SubjectsMembranes (Biology), Oxidation-reduction reaction, Membranes (Biology), Reacció d'oxidació-reducció

ProvenanceThe master thesis in chemical processes I present here is part of a four years project with the objective of plastoquinone (PQ) redox processes in natural cell membranes is fully understood. This is a complex process, so studying techniques must be adapted to work with PQ. Here we use duroquinone (DQ) and ubiquinone (UQ) to obtain the better conditions and 1,2-dipalmitoil-sn-glicero-3-phosphocoline (DPPC) to model natural cell membranes. The bibliography research shows two main techniques to mimic natural cell membrane. These are supported planar bilayer (SPB) and Langmuir-Blodgett films (LB) and I apply them to DQ and UQ. Previously to the SPB or LB formation, DQ redox processes in hydro-ethanolic solution are studied. Processes in solution give us information of the bare substrate behavior which will be useful when comparing the substrate coverture with SPB or LB. UQ is not able to be studied in hydro-ethanolic solution due to its high hydrophobic character. SPB of mixtures DPPC:DQ or DPPC:UQ are prepared and imaged using Atomic Force Microscopy (AFM), these images show a SPB fully formed with short hole density. In the images, DQ or UQ expulsion or agregates are not appreciated; this means that the main part of the quinones present in SPB preparation is retained between layers of the SPB. The peak current linear dependence with the scan rate shows specie confined behavior in the case of DQ and control diffusion behavior for UQ. Peak potentials and peak currents of DQ and UQ in SPB are close showing a similar redox process not depending on the isoprenoid chain length. Langmuir technique and LB films are not able to be applied for DQ due to its slight solubility in water. Surface pressure-Area per molecule isotherms show that UQ difficults the DPPC matrix formation. The monolayer compression expels the exceeding UQ at high surface pressure achieving the pure DPPC isotherm behavior. LB films characterization confirms the DPPC:UQ monolayer fully formation, UQ expulsion at high surface pressure and the increasing monolayer compactation grade as the surface pressure does it. Cyclic voltammetry of DPPC:UQ LB films shows the diffusion of the electroactive species is the controlling step. In summary, the initial objectives have been achieved adapting the most common techniques used for mimicking membranes to use them with PQ and also the results obtained are helpful for detailing the PQ behavior in natural cell membranes.

DegreeMÀSTER UNIVERSITARI EN RECERCA EN ENGINYERIA DE PROCESSOS QUÍMICS (Pla 2009)