Ernesto Brunet

Supramolecularly Organized Lanthanide Complexes for Efficient Metal Excitation and Luminescence as Sensors in Organic and Biological Applications

Using molecular shape for the functional control of multicomponent systems is one of the challenges in the field of supramolecular chemistry. The well-known emission in the visible region of certain lanthanide (III) salts has found a new dimension by the controlled assembly of supramolecular architectures to enshroud and excite the metal. The emission properties of these systems find applications as luminescent probes in sensing schemes, interaction with bio- molecules, or light conversion systems. Complexes of Tb(III) and Eu(III) can in some cases be highly luminescent and typically exhibit emission lifetimes in the millisecond range. These long lifetimes provide a facile means to detect biomolecules labeled with lanthanide from the short-lived background emission of biosystems. The strongly ionic nature of the bonding in solid lanthanide complexes results in coordination geometries that reveal a balance between electrostatic and steric demands. The inclusion of lanthanide guests into macrocycles, cryptands, cavi- tands and spherands had the purpose of shielding the metals from solvent molecules whose OH, NH or CH groups are able to heavily quench lanthanide luminescence (intensity and lifetime) by deactivation of their emissive levels by vi- bronic coupling. The literature on the various chemical systems, based on nitrogen heteroaromatic rings, used to sensitize lanthanides will be thoroughly reviewed including those molecules synthesized by the authors which displayed high quantum yield of lan- thanide emission.

Lanthanide complexes of polycarboxylate-bearing dipyrazolylpyridine ligands with near-unity luminescence quantum yields: the effect of pyridine substitution.

The title complexes displayed a marked dependence of their luminescence properties upon pyridine substitution. The ligand with the 4-carbamoyl-substituted pyridine showed a long-lived luminescence of near-unity quantum yield for Tb3- and quite reasonable values for Eu3+, Sm3+ and Dy3-, thus making it an excellent candidate for a luminescent probe to be attached to biomolecules by a peptide-like linkage.

Synthesis and photochemical properties of new coumarin-derived ionophores and their alkaline-earth and lanthanide complexes

Several new ionophores derived from crown ethers and iminodiacetic subunits attached to 3-aroylcoumarins have been synthesized and fully characterized. The alkaline-earth complexes of these new ligands were studied from their UV–visible and fluorescence data. Some systems displayed strong bathochromic shifts upon complexation with Mg 2+ that may make them useful signaling devices of this cation. The corresponding Eu 3+ and Tb 3+ chelates were easily formed and their photophysical properties were measured. In all the cases, lanthanide emission lifetimes were in the range of milliseconds albeit quantum yields were low. Possible energy-transfer mechanisms are discussed.

Synthesis and complexation properties of 3-Aroylcoumarin crown ethers. A new class of photoactive macrocycles.

Abstract Synthesis of fluoroionophores consisting of 3-benzoylcoumarins fused with crown ethers in two different modes are described. The resulting macrocycles bore emission properties strongly dependent on metal ions and coumarin substitution and may be therefore used as cation dependent fluorescence signaling systems or triplet sensitizers for lanthanide luminescence.

Macrocyclization of cyclic thiosemicarbazones with mercury salts

Abstract A new cyclic Schiff base L1H3 derived from benzil and thiosemicarbazide has been prepared in the presence of NaBH4. Reactions of the new molecule and the cyclic 5-methoxy-5,6-diphenyl-4,5-dihydro-2H-[1,2,4]triazine-3-thione L2H2 with mercury chloride and nitrate are reported. Complexes of 1:2 stoichiometry are obtained from L1H3, but the reactions from L2H2 yield complexes of the macrocyclic Schiff base 5,6,11,12-tetraphenyl-1,2,4,7,8,10-hexaaza-cyclododeca-4,6,10,12-tetraene-3,9-dithione L3H2, which indicates the macrocyclization of L2H2. A mechanism for the cyclization reaction based on the rupture of the C–N single bond in L2H2 is proposed. The electrochemical results of complex L3Hg makes it and its precursors, L2H2 and L3H2, outstanding candidates for mercury determination by appropriate electrode modification.

New chiral crown ethers derived from camphor and their application to asymmetric Michael addition. First attempts to rationalize enantioselection by AM1 and AMBER calculations

Abstract The synthesis of novel optically active crown ethers derived from (1 R )-(+)-camphor is described. The mechanism of their catalytic effect upon the Michael addition of phenylacetate to acrylate is discussed in terms of kinetic vs . thermodynamic control in the formation of the catalytic ion-pair complexes. The relative basicity of the complexes formed between the alkaline metals and the unprotonated chiral crown ethers plays an important role in the sterochemical outcome. AMBER and AM1 calculations support that the reaction in which the best e.e. (83%) is obtained proceeds under kinetic control.

New Macrobicycles Containing a Tetralactam Moiety: Template Synthesis and Study of their Binding with Lanthanides

Abstract The synthesis of macrobicyclic cryptands 1 , 2 from an 18-membered diazatetralactam and 6,6′-bis(bromomethyl)-2,2′-bipyridine or 2,6-bis(3-bromomethyl-1-pyrazolyl)pyridine has been investigated using various metal carbonates. The analysis of the distribution products by gel permeation chromatography showed that macrocyclization process was markedly conditioned by cation template effects. Optimum yields were obtained for Li + and Na + in the preparation of 1 and 2 , respectively. The cryptate structure of the corresponding complexes of Ln(III) (Ln=Eu, Tb, Gd) is discussed on the basis of spectroscopic and photophysical data.

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement ofγ-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.

Stereochemistry of organic sulphur compounds. part 13. Configurational assignment of diastereoisomers of 2-methylsulphinyl-1,2-diphenylethanol and of their O-methyl and O-acetyl derivatives

Abstract The synthesis, isolation and conformational analysis of the diastereomeric 2-methylsulphinyl-1,2-diphenylethanol and of its O -methyl and O -acetyl derivatives are reported. Chemical correlations and the study of the influence of solvent polarity changes on the coupling constants have permitted the configurational assignment. Lanthanide shift reagents have been used also. to this effect. The role of hydrogen bonding in the hydroxysulphoxides has been evaluated in diluted solutions by IR and NMR spectroscopy. A donor-acceptor interaction between oxygen and sulphur has been invoked to explain the differences in conformational behaviour between epimeric sulphoxides at sulphur atom.

Luminescence of lanthanides in covalently pillared zirconium phosphate

The luminescence of certain lanthanides can be obtained in full if the metals are chelated to a suitable chromophor (antenna effect). This phenomenon may be achieved within the body of a porous solid. There are many examples in the literature regarding this approach. The present paper accounts for our recent findings concerning lanthanide luminescence within zirconium phosphate, a quite versatile laminar inorganic salt. The strategy of building 3D scaffolds from the 2D inorganic salt and 1D organic pillars is detailed. The covalent attachment of conveniently functionalized chromophores to the lanthanide-containing inorganic lamellae renders solid materials that can be used as organic–inorganic phosphors. The creation of supramolecular chirality within these layered solids, something that have been easily achieved by us in previous work, may lead to a new kind of phosphor producing circularly polarized luminescence with high efficiency.