Synthesis and optical properties of macrocyclic lanthanide(III) chelates as new reagents for luminescent biolabeling

Bright red emission with high color purity from Eu(iii) complexes with π-conjugated polycyclic aromatic ligands and their sensing applications

Eu(iii) complexes emit red light with a high color purity and have consequently attracted attention for development toward display and physical sensing applications. The characteristic pure color emission originates from the intra-4f-4f transition, and the brightness strongly depends on the electronic and steric structures of organic ligands. A large π-conjugated ligand design with a large absorption coefficient has been actively studied for achieving bright emission. The π-conjugated Eu(iii) luminophores also provide oxygen and temperature sensing properties by controlling their excited state dynamics based on π-electron systems. A comprehensive understanding of the design strategy of large π-conjugated ligands is crucial for the further development of luminescent Eu(iii) complexes. In this review, we summarize the research progress on π-conjugated Eu(iii) luminophores exhibiting bright emission and their physical sensing applications.

Luminescent lanthanide complexes for reactive oxygen species biosensing and possible application in Alzheimer's diseases

Histopathological hallmarks of Alzheimer's disease (AD) are intracellular neurofibrillary tangles and extracellular formation of senile plaques composed of the aggregated amyloid-beta peptide along with metal ions (copper, iron or zinc). In addition, oxidative stress is considered as an important factor in the etiology of AD and a multitude of metalloproteins and transporters is affected, leading to metal ion misregulation. Redox-active metal ions (e.g., copper) can catalyze the production of reactive oxygen species (ROS) in the presence of molecular oxygen and a reductant such as ascorbate. The ROS thus produced, in particular the hydroxyl radical which is the most reactive one, may contribute to oxidative stress conditions. Thus, detecting ROS in vivo or in biological models of AD is of interest for better understanding AD etiology. The use of biocompatible and highly specific and sensitive probes is needed for such a purpose, since ROS are transient species whose steady-state concentrations are very low. Luminescent lanthanide complexes are sensitive probes that can meet these criteria. The present review focuses on the recent advances in the use of luminescent lanthanide complexes for ROS biosensing. It shows why the use of luminescent lanthanide complexes is of particular interest for selectively detecting ROS ( O 2 · - , HO^• , ¹ O₂ , H₂ O₂ , etc.) in biological samples in the µM-nM range. It particularly focuses on the most recent strategies and discusses what could be expected with the use of luminescent lanthanide complexes for better understanding some of the molecular mechanisms underlying the development of Alzheimer's disease.

Aromatic and heteroaromatic azacrown compounds: advantages and disadvantages of rigid macrocyclic ligands

Current approaches to the synthesis of aromatic and heteroaromatic azamacrocycles and their derivatives are summarized and systematized. The relationship between the structure of azacrown compounds and their complexation behaviour towards metal cations is analyzed. The diversity of practical applications of azamacrocyclic derivatives in medicine, biology and analytical and organic chemistry, as well as for the design of molecular devices is demonstrated.

The bibliography includes 307 references.

Dual-Action Ru(II) Complexes with Bulky π-Expansive Ligands: Phototoxicity without DNA Intercalation

We report the synthesis and photochemical and biological characterization of Ru(II) complexes containing π-expansive ligands derived from dimethylbenzo[i]dipyrido[3,2-a:2',3'-c]phenazine (Me₂dppn) adorned with flanking aryl substituents. Late-stage Suzuki couplings produced Me₂dppn ligands substituted at the 10 and 15 positions with phenyl (5), 2,4-dimethylphenyl (6), and 2,4-dimethoxyphenyl (7) groups. Complexes of the general formula [Ru(tpy)(L)(py)](PF₆)₂ (8-10), where L = 4-7, were characterized and shown to have dual photochemotherapeutic (PCT) and photodynamic therapy (PDT) behavior. Quantum yields for photodissociation of monodentate pyridines from 8-10 were about 3 times higher than that of parent complex [Ru(tpy)(Me₂dppn)(py)](PF₆)₂ (1), whereas quantum yields for singlet oxygen (¹O₂) production were ∼10% lower than that of 1. Transient absorption spectroscopy indicates that 8-10 possess long excited state lifetimes (τ = 46-50 μs), consistent with efficient ¹O₂ production through population and subsequent decay of ligand-centered ³ππ* excited states. Complexes 8-10 displayed greater lipophilicity relative to 1 and association to DNA but do not intercalate between the duplex base pairs. Complexes 1 and 8-10 showed photoactivated toxicity in breast and prostate cancer cell lines with phototherapeutic indexes, PIs, as high as >56, where the majority of cell death was achieved 4 h after treatment with Ru(II) complexes and light. Flow cytometric data and rescue experiments were consistent with necrotic cell death mediated by the production of reactive oxygen species, especially ¹O₂. Collectively, this study confirms that DNA intercalation by Ru(II) complexes with π-expansive ligands is not required to achieve photoactivated cell death.

Potent and selective inhibition of matrix metalloproteinases by lanthanide trichloride

Matrix metalloproteinases (MMPs) are a family of Zn-containing and Ca-dependent proteases with vital roles in extracellular matrix remodeling. Deregulation of MMPs occurs in many pathological conditions such as cardiovascular diseases, inflammation, and cancer. The therapeutic potential of MMP inhibitors has been demonstrated in diseases such as arthritis and cancer. Here we demonstrated that the 3-valent lanthanide compounds LaCl₃, TbCl₃, GdCl₃, YbCl₃, and EuCl₃ inhibit MMPs such as MMP-2, MMP-13, and MMP-14 (MT1-MMP). The inhibition is more potent and selective toward MT1-MMP compared to the other MMPs. EuCl₃ was further selected to study the enzyme kinetics of the MT1-MMP inhibition. The results showed that the inhibition is a mixed type with anti-competition and non-competitive types, which indicated that inhibition was achieved by the compound bound to the non-active center of MT1-MMP and changing the enzyme conformation. The interaction between EuCl₃ and MT1-MMP was further studied by UV-visible (UV-vis) light absorption. EuCl₃ caused a slight blue shift of the maximum absorption wavelength of MT1-MMP, indicating the interaction reduced protein hydrophobicity. Moreover, EuCl₃ exerted substantial inhibitory effects on the migration of HT-1080 cells. Thus, EuCl₃ may play a role in modulating tumor cell behavior by inhibiting MMPs activities especially the MT1-MMP activity. These findings provide initial insight into the biological activity and potential therapeutic value of EuCl₃.

Stable Europium(III) Complexes with Short Linkers for Site-Specific Labeling of Biomolecules

In this study, two new terpyridine-based Eu^III complexes were synthesized, the structures of which were optimized for luminescence resonance energy-transfer (LRET) experiments. The complexes showed high quantum yields (32 %); a single long lifetime (1.25 ms), which was not influenced by coupling to protein; very high stability in the presence of chelators such as ethylenediamine-N,N,N',N'-tetraacetate and ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid; and no interaction with cofactors such as adenosine triphosphate and guanosine triphosphate. A special feature is the short length of the linker between the Eu^III ion and the maleimide or hydrazide function, which allows for site-specific coupling of cysteine mutants or unnatural keto amino acids. As a consequence, the new complexes appear particularly suited for accurate distance measurements in biomolecules by LRET.

Sensitized luminescence from water-soluble LaF3:Eu nanocrystals via partially-capped 1,10-phenanthroline: time-gated emission and multiple lifetimes

Novel LaF₃:Eu(5%) nanocrystals containing partially-capped 1,10-phenanthroline ligands have been obtained, which display intense phen-sensitized europium emission in water and multiple lifetimes from Eu³⁺-dopant sites.

AMPED: a new platform for picolinate based luminescent lanthanide chelates

Anchoring three picolinate units on a AMPED scaffold affords a strongly pre-organized ligand for the formation of luminescent lanthanide complexes.

Luminescent lanthanide cryptates: from the bench to the bedside

The design and application of luminescent lanthanide cryptates for sensing biological interactions is highlighted through the review of the work performed in our laboratory and with academic collaborations. The path from the initial applications probing biochemical interaction in vitro to "state-of-the-art" cellular assays toward clinical applications using homogeneous time-resolved fluorescence technology is described. An overview of the luminescent lanthanide macrocyclic compounds developed at Cisbio in the recent past is given with an emphasis on specific constraints required by specific applications. Recent assays for drug-discovery and diagnostic purposes using both antibody-based and suicide-enzyme-based technology are illustrated. New perspectives in the field of molecular medicine and time-resolved microscopy are discussed.

A luminescent terbium coordination polymer for sensing methanol

A new promising sensor for detecting methanol has been prepared, which exhibits highly sensitive and selective luminescence quenching to methanol.