Atrazine hydrogen bonds

Welhouse, G. J., and Bleam, W. F. (1993a). Atrazine hydrogen-bonding potentials. Environ. Sci. Technol. 27,494-500. 

Welhouse, G.J. and W.F. Bleam (1993b). Cooperative hydrogen bonding of atrazine. Environ. Sci. Technol., 27 500-505. 

Figure 9.5. Sorption of atrazine to diol sorbent via hydrogen bonding.

Atrazine is eluted with a solvent that is capable of breaking hydrogen bonds, such as 2 mL of methanol. Figure 9.5 shows the mechanism of hydrogen bonding between atrazine and the diol hydroxyl groups. 

In aprotic solvents, the carboxylic acid residues in methacrylic acid and acrylic acid form hydrogen bonds with various basic templates and form non-covalent adducts. These two monomers are being widely used in the current polymer industry, and are available on quite a large scale at low cost. Molecular imprinting with the use of hydrogen bonding between methacrylic acid and atrazine (a herbicide) is described in detail in Chapter 6. 

Atrazine (the template) has a triazine ring and two amino groups, all of which form hydrogen bonds with appropriate residues in aprotic solvents (Fig. 6.2). Accordingly, methacrylic acid, having a carboxylic acid (hydrogen-bonding site), is chosen as the functional monomer. Acrylic acid is also useful. The two types of interactions at the two amino... 

Fig. 6-3 Tautomers of hydrogen-bonding complex between atrazine and methacrylic acid...

The typical mole ratio of atrazine, methacrylic acid, and ethylene glycol dimethacrylate in chloroform is 1 3-5 25-30. Although the adduct is formed from one atrazine and two methacrylic acids (Fig. 6.2), the atrazine/methacrylic acid ratio in the mixtures is usually kept around 4 to move the equilibrium toward the formation of these hydrogen-bonding adducts. The mole ratio of crosslinking agent to the template is in general 20-30. 

Commercially obtained chloroform was distilled to remove ethanol (the stabilizer for storage), which would suppress hydrogen bonding if it were present. Into 25 mL of a chloroform solution of atrazine (0.36 g, 1.7 mmol), methacrylic acid (0.58 g, 6.7 mmol), ethylene glycol dimethacrylate (9.4 g, 47 mmol), and AIBN (0.12 g, 0.73 mmol) were added. Nitrogen gas was bubbled into this pre-polymerization mixture for 5 min. The polymerization tube was sealed, placed in a water bath at 0 °C, and irradiated with UV light for 4 h. 

The primary ozonation by-products of atrazine (15 mg/L) in natural surface water and synthetic water were deethylatrazine, deisopropylatrazine, 2-chloro-4,6-diamino-s-triazine, a deisopropylatrazine amide (4-acetamido-4-amino-6-chloro-5-triazine), 2-amino-4-hydroxy-6-isopropylamino-5-triazine, and an unknown compound. The types of compounds formed were pH dependent. At high pH, low alkalinity, or in the presence of hydrogen peroxide, hydroxyl radicals formed from ozone yielded 5-triazine hydroxy analogs via hydrolysis of the Cl-Cl bond. At low pH and low alkalinity, which minimized the production of hydroxy radicals, dealkylated atrazine and an amide were the primary byproducts formed (Adams and Randtke, 1992). 

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