*2.1. Material*

2-Isopropenyl-2-oxazoline (Sigma-Aldrich, Weinheim, Germany) was distilled in the presence of 2,6-di-tert-butyl-4-methylphenol (Sigma-Aldrich, Weinheim, Germany) under reduced pressure, and stored at −20 ◦C under argon atmosphere. N,N-Dimethylacetamide (DMAc) (Sigma-Aldrich, Weinheim, Germany) was distilled over phosphorus pentaoxide (Sigma-Aldrich, Weinheim, Germany) under reduced pressure. Fluorescein isothiocyanate (FITC) and dimethylsulfoxide (DMSO) were purchased from Sigma-Aldrich (Weinheim, Germany) and used as received. 4-Aminobutyric acid (ABA) was purchased from Fluka (Buchs, Germany) and used as received.
