M. Talha Gokmen

Thiol-ene and thiol-yne chemistry in microfluidics: a straightforward method towards macroporous and nonporous functional polymer beads

Thiol-ene and thiol-yne reactions are explored as efficient pathways towards rapid production of diverse monodisperse macroporous and nonporous functional beads. In a straightforward method, polymer beads containing amine, hydroxyl and carboxyl groups have been prepared by reacting a tetrafunctional thiol with a range of mono and/or multifunctional -enes/-ynes containing the desired functional groups. The thiol-ene and thiol-yne reactions have been performed in a simple home-made microfluidic device utilizing thiol and ene/yne monomers at a 1 : 1 ratio of thiol to π-bond. The porous functional beads were prepared making use of a porogen in combination with a photoinitiator. The optical and scanning electron microscopy images demonstrated monodispersity of the beads with a spherical shape ranging in size from 210 to 600 μm. The beads were characterized in terms of glass transition temperature, surface area measurement and composition. The accessible amine and hydroxyl loading in the beads ranges from 0.23 to 0.69 mmol g−1 and 0.24 to 0.64 mmol g−1 respectively, as determined by the Fmoc method. This work demonstrates the applicability of thiol-ene and thiol-yne reactions in microfluidics as a powerful tool for the rapid design of functional beads for diverse applications.

“Sandwich” Microcontact Printing as a Mild Route Towards Monodisperse Janus Particles with Tailored Bifunctionality

A “sandwich” microcontact printing method is reported. A monolayer of porous epoxy polymer microspheres is transformed into Janus particles with distinct functionality on each face by reaction with amine functional fluorescent dyes, carbohydrates, and magnetic nanoparticles.

Kinetic comparison of 13 homogeneous thiol–X reactions

An extensive kinetic comparison of 13 thiol–X reactions is presented using online FT-IR. Besides the effect of catalysts (tertiary phosphine or tertiary amine), a significant catalytic effect of dipolar solvents on many thiol–X reactions is observed. Thus, different overall reactivity orders of the studied substrates toward the thiol group are shown in polar aprotic and nonpolar solvents and compared with previous results in analogous heterogeneous reactions. The reactivities of some substrates toward n-octylamine are also investigated and their reactions with the amine and the thiol are compared. This study can serve as a useful guide for the choice and application of many thio-click reactions as efficient chemical conjugation tools.

Revealing the nature of thio-click reactions on the solid phase.

Thiol- and yne-functionalized beads were manufactured in a simple microfluidic setup. While CuAAC and thiol-yne reactions were performed on yne-functionalized beads, 9 different thiol-X reactions were compared, in terms of kinetics and conversion, on thiol-functionalized beads.

Bifunctional Janus beads made by “sandwich” microcontact printing using click chemistry

This article describes the preparation of spherical Janus particles by microcontact printing. A set of three different polymer beads (diameter ca. 170 μm), each bearing different functional groups at their surface, are used to covalently attach distinct functional molecules exclusively on opposing poles of the beads. The covalent modification of the beads involves three different types of click chemistry: epoxide ring opening (ERO), copper catalysed azide–alkyne cycloaddition (CuAAC) and thiol–yne addition (TYA). These reactions are compared with regard to their advantages and disadvantages in the context of “sandwich” microcontact chemistry. The success of surface modification of the beads is verified by fluorescence microscopy and 3D-time of flight secondary ion mass spectrometry measurements and is further supported by reference experiments on planar surfaces bearing the same surface functionality and analysed by X-ray photoelectron spectroscopy, secondary ion mass spectrometry, atomic force microscopy and fluorescence microscopy. Furthermore we demonstrate that sandwich microcontact printing can also be performed on smaller polymer beads with a diameter of ca. 5 μm. The broad scope of surface chemistry in combination with the simple experimental setup makes this method attractive to a wide range of material science applications, since it combines orthogonality of surface functionalization with high pattern fidelity.