Metal luminescence lanthanide complexes

Until very recently, studies of the use of luminescent lanthanide complexes as biological probes concentrated on the use of terbium and europium complexes. These have emission lines in the visible region of the spectrum, and have long-lived (millisecond timescale) metal-centered emission. The first examples to be studied in detail were complexes of the Lehn cryptand (complexes (20) and (26) in Figure 7),48,50,88 whose luminescence properties have also been applied to bioassay (vide infra). In this case, the europium and terbium ions both have two water molecules... 

This brief overview has shown that there are many possibilities when choosing ligands for the design of luminescent lanthanide complexes. From the examples shown it is apparent that the most luminescent of the lanthanide complexes are formed when macrocyclic ligands are used that fully or almost fully coordinate the metal centre. It should also be apparent that there are many examples and options available when it comes to choosing possible antenna within the criteria set out above (Sect. 2.3.2). 

The formation of these ternary luminescent lanthanide complexes was the result of displacement of the two labile metal-bound water molecules, which was necessary because the energy transfer process between the antenna and the Ln(III) metal centre is distance-dependent. This ternary complex formation was confirmed by analysis of the emission lifetimes in the presence of DMABA and showed the water molecules were displaced by a change in the hydration state q from 2 to 0, with binding constants of log fCa = 5.0. The Eu(III) complexes were not modulated in either water or buffered solutions at pH 7.4. Lifetime analysis of these complexes showed that the metal-bound water molecules had not been displaced and that the ternary complex was not formed. Of greater significance, both Tb -27 and Tb -28 could selectively detect salicylic acid while aspirin was not detected in buffered solutions at pH 7.4, using the principle as discussed for DMABA where excitation of the binding antenna resulted in a luminescent emission upon coordination of salicylic acid to the complex. 

Zhongning Chen received his Ph.D. in Chemistry from Nanjing University in 1994. He worked as an Alexander von Humboldt Research Fellow at Feiburg University (Germany) in 1998 and as a JSPS Fellow at Hokkaido University (Japan) in 1999-2001. He has been a chemistry professor at the Fujian Institute of Research on the Structure of Matter since 2001. His research interest is focused on luminescent transition metal and lanthanide complexes, organometallic wires, and molecular switches. 

In general, all of the fundamental principles concerning spectral overlap, absorption strength, etc., that are critical to understanding the ligand to metal energy transfer process in the design of luminescent lanthanide complexes, also apply to the luminescence from chiral complexes. 

Bray KL (2001) High Pressure Probes of Electronic Structure and Luminescence Properties of Transition Metal and Lanthanide Systems. 213 1 - 94 Bunz UHF (1999) Carbon-Rich Molecular Objects from Multiply Ethynylated rr-Complexes. 201 131-161... 

The aim of this chapter is limited to reviewing some recent developments concerning luminescent dendrimers that can play the role of ligands and sensors for luminescent and nonluminescent metal ions, mainly investigated in our laboratories, with particular references to transition metal or lanthanide ions. We will not discuss dendrimers constituted by polypyridine metal complexes [21] and porphyrins [22] since it is outside the scope of the present paper. 

The present volume is a non-thematic issue and includes seven contributions. The first chapter byAndreja Bakac presents a detailed account of the activation of dioxygen by transition metal complexes and the important role of atom transfer and free radical chemistry in aqueous solution. The second contribution comes from Jose Olabe, an expert in the field of pentacyanoferrate complexes, in which he describes the redox reactivity of coordinated ligands in such complexes. The third chapter deals with the activation of carbon dioxide and carbonato complexes as models for carbonic anhydrase, and comes from Anadi Dash and collaborators. This is followed by a contribution from Sasha Ryabov on the transition metal chemistry of glucose oxidase, horseradish peroxidase and related enzymes. In chapter five Alexandra Masarwa and Dan Meyerstein present a detailed report on the properties of transition metal complexes containing metal-carbon bonds in aqueous solution. Ivana Ivanovic and Katarina Andjelkovic describe the importance of hepta-coordination in complexes of 3d transition metals in the subsequent contribution. The final chapter by Sally Brooker and co-workers is devoted to the application of lanthanide complexes as luminescent biolabels, an exciting new area of development. 

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