| There are many types of bacteria that can convert light energy into chemical energy through the process of photosynthesis. This process has been studied for some time now, and in general is well understood. The process of funneling the light energy from the cell membrane to the reaction center is achieved by an array of molecules called antenna complexes. They consist of a series of bacteriochlorophyll and carotenoid molecules located close enough to each other to pass singlet excitation energy to the reaction center. The carotenoids are there to rid the complex of unwanted triplet energy by thermal relaxation. In this research, the energetic process of singlet fission has been conclusively confirmed for the first time in this type of antennae system. In this process, the energy of an excited carotenoid singlet state is converted into two triplet states on two separate carotenoid molecules. This process requires the two carotenoids to be in close proximity, and the energy of the excited singlet state to be twice that of the triplet state. The fact that two spirilloxanthin molecules (the carotenoid in Rsp. rubrum) are in van der Waals contact has not been known before, and therefore this work has given structural data of these complexes. This knowledge is important due to the difficulty of crystallizing the molecules for X-ray analysis.; Studies were also performed on the PCP A antenna complex of the algae Amphidinium carterae. Early projects focused on electron nuclear double resonance to investigate hydrogen hyperfine couplings with the triplet excitation on the carotenoid of the algae, peridinin. Spin densities were calculated which gave specific HOMO and LUMO data about the two unpaired electrons. This is the first pulsed ENDOR study of a carotenoid triplet state in an antenna system, and should open the door for many more studies to gain much more information about the structure and function of the antenna systems in their role as photo-protectants. |
