Dynamic and reversible self-assembly of photoelectrochemical complexes based on lipid bilayer disks, photosynthetic reaction centers, and single-walled carbon nanotubes

An aq. soln. contg. photosynthetic reaction centers (RCs), membrane scaffold proteins (MSPs), phospholipids, and single-walled carbon nanotubes (SWCNTs) solubilized with the surfactant sodium cholate (SC) reversibly self-assembles into a highly ordered structure upon dialysis of the latter. The resulting structure is photoelectrochem. active and consists of 4-nm-thick lipid bilayer disks (nanodisks, NDs) arranged parallel to the surface of the SWCNT with the RC housed within the bilayer such that its hole injecting site faces the nanotube surface. The structure can be assembled and disassembled autonomously with the addn. or removal of surfactant. We model the kinetic and thermodn. forces that drive the dynamics of this reversible self-assembly process. The assembly is monitored using spectrofluorimetry during dialysis and subsequent surfactant addn. and used to fit a kinetic model to det. the forward and reverse rate consts. of ND and ND-SWCNT formation. The calcd. ND and ND-SWCNT forward rate consts. are 79 mM-1 s-1 and 5.4 × 102 mM-1 s-1, resp., and the reverse rate consts. are negligible over the dialysis time scale. We find that the reaction is not diffusion-controlled since the ND-SWCNT reaction, which consists of entities with smaller diffusion coeffs., has a larger reaction rate const. Using these rate parameters, we were able to develop a kinetic phase diagram for the formation of ND-SWCNT complexes, which indicates an optimal dialysis rate of approx. 8 × 10-4 s-1. We also fit the model to cyclic ND-SWCNT assembly and disassembly expts. and hence mimic the thermodn. forces used in regeneration processes detailed previously. Such forces may form the basis of both synthetic and natural photoelectrochem. complexes capable of dynamic component replacement and repair. [on SciFinder(R)]