Surface behavior and reactivity of dialkylated tetrazine with norbornene at the air–water interface

The inverse electron-demand Diels–Alder (IEDDA) reaction is a powerful tool for bioorthogonal chemistry and materials engineering, yet its efficiency at structurally confined interfaces remains incompletely understood. In this study, we investigated the interfacial reactivity and monolayer behavior of a newly synthesized symmetric tetrazine derivative, C18-Tz-C18, in combination with a norbornene-functionalized amphiphile, C16-NCA, at the air–water interface. Langmuir monolayers of the binary system were fabricated via two distinct methods—vial pre-reaction and cospreading—and characterized using surface pressure–area and surface potential–area isotherms, along with fluorescence microscopy. The symmetric architecture of C18-Tz-C18 facilitated condensed phase formation and enhanced interfacial ordering compared to its previously reported monoalkylated counterpart. Notably, interfacial IEDDA reactions proceeded efficiently only when conducted in solution prior to film formation; spontaneous reactivity at the interface was markedly suppressed. Bayesian machine learning predicted similar second-order rate constants for C18-Tz-C18 and monoalkylated analogs in bulk solvents, suggesting that the observed differences arise from spatial constraints rather than intrinsic reactivity. These findings demonstrate the pivotal role of molecular symmetry and preorganization in governing surface-confined chemical ligation, offering design principles for functional interfacial systems in diagnostics, coatings, and drug delivery.