Ester compounds physicochemical properties

The disappearance of a plasticizer from water can be the result of a number of abiotic and biotic processes that can transform or degrade the compound into daughter compounds that have different physicochemical properties from the parent compound. Hydrolysis is a family of chemical reactions where a plasticizer reacts with water. Phthalate esters may hydrolyze to form monoesters and then dicarboxylic acid. It has been predicted that di-(2-ethylhexyl) sebacate will form 2-ethylhexanol and decanedioic acid. Wolfe et al experimentally measured second-order alkaline hydrolysis rate constants for dimethyl, diethyl, di-n-butyl, and di-(2-ethylhexyl) phthalates, and it appears that hydrolysis may be too slow to have a major impact on the fate of most dissolved plasticizers. The estimated hydrolysis half-lives at pH 7 for 20 plasticizers were longer than 100 days. No information was located for diallyl, ditridecyl and diundecyl phthalates. Under alkaline conditions, hydrolysis may be important for tricresyl phosphate and tri-(2-ethylhexyl) trimellitate at pH 8 their predicted half-lives are 3.2 and 12 days respectively. 

Flavonoids are characterized by having an aromatic ring with different degrees of substitution, including functional derivatives such as esters, methyl ethers, and glycosides. These structural characteristics determine the general physicochemical properties of these compounds. 

The physicochemical properties of compounds affect not only the transport of compounds in plants but also their penetration through the leaf cuticle. This topic is discussed in Chapter 8, and here only brief comment is made on the implications of penetration for subsequent transport. The influence of physicochemical properties on the movement of compounds across cuticles seems to be rather similar to that observed for membranes, in that compounds of intermediate lipophilicity (log Ko values of 1 to 3) appear to penetrate the most rapidly. Uptake of more polar and more lipophilic compounds can, however, be greatly increased by the use of appropriate surfactants. Acidic compounds are taken up relatively slowly, presumably because of poor penetration of the anions in consequence, they are often applied as esters which enter the plant rapidly and are then metabolized to the active acid. Thus, herbicides of a wide range of structures and physical properties are applied to plant foliage the use of surfactants and adjuvants increases the uptake of chemical into the leaf and hence its availability for transport via xylem and phloem but does not otherwise influence transport patterns. 

Gallic acid (3,4,5-trihydroxybenzoic acid) can be formed by acid hydrolysis of hydrolyzable tannins. Differences among the ester derivatives are only in the number of carbon atoms in the aliphatic side-chain. These differences confer different physicochemical characteristics, especially in lipophilicity evaluated by the value of partition coefficient (C log P). Chemical modifications in the gallic acid molecule can alter the pharmacokinetic and pharmacodynamic properties, such as changing the solubility and the degree of ionization. The names of the compounds are abbreviated according to the length of the side-chain (Locatelli et al., 2013). 

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