UV‐Induced Tetrazole‐Thiol Reaction for Polymer Conjugation and Surface Functionalization

Abstract

A UV-induced 1,3-dipolar nucleophilic addition of tetrazoles to thiols is described. Under UV irradiation the reaction proceeds rapidly at room temperature, with high yields, without a catalyst, and in both polar protic and aprotic solvents, including water. This UV-induced tetrazole-thiol reaction was successfully applied for synthesis of small molecules, protein modification, and rapid and facile polymer-polymer conjugation.The reaction has been also demonstrated for the formation of micropatterns by site-selective surface functionalization. Superhydrophobic-hydrophilic micropatterns were successfully created by sequential modifications of a tetrazole-modified porous polymer surface with hydrophobic and hydrophilic thiols. A biotin functionalized surface could be fabricated in aqueous solutions under long-wavelength UV irradiation.Ever since the first reported photoreaction of an organic compound, santonin, in 1834 by Trommsdorf, [1] the spatially and temporally controllable photochemistry has found diverse and widespread applications, [2] including surface functionalization to create patterned or gradient immobilization of various substrates.[3] Photo-induced click reactions have been actively investigated during the last decade in attempts to combine the benefits of click reactions with the excellent spatial and temporal controllability of photochemical processes.[4] UV-induced thiolene and thiol-yne reactions are the most known radical photoclick reactions.[5] Non-radical photoreactions have also attracted a lot of attention in recent years.[6] For instance, Lin et al, [7] introduced a photo-click 1,3-dipolar tetrazole-ene reaction based on Huisgen's studies. [8] The tetrazole-ene reaction presents several advantages: simplicity of implementation, fast reaction kinetics, high yields, it is catalyst free, yields inoffensive byproducts (N2) and, therefore, bio-compatible. This and other photo reactions have been implemented in many different applications such as dendrimers synthesis, [9] bioconjugation, [6b, 6d, 6e, 10] in situ bio-labeling, [6c, 11] hydrogels formation, [12] surface functionalization [13] etc. Nevertheless, the implementation of photo reactions in bio-applications is still limited, partly because unnatural functional groups have to be first introduced to a biomolecule. In addition, only a few photo reactions could be applied for polymer-polymer coupling and site-selective conjugation of biomolecules on surfaces. [13b, 14] Thus, despite a progress in the field of photo-induced reactions, there is a clear need for novel efficient photo reactions that are selective to different types of functionalities, compatible with polymerpolymer conjugation and bioapplications. 50 years ago Huisgen et al. reported that thiophenol could be added to the intermediate nitrilimine generated from decomposition of 2,5-diphenyltetrazole in boiling thiophenol. [8a, 8b] Photolytic decomposition of tetrazoles with release of nitrogen and nitrilimines was also described.[8c] In this work, we repo...

UV‐Induced Disulfide Formation and Reduction for Dynamic Photopatterning

“…In this context, photochemical reactions attracted attention, because they offer both spatial and temporal control of surface modification . To date, a variety of light‐triggered reactions, for example, thiol–ene/yne, photoinitiated azide–yne, tetrazole–ene, tetrazole–thiol, and phototriggered Diels–Alder reactions, have been exploited for surface functionalization. However, the majority of the existing methods are restricted to irreversible surface functionalization because of the formation of relatively non‐reactive covalent bonds.…”

UV‐Induced Disulfide Formation and Reduction for Dynamic Photopatterning

“…[3] In this context, photochemical reactions attracted attention, because they offer both spatial and temporal control of surface modification. [4] To date, a variety of light-triggered reactions, for example, thiol-ene [5] /yne, [6] photoinitiated azide-yne, [7] tetrazole-ene, [8] tetrazole-thiol, [9] and phototriggered Diels-Alder reactions, [10] have been exploited for surface functionalization. However, the majority of the existing methods are restricted to irreversible surface functionalization because of the formation of relatively non-reactive covalent bonds.…”

Surface Functionalization with Carboxylic Acids by Photochemical Microcontact Printing and Tetrazole Chemistry

“…19 The nucleophilic addition of thiols to nitrile imines has been used in polymer-polymer conjugation and site-selective surface functionalization. 20 BARNER-KOWOLLIK and coworkers used the cycloaddition of maleimides to nitrile imines to ligate macromolecules onto biosurfaces 21 and to create photoswitchable surfaces by using azobenzene bearing dipolarophiles. 22 Although tetrazole photoclick chemistry was described as bioorthogonal multiple times [23][24][25] it was found by YAO that nitrile imines readily react with various biological nucleophiles and therefore disproved this statement.…”