Herbicides, cyclodextrins

Garbow, J.R. and B.J. Gaede. 1992. Analysis of a phenyl ether herbicide-cyclodextrin inclusion complex by CPMAS 13C NMR. J. Agric. Food Chem. 40 156-159. 

Proton nuclear magnetic resonace ( H NMR) spectra were recorded in DMSO-d or trifluoroacetic acid (TFA-di) solution on a Varian EM-360L 60-MHz NMR spectrometer, chemical shifts are repotted in parts per million from internal tetramethylsilane (TMS). Ultraviolet (UV) spectra were recorded on a Gilford Response UV-visible spectrometer using deionized water as solvent Infrared (IR) spe were recorded on a Beckman AccuLab 8 spectrometer and were calibrated with the 3027.9, 1601.8, and 1028.3 cm bands of polystyrene. Potassium bromide (KBr) disks of herbicide-cyclodextrin complexes and of propoitional mechanical mixtures of heibicide and cyclodextrin were prepared for the analysis. 

Otsuka, K., Smith, C. J., Grainger, J., Barr, J. R., Patterson, J., Tanaka, N., and Terabe, S. (1998). Stereoselective separation and detection of phenoxy acid herbicide enantiomers by cyclodextrin-modified capillary zone electrophoresis-electrospray ionization mass spectrometry. /. Chromatogr. A 817, 75-81. 

Fig. 1 Electropherograms of dichlorprop herbicide enantiomers with increasing concentrations of a-cyclodextrin. (From Ref. [18].)...

Miura, M. Terashita, Y. Funazo, K. Tanaka, M. Separation of phenoxy acid herbicides and their enantiomers in the presence of selectively methylated cyclodextrin derivatives by capillary zone electrophoresis. J. Chromatogr., A 1999, 846, 359-367. 

Tsunoi, S. Harino, H. Miura, M. Eguchi, M. Tanaka, M. Separation of phenoxy acid herbicides by capillary electrophoresis using a mixture of hexakis(2,3-di-0-methyl)- and sulfopropylether-a-cyclodextrins. Anal. Sci. 2000, 16, 991-993. 

Penmetsa, K.V. Leidy, R.B. Shea, D. Enantiomeric and isomeric separation of herbicides using cyclodextrin-modified capillary zone electrophoresis. J. Chromatogr.,... 

Zhang, M., and El Rassi, Z., Enantiomeric separation by capillary electrochromatography II. Chiral separation of dansyl amino acids andphenoxy acid herbicides on sulfonated silicahaving surface-bound hydroxypropyl-P-cyclodextrin, Electrophoresis, 21, 3135, 2000. 

The inclusion complexes formed between p-cyclodextrin (p-CD) and various optically active solutes (drugs and herbicides, Table 8.14) were modeled and refined using molecular modeling methods. The interaction energies of the complexes formed were calculated for both enantiomers and were correlated with the experimental retention data measured by normal-phase HPLC. A model cyclodextrin containing 441 atoms, 469 bonds, and 3513 connectors... 

F. Tazerouti, A. Y. Badjah-Hadj-Ahmed, B. Y. Meklati, F. Pilar and C. Minguillon, Enantiomeric separation of drugs and herbicides on a p-cyclodextrin-bonded stationary phase. Chirality, 2002, 14, 59-66. 

Phenoxy acid herbicides, sulfonyl ureas, quaternary ammonium derivatives (quats), and aryloxy propanoic acids are the main classes of compounds subjected to capillary zone electrophoresis (CZE). Triazines are also separated using nonaqueous CZE, while low pfCa characterized chlorotriazines require an ion-pair-like solubilization using cationic surfactants (tetradecylammonium bromide, dodecyltrimethyl-ammonium bromide). Chiral selectors are added in CZE for obtaining enantioselectivity. Chiral selectors used for herbicide enantiomeric discrimination are vancomycin, y-cyclodextrin, ethyl carbonate -cyclo-dextrin, cyclohexyl-alkyl-)S-D-maltoside, sulpropyl ether a-cyclodextrin, and hexakis(2,3-di-0-methyl)-a-cyclodextrin. 

Zerbinati, O. Trotta, F. Giovannoli, C. Optimization of the cyclodextrin assisted capillary electrophoresis separation of the enantiomers of phenoxy acid herbicides. J. Chromatogr. A, 2000, 875, 423 30. 

Mechref, Y. El Rassi, Z. Capillary electrophoresis of herbicides I. Pre-coluiim derivatization of chiral and achiral phenoxy acid herbicides with a fluorescent tag for electrophoretic separation in the presence of cyclodextrins and micellar phases. Anal. Chem. 1996, 68, Yll - 111. 

Table 9.4 The chiral resolution of phenoxy acid herbicides (underivatized and deriva-tized with 7-aminonaphthalene-l,3-disulfonic acid) using various cyclodextrins as chiral selectors [37]...

Figure 9.4 The effect of the cyclodextrin concentration on the chiral resolution of phenoxy acid herbicides, using 25 mM sodinm phosphate and 600 mM borate buffers (pH 5.0) containing different concentrations of (a) fi-CD, (b) DM-jS-CD, (c) HP-yJ-CD and (d) TM-jS-CD as BGEs. 1 = dichlorprop, 3 = mecoprop, 4 = 2,3-CPPA, 5 = 2,4-CPPA, 6 = silvex, 8 = 2, 2-CPPA, 9 = 2-PPA [34],...

The chiral resolution of environmental pollutants by CE depends on the formation of diastereomeric complexes and, therefore, the stmctures and sizes of the chiral pollutants are responsible for their enantiomeric resolution. To study this aspect, phenoxy acid herbicides (see Table 9.4) may be considered as the best class of chiral pollutant. Mechref and El Rassi [40] studied these herbicides using cyclodextrins as chiral selectors. It has been reported that the chiral resolution of these herbicides was in the order 2-PPA > 2,2-CPPA > 2,3-CPPA. 2-PPA has no chlorine atom on the phenyl ring, while 2,2-CPPA and 2,3-CPPA have chlorine atoms in the ortho- and meta- positions, respectively. Therefore, it may be concluded that the chlorine atom creates some sort of hindrance in the formation of diastereomeric complexes. Furthermore, it may be observed that the ortho- position creates a greater strain in comparison to the meta- position in the formation of diastereoisomeric complexes, and hence the above-mentioned order of resolution is observed. Briefly, the steric effect due to... 

Preparation and Characterization of Cyclodextrin Complexes of Selected Herbicides... 

Cyclodextrins have found particular application for the formulation of poorly water soluble, volatile, or unstable herbicides. Among the advantages of cyclodextrin complexes of pesticides are enhanced stabilization, reduced volatility, masked bad odor, enhanced wettability, solubility and bioavailability, and controlled release properties. Of the cyclodextrins, BCD is the only one available at a reasonid)le price, and its use may be economically feasible within a few years (. Several herbicides that have been frequently implicated in groundwater contamination (1-2) were selected as candidates for complexation with BCD in an attempt to develop formulations that could prevent entry of the chemical into the groundwater while maintaining effective weed control. 

Physical Properties of BCD and GCD Complexes. A number of physical properties were taken into account in determining whetiier or not the aforementioned herbicides did indeed form true cyclodextrin inclusion compounds. 

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