Structural information from spectral data

Structural Information from Spectral Data. The kinds of information that can be derived from an unknown mass spectrum by either human or computer examination include the identities of substructural parts of the molecule (parts that both should, and should not, be present), data concerning the size of the molecule (molecular weight, elemental composition), and the reliability of each of these postulations. In our opinion, the latter is much more critical for mass-spectral interpretive algorithms than those for techniques such as NMR and IR the effect of a particular substructure on the mass spectrum is often dependent on other parts of the molecule, and a thorough understanding of these effects can only be achieved by studying the spectra of closely related molecules. 

From another shallow-water variety of L majuscula found in Hawaii, a new crystalline metabolite pukeleimide C (102) was isolated. The structure was secured by X-ray studies [163]. Chiroptical studies showed the compound to be racemic and, probably, an artefact. A separate collection of the cyanophyte did not contain pukeleimide C but, instead, yielded a group of related metabolites, e.g. 103, whose structures were assigned from spectral data [164], Unfortunately, no information is available on the bioactivity of these metabolites. 

Collette (1992) proposed a novel approach to developing and applying QSARs for the alkaline hydrolysis of carboxylic acid esters using infrared (IR) spectroscopic data. The concept is to extend QSARs to a larger and more diverse group of organic compounds by including the structural information encoded in IR spectra. Such data are available from spectral data bases, but even in the absence of literature data, IR frequencies are readily measurable. 

The two most important computer-assisted strategies for the recognition of structural information from mass spectral data are ... 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

This chapter extends the information provided by the two preceding reviews (1,2) to the literature that appeared within the years 1976-1986, focusing on spectral data, structural elucidation, synthesis, biosynthesis, and pharmacology. Some references that appeared in the foregoing reviews are omitted from this chapter with exception of those related to the present treatise. Although previously presented in Volume 16 of this treatise (2), the numbering system of the hasubanan skeleton (la) and the hasubanalactam skeleton (lb), which is used in this chapter except for the most part of Section V, is represented anew. 

Because protein ROA spectra contain bands characteristic of loops and turns in addition to bands characteristic of secondary structure, they should provide information on the overall three-dimensional solution structure. We are developing a pattern recognition program, based on principal component analysis (PCA), to identify protein folds from ROA spectral band patterns (Blanch etal., 2002b). The method is similar to one developed for the determination of the structure of proteins from VCD (Pancoska etal., 1991) and UVCD (Venyaminov and Yang, 1996) spectra, but is expected to provide enhanced discrimination between different structural types since protein ROA spectra contain many more structure-sensitive bands than do either VCD or UVCD. From the ROA spectral data, the PCA program calculates a set of subspectra that serve as basis functions, the algebraic combination of which with appropriate expansion coefficients can be used to reconstruct any member of the... 

Stylotelline (23) is a constituent of a Stylotella sp. collected offshore in New Caledonia. 13C NMR spectra involving 2D NMR techniques provided the bulk of information leading to its structure. The absolute configuration was demonstrated after the tertiary isocyano group was removed to yield the known conjugated diene, ( + )-d-selinene (24). Optical rotation and spectral data of the transformation product were identical in all respects to those of the corresponding product obtained from eudesmols [42], Although neither the isothiocyanato nor the formamido compounds were isolated, the latter was prepared, which allowed an nOe observation between the axial C-3 and the amide protons. 

We examine the derivation of information about molecular structure and properties from analysis of pure rotational and vibration-rotational spectral data of diatomic molecular species on the basis of Dunham s algebraic formalism, making comparison with results from alternative approaches. According to an implementation of computational spectrometry, wave-mechanical calculations of molecular electronic structure and properties have already played an important role in spectral reduction through interaction of quantum chemistry and spectral analysis. 

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