Polymers xenobiotic

Polymerization, or conjugation, is the process in which toxic organic molecules undergo microbially mediated transformation by oxidative coupling reactions. In this case, a contaminant or its intermediate product(s) combines with itself or other organic molecules (e.g., xenobiotic residues, naturally occurring compounds) to form larger molecular polymers that can be incorporated in subsurface humic substances. 

Kawai F (2010) The biochemistry and molecular biology of xenobiotic polymer degradation by microorganisms. Biosci Biotechnoi Biochem 74 1743-1759... 

Figure 12. Generalized scheme for the formation of a polymeric network with imprinted cavities base d on the chemical and special characteristics of the template (T) the natural polymerlike antibody-type proteins recognize xenobiotics, a fully synthetic polymer may recognize the preentrapped and afterwards washed out template (T) molecule.

Data shown in Table 3 indicate a definite increase of chlorine content in the products of interaction between HAs and chlorophenoxy compounds, thus suggesting the occurred incorporation of xenobiotic chlorinated units into the humic polymer. 

The application of ESR spectrometry and in particular the determination of free radical concentrations in the interaction products between HAs and chlorophenoxyalkanoic compounds, has experimentally confirmed the occurrence of already suggested homolytic cross-coupling reactions, leading to the incorporation of xenobiotic chlorophenoxy units into the humic polymers through covalent bonds. 

In conclusion, toxic chlorinated phenol intermediates formed during the chemical, photochemical and/or enzymatic degradation of chlorophenoxyalkanoic compounds would temporarily be detoxified when they are incorporated into the humic acid, since their bioavailability and movement into terrestrial and aquatic ecosystems would be greatly reduced. However, the knowledge of the potential toxicity problems which these bound-residues could give rise to in the environment is still very limited. Xenobiotic chemicals incorporated into humic polymers are not really removed from the ecosystem and they may maintain their identity and toxic properties for unknown time spans, eventually causing time-delayed pollution problems, if and when they will be released from humic substances. 

Xenobiotics are frequently metabolized in plants by mechanisms that lead to the incorporation or inclusion of the xenobiotic into biological polymers or tissue residues that are not soluble in commonly used nonreactive solvents. These residues are frequently refered to as bound, insoluble, or nonextractable residues (2 ). Bound residues in plants have most commonly been detected in plant tissues treated with radloactlvely-labeled pesticides. These residues were an important topic of a symposium held in Vail, Colo, in 1975 (17) they have been discussed in mauiy more recent papers (11,154-1577"and they were discussed at a symposium at the l88th ACS National Meeting, 1984 "Non-extractable Pesticide Residues Characteristics, Bioavailability and Toxicological Significance". 

Occasionally, xenobiotics may be extensively metabolized in plants to CO2 or other low MW endogenously occuring products which can produce bound residues by reincorporation into biological polymers. Residues of this type are generally of little concern to toxicologists and residue chemists because these residues do not represent an unusual hazard to the biosphere. A recently proposed... 

In some cases, such as with 3,4-dlchloroanlllne, xenobiotics appear to be incorporated into lignin by covalent bonding (J, J ), but in other examples, such as swep, buturon, and carboxln, the xenobiotic may simply become entrapped in the cage-like matrix of the lignin polymer (155). 

The fate of plant xenobiotic conjugates I.e. glycosides, malonates, N-acyl-amlno acids, alkyl/aryl glutathiones and derivatives, lipophilic conjugates and polymer conjugates (bound residues). In animals Is reviewed. Some classes are reasonably well-studied but no Information Is available for others. 

Xenobiotic polymers can also be emitted into the aquatic environment (e.g. polysiloxanes). 

In addition to the input of modified natural macromolecules a further mode of anthropogenic alteration of the non-extractable organic matter is the emission of technical macromolecular products. Only very few investigations were reported concerning these emissions of xenobiotic polymers. Examples are the investigations by Fabbri et al. (1998a), as well as Requejo et al. (1985), characterising the input of polystyrene into the... 

The vision that a single species will be responsible for the complete degradation of a substrate (polymer) is very common but unrealistic, because xenobiotics are normally... 

Much of the negative attitude about antibiotics arises because the aforementioned problems are inherent in the nature of penicillin and other common antibiotics—namely, they are xenobiotic compounds that have evolved in a context that virtually assures that for every antibiotic. Nature has co-evolved a defense, or resistance, to it. If each and every one of Nature s antibiotic substances conformed to this same general pattern, then we would indeed be in a difficult situation. Fortunately, this is not the case, and nisin is an excellent example of an antibiotic with something very different to offer. First of all, it is a peptide and, therefore, a polymer of amino acids. Peptides are not alien things, and our metabolism has evolved around utilizing polypeptides as food. An antimicrobial peptide such as nisin will be digested in a normal residue-free fashion, unlike penicillin, which persists in the gut and floods out into the tissues, where its fate is problematic. 

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