The two-dimensional infrared spectrum of an octameric helical peptide in chloroform was measured as a function of temperature. Isotope labelling of the carbonyl group of one of the amino acids was used to obtain information for an isolated vibration. The antidiagonal width of the 2D-IR signal, which is a measure of the homogeneous dephasing time T2, is constant from 220 to 260 K (within experimental error), and increases steeply above. The homogeneous dephasing time of the carbonyl vibration is attributed to the flexibility of the system and/or its immediate surrounding. The system undergoes a dynamical transition at about 270 K, with similarities to the glass transition in proteins. Furthermore, the temperature dependence of the antidiagonal width strongly resembles that of the efficiency of vibrational energy transport along the helix, which has been studied in a recent paper (J. Phys. Chem. B 2008, 112, 15487). The connection between the two processes, structural flexibility and energy transport mechanism, is discussed.
Dynamical transition in a small helical peptide and its implication for vibrational energy transport
Moretto A;Crisma M;Toniolo C;
2009
Abstract
The two-dimensional infrared spectrum of an octameric helical peptide in chloroform was measured as a function of temperature. Isotope labelling of the carbonyl group of one of the amino acids was used to obtain information for an isolated vibration. The antidiagonal width of the 2D-IR signal, which is a measure of the homogeneous dephasing time T2, is constant from 220 to 260 K (within experimental error), and increases steeply above. The homogeneous dephasing time of the carbonyl vibration is attributed to the flexibility of the system and/or its immediate surrounding. The system undergoes a dynamical transition at about 270 K, with similarities to the glass transition in proteins. Furthermore, the temperature dependence of the antidiagonal width strongly resembles that of the efficiency of vibrational energy transport along the helix, which has been studied in a recent paper (J. Phys. Chem. B 2008, 112, 15487). The connection between the two processes, structural flexibility and energy transport mechanism, is discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
