Hi Paul,
The positive peak you speak of is not wrong at all. Look at this weblink to see the typical behaviour of CD spectra by ss type, taken over a wide spectrum, extending way beyond 200 nm.
http://www.britishbiophysics.org.uk/what-is/cd/cd.html
This was often cited as justification for using SR CD as opposed to bench top CD.
As for analysis of the spectra, you might want to look up this server
http://dichroweb.cryst.bbk.ac.uk/
I must say that I never measured a CD spectrum or analysed one, so I would not be able to comment on the results output. Good Luck.
Pierre
**********************************************************************
Dr. Pierre Rizkallah, Senior Lecturer in Structural Biology, WHRI, School of Medicine, Academic Avenue, Heath Park, Cardiff CF14 4XN
email: [log in to unmask] phone + 44 29 2074 2248
>>> P Hubbard <[log in to unmask]> 12/09/09 7:00 PM >>>
Hi all,
I've limited experience interpreting CD spectra, so I might be missing something, but I've collected CD data for a hydrophobic 15-mer peptide that forms a putative alpha-helix. I get a region of strong negative ellipticity, bottoming out at ~222nm; however, I also get a strong positive peak (of equal magnitude to the 222nm minimum) at ~208nm. This 208 peak is opposite to a textbook alpha-helical spectrum (like it's been inverted).
From what I've read, short alpha-heical peptides often lack 208nm minima, and protonated carboxyl groups producce positive ellipticity at this wavelength; however, apart from the C-terminus, I don't have any carboxyl groups, and the peptide is in standard PBS buffer to boot. Any suggestions on what might be causing this odd 208 peak? NOTE: current data isn't below 200nm.
Thanks!
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