Michael Kaupp

(Ultra)fast catalyst-free macromolecular conjugation in aqueous environment at ambient temperature.

Tailor-made water-soluble macromolecules, including a glycopolymer, obtained by living/controlled RAFT-mediated polymerization are demonstrated to react in water with diene-functionalized poly(ethylene glycol)s without pre- or post-functionalization steps or the need for a catalyst at ambient temperature. As previously observed in organic solvents, hetero-Diels-Alder (HDA) conjugations reached quantitative conversion within minutes when cyclopentadienyl moieties were involved. However, while catalysts and elevated temperatures were previously necessary for open-chain diene conjugation, additive-free HDA cycloadditions occur in water within a few hours at ambient temperature. Experimental evidence for efficient conjugations is provided via unambiguous ESI-MS, UV/vis, NMR, and SEC data.

Wavelength selective polymer network formation of end-functional star polymers.

A wavelength selective technique for light-induced network formation based on two photo-active moieties, namely ortho-methylbenzaldehyde and tetrazole is introduced. The network forming species are photo-reactive star polymers generated via reversible activation fragmentation chain transfer (RAFT) polymerization, allowing the network to be based on almost any vinylic monomer. Direct laser writing (DLW) allows to form any complex three-dimensional structure based on the photo-reactive star polymers.

Modular design of glyco-microspheres via mild pericyclic reactions and their quantitative analysis

The facile and efficient functionalization of porous poly(glycidyl methacrylate) (pGMA) microspheres via hetero Diels–Alder (HDA) chemistry with poly(3-O-acryloyl-1,2:5,6-di-O-isopropylidene-α-D-glucofuranoside) (pAIpGlc) prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization employing electron deficient thiocarbonylthio compounds (benzyl pyridin-2-yldithioformate (BPDF)) is described in detail. The efficiency of the employed ‘grafting to’ approach is qualitatively and quantitatively analyzed. Initially the microspheres are functionalized with a highly reactive diene – cyclopentadiene (Cp) – in one step with sodium cyclopentadienide, and subsequently reacted with a protected glycopolymer (number-average molecular weight, Mn = 4200 g mol−1; polydispersity index, PDI = 1.2) that carries a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved under mild conditions (T = 50 °C) with trifluoroacetic acid (TFA) as a readily removable catalyst. Deprotection of the grafted pAIpGlc to poly(3-O-acryloyl-α,β-D-glucopyranoside) (pAGlc) can be performed after functionalization in one pot with formic acid at ambient temperature. The obtained loading capacity is 2.63 × 1019 chains per g and the grafting density is close to 0.16 chains per nm2. Quantitative analysis of the grafting densities is achieved via elemental analysis; the pore size distribution before functionalization was analyzed by inverse size exclusion chromatography (iSEC). Further employed characterization techniques include scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and high resolution attenuated total reflectance (ATR) FT-IR microscopy supporting the successful modification of the microspheres.

A Facile Route to Boronic Acid Functional Polymeric Microspheres via Epoxide Ring Opening

Boronic acid-functionalized microspheres are prepared for the first time via mild epoxide ring opening based on porous cross-linked polymeric microspheres (diameter ≈ 10 μm, porosity ≈ 1000 Å). Quantitative chemical analysis by XPS and EA evidences that there is a greater functionalization with boronic acid when employing a sequential synthetic method [1.7 atom% boron (XPS); 1.12 wt% nitrogen (EA)] versus a one-pot synthetic method [0.2 atom% boron (XPS); 0.60 wt% nitrogen (EA)] yielding grafting densities ranging from approximately 2.5 molecules of boronic acid per nm(2) to 1 molecule of boronic acid per nm(2), respectively. Furthermore, the boronic acid-functionalized microspheres are conjugated with a novel fluorescent glucose molecule demonstrating a homogeneous spatial distribution of boronic acid.

Ugi multicomponent reaction to prepare peptide–peptoid hybrid structures with diverse chemical functionalities

Monodisperse sequenced peptides and peptoids present unique nano-structures based on their self-assembled secondary and tertiary structures. However, the generation of peptide and peptoid hybrid oligomers in a sequence-defined manner via Ugi multicomponent reaction has not yet been studied. Herein, we report a synthetic strategy that enables both the modification of peptides as well as the generation of sequence-defined peptide–peptoid hybrid structures. Our synthetic methodology rests on the fusion of solid phase peptide synthesis with Ugi multicomponent reactions. We evidence that a diversity of chemical functionalities can be inserted into peptides or used in the design of peptide–peptoid hybrids exploiting a wide functional array including amines, carboxylic acids, hydrocarbons, carbohydrates as well as polymers, introducing a sequence-defined synthetic platform technology for precision peptoid hybrids.

Photo-Induced Click Chemistry for DNA Surface Structuring by Direct Laser Writing

Oligonucleotides containing photo-caged dienes were prepared and shown to react quantitatively in a light-induced Diels-Alder cycloaddition with functional maleimides in aqueous solution within minutes. Due to its high yield and fast rate, the reaction was exploited for DNA surface patterning with sub-micrometer resolution employing direct laser writing (DLW). Functional DNA arrays were written by direct laser writing (DLW) in variable patterns, which were further encoded with fluorophores and proteins through DNA directed immobilization. This mild and efficient light-driven platform technology holds promise for the fabrication of complex bioarrays with sub-micron resolution.

Access to Intrinsically Glucoside‐Based Microspheres with Boron Affinity

Intrinsically glucoside-based microspheres are prepared in olive oil via a water in oil inverse suspension polymerization. The microspheres are characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) microscopy, and X-ray photoelectron spectroscopy (XPS), evidencing the intrinsic glucose character of the spheres. A novel boronic acid fluorescent molecule was subsequently conjugated to the microspheres in an aqueous environment, exhibiting the spatial and uniform distribution of glucoside as well as the affinity of the microspheres to bind with boron, evidenced via fluorescence spectroscopy measurements.