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

Molecules ◽  
2020 ◽  
Vol 25 (22) ◽  
pp. 5282
Author(s):  
Salauat R. Kiraev ◽  
Emilie Mathieu ◽  
Fiona Siemens ◽  
Daniel Kovacs ◽  
Ellen Demeyere ◽  
...  
Keyword(s):  
Metal Binding ◽  
Photophysical Properties ◽  
Complex Structure ◽  
Macrocyclic Ligand ◽  
Lanthanide Ions ◽  
Full Potential ◽  
Tertiary Amide ◽  
Apparent Reduction ◽  
Light Harvesting Antenna ◽  
The Eu

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.

Azaoxa Macrocyclic and Acyclic Complexesof Lanthanides

1998 ◽  
Vol 63 (3) ◽  
pp. 363-370 ◽  
Author(s):  
Violetta Patroniak-Krzyminiewska ◽  
Wanda Radecka-Paryzek
Keyword(s):  
Schiff Base ◽  
Spectral Data ◽  
Macrocyclic Ligand ◽  
Lanthanide Ions ◽  
H Nmr ◽  
Elemental Analyses ◽  
Acyclic Complexes ◽  
Schiff Base Cyclocondensation

The template reactions of 2,6-diacetylpyridine with 3,6-dioxaoctane-1,8-diamine in the presence of dysprosium(III), thulium(III) and lutetium(III) chlorides and erbium(III) perchlorate produce the complexes of 15-membered macrocyclic ligand with an N3O2 set of donor atoms as a result of the [1+1] Schiff base cyclocondensation. In contrast, analogous reactions involving the lighter lanthanide ions (lanthanum(III), samarium(III) and europium(III)) yield the acyclic complexes with terminal acetylpyridyl groupings as products of the partial [2+1] condensation. The complexes were characterized by spectral data (IR, UV-VIS, 1H NMR, MS), and thermogravimetric and elemental analyses.

Synthesis, Spectral Characterization and Luminescent Properties of Ternary Rare Earth Nitrates Complexes with 2-Acetylpyridine-tris(2-aminoethyl)amine and Pyridine-N-oxide Ligand

2011 ◽  
Vol 322 ◽  
pp. 337-340
Author(s):  
Lian Cai Du
Keyword(s):  
Thermal Analysis ◽  
Rare Earth ◽  
Luminescent Properties ◽  
Ternary Complexes ◽  
Molar Conductivity ◽  
Lanthanide Ions ◽  
Fluorescent Properties ◽  
Tripodal Ligand ◽  
Rare Earth Nitrates ◽  
The Eu

A tripodal ligand, 2-acetylpyridine-tris(2-aminoethyl)amine (L), pyridine-N-oxide and their ternary complexes with rare earth nitrates have been synthesized. These new complexes with the general formula of Ln·L·PyNO·(NO3)3·nH2O (where Ln = La, Nd, Tb, Pr, Eu, n = 1~3 ) were characterized by elemental analysis, IR spectra, thermal analysis and molar conductivity. All the complexes are stable in air. The results show that the lanthanide ions in each complex are coordinated by nitrogen atoms of the ligand, oxygen atoms of PyNO and the nitrates. The fluorescent properties of the Eu(III) and Tb(III) complexes in solid were investigated.

scholarly journals The Temperature Dependence of Fundamental Photophysical Properties of [Eu(MeOH-d4)9]3+ Solvates and [Eu.DOTA(MeOH-d4)]- Complexes

2021 ◽  
Author(s):  
Nicolaj Kofod ◽  
Lea Gundorff Nielsen ◽  
Thomas Just Sørensen
Keyword(s):  
Transition Probabilities ◽  
Photophysical Properties ◽  
Transition Probability ◽  
Energy Levels ◽  
Emission Spectra ◽  
Lanthanide Ions ◽  
Quantum Yields ◽  
Luminescence Spectra ◽  
Absorption Cross ◽  
Apparent Lack

The trivalent lanthanide ions show optical transitions between energy levels within the 4f shell. All these transitions are formally forbidden according to the quantum mechanical selection rules used in molecular photophysics. Nevertheless, highly luminescent complexes can be achieved, and terbium(iii) and europium(iii) ions are particularly efficient emitters. This report started when an apparent lack of data in the literature led us to revisit the fundamental photophysics of europium(iii). The photophysical properties of two complexes – [Eu.DOTA(MeOH-d4)]- and [Eu(MeOH-d4)9]3+ – were investigated in deuterated methanol at five different temperatures. Absorption spectra showed decreased absorption cross sections as the temperature was increased. Luminescence spectra and time-resolved emission decay profiles showed a decrease in intensity and lifetime as a temperature was increased. Having corrected the emission spectra for the actual number of absorbed photons and differences in non-radiative pathways, the relative emission probability was revealed. These were found to increase with increasing temperature. The transition probability for luminescence was shown to increase with temperature, while the transition probability for light absorption decreased. The changes in transition probabilities were correlated to a change in the symmetry of the absorber or emitter, with an average increase in symmetry lowering absorption cross section and access to more asymmetric structures increasing the emission rate constant. Determining luminescence quantum yields and the Einstein coefficient for spontaneous emission allowed us to conclude that lowering symmetry increases both. Further, it was found that collisional self-quenching is an issue for lanthanide luminescence, when high concentrations are used. Finally, detailed analysis revealed results that show the so-called ‘Werts’ method’ for calculating radiative lifetimes and intrinsic quantum yields are based on assumption that does not hold for the two systems investigated here. We conclude that we are lacking a good theoretical description of the intraconfigurational f-f transition, and that there are still aspects of fundamental lanthanide photophysics to be explored.<br>

scholarly journals SOLIDARITY CHECK IN TIMES OF COVID-19. ANALYSIS OF THE EU APPROACH TOWARDS ITS CLOSEST NEIGHBOURS WITH A SPECIAL FOCUS ON MONTENEGRO

2021 ◽  
Author(s):  
Stefan Đurić ◽  
Bojana Lalatović
Keyword(s):  
European Union ◽  
Complex Structure ◽  
Special Focus ◽  
The European Union ◽  
Negative Consequences ◽  
Western Balkans ◽  
Governance System ◽  
Member States ◽  
Balkan Countries ◽  
The Eu

Solidarity as one of the cornerstone values of the European Union has been once again seated on the red chair and intensively discussed within the European Union and broader. After the economic recession and migrant crisis that marked the last two decades, the outbreak of the COVID-19 pandemic has once again harshly tested the fundamental objectives and values of the European Union and the responsiveness and effectiveness of its governance system on many fronts. In April, 2020 several EU Member States were among the worst affected countries worldwide and this situation soon became similar in their closest neighbourhood. It put a huge pressure on the EU to act faster, while at the same time placing this sui generis community to the test that led to revealing its strengths and weaknesses. As it happened in the previous crises, the Union launched policies and various programmes that were meant to lessen the burden of the Member States and aspiring countries caused by the crises. The objectives of the mentioned soft law instruments that the EU adopted during the COVID-19 crisis has been not only to show that EU law is equipped to react to health and economic crises rapidly but to deliver its support in terms of solidarity to its Member States and its closest neighbours facing the unprecedented health and economic crisis. This article will explore the value and implication of the solidarity principle in times of Covid-19 in its various manifestations. A special focus will be on the financial and material aspects of the EU instruments created to combat the negative consequences of the pandemic and their further impact on shaping the solidarity principle within the EU system. While examining the character and types of these mechanisms a special focus will be placed on those available to Western Balkan countries, whereas Montenegro as the “fast runner” in the EU integration process will be taken as a case study for the purpose of more detailed analyses. One of the major conclusions of the paper will be that although the speed of the EU reactions due to highly complex structure of decision making was not always satisfying for all the actors concerned, the EU once again has shown that it is reliable and that it treats the Western Balkan countries as privileged partners all for the sake of ending pandemic and launching the socio-economic recovery of the Western Balkans. Analytical and comparative methods will be dominantly relied upon throughout the paper. This will allow the authors to draw the main conclusions of the paper and assess the degree of solidarity as well as the effectiveness of the existing EU instruments that are available to Montenegro and aimed at diminishing negative consequences of the crisis.

Interaction of 4-Hydroxybiphenyl with Cyclodextrins: Effect of Complex Structure on Spectroscopic and Photophysical Properties

2000 ◽  
Vol 6 (9) ◽  
pp. 1578-1591 ◽  
Author(s):  
Pietro Bortolus ◽  
Giancarlo Marconi ◽  
Sandra Monti ◽  
Bernd Mayer ◽  
Gottfried Köhler ◽  
...  
Keyword(s):  
Photophysical Properties ◽  
Complex Structure

scholarly journals Tight and specific lanthanide binding in a de novo TIM barrel with a large internal cavity designed by symmetric domain fusion

2020 ◽  
Vol 117 (48) ◽  
pp. 30362-30369
Author(s):  
Shane J. Caldwell ◽  
Ian C. Haydon ◽  
Nikoletta Piperidou ◽  
Po-Ssu Huang ◽  
Matthew J. Bick ◽  
...  
Keyword(s):  
Protein Design ◽  
Metal Binding ◽  
De Novo ◽  
Enzymatic Reaction ◽  
Symmetric Domain ◽  
Lanthanide Ions ◽  
Internal Cavity ◽  
Tim Barrel ◽  
Reaction Chambers ◽  
Modular Platform

De novo protein design has succeeded in generating a large variety of globular proteins, but the construction of protein scaffolds with cavities that could accommodate large signaling molecules, cofactors, and substrates remains an outstanding challenge. The long, often flexible loops that form such cavities in many natural proteins are difficult to precisely program and thus challenging for computational protein design. Here we describe an alternative approach to this problem. We fused two stable proteins with C2 symmetry—a de novo designed dimeric ferredoxin fold and a de novo designed TIM barrel—such that their symmetry axes are aligned to create scaffolds with large cavities that can serve as binding pockets or enzymatic reaction chambers. The crystal structures of two such designs confirm the presence of a 420 cubic Ångström chamber defined by the top of the designed TIM barrel and the bottom of the ferredoxin dimer. We functionalized the scaffold by installing a metal-binding site consisting of four glutamate residues close to the symmetry axis. The protein binds lanthanide ions with very high affinity as demonstrated by tryptophan-enhanced terbium luminescence. This approach can be extended to other metals and cofactors, making this scaffold a modular platform for the design of binding proteins and biocatalysts.

scholarly journals Participation of γ-Carboxyglutamic Acid Residues in Metal Binding: 13C nmr Studies of The Interaction of Lanthanide Ions with Bovine Prothrombin Fragment (12-44)

1977 ◽  
Author(s):  
B.C. Furie ◽  
M. Blumenstein ◽  
B. Furie
Keyword(s):  
Metal Ions ◽  
Metal Binding ◽  
Tertiary Structure ◽  
Chemical Shifts ◽  
Lanthanide Ions ◽  
Nmr Studies ◽  
Prothrombin Fragment ◽  
Carboxyglutamic Acid ◽  
The Relationship ◽  
Carboxyl Carbon

Comparative studies of Ca(II) binding to bovine prothrombin and abnormal prothrombin have led to the hypothesis that γ-carboxyglutamic acid (Gla) residues either participate directly in metal liganding or stabilize the tertiary structure of the protein to facilitate metal binding, or both. Extending previous studies of the binding of lanthanide ions to factor X, prothrombin and prothrombin fragment 1, the interaction of lanthanide ions with prothrombin fragment (12-44), which contains eight Gla residues, has been examined by natural abundanceC NMR spectroscopy at 67.88 mHz. The relationship between bound metal ions and carbon atoms in fragment (12-44) was determined using paramagnetic Pr(III) and Eu(III) based upon the strategy that the magnitude of the change in the chemical shift of resonances of the carbon atoms induced by bound metals is related to the interatomic distance between bound metal and carbon nuclei. Assignments of the resonances in the 13C spectrum of fragment (12-44) were based upon our studies of the chemical shifts of carbon resonances in DL-Gla and known chemical shifts of carbon resonances of the other amino acid residues. Titration of fragment (12-44) with Pr(III) or Eu(III) was accompanied by a downfield or upfield shift, respectively, of the γ-carboxyl carbon resonances and no shifts were observed for other carbon resonances. The shift of resonances within the γ-carboxyl carbon envelope appeared selective, suggesting the non-equivalence of the relationship of the γ-carboxyl group of the eight Gla residues to the bound metal ions. These data offer direct evidence that some, but perhaps not all, Gla residues participate in metal liganding.

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