Luminescent Lanthanide Helicates Self-Assembled from Ditopic Ligands Bearing Phosphonic Acid or Phosphoester Units

Abstract

A series of hexadentate ditopic receptors incorporating benzimidazole moieties have been designed, which are fitted with phosphonic acid or phosphoethylester coordinating units. In addition, poly(oxyethylene) pendants have been introduced on the benzimidazole backbone of two ligands to increase water solubility. The ligands self-assemble with lanthanide ions under stoichiometric conditions, yielding triple-stranded homobimetallic helicates, as ascertained by mass spectrometry and UV-visible titrations. The helicates display large thermodynamic stability, for example, log β 23 ≈ 21-24 for all the Eu III complexes. Photophysical measurements reveal sensitization of the metal-centered luminescence in the europium and terbium complexes, which is modulated by the nature of the ligand. Hydration numbers determined by the lifetime method are essentially zero. The Eu( 5 D 0 ) lifetimes are long and reach values up to 3.2 ms, while quantum yields as high as 25% are obtained in water at pH 7.4. Back transfer limits the sensitization efficiency for Tb III luminescence, and both lifetimes and quantum yields are much smaller. The properties of the helicates are discussed with respect to those self-assembled from ligands bearing carboxylate coordinating units.

Lanthanide diphosphonates based on a V-shaped ligand: syntheses, structures, experimental and theoretical luminescence properties

“…24 As expected, both the excitation and emission spectra of compound 2 resemble those of ligand H 4 L (see Fig. 4).…”

Synthesis and cell localization of self-assembled dinuclear lanthanide bioprobes

“…In our previous 3 ] (scheme 1) because its quantum yield is much larger (25% versus only 2.5%; [22]). All the helicates bearing different coordinating and terminal groups permeate into HeLa cells and stain the cytoplasm.…”

“…Solvents were purified by a non-hazardous procedure by passing them onto activated alumina columns (Innovative Technology Inc. system; [35]). Previously reported syntheses include 4-hydroxy-pyridine-2,6-dicarboxylic acid diethyl ester 2 from chelidamic acid 1 (yield: 75%; [16,36]), 3,3 -dinitro-4,4 -bis (N-aminomethyl-diphenyl)methane 6 (yield: 75%) and 4,4 -methanediyl-bis(N-methylbenzene-1,2-diamine) 7 (yield: 85%) [16,22,37], H 2 L POEt [22], Et 2 L C2 and H 2 L C2 [17], the phthalimide-fitted arm 10 [26], as well as the bromination of 2-[2-(2-methoxy-ethoxy)-ethoxy]-ethanol with PBr 3 to yield arm 8 [38,39], see scheme 2 for the numbering of the compounds. (c) 4-Methoxy-pyridine-2,6-dicarboxylic acid diethyl ester (3) This synthesis was adapted from Horvath et al [40].…”

“…Several modifications have been implemented to explore the versatility of the new probes: lengthening of the polyoxyethylene arms [20], modification of the aromatic backbone to shift the excitation wavelength towards the visible in [Ln 2 (L C5 ) 3 ]; [21], and substitution of the carboxylate coordinating units by phosphonate or phosphoester ones (e.g. H 2 L POEt ) [22]. Through all this work, H 2 L C2 emerged as being the best ligand, and suitable derivatization with carboxylic acid…”

Lighting up cells with lanthanide self-assembled helicates

“…We have therefore investigated whether derivatization of the pendant polyoxyethylene moieties and/or modification of the coordination unit would introduce some selectivity or at the least modify the localization of the helicates within the cells. 3 ] was chosen in place of the polyoxyethylenefitted one because its quantum yield is much larger (25% versus only 2.5%) [62]. All the helicates bearing different coordinating and terminal groups permeate into HeLa cells and stain the cytoplasm.…”