What is the basic theory of peak shift (Blue or Red) in circular dichroism spectrum of proteins (208,222 nm of alfa-helix or 218nm of betta sheet). and what is the mean of this blue/red shifts? Could scattering lead to any shift in CD spectrum !?
As it is appear in attached figure, all spectrums belongs to a whole alpha-helix protein, but in different condition. in Uv-vis spectroscopy we could interpret the reason of any shift according to chemical environments and its effects on energy level of molecular orbitals n,pi,pi*. Now I need to know the theory/reason of any shift in CD. Is it similar to UV-vis?
Hi there,
I do not exactly know what's your problems. But I think these two references may have some hints.
UV and CD spectroscopy are very different. CD gives information about the secondary structural elements in a protein. Any difference in the CD spectrum of a protein under different conditions (in your words peak shift) indicates structural changes in that protein. UV is mostly used for concentration dependent measurements of a particular chromophore. Hope this helps.
Good Luck
Venu.
I want to ask one thing about the peaks that obtained when did CD of denatured albumin. in compared to native albumin, denatured showed the blue shifting of 208 to 202, but 218 peak was not shifted, what does it mean ? Kindly request your responses.
Please see
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4305290/
Decreasing intensity and broadening of both the positive and the negative CD bands leads to a shift in the x-axis intersection point towards higher wavelengths, and both bands also exhibit a slight red shift. These changes can be attributed to absorption flattening and differential scattering phenomena. Absorption flattening is a consequence of the non-random distribution of chromophores within the sample, i.e. to differential absorption from different portions of the sample. In peptide-membrane samples it occurs when the peptide chromophores are sequestered in discrete regions of the sample with high local density. The extent of absorption flattening is proportional to the concentration of absorbers in each particle [43]. Thus, with increasing binding, more and more peptides seem to form extended β-pleated aggregates on the bilayer and thereby enhance the absorption flattening effects in the CD spectrum. Differential scattering of the incident radiation becomes more and more important with increasing aggregate size [44]. Thus, the more extended the β-sheets, the more severe is the loss in spectral intensity.
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