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21 pages, 2936 KiB

Open AccessFeature PaperArticle

Lanthanide(III) Complexes of Cyclen Triacetates and Triamides Bearing Tertiary Amide-Linked Antennae

by Salauat R. Kiraev, Emilie Mathieu, Fiona Siemens, Daniel Kovacs, Ellen Demeyere and K. Eszter Borbas

Molecules 2020, 25(22), 5282; https://doi.org/10.3390/molecules25225282 - 12 Nov 2020

Cited by 11 | Viewed by 3410

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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25 pages, 12327 KiB

Open AccessArticle

Synthesis of Organosilicon Ligands for Europium (III) and Gadolinium (III) as Potential Imaging Agents

by James I. Bruce, Patrick J. O’Connell, Peter G. Taylor, David P.T. Smith, Roy C. Adkin and Victoria K. Pearson

Molecules 2020, 25(18), 4253; https://doi.org/10.3390/molecules25184253 - 16 Sep 2020

Cited by 3 | Viewed by 2662

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 r_1p/mM⁻¹s⁻¹). Full article

(This article belongs to the Special Issue Luminescent Lanthanide Complexes)

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17 pages, 4821 KiB

Open AccessArticle

Luminescent Sensor Based on Ln(III) Ternary Complexes for NAD(P)H Detection

by Filip Smrčka and Přemysl Lubal

Molecules 2020, 25(18), 4164; https://doi.org/10.3390/molecules25184164 - 11 Sep 2020

Cited by 2 | Viewed by 2902

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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18 pages, 3659 KiB

Open AccessFeature PaperArticle

Colorimetry of Luminescent Lanthanide Complexes

by Julien Andres and Anne-Sophie Chauvin

Molecules 2020, 25(17), 4022; https://doi.org/10.3390/molecules25174022 - 3 Sep 2020

Cited by 9 | Viewed by 3930

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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18 pages, 2848 KiB

Open AccessArticle

Triplexed CEA-NSE-PSA Immunoassay Using Time-Gated Terbium-to-Quantum Dot FRET

by Shashi Bhuckory, K. David Wegner, Xue Qiu, Yu-Tang Wu, Travis L. Jennings, Anne Incamps and Niko Hildebrandt

Molecules 2020, 25(16), 3679; https://doi.org/10.3390/molecules25163679 - 12 Aug 2020

Cited by 6 | Viewed by 3276

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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15 pages, 2153 KiB

Open AccessArticle

Two Beta-Phosphorylamide Compounds as Ligands for Sm³⁺, Eu³⁺, and Tb³⁺: X-ray Crystallography and Luminescence Properties

by Alan R. Lear, Jonah Lenters, Michael G. Patterson, Richard J. Staples, Eric J. Werner and Shannon M. Biros

Molecules 2020, 25(13), 2971; https://doi.org/10.3390/molecules25132971 - 28 Jun 2020

Cited by 2 | Viewed by 2631

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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23 pages, 6807 KiB

Open AccessArticle

HOCl Responsive Lanthanide Complexes Using Hydroquinone Caging Units

by Elena Del Giorgio and Thomas Just Sørensen

Molecules 2020, 25(8), 1959; https://doi.org/10.3390/molecules25081959 - 23 Apr 2020

Cited by 3 | Viewed by 3563

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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20 pages, 3224 KiB

Open AccessReview

Lanthanide Luminescence in Visible-Light-Promoted Photochemical Reactions

by Ramiro Barraza, Jr. and Matthew J. Allen

Molecules 2020, 25(17), 3892; https://doi.org/10.3390/molecules25173892 - 26 Aug 2020

Cited by 13 | Viewed by 5815

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 Sm^II, Eu^II, and Ce^III. By understanding the effects that ligands have on the 5d orbitals of Sm^II, Eu^II, and Ce^III, luminescence and reactivity can be rationally modulated using coordination chemistry. This review briefly overviews the photochemical reactivity of Sm^II, Eu^II, and Ce^III 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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34 pages, 10515 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Luminescence Imaging of Biological Systems Using Lanthanide(III) Luminescent Complexes

by Jorge H. S. K. Monteiro

Molecules 2020, 25(9), 2089; https://doi.org/10.3390/molecules25092089 - 29 Apr 2020

Cited by 65 | Viewed by 8027

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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