Electron-transfer dynamics of photosynthetic reaction centers in thermoresponsive soft materials

Philip D. Laible, Richard F. Kelley, Michael R Wasielewski, Millicent A. Firestone

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Poly(ethylene glycol)-grafted, lipid-based, thermoresponsive, soft nanostructures are shown to serve as scaffolding into which reconstituted integral membrane proteins, such as the bacterial photosynthetic reaction centers (RCs) can be stabilized, and their packing arrangement, and hence photophysical properties, can be controlled. The self-assembled nanostructures exist in two distinct states: a liquid-crystalline gel phase at temperatures above 21°C and a non-birefringent, reduced viscosity state at lower temperatures. Characterization of the effect of protein introduction on the mesoscopic structure of the materials by 31P NMR and small-angle X-ray scattering shows that the expanded lamellar structure of the protein-free material is retained. At reduced temperatures, however, the aggregate structure is found to convert from a two-dimensional normal hexagonal structure to a three-dimensional cubic phase upon introduction of the RCs. Structural and functional characteristics of the RCs were determined by ground-state and femtosecond transient absorption spectroscopy. Time-resolved results indicate that the kinetics of primary electron transfer for the RCs in the low-viscosity cold phase of the self-assembled nanostructures are identical to those observed in a detergent-solubilized state in buffered aqueous solutions (∼4 ps) over a wide range of protein concentrations and experimental conditions. This is also true for RCs held within the lamellar gel phase at low protein concentrations and at short sample storage times. In contrast are kinetics from samples that are prepared with high RC concentrations and stored for several hours, which display additional kinetic components with extended electron-transfer times (∼10-12 ps). This observation is tentatively attributed to energy transfer between RCs that have laterally (in-plane) organized within the lipid bilayers of the lamellar gel phase prior to charge separation. These results not only demonstrate the use of soft nanostructures as a matrix in which to stabilize and organize membrane proteins but also suggest the possibility of using them to control the interactions between proteins and thus to tune their collective optical/electronic properties.

Original languageEnglish
Pages (from-to)23679-23686
Number of pages8
JournalJournal of Physical Chemistry B
Volume109
Issue number49
DOIs
Publication statusPublished - Dec 15 2005

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Photosynthetic Reaction Center Complex Proteins
electron transfer
Nanostructures
proteins
Proteins
Electrons
Gels
Kinetics
Membrane Proteins
gels
Viscosity
lipids
Lipid bilayers
Lamellar structures
kinetics
X ray scattering
viscosity
Absorption spectroscopy
membranes
Membranes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Electron-transfer dynamics of photosynthetic reaction centers in thermoresponsive soft materials. / Laible, Philip D.; Kelley, Richard F.; Wasielewski, Michael R; Firestone, Millicent A.

In: Journal of Physical Chemistry B, Vol. 109, No. 49, 15.12.2005, p. 23679-23686.

Research output: Contribution to journalArticle

Laible, Philip D. ; Kelley, Richard F. ; Wasielewski, Michael R ; Firestone, Millicent A. / Electron-transfer dynamics of photosynthetic reaction centers in thermoresponsive soft materials. In: Journal of Physical Chemistry B. 2005 ; Vol. 109, No. 49. pp. 23679-23686.
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