Red Shifted Chlorophyll:
Chlorophylls are molecules which absorb light during photosynthesis. We are familiar with four different types of chlorophylls molecules, termed as Chlorophyll a, Chlorophyll b, Chlorophyll c, and Chlorophyll d. All these pigments can be found within light harvesting complex of photosystem. For a long time Chl a pigment has been demonstrated as main pigment which carry out the energy transduction in the photosynthates. But after that it was determined that Chl d can also serve the same role in oxygenic photosynthesis. This assumption was based on discovery that Acaryochloris marina a cyanobacteria has 99% chlorophyll d of total pigment in its photosystem.
In the study carry out by Chen et al., (2010) a new chlorophyll pigment has been demonstrated, which is named as Chl f. In this study a sample from the Hamelin pool was cultured under the light near infrared. The extract of chlorophylls, from stromatolites of Shark Bay which is locality in Western Australia, was obtained by the methane. This extract was analyzed by HPLC, the results shows a large amount of Chl a and bacteriochlorophyll a, traces of Chl d and a new pigment Chl f.
The study on optimum absorption, shows that this Chl f molecule absorb maximum wavelength of 706 nm. This shows a red shift in absorption spectrum compared to other molecules of chlorophyll. A change in absorption spectrum was also noted in blue region of light. This shift in blue absorption shows that maximum absorption is at 407 nm. Further analysis shows that Chl f is synthesized in filamentous cyanobateria. This discovery about synthesis is based on 16S ribosomal RNA sequencing of purest culture which contain only Chla and Chl f.
Molecular formula of Chl f assigned is C55H70O6N4Mg by mass spectral analysis. Formyle group was indentified by NMR spectroscopy of Chl f. Structure of other chlorophyll molecules shows that Chl d has fomyle group at carbon number 3 and methyl group at C-2, Chl a has CH3 at C-2, and Chl b has methyl group at C-2 and formyle group at C-7. But newly discovered Chl f molecule has formyle group at C-2 position. This structural change in Chl f compared to other molecules of Chlorophylls, enable it to absorb a light of different wavelength.
λmax(red region) = 706nm and λmax (blue region) = 406nm
Chen, M., M. Schliep, R. D. Willow, Z. Cai, B. A. Neilan and H. Scheer. (2010). A red shifted chlorophyll. Science. 329: 1318-1319.