Transmembrane Electron Transfer Reaction assisted by Semiconductor Nanoparticles

A. G. BRACAMONTE; PROF. NITA SAHAI

Galveston

Congreso; Gordon Research Conferences; 2014

Gordon Research Conferences

Transmembrane Electron Transfer Reaction Assisted by Minerals (TM-ETR) This project is related to the development of a synthetic mimetic system of protocells. The aim is to design a supramolecular system for transmembrane electron potential and energy transfer from outside the cell to inside, in order to mimic metabolism in the Origins of the Life. In modern cells, TM-ETR is achieved by enzymes in the phospholipid membranes. We propose that photocatalytic minerals, such as CdS or FeS2, may have acted as prebiotic enzymes. Sulfide minerals would have been stable, because of the the O2 content on the early Earth atmosphere.[1] TM-ETR has been achieved previously using an intramembrane polyaromatic hydrocarbon which played the role of both photoinitator and transmembrane electron-shuttle.[2] We believe that many pathways could have lead to the emergence of protocells in the origins of life, including minerals as prebiotic enzymes in TM-ETR. The model organized model system is formed by: 1) CdS Photoinitiator that it is grafted over decanoic acid/decanol vesicle membranes, 2) Oxidant (O) loaded inside the vesicle (methyl viologen, MV2+), 3) Transmembrane electron-shuttle (Q) incorporated into the bilayer (naphtopyrene or anthraquinone), 4) extravesicular Reductant (R) (Methanol or EDTA). MV2+ is chosen as the model oxidant, because it changes from colorless to blue colour in the reduced form, which facilitates analytical detection of the redox reaction. Single chain amphiphiles, Q and R species chosen are simple compounds, which were likely present on early Earth. Vesicles of decanoic acid/ decanol were synthesized and the bilayer was modified with CdS. Two approaches were tested. In the first method, CdS was added to a pre-formed vesicle suspension, with the expectation that CdS would be incorporated in the bilayer due to the mineral?s hydrophobicity. Another approach was to stabilize CdS with a hydrophilic capping agent, L-Cysteine, to render the CdS soluble in water, using methods described previously. [3] Both methods for incorporating CdS into the membrane were potentially possible in prebiotic conditions. The kinetic stability of decanoic acid/decanol (2:1 ratio) vesicles in phosphate buffer at pH 7.4 was examined using Dynamic Light Scattering (DLS) and Zeta-Potential measurements. Vesicles with a diameter ~ 1 m were found to be stable at 3 h of vortex agitation. The viability of using the two approaches to incorporate CdS into the vesicle membrane was studied by UV absorption, fluorescence emission by spectrophotometry, fluorescence and phase-contrast microscopy and Transmission Electron Microscopy. It was observed that CdS was successfully incorporated in the membrane by both methods. The oxidant was successfully encapsulated into the vesicle and permeability was determined to be negligible. Experiments are currently in progress to complete the phtocatalyzed TM-ETR.