In this work biomimetic monolayers of a MGDG, monogalactosyldiacylglycerol, and DGDG, digalactosyldiacylglycerol mixture (MD), in a ratio close to that of the thylakoid membranes of oxygenic photosynthetic organisms, have been prepared. The lipid mixture incorporates plastoquinone-9 (PQ), that is the election and proton shuttle of the photosynthetic reaction centres. The MD:PQ mixtures have been firstly studied using surface pressure-area isotherms. Langmuir-Blodgett (LB) films of those mixtures have been transferred onto a substrate forming a monolayer that mimics one of the bilayer sides of the thylakoid membranes. These monolayers have been characterized topographically and electrochemically. The results show the influence of PQ in the MD matrix and its partial expulsion when increasing the surface pressure, obtaining two main PQ positions in the MD matrix. The calculated apparent electron transfer rate constants indicate a different kinetic control for the reduction and the oxidation of the PQ/PQH(2) couple, being k(Rapp)(I) = 0.7 . 10(-6) s(-1), k(Rapp)(II) = 2.2 . 10(-9) s(-1), k(Oapp)(I) = 7.4 . 10(-4) s(-1) and k(Oapp)(II) = 5.2 . 10(-5) s(-1), respectively. The comparison of the different galactolipid:PQ systems that our group has studied is also presented, concluding that the PQ position in the galactolipid matrix can be tuned according to several controlled variables. (C) 2016 Elsevier B.V. All rights reserved.
García-Sánchez, T.; Azan, A.; Leray, I.; Rosell, F.; Bragos, R.; Mir, Lluís M. Bioelectrochemistry Vol. 105, p. 123-135 DOI: 10.1016/j.bioelechem.2015.05.018 Data de publicació: 2015-10-01 Article en revista
In this study, electrical impedance spectroscopy measurements are performed during electroporation of monolayers of differentiated myotubes. The time resolution of the system (1 spectrum/ms) enable 860 full spectra (21 frequencies from 5 kHz to 13 MHz) to be acquired during the time gap between consecutive pulses (interpulse) of a classical electroporation treatment (8 pulses, 100 mu s, 1 Hz). Additionally, the characteristics of the custom microelectrode assembly used allow the experiments to be performed directly in situ in standard 24 multi-well plates. The impedance response dynamics are studied for three different electric field intensities (400, 800 and 1200 V/cm). The multifrequency information, analysed with the Cole model, reveals a short-term impedance recovery after each pulse in accordance with the fast resealing of the cell membrane, and a long-term impedance decay over the complete treatment in accordance with an accumulated effect pulse after pulse. The analysis shows differences between the lowest electric field condition and the other two, suggesting that different mechanisms that may be related with the reversibility of the process are activated. As a result of the multifrequency information, the system is able to measure simultaneously the conductivity variations due to ion diffusion during electroporation. Finally, in order to reinforce the physical interpretation of the results, a complementary electrical equivalent model is used.