@article{pittir17211,
          volume = {128},
          number = {42},
           month = {October},
          author = {AV Mikhonin and SA Asher},
           title = {Direct UV Raman monitoring of 3{\ensuremath{<}}inf{\ensuremath{>}}10{\ensuremath{<}}/inf{\ensuremath{>}}-helix and {\ensuremath{\pi}}-bulge premelting during {\ensuremath{\alpha}}-helix unfolding},
         journal = {Journal of the American Chemical Society},
           pages = {13789 -- 13795},
            year = {2006},
             url = {http://d-scholarship-dev.library.pitt.edu/17211/},
        abstract = {We used UV resonance Raman (UVRR) spectroscopy exciting at {$\sim$}200 nm within the peptide bond {\ensuremath{\pi}}{$\rightarrow$}{\ensuremath{\pi}}* transitions to selectively study the amide vibrations of peptide bonds during {\ensuremath{\alpha}}-helix melting. The dependence of the amide frequencies on their {\ensuremath{\Psi}} Ramachandran angles and hydrogen bonding enables us, for the first time, to experimentally determine the temperature dependence of the peptide bond {\ensuremath{\Psi}} Ramachandran angle population distribution of a 21-residue mainly alanine peptide. These {\ensuremath{\Psi}} distributions allow us to easily discriminate between {\ensuremath{\alpha}}-helix, 310-helix and {\ensuremath{\alpha}}-helix/bulge conformations, obtain their individual melting curves, and estimate the corresponding Zimm and Bragg parameters. A striking finding is that {\ensuremath{\alpha}}-helix melting is more cooperative and shows a higher melting temperature than previously erroneously observed. These {\ensuremath{\Psi}} distributions also enable the experimental determination of the Gibbs free energy landscape along the {\ensuremath{\Psi}} reaction coordinate, which further allows us to estimate the free energy barriers along the AP melting pathway. These results will serve as a benchmark for the numerous untested theoretical studies of protein and peptide folding. {\copyright} 2006 American Chemical Society.}
}