@article{Photosynthetic:1877,
      recid = {1877},
      author = {Massey, Sara Chamberlin},
      title = {Ultrafast Energy Transfer and Orientational Dynamics in  Photosynthetic Bacterial Membranes},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2019-06},
      pages = {131},
      abstract = {Photosynthetic organisms have adapted to survive in their  diverse native habitats, whether by maximizing  light-harvesting efficiency in low-light environments or by  quenching excess excitations to prevent the formation of  damaging reactive oxygen species. Photosynthetic species  follow a number of principles in the design of  pigment-protein light-harvesters, including the dense  packing of chromophores, repeating the same pigment many  times, and using interactions with other pigments and the  environment to tune the absorbance spectrum. We seek to  understand the ultrafast dynamics of light harvesting in  these organisms that take place on the femtosecond  timescale. In this thesis, I track energy moving through  both energetically distinct and degenerate states by  integrating ultrafast two-dimensional electronic  spectroscopy with anisotropy and power-dependence  experiments. I present results on the ultrafast energy  transfer processes in the anoxygenic photosynthetic purple  bacterium Rhodobacter sphaeroides and the oxygenic  cyanobacterium Synechocystis sp PCC 6803 in their native  membrane environments. Both of these organisms use  light-harvesting antenna complexes to collect light energy  and funnel that energy to an energetic trap known as the  reaction center which produces a trans-membrane electron  gradient that drives photosynthetic reactions. 

In  Rhodobacter sphaeroides, we collected the first  two-dimensional electronic anisotropy spectra, revealing  time-dependent dynamics of the transition dipole  orientations in membrane-bound light harvesting complex 2  (LH2). This pioneering spectroscopy reveals orientational  preferences for sequential absorption processes, ultrafast  intra-band equilibrations, and differentiates energy  transfer processes from spectrally overlapped states that  are otherwise unresolvable. We investigated  light-harvesting pathways in LH2 from organisms grown under  varied light and oxygen conditions to determine whether an  energy quenching pathway was introduced. We present a  revised picture of the B850 dynamics in LH2, showing power  dependent dynamics that were previously thought to be  inherent to the B850 ring.

The first two-dimensional  spectra of intact cyanobacterial thylakoid membranes are  also presented here. We seek to disentangle the spectral  contributions of the fused antenna/reaction center  photosystems in Synechocystis sp PCC 6803 and map out  inter-complex energy transfer. Mutations deleting specific  portions of the photosynthetic machinery enable us to  attribute spectral features and dynamics to specific  complexes that would otherwise be indistinct. Future  planned experiments include the investigation of  cyanobacterial photoprotection and the effect of iron  stress on energy transfer pathways.},
      url = {http://knowledge.uchicago.edu/record/1877},
      doi = {https://doi.org/10.6082/uchicago.1877},
}