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Analysis of the delocalized Raman modes of conformationally disordered polypeptides
L X Chen1, H L Strauss, R G Snyder
1Department of Chemistry, University of California, Berkeley 94720.
Biophysical Journal
|May 1, 1993
Summary
Raman spectra reveal that disordered polyglycine chains in solution quickly resemble infinite chains, even at short lengths. This rapid convergence is due to vibrational mode localization in disordered structures.
Area of Science:
- Spectroscopy
- Computational Chemistry
- Biophysics
Background:
- Polyglycine oligomers exist in aqueous solution as zwitterions and cations.
- Understanding vibrational modes in peptides is crucial for characterizing their structure and dynamics.
Purpose of the Study:
- To identify and analyze bands associated with delocalized vibrational modes in polyglycine oligomers.
- To determine the dependence of these bands on conformational disorder and chain length.
Main Methods:
- Isotropic Raman spectroscopy was used to study polyglycine oligomers in aqueous solution.
- Computational simulations of polypeptide spectra were performed using a skeletal approximation for disordered chain ensembles.
Main Results:
- Bands linked to delocalized vibrational modes were observed in the Raman spectra.
- Observed spectral dependencies on disorder and chain length were accurately reproduced by calculated spectra.
- Disordered polyglycine spectra rapidly converged to the infinite chain spectrum, especially at the tripeptide level.
- Convergence was faster for disordered than ordered polyglycines due to mode localization.
Conclusions:
- Conformational disorder significantly influences the vibrational spectra of polyglycine oligomers.
- The study provides insights into the relationship between chain length, disorder, and vibrational modes in polypeptides.
- Simulated spectra accurately reflect experimental observations, validating the computational approach.