Phenols, lipid soluble

Anions of lipid-soluble phenols such as 2,4-dini-trophenol can serve as effective carriers of protons (Chapter 18). However, proteins usually serve as the natural carriers, both of protons and of other ions. A protein is sometimes pictured as rotating to present the solute-binding surface first to one side, then to the other side of a membrane. However, gated pores or channels are probable for most biological transport. 

The problem of lipophiles remained and here again we could make use of the acid functionality of the phenols. With less lipid soluble phenols such as the steroids, simple back extraction from organic solvent into strong base would have been sufficient. However, the high lipid solubility of A9-THC necessitated that extraction be carried out with Brodie s solvent (hexane and isoamyl alcohol) and that back extraction be done with Claisen s alkali, which is a mixture of KOH, methanol, and water. After acidification of the Claisen s alkali, A9-THC could be recovered by extraction. The external standard and the trimethylanilinium hydroxide were added and the extracted phenol (i.e. A9-THC) was converted to the 1-0-methyl derivative in the injector port and the determination carried out... 

Richheimer, S.L., Bernart, M.W., King, G.A., Kent, M.C. and Bailey, D.T. 1996. Antioxidant activity of lipid-soluble phenolic diterpenes from rosemary. J. Am. Oil Chem. Soc. 73 507-514. 

Peat materials are often richer in nonhumified plant residues than in humus. Exhaustive alkaline extraction and estimation of humic substances are therefore hampered by the presence of hydrophobic lipids, and by coextraction of phenolic compounds from undecomposed plant residues, particularly from lignihed tissues. Artifacts may occur also during the solvation, separation, or concentration steps of the procedure, as discussed by Hayes in Chapter 13. Some of the problems can be mitigated by prior extraction of the lipids, soluble phenols, and sugars, as in the various schemes of proximate analysis discussed by Walmsley (1973). 

Phenols are important antioxidants, with vitamin E being the most important endogenous phenolic membrane-bound antioxidant. Membrane levels of vitamin E are maintained through recycling of the vitamin E radical with ascorbate and thiol reductants. Vitamin E is a mixture of four lipid-soluble tocopherols, a-tocopherol being the most efiective radical quencher. The reaction of a-tocopherol with alkyl and alkylperoxyl radicals of methyl linoleate was recently reported. These are facile reactions that result in mixed dimer adducts (Yamauchi etal., 1993). 

Plant resins are lipid-soluble mixtures of volatile and nonvolatile terpenoid and/or phenolic secondary compounds that are usually secreted in specialized structures located either internally or on the surface of the plant. Although terpenoid resins constitute the majority of the resins produced and used, some other important resins are phenolic. Phenolic resin components, which occur on the surfaces of plant organs, have been used particularly in medicines [86]. 

Ju Z and WJ Bramlage. 1999. Phenolics and lipid-soluble antioxidants in fruit cuticle of apples and their antioxidant activities in model systems. Postharv Biol Technol 16 107—118. 

Phenolics. The phenolics of citrus represent a varied and widely studied class of compounds. They range from the lipid-soluble methoxylated coumarins and psoralens to the water-soluble glycosides of the flavanones and flavones. They include the intensely bitter naringin and the highly insoluble hesperidin. Different classes within the group have characteristic UV spectra which have been used to detect adulterations in juices and oils. 

The permeability of the skin to a toxic substance is a function of both the substance and the skin. The permeability of the skin varies with both the location and the species that penetrates it. In order to penetrate the skin significantly, a substance must be a liquid or gas or significantly soluble in water or organic solvents. In general, nonpolar, lipid-soluble substances traverse skin more readily than do ionic species. Substances that penetrate skin easily include lipid-soluble endogenous substances (hormones, vitamins D and K) and a number of xenobiotic compounds. Common examples of these are phenol, nicotine, and strychnine. Some military poisons, such as the nerve gas sarin (see Section 18.8), permeate the skin very readily, which greatly adds to then-hazards. In addition to the rate of transport through the skin, an additional factor that influences toxicity via the percutaneous route is the blood flow at the site of exposure. 

Action on the plasma membrane is the first and most fundamental of the bewildering array of deleterious effects of the cinnamic and benzoic acids. They reduce the transmembrane electrochemical potential with the immediacy and extent of that action depending on the concentration and lipid solubility of the compound.35,37,45,60 Rate of uptake also is concentration and pH-dependent, with transfer into and across the membrane greatest with lower pH conditions and higher external concentrations.60 Phenolic acid-induced depolarization of membranes causes a nonspecific efflux of both anions and cations accompanying the increased cell membrane permeability, and these membrane effects correlate with an inhibition of ion uptake. The phenolic acids suppress absorption of phosphate, potassium, nitrate, and magnesium ions, and overall changes in tissue... 

Fifty-six years ago the very first siderophore, mycobactin, was isolated by the crystallization of the aluminum complex. Mycobactins from Gram-positive Mycobacteria and the closely related nocobactins from Nocardia embody a series of lipid-soluble siderophores located in the lipid-rich boundary layers of these bacteria (Figure 2(c)). The X-ray structure revealed that iron binding in mycobactins is accomplished by two hydroxamates, a phenolate group, and oxazoline nitrogen. 

Sulfolipids Free fatty acids Lipid-soluble vitamins Pigments Phenolic compounds Metals and Metalloproteins... 

Phenols Can be. highly toxic as they are... lipid soluble and therefore can crQss cell membranes . yhasilyC ... 

Cauliflower has a very high waste index (Kulkami et ah, 2001) and is an excellent source of protein (16.1%), cellulose (16%), and hemicellulose (8%) (Wadhwa et ah, 2006). It is considered as a rich source of dietary fiber and it possess both antioxidant and anticarcinogenic properties. Phenolic compounds and vitamin C are the major antioxidants of brassica vegetables, due to their high content and high antioxidant activity (Podsedek, 2007). Lipid-soluble antioxidants (carotenoids and vitamin E) are responsible for up to 20% of the brassica total antioxidant activity. The level of nonstarch polysaccharide (NPS) in the upper cauliflower stem is similar to that of the floret and both are rich in pectic polysaccharides, while the cauliflower lower stem is rich in NPS due mainly to cellulose and xylan deposition (Femenia et ah, 1998). 

Another milestone in the 1980s was the discovery that either water-soluble or hpid-soluble initiators with water-soluble or hpid-soluble phenolic antioxidants can be used for quantitative kinetic studies in micelles and lipid membranes . This made measurements in these systems less difficult than before when the initiators were included in high concentrations in lipid membranes due to low initiator efficiency. ... 

As indicated before, the distribution of carbon in humic substances is often determined as part of a proximate analysis in which soluble phenols, carbohydrates, lipids, and lignins are removed by acid hydrolysis or selective solvation to obtain data of the type presented in Table 9. Perhaps a less... 

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