CHARACTERIZATION OF BIOLOGICAL SAMPLES BY 2-DIMENSIONAL INFRARED-SPECTROSCOPY - SIMULATION OF FREQUENCY, BANDWIDTH, AND INTENSITY CHANGES

Two-dimensional infrared (2D IR) spectroscopy has been shown to be a p owerful tool for the analysis of spectra with highly overlapped bands, as often found in IR spectra of biological samples. To date, most 2D IR analyses have focused primarily on intensity changes of the bands u nder investigation. However, information concerning 2D IR characterist ics of bands that change in position or width is sparse. We have thus simulated the effects of frequency and bandwidth changes on 2D IR spec tra. In the synchronous plot of a band undergoing a frequency shift; t wo autopeaks and two crosspeaks are found at the initial and final pos itions, while the asynchronous plot exhibits two weaker crosspeaks for these positions and a stronger, somewhat elongated feature close to t he diagonal. The latter feature is characteristic of a shifting band. Thus, to distinguish a frequency shift in a single band from intensity changes of two overlapped bands it is important to examine the asynch ronous plot, since the synchronous plots exhibit comparable characteri stics in both cases. A bandwidth change results in a series of crosspe aks. However, when bandwidth changes are coupled with either frequency shifts and/or intensity changes, the effect of the bandwidth change i s reduced. Finally, it is shown that the resolution enhancement genera lly found for the asynchronous plot is accompanied by an error in the positions of the original spectral features as determined from 2D IR p eaks. The magnitude of the error increases as the original spectral fe atures approach each other in frequency. (C) 1996 John Wiley & Sons, I nc.