i want to use chlorophyll as photosensitizer for my dye sensitized solar cell, i found through many research sources that chlorophyll after having been extracted from the leaves will deteriorate when been exposed to sunlight, if that is the case then how do plants protect their chlorophyll pigment?
Hi,
We use norflurazon to block the synthesis of carotenoids in Arabidopsis seedlings. Carotenoids are needed to protect chlorophyll against light. The seedlings are almost colorless in the absence of these carotenoids, because they are lacking chorophyll as well.
Maybe this work is interesting for your application:
http://www.pnas.org/content/97/20/11098.full.pdf
Best,
Boas
Dear Lokesh Murali,
The protection of chlorophylls from photooxidation is a very complex subject in plant physiology. The whole photosynthetic apparatus ensures this protection, at least partially. The existence of chlorophyll-protein complexes (with light harvesting and reaction centre functions) is needed but the functioning electron transport chain has similar importance. Of course, carotenoids are very important if they are arranged in proper geometry. There are plenty of books describing how the photochemical reaction centres can convert the light energy into chemical energy; you can find the details in them.
Coming to isolated chlorophylls, the problem is that the absorbed light energy excites the pigment but the native energy or electron acceptor is missing. The energy, however, can be transferred to oxygen, excite it and produce singlet oxygen molecules, which decompose chlorophylls. Lots of other chemical reactions can proceed even during isolation of chlorophylls. An example is the pheophytin production when the Mg leaves the porphyrin ring.
I would suggest you to use Cu-porphyrin in your system; it is more stable than Mg-porphyrins (i.e. chlorophylls).
Greetings,
Bela Böddi
Are you using isolated chlorophyll? Free chlorophyll and chlorophyll bound to proteins are very different. The later ones are very stable because: (1) chemical environment is different; (2) Energy transfer is fast enough to avoid over excitation; (3) plants have many photo-protection mechanisms.
Even though a lot of research has been done in the topic, still we do not really understand how does photodamage affects plants. The same goes for photoprotection. Even though many scientist may tell you this is well studied, the reality is that there is no consensus.
For every event of excitation a percentage of chlorophyll will go through inter system crossing in triplet state. This triplet is quite reactive and potentially damaging. At oxygenic conditions, most of the triplets induce singlet oxygen formation. Singlet oxygen is very reactive and oxydices everything around or can be converted in to other radical species. This radicals oxidize the pigment systems bleaching them (a type of photobleaching). Carotenes and other molecules seem to act as scavengers of ROS.
The most traditional view about this topic is that if plants are not in excess of energy (via metabolic reactions) and excitation quenching mechanisms are present, then excessive energy and photodamage is prevented. Also, chloroplast movement and synthesis of other molecules prevent damage. However, evidence from 2000 onward seem to suggest that the quenching mechanism maybe protective in certain cases only.
It is a rather complicated topic, the best is to read papers of Alexander Ruban, Herbert van Amerongen and Demming-Adams to get the whole picture about the traditional paradigm of photoprotection. Tyystyarvii, Murata, Tersashima and Chow about alternatives.
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