Lipid amphoteric nature

The pH-partition hypothesis relating to membrane penetrability was outlined in Chapter 1. This hypothesis would allow one to make reasonable assumptions of a drug s behavior whose pKa and aqueous-lipid partition were determined. The amphoteric nature of tetracyclines with their multiple pKas, however, presents a more complex situation than simply improving lipid solubility by the deletion of polar hydroxyl groups from positions such as 5 and 6 (e.g., DC, MC, MNC) or the addition of a halogen on C-7 (e.g., DMCTC, CTC). 

Several clean-up methods have incorporated the use of additional liquid-liquid steps with solvents such as chloroform and ethyl acetate. Alternatively, some authors have turned to ultrafiltration for further purification.Additionally, hexane is extensively used in several methods to further remove non-polar matrix components such as fats and lipids. By far, the most popular clean-up technique reported in the literature is the use of solid phase extraction (SPE). Some common phases reported include CIS cartridges such as SepPak C18, Strata Chromobond C18, " and Mega Bond Elut C18. The use of silica, alumina, and Extralut " " has also been reported, as well as polymeric cartridges such as Oasis HLB. The latter phase has been reported as the basis of an on-line clean-up procedure. Because of their amphoteric nature, as both weak acids and weak bases, the sulfonamides also lend themselves to analysis by ion exchange. Cationic SPE has been reported by several authors.On the basis of the same principles, anionic exchange has also been used. " ... 

Drugs of the tetraeycline group are amphoteric, forming salts with both acids and bases. They are used as parent compounds (e.g., oxytetracycline dihydrate) or as salts (e.g., oxytetracycline hydrochloride). Their lipid solubilities range from moderate (oxytetracycline and chlortetracycline) to high (doxycycline and minocycline), so that they are able to traverse cell membranes moderately or readily. The former two drugs are natural tetracyclines, while the latter two are semi-synthetic. 

Naturally occurring fatty add amides are described in Section 3.6.1. In non-food uses of lipids, fatty amides are produced synthetically in industry for use as ingredients of detergents, lubricants, inks and many other products. Ammonium salts of fatty adds are gradually dehydrated to amides and aliphatic nitriles that are used for the production of fatty primary amines, which are then used as reactants for the synthesis of cationic and amphoteric surfactants. 

Chem. Descrip. Milk lipid amidopropyl betaine Ionic Nature Amphoteric... 

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