How to boost antioxidants by lipophilization?

Covalent modification of antioxidants through lipophilization is an important field of research aiming at developing antioxidants with improved efficacy. However, due to insufficient knowledge on how hydrophobicity affects antioxidant activity, lipophilization strategies have been largely based on empirism. Often, the resulting lipophilized antioxidants were not optimal. Here we described how the body of knowledge regarding hydrophobicity has been dramatically redefined as unexpected results were recently published. Using a broad range of lipophilized antioxidants assessed in dispersed lipids models and cultured cells, it has been demonstrated that the antioxidant activity increases progressively with increasing chain length up to a critical point, beyond which the activity of the compounds dramatically decreases. Taking into account this nonlinear phenomenon, also known as cut-off effect, antioxidant drug designers now have to seek the critical chain length to synthesize the optimal drug in a rational manner. Here, we briefly presented three putative mechanisms of action to try to account for the cut-off effect. ► The relationship between antioxidant activity and hydrophobicity is nonlinear. ► This cut-off effect is widespread in emulsions, membranes, and cells. ► A critical chain length exists within homologous series of antioxidants.