Studies on the Initial Photochemical Event in Photosynthetic Systems
Michael C. Zerner
Quantum Theory Project
Departments of Chemistry and Physics
University of Florida
Gainesville, FL 32611
Photosynthesis is the process which converts atmospheric carbon dioxide
into sugars and starches and begins the process of biosynthesis. Nearly
all of the fixed carbon on earth is due to photosynthesis, and the
atmosphere of the earth has been transformed from one of reducing power
to one of oxidizing power.
Carbon dioxide is the product of combustion of hydrocarbons and carbohydrates.
Our sun supplies the energy to reverse the process of combustion and
drive the synthesis of complex organic molecules.
We report on quantum mechanical studies on the reaction center (RC) found in
photosynthetic bacteria, and study, in particular, the initial photochemical
events. The study begins with adressing the excited states of chlorophyll,
and then the special pair (dimer) of chlorophyll molecules that is the
energy trap in these systems. A summary is then made of the electron
transfer that shortly follows the excitation, and that supplies the energy
to fix atmospheric carbon dioxide, a very stable molecule, into sugars and
There are approximately 250 antenna chlorophyll molecules for every
reaction center. The photochemistry usually begins with excitation to
"light harvesting system 2" (LHII), and this energy is than transfered to
LH1 that surrounds the RC of bacterial photosynthetic systems. We examine
the excitastion energies of LHI and LHII, and speculate on the highly
efficient energy transfer through the antenna to the RC.