The objective of this Feature Article is to reflect on the importance of established and emerging principles of supramolecular organic chemistry to address one of the most persistent problems in life sciences. The main topic is dynamic covalent chemistry on cell surfaces, particularly disulfide exchange for thiol-mediated uptake. Examples of boronate and hydrazone exchange are added for contrast, comparison and completion. Of equal importance are the discussions of proximity effects in polyions and counterion hopping, and more recent highlights on ring tension and ion pair-π interactions. These lessons from supramolecular organic chemistry apply to cell-penetrating peptides, particularly the origin of "arginine magic" and the "pyrenebutyrate trick," and the currently emerging complementary "disulfide magic" with cell-penetrating poly(disulfide)s. They further extend to the voltage gating of neuronal potassium channels, gene transfection, and the delivery of siRNA. The collected examples illustrate that the input from conceptually innovative chemistry is essential to address the true challenges in biology beyond incremental progress and random screening.

Dynamic amphiphiles are amphiphiles with dynamic covalent bridges between their hydrophilic heads and their hydrophobic tails. Their usefulness to activate ion transporters, for odorant release, and for differential sensing of odorants and perfumes, has been demonstrated recently. Here, we report that the same "fragrant" dynamic amphiphiles are ideal to screen for new siRNA transfection agents. The advantages of this approach include rapid access to fairly large libraries of complex structures, and possible transformation en route to assist uptake and minimize toxicity. We report single-component systems that exceed the best commercially available multicomponent cocktails with regard to both efficiency and velocity of EGFP knockdown in HeLa cells. In human primary fibroblasts, siRNA-mediated enzyme knockdown nearly doubled from >30% for Lipofectamine to >60% for our best hit. The identified structures were predictable neither from literature nor from results in fluorogenic vesicles and thus support the importance of conceptually innovative screening approaches.

The objective of the study was to explore the potential of ring tension in cyclic disulfides for thiol-mediated cellular uptake.Fluorescent probes that cannot enter cells were equipped with cyclic disulfides of gradually increasing ring tension. As demonstrated by flow cytometry experiments, uptake into HeLa Kyoto cells increased with increasing tension. Differences in carbon-sulfur-sulfur-carbon (CSSC) dihedral angles as small as 88 8 caused significant changes in uptake efficiency.Uptake with high ring tension was better than with inactivated or activated linear disulfides or with thiols. Conversion of thiols on the cell surface into sulfides and disulfides decreased the uptake.R eduction of exofacial disulfides into thiols increased the uptake of transporters with disulfides and inactivated controls with thiols.T hese results confirm the occurrence of dynamic covalent disulfideexchange chemistry on cell surfaces.Mechanistic and colocalization studies indicate that endocytosis does not fully account for this cellular uptake with ring tension.