Mario Smet

Catalytic production of levulinic acid from cellulose and other biomass-derived carbohydrates with sulfonated hyperbranched poly(arylene oxindole)s

Innovative catalyst design holds the key to fundamental advances in the transformation of cellulose to chemicals and transportation fuels, both of which are vital to meet the challenge of increasing energy costs and the finite nature of fossil fuel reserves. Here we report on the functionalization, characterization and successful application of sulfonated hyperbranched poly(arylene oxindole)s for the direct catalytic conversion of cellulose to levulinic acid. The use of water-soluble hyperbranched polymers in combination with ultrafiltration is conceptually novel and opens new horizons in the aqueous-phase processing of cellulose substrates with various degrees of crystallinity. Compared to most conventional types of acid catalysts, these highly acidic polymers demonstrate superior catalytic performance in terms of both activity and selectivity. Additionally, this molecular approach can be successfully transferred to the acid-catalyzed degradation of other abundant biomass resources, including starch, inulin and xylan.

Enzyme-Catalyzed Synthesis of Hyperbranched Aliphatic Polyesters

Hyperbranched aliphatic copolyesters have been prepared by copolymerization of e-caprolactone with 2,2-bis(hydroxymethyl)butyric acid, catalyzed by immobilized Lipase B from Candida antarctica (Novozyme 435) under mild conditions. Via this novel combination of ring-opening AB polymerization and AB 2 polycondensation, the degree of branching (DB) and, consequently, the density of functional end groups can be controlled by the comonomer ratio in the feed (0 < DB < 0.33).

Synthesis and spectroscopic characterisation of BODIPY® based fluorescent off–on indicators with low affinity for calcium

Two fluorescent off-on Ca2+ indicators based on APTRA (o-aminophenol-N,N,O-triacetic acid) as low-affinity ligand for Ca2+ and BODIPY(4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) as a fluorophore were synthesized. The new BODIPY-APTRA compounds absorb in the visible spectrum, with absorption maxima from 505 nm to 570 nm, and have fluorescence spectra that span the visible spectrum, with emission maxima ranging from 525 nm to 625 nm dependent on the substituents at the alpha-positions to the nitrogen atoms. The indicators show a large increase of the fluorescence quantum yield upon increasing Ca2+ concentration. The ground-state dissociation constants Kd estimated at 20 degrees C in 100 mM KCl aqueous buffered solution, pH 7.20, for the two complexes with Ca2+ were found to be around 100 microM.

Light-Controlled Single-Walled Carbon Nanotube Dispersions in Aqueous Solution

We have succeeded in dispersing single-walled carbon nanotubes (SWNTs) into an aqueous solution of poly(ethylene glycol)-terminated malachite green derivative (PEG-MG) through simple sonication. It was found that UV exposure caused reaggregation of these predispersed SWNTs in the same aqueous medium, as adsorbed PEG-MG photochromic chains could be effectively photocleavaged from the nanotube surface. The observed light-controlled dispersion and reaggragation of SWNTs in the aqueous solution should facilitate the development of SWNT dispersions with a controllable dispersity for potential applications.

PLA architectures: the role of branching

Biobased and biodegradable polymers have become more and more interesting in view of waste management and crude oil depletion. Several biopolymers have been researched, among which poly(lactide) (PLA) seems to be the most promising. Although a lot of research has been conducted on this polymer, PLA still displays some serious drawbacks such as limited melt strength, limited toughness, a lack of functional groups etc. One possibility to overcome such problems is by introducing branching. This can be done in several ways, resulting in PLA polymers with different topologies, ranging from star-branched to long chain branched. After a general introduction, several of these topologies will be described in detail.

Synthesis and photophysical characterization of chalcogen substituted BODIPY dyes

Synthetic details and stationary and time-resolved photophysical properties of five BODIPY derivatives containing chalcogen atoms are presented. The photophysical data are compared to those of a chlorine atom containing BODIPY, acting as a reference. A strong impact in the HOMO–LUMO transition energy is achieved via nucleophilic substitution with chalcogen based units. Going from oxygen to tellurium a bathochromic shift in both absorption and emission spectra from the green to the near infrared region was observed. By employing fluorescence single photon timing experiments in two solvents of different polarity, the excited state dynamics and their solvent dependence indicate the presence of a mechanism involving a photoinduced charge transfer that dramatically affects the optical radiative processes of these derivatives.

Thiol-promoted catalytic synthesis of diphenolic acid with sulfonated hyperbranched poly(arylene oxindole)s

Acid-catalyzed condensation of levulinic acid and phenol into high yields of diphenolic acid (>50%) is possible with a combination of sulfonated hyperbranched polymers and thiol promotors, either added as a physical mixture or bound to the polymer by ion-pairing.

Stability of mixed PEO-thiol SAMs for biosensing applications.

The secret of a successful affinity biosensor partially hides in the chemical interface layer between the transducer system and the biological receptor molecules. Over the past decade, several methodologies for the construction of such interface layers have been developed on the basis of the deposition of self-assembled monolayers (SAMs) of alkanethiols on gold. Moreover, mixed SAMs of polyethylene oxide (PEO) containing thiols have been applied for the immobilization of biological receptors. Despite the intense research in the field of thiol SAMs, relatively little is known about their biosensing properties in correlation with their long-term stability. Especially the impact of the storage conditions on their biosensing characteristics has not been reported before to our knowledge. To address these issues, we prepared mixed PEO SAMs and tested their stability and biosensing performance in several storage conditions, i.e., air, N2, ethanol, phosphate buffer, and H2O. The quality of the SAMs was monitored as a function of time using various characterization techniques such as cyclic voltammetry, contact angle, grazing angle Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the impact of the different storage conditions on the biosensor properties was investigated using surface plasmon resonance. Via the latter technique, the receptor immobilization, the analyte recognition, and the nonspecific binding were extensively studied using the prostate specific antigen as a model system. Our experiments showed that very small structural differences in the SAM can have a great impact in their final biosensing properties. In addition it was shown that the mixed SAMs stored in air or N2 are very stable and retain their biosensor properties for at least 30 days, while ethanol appeared to be the worst storage medium due to partial oxidation of the thiol headgroup. In conclusion, care must be taken to avoid SAM degradation during storage to retain typical SAM characteristics, which is very important for their general use in many proposed applications.

UV-responsive polymeric superamphiphile based on a complex of malachite green derivative and a double hydrophilic block copolymer.

We have prepared a UV-responsive polymeric superamphiphile, formed by a malachite green derivative and the double hydrophilic block copolymer methoxy-poly(ethylene glycol)(114)-block-poly(l-lysine hydrochloride)(200) (PEG-b-PLKC) on the basis of electrostatic interactions. The malachite green derivative undergoes photo-ionization upon UV irradiation, which makes it more hydrophilic, resulting in changes in the self-assembly behavior of the polymeric superamphiphile. For this reason, the polymeric superamphiphile originally self-assembles to form sheetlike aggregates, which disassemble after UV irradiation because of the increased solubility of the malachite green derivative. By use of Nile red as a probe, the polarity of the polymeric superamphiphile solution is confirmed to be increased after UV irradiation by fluorescence spectra, which also explains the disassembly of the polymeric superamphiphile.

Construction of rod-like diketopyrrolopyrrole oligomers with well-defined length

Abstract Oligomers of well-defined length were prepared by a stepwise sequence of Suzuki couplings using brominated 1,4-dioxo-3,6-diphenylpyrrolo[3,4- c ]pyrrole (DPP) derivatives and 1,4-dibromo-2,5-di- n -hexylbenzene as the monomers. The resulting oligomers contained three, five and seven DPP units, respectively, and could be characterized by 1 H NMR spectroscopy. These compounds could be of potential use as new electroluminescent materials.