Doctoral Dissertations

Date of Award

5-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Bamin Khomami

Committee Members

Dibyendu Mukherjee, Pat Collier, Paul Frymier

Abstract

The robust structural and photoactive electrochemical properties of Photosystem I (PSI), a transmembrane photosynthetic protein complex, make it an ideal candidate for incorporation into solid state bioelectronic or hybrid photovoltaic devices. However, the first step towards the successful fabrication of such devices requires systematic assembly of oriented and functional PSI onto desired bio-abio interfaces via suitable protein scaffoldings. Hence, this dissertation focuses on utilizing the cyanobacterial PSI for integration into organic/inorganic interfaces that mediate photo-electrochemical energy conversions for electricity and/or solar fuel production. To this end, in this study the effect of systematic incorporation of PSI complexes into synthetic membrane-bound structures that mimic the natural thylakoid membrane housing of PSI quantifies via its performance and photocurrent response is demonstrated. Therefore, the surfactant-induced membrane solubilization of three phospholipids, namely DPhPC (1,2-diphytanoyl-sn-glycero-3-phosphocholine), DPPG (1,2-dipalmitoyl-sn-glycero-3-phospho-(1'-rac-glycerol)), and DPhPG (1,2-diphytanoyl-sn-glycero-3-phospho-(1'-rac-glycerol)) with the motivation of creating biomimetic reconstructs of PSI reconstitution in these liposomes are studied via isothermal titration calorimetry, turbidity measurements, dynamic light scattering and cryo-transmission electron microscopy imaging. The results indicate the typical three-stage solubilization process during lamellar-to-micellar transitions for liposomes is dictated by the critical detergent/phospholipid ratios. Considering that most successful protein incorporation occurs during the second stage of solublization, these studies set the backdrop for ideal concentration ratios for successful protein insertion in this stage. Furthermore, a facile yet elegant method for incorporation of PSI trimeric complexes into DPhPG bilayer membranes is introduced. The efficacy of this method is demonstrated via absorption and fluorescence spectroscopy measurements as well as direct visualization using atomic force microscopy. This study also provides direct evidence that PSI confinements in synthetic lipid scaffolds can be used for tuning the photoexcitation characteristics of PSI. Finally, detailed chronoamperometry measurements were conducted on PSI-proteoliposomes made from PSI incorporated within biomimetic membrane scaffolds and supported on suitable SAM substrates to investigate the enhancement in photocurrent responses arising from such confinement. The significant observation here is that the photo currents generated from PSI complexes under liposome confinements produce photocurrents four times higher than that produced from dense monolayer of individual PSI on SAM substrates using an equivalent concentration of PSI.

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