The Spectral Properties of Chlorophyll and Bacteriochlorophyll Dimers; a Comparative Study
Reaction centers (RCs) of photosynthetic bacteria generally contain four bacteriochlorophylls (Bchls) and two bacteriopheophytins (Bphs) that have three main absorption bands in the near infrared (NIR) (1). The transitions occur at 860–870, 803–814 and 760 nm in species that contain Bchla, and at 960–1000, 820–850 and 790–810 nm in species that contain Bchlb. They are all optically active with a net positive rotation for the lowest energy transition (2). The total oscillator strength in the NIR region is larger by 10–20% than the oscillator strength of the chromophore extract in that region (3). In the visible region, the reaction centers absorb at ≈ 600 nm with a double Cotton effect (2) and an oscillator strength which is smaller than that of the in vitro extract by ≈ 10% (3). There is another band at ≈ 540 nm, which splits at low temperature. A strong absorption with a complicated circular dichroism pattern is seen in the UV; Its oscillator strength is weaker and it is red shifted relative to the maximum absorption of the pigment extract in that region.
KeywordsOscillator Strength Transition Dipole Photosynthetic Bacterium Soret Band Special Pair
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