Raman optical activity study of poly-L-proline chains of various lengths

V. Profant¹*, M. Šafařík², P. Bouř², V. Baumruk¹

¹Institute of Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, 121 16, Prague, Czech Republic

²Institute of Organic Chemistry and Biochemistry, Academy of Sciences, Flemingovo nám 2, 166 10, Prague, Czech Republic

profant@karlov.mff.cuni.cz

Raman scattering and Raman optical activity (ROA) [1, 2] techniques were used for study of oligo- and poly-L-proline samples. Specifically, formation of polyproline II (PPII) helical conformation was studied in dependence on the increasing chain length N of the (L-proline)_N sample. Although PPII conformation is believed to be the main content of so-called random coil structure [3], it remains not to be completely characterized so far and problematic of its creation has not been thoroughly studied yet.

The whole study was strongly related to previous experiments [4], which were focused on the characterization of proline side chain conformation and its interaction with solvent.

For the analysis, five oligopeptide of different lengths (N=2,3,4,6,12) and three polypeptide samples of different mean molecular weight were used for preparation of highly concentrated water solution. Raman scattering and ROA spectra were measured in a wide frequency range between 120 cm^-1 and 1800 cm^-1 and analysed with respect to the main peptide chain conformation.

Due to high sensitivity of the ROA technique to the conformational stability and rigidity of peptide chain we were able to determine the characteristic spectral peaks associated with formation of stable PPII helical conformation in studied systems. The most relevant peaks are located at 405, 535 and 945 cm-1. Additionally, we were able to determine the minimal length of (L-proline) _N chain necessary for creation of the stable PPII conformation as N=6.

References

1. P.W. Atkins, L.D. Barron, Mol. Phys. 16, (1969), 453-466.

2. L.D. Barron, M.P. Boggard, A.D. Buckingham, Nature 241, (1973), 113-114.

3. Z. Shi, R.W. Woody, N.R. Kallenbach, Adv. Prot. Chem. 62, (2002) 163-240.

4. J. Kapitán, V. Baumruk, P. Bouř, JACS 128, (2006), 2438-2443.

Acknowledgement

The work was supported by the Grant Agency of the Czech Republic (grant No. 202/07/0732) and by the Ministry of Education of the Czech Republic (MSM 0021620835).