Raman Optical Activity of Biological Molecules - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 157

has neutral side chains and so adopts an -helical conformation stabilized both

by internal hydrogen bonds and by hydrogen bonds to the solvent; whereas
poly(l-lysine) at neutral and acidic pH has charged side chains that repel
each other, which leads to a disordered structure [34]. Heating of

α

α -helical

polylysine leads to adoption of a -sheet conformation. The backscattered

ICP Raman (top) and ROA (bottom) spectra of these samples are shown
in Fig. 7.4a-c, respectively [3, 4, 35]. There are obvious differences between
the Raman spectra for the

β

-sheet conformations of
poly(l-lysine) but it is clear that the differences between the corresponding
ROA spectra are far more significant, particularly in the fingerprint amide
III region, indicating the enhanced sensitivity of ROA spectra to secondary
structure.

α -helical, disordered and β

7.4.1 ROA Signatures of α -Helix

The ROA spectra of hen lysozyme [3, 35] and bovine -lactoglobulin [3] are

shown in Fig. 7.5. These spectra contain marker bands for the secondary
structural motifs discussed above showing that this information is retained

β

Fig. 7.5. Backscattered ICP Raman I R + I L and ROA I R − I L spectra of ( a )

hen lysozyme and ( b ) bovine β-lactoglobulin