title: Thermal stability of dehydrophenylalanine-containing model peptides as probed by infrared spectroscopy: a case study of an alpha-helical and a 3(10)-helical peptide.
abstract: The temperature-dependent secondary-structural changes in the two known helical model peptides Boc-Val-deltaPhe-Ala-Leu-Gly-OMe (1; alpha-helical) and Boc-Leu-Phe-Ala-deltaPhe-Leu-OMe (2; 3(10)-helical), which both comprise a single dehydrophenylalanine (deltaPhe) residue, were investigated by means of FT-IR spectroscopy (peptide film on KBr). Both the first-order and the better-resolved second-order derivative IR spectra of 1 and 2 were analyzed. The nu(NH) (3240-3340 cm(-1)), the Amide-I (1600-1700 cm(-1)), and the Amide-II (1510-1580 cm(-1)) regions of 1 and 2 showed significant differences in thermal-denaturation experiments (22 degrees --> 144 degrees), with the 3(10)-helical peptide (2) being considerably more stable. This observation was rationalized by different patterns and strengths of intramolecular H-bonds, and was qualitatively related to the different geometries of the peptides. Also, a fair degree of residual secondary-structural elements were found even in the 'denatured' states above 104 degrees (1) or 134 degrees (2).
authors.affiliation: Optical Radiation Standards, National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India.
authors.forename: Alka
authors.initials: A
authors.lastname: Gupta
authors.forename: Ranjana
authors.initials: R
authors.lastname: Mehrotra
authors.forename: Evgueni
authors.initials: E
authors.lastname: Klimov
authors.forename: Heinz Wilhelm
authors.initials: HW
authors.lastname: Siesler
authors.forename: Ratanmani M
authors.initials: RM
authors.lastname: Joshi
authors.forename: Virander Singh
authors.initials: VS
authors.lastname: Chauhan
mesh_terms: D004355:Drug Stability; D006358:Hot Temperature; D008958:Models, Molecular; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry*; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013816:Thermodynamics
chemical_list: D010446:Peptide Fragments; D010649:Phenylalanine; C018632:phenyldehydroalanine