ on ITO has been studied, being the thermodynamic and topographic results of these films presented in a previous article [31]. MGDG has been chosen because it is the principal component in the thylakoid membrane and UQ seems a good substitute for PQ.…”

Langmuir films study on lipid-containing artificial tears

“…The Langmuir technique has been applied previously by the author to study the behaviour of lipid and phospholipid films [28,29]. In this work Langmuir films have been obtained from lipid-containing artificial tears and the corresponding surface pressure-area isotherms registered.…”