Surface active agents lipophilic group

Surfactants, sometimes called surface active agents or detergents, are amphiphilic materials which contain both apolar, hydrophobic (lipophilic) and polar, hydrophilic (lipophobic) groups (Hartley, 1948, 1977 Fendler and Fendler, 1975 Fendler, 1982 Lindman and Wennerstrom, 1980 Sudholter... 

In their similar action on the cell membrane the tyrocidines, gramicidins and the polymyxins resemble other surface active agents. Like these, they contain also lipophilic and lipophobic groups, which, as has been revealed by studies on gramicidins, may be separated in the molecule by being fixed on different sides of the molecular plane. 

The word surfactant derives from the contraction of the terms surface—active—agent and covers a group of molecules which are able to modify the interfacial properties of the liquids (aqueous or nonaqueous) in which they are present. The peculiar properties of these molecules reside in their amphiphilic character which stems from the fact that each surfactant molecule has both a hydrophilic part and a hydrophobe (or lipophilic) part. As a result, they concentrate at the interfaces separating immiscible phases, thereby decreasing the interfacial tension. 

The word surfactant is an acronym for surface-active agents. It stands for molecules that tend to adsorb at interfaces when they are in solution. The molecular structure of surfactants is characterized by a polar group connected to a typically long nonpolar hydrocarbon chain. The polar group, frequently referred to as the head of the molecule, is also known as the hydrophilic group because it is compatible with water (hydro). The nonpolar part, frequently referred to as the tail of the molecule, is also known as the hydrophobic (water hating) or lipophilic group because it is compatible with lipids. The relative size of (balance between) the hydrophilic to the lipophilic (frequently abbreviated and known as HLB) determines whether a surfactant will be predominantly water soluble or oil soluble. 

The steric effect of substituents ortho to the phenohc group was foimd to be critical in reducing antibacterial activity despite having increased hpid solubihty approaching the optimum lipophilicity value. The antibacterial activity of phenohc compoimds is hkely exerted by multiple functions, primarily comes from its capability to act as a nonionic surface-active agent therefore disrupting the lipid-protein interface. 

A surface-active agent usually an organic compound whose molecules contain a hydrophilic group at one end and a lipophilic group at the other. 

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