Behavior of phenolic acids

Figure 2.8 Summary of behavior of phenolic acid esters and free forms in the GIT and the liver. 5-O-CQA, 5-O-caffeoylquinic acid 5-O-FAAF, 5-O-feruloyl-L-arabinofura-nose C, conjugate (sulfate, glucuronide or methyl) CA, caffeic acid FA, ferulic acid FA-FA, dimer of ferulic acid FA-oligosac., ferulic acid esterified to an oligosaccharide FA-Xy, ferulic acid esterified to xylan R, alkyl group.

Chromatographic Behavior of Phenolic Acids and Their Derivatives... 

CHROMATOGRAPHIC BEHAVIOR OF PHENOLIC ACIDS AND THEIR DERIVATIVES... 

Phenolics are an important class of natural products that have received immense interest for their remarkable biological activities. These are widely distributed in the plant kingdom. Nowadays, increasing attention is paid on rapid identification and characterization of phenolic acids from natural sources. This chapter particularly emphasizes on the diverse mass spectrometric application for the detection of phenolic acids, and several aspects related to fragmentation behavior of phenolic acids are discussed. 

Historically, simple phenolic acids have been the most frequently identified allelopathic agents (see literature reviews by Rice 1974, 1979, 1983, 1984, 1986). One would assume this was partly because of the fact that the necessary technology to isolate, identify, and quantify phenolic acids, even though crude in the early days, was readily available to most researchers. Furthermore, simple phenolic acids, such as the benzoic acid and cinnamic acid derivatives serve a variety of plant and ecosystem functions and are widespread in higher plants (Fig. 2.4 Bates-Smith 1956 Harborne 1982,1990 Goodwin and Mercer 1983 Siqueira et al. 1991). The ubiquitous distribution in nature and their apparent rapid turnover rates in soils, however, have lead to some controversy as to the importance of phenolic acids in plant-plant allelopathic interactions (Schmidt 1988 Schmidt and Ley 1999 Blum 2004, 2006). Finally, the behavior of phenolic acids in soil systems are somewhat similar to the behavior of a whole host of other organic acids (e.g., acetic acid, butyric acid, citric acid, formic acid, fiimaric acid, lactic acid, malonic acid, tannic acids and tartaric... 

Phenolic resins were the first totally synthetic plastics invented. They were commercialized by 1910 [I]. Their history begins before the development of the structural theory of chemistry and even before Kekule had his famous dreams of snakes biting their tails. It commences with Gerhardt s 1853 observations of insoluble resin formation while dehydrating sodium salicylate [2]. These were followed by similar reports on the behavior of salicylic acid derivatives under a variety of reaction conditions by Schroder et al. (1869), Baeyer (1872), Velden (1877), Doebner (1896 and 1898), Speyer (1897) and Baekeland (1909-1912) [3-17]. Many of these early reports appear to involve the formation of phenolic polyesters rather than the phenol-aldehyde resins that we think of today. For... 

Kotanigawa and co-workers [7-9] studied the adsorption behavior of phenol and methanol on a Zn0-Fe203 system and highlighted the importance of acid-base sites for the selective ortho methylation. However, detailed studies of the adsorption behavior of possible products and reactants of phenol methylation on catalytic systems and their interaction among them are not available widely. 

There is some confusion in the literature as to when it is appropriate to apply the term allelochemical to phenolic acids. Since phenolic acids and their derivatives are found essentially in all terrestrial soils, it should be understood that the presence of phenolic acids in soil does not automatically imply that these phenolic acids are functionally allelochemicals. In theory, phenolic acids in soils, depending on their chemical state, concentrations, and the organisms involved, can have no effect, a stimulatory effect, or an inhibitory effect on any given plant or microbial process. For phenolic acids in the soil to be classified as allelochemicals requires that a) the phenolic acids are in an active form (e.g., free and protonated), b) they are involved in chemically mediated plant, microbe, or plant/microbial interactions and c) the concentrations of the active forms in the soil solution are sufficient to modify plant or microbial behavior, either in a positive or negative manner.8,49 However, changes in microbial behaviour associated with the utilization of phenolic acids as a carbon or energy source would not qualify as an allelopathic response. 

As mentioned in Section IV.A.2, Leng and Pinto [3861 specifically addressed the effect of surface properties on the oxic and anoxic adsorption behavior of phenol, benzoic acid, and o-cresol. Commercial carbons were oxidized in air at 350°C, which is known [37] to introduce both CO- and C02-yielding surface groups nevertheless, from FTIR spectra, they concluded that the main differences are due to relative quantities of surface carboxylic groups. Presumably because the experiments were performed at pFl = 7.0, i.e., below the pK, of phenol, their explanation for the decrease in uptake with increasing surface oxygen was not the electrostatic repulsion but increased water cluster formation as well as increased removal of n electrons from the basal planes [450,674], which results in weaker dispersion interactions with phenol. ... 

No article was found reporting anxiolytic activity of phenolic acids. However, the anxiolytic activity of the alkaloids is known. Anxiolytic properties may be a crucial feature of newer antipsychotics associated with the improvement of negative symptoms in schizophrenic patients. The indole alkaloid alstonine acts as an atypical antipsychotic in behavioral models, but differs in its dopamine and serotonin binding profile [310]. Behavioral effects of psychollatine, a glycoside indole monoterpene alkaloid isolated from Psychotria umbellate Thoim., was investigated in models of anxiety, depression, memory, tremor, and... 

Laurent was well aware of the limitations of the basicity law, as was Gerhardt. In fact, the same example, the neutral and acid behavior of phenol, was used by Laurent and Kekule to point up these limitations. —O.T.B.]... 

Sorption behavior of inorganic and carboxylic acids is reported in Table 4.2 (anions), but sorption behavior of amino acids and phenols is reported in Table 4.4 (organic compounds). This classification is arbitrary, e.g. some derivatives of phenol whose sorption is reported in Table 4.4 have higher acidic dissociation... 

Identification of Phenols.—The reactions of phenols which are of particular value in their identification, are those that take place with alkalies, ferric chloride, and bromine water. Most phenols react with an aqueous solution of sodium hydroxide to form soluble salts, but are insoluble in a solution of sodium carbonate. The behavior of phenols with these two reagents shows their weakly acidic properties, and serves to distinguish them from acids. Phenols which contain strongly negative substituents decompose carbonates, and show all the properties of acids. It is difficult, therefore, to identify as a phenol substances which contain such substituents. Ferric chloride produces marked colorations in aqueous solutions of most phenols. The reagent produces a similar effect with certain other compounds, and the formation of a color with ferric chloride can be taken, therefore, only as an indication of the presence of a phenol. With bromine water most phenols yield a precipitate of a brominated phenol. Other compounds, amines for example, are also converted into insoluble substitution-products by bromine water. Notwithstanding this fact the test is of value. Many phenols form colored products when heated with phthalic anhydride and concentrated sulphuric acid. The reaction will be described under phenolphthalein (558, 639). 

In 1975 McCallum and Pethybridge [422] examined the behavior of strong acids, such as methane sulfonic, sulfuric, and nitric acids, in DMSO and concluded that these acids can be considered to be completely dissociated in dilute solution. Farrell, Terrier, and Schaal [267] later compared the pK s of nitroaromatics in both water and DMSO to examine the effects of solvation on these compounds. For the most part the pK s of the nitro-phenols, -anilines, -toluenes, and -diphenylamines were slightly higher in DMSO than in water, but in some cases this order was reversed. These authors concluded that these compounds undergo only very limited specific solvation in both solvents, and the charges in their anions are largely delocalized. 

What follows this introduction to plant-plant interactions (Chapter 1) are three additional chapters. The first chapter (Chapter 2) describes the behavior of allelopathic agents in nutrient culture and soil-microbe-seedling systems under laboratory conditions. Simple phenolic acids were chosen as the allelopathic agents for study in these model systems (see justifications in Section 2.2.6). The next chapter (Chapter 3) describes the relationships or lack of relationships between weed seedling behavior and the physicochemical environment in cover crop no-till fields and in laboratory bioassays. Here as well the emphasis is on the potential role of phenolic acids. The final chapter (Chapter 4) restates the central objectives of Chapters 2 and 3 in the form of testable hypotheses, addresses several central questions raised in these chapters, outlines why a holistic approach is required when studying allelopathic plant-plant interactions, and suggests some ways by which this may be achieved. 

The focus of the research just described utilizing the cucumber-nutrient culture and the cucumber-microbe-soil model systems was to identify and characterize what happens to phenolic acids once they enter the soil environment and how in turn this may influence the behavior and processes of phenolic acid-sensitive seedlings. The research was thus hypothetical, theoretical, and process oriented and not designed to answer speciflc questions related to actual field observations. When choosing any model system for study one hopes and assumes that the model system chosen is not unique but that the relationships and processes observed for the system chosen are representative of a broader array of other systems and hopefully relevant to field systems. 

FIGURE 3.55 Decomposition behaviors of phenol in the dark and under visible light irradiation for carbon-coated W18O49, W18O49 without carbon coating, and WO3 (a) and the relation between dimethylsulfoxide (DMSO) and the decomposition product methanesul-fonic acid (MSA) when carbon-coated W18O49 was used under visible light irradiation (b). 

KUWATSUKA S. and SHINDO H. 1973. Behavior of phenolic substances in the decaying process of plants. 1. Identification and quantitative determination of phenolic acids in rice straw and its decayed product by gas chromatography. Soil Science and Plant Nutrition, 19, 219-227. 

The photoprototopic behavior of phenols and hydroxyarenes in general has been well studied and is based on the enhanced acidity of these types of compounds in Sj (Scheme 1 ). For example, the pK (S )... 

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