(172c) “Clicking” Biomolecules Onto Alkyne-Functionalized Surfaces
In the past, chemical vapor deposition (CVD) polymerization has been used to synthesize a wide variety of functionalized poly-(p-xylylenes), which were further used for the immobilization of biomolecules. Herein we present an alkyne-containing vapor-deposited polymer for the immobilization of biological ligands using the stereoselective ?click? reaction between alkyne groups and azide-functionalized biomolecules.
Click chemistry represents a family of powerful and efficient chemical reactions, which are modular, widely applicable, relatively insensitive to solvents and pH value, while resulting in stereoselective conversions with high to very high yields. Huisgen 1,3-dipolar cycloaddition, which is the most widely used click reaction, has been used for drug discovery applications and for tailoring surface functionalities. Further applicability of this versatile reaction has been limited by the availability of alkyne or azide functionalized surface coatings.
We demonstrate the synthesis of alkyne-functionalized polymer coatings via CVD polymerization and demonstrate their applicability towards the spatially-directed immobilization of azide-functionalized biomolecules. The reactive polymer was characterized using FTIR spectroscopy with revealed a strong band at 3286 cm-1 for the alkyne C-H stretch and signal at 2100 cm-1 which can be attributed to the C-C triple bond, confirming the presence of the alkyne group. The elemental composition was quantified using X-ray photoelectron spectroscopy (XPS) which reaffirmed the FTIR data. The polymer was stable in a variety of organic solvents and exhibited good adhesion to a wide range of substrates.
These reactive coatings showed remarkable reactivity towards an azide-containing biotin-based ligand through 1,3-dipolar cycloaddition click reaction. Specifically, the cycloaddition reaction between the alkyne-containing polymer and biotin azide in the presence of copper(II) sulfate and sodium ascorbate was studied. To ensure spatial control over the reaction a microcontact printing approach was employed where the Cu catalyst and the reductant were used separately. This demonstrated that the alkyne groups are reactive and they can be further used as anchoring sites for bio-immobilization. We also found that the alkyne functionality is reactive when it is copolymerized with the 4-benzoyl[2.2]paracyclophane which would provide us with the ability to immobilization multiple biomolecules in controllable ratios.
This regioselective immobilization strategy could be applicable in the design of biofunctional surfaces for diagnostics (e.g. microarrays), biosensors, and biomedical device coatings.
References:  H. Nandivada, H-Y Chen, J. Lahann, Reactive polymer coatings that "click", Angew. Chem. Int. Ed., 2006 (in press)