Birgit Stubbe

Thermoresponsive polymer coated gold nanoparticles: from MADIX/RAFT copolymerization of N-vinylpyrrolidone and N-vinylcaprolactam to salt and temperature induced nanoparticle aggregation

In the present contribution, we report the MADIX/RAFT polymerization for the synthesis of thermoresponsive homo and statistical copolymers of N-vinylcaprolactam (NVCL) and N-vinylpyrrolidone (NVP). The conditions for the polymerization of NVP were optimized using an automated parallel synthesizer and these optimal conditions were applied for preparing copolymers with systematical variation in composition. The cloud point temperatures (TCPs) of aqueous solutions of PNVCL and P(NVCL-stat-NVP)’s (CP1–CP5) were found to be tuneable between 40 °C and >95 °C at 5 mg mL−1. Next, stable colloidal solutions of AuNPs coated with PNVCL and CP1–CP5 were obtained via an exchange reaction of pre-synthesized citrate stabilized AuNPs with PNVCL and CP1–CP5 by a direct ‘grafting to’ approach. The maximum absorbance wavelength (λmax) of the surface plasmon resonance (SPR) band and size of all the thermoresponsive polymer coated AuNPs were found to be almost unchanged up to 65 °C (above the TCP of PNVCL and CP5) in MilliQ water which is presumably due to electrostatic stabilization of the AuNPs by residual citrate groups on the surface. However, in 0.1 M NaCl aqueous solution the λmax of the thermoresponsive AuNPs were red shifted when heated up to 65 °C which is attributed to the screening of the citrate negative charges on the surface of AuNPs that suppress electrostatic stabilization enabling T-induced aggregation leading to a shift in the SPR band. These thermoresponsive AuNPs may find applications as colorimetric temperature and/or salt sensors.

Combinatory approach of methacrylated alginate and acid monomers for concrete applications.

Polysaccharides, and especially alginate, can be useful for self-healing of cracks in concrete. Instead of weak electrostatic bonds present within calcium alginate, covalent bonds, by methacrylation of the polysaccharides, will result in mechanically stronger superabsorbent polymers (SAPs). These methacrylated alginate chains as backbone are combined with two acrylic monomers in a varying molar fraction. These SAPs show a moisture uptake capacity up to 110% their own weight at a relative humidity of 95%, with a negligible hysteresis. The swelling capacity increased (up to 246 times its own weight) with a decreasing acrylic acid/2 acrylamido-2-methylpropane sulfonic acid ratio. The SAPs also showed a thermal stability up to 200°C. Interestingly, the SAP composed of alginate and acrylic acid exerted a very limited decrease in compressive strength (up to 7% with addition of 1wt% SAP) rendering this material interesting for the envisaged self-healing application.

Protein functionalization revised: N‐tert‐butoxycarbonylation as an elegant tool to circumvent protein crosslinking

The protection of primary amines available in proteins holds great potential to introduce a plethora of diverse functionalities along the protein backbone (e.g., via its carboxylic acid or alcohol moieties) while circumventing the crosslinking issue using conventional approaches. This paper reports on a straightforward and efficient proof-of-concept including the chemoselective N-tert-butyloxycarbonylation of the primary amines in the protein gelatin (gel-NH-BOC), followed by introducing crosslinkable methacrylamide moieties. The reaction is performed successfully under relatively mild conditions (50 °C). Following selective protein functionalization, the deprotection is realized by adding a catalytic amount of an aqueous hydrogen chloride solution. The present communication illustrates the occurrence of a straightforward and selective deprotection procedure, which is typically required to circumvent the occurrence of acidic hydrolysis of the protein backbone. The results hold promise for a large range of biomedical applications in which the presence of primary amines is essential for preserving the biological activity.

Development of chemically cross-linked biopolymer based burn wound dressings with antimicrobial properties

Abstracts from the XLII Congress of the European Society for Artificial Organs, 2-5 September 2015, Leuven, Belgium.