Spectral fingerprint

Dudovich, N., Oron, D., and Silberberg, Y. 2003. Single-pulse coherent anti-Stokes Raman spectroscopy in the fingerprint spectral region. J. Chem. Phys. 118 9208-15. 

There has been much less study of other modes, such as the A—H bending and torsional vibrations, than of v,. Yet, the effects of the H bond on the spectral properties of these vibrations are quite as important as its effects on v,. We shall examine what is known about these vibrations in the hope of stimulating further work. Invariably the discussion must deal with two problems first, the identification of the mode of interest, and second, the effect of the H bond upon it. Since these absorptions fall in the heavily populated fingerprint spectral region, seldom is either of these questions easily answered. The literature contains much conflict of opinion. 

FIGURE 9.8 IR-absorption spectra of DND in the fingerprint spectral range 800-1900 cm. Positions of the oxygen-containing groups are highlighted. 

Figure 4.14 Mean Raman (left) and FTIR (right) spectra obtained from oesophageal lymph nodes. Both figures cover the fingerprint spectral range, which is the region of both spectra where most spectral features are found. ...

The spectrum of Figure lb is a fingerprint of the presence of a CO molecule, since it is different in detail from that of any other molecule. UPS can therefore be used to identify molecules, either in the gas phase or present at surfaces, provided a data bank of molecular spectra is available, and provided that the spectral features are sufficiently well resolved to distinguish between molecules. By now the gas phase spectra of most molecules have been recorded and can be found in the literature. Since one is using a pattern of peaks spread over only a few eV for identification purposes, mixtures of molecules present will produce overlapping patterns. How well mixtures can be analyzed depends, obviously, on how well overlapping peaks can be resolved. For molecules with well-resolved fine structure (vibrational) in the spectra (see Figure lb), this can be done much more successfiilly than for the broad. 

In conclusion RAIRS, which affords high spectral resolution, is a very versatile nondestructive optical technique which does not depend on a vacuum environment. Vibrational spectra also serve as characteristic fingerprints for adsorbate molecules, adsorption configurations, and structures on metallic and dielectric substrates. Extension to include dielectric substrates opened new fields of application in polymer and biochemical research. 

For large molecules, at least, Raman spectra contain numerous bands which cannot always completely he assigned to particular vibrational modes. The large number of bands can, however, when measured with appropriate spectral resolution, enable unambiguous identification of substances by comparing the spectral pattern ("fingerprint") with those of reference spectra, if they are available. 

When evaluating gas concentrations in practical applications, a reterence spectrum is least squares fitted to the received absorption spectrum. This im proves the system accuracy, since the spectral fingerprint over the whole scanning range contributes to the result.- ... 

One of the most common uses of vibrational spectroscopy is as a molecular fingerprinting tool whereby spectral features are assigned to the presence of particular fragments in molecules. These assignments are, however, only... 

The characteristic derivative-shaped feature at g 1.94 first observed in mitochondrial membranes has long been considered as the sole EPR fingerprint of iron-sulfur centers. The EPR spectrum exhibited by [4Fe-4S] centers generally reflects a ground state with S = I and is characterized by g values and a spectral shape similar to those displayed by [2Fe-2S] centers (Fig. 6c). Proteins containing [4Fe-4S] centers, which are sometimes called HIPIP, essentially act as electron carriers in the photoinduced cyclic electron transfer of purple bacteria (106), although they have also been discovered in nonphotosynthetic bacteria (107). Their EPR spectrum exhibits an axial shape that varies little from one protein to another with g// 2.11-2.14 and gi 2.03-2.04 (106-108), plus extra features indicative of some heterogeneous characteristics (Pig. 6d). 

To detect adulteration of wine. Bums et al. (2002) found that the ratios of acetylated to p-coumaroylated conjugates of nine characteristic anthocyanins served as useful parameters to determine grape cultivars for a type of wine. Our laboratory utilized mid-infrared spectroscopy combined with multivariate analysis to provide spectral signature profiles that allowed the chemically based classification of antho-cyanin-containing fruits juices and produced distinctive and reproducible chemical fingerprints, making it possible to discriminate different juices. " This new application of ATR-FTIR to detect adulteration in anthocyanin-containing juices and foods may be an effective and efficient method for manufacturers to assure product quality and authenticity. 

When considering libraries of spectra for identification purposes, the effect of sample preparation on spectral characteristics is also important. Two FUR sampling methods have been adopted for IR analysis of TLC eluates in the presence of a stationary phase, namely DRIFTS [741] and PAS [742], of comparable sensitivity. It is to be noted that in situ TLC-PA-FTIR and TLC-DRIFT spectra bear little resemblance to KBr disc or DR spectra [743,744]. This hinders spectral interpretation by fingerprinting. For unambiguous identification, the use of a reference library consisting of TLC-FTIR spectra of adsorbed species is necessary. 

Because much smaller differences are anticipated at the strain level, strain-level differentiation and spectral reproducibility have received much attention. A 1998 work from Riley s group21 is representative of a common approach to this issue. In Riley s studies E. coli strains shared many peaks in common but also showed strain-unique ions as well. Many of these ions fell in the fingerprint region near 3630, 3850, 4170, 4780, 5100, 5380, 7280, 8320,... 

Jarman, K. H. Daly, D. S. Peterson, C. E. Saenz, A. J. Valentine, N. B. Wahl, K. L. Extracting and visualizing matrix-assisted laser desorption/ionization time-of-flight mass spectral fingerprints. Rapid Comm. Mass Spectrom. 1999, 13, 1586-1594. 

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