Thiol-ene coupling

Thiol-ene coupling is a click-chemistry reaction between a thiol (R-SH) and an alkene (C=C) that forms a new C–S covalent bond. The reaction is high-yield, oxygen-tolerant, and proceeds at room temperature, making it well-suited for biological substrates including hair keratin.

Background

The mechanism is radical addition. A thiyl radical (R-S·) adds across the alkene's double bond, forming a new C–S bond and producing a carbon-centered radical that abstracts a hydrogen to terminate the chain. In well-designed substrates, the reaction is highly selective and produces a single product cleanly.

In haircare, thiol-ene coupling is one of two click reactions ANATOMY uses to form new covalent crosslinks at damage sites in the cortex. Pro-amino X is a bifunctional molecule with alkene functional groups that react with free thiol groups on cysteine residues — the chemical signatures of broken disulfide bonds.

Why thiol-ene is suited to hair: - Aqueous compatibility. The reaction tolerates water, which matters for a treatment that contacts wet hair. - Mild conditions. Room temperature and physiological pH; no harsh activation needed. - Selectivity. Free thiols are abundant in damaged hair and react preferentially. - Stability. The product C–S bond is covalent and not thermally reversed at typical heat-styling temperatures.

Thiol-ene's industrial use spans polymer crosslinking, photoresist patterning, and bioconjugate chemistry. Its application to hair reconstruction is the chemistry ANATOMY publishes against (SGS Proderm 24.0172-96).