N.A.J.M. Sommerdijk

Sol-gel entrapped materials for optical sensing of solvents and metal ions

Abstract The preparation and characterization of sol-gel composites for fluorescent detection of solvents (using dansyl-labelled β -cyclodextrin) and Al 3+ ions (using Morin), and for colourimetric detection of Cu 2+ (using Eriochrome Cyanine R) is described. The active roles played by both the entrapped reagent and the sol-gel matrix in the sensing processes are discussed.

The detection of phenols in water using a surface plasmon resonance system with specific receptors

A number of receptor molecules designed to bind phenols selectively have been synthesised and evaluated for use in a surface plasmon resonance (SPR) optical sensing system. To optimise sensitivity, films of the receptors entrapped in sol-gel and polymer matrices have been prepared. The most promising receptor systems are shown to give high sensitivity to phenols, together with SPR responses whose characteristics depend on the particular phenol present. These systems offer the promise of identification and quantification of phenol pollutants in water.

Cationic Gemini Surfactants Based on Tartaric Acid: Synthesis, Aggregation, Monolayer Behaviour, and Interaction with DNA

The synthesis of three novel cationic gemini surfactants (10, 12, and 14) based on tartaric acid appended with biocompatible palmitoyl tails and head groups is described, and their aggregation in water, monolayer behaviour, DNA binding, and gene transfection activities are reported. The monolayer studies showed that the molecular area of the surfactants is determined by the head group, as it increased going from the ethylenediamine head group of 10 via the lysine head group of 12 to the combined lysine/ethylenediamine head group of 14. Electron microscopy showed that the surfactants with the smaller head groups (10 and 12) form plate-like structures, probably stacked bilayers, in line with the shapestructure concept, whereas no structures are observed for the largest surfactant 14. A CD spectroscopic titration of o-phage

Silicon-based surface plasmon resonance chemical sensors

Abstract A silicon-based surface plasmon resonance (SPR) technique has been successfully applied to NO2 sensing at ppm level using devices with uncoated and phthalocyanine-coated gold films. Surface-enhanced Raman scattering (SERS) has been used as an additional data-acquisition channel capable of providing spectroscopic selectivity and amplified sensitivity. Reversible responses of both SERS and SPR-induced photosignals produced by Au-on-Si grating structures coated with thin 18-crown-6 H2pc phthalocyanine films are simultaneously recorded for exposures of the films to 10 ppm of NO2 in air. Possible sensing applications are discussed.

The polymerisation of oligo(ethylene glycol methyl ether) methacrylate from a multifunctional poly(ethylene imine) derived amide: a stabiliser for the synthesis and dispersion of magnetite nanoparticles

A facile synthetic route to poly(ethylene imine)-graft-poly(oligo(ethylene glycol methyl ether)) (PEI-graft-POEGMA) functionalised superparamagnetic magnetite nanoparticles is described. The polymerisation of OEGMA from a model molecular amide demonstrated the feasibility of POEGMA synthesis under mild ATRP conditions (20 °C in ethanol) albeit with low initiator efficiencies. DFT studies suggest that the amide functionality is intrinsically of lower activity than ester functional monomers and initiators for atom transfer polymerisation (ATRP) as a consequence of higher bond dissociation energies and bond dissociation free energies (BDFE). However these studies further highlighted that use of an appropriate solvent could reduce the free energy of dissociation thereby reducing the relative difference in BDFE between the ester and amide groups. A commercial branched PEI sample was functionalised by reaction with 2-bromo-2-methylpropanoyl bromide giving an amide macroinitiator suitable for the atom transfer radical polymerisation (ATRP) of oligo(ethylene glycol methyl ether) methacrylate. The resulting PEI-graft-POEGMA copolymers were characterised by SEC, FT-IR and 1H and 13C NMR spectroscopy. PEI-graft-POEGMA coated magnetite nanoparticles were synthesised by a basic aqueous co-precipitation method and were characterised by transmission electron microscopy, thermogravimetric analysis and vibrating sample magnetometry and dynamic light scattering. These copolymer coated magnetite nanoparticles were demonstrated to be effectively stabilised in an aqueous medium. Overall the particle sizes and magnetic and physical properties of the coated samples were similar to those of uncoated samples.

Matrix effects on selective chemical sensing by sol-gel entrapped complexing agents

Changes in the selectivity of molecular recognition systems on sol-gel entrapment are reported. Thermodynamic effects are exemplified by studies of the metal-ion complexing agent Eriochrome Cyanine R (ECR). In aqueous solution this binds strongly and selectively to Al3+, whereas in a TMOS-based sol-gel matrix it is selective for Cu3+. Thermodynamic effects, due to restricted translational freedom of water molecules or different solvent structure and isolation of ligands, can explain these observations. Effects of entrapment on molecular recognition by a large conformationally flexible molecule have been studied using a tris-terminated PAMAM dendrimer. The dendrimer conformation and its complexation with Cu2+ changes on entrapment, and binding of aromatic carboxylic acids such as ibuprofen can be detected by changes in visible absorption and surface plasmon resonance using spun films of the sol-gel composite. These effects show that in addition to providing a porous entrapment matrix of good optical quality, sol-gels may be used to alter the binding characteristics of the entrapped receptors.

Electron tomography shows molecular anchoring within a layer-by-layer film.

The layer-by-layer self-assembly of thin films consisting of alternating layers of DNA and bis-urea nanoribbons prevents diffusion of the components within the film and allows the anchoring of biotinylated molecules through molecular recognition in a predetermined layer of the film. Electron tomography demonstrates with nanometer precision the location of gold-labeled streptavidin bound to the incorporated biotinylated molecules.

Synthesis and crystal structure of (+)-(2R,3R)-N, N′-bis-trityl-2,3-bis-aziridine

A new C2 symmetric bis-aziridine derivative was synthesized starting from L-(+)-tartaric acid. The molecular structure of (+)-(2R, 3R)-N, N′-bis-trityl-2,3-bis-aziridine 4, was determined by 1H, 13C NMR and elemental analysis and was confirmed by single-crystal X-ray diffraction. Crystal data for 4: C42H36N2, orthorhombic, space group: P212121, a = 12.7633(14), b = 14.5661(6), c = 17.4184(14) Å, and Z = 4.

From Molecular to Supramolecular Chirality

The formation of supramolecular assemblages from chiral amphiphilic molecules has been studied in monolayers by Brewster angle and epifluorescence microscopy, and in solution by electron microscopy. The expression of the molecular chirality at the supramolecular level depends strongly on the packing properties of the amphiphiles. The morphology of the supramolecular structures can be tuned by changing the pH or by complexation of metal ions.