Chiral Eu Research Articles

Lanthanide directed self-assembly synthesis and photophysical evaluation of chiral Eu(iii) luminescent “half-helicates”

The reaction between the asymmetrical pyridyl ligands 3 (R) and 4 (S) and Eu(III) in CH(3)CN give rise to the formation of lanthanide luminescent 'half-helicates' in 1 : 3 (Ln:ligand) stoichiometry; the formation of which was observed by monitoring the changes in the ground and the excited state properties of the ligands, and in the time-resolved Eu-centred and the CPL emission.

Circularly Polarized Luminescence of Eu(III) Complexes with Point- and Axis-Chiral Ligands Dependent on Coordination Structures

Circularly polarized luminescence (CPL) of Eu(III) complexes with point- and axis-chiral ligands, [Eu((R/S)-BINAPO)(D-facam)(3)] ((R/S)-BINAPO, (R/S)-2,2'-bis(diphenylphosphoryl)-1,1'-binaphthyl; D-facam, 3-trifluoroacetyl-d-camphor), [Eu(BIPHEPO)(D-facam)(3)] (BIPHEPO, 2,2'-bis(diphenylphosphoryl)-biphenyl), [Eu(TPPO)(2)(D-facam)(3)] (TPPO, triphenylphosphine oxide), and [Eu((R)-BINAPO)(hfa)(3)] (hfa, 1,1,1,5,5,5-hexafluoropentane-2,4-dione) are reported. The photophysical properties of chiral Eu(III) complexes were characterized by circular dichroism spectra, emission spectra, emission quantum yields, emission lifetimes, and CPL spectra. The dissymmetry factors of their CPL (|g(CPL)|) at the magnetic-dipole transition of [Eu((R)-BINAPO)(D-facam)(3)], [Eu((S)-BINAPO)(D-facam)(3)], [Eu(BIPHEPO)(D-facam)(3)], and [Eu(TPPO)(2)(D-facam)(3)] were as high as 0.44, 0.34, 0.24, and 0.47, respectively, while [Eu((R)-BINAPO)(hfa)(3)] exhibited a relatively smaller dissymmetry factor (|g(CPL)| = 0.03). Their coordination structures were determined by the X-ray single-crystal analyses with shape-measure estimations. The photophysical relationship between the CPL properties and the electric transition probabilities of the chiral Eu(III) complexes is elucidated in terms of the coordination structures.

Circularly polarized luminescence from chiral Eu(III) Complex with high emission quantum yield

Luminescent Eu(III) complex with axis-chiral ligand, [Eu(( R)-BINAPO)(hfa) 3] (( R)-BINAPO: ( R)-2,2′-bis(diphenylphosphoryl)-1,1′-binaphthyl, hfa: 1,1,1,5,5,5-hexa-fluoropentanedione) was synthesized. Its emission quantum yield and the emission lifetime in acetone- d 6 were found to be 0.53 and 2.1 ms, respectively. The circularly polarized luminescence of the Eu(III) complex was also measured. The dissymmetry factor at the magnetic dipole transition (| g lum |) of [Eu(( R)-BINAPO)(hfa) 3] was found to be 0.03.

The measurement of the fluorescence detected circular dichroism (FDCD) from a chiral Eu(iii) system

The first measurement of the fluorescence detected circular dichroism (FDCD) from a chiral Eu(III) system, made possible by use of a variable liquid crystal circular polarizer, is reported.

Chirality-dependent excited-state quenching of Eu(dpa) 33− and Tb(dpa) 3+3 luminophores by diastereomeric structures of Δ-[Co( trans-1,2-cyclohexanediamine) 3] 3+ in aqueous solution

Four diastereomers of Δ-[Co( trans-1,2-cyclohexanediamine) 3] 3+ are examined as enantioselective excited-state quenchers of chiral Eu(dpa) 3 3− and Tb(dpa) 3 3− luminophores (dpadipicolinate dianion) in solution. In their quenching actions, all four diastereomers can distinguish between and interact differentially with the Λ and Δ enantiomers of the luminophores, but their enantiomeric preferences show interesting variations that may be correlated with chelate-ring conformational structure.

Determination of the optical purity and absolute configuration of threo-methylphenidate by proton nuclear magnetic resonance spectroscopy with chiral solvating agent

The direct determination of both the optical purity and absolute configuration of threo-methylphenidate has been accomplished in a simple, specific, and accurate manner by 1H-NMR spectroscopy. The enantiomeric resonances of threo-methylphenidate were effectively resolved in CDCl3 solution by the addition of the chiral solvating agents (R)-(-)- or (S)-(+)-2,2,2,-trifluoro-1-(9-anthryl)ethanol. Optical purities were determined on the basis of the intensities of the enantiomeric ester methyl proton resonances; the assignment of enantiomeric configurations was based on the relative field positions of these resonances and the examination of molecular models. The analysis of synthetic enantiomeric mixtures of threo-methylphenidate by the proposed NMR method resulted in assay values that agreed closely with the known quantities of each enantiomer in the mixtures tested. The mean +/- SD recovery value for the (2S,2'S)-(-)-threo-enantiomer, amounting to 99.9 +/- 0.6% of added (n = 10), correlated well with that previously found by 1H-NMR spectroscopy with a chiral Eu(III) shift reagent. However, the present approach is simpler, shows less reliance on reagents and solvents of a high purity, and does not require strict anaerobic working conditions.

Synthèse de “sulfahydatoïnes” chirales. Aspects stéréochimiques et protection régiospécifique.

The enantiospecific synthesis of N 2-benzyl-1-thia-2,5-diazolidin-3-one dioxides (sulfa-analogues of hydantoins) was carried out through two convergent pathways starting from chlorosulfonyl isocyanate (CSI) and chiral α-amino- and hydroxyesters. The intermediate carboxylsulfamides (containing “activated sulfamoyl group”) react easily in the Mitsunobu conditions to give ultimately the N-protected sulfa-hydantoins, or symmetric and dissymmetric sulfones of bis-N-aminoesters. The non-racemization during the cyclization of N-sulfamylaminoesters in alkaline conditions was established by chemical and spectroscopic methods (nmr with chiral Eu(hfc) 3).

1H NMR Spectroscopic Method with Chiral Eu(III) Shift Reagent for the Determination of the Enantiomeric Composition of Naproxen

Abstract A simple method based on the use of 1H NMR spectroscopy with chiral Eu(lll) shift reagent is described for the determination of (S)-(+)- and (R)-(-)-naproxen In the presence of each other. To enhance the coordinating affinity of the substrate for the lanthanide Ion, the sample was first derivatized to a mixture of methyl esters, which in the presence of Eu(hfc)3 formed short-lived diastereomeric complexes with sufficient nonequivalency In the 1H NMR spectrum. Optimum complexing conditions corresponded to concentrations of substrate and Eu(hfc)3 of 0.1 M each in CDCI3. In this matter, the enantiomeric ester-methyl protons and α-methyl protons yielded well-resolved resonance signals of utility in the measurement of enantiomeric compositions. Recovery studies demonstrated that the proposed method Is quantitative.

First experimental evidence of circularly polarized X-ray excited optical luminescence (XEOL) from chiral Eu 3+ complexes

The X-ray excited optical luminescence (XEOL) spectra of chiral Eu 3+ complexes are shown to exhibit a small degree of circular polarization and a Kuhn asymmetry factor which is quite comparable to what can be measured in conventional CPL spectroscopy. Additional selectivity could be introduced in EXAFS or XANES data by recording CP XEOL excitation spectra. This next step may require more brilliant X-ray sources, but will also imply a far better control of the radiation damages to the sample.

Optical purity determination of threo-methylphenidate hydrochloride using a chiral europium nuclear magnetic resonance (NMR) shift reagent.

A 1H-NMR spectroscopic method for the determination of the optical purity of threo-methylphenidate hydrochloride is presented. Complexation of the free-base form of the substrate with a chiral Eu(III) shift reagent resulted in two distinct enantiomeric ester methyl proton signals of utility for quantitative work. The accuracy of the method was validated by analyzing six synthetic mixtures of various proportions of (+)- and (-)-threo-methylphenidate. In addition to yielding assay results that were in close agreement with the known weights of each enantiomer in the mixture, and a mean recovery of the (-)-threo-enantiomer of better than 99.0%, the proposed method was capable of accurately measuring as little as 2% of one enantiomer in the presence of the other.

Stereoselectivity in the adduct formation between chiral Eu(III) β-diketone complexes and sulphoxides, sulphones and phosphate esters

Abstract The adduct formation which takes place when Eu(III) chelates of triflouroacetyl-d-camphor and heptaflourobutyryl-d-camphor bind substrates has been studied. Enhancement of Eu(III) luminescence as a function of substrate concentration has been used to obtain information on the nature of the chelate/substrate adducts, and the stereochemistry of the complexes was studied by means of circularly polarized luminescence (CPL) spectroscopy. While no optical activity can be measured for, the free chelates, formation of the adduct complexes usually led to the observation of very strong chirality even though the substrates were themselves achiral. It was concluded that adduct formation causes the bulky camphorato ligands to interact and adopt a configuration of lowest energy. This process perturbs the diastereomer ratios and yields a partial resolution of these very labile complexes.