Microcontact printing (mCP) is commonly used to pattern self-assembled monolayers (SAMs) as etch resists or chemical templates on gold and silicon oxide substrates. [1] However, mCP can also be used for chemical synthesis on gold and silicon oxide in the nanoscale confinement between stamp and substrate. Amines can be printed onto reactive anhydride SAMs. [2] Peptides can be synthesized by printing N-protected amino acids onto an amine SAM. [3] It has been proposed that the confinement of the ink at the interface between the elastomeric stamp and the SAM, in combination with the preorganization of the reactants in the monolayer, facilitates the formation of covalent peptide bonds. [3] Recently, we demonstrated imine formation through the mCP of amines on aldehyde SAMs [4] and applied this chemistry to directing the immobilization of cytophilic proteins. [5] Herein, we present a Huisgen 1,3-dipolar cycloaddition, as a representative example of the Sharpless "click" chemistry, [6] induced without any catalyst by mCP of acetylenes onto azido-terminated SAMs on silicon oxide substrates.
Click chemistry includes a range of reactions that proceed in high yield under ambient conditions, preferably in water, with regioselectivity and a broad tolerance of functional groups. [6] The Cu-catalyzed 1,3-dipolar cycloaddition reaction of azides and acetylenes is known as the "cream of the crop" of all click reactions. [7] This cycloaddition is irreversible and proceeds in quantitative yield without any side products in many solvents, including water. Acetylenes and azides are stable starting materials that do not react among themselves. Azides are known for their ease of introduction, and both azides and acetylenes are tolerant of many other functionalities. The triazole group is a thermally and hydrolytically stable, conjugated linkage. Increasingly, click chemistry is used for the preparation of biological conjugates and the immobilization of biomacromolecules. [8] Triazole formation