Pesticides molecular characterization

Sorption and Desorption Processes. Sorption is a generalized term that refers to surface-induced removal of the pesticide from solution it is the attraction and accumulation of pesticide at the sod—water or sod—air interface, resulting in molecular layers on the surface of sod particles. Experimentally, sorption is characterized by the loss of pesticide from the sod solution, making it almost impossible to distinguish between sorption in which molecular layers form on sod particle surfaces, precipitation in which either a separate soHd phase forms on soHd surfaces, covalent bonding with the sod particle surface, or absorption into sod particles or organisms. Sorption is generally considered a reversible equdibrium process. 

Molecules of similar biochemical activity often show common 3D shape features. Consequently, the characterization of the shapes of formal molecular bodies and the recognition, description, and, ultimately, the numerical evaluation of similarity among molecules are of major importance in modern pharmaceutical research, as well as in pesticide and herbicide chemistry. The analysis of molecular shape is an important component of research aimed at the elucidation of drug-receptor interactions and in studies of quantitative structure-activity relationships in contemporary drug design. 

The recent development of commercial HPLC systems has provided a powerful instrumentation for the separation, characterization, identification, and quantitation of minute amounts of essential dietary components (68,69). Developments in hardware and packings for HPLC have overcome the problems of nonreproducible behavior and low efficiency separations previously associated with column chromatography (70). HPLC has already been applied to the quantitative analysis of analgesics, pesticides, and fat-soluble vitamins with precision and accuracy and a minimum of sample clean-up. Such instrumentation provides a rapid, accurate, and sensitive technique for the separation and analysis of subnanomole quantities of a wide range of complex high-molecular-weight, nonvolatile, thermally labile, compounds that are vital for metabolic and nutritional studies. 

Rau D., Kramer K., and Hock B., Cloning, functional expression and kinetic characterization of pesticide-selective Fab fragment variants derived by molecular evolution of variable antibody genes. Anal. Bioanal. Chem., 372(2), 261-267, 2002. 

The separation and characterization of environmental pollutants in aqueous samples is a demanding task. The concentration of contaminants is usually very low (typical < 10 xg/L) and the matrices may be complex. GC is necessary for analyte separation while, in most cases, IR is very suitable for this purpose because of its unique molecular fingerprinting properties. Applications of GC/ FTIR are found in a wide variety of analytical fields. Most applications have been reported on the analysis of environmental samples. A representative example of what can be achieved nowadays is the identification of pesticides in water samples at the European alert and alarm levels of 0.1-1 ng/ml, as described by Hankemeier et al., ... 

Matrix effects can be avoided by using MS. Mass spectrometry is characterized by being highly selective and sensitive and, in addition, it oHers spectral iirformation that permits the imequivocal identification of target compounds. LC/MS with atmospheric pressure chemical ionization (APCl) and electrospray ionization (ESI) interfaces have been applied to monitor pesticides and produce chemical ionization mass spectra with molecular information, depending on set-up conditions. Limits of detection at ng/L and the linear response range over two orders of magnitude have been reported. 

LC-MS finds wide application in the analysis of compounds that are not amenable to GC-MS, i.e. compounds that are highly polar, ionic and thermo-labile, as well as (bio)macromolecules. In environmental applications, LC-MS is applied, often in combination with off-line or on-line solid-phase extraction, to identify pesticides, herbicides, surfactants and other environmental contaminants. LC-MS plays a role in the confirmation of the presence of antibiotic residues in meat, milk and other food products. Furthermore, there is a substantial role for LC-MS in the detection and identification of new compounds in extracts from natural products and the process control of fermentation broths for industrial production of such compounds, e.g. for medicinal use. LC-MS technology is also widely applied in the characterization of peptides and proteins, e.g. rapid molecular-mass determination, peptide mapping, peptide sequencing and the study of protein conformation and noncovalent interactions of drugs, peptides and other compounds with proteins and DNA. However, the most important application area... 

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