Fingerprinting of compounds

These energy spectra have been extensively utilized. Termed IKE spectra, they are veritable fingerprints of compounds [105b,c,l 18,119a,b], thus leading to the otherwise impossible characterization of isomeric compounds. 

Characterization may involve simple fingerprinting of compounds already known, or more extensive investigation designed to establish the formula and structure of a new compound. The proportions of each element allow a stoichiometric formula to be obtained. Chemical methods can be used, but instrumental methods are more routine and include combustion analysis (for C, H, N and sometimes S) and methods based on atomic spectroscopy of samples atomized at high temperature. 

The need for an overall and combined chemical structure and data search system became clear to us some time ago, and resulted in the decision to build CHIRBASE, a molecular-oriented factual database. The concept utilized in this database approach is related to the importance of molecular interactions in chiral recognition mechanisms. Solely a chemical information system permits the recognition of the molecular key fingerprints given by the new compound among thousands of fingerprints of known compounds available in a database. 

FI CU RE 35.12 Typical fingerprint of a masterbatch mixing process on an intermeshing internal mixer (GK 320E (Harburg Freudenberger) with PES5 rotors styrene-butadiene rubber/carbon black [SBR/CB] tread compound). 

Clustering is the process of dividing a collection of objects into groups (or clusters) so that the objects within a cluster are highly similar whereas objects in different clusters are dissimilar [41]. When applied to databases of compounds, clustering methods require the calculation of all the pairwise similarities of the compounds with similarity measures such as those described previously, for example, 2D fingerprints and the Tanimoto coefficient. 

Additional support for this suggestion came from a study of L. distichophylla J. Agardh collected off the northeastern coast of New Zealand by Blunt et al. (1984). These workers examined the sesquiterpene chemistry of plants collected at three depths (1) low intertidal to upper subtidal (2) mid-intertidal and (3) upper intertidal. Chromatographic fingerprints of the latter two collections were identical, but the profile of fhe deep-gathered planfs differed in botti ttie number of compounds... 

To identify the volatile components, gas chromatography-mass spectrometry (GC-MS) is still the method of choice. A comparison of the GC fingerprints of B. carter a and B. serrata reveals the different composition of the volatile fractions (Figure 16.1). Common monoterpenes, aliphatic, and aromatic compounds of olibanum are, e g., pinene, limonene, 1,8-cineole, bomyl acetate, and methyleugenol (Figure 16.2). 

Ehret-Henry et al. [220] have shown that H NMR spectra can be used without chromatographic analysis, to shorten the total identification time necessary, and as a fingerprint of all the extractable nonvolatile compounds present in food packaging material (safety control). Figure 5.10 shows a H NMR spectrum (in CDCI3 with TMS as internal standard) of a Soxhlet extract of a 35 pirn PP film (after solvent evaporation). The assignments of the resonances of Irgafos 168 and its decomposition products were confirmed by a 31P- H 2D correlation NMR experiment [220],... 

In the broadest sense, thermal analysis (TA) measures physical changes in a material as a function of temperature. TA instruments measure variables in a sample such as heat flow, weight, dimensions, etc. A typical fingerprint of a compound might be the endothermic peak on a thermogram indicating a sample s crystalline melt. 

Figure 10.8 Total ion current chromatograms obtained after headspace SPME for (a) Kyphi and (b) B. sacra olibanum. Peak labels correspond to compound identification given in Table 10.3. The occurrence of isoincensole acetate (128) as well as the occur rence of the oxygenated sesquiterpene 98 and of dimer 2 (111) in Kyphi are clear fingerprints of the botanical origin of the olibanum used. Peaks labelled by letters correspond to the following compounds a, cinnamaldehyde b, vanilline c, curzerene d, furanoeudesma 1,3 diene e, a santalol f, 2 methoxyfuranodiene. Reproduced from S. Hamm, j. Bleton, j. Connan, A. Tchapla, Phytochemistry, 66, 1499 1514. Copyright 2005 Elsevier Limited...

For a commercial database of known metabolic transformations, Borodina et al. [76] extracted all known sites of aromatic hydroxylations. These observed transformations were used to generate all possible transformations for each molecule, giving an estimate of the probability that each transformation would actually occur. The method was 85% accurate in predicting site of aromatic hydroxylation when tested against a second metabolism database containing 1552 molecules. Boyer et al. [77] took a similar approach using reaction center fingerprints to estimate the occurrence ratio of a particular metabolic transformation. The method successfully predicted the three most probable sites of metabolism in 87% of compounds tested. 

Because the fragmentation pattern produced by a mass spectrometer can be used as a fingerprint of molecule, the mass spectrum reveals, for example, whether the correct compound has been synthesized and whether contaminants are present. One can see that it is a molecular fingerprint, just as absorption spectra are molecular fingerprints, and that it is a powerful tool for identification purposes. 

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