Simazine 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). 

Distinct differences in cells with regard to the presence or absence of target structures or metabolic processes also offer opportunities for selectivity. Herbicides such as phenylureas, simazine, and so on, block the Hill reaction in chloroplasts, thereby killing plants without harm to animals. This is not always the case because paraquat, which blocks photosynthetic reactions in plants, is a pulmonary toxicant in mammals, due apparently to analogous free-radical reactions (see Figure 18.4) involving enzymes different from those involved in photosynthesis. 

The triazine herbicides can be divided into four different structural classes chlorotriazines, methylthiotriazines, methoxytriazines, and atypical or asymmetrical triazines. The chlorotriazine group includes atrazine, simazine, pro-pazine, terbuthylazine, and cyanazine. The methylthiotriazine group includes ametryn, prometryn, and terbutryn. The methoxytriazine group will include prometon and secbumeton. Hexazinone and metribuzin were chosen to represent the atypical triazine group. The plant metabolism of the most researched member of each triazine group will be discussed in detail to cover all major biological and chemical transformations reported in the literature. 

The structures and other properties for simazine, propazine, prometryn, prometon, and other triazine herbicides and many of their degradation products can be found in the Appendices, Tables Al, A2 and A3. As shown in Figure 30.12, atrazine and simazine degrade to DIA. 

Increased stands of wild carrots show up, for example, after Propazine treatment, of birdsfoot trefoil after Simazine treatment and of green foxtail and crab grass after Atrazine treatment. Are these biological particularities not amazing in view of the very small structural differences ... 

The broad-spectrum, moderate, cross-resistance of black-grass is quite unlike the almost complete immunity to a single herbicide or specific group of herbicides which can arise as a result of structural modifications to sites of action, as is observed in cases of triazine and simazine resistance ( 2 Rather, it indicates a deficiency of herbicide arriving at the site of action. This could be due to restricted uptake and/or inhibited translocation to the site of action, or rapid degradation and detoxification of the herbicide within the resistant plant. 

The triazine herbicides are based on an s-triazine structure containing two amino groups. Atrazine, simazine and terbutryne present an absorption peak around 225 nm (Fig. 55), whereas hexazinone (Fig. 56) has an absorption maximum at 248 nm. 

The triazine herbicides, atrazine and simazine have recently been encountered in groundwater in Northern California and in the Los Angeles Basin at levels ranging from 0.4 to 2.0 ppb (2J5). The chemical structures of these two compounds are shown below ... 

Cyclic nitramine compounds such as RDX and HMX appear to have different modes of action in plants compared to the nitroaromatic compounds. Their basic structure and behavior in plants are similar to those of the triazine herbicides such as atrazine and simazine, which inhibit photosystem II in photosynthesis [32], The inhibition of photosynthesis may also be one of the modes of toxicity of cyclic nitramines based on symptoms such as chlorosis, necrosis, yellow leaf spots, and anthocyanin expression [27], However, the mechanism(s) of phytotoxicity of cyclic nitramines have not been investigated thoroughly. 

Hypersol, are now available. These sorbents have a higher degree of cross-linking and, thereby, an open structure (high-porosity materials) that increases their specific area (400 to 1000 m /g) and allows greater 11-11 interactions between analytes and sorbent. This means that the breakthrough volumes will be higher than those obtained when the cross-linked sorbents are used. The three sorbents allowed the same percent recoveries for atrazine and simazine (80 to 86%) in water. ... 

Finally, Q-TOF/MS was very recently applied to study the transformation products of terbutylazine, simazine, terbutryn, and terbumeton in water after UV exposure. MS/MS helped to elucidate structures of degradation products (even those with only 2% of the total peak area) and to differentiate isomeric metabolites. 

Figure 1. Atrazine (D, simazine (ID, and haptens and conjugates used in this work, m— atrazine-mercaptopropionic acid hapten, and IV — atrazine aminohexanoic acid hapten, which were conjtigated to BSA, CON, or KLH, and used as immunizing and EIA coating antigens. V — simazine-alkaline phosphatase 1iaptenated enzyme, xised as the detector in competition EIAs where the monoclonal antibody was immobilized on the solid phase. Atoms on l e triazine ring are numbered dodEwise from Ni diown in structure L...

Synthesis of triazine haptens and hapten-protein conjugates. Simazine and atrazine were derivatized with mercaptopropionic add (mpa) at Rl, or aminohexanoic acid (aha) at R2, and these haptens were covalently linked to keyhole limpet hemoyanin (KLH), conalbumin (CON), or bovine serum albumin (BSA), by forming active esters with N-hydroxysucdnimide (g) (Figure 1, structures III and IV). This technique was also used to couple simazine-aminohexanoic add to calf intestine alkaline phosphatase (Figure 1, structure V), for use as the %aptenated enzyme in the EIA format described below. 

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... 

Examples Terbutylazine and simazine were used as structural analogue of the target atrazine [2], pentycaine for bupivacaine [3], compound E for the lead drug F [4] Check Table 1 for the structures. 

Simazine, atrazine, trietazine, propazine, terbutylazine, and sebutylazine belong to the group of symmetric triazines characterized by dte structure XIV prometon and atraton are characterized by structure XV and simetryn, prometryn, desmetryn, methoprotryn, and terbutryn by structure XVI. Triazines can be determined without thorough cleanup using detection by the Hill reaction (see Section V.C. 1), but several other sensitive methods are also known. 

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