The temperature dependence of the d-electron dipole strengths of cobalt(II) tetrahalides

The dipole strengths of the ⁴A₂ → ⁴T₁(F), ⁴T₁(P), d-electron transitions of the cobalt(II) tetrahalides are found to decrease with an increase in temperature, in agreement with a dynamic ligand-polarisation model for the absorption mechanism. The reduction in dipole strength is accounted for by a decrease in the coulombic coupling between the quadrupole moment of the d-electron transition of the metal ion and the transient electric dipole moment induced in the ligands, due to the anharmonic increase in the mean bond length and the progressively larger mean-square amplitudes of the bending modes of the complex ion in its ground electronic state as the temperature is raised.     

Formation of nanostructured polymer filaments in nanochannels

We describe the use of hard etching methods to create nanodimensional channels and their use as templates for the formation of polymer filament arrays with precise dimensional and orientational control in a single integrated step. The procedure is general as illustrated by the radical, coordination, and photochemical polymerizations that were performed in these nanochannels. The nanochannel templates (20 nm high, 20-200 nm wide, and 100 mum long) were fabricated by the combined use of electron-beam lithography and a sacrificial metal line etching technique. Radical polymerization of acrylates, metal-catalyzed polymerization of norbornene, and photochemical polymerization of 1,4-diiodothiophene were carried out in these nanochannels. The polymers grown follow the dimensions and orientation of the channels, and the polymer filaments can be released without breaking. The approach opens up the possibility of just-in-place manufacturing and processing of patterns and devices from nanostructured polymers using well-established polymer chemistry.     

XeAuF

XeAuF has been detected and characterized using microwave rotational spectroscopy. It was prepared by laser ablation of Au in the presence of Xe and SF(6), and stabilized in a supersonic jet of Ar. The spectrum was measured with a cavity pulsed jet Fourier transform microwave spectrometer, in the frequency range 6-26 GHz. Rotational constants, centrifugal distortion constants, and (131)Xe and (197)Au nuclear quadrupole coupling constants have been evaluated. The molecule is linear, with a short XeAu bond (2.54 A), and is rigid. The (131)Xe nuclear quadrupole coupling constant (NQCC) is large (-135 MHz). The (197)Au NQCC differs radically from that of uncomplexed AuF. The results are supported by those of ab initio calculations which have given an XeAu dissociation energy approximately 100 kJ mol(-1), plus Mulliken and natural bond orbital populations, MOLDEN plots of valence orbitals, and an energy density distribution. All evidence is consistent with XeAu covalent bonding in XeAuF.     

Stereoselective synthesis of erythro-β-hydroxy carboxylic acids via iron acyl complexes

β-Hydroxy acyl ligands bound to (η⁵-C₅H₅)Fe(CO)(PPh₃) are stereoselectively alkylated on the α-carbon to give after decomplexation erythro-β-hydroxy carboxylic acids.     

Bioluminescent detection of insect pheromones using an enzyme-based flow injection analysis system

The combination of flow injection analysis with chemiluminescent detection is shown to provide extremely selective and sensitive detection of insect pheromones which possess an aldehyde moiety. The flow injection analysis system provides reproducible control of both the reaction chemistry and the sample introduction process. Microliter volume samples can be precisely handled and analyzed with this experimental configuration. The detection system is based on the luciferase-catalyzed oxidation of reduced flavin mononucleotide which occurs in the presence of aldehydes with carbon backbones of between 14 and 16 carbons. A limit of detection of 3 fmol of tetradecyl aldehyde is demonstrated and the system is shown to be insensitive to the presence of various organic solvents up to concentrations of approximately 10%. The key experimental variables which control sensitive detection of pheromone at the femtomole level with be investigated and discussed.     

An evaluation of the performance of porous polymer monolith assisted electrospray

A novel electrospray interface, which has distinct advantages over conventional pulled silica emitters, has been developed. This novel interface can be easily fabricated by forming a porous polymer monolith (PPM) at the end of a fused-silica capillary that facilitates a stable electrospray over a wide range of flow rates with only a modest increase in back-pressure. A comparison was made between the PPM-assisted electrospray and a commercial nanosprayer in terms of sensitivity, stability and robustness. A PPM-filled electrospray tip produced a day-to-day signal variation of 23% relative standard deviation (RSD) over a 3-day period when spraying a 1.0 microM test peptide solution. Furthermore, three different capillaries fabricated by the same process produced a signal variation of 17% RSD, indicating that the fabrication process shows good reproducibility. The multiple flow paths of the PPM function to split the flow and reduce clogging. Even following the accumulation of debris after prolonged use, a stable spray could still be generated with the PPM-filled capillary while the commercial nanosprayer ceased to function properly. In terms of sensitivity, PPM-assisted electrospray showed an enhancement in sensitivity at infusion flow rates between 100 to 1000 nL/min while commercial nanosprayers performed slightly better at flow rates below 100 nL/min. A sample purification step can be combined with the PPM-assisted sprayer, using the PPM as a stationary phase to desalt and preconcentrate samples prior to mass spectrometric detection.     

The asymmetric synthesis of trans-substituted cyclopropanecarboxylic acid derivatives

The asymmetric synthesis of trans-substituted cyclopropanecarboxylic acid derivatives is achieved via stereoselective nucleophilic methylene transfer to E-,β-unsaturated acyl ligands bound to the iron chiral auxiliary [(η⁵-C₅H₅)Fe(CO)(PPh₃)].     

Maleation of poly(3,4‐epoxy‐1‐butene) for accelerated crosslinking in the presence of a redox catalyst

Accelerated crosslinking of novel poly(3,4‐epoxy‐1‐butene) (3,4‐PEPB) oligomers in the presence of a cobalt‐based redox catalyst was investigated. Previous studies using model compounds, 3,4‐dimethoxy‐1‐butene and 1,4‐dimethoxy‐2‐butene, suggested that maleation of hydroxyl‐terminated 3,4‐PEPB oligomers would result in more rapid crosslinking in thin films. Novel maleated oligomers offered a unique combination of both electron‐rich and electron‐poor olefinic sites, and quantitative maleation significantly increased the crosslinking rate of 3,4‐PEPB. Efficient copolymerization between terminal maleate groups and olefinic groups in the repeating unit was proposed to account for accelerated crosslinking rates. Furthermore, the addition of novel reactive diluents, such as maleic acid mono‐ethyl ester, also effectively improved the 3,4‐PEPB crosslinking rate. Sol fraction measurements as a function of coating thickness revealed that the crosslinking rate versus oxygen diffusion was less significant for the maleated oligomers because of the presence of reactive electron‐poor olefins. Sol fractions were constant for catalyst concentrations greater than 0.25–0.50 wt % (as compared with oligomer feed). This observation suggested that a redox process was not a dominant factor in determining crosslinking rates at various experimental conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2789–2798, 2002     

Metabolic profiling of normal and hypertensive rat kidney tissues by hrMAS-NMR spectroscopy

Intact kidney tissue samples of normal and spontaneously hypertensive rats (SHRs) were analyzed by hrMAS-NMR spectroscopy and principal component analysis (PCA). Radial components (cortex, outer stripe of the outer medulla, inner stripe of the outer medulla, and papilla) were sampled from various regions across the kidney from multiple animals in order to establish inter- and intra-animal variability. The effects of temperature were also measured. Papilla was differentiated from the other tissue types, and this variation by tissue type was greater than the effect of temperature on the samples (spectra were compared from samples at 2 and 30 °C). This study also revealed long term stability issues of tissue storage at -80 °C. The PCA showed that the greatest differentiation between normal rats and SHRs was found in the cortex and the regions in the NMR spectra that were correlated with this variation were identified.Abbreviations hrMAS High-resolution magic angle spinning - NMR Nuclear magnetic resonance - PCA Principal component analysis - CSA Chemical shift anisotropy - DD Dipolar coupling - SHR Spontaneously hypertensive rat