Circularly Polarized Luminescence from an Eu(III) Complex Based on 2-Thenoyltrifluoroacetyl-acetonate and a Tetradentate Chiral Ligand.

A new chiral complex {[EuL(tta)2(H2O)]CF3SO3; L = N, N'-bis(2-pyridylmethylidene)-1,2-( R, R + S, S)-cyclohexanediamine; tta = 2-thenoyltrifluoroacetyl-acetonate} has been synthesized and characterized from a structural and spectroscopic point of view. The molecular structure in the solid state shows the presence of one chiral L, two tta, and one water molecules bound to the metal center. L and tta molecules can efficiently harvest and transfer to Eu(III) the UV light absorbed in the 250-400 nm range. The forced electric-dipole 5D0 → 7F2 emission band dominates the Eu(III) emission spectra recorded in the solid state and in solution of acetonitrile or methanol and the calculated intrinsic quantum yield of the metal ion is around 40-50%. The light emitted by the enantiopure complex shows a sizable degree of polarization with a maximum value of the emission dissymmetry factor ( glum) equal to 0.2 in methanol solution. If compared with the complex in the solid state or in acetonitrile solution, then the first coordination sphere of Eu(III) when the complex is dissolved in methanol is characterized by the presence of one CH3OH molecule instead of water. This fact is related to different Eu(III) CPL signatures in the two solvents.

Strongly Circularly Polarized Emission from Water-Soluble Eu(III)- and Tb(III)-Based Complexes: A Structural and Spectroscopic Study.

Water-soluble Eu(III) and Tb(III) complexes with N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetic acid (H2bpcd) have been synthesized and characterized in their racemic and enantiopure forms. The ligand has been designed to bind Ln(III) ions, providing a dissymmetric environment able to solicit strong chiroptical features while at the same time leaving a few coordination sites available for engaging further ancillary ligands. Potentiometric studies show that Ln(III) complexes have a relatively good stability and that at pH 7 the [Ln(bpcd)]+ species is largely dominant. DFT calculations carried out on the (S,S)-[Y(bpcd)(H2O)5]+ complexes (the closed-shell equivalents of [Eu(bpcd)(H2O)5]+ and [Tb(bpcd)(H2O)5]+) indicate that the two trans-O,O and trans-Npy,Npy configurations are equally stable in solution and present two coordinated water molecules. This is in agreement with the hydration number ∼2.6 determined by luminescence lifetime measurements on Tb(III) and Eu(III) complexes. A detailed optical and chiroptical spectroscopic characterization has been carried out and reveals that the complexes display an efficient luminescence in the visible spectral range accompanied by a strong CPL activity. A value for glum (around 0.1 on the top of the 546 nm band) for the Tb-based complex has been found. This is one of the highest glum values measured up to now for chiral Tb complexes. These results suggest that in principle Tb(bpcd)Cl is suitable to be employed as a CPL bioprobe for relevant analytes in aqueous media.

Tuning of the sensing properties of luminescent Eu(3+) complexes towards the nitrate anion.

A new family of imine-based ligands containing pyridine or furan as an aromatic donating ring [N,N'-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine, L1; N,N'-bis(2-furanylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine, L2 and N,N'-bis(2-thienylmethylidene)-1,2-(R,S)-cyclohexanediamine, L3] has been prepared in high yield by means of an easy synthetic protocol. Their trifluoromethansulphonate (CF3SO3(-), OTf(-)) Eu(iii) complexes have been employed for luminescence sensing of the NO3(-) anion in an anhydrous acetonitrile solution. Spectrophotometric titrations have been carried out to define the speciation in the solution and study the formation of ternary species occurring with the addition of NO3(-) anions. The sensing response towards this anion is strongly dependent on the nature of the ligand, the stoichiometry of the complexes and their concentration.

Synthesis, cytotoxicity and anti-cancer activity of new alkynyl-gold(I) complexes.

Alkynyl(triphenylphosphine)gold(i) complexes carrying variously substituted propargylic amines have been synthesized and fully characterized in solution and solid state. High levels of toxicity (i.e. micromolar range) were recognized for a series of cancer cell lines with particular emphasis on HT29, IGROV1, HL60 and I407. In particular the lead compound 3ab was identified as the most active compound in all cell lines (IC50: 1.7-7.9 µM).

Explaining fullerene dispersion by using micellar solutions.

An effective computational strategy to describe the dispersion of C60 by surfactants is presented. The influence of parameters such as surfactant concentration and molecular length on the final morphology of the system is explored to explain the experimental results and to understand the incorporation of C60 inside micelles. Both neutral and charged amphiphilic molecules are simulated. The long-discussed problem of the location of fullerenes in micelles is addressed and C60 is found in the hydrocarbon-chain region of the micelles. If the available hydrophobic space increases, C60 is localized in the inner part of the micellar core. Short, charged amphiphilic stabilizers are more efficient at dispersing fullerenes monomolecularly. Two different phases of C60 are observed as the C60/surfactant ratio varies. In the first, aggregates of C60 are entrapped inside the micelles, whereas, in the second, colloidal nanoC60 is formed with surfactants adsorbed on the surface.