Lanthanide probes

Résumé

Lanthanide probes are a non-invasive analytical tool commonly used for biological and chemical applications. Lanthanides are metal ions which have their 4f energy level filled and generally refer to elements cerium to lutetium in the periodic table. The fluorescence of lanthanide salts is weak because the energy absorption of the metallic ion is low; hence chelated complexes of lanthanides are most commonly used. The term chelate derives from the Greek word for “claw,” and is applied to name ligands, which attach to a metal ion with two or more donor atoms through dative bonds. The fluorescence is most intense when the metal ion has the oxidation state of 3+. Not all lanthanide metals can be used and the most common are: Sm(III), Eu(III), Tb(III), and Dy(III). History It has been known since the early 1930s that the salts of certain lanthanides are fluorescent. The reaction of lanthanide salts with nucleic acids was discussed in a number o

Source officielle

https://en.wikipedia.org/wiki/Lanthanide_probes

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (54)

Publications associées

Chargement

Personnes associées (6)

Personnes associées

Chargement

Unités associées (2)

Unités associées

Chargement

Concepts associés

Chargement

Cours associés (1)

The course will provide a synopsis of the chemistry of f elements (lanthanides and actinides) covering structure, bonding, redox and spectroscopic properties and reactivity. The coordination and organometallic chemistry of these ions will be discussed with an overview of their main applications.

Cours associés

Chargement

Séances de cours associées (3)

Séances de cours associées

Chargement

Heterobimetallic lanthanide helicates

Thomas Binderup Jensen

Based on the ligand LAB the new heterobitopic ligands LAB2, LAB3, LAB4 and LAB5 have been designed and synthesised. The five ligands were designed to selectively form heterobimetallic complexes of composition LnLn'(L)36 when reacted with a pair of lanthanide ions Ln(ClO4)3 and Ln'(ClO4)3 in solution. The benzimidazole-pyridine-benzimidazole (bpb) moiety codes for the larger and softer lanthanide ions, while the benzimidazole-pyridine-amide (bpa) moiety codes for the smaller and harder ions of the lanthanide series. When reacted with 1/3 equivalent La3+ and 1/3 equivalent Lu3+ LAB forms in excess of 90 % [LnLn'(L)3]6+, the percentage being lower for pairs of lanthanide ions closer in size. The substituents on the new ligands modify the hardness of the nitrogen atom of the pyridyl group. The electron donating NEt2 group in LAB2 increases the hardness of the bpa group, which should improve the selectivity of the ligand. A similar improvement was expected for LAB5 in which the electron withdrawing Cl substituent makes the bpb moiety of the ligand softer. The two other new ligands LAB3 and LAB4 were, based on similar arguments, not expected to exhibit improved selectivity and were synthesised for comparison. Due to the tendency of LAB2 and LAB5 to form high proportions of HHT (Head-Head-Tail) isomers their selectivity turned out to be lower than anticipated. The proportion of heterobimetallic complexes reaches only 65 and 92 %, respectively, for the LaLu couple of lanthanides. The ligands LAB3 and LAB4, as expected, also give lower yields (up to 87 and 79 %) of heterobimetallic complexes. To investigate the details of the Head-Head-Head/Head-Head-Tail equilibrium variable temperature NMR measurements were carried out and the H and S values were determined for 26 different complexes. It was found that the equilibria were characterised by a subtle interplay of enthalpic and entropic effects, with the two isomers differing only by a few kJ/mol. Structures of five complexes of LAB3 were determined by X-ray diffraction. The structures contain molecular ions of composition [LnLn'(L)3]6+ in which the three ligand strands are wrapped around the two lanthanide ions in a helical fashion. To obtain information about the structure of the complexes in solution analysis of the lanthanide induced paramagnetic shift has been carried out. The so-called one proton analysis showed that contributions from two paramagnetic lanthanide ions in the same complex are additive. Extraction of structural factors demonstrated that the complexes of all the ligands are isostructural in solution. Comparison with the X-ray data proved that the solid state structures are maintained in solution. Finally, a modified one proton analysis has been devised to separate contact and pseudo contact shifts while taking into account the variation of the crystal field parameter B20 along the lanthanide series.

EPFL2006

Chargement

Rare earths: jewels for functional materials of the future

Svetlana Eliseeva

In recent decades, rare earths have become vital to a wealth of advanced materials and technologies including catalysts, alloys, magnets, optics and lasers, rechargeable hydride batteries, electronics, economical lighting, wind- and solar-energy conversion, bio-analyses and imaging. In this perspective article we give a broad overview of rare earth resources and uses first and then of selected applications in dedicated fields such as telecommunications, lasers, photovoltaics (solar-energy conversion), lighting (fluorescent lamps and OLEDs), luminescent probes for bio-analyses and bio-imaging, as well as magnetism and magnetic refrigeration.

2011

Chargement

In 2003, the Nobel Assembly at the Karolinska Institute has awarded the Nobel Prize in Medicine or Physiology to Paul Lauterbur and Peter Mansfield for their seminal discoveries concerning the development of Magnetic Resonance Imaging (MRI), a non-invasive diagnosis technique notably used in medicine to visualize the human internal organs and to distinguish between healthy and pathological cells. For this purpose, contrast agents are valuable tools that enhance this distinction which is resulting from the difference in the water content of the different tissues. These drugs are used nowadays in more than 30% of the 60 millions MRI examinations performed each year. And both numbers are still growing fast. Most of the contrast agents contain a paramagnetic ion (GdIII) that accelerates the relaxation of the water protons by providing them a new relaxation pathway. Relaxivity is a way of quantifying the contrast agent efficiency and is governed by four key parameters: hydration number of the lanthanide ion, water exchange rate, electronic relaxation rate and rotational correlation time of the system. A judicious simultaneous optimization of these parameters is predicted to result in a 20-fold increase in relaxivity compared to the currently used contrast agents. In this work, with the aim of increasing the relaxivity and better understanding the involved mechanisms, the synthesis and physico-chemical characterization of new dinuclear GdIII complexes, based on thoroughly studied monomeric equivalents, were performed. We particularly stressed the outmost importance of introducing rigidity together with the increased size of the system, for a flexible assembly will hinder the relaxivity gain brought by the higher molecular weight. This rigidity is induced by using an aromatic linker between the chelating subunits or by means of the self-assembling properties of terpyridine units around FeII or RuII. We investigated the thermodynamic stability, which in crucial for toxicological reason, the spectrophotometric properties, and the rotational and water exchange dynamics of these complexes. As a result, a remarkable increase in relaxivity is obtained for all the studied compounds with respect to the clinically used actual contrast agents. Finally, insights into a promising novel class of MRI contrast agents acting simultaneously as luminescence probes are provided.

EPFL2005

Chargement

Heterobimetallic lanthanide helicates

Thomas Binderup Jensen

EPFL2006

EPFL2005