Chiral pollutants structures

Capillary electrophoresis has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear-aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various... 

CE has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various toxic pollutants such as phenols, polyaromatic hydrocarbons, and so on. Sarac, Chankvetadze, and Blaschke " resolved the enantiomers of 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid using CD as the BGE additive. The CDs used were native, neutral, and ionic in nature with phosphate buffer as BGE. Welseloh, Wolf, and Konig investigated the CE method for the separation of biphenyls, using a phosphate buffer as BGE with CD as the chiral additive. Miura et al., used CE for the chiral resolution of seven phenoxy acid herbicides using methylated CDs as the BGE additives. Furthermore, the same group resolved 2-(4-chlorophenoxy) propionic acid (MCPP), 2-(2,4-dichlorophenoxy) propionic acid (DCPP), (2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chlorophenoxy) propionic acid (2,4-CPPA), [(2,4,5-... 

Many xenobiotics and pollutants are chiral in nature and the two enantiomers of these pollutants may have different toxicities [13]. Additionally, the degradation of some chiral pollutants is stereospecific in the environment, and the degradation of some achiral pollutants may result in chiral toxic metabolites. Moreover, it has also been reported that enantiomers may react at different rates with achiral molecules in the presence of a chiral catalyst [13]. It is also obvious that most of the identities and the structures in nature are chiral and, therefore, that there is a greater chance that the environmental pollutants will react at different rates. Therefore,... 

Figure 2.1 The chemical structures of some chiral pollutants, (a) Aliphatic organochlorine pesticides (b) aromatic organochlorine pesticides (c) phosphorous pesticides.

As in the case of GC and HPLC, a chiral selector is also required in CE for enantiomeric resolution. In general, chiral compounds are used in background electrolyte (BGE) as additives, and hence they are called chiral selectors or chiral BGE additives. There are only a few publications available that deal with chiral resolution on a capillary coated with a chiral selector in CE [4]. The enantiomeric resolution of chiral pollutants discussed in this chapter has been confined to the use of chiral selectors in the BGE. As a chiral resolution technique, CE has been used widely for the enantiomeric resolution of dmgs and pharmaceuticals [5]. Several reviews have also appeared on this issue, and they describe the use of many chiral compounds as chiral BGE additives [6-13]. The most commonly used chiral BGE additives are cyclodextrins, macrocyclic glycopeptide antibiotics, proteins, crown ethers, ligand exchangers, alkaloids [6-16] and so on. The structures and properties of these chiral BGE additives have been described in previous chapters and, therefore, this aspect will not be discussed here again. However, a list of these chiral BGE additives is presented in Table 9.1. a-, and y-Cyclodextrins and their derivatives have been used frequently in chiral CE, because of their water solubility... 

The second type of stereoisomerism encompasses all other cases in which the three-dimensional structures of two isomers exhibiting the same connectivity among the atoms are not superimposable. Such stereoisomers are referred to as diastereomers. Diastereomers may arise due to different structural factors. One possibility is the presence of more than one chiral moiety. For example, many natural products contain 2 to 10 asymmetric centers per molecule, and molecules of compound classes such as polysaccharides and proteins contain hundreds. Thus, organisms may build large molecules that exhibit highly stereoselective sites, which are important for many biochemical reactions including the transformation of organic pollutants. 

The application of bacterial strains containing these dioxygenases has used for transformation of environmental pollutant aromatic compounds to nonaromatic compounds (Cavalca et al. 2004 Parales and Haddock 2004). Moreover, the c/5-diols produced by dioxygenases are attractive because of their inimitable chiral structures and their potentials in industrial synthesis for useful chemical products... 

The chiral resolution of environmental pollutants by CE is a very interesting feature, since one of the chiral isomers may be more toxic than the other. In addition, biological transformation of the enantiomers is many times stereoselective, and, therefore, their uptake, metabolism, and excretion can be different. Besides, CE has also been utilized to separate the structural isomers of various toxic pollutants such as phenols, polyaromatic hydrocarbons, etc. 

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