Diphenols, toxicity

In an attempt to identify new, biocompatible diphenols for the synthesis of polyiminocarbonates and polycarbonates, we considered derivatives of tyrosine dipeptide as potential monomers. Our experimental rationale was based on the assumption that a diphenol derived from natural amino acids may be less toxic than many of the industrial diphenols. After protection of the amino and carboxylic acid groups, we expected the dipeptide to be chemically equivalent to conventional diphenols. In preliminary studies (14) this hypothesis was confirmed by the successful preparation of poly(Z-Tyr-Tyr-Et iminocarbonate) from the protected tyrosine dipeptide Z-Tyr-Tyr-Et (Figure 3). Unfortunately, poly (Z-Tyr-Tyr-Et iminocarbonate) was an insoluble, nonprocessible material for which no practical applications could be identified. This result illustrated the difficulty of balancing the requirement for biocompatibility with the need to obtain a material with suitable "engineering" properties. 

CEs are known to react with phenols to form iminocarbonates which eventually lead to polycyanurates with the liberation of more acidic phenol moiety. This can be a method to alter the gel point of the resin, Tg, and thermal stability of the network by co-curing diphenol with CE. Thus, copolymerization of dicyanate with diphenols resulted in polycyanurates with altered network structure and diminished crosslink density [237]. However, an earlier report claims poly(imi-nocarbonate) by reaction of these two in equimolar quantities. The thermoplastic so formed was reported to retain the mechanical properties like a polycarbonate. This approach can produce strong, non-toxic, biodegradable films and molded plastics that are degradable at temperatures above 140 °C [169,238]. Except for a few very early reports [239], the reaction of CE with anhydrides to form poly(iminocarbamates) has not been explored much. 

In comparison with many other classes of organic compounds, phenols show relatively greater toxicity. Most alkyl phenols, chlorophenols, and nitrophenols, although following different metabolic pathways and toxicokinetic patterns, exhibit a high degree of toxicity. The symptoms of acute toxicity are discussed under individual compounds in the following sections. The alkyl phenols, diphenols (benzenediols), and triphenols (benzenetriols) exhibit toxicities quite similar to those of phenols. The symptoms and severity of toxic effects are more or less similar. 

Phenolic compounds are found in most fruits and vegetables. These endogenous compounds show interesting properties such as antioxidant activity, enzymatic inhibition and free radical scavenging action [42]. In particular, catechol is a diphenol compound of interest in the food industry and has been involved in ghal cell toxicity. Thus, there is a great appeal to produce novel sensors of higher stability and lower cost for catechol detection [43]. 

Ba" and Sr and with the strong non-specific toxicity of heavy metals (Cu , Zn , Hg , Hg , Ag ). Some other p- and o-quinones, diphenols and amidophenols are also inhibitory (Kritzmann and Vyshepan, unpubl.) ... 

The potential release of the toxic BPA from the polymer is driving the search for an alternative monomer. Diphenolic acid (DPA) is a potential substitute for BPA in polymer synthesis. The synthesis of polycarbonates involves a two-step process. First, DPA is treated with NaOH to produce a sodium diphenoxide. This intermediate reacts with phosgene (COCy to start the polymerisation. A disadvantage of this process is the toxicity of phosgene (phosgene was used as a chemical weapon during World War 1). An alternative route to polycarbonates consists of the transesterification of DPA with diphenyl carbonates. DPA can also be copolymerised using the same reaction route. 

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