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Mon, 16 Feb 2009 21:47:29 +0900 |
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John,
From the non physicist's point of view the answer could go
something like this. If you have a power surge it can fry your
computer. But if your computer is not plugged into the mains then it
would take a very big power surge indeed to do the damage. A molecule
in the ground state can of course be damaged by free radical attack
but no more or less than other molecules. But once a molecule has
absorbed a photon then it is not in the ground state any more. To
continue my hoaky analogy, a chromophore in light is like your
computer plugged in to the mains.
Hope this helps. The physicists (and musicians) can go for
the triplets.
Tobias
>Hi Everyone, this question follows on from a helpful discussion
>that we had about photobleaching back in November. I have recently
>tried to explain to a group of colleagues about the mechanism of
>photobleaching. The answer is based on the transition of molecules
>from the excited singlet state (S1) to the triplet state (T1) which
>is long-lived and therefore more susceptible to bleaching by free
>radicals (my entire discussion of this is below).
>
>My question that arises from my attempted answer is: why are excited
>molecules more susceptible to oxidative attack than ground state
>molecules. I hope I'm not completely mucking up the mechanism here.
>Would the physicists out there please help.
>
>Thanks, John.
>
>The original answer: When excited, fluorophores generally transition
>from singlet ground state (S0) to singlet excited state (S1).
>Relaxation from S1 to S0 results in emission of heat and light
>(fluorescence). Lifetime in S1 is in the nano to pico second range
>and allows very little time for the excited molecule to interact
>with free radicals. Periodically, however, an excited molecule will
>do a transition from S1 to the triplet excited state (T1 - the
>physics of this is a bit difficult to understand). T1 is a very
>long-lived state - molecules can remain in T1 for up to the
>microsecond range - i.e. a thousand to a million times longer than
>for normal S1 state. It is during this long T1 state that molecules
>are attacked by free radicals and destroyed.
>
>--
>Runions signature
>
>(Sent from my cra%#y non-Blackberry electronic device that still has wires)
>
>
>
>*********************************
>John Runions, Ph.D.
>School of Life Sciences
>Oxford Brookes University
>Oxford, UK
>OX3 0BP
>
>email: <mailto:[log in to unmask]>[log in to unmask]
>phone: +44 (0) 1865 483 964
>
><http://www.brookes.ac.uk/lifesci/runions/HTMLpages/index.html%21>Runions'
>lab web site
>
>
>
>Visit <http://www.illuminatedcell.com/ER.html>The Illuminated Plant
>Cell dot com
>Oxford Brookes Master's in
><http://www.brookes.ac.uk/studying/courses/postgraduate/2007/bmt>Bioimaging
>with Molecular Technology
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