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

Near-infrared luminescence of Yb3+, Nd3+, and Er3+ azatriphenylene complexes

Near-infrared luminescent ytterbium(III), neodymium(III), and erbium(III) complexes containing novel organic chromophores derived from azatriphenylene have been prepared and spectroscopically studied. The complexes can be excited from 350 to 450 nm, leading after intramolecular energy transfer to intense lanthanide luminescence in acetonitrile. Quenching of the luminescence of the complexes by molecular oxygen reveals information on the rate of energy transfer from the “antenna” to the lanthanide ion

Luminescence properties of m-terphenyl-based Eu3+ and Nd3+ complexes: visible and near-infrared emission

Two novel m-terphenyl-based organic ligands (2 and 3) have been synthesized. Photophysical studies show that the ligands form stable complexes with Eu3+, since typical Eu3+ luminescence is observed upon excitation of the ligand. The acyclic complex 2·Eu3+ shows relatively long lifetimes in methanol (e.g. = 0.72 ms in CH3OH). The acylic ligand 2 allows the additional coordination of two solvent molecules and their high-energy vibrational modes form the main quenching pathway for the Eu3+ luminescence. In comparison with 1·Eu3+, the more rigid dioxolane-containing complex 3·Eu3+ provides an additional donor atom, which reduces the solvent coordination of 3·Eu3+ (3·Eu3+ = 1.42 ms compared to 1·Eu3+ = 0.75 ms in CH3OH). The high-energy vibrational modes of the organic ligand 3 are the most important quenchers. Typical near-infrared Nd3+ emission at 1060 and 1350 nm resulting from 3·Nd3+ has been observed. Quenching by the solvent is still operative for 3·Nd3+, because of the larger ionic radius of the Nd3+ ion

Cation sensing by patterned self-assembled monolayers on gold

X-Ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to study the interactions between self-assembled monolayers (SAMs) of crown ether adsorbates and metal ions. Both analytical techniques confirmed the selectivities of the 12-crown-4 and 15-crown-5 SAMs that had previously been determined by electrochemical impedance spectroscopy. AFM has also been used to characterize microcontact-printed crown ether monolayers. The electrochemical patterning of monolayers on gold allowed the design of a dual sensor for the electrochemical detection of cations. However, due to cross-contamination of both monolayers during the patterning process a significant selectivity reduction of the layers was observed. Nevertheless, the remaining Na+ selectivity of the 12-crown-4 SAM and the K+ selectivity of the 15-crown-5 SAM allowed the unambiguous discrimination between both metal ions. \u

Novel preorganized hemispherands to encapsulate rare earth ions: shielding and ligand deuteration for prolonged lifetimes of excited Eu3+ ions

Quenching of the luminescent excited state of Eu3+ ions by C-H high-vibrational modes was studied by deuteration of the encapsulating ligand and the solvent. Novel polydentate hemispherands providing nine donor atoms, which form overall neutral complexes with rare earth ions, were synthesized in nine steps, allowing the easy incorporation of deuterium atoms (11a-d·Eu3+). The introduction of tert-butyl groups at the aromatic rings of the ligand further increased the solubility of the complexes in organic solvents (29·Eu3+ and 34·Eu3+). Photophysical studies, viz., luminescence spectra and lifetime measurements, revealed that significant quenching of the Eu3+ excited state is induced by nearby C-H vibrational modes. Substitution of these quenching C-H modes for C-D bonds in the azacrown bridge leads to an enhancement of the luminescent lifetime by a factor of 1.5. C-H high-vibrational modes of the pendant arms which are at a larger distance to the Eu3+ ion than the azacrown bridge hydrogen atoms (determined from the MD calculations) are less efficient quenchers. The number of coordinating methanol molecules to 11a·Eu3+, 29·Eu3+, and 34·Eu3+ estimated by the "Horrocks equation" is 0.9, 1.2, and 1.9, respectively, as was predicted by MD calculations. Moreover, the experimental data show that quenching of the excited state of well-shielded Eu3+ ions by the C-H modes of the ligand is of the same order of magnitude as quenching by one O-H mode

Photophysical studies of m-terphenyl-sensitized visible and near-infrared emission from organic 1:1 lanthanide ion complexes in methanol solutions

The luminescence properties of several 11 lanthanide ion (Sm3+, Tb3+, Dy3+, Pr3+, Nd3+, Ho3+, Tm3+ and Yb3+) complexes based on the m-terphenyl-containing ligands 1–3 have been studied in methanol solutions. The organic complexes show their typical luminescence in the visible (Sm3+, Tb3+, Dy3+ and Pr3+) and in the near-infrared (Nd3+, Er3+ and Yb3+) region of the electromagnetic spectrum. The degree of shielding of the lanthanide ions from high-energy quenching modes of the solvent by the acyclic ligand 3 is less than the shielding by the macrocyclic ligands 1 and 2.Not only the high-energy vibrational modes of the solvent quench the luminescent state, but also the C–H modes of the organic ligand, and even O–D and C–D modes can contribute significantly to the quenching. In general, the high-energy vibrational O–H and C–H modes are most efficient in luminescence quenching, but the quenching is strongly dependent on the magnitude of the energy gap between the lowest luminescent state and a lower-lying state. Luminescence at longer wavelengths can be quenched relatively easily because of the smaller energy gaps, rendering all quenching pathways, especially quenching by the remaining C–H modes in the partially deuterated ligand, efficient. When the energy gap is resonant with (an overtone of) a vibrational mode, i.e. O–H, C–H, O–D or C–D, the luminescence is very efficiently quenched by these modes and can even be extinguished. For instance: Ho3+ luminescence was not observed because the 5S25F5 transition is resonant with the C–H vibrational mode, deuteration is less effective than expected for Pr3+ because the energy gap is resonant with the first overtone of the C–D vibration, and Nd3+ is efficiently quenched by the deuterated solvent because the energy gap is resonant with the first overtone of the O–D vibration. \u

Sensitized near-infrared emission from Nd3+ and Er3+ complexes of fluorescein-bearing calix[4]arene cages

Efficient intramolecular energy transfer (ET) from an excited chromophore to Nd3+ and Er3+ ions with subsequent emission in the near-infrared (h2) is possible in novel compounds (1). These are made by covalent attachment of fluorescein to a calix[4]arene possessing a cavity at the lower rim in which the trivalent lanthanoid ions are complexed

Biscalix[4]arene ligands for dinuclear lanthanide ion complexation

Three types of lower-lower rim linked biscalix[4]arenes that contain carboxylic ester (1) and/or amide functions (2 and 3) at their remaining phenolic oxygen atoms were synthesized. The homo- and heterodinuclear lanthanide ion complexes based on these ligands were used to study the energy transfer between different lanthanide ions. Photophysical studies comparing the luminescence properties of the homodinuclear Eu3+ complex and the heterodinuclear Eu3+-Nd3+ complex of 2 indicated that energy transfer is likely to occur from Eu3+ to Nd3+ with an efficiency of > 50%. The luminescence properties turned out to be strongly solvent dependent, which is attributed to structural changes leading to different positions of the lanthanide ions in the cavities provided by the biscalix[4]arene