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Special Issue "Luminescent Lanthanide Complexes"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (31 July 2020).

Special Issue Editor

Dr. Eszter Borbas
E-Mail Website
Guest Editor
Department of Chemistry, Ångström Laboratory Box 523, Uppsala University, 75120 Uppsala, Sweden
Interests: lanthanide luminescence; multiplex detection; responsive lanthanide-based probes; lanthanide coordination chemistry and ligand design; organic synthesis; heterocyclic chemistry; tetrapyrroles

Special Issue Information

Dear Colleagues,

Luminescence spectroscopy is a sensitive technique that plays a key role in the investigation of biological processes. The overwhelming majority of commercially available fluorophores are based on organic structures, and a variety of strategies exist to attach such fluorophores to biomolecules, to target them to cellular structures, and to render them environmentally responsive. Lanthanide-based emitters have properties that render them exceptionally well-suited for detection in complex media, of which biological samples are an example. The reason for this is the essentially atomic emission spectra of the trivalent lanthanide ions, and their long emission lifetimes, in combination with time-gated techniques detection with very low background.

Terbium and europium complexes have long dominated the field because their emissive complexes can have high overall quantum yields and lifetimes in the millisecond range. Luminescent lanthanide emitters with excitations and/or emissions in the near infrared are increasingly important. Emitters based on ions in nonconventional oxidation states have appeared, and attention has also turned to the less-used ions. Multimodal probes that combine lanthanide-based luminophores with MRI or PET active units are much sought after. The unique lanthanide luminescence provides opportunities for development in areas to which traditional organic fluorophores are less-suited, such as multiplex detection. The challenges of emitter design have propelled developments in materials chemistry, physical, and physical organic chemistry and organic and inorganic synthesis.

The present Special Issue includes a selection of articles demonstrating several intriguing recent developments and the current standing of lanthanide luminescence, coordination chemistry, and biological applications.

Dr. Eszter Borbas
Guest Editor

Manuscript Submission Information

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Keywords

  • lanthanide luminescence
  • near-infrared emitters
  • multiphoton processes
  • ligand design
  • quenching
  • multiplex detection
  • multimodal probes

Published Papers (9 papers)

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Research

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Open AccessFeature PaperArticle
Lanthanide(III) Complexes of Cyclen Triacetates and Triamides Bearing Tertiary Amide-Linked Antennae
Molecules 2020, 25(22), 5282; https://doi.org/10.3390/molecules25225282 - 12 Nov 2020
Cited by 2 | Viewed by 489
Abstract
The coordination compounds of the trivalent lanthanide ions (Ln(III)) have unique photophysical properties. Ln(III) excitation is usually performed through a light-harvesting antenna. To enable Ln(III)-based emitters to reach their full potential, an understanding of how complex structure affects sensitization and quenching processes is [...] Read more.
The coordination compounds of the trivalent lanthanide ions (Ln(III)) have unique photophysical properties. Ln(III) excitation is usually performed through a light-harvesting antenna. To enable Ln(III)-based emitters to reach their full potential, an understanding of how complex structure affects sensitization and quenching processes is necessary. Here, the role of the linker between the antenna and the metal binding fragment was studied. Four macrocyclic ligands carrying coumarin 2 or 4-methoxymethylcarbostyril sensitizing antennae linked to an octadentate macrocyclic ligand binding site were synthesized. Complexation with Ln(III) (Ln = La, Sm, Eu, Gd, Tb, Yb and Lu) yielded species with overall −1, 0, or +2 and +3-charge. Paramagnetic 1H NMR spectroscopy indicated subtle differences between the coumarin- and carbostyril-carrying Eu(III) and Yb(III) complexes. Cyclic voltammetry showed that the effect of the linker on the Eu(III)/Eu(II) apparent reduction potential was dependent on the electronic properties of the N-substituent. The Eu(III), Tb(III) and Sm(III) complexes were all luminescent. Coumarin-sensitized complexes were poorly emissive; photoinduced electron transfer was not a major quenching pathway in these species. These results show that seemingly similar emitters can undergo very different photophysical processes, and highlight the crucial role the linker can play. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessArticle
Synthesis of Organosilicon Ligands for Europium (III) and Gadolinium (III) as Potential Imaging Agents
Molecules 2020, 25(18), 4253; https://doi.org/10.3390/molecules25184253 - 16 Sep 2020
Viewed by 598
Abstract
The relaxivity of MRI contrast agents can be increased by increasing the size of the contrast agent and by increasing concentration of the bound gadolinium. Large multi-site ligands able to coordinate several metal centres show increased relaxivity as a result. In this paper, [...] Read more.
The relaxivity of MRI contrast agents can be increased by increasing the size of the contrast agent and by increasing concentration of the bound gadolinium. Large multi-site ligands able to coordinate several metal centres show increased relaxivity as a result. In this paper, an “aza-type Michael” reaction is used to prepare cyclen derivatives that can be attached to organosilicon frameworks via hydrosilylation reactions. A range of organosilicon frameworks were tested including silsesquioxane cages and dimethylsilylbenzene derivatives. Michael donors with strong electron withdrawing groups could be used to alkylate cyclen on three amine centres in a single step. Hydrosilylation successfully attached these to mono-, di-, and tri-dimethylsilyl-substituted benzene derivatives. The europium and gadolinium complexes were formed and studied using luminescence spectroscopy and relaxometry. This showed the complexes to contain two bound water moles per lanthanide centre and T1 relaxation time measurements demonstrated an increase in relaxivity had been achieved, in particular for the trisubstituted scaffold 1,3,5-tris((pentane-sDO3A)dimethylsilyl)benzene-Gd3. This showed a marked increase in the relaxivity (13.1 r1p/mM−1s−1). Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessArticle
Luminescent Sensor Based on Ln(III) Ternary Complexes for NAD(P)H Detection
Molecules 2020, 25(18), 4164; https://doi.org/10.3390/molecules25184164 - 11 Sep 2020
Viewed by 539
Abstract
Ln(III) complexes of macrocyclic ligands are used in medicinal chemistry, for example as contrast agents in MRI or radiopharmaceutical compounds, and in diagnostics using fluorescence imaging. This paper is devoted to a spectroscopic study of Ln(III) ternary complexes consisting of macrocyclic heptadentate DO3A [...] Read more.
Ln(III) complexes of macrocyclic ligands are used in medicinal chemistry, for example as contrast agents in MRI or radiopharmaceutical compounds, and in diagnostics using fluorescence imaging. This paper is devoted to a spectroscopic study of Ln(III) ternary complexes consisting of macrocyclic heptadentate DO3A and bidentate 3-isoquinolinate (IQCA) ligands. IQCA serves as an efficient antenna ligand, leading to a higher quantum yield and Stokes shift (250–350 nm for Eu, Tb, Sm, Dy in VIS region, 550–650 nm for Yb, Nd in NIR region). The shielding-quenching effect of NAD(P)H on the luminescence of the Ln(III) ternary complexes was investigated in detail and this phenomenon was utilized for the analytical determination of this compound. This general approach was verified through an enzymatic reaction during which the course of ethanol transformation catalyzed by alcohol-dehydrogenase (ADH) was followed by luminescence spectroscopy. This method can be utilized for selective and sensitive determination of ethanol concentration and/or ADH enzyme activity. This new analytical method can also be used for other enzyme systems coupled with NAD(P)H/NAD(P)+ redox pairs. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessFeature PaperArticle
Colorimetry of Luminescent Lanthanide Complexes
Molecules 2020, 25(17), 4022; https://doi.org/10.3390/molecules25174022 - 03 Sep 2020
Cited by 1 | Viewed by 784
Abstract
Europium, terbium, dysprosium, and samarium are the main trivalent lanthanide ions emitting in the visible spectrum. In this work, the potential of these ions for colorimetric applications and colour reproduction was studied. The conversion of spectral data to colour coordinates was undertaken for [...] Read more.
Europium, terbium, dysprosium, and samarium are the main trivalent lanthanide ions emitting in the visible spectrum. In this work, the potential of these ions for colorimetric applications and colour reproduction was studied. The conversion of spectral data to colour coordinates was undertaken for three sets of Ln complexes composed of different ligands. We showed that Eu is the most sensitive of the visible Ln ions, regarding ligand-induced colour shifts, due to its hypersensitive transition. Further investigation on the spectral bandwidth of the emission detector, on the wavelengths’ accuracy, on the instrumental correction function, and on the use of incorrect intensity units confirm that the instrumental correction function is the most important spectrophotometric parameter to take into account in order to produce accurate colour values. Finally, we established and discussed the entire colour range (gamut) that can be generated by combining a red-emitting Eu complex with a green-emitting Tb complex and a blue fluorescent compound. The importance of choosing a proper white point is demonstrated. The potential of using different sets of complexes with different spectral fingerprints in order to obtain metameric colours suitable for anti-counterfeiting is also highlighted. This work answers many questions that could arise during a colorimetric analysis of luminescent probes. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessArticle
Triplexed CEA-NSE-PSA Immunoassay Using Time-Gated Terbium-to-Quantum Dot FRET
Molecules 2020, 25(16), 3679; https://doi.org/10.3390/molecules25163679 - 12 Aug 2020
Cited by 1 | Viewed by 689
Abstract
Time-gated Förster resonance energy transfer (TG-FRET) between Tb complexes and luminescent semiconductor quantum dots (QDs) provides highly advantageous photophysical properties for multiplexed biosensing. Multiplexed Tb-to-QD FRET immunoassays possess a large potential for in vitro diagnostics, but their performance is often insufficient for their [...] Read more.
Time-gated Förster resonance energy transfer (TG-FRET) between Tb complexes and luminescent semiconductor quantum dots (QDs) provides highly advantageous photophysical properties for multiplexed biosensing. Multiplexed Tb-to-QD FRET immunoassays possess a large potential for in vitro diagnostics, but their performance is often insufficient for their application under clinical conditions. Here, we developed a homogeneous TG-FRET immunoassay for the quantification of carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), and prostate-specific antigen (PSA) from a single serum sample by multiplexed Tb-to-QD FRET. Tb–IgG antibody donor conjugates were combined with compact QD-F(ab’)2 antibody acceptor conjugates with three different QDs emitting at 605, 650, and 705 nm. Upon antibody–antigen–antibody sandwich complex formation, the QD acceptors were sensitized via FRET from Tb, and the FRET ratios of QD and Tb TG luminescence intensities increased specifically with increasing antigen concentrations. Although limits of detection (LoDs: 3.6 ng/mL CEA, 3.5 ng/mL NSE, and 0.3 ng/mL PSA) for the triplexed assay were slightly higher compared to the single-antigen assays, they were still in a clinically relevant concentration range and could be quantified in 50 µL serum samples on a B·R·A·H·M·S KRYPTOR Compact PLUS clinical immunoassay plate reader. The simultaneous quantification of CEA, NSE, and PSA at different concentrations from the same serum sample demonstrated actual multiplexing Tb-to-QD FRET immunoassays and the potential of this technology for translation into clinical diagnostics. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessArticle
Two Beta-Phosphorylamide Compounds as Ligands for Sm3+, Eu3+, and Tb3+: X-ray Crystallography and Luminescence Properties
Molecules 2020, 25(13), 2971; https://doi.org/10.3390/molecules25132971 - 28 Jun 2020
Viewed by 552
Abstract
This paper describes the synthesis of two beta-phosphorylamide ligands and their coordination chemistry with the Ln ions Tb3+, Eu3+, and Sm3+. Both the ligands and Ln complexes were characterized by IR, NMR, MS, and X-ray crystallography. The [...] Read more.
This paper describes the synthesis of two beta-phosphorylamide ligands and their coordination chemistry with the Ln ions Tb3+, Eu3+, and Sm3+. Both the ligands and Ln complexes were characterized by IR, NMR, MS, and X-ray crystallography. The luminescence properties of the Tb3+ and Eu3+ complexes were also characterized, including the acquisition of lifetime decay curves. In the solid state, the Tb3+ and Sm3+ ligand complexes were found to have a 2:2 stoichiometry when analyzed by X-ray diffraction. In these structures, the Ln ion was bound by both oxygen atoms of each beta-phosphorylamide moiety of the ligands. The Tb3+ and Eu3+ complexes were modestly emissive as solutions in acetonitrile, with lifetime values that fell within typical ranges. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessArticle
HOCl Responsive Lanthanide Complexes Using Hydroquinone Caging Units
Molecules 2020, 25(8), 1959; https://doi.org/10.3390/molecules25081959 - 23 Apr 2020
Viewed by 900
Abstract
Redox biology is still looking for tools to monitor redox potential in cellular biology and, despite a large and sustained effort, reliable molecular probes have yet to emerge. In contrast, molecular probes for reactive oxygen and nitrogen have been widely explored. In this [...] Read more.
Redox biology is still looking for tools to monitor redox potential in cellular biology and, despite a large and sustained effort, reliable molecular probes have yet to emerge. In contrast, molecular probes for reactive oxygen and nitrogen have been widely explored. In this manuscript, three kinetically inert lanthanide complexes that selectively react with hypochlorous acid are prepared and characterized. The design is based on 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) and 1,4,7,10-tetraazacyclododecane-1,7-diacetic acid (DO2A) ligands appended with one or two redox active hydroquinone derived arms, thereby forming octadentate ligands ideally suited to complex trivalent lanthanide ions. The three complexes are found to react selectively with hypochlorous acid to form highly symmetric lanthanide(III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacedic acid (DOTA) complexes. The conversion of the probe to [Ln.DOTA] is followed by luminescence, absorption, and NMR spectroscopy in a model system comprised of a Triton-X modified HEPES buffer. It was concluded that the design principle works, and that simple caging units like hydroquinones can work well in conjugation with lanthanide(III) complexes. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Review

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Open AccessReview
Lanthanide Luminescence in Visible-Light-Promoted Photochemical Reactions
Molecules 2020, 25(17), 3892; https://doi.org/10.3390/molecules25173892 - 26 Aug 2020
Viewed by 1020
Abstract
The excitation of lanthanides with visible light to promote photochemical reactions has garnered interest in recent years. Lanthanides serve as initiators for photochemical reactions because they exhibit visible-light-promoted 4f→5d transitions that lead to emissive states with electrochemical potentials that are more negative than [...] Read more.
The excitation of lanthanides with visible light to promote photochemical reactions has garnered interest in recent years. Lanthanides serve as initiators for photochemical reactions because they exhibit visible-light-promoted 4f→5d transitions that lead to emissive states with electrochemical potentials that are more negative than the corresponding ground states. The lanthanides that have shown the most promising characteristics for visible-light promoted photoredox are SmII, EuII, and CeIII. By understanding the effects that ligands have on the 5d orbitals of SmII, EuII, and CeIII, luminescence and reactivity can be rationally modulated using coordination chemistry. This review briefly overviews the photochemical reactivity of SmII, EuII, and CeIII with visible light; the properties that influence the reactivity of these ions; and the research that has been reported towards modulating their photochemical-relevant properties using visible light and coordination chemistry. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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Open AccessEditor’s ChoiceReview
Recent Advances in Luminescence Imaging of Biological Systems Using Lanthanide(III) Luminescent Complexes
Molecules 2020, 25(9), 2089; https://doi.org/10.3390/molecules25092089 - 29 Apr 2020
Cited by 5 | Viewed by 1105
Abstract
The use of luminescence in biological systems allows one to diagnose diseases and understand cellular processes. Molecular systems, particularly lanthanide(III) complexes, have emerged as an attractive system for application in cellular luminescence imaging due to their long emission lifetimes, high brightness, possibility of [...] Read more.
The use of luminescence in biological systems allows one to diagnose diseases and understand cellular processes. Molecular systems, particularly lanthanide(III) complexes, have emerged as an attractive system for application in cellular luminescence imaging due to their long emission lifetimes, high brightness, possibility of controlling the spectroscopic properties at the molecular level, and tailoring of the ligand structure that adds sensing and therapeutic capabilities. This review aims to provide a background in luminescence imaging and lanthanide spectroscopy and discuss selected examples from the recent literature on lanthanide(III) luminescent complexes in cellular luminescence imaging, published in the period 2016–2020. Finally, the challenges and future directions that are pointing for the development of compounds that are capable of executing multiple functions and the use of light in regions where tissues and cells have low absorption will be discussed. Full article
(This article belongs to the Special Issue Luminescent Lanthanide Complexes)
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