FTIR-VCD spectrometer

The most recent advance in VCD instrumentation has been its adaptation to Fourier transform infrared (FTIR) measurement (23-25). The details of this technique involve a new method of FTIR measurement termed double-modulation FTIR spectroscopy. Thus spectra of very high quality and resolution have been obtained using a standard VCD modulator and detector, a glower source, and a commercially available FTIR spectrometer system. In fact an entire FTIR-VCD spectrometer can be assembled from a few commercially available components. It is found that the major advantages of resolution, throughput, and... 

Fig. 1 Block diagram of the optical-electronic layout of an FTIR-VCD spectrometer...

Fig. 2 The VCD spectra of camphor with the anisotropy ratio on the order of magnitude of 10 5 are used as examples to illustrate the performance of several generations of FTIR-VCD spectrometers. Raw (bottom traces) and subtracted (top traces) VCD spectra of 0.6 M R-camphor in CC14 in a 0.10 mm CaF2 cell from 4,000 to 2,000 cm-1 are shown (a) SPM, single PEM only, for a pair of enantiomers. The subtracted spectrum is the true spectrum (b) SPM, single PEM, with only solvent baseline correction (c) SPM/RHWP, single PEM (SPM) with RHWP, with only solvent baseline correction (d) DPM, DPM only, with only solvent baseline correction (e) DPM/RHWP, with both DPM and RHWP, with only solvent baseline correction. Reproduced with permission from [41]. Copyright (2008) Springer...

A few scanning dispersive VCD instruments are still in use for biological applications in the mid-IR region [46,47]. In 2009, a newly designed and optimized dispersive VCD instrument was reported [47]. A collection of spectra for peptides and proteins having different dominant secondary structures (alpha-helix, beta-sheet, and random coil) measured with this new instrument showed substantially improved signal-to-noise (S/N) ratios as compared with the earlier version. The instrument provides protein VCD spectra for the amide I region that are of comparable or better quality than those obtained with a standard commercial FTIR-VCD spectrometer [47]. 

Besides the continuous improvements of FTIR-VCD instruments described above, some exciting new developments related to VCD measurements have been reported in recent years. These include the developments of matrix isolation FTIR-VCD instruments and of laser based real time VCD spectrometers. These new developments are associated with brand new applications and research directions, such as combining the matrix isolation technique with VCD spectroscopy to probe conformationally flexible chiral molecules and H-bonded chiral molecular complexes, and using femtosecond laser VCD instruments to record time resolved VCD spectra for monitoring fast chemical reactions or folding and unfolding events of peptides and proteins in solution. These will be discussed in more detail in Sects. 4.5 and 4.6. 

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