Iridium N-heterocyclic carbene complexes as efficient catalysts for magnetization transfer from para-hydrogen

While the characterization of materials by NMR is hugely important in the physical and biological sciences, it also plays a vital role in medical imaging. This success is all the more impressive because of the inherently low sensitivity of the method. We establish here that [Ir(H)(2)(IMes)(py)(3)]Cl undergoes both pyridine (py) loss as well as the reductive elimination of H(2). These reversible processes bring para-H(2) and py into contact in a magnetically coupled environment, delivering an 8100-fold increase in (1)H NMR signal strength relative to non-hyperpolarized py at 3 T. An apparatus that facilitates signal averaging has been built to demonstrate that the efficiency of this process is controlled by the strength of the magnetic field experienced by the complex during the magnetization transfer step. Thermodynamic and kinetic data combined with DFT calculations reveal the involvement of [Ir(H)(2)(η(2)-H(2))(IMes)(py)(2)](+), an unlikely yet key intermediate in the reaction. Deuterium labeling yields an additional 60% improvement in signal, an observation that offers insight into strategies for optimizing this approach.     

Substitution-closed pattern classes

The substitution closure of a pattern class is the class of all permutations obtained by repeated substitution. The principal pattern classes (those defined by a single restriction) whose substitution closure can be defined by a finite number of restrictions are classified by listing them as a set of explicit families.     

Simultaneous use of gas chromatography/ion trap mass spectrometry - electron capture detection to improve the analysis of bromodiphenyl ethers in biological and environmental samples

Bromodiphenyl ethers (BDEs) are a class of synthetic flame retardants and are widely present in the environment. Analysis of higher BDE congeners has proven to be a challenge. We report the development of a method that enhances their analysis by splitting the eluent of a gas chromatograph (GC) between an electron capture detector (ECD) and an ion trap mass spectrometer (ITMS): 1:10, ECD:ITMS. This allowed the quantitation of the lower molecular weight (MW) BDE congeners (Br1-Br7) with the ITMS and of the higher MW BDEs (Br8-Br10) with the highly sensitive ECD. The IT temperature, ionization mode, and MS/MS parameters (excitation amplitude and stability parameter) were optimized. This method took the advantages of the best detector for the different BDE homologues and was suitable for the analysis of BDEs in environmental and biological samples. Average recoveries were 52-112% for BDEs from spiked sand samples and 57-126% from spiked lard samples after accelerated solvent extraction followed by silica gel and alumina column clean-up. Average recoveries ranged from 51% to 130% for 13C-labeled BDEs spiked in the real and in matrix samples. The method detection limits for specific congeners were 0.18-120 pg/g of the BDEs in animal tissue samples, and 0.05-40 pg/g in soil and indoor dust samples. The utility of the method was demonstrated by analyzing actual harbor seal blubber, indoor dust and soil samples. The concentration of each BDE ranged from non-detectable (nd) to 41 ng/g in the dry soil sample, nd to 1042 ng/g in the indoor dust, nd to 15 ng/g wet weight in the Alaskan harbor seal blubber sample, and 0.02 to 11 ng/microL of the identified 23 of the 42 breakdown products from BDE-209 after zerovalent iron treatment. Finally, an interlaboratory comparison showed high correspondence between the GC/ITMS-ECD method and a GC high-resolution MS system for the analysis of BDEs in soil samples.     

Preparation and catalytic evaluation of ruthenium-nickel dendrimer encapsulated nanoparticles via intradendrimer redox displacement of nickel nanoparticles

Ru and Ru(x)Ni(30) dendrimer encapsulated nanoparticles (DENs) were synthesized using a redox-displacement method. DEN catalytic activity for the reduction of p-nitrophenol was evaluated and found to be dependent on the ratio of metals present.     

Role of strong electronic correlations in the metal-to-insulator transition in disordered LiAlyTi2-yO4

The compound LiAlyTi2-yO4 undergoes a metal-to-insulator transition for yc approximately 0.33. It is known that disorder alone is insufficient to explain this transition; e.g., a quantum site percolation model predicts yc approximately 0.8. We have included (Hubbard) electronic interactions into a model of this compound, using a real-space Hartree-Fock approach that achieves self-consistency at every site, and have found that for a Hubbard energy equal to 1.5 times the non-interacting bandwidth one obtains yc approximately 0.3. Further, with increasing Hubbard energy we find an Altshuler-Aronov suppression of the density of states, deltaN(epsilon) approximately square root /epsilon-epsilonF/, that reduces the density of states at the Fermi energy to zero at the critical Hubbard interaction. Using this ratio of correlation to hopping energy one is led to a prediction of the near-neighbor superexchange (J/t approximately 1/3) which is similar to that for the cuprate superconductors.     

Azaxanthones and azathioxanthones are effective sensitisers for europium and terbium luminescence

Several azaxanthone and azathioxanthone sensitising chromophores have been incorporated into macrocyclic ligands and form well-defined Eu and Tb complexes in polar media. Excitation of the heterocyclic chromophore in the range 330 to 382 nm leads to modest amounts of aromatic fluorescence and relatively efficient metal-based luminescence, with absolute metal-based quantum yields of up to 24% in aqueous media.     

New S/O-substituted ferrocenediyl ligands and their metal complexes

New unsymmetrical S/O 1,1'-disubstituted ferrocenediyl ethers and hydroxides have been synthesised. The coordination chemistry of 1-(methylsulfanyl)-1'-(methoxy)ferrocene has been investigated with palladium(II) and platinum(II) precursors. With palladium(II), a bis-mu-chloro-bridged dimeric complex was obtained with the ligand bound solely through the thioether donor group. With platinum(II), a bis-ligand trans-sulfur ligated complex was obtained and structurally characterised.     

A continuous-flow crushing device for on-line delta2H analysis of fluid inclusion water in speleothems

A method for the isotope analysis of fluid inclusion water in speleothem calcite is presented. The technique is based on a commercially available continuous-flow pyrolysis furnace (ThermoFinnigan TC-EA). The main adaptation made to the standard TC-EA configuration is the addition of a crusher and cold trap unit, which is connected to the carrier gas inlet at the top of the TC-EA reactor tube. A series of tests conducted with this device shows that: (1) standard waters, injected in the crusher, and passed through a cryogenic trapping routine, yield accurate delta(2)H values; (2) crushed cubes of speleothem calcite from two Peruvian caves with rather dissimilar seepage water delta(2)H values yield fluid inclusion delta(2)H values in good accordance with these drip waters. The clear advantage of this continuous-flow technique for fluid inclusion isotope analysis is that it is relatively quick compared with other techniques. Since the conditions of water sample introduction into the TC-EA are identical for delta(2)H and delta(18)O analysis, we expect that only limited adaptations to the extraction procedure are required to provide delta(18)O analysis of fluid inclusion samples with the same device.     

Vibrational Analysis of Coherent Anti-Stokes Resonance Raman Spectra from Bacteriorhodopsin Containing Isotopically Substituted Retinal Chromophores

Vibrational spectra recorded by coherent anti-Stokes resonance Raman scattering (CARS) from bacteriorhodopsin (BR) samples containing isotopically substituted (²H and ¹³C) retinal chromophores were measured using high repetition rate, low-power, picosecond pulsed excitation (λ₁=580 nm and λ_s=640±3 nm). These picosecond resonance CARS (PR/CARS) data were analyzed via third-order susceptibility relationships [χ ^{( 3 )} ] to obtain band origins, bandwidths, relative intensities, and electronic phase factors assignable to all significant vibrational Raman features in the 1490–1700 cm⁻¹ wavenumber region (the ethylenic stretching and C = N–H rocking or Schiff base modes). Isotopic substitution selectively places ²H at C₁₅, ¹³C singly at the C₁₀ position and at the C₁₄ position, and ¹³C simultaneously in positions of C₁₄ and C₁₅. Each isotopic BR sample was examined not only in H₂O, but also in D₂O, which places a ²H at the Schiff base nitrogen of the retinal. In addition, PR/CARS data were recorded from each isotopic BR sample following either light adaptation [i.e. the BR sample contained a single retinal isomer (all- trans , 15- anti or BR-570)] or dark adaptation [i.e. the BR sample contained a mixture of comparable amounts of retinal isomers (BR-570 and 13- cis , 15- syn or BR-548)]. Excellent agreement was found between the vibrational features observed by PR/CARS and those obtained from spontaneous resonance Raman measurements from the same isotopically substituted BR pigments. Several new vibrational features were also found from the PR/CARS data. Vibrational Raman data from three of the isotopic BR samples in D₂O are reported for the first time.