General structural identification

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. 

Table 16.5 General structure of a sulfa drug, structure of five sulfa drugs containing six-mem-bered heterocyclic R substituents, and measured pK values pK values were calculated using a spectrophotometric titration. Errors represent the 95% confidence levels and both the values and the associated errors were obtained from fits of the data using Scientist for Windows. Reprinted with permission from Boreen AL, Arnold WA, McNeil K (2005) Triplet-sensitized photodegradation of sulfa drugs containing six-membered heterocyclic groups identification of an S02 extrusion photoproduct. Environ Sci Technol 39 3630-3638. Copyright 2005 American Chemical Society...

A number of physical tests emphasizing stress-strain behavior will be covered in Chapter 14. Here, we will concentrate on other areas of testing, emphasizing thermal and electrical properties and on the characterization of polymers by spectral means. Spectroscopic characterization generally concentrates on the structural identification of materials. Most of these techniques, and those given in Chapter 14, can also be directly applied to nonpolymeric materials such as small organic molecules, inorganic compounds, and metals. 

X-ray diffraction is a widely used tool for structural identification for almost all solids under the right conditions. X-ray diffractometers are generally either single crystal or powder. 

Section 5 covers complexity measures for computer algorithms. Section 1+ surveys what is known about the structure identification problem in general. Section 5 solves the problem for molecules without rings. Section 6 gives a method for analyzing a molecule by systematically breaking it into smaller parts. 

Aldehydes and ketones generally give moderately intense signals due to their molecular ions, M+. Thus the determination of the molecular weight of a ketone by mass spectroscopy usually is not difficult. Furthermore, there are some characteristic fragmentation patterns that aid in structural identification. These are ... 

Generally die NMR spectrum of a compound is used in conjunction witii otiier available information for identification purposes. The reactants and die reagents and reaction conditions can serve as a guide to die types of products diat might be expected. Structure identification often merely confirms die structures of products that were predicted from die chemistry employed in die syndiesis. In odier cases products are obtained whose spectta do not match die predicted products. In such cases more information is usually required to solve die structure. Thus while NMR is an extraordinarily powerful tool, it is not sufficient to solve all structural problems. This latter fact must be kept in mind. 

What is lacking at this point in theories relating lattice restraints and chemical reactivity is the identification of specific steric interactions which alter reactivity and an estimation of their magnitude. This requires an extensive database of structure-reactivity information for a series of closely related compounds. This we have from our studies on the solid state photochemistry and X-ray crystallography of a large number of variously substituted bicyclic dienones of general structure L (5). In this series, we recently observed a photorearrangement... 

Very generally, the identification of a molecule of interest by a combinatorial strategy requires (i) the random synthesis of a balanced library in which the different candidates are statistically equi-represented, (the over-representation of some compounds and the under-representation of others will bias the population and subsequently may affect the outcome of the selection) (ii) the efficient partitioning of candidates which display the desired property depends upon a carefully adjusted selection pressure combined with an effective procedure allowing the physical separation of the winners, and (iii) the identification of these winning molecules and their defined synthesis at high yield and low cost for further use. This means either a very sensitive analytical method to determine the chemical structure of the selected molecules must be used... 

The identification of metabolite structures with LC/MS and LC/MS/MS techniques are an effective approach due to their ability to analyze trace mixtures from complex samples of urine, bile, and plasma. The key to structure identification approaches is based on the fact that metabolites generally retain most of the core structure of the parent drug (Perchalski et al, 1982). Therefore, the parent drug and its corresponding metabolites would be expected to undergo similar fragmentations and to produce mass spectra that indicate major substructures. 

This review summarized our systematic studies on dinuclear platinum compounds leading to identification of a novel clinical agent BBR 3464. The profile of antitumor activity is shared by the general structure with po-... 

Column separation of proteins and peptides is used for both preparative and analytical purposes. Generally, in the former case low- or medium-pressure systems are preferred, whereas in the latter, high-performance-liquid-chromatography (HPLC) is the method of choice. These systems are coupled with a spectrophotometric detector normally set at wavelengths 280 and (around) 220 nm for proteins and peptides, respectively. Coupling of HPLC with mass spectrometry allows structural identification of compounds after the separation. 

Structural identification of anthocyanin derived pigments and the studies carried out on their mechanisms of formation allowed us to bring out a general pattern of the flavonoid reactivities (figure 2). Basically, flavonoids are built on a three-ring core consisting of A and B aromatic systems bearing hydroxyl... 

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