Vibrational self-trapping in beta-sheet structures observed with femtosecond nonlinear infrared spectroscopy.
Self-trapping of NH-stretch vibrational excitations in synthetic beta-sheet helices is observed using femtosecond infrared pump-probe spectroscopy. In a dialanine-based beta-sheet helix, the transient-absorption change upon exciting the NH-stretch mode exhibits a negative absorption change at the fundamental frequency and two positive peaks at lower frequencies. These two induced-absorption peaks are characteristic for a state in which the vibrational excitation is self-trapped on essentially a single NH-group in the hydrogen-bonded NH...OC chain, forming a small (Holstein) vibrational polaron. By engineering the structure of the polymer we can disrupt the hydrogen-bonded NH...OC chain, allowing us to eliminate the self-trapping, as is confirmed from the NH-stretch pump-probe response. We also investigate a trialanine-based beta-sheet helix, where each side chain participates in two NH...OC chains with different hydrogen-bond lengths. The chain with short hydrogen bonds shows the same self-trapping behavior as the dialanine-based beta-sheet helix, whereas in the chain with long hydrogen bonds the self-trapping is too weak to be observable.
Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands.
Pavol
P
Bodis
Erik
E
Schwartz
Matthieu
M
Koepf
Jeroen J L M
JJ
Cornelissen
Alan E
AE
Rowan
Roeland J M
RJ
Nolte
Sander
S
Woutersen
D003198:Computer Simulation; D008956:Models, Chemical; D008968:Molecular Conformation; D017711:Nonlinear Dynamics; D011108:Polymers / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods*; D014732:Vibration
D011108:Polymers