Phenolic acids structure

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

Many studies have been undertaken to establish the structural criteria for the activity of polyhydroxy flavonoids in enhancing the stability of fatty acid dispersions, lipids, oils, and LDL. " As for phenolic acids, the inhibition of oxidation by flavonoids is related to the chelation of metal ions via the... 

RICE-EVANS c A, MILLER N J and PAGANGA G (1996) Structure-antioxidant activity relationships of flavonoids and phenolic acids, Free Rad Biol Med, 20, 933-56. 

Two hypotheses have been proposed to explain how phenolic acids directly increase membrane permeability. The first is that the compounds solubilize into cellular membranes, and thus cause a "loosening" of the membrane structure so that minerals can leak across the membrane (28-30, 42). Support for this hypothesis comes from the fact that the extent of inhibition of electrical potentials correlates with the log P (partition coefficient of a compound between octanol and water) for various benzoic and cinnamic acid derivatives (Figure 5). 

A number of spectrophotometric methods for the quantification of phenolic compounds in plant materials have been developed. Based on different principles, these assays are used to determine various structural groups present in phenolic compounds. Spectrophotometric methods may quantify all extractable phenolics as a group (Marshall and others 2008), or they may determine a specific phenolic substance such as sinapine (Ismail and Eskin 1979) or a given class of phenolics such as phenolic acids (Brune and others 1989). 

Phenolic Acids and Derivatives Studies on the Relationship Structure,... 

Silva, E. A. M. Borges, E Gulmaraes, C. Lima,]. L. F. C. Matos, C. Reis, S. Phenolic Acids and Derivatives Studies on the Relationship among Structure, Radical Scavenging Activity, and Physicochemical Parameters.]. Agric. Food Chem. 2000, 48, 2122-2126. 

Phenolic acids are often found in plant tissue, and have been implicated in many cases of allelopathy (4). Figure 6 shows a separation of three free phenolic acids and Figure 7 shows mass spectra obtained from these compounds. These spectra give both molecular weight and structural information. Phenolic acids can easily be thermally decarboxylated. The height of the molecular ion peak varies owing to ion source temperature. The variation depends also to some extent on the composition of the LC eluent, and this will be further examined. 

Shahjahan, M., M. Mosihuzzaman, and A. Mian. Phenolic acids in rice plant (Oryza sativa). J Bangladesh Chem Soc 1992 5(1) 59-63. Nakashima, R., K. Hakamoto, Y. Katagiri, T. Mizutani, N. Ueda, and J. Yamamoto. Structure determination of a pigment from Oryza sativa Linn. (Kurogome). Chem Express 1993 8(6) 393-396. 

Materska, M. et al.. Isolation and structure elucidation of flavonoid and phenolic acid glycosides from pericarp of hot pepper fruit Capsicum annum L., Phytochemistry, 63, 893, 2003. 

In the presence of nitric acids, 4-hydroxylated phenolic acids (and to some extent also hydroxylated indoles from tryptophan) conjugate with l-nitroso-2-naphthol to yield orange/red chromophores [4]. The structure of l-nitroso-2-naphthol is shown in Fig. 1.3.1. 

Polyphenols constitute one of the most and widely distributed groups of substances in the plant kingdom, with more than 8000 phenolic structures currently known. They can be divided into at least 10 different classes based upon their chemical structure, ranging from simple molecules, such as phenolic acids, to highly polymerized compounds, such as tannins. 

Polyphenols can act as antioxidants by a number of potential pathways. The most important is likely to be by free radical scavenging, in which the polyphenol can break the radical chain reaction. Polyphenols are effective antioxidants in a wide range of chemical oxidation systems, being capable of scavenging peroxyl radicals, alkyl peroxyl radicals, superoxide, hydroxyl radicals, nitric oxide and peroxynitrate in aqueous and organic environments [121]. This activity is due to the ability of donating an H atom from an aromatic hydroxyl group to a free radical, and the major ability of an aromatic structure to support an unpaired electron by delocalization around the 7i-electron system. Phenolic acids... 

---