Chapter 73 - Multidimensional and dual frequency infrared analogues of NMR: Applications to peptides and isotopomers of secondary structures

Abstract

The development of methods to time resolve structural changes in complex systems is an important challenge. Because of its time resolution, multidimensional infrared spectroscopies 2D-IR and 3D-IR, can contribute to this challenge complementing the knowledge on average structures obtained by the established methods of structural biology and their time dependent variants. The multidimensional infrared experiment arose from many years of theoretical and experimental research on laser technology, nonlinear optics, and infrared spectroscopy. The manipulation of multidimensional data sets in time or frequency domains are also basic material in NMR even though the practical aspects of the two experiments are quite different and they arose quite independently. The heterodyned 2D-IR approach has proven useful in determining structures of peptides in solution and the anharmonic nature of the potential surfaces of peptides and secondary structures, as have polarized photon echo or pump-probe techniques. A full 2D-IR spectrum is obtained in which the two frequency axes correspond to the quite different spectral regions at 3300 cm-1 and 1650 cm-1: the amide-A and amide-I modes influence each other in N-H O=C hydrogen bonding configurations.