D. N. Reinhoudt

Calixarenes, chemical chameleons

Methods for the synthesis of selectivety functionalized calix[4]arenes have been developed. These functionalized calix[4]arenes have been coupled to cavitands and cyclodextrins. A number of practical applications of calix[4]arenes are described.

Complexation of tert-butylammonium perchlorate by crown ethers in polar solvents studied by proton NMR spectroscopy

Determination des constantes dassociation des complexes de perchlorate de t-butylammonium et du 18-crown-6 et du pentaoxa [15] metacyclophane par spectroscopie RMN 1 H a diverses temperatures (240-306,5 K) et dans differents solvants polaires (methanol (D 4 ), acetone (D 6 ) et acetonitrile (D 3 ))

Self-Assembled Monolayers on Gold for the Fabrication of Radioactive Stents

An innovative and easily applicable method for the fabrication of radioactive stents, to be used for the treatment of restenosis, is presented. By incorporating the b-emitting radioisotopes 186Re, 188Re, 90Y, or 32P into sulfur-containing adsorbates, it becomes possible to cover a gold surface with a radioactive self-assembled monolayer (SAM). Two methods have been investigated. In the first, SAMs consisting of potentially radioactive rhenium-, yttrium-, and phosphorus-containing adsorbates have been assembled on 2D gold substrates, after which they have been studied by wettability measurements, electrochemistry, and X-ray photoelectron spectroscopy (XPS). The stability of these SAMs under simulated physiological conditions (phosphate buffered saline, PBS solution) for periods up to two months has been demonstrated. Alternatively, potentially radioactive monolayers have been prepared by exposure of SAMs of mono-, bi-, and tridentate ligands to a solution containing a radiometal (rhenium) in order to bind the metal to the monolayer. The polydentate ligands exhibit excellent binding capacity, leading to SAMs containing over 10±10 mol/cm2 of the radiometal, which is more than sufficient to make this system viable for the delivery of therapeutical dosages of radiation.

A salophene-uranium-water complex

In dioxo{2,2-[1,2-phenylenebis(nitrilomethylidyne)]bis(6-methoxyphenolato)(2 -)-N,N,O,O]uranium-water (2/3), 2[UO 2 (C 22 H 18 N 2 O 4 )].3H 2 O, the two independent uranium cations have pentagonal bipyramidal coordination

Radiative and nonradiative decay rates of chromophores bound to differently sized gold nanoparticles

Resonant energy transfer (RET) systems consisting of organic dye molecules bound to gold nanoparticles have recently gained considerable interest in materials science as well as in biophotonics. Gold-nanoparticles are chemically inert, so no photobleaching occurs, they have a high extinction coefficient leading to a larger transfer radius and finally gold-nanoparticles do not luminesce, thus crosstalk between donor and acceptor does not exist. The results for various nanoparticle radii show time constants for the energy transfer which turn out to decrease with increasing radii. Supplementary to this nonradiative decay process one has to consider the effect the nanoparticle exerts on the radiative rate of the dye molecule. Changes in the radiative lifetime can be calculated by measuring the signal intensity at t=0. The reduced intensity at t=0 indicates a strong decrease in the molecules radiative rate by more than an order of magnitude in the presence of a gold nanoparticle. This drastically decreased emission rate is a consequence of a phase shift between the molecular and the metal dipole leading to a destructive interference effect.

Stability and Applications of Electrochemically-Active Self-Assembled Monolayers

The electrochemical stability of monolayers is important for future applications. A potential window for self-assembled monolayers in aqueous inert electrolyte was obtained using Cyclic Voltammetry, Electrochemical Impedance Spectroscopy and Heterogeneous Electron Transfer. Also electrochemical techniques can be used for sensing applications. We investigated mixed monolayers of ferrocenethiol and an acid alkylthiol. Deprotonation of the acid by an alkaline electrolyte influences the other part of the mixed monolayer. The formal potential of ferrocene is shifted about 150 mV cathodically by the negative charge in the carboxylate part of the layer.