FOURIER TRANSFORM IR-VIBRATIONAL CIRCULAR DICHROISM AND THE PROBLEM OF ARTIFACT SIGNALS
Publisher:Ohio State University
FTIR-VCD has become a popular method of obtaining vibrational circular dichroism (VCD) data since its recent development by Nafie and coworkers. We have just assembled a new FTIR-VCD instrument based on a Digilab FTS-60 with some design improvements that suggest an apparent solution of the baseline problem. In the FTIR-VCD data presented to data, it has always been necessary to have a racemic mixture or opposite enantiomer to correct for baseline artifacts which were correlated to absorption bands and often were much larger than the VCD signal. By correcting the baseline through optical alignment and modification to a lens system from the standard focussing mirror, we have minimized these artifacts to the point where, under favorable conditions, no baseline correction is needed other than solvent. Examples of FTIR-VCD on ""standard"" molecules will be presented, both with and without the artifacts. Such a development is very important for the application of FTIR-VCD to biological systems such as peptides and proteins where only one enantiomer is available. We have also found this baseline correction to affect the observed FTIR-VCD band-shape, which brings these results into closer agreement with our previously published dispersive VCD results. The latter are less affected by baseline artifacts than were the original FTIR-VCD results. These developments suggest that the deconvolution of FTIR-VCD is at present premature, since the conditions of measurement affect the band-shape, and that determines the resolution enhanced result.
Author Institution: Institute of Organic and Biochemistry, Czechoslovak Academy of Science; Department of Chemistry, University of Illinois at Chicago