Brilliant Sm, Eu, Tb, and Dy chiral lanthanide complexes with strong circularly polarized luminescence

The synthesis, characterization, and luminescent behavior of trivalent Sm, Eu, Dy, and Tb complexes of two enantiomeric, octadentate, chiral, 2-hydroxyisophthalamide ligands are reported. These complexes are highly luminescent in solution. Functionalization of the achiral parent ligand with a chiral 1-phenylethylamine substituent on the open face of the complex in close proximity to the metal center yields complexes with strong circularly polarized luminescence (CPL) activity. This appears to be the first example of a system utilizing the same ligand architecture to sensitize four different lanthanide cations and display CPL activity. The luminescence dissymmetry factor, g(lum), recorded for the Eu(III) complex is one of the highest values reported, and this is the first time the CPL effect has been demonstrated for a Sm(III) complex with a chiral ligand. The combination of high luminescence intensity with CPL activity should enable new bioanalytical applications of macromolecules in chiral environments.     

Octadentate cages of Tb(III) 2-hydroxyisophthalamides: a new standard for luminescent lanthanide labels

The synthesis, structure, and photophysical properties of several Tb(III) complexes with octadentate, macrotricyclic ligands that feature a bicapped topology and 2-hydroxyisophthalamide (IAM) chelating units are reported. These Tb(III) complexes exhibit highly efficient emission (Φ(total) ≥ 50%), large extinction coefficients (ε(max) ≥ 20,000 M(-1) cm(-1)), and long luminescence lifetimes (τ(H(2)O) ≥ 2.45 ms) at dilute concentrations in standard biological buffers. The structure of the methyl-protected ligand was determined by single-crystal X-ray diffraction and confirms the macrotricyclic structure of the parent ligand; the amide groups of the methyl-protected cage compound generate an anion binding cavity that complexes a chloride anion. Once the ligand is deprotected, a conformational change generates a similar cavity, formed by the phenolate and ortho amide oxygen groups that strongly bind lanthanide ions. The Tb(III) complexes thus formed display long-term stability, with little if any change in their spectral properties (including lifetime, quantum yield, and emission spectrum) over time or in different chemical environments. Procedures to prepare functionalized derivatives with terminal amine, carboxylate, and N-hydroxysuccinimide groups suitable for derivatization and protein bioconjugation have also been developed. These bifunctional ligands have been covalently attached to a number of different proteins, and the terbium complexes' exceptional photophysical properties are retained. These compounds establish a new aqueous stability and quantum yield standard for long-lifetime lanthanide reporters.     

A Mild, Large-Scale Synthesis of 1,3-Cyclooctanedione: Expanding Access to Difluorinated Cyclooctyne for Copper-Free Click Chemistry

We report the large-scale synthesis of 1,3-cyclooctanedione in five steps with 29% yield. This molecule is a synthetic precursor to difluorinated cyclooctyne, which participates in a bioorthogonal copper-free click reaction with azides. The final step demonstrates the first successful application of the Wacker-Tsuji oxidation to form a cyclic 1,3-dione.     

Conformation-specific spectroscopy and populations of diastereomers of a model monolignol derivative: chiral effects in a triol chain

Single-conformation spectroscopy of two diastereomers of 1-(4-hydroxy-3-methoxyphenyl)propane-1,2,3-triol (HMPPT) has been carried out under isolated, jet-cooled conditions. HMPPT is a close analog of coniferyl alcohol, one of the three monomers that make up lignin, the aromatic biopolymer that gives structural integrity to plants. In HMPPT, the double bond of coniferyl alcohol has been oxidized to produce an alkyl triol chain with chiral centers at C(α) and C(β), thereby incorporating key aspects of the β-O-4 linkage between monomer subunits that occurs commonly in lignin. Both (R,S)- and (R,R)-HMPPT diastereomers have been synthesized in pure form for study. Resonant two-photon ionization (R2PI), UV hole-burning (UVHB)/IR-UV hole-burning (IR-UV HB), and resonant ion-dip infrared (RIDIR) spectroscopy have been carried out, providing single-conformation UV spectra in the S(0)-S(1) region (35200-35800 cm(-1)) and IR spectra in the hydride stretch region. Five conformers of (R,S)- and four conformers of (R,R)-HMPPT are observed and characterized, leading to assignments for all nine conformers. Spectroscopic signatures for α-β-γ, γ-β-α, and α-γ-β-π chains and two cyclic forms [(αβγ) and (αγβ)] of the glycerol side chain are determined. Infrared ion-gain (IRIG) spectroscopy is used to determine fractional abundances for the (R,S) diastereomer and constrain the populations present in (R,R). The two diastereomers have very different conformational preferences. More than 95% of the population of (R,R) configures the glycerol side chain in a γ-β-α triol chain, while in (R,S)-HMPPT, 51% of the population is in α-β-γ chains that point in the opposite direction, with an additional 21% of the population in H-bonded cycles. The experimental results are compared with calculations to provide a consistent explanation of the diastereomer-specific effects observed.     

Raman, infrared and computational analysis of genistein and its methoxy derivatives

Structural vibrational analyses of four 5-hydroxyisoflavones: genistein, biochanin A, prunetin and 4′,7-dimethoxygenistein have been performed using a combination of computational and experimental investigations of Raman and infrared spectra. Normal vibrational modes in the Raman and infrared spectra were assigned and correlated with the aid of calculations using density functional theory (DFT), adopting the B3LYP functional with the 6-31+G(d) basis set. As the four isoflavones differ by methoxy substitutions of the hydroxyl groups, shifts between phenol and anisole were also used to assist in the assignments. This work offers insight into some of the variations observed in the vibrational spectra of genistein and other isoflavones and lays the foundation for analysis of related compounds as well as further spectral analysis of the present isoflavones.     

Reduced basis catalogs for gravitational wave templates

We introduce a reduced basis approach as a new paradigm for modeling, representing and searching for gravitational waves. We construct waveform catalogs for nonspinning compact binary coalescences, and we find that for accuracies of 99% and 99.999% the method generates a factor of about 10-10(5) fewer templates than standard placement methods. The continuum of gravitational waves can be represented by a finite and comparatively compact basis. The method is robust under variations in the noise of detectors, implying that only a single catalog needs to be generated.     

Method of Continuous Variations: Applications of Job Plots to the Study of Molecular Associations in Organometallic Chemistry

Applications of the method of continuous variations (MCV or the Method of Job) to problems of interest to organometallic chemists are described. MCV provides qualitative and quantitative insights into the stoichiometries underlying association of m molecules of A and n molecules of B to form A_mB_n . Applications to complex ensembles probe associations that form metal clusters and aggregates. Job plots in which reaction rates are monitored provide relative stoichiometries in rate‐limiting transition structures. In a specialized variant, ligand‐ or solvent‐dependent reaction rates are dissected into contributions in both the ground states and transition states, which affords insights into the full reaction coordinate from a single Job plot. Gaps in the literature are identified and critiqued.