ABSTRACT Amphiphiles are natural or synthetic molecules that have two different moieties - a relatively long hydrophobic (lipophilic) chain (the tail) and a hydrophilic group (the head). Among the most studied of all amphiphiles are fatty acids, steroids and their inorganic esters and glycosides, sphingo-lipids, glycerolipids, polyprenyl (glyco)lipids, the glycosides of lipophilic vitamins, bilirubin glycosides and prostaglandins. In this paper, a series of chemical modifications of amphiphiles, undertaken by chemical and biochemical means, are described. These chemical modifications are aimed at both the hydrophilic head and the hydrophobic tail and are designed for the tracing of amphiphiles. Doubly-labelled amphiphiles - in the two moieties - are also described. Every type of labelling needs specialized equipment for the detection and quantification of the tracer and the equipment determines important parameters of research (i.e., accuracy and sensitivity). Redox reactions were especially used for labelling: the oxidation-reduction of primary or secondary hydroxyl, the reduction of alkenes to alkanes or of alkynes to alkenes, etc. The covalent linkage formation of a previous hydrolyzed bond - especially in substituted amides - is also a currently used method. The following atoms or groups accomplishing peculiar qualities were linked in amphiphiles: radioactive isotopes (14C, 3H, 32P, 35S, 18F) stable isotopes (13C, 2H, 18O, 15N, 19F), fluorescent markers (NBD, pyrene) and other chemical fragments with specific properties (biotin, DNPH, eosin).
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