Modular Synthetic Platform for the Construction of Functional Single-Chain Polymeric Nanoparticles: From Aqueous Catalysis to Photosensitization.

Single-chain polymeric nanoparticles (SCPNs) are intriguing systems for multiple applications. In order to arrive at a controlled, but random, positioning of the different side groups to the polymer backbone, alternative synthetic routes have to be developed. Here, a general postpolymerization modification strategy of poly(pentafluorophenyl acrylate) (pPFPA) is presented as a versatile method to rapidly access functional SCPNs. We first show that the sequential addition of a benzene-1,3,5-tricarboxamide-based amine, acting as the supramolecular recognition motif, and water-soluble polyetheramine (Jeffamine) to pPFPA affords random copolymers that fold in water into SCPNs. The scope of the modular platform is illustrated by preparing two types of functional SCPNs. First, we prepared SCPNs designed for bio-orthogonal catalysis by attaching pendant mono(benzimidazoylmethyl)-bis(pyridylmethyl) (Bimpy), phenanthroline (Phen), or 2,2'-bipyridine (BiPy), ligands capable of binding either Cu(I) or Pd(II). The Bimpy- and Phen-containing SCPNs ligated to Cu(I) significantly accelerate azide-alkyne cycloaddition reactions while Bipy-containing SCPNs ligated to Pd(II) efficiently catalyze depropargylation reactions. In all cases, reactions proceeded efficiently in phosphate buffer at a physiological pH and at low substrate concentrations. Next, the potential of SCPNs for photodynamic therapy was evaluated. Introducing porphyrins in SCPNs leads to novel photosensitizers that can produce singlet oxygen ((1)O2) upon photoirradiation. Additionally, by attaching both porphyrins and prodrug models, attached via (1)O2-cleavable amino-acrylate linker, to the SCPNs, we show that irradiation of the SCPNs results in a cascade reaction of (1)O2 generation followed by cleavage of the amino-acrylate linkers, releasing the drug model. The modular synthesis strategy reported here provides rapid and controlled access to SCPNs with tunable amounts of active units that fulfill different functions.

λ-Orthogonal pericyclic macromolecular photoligation.

A photochemical strategy enabling λ-orthogonal reactions is introduced to construct macromolecular architectures and to encode variable functional groups with site-selective precision into a single molecule by the choice of wavelength. λ-Orthogonal pericyclic reactions proceed independently of one another by the selection of functional groups that absorb light of specific wavelengths. The power of the new concept is shown by a one-pot reaction of equimolar quantities of maleimide with two polymers carrying different maleimide-reactive endgroups, that is, a photoactive diene (photoenol) and a nitrile imine (tetrazole). Under selective irradiation at λ=310-350 nm, any maleimide (or activated ene) end-capped compound reacts exclusively with the photoenol functional polymer. After complete conversion of the photoenol, subsequent irradiation at λ=270-310 nm activates the reaction of the tetrazole group with functional enes. The versatility of the approach is shown by λ-orthogonal click reactions of complex maleimides, functional enes, and polymers to the central polymer scaffold.

Three-dimensional microscaffolds exhibiting spatially resolved surface chemistry.

Spatial control over the surface chemistry of 3D organic-inorganic hybrid microscaffolds is achieved by a two-photon-triggered cycloaddition. Following a coating step with photoactivatable dienes via silanization, surface irradiation with a femtosecond-pulsed laser in the presence of functional dienophiles enables a site-selective alteration of the surface chemistry. Bioconjugation with fluorescent protein tags is employed to reveal the 3D molecular patterns.

Preparation of reactive three-dimensional microstructures via direct laser writing and thiol-ene chemistry.

Three-dimensional microstructures are fabricated employing the direct laser writing process and radical thiol-ene polymerization. The resin system consists of a two-photon photoinitiator and multifunctional thiols and olefins. Woodpile photonic crystals with 22 layers and a rod distance of 2 µm are fabricated. The structures are characterized via scanning electron microscopy and focused ion beam milling. The thiol-ene polymerization during fabrication is verified via infrared spectroscopy. The structures are grafted in a subsequent thiol-Michael addition reaction with different functional maleimides. The success of the grafting reaction is evaluated via laser scanning microscopy and X-ray photoelectron spectroscopy. The grafting density is calculated to be close to 200 molecules µm(-2) .

(Bio)molecular surface patterning by phototriggered oxime ligation.

Making light work of ligation: A novel method utilizes light for oxime ligation chemistry. A quantitative, low-energy photodeprotection generates aldehyde, which subsequently reacts with aminooxy moieties. The spatial control allows patterning on surfaces with a fluoro marker and GRGSGR peptide, and can be imaged by time-of-flight secondary-ion mass spectrometry.