Diuron structure

Ureides (e.g., diuron, linuron) and triazines (e.g., atrazine, simazine, ametryne) all act as inhibitors of photosynthesis and are applied to soil (see Figure 14.1 for structures). They are toxic to seedling weeds, which they can absorb from the soil. Some of them (e.g., simazine) have very low water solubility and, consequently, are persistent and relatively immobile in soil (see Chapter 4, Section 4.3, which also mentions the question of depth selection when these soil-acting herbicides are used for selective weed control). 

Figure 13 Structures of haptens used for immunizing and coating antigens in a monoclonal antibody-based immunoassay for diuron. A sensitive assay was developed using coating hapten I that had the handle in a position different from the immunogen hapten. When the oxygen in the urea moiety of hapten I was replaced with a sulfur (hapten 11), increasing the heterology, even greater sensitivity was achieved...

The chemical structures of herbicides are shown in Figure 9.7. Herbicides containing secondary amino moieties such as Basagran and diuron are more... 

Inhibitory action was associated with a wide variety of structural groups substituted on the carbonyl carbon of the amide moiety. In general, derivatives with nonpolar side chains were more active than those with polar side chains. The most active inhibitors, represented by diuron, possessed a dialkyl-amino substituent. However, derivatives with aliphatic side chains, such as propanil, and alicyclic side chains, such as cypromid, were also strong inhibitors (6). 

A method for analysis of polar pesticides in wine by the use of automated in-tube SPME coupled with LC/ESI-MS was proposed (Wu et al., 2002). In-tube SPME is a microextraction and preconcentration technique that can be coupled on-line with high-performance liquid chromatography (HPLC), suitable for the analysis of less volatile and/ or thermally labile compounds. This technique uses a coated open tubular capillary as an SPME device and automated extraction. Using a polypyrrole coating, six phenylurea pesticides (diuron, fluometuron, linuron, monuron, neburon, siduron) and six carbamates (barban, car-baryl, chlorpropham, methiocarb, promecarb, propham) were analyzed in wine. Structures of compounds are reported in Fig. 9.4. Due to the high extraction efficiency of the fiber toward polar compounds, benzene compounds, and anionic species, LODs ranging between 0.01 and 1.2pg/L were achieved, even if the sample ethanol content affects the recoveries of analytes. 

Figure 9.4. Phenylurea pesticides and carbamates detected in wine by automated intube SPME and LC/ESI-MS analysis (Wu et al., 2002). (14) monuron, (15) fluome-turon, (16) siduron, (17) diuron, (18) linuron, (19) neburon, (20) propham, (21) chlorpropham, (22) barban, (23) promecarb (structures of carbaryl and methiocarb are reported in Figs. 9.1 and 9.11, respectively).

Tixier et al. [4] have identified, synthesized, and assessed the toxicity of all transformation products of diuron. The bio assay they used was a bioluminescence inhibition test with the marine bacterium Vibrio fischert Since diuron does not exhibit any specific mode of toxic action towards bacteria, the QSAR analysis using a rescaled QSAR for Vibrio fischeri [42] only confirmed that diuron and all its metabolites with the exception of DCA (3,4-dichloroaniline) act as baseline toxicants (Table 3, for full names of metabolites see Fig. 4). However, DCA was 46-times more toxic than predicted with the baseline toxicity QSAR and almost two orders of magnitude more toxic than the parent compound. Such a specific mode of toxic action of a transformation product cannot easily be predicted unless toxicophores like the aniline structure present in DCA are considered as a signal. This is discussed in the conclusion section in more detail. 

Two other Lolium ri dum biotypes from Australia (WLR2 and VLR69) developed metabolism-based resistance to PSII inhibitors. WLR2 came from a field with selection pressure by atrazine and amitrole, but never by phenylureas, and VLR69 from a field with selection pressure by diuron and atrazine. Both biotypes were resistant to triazines, and, despite the field selection by atrazine, resistance was more pronounced to the structurally related simazine. Furthermore, both biotypes were resistant to chlorotoluron, though only VLR69 was previously exposed to phenylureas. Analytical work revealed that in both resistant biotypes... 

Agulhon P, Markova V, Robilzer M, Quignard F, Mineva T (2012) Structure of alginate gels interaction of diuronate units with divalent cations from density functional calculations. Bio-macromol 13(6) 1899 1907. doi 10.1021/bm300420z... 

The SSF products exhibit unique pseudoplastic rheology. Figure 3 shows the general behavior of Diuron SSF system. At zero or very low shear rates the system has a very high viscosity. This high viscosity contributes to the high physical stability of SSF products with no settling of the suspended solids. After die yield stress is reached the structure of the system breaks and the viscosity quickly decreases to very low values. This low viscosity allows die SSF product... 

Quantitative Structure Activity Relationships. The goal of our structure activity studies was not the prediction of more active compounds in order to finally get new hints for the development of a herbicide. Instead, we wanted to corroborate our concept that phenols with the appropriate substitution enter the binding niche in the D1 protein just as the classical herbicidal inhibitors like atrazine and diuron do. 

Sorgoleone was initially found to inhibit mitochondrial respiration, but it was later found to be a more potent inhibitor of photosyndietic electron transport of photosystem II (PSII) IS, 16). Sorgoleone is structurally similar to plastoquinone (PQ), a benzoquinone involved in photosyndietic electron transport. Sorgoleone competes for the PQ binding site of die D-1 protein in a manner similar to most commercial photosynthetic inhibitors IT). The in vitro PSII inhibiting activity of sorgoleone is similar to some of the commercial herbicides targeting this site e.g., atrazine and diuron). 

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