birefringence

[Tony Planchart]

In <3cs2ol$kdn at lyra.csx.cam.ac.uk> sgb12 at mole.bio.cam.ac.uk writes:

> Can anyone advise me how to visualise birefringence of a peptide in 
> solution drawn up into a capillary tube. The peptide polymerises and I am 
> told that if it has birefringence when drawn into a capillary it is 
> possible to obtain useful x-ray data. The problem is that I don't know 
> what I'm looking for or how to look for it!


You will need a light microscope with cross-polarizers.  Rotate the 
polarizer directly attached to the nosepiece until the field is black and 
place your specimen on the stage.  Rotate the stage and you should see 
colors fade in and out of your specimen.  These are the first (and higher) 
order birefringence colors (colours).  When you find the most intense color 
distribution, note the position of the stage and rotate 45 degrees in 
either direction.  If the specimen is ordered, you should see the colors 
extinguish completely.  The full effect is truly spectacular in a darkened 
room.

Alternatively, use Kodak gratings (sheets of plastic with finely spaced 
etchings) as the cross-polarizers and use a light box.  Not the most 
sophisticated setup but usually sufficient to do the job.

BTW, your system sounds like a potential fiber diffraction experiment 
specimen.  Good Luck.

Tony