Structural identification

Investigations of the structure of bile acids and sterols were undertaken separately but eventually became fused into the common problem of determining the structure of the steroid nucleus. Such a relationship was suspected 

Several other atypical acids were eventually isolated from various species. Ursodeoxycholic acid, first isolated in crystalline form from bear bile in 1927 (58), was identified as the 7/S-epimer of chenodeoxycholic acid. The so-called /3-hyodeoxycholic acid (3 3,6a), which Kimura obtained in small amounts from pig bile (59), was structurally identified in the course of a thorough investigation of the four possible 3,6-dihydroxycholanic acids (60). The lagodeoxycholic acids isolated from rabbit bile by Kishi (61) were not characterized until the recent studies of Danielsson et al. (62) identified one of these compounds as allodeoxycholic acid. The contention that one of them may have been the 12 -epimer of deoxycholic acid was placed in doubt by Koechlin and Reichstein (63), who prepared that acid and found that it did not exhibit the physical properties of the natural material. 

A thorough review of the chemistry of many of the naturally occurring bile acids and related substances may be found in the monograph by Fieser and Fieser (1). A tabulation of known acids and alcohols, their properties, and a brief description of their origins is presented in the next section of this chapter. Identifications in some cases have not been confirmed but the burden of accuracy has been left with the original authors. 

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Weber P L, Brown S 0 and Mueller L 1987 Sequential NMR assignment and secondary structure identification of human ubiquitin Biochemistry 26 7282-90... 

A. J. Panshin and C. deZeeuw, Textbook of Wood Technology Structure, Identification, Uses, and Properties of the Commercial Woods of the United States, 4th ed., McGraw-Hill Book Co., Inc., New York, 1980. 

Syntheses, crystallization, structural identification, and chemical characterization of high nuclearity clusters can be exceedingly difficult. Usually, several different clusters are formed in any given synthetic procedure, and each compound must be extracted and identified. The problem may be compounded by the instabiUty of a particular molecule. In 1962 the stmcture of the first high nuclearity carbide complex formulated as Fe (CO) C [11087-47-1] was characterized (40,41) see stmcture (12). This complex was originally prepared in an extremely low yield of 0.5%. This molecule was the first carbide complex isolated and became the foremnner of a whole family of carbide complexes of square pyramidal stmcture and a total of 74-valence electrons (see also Carbides, survey). 

Not all consequences of fluonne mcorporaton m a molecule aid m structure identification Long range coupling and conformational preferences can comph... 

Consistent with this, dissolution of KF increases the conductivity and KIFe can be isolated on removal of the solvent. Likewise NOF affords [NO]+[IF6] . Antimony compounds yield ISbFio, i-2. [IF4]+[SbF6], which can be titrated with KSbFfi. However, the milder fluorinating power of IF5 frequently enables partially fluorinated adducts to be isolated and in some of these the iodine is partly oxygenated. Complete structural identification of the products has not yet been established in all cases but typical stoichiometries are as follows ... 

The McLafferty rearrangement, as it is known, is useful for structure identification. For example, the mass spectmm of 2-methylbutanal shows a peak at m/e 58, while that of 3-methylbutanal shows a peak at m/e 44. 

Reaction of nitro-2f/-chromene derivatives 134 with 135 in methanol at room temperature afforded a mixture of the Z-isomer 136 and tricyclic compound 137, which could be formed by denitrocyclization reaction of the corresponding primarily formed E-isomer and the following dehydrogenation (Eq. 15). The structural identification was based on the MS and H-NMR, however, it is not sufficiently documented and similar examples are not known (91IJC(B)297). 

There is evidence to suggest that drug-like structures exist in clusters in chemical space (privileged structures). Identification of these can greatly enhance success in screening. 

Eberhard, A., et al. (1981). Structural identification of autoinducer of Photobacterium fischeri luciferase. Biochemistry 20 2444-2449. 

Ohtsuka, H., Rudie, N. G., and Wampler, J. E. (1976). Structural identification and synthesis of luciferin from the bioluminescent earthworm, Diplocardia longa. Biochemistry 15 1001-1004. 

Gas chromatography/mass spectrometry (GC/MS) is the synergistic combination of two powerful analytic techniques. The gas chromatograph separates the components of a mixture in time, and the mass spectrometer provides information that aids in the structural identification of each component. The gas chromatograph, the mass spectrometer, and the interface linking these two instruments are described in this chapter. 

Mass Spectra and Chemical Structure While there are a number of books (Refs 16, 30, 49 64) already referred to, which deal with details of the instrumentation and techniques of mass spectrometry, there are several concise introductory texts (Refs 10, 21 52) on the interpretation of mass spectra. Still other recent books deal comprehensively with organic structural investigation by mass spectrometry. One of these (Ref 63) discusses fundamentals of ion fragmentation mechanisms, while the others (Refs 7, 15, 20, 28 29) describe mass spectra of various classes of organic compounds. In the alloted space for this article methods of interpretation of mass spectra and structural identification can not be described in depth. An attempt is, therefore, made only to briefly outline the procedures used in this interpretation... 

Structural Identification of Isomeric O-Trimethylsilyl Derivatives of Some Hexuronic Acids, J. F. Kennedy, S. M. Robertson, and M. Stacey, Carbohydr. Res., 57 (1977) 205-214. 

The general procednre is to nse reconstrncted ion chromatograms at appropriate m/z values in an attempt to locate componnds of interest and then look at the mass spectrum of the unknown to determine its molecnlar weight. MS-MS can then be employed to obtain spectra from this and related compounds to find ions that are common to both and which may therefore contain common stmctmal features. Having the same m/z value does not necessarily mean the ions are identical and further MS-MS data or the elemental composition may be required. If these data do not allow unequivocal structure identification, then further MS" information may be required. 

Caliceti P, Veronese FM, Marsilio F, Lora S, Seraglia R, and Traldi P. Fast atom bombardment in the structural identification of intermediates in the hydrolytic degradation of polyphosphazenes. Org Mass Spectrom, 1992, 27, 1199-1202. 

McGhie, T.K., Rowan, D.R., and Edwards, P.J., Structural identification of two major anthocyanin components of boysenberry by NMR spectroscopy, J. Agric. Food Chem., 54, 8756, 2006. 

Purification of anthocyanin-containing extracts is often necessary for further structural identification. Since none of the solvents used for extraction is specific for anthocyanins, considerable amounts of other compounds may be also extracted and concentrated. The variety and concentration of other compounds will depend on the solvent and methodologies used. The presence of extraneous materials could affect the stability and/or analysis of anthocyanins. Therefore, the next step toward anthocyanin characterization is the purification of those extracts. 

Wedzicha, B.L., Chemistry of Sulphur Dioxide in Foods, Elsevier, Amsterdam, 1984. Damant, A., Reynolds, S., and Macrae, R., The structural identification of a secondary dye produced from the reaction between sunset yellow and sodium metabisulphite, FoodAddit. Contam., 6, 273, 1989. 

Structural analysis of the two pectate lyases PelC and PelE (5, 6), demonstrated that these proteins fold in a large heHx of parallel P strands. A stack of asparagine residues parallel to the helix probably plays a role in the stabUity of this structure. Identification of the structurally conserved amino adds lead to a reaHgnment of the protein sequences (7). In addition to Erwinia extracellular pectate lyases, the multiple aHgnment indudes the Bacillus subtilis pectate lyase, Aspergillus tdger and E. carotovora pectin lyases and plant proteins. 

Kami H, T Watanabe, S Takemura, Y Kameda, T Hirayama (2000) isolation and chemical-structural identification of a novel aromatic amine mutagen in an ozonized solution of m-phenylenediamine. Chem Res Toxicol 13 165-169. 

The basic aim of PEC applications in clinical chemistry, apart from the recovery of standards of endogenous substances, consists of structural identification of isolated (without further separation) substances of relatively high purity. Therefore, the majority of works devoted to this topic pertain to semipreparative separation. Obtaining low amounts of analytes, achieved by coupling TEC with modem... 

M. Lopez-Lara, J. D. J. van den Berg, J. E. Thomas-Oates, J. Glushka, B. J. J. Lugtenberg, and H. P. Spaink, Structural identification of the lipo-chitin oligosaccharide nodulation signals of Rhizobium loti. Mol. Microbiol. 15 621 (1995). 

In recent years advances in the chemistry of leuco dyes have taken place particularly in the areas of structural identification by means of H- and 13C-NMR and selective syntheses of aminoquinones, etc. New applications of leuco quinones such as in electro-optical devices and information recording media have enhanced their importance. In these applications, the chemistry of leuco quinones is interesting mainly due to switching from a colored to a colorless system by a redox process. 

This procedure was compared with sequential extractive techniques employing alkaline hydrolysis of dried plant tissue followed by extraction of the acidified mixture with ethyl acetate. Fractions were individually evaluated for phytotoxic properties. Selected fractions from those showing a positive response were analyzed by gas-liquid chromatography. Structural identification and characterization of the individual components in these selected fractions were accomplished by gas chromatography-mass spectrometry. 

IR or MS and does not easily distinguish between a monomer and a dimer. NMR is found to be most precious for the identification of P-containing additives. It should be realised that high investments are needed for a universal artificial intelligence structural identification software package based on NMR, MS and IR (Chemical Concepts/Spec Info). 

Resolution does not affect the accuracy of the individual accurate mass measurements when no separation problem exists. When performing accurate mass measurements on a given component in a mixture, it may be necessary to raise the resolution of the mass spectrometer wherever possible. Atomic composition mass spectrometry (AC-MS) is a powerful technique for chemical structure identification or confirmation, which requires double-focusing magnetic, Fourier-transform ion-cyclotron resonance (FTICR) or else ToF-MS spectrometers, and use of a suitable reference material. The most common reference materials for accurate mass measurements are perfluorokerosene (PFK), perfluorotetrabutylamine (PFTBA) and decafluorotriph-enylphosphine (DFTPP). One of the difficulties of high-mass MS is the lack of suitable calibration standards. Reference inlets to the ion source facilitate exact mass measurement. When appropriately calibrated, ToF mass... 

Fast screening techniques, such as temperature-resolved in-source filament pyrolysis and laser-assisted pyrolysis, benefit from the high cycle time and mass accuracy of FUCR-MS [214]. An additional advantage of FUCR-MS in the study of pyrolysis processes is that MS can be readily used for structural identification of desorption and pyrolysis products. 

Major components Chemical formula Chemical structure Identification numbers Tri-o-cresyl phosphate C2iH2i04P (RO) (RO) (RO) P=0 Predominantly saturated hydrocarbons predominantly in the range C15 through C30 Hydrocarbons predominantly in the range C11 through C20... 

Mass Spectrometry. Mass spectrometric (MS) analysis has been utilized for polymer and copolymer structural identification. Recently Dussel et al. utilized pyrolysis-MS to characterize... 

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