Dynamics of secondary and tertiary structure relaxation of a cyclic penta-peptide: Time-resolved FTIR studies

In the present study, dynamics of the FTIR absorption spectrum induced by an acoustic pulse was investigated. Acoustic excitation was provided by a piezoelectric transducer or by a nanosecond laser pulse that created a shock wave in the solution. The acoustic energy was preferentially absorbed by the low-frequency vibrational modes of the cyclo(Mamb-Abu-Arg-Gly-Asp) pentapeptide dissolved in deuterated water. The time evolution of the IR absorption monitored in the amide I band at 1648 cm−1 could be fitted by a sum of five exponential terms over the microsecond to millisecond time range, being largely independent on the acoustic excitation method. The kinetics observed in the IR absorption is attributed to relaxation of the secondary and tertiary structure, perturbed by the acoustic excitation. Sub-microsecond time resolution was achieved when shock waves were created in the bulk of the sample solution.