UV RAMAN INVESTIGATION OF PEPTIDEHYDRATION AND HYDROPHOBIC COLLAPSE

Hydration of an alpha-helical, 21 residue, mainly Ala peptide was investigated by UV resonance Raman (UVR) spectroscopy. UVR spectra in the dehydrated solid state were compared to those in aqueous solution at different temperatures. The amide band frequencies of a dehydrated solid alpha-helix peptide show frequency shifts compared to those in aqueous solution due to the loss of amide backbone hydrogen bonding to water; the amide II and amide III bands of the solid alpha-helix downshift, while the amide I band upshifts. The shifts are identical in direction but smaller than those that occur for alpha-helices in aqueous solution as the temperature increases; water hydrogen bonding strengths decrease as the temperature increases. The UV Raman amide band frequency shifts can be used to monitor alpha-helix hydrogen bonding.In addition, the phenomenon of hydrophobic collapse was investigated in poly(N-isopropylacrylamide) hydrogel nanoparticles. ~100 nm hydrogel particles were synthesized and analyzed with variety of methods including UVR spectroscopy. The changes in UVR amide spectra are similar to those observed for peptide dehydration. The Raman bands associated with C-H stretching vibrations change in a manner expected to dehydration as well. Comparison of spectral changes of isopropyl group vibrations to that of amide group suggests different dehydration pattern of the two groups. Kinetics of the dehydration of the amide groups indicates a complex process, which can not be described by a two state model