Definitions of the degree of polarization of a light beam

A necessary and sufficient condition is derived for certain ad hoc expressions that are frequently used in the literature to represent correctly the degree of polarization of a light beam.     

Bis(imino)pyridine iron alkyls containing beta-hydrogens: synthesis, evaluation of kinetic stability, and decomposition pathways involving chelate participation

Bis(imino)pyridine iron alkyl complexes bearing beta-hydrogens, ((iPr)PDI)FeR (((iPr)PDI = 2,6-(2,6-(i)Pr2-C6H3N=CMe)2C5H3N; R = Et, (n)Bu, (i)Bu, CH2 (cyclo)C5H 9; 1-R), were synthesized either by direct alkylation of ((iPr)PDI)FeCl (1-Cl) with the appropriate Grignard reagent or more typically by oxidative addition of the appropriate alkyl bromide to the iron bis(dinitrogen) complex, ((iPr)PDI)Fe(N2)2 (1-(N2)2). In the latter method, the formal oxidative addition reaction produced ((iPr)PDI)FeBr (1-Br), along with the desired iron alkyl, 1-R. Elucidation of the electronic structure of 1-Br and related 1-R derivatives by magnetic measurements, structural studies and NMR spectroscopy established high spin ferrous compounds antiferromagnetically coupled to chelate radical anions. Thus, the formal oxidative process is bis(imino)pyridine ligand-based (one electron is formally removed from each chelate, not the iron) during oxidative addition. The kinetic stability of each 1-R compound was assayed in benzene-d6 solution and found to produce a mixture of the corresponding alkane and alkene. The kinetic stability of the iron alkyl complexes was inversely correlated with the number of beta-hydrogens present. For example, the iron ethyl complex, 1-Et, underwent clean loss of ethane over the course of three hours, whereas the corresponding 1-(i)Bu compound had a half-life of over 12 h under identical conditions. The mechanism of the decomposition was studied with a series of deuterium labeling experiments and support a pathway involving initial beta-hydrogen elimination followed by cyclometalation of an isopropyl methyl group, demonstrating an overall transfer hydrogenation pathway. The relevance of such pathways to chain transfer in bis(imino)pyridine iron catalyzed olefin polymerization reactions is also presented.     

Indenyl zirconium dinitrogen chemistry: N2 coordination to an isolated zirconium sandwich and synthesis of side-on, end-on dinitrogen compounds

Exposure of the isolable zirconocene sandwich compounds, (eta(5)-C5Me5)(eta(5)-C9H5-1-R(1)-3-R(2))Zr (R(1) = Me, (i)Pr, (t)Bu; R(2) = Me) to one atmosphere of dinitrogen resulted in N2 coordination. X-ray diffraction and NMR spectroscopy establish that the resulting dimeric dinitrogen compounds contain an unusual mu2,eta(2)-bridging indenyl ring and a weakly activated N2 ligand. N2 coordination from the isolable zirconium sandwich compounds is extremely sensitive to the number and size of the indenyl subsituents. Compounds bearing two [(i)Pr] or three methyl substituents are stable as eta(9) sandwich compounds for weeks under dinitrogen likely due to the inability to dimerize through a two-atom N2 bridge. Performing the reduction of (eta(5)-C5Me5)(eta(5)-C9H5-1-R(1)-3-R(2))ZrCl2 (R(1) = (i)Pr, (t)Bu; R(2) = Me; R(1) = R(2) = SiMe3) under an N2 atmosphere produced a different outcome; rare examples of side-on, end-on zirconium dinitrogen compounds were isolated and in one case, crystallographically characterized. Protonolysis studies with weak Br?nsted acids were used to evaluate the relative activation of the bridging dinitrogen ligands.     

Synthesis and Photophysical Properties of 3,6-Diphenyl-9-hexyl-9H-carbazole Derivatives Bearing Electron Withdrawing Groups

3,6-Diphenyl-9-hexyl-9H-carbazole derivatives bearing electron withdrawing groups, such as the formyl or the nitro-group in 4-positions of the phenyl substituents, were prepared and characterized. Their photophysical properties were evaluated and compared with those of the unsubstituted counterpart 3,6-diphenyl-9-hexyl-9H-carbazole. The electron withdrawing groups bearing compounds exhibited considerable red shifts of the absorption and the emission maxima. While 3,6-di(4-nitrophenyl)-9-hexyl-9H-carbazole emitted in the orange region of the visible spectrum with its emission maximum peaking at 585 nm, 3,6-di(4-formylphenyl)-9-hexyl-9H-carbazole gave a pure blue emission with a luminescence quantum yield of 95% peaking at 450 nm. Observed features were explained using quantum mechanical calculations and organic light emitting diodes using the formylphenyl substituted compound as emissive layer were built demonstrating the practical applicability of this class of compounds.     

Sediment extraction and clean-up for organic phosphorus analysis by electrospray ionization tandem mass spectrometry

A method to prepare NaOH sediment extracts for organic P compound analysis with electrospray ionization tandem mass spectrometry (ESI-MS-MS) was developed on natural samples. Ion exchange, rotary evaporation and mass cut-off filtering proved to be suitable for sample preparation. Samples were analyzed with ESI-MS-MS, and reproducibility and repeatability of the method was calculated. In addition, ³¹P-nuclear magnetic resonance spectroscopy (³¹P NMR) was used to measure recovery of different P compound groups such as orthophosphate (Ortho-P), orthophosphate monoesters (Monoester-P), orthophosphate diesters (Diester-P) and pyrophosphates (Pyro-P).

The developed sample preparation method resulted in an easy-to-spray liquid for the ESI-MS-MS instrumentation. The overall P recovery was 65% and ³¹P NMR showed that Diester-P, possibly in the form of DNA, was apparently lost through the filtering step most likely due to their size. Variances in the total intensities of the MS scans (relative standard deviation (R.S.D.) 35–54%) were for about 50% due to repeated MS runs. Covariances of the peaks in the MS spectra were calculated to be for about 30% due to the sample preparation procedure. Finally, with the ESI-MS-MS approach, 11 peaks in the mass spectra were found likely to represent phosphate containing compounds.     

Direct determination of celiprolol in human urine using on-line coupled ITP-CZE method with fiber-based DAD

The present work illustrated possibilities of column-coupling electrophoresis combined with DAD for the direct quantitative determination of trace drug (celiprolol, CEL) in clinical human urine samples. ITP, on-line coupled with CZE, served as an ideal injection technique (high sample load capacity, narrow and sharp drug zone). Moreover, the ITP provided an effective on-line sample pretreatment (preseparation, purification and preconcentration of the drug) producing analyte zone suitable for its direct detection and quantitation in CZE stage. Spectral DAD in comparison with single wavelength ultraviolet detection enhanced value of analytical information (i) verifying purity (i.e., spectral homogeneity) of drug zone (according to differences in spectrum profiles when compared tested and reference drug spectra) and (ii) indicating zones/peaks with spectra similar to the drug spectrum (potential structurally related metabolites). The characterization of trace analyte signals superposed on the baseline noise was more definite thanks to the application of background correction and smoothing procedure to the raw DAD spectra (producing relevant spectral response). The proposed ITP-CZE-DAD method was characterized by favorable performance parameters for CEL in urine matrices {e.g., the lower limit of quantification was 9.7 ng/mL, RSD and relative error of the determinations were lower than 3% (precision) and 1% (accuracy), respectively, analyte peak exhibited spectral homogeneity (reflecting separation selectivity), separation efficiency was 84,500 theoretical plates} and successfully applied in a trial pharmacokinetic study of CEL.     

Nitrene Insertion into C?C and C?H Bonds of Diamide Diimine Ligands Ligated to Chromium and Iron

The impact of redox non‐innocence (RNI) on chemical reactivity is a forefront theme in coordination chemistry. A diamide diimine ligand, [{‐CHN(1,2‐C₆H₄)NH(2,6‐iPr₂C₆H₃)}₂]ⁿ (n=0 to −4), (dadi)ⁿ, chelates Cr and Fe to give [(dadi)M] ([ 1 Cr(thf)] and [ 1 Fe]). Calculations show [ 1 Cr(thf)] (and [ 1 Cr]) to have a d⁴ Cr configuration antiferromagnetically coupled to (dadi)²⁻*, and [ 1 Fe] to be S=2. Treatment with RN₃ provides products where RN is formally inserted into the C C bond of the diimine or into a C H bond of the diimine. Calculations on the process support a mechanism in which a transient imide (imidyl) aziridinates the diimine, which subsequently ring opens.     

Fe(iv) alkylidenes via protonation of Fe(ii) vinyl chelates and a comparative M?ssbauer spectroscopic study

Treatment of cis-Me₂Fe(PMe₃)₄ with di-1,2-(E-2-(pyridin-2-yl)vinyl)benzene ((bdvp)H₂), a tetradentate ligand precursor, afforded (bdvp)Fe(PMe₃)₂ (1-PMe₃) and 2 equiv. CH₄, via C–H bond activation. Similar treatments with tridentate ligand precursors PhCHNCH₂(E-CHCHPh) ((pipp)H₂) and PhCHN(2-CCMe-Ph) ((pipa)H) under dinitrogen provided trans-(pipp)Fe(PMe₃)₂N₂ (2) and trans-(pipvd)Fe(PMe₃)₂N₂ (3), respectively; the latter via one C–H bond activation, and a subsequent insertion of the alkyne into the remaining Fe–Me bond. All three Fe(ii) vinyl species were protonated with H[BAr^F ₄] to form the corresponding Fe(iv) alkylidene cations, [(bavp)Fe(PMe₃)₂][BAr^F ₄] (4-PMe₃), [(piap)Fe(PMe₃)₃][BAr^F ₄] (5), and [(pipad)Fe(PMe₃)₃][BAr^F ₄] (6). Mössbauer spectroscopic measurements on the formally Fe(ii) and Fe(iv) derivatives revealed isomer shifts within 0.1 mm s^–1, reflecting the similarity in their bond distances.     

Coupling of Gaussian Beam and Finite Difference Solvers for Semiclassical Schrödinger Equations

In the semiclassical regime, solutions to the time-dependent Schrödinger equation for molecular dynamics are highly oscillatory. The number of grid points required for resolving the oscillations may become very large even for simple model problems, making solution on a grid intractable. Asymptotic methods like Gaussian beams can resolve the oscillations with little effort and yield good approximations when the atomic nuclei are heavy and the potential is smooth. However, when the potential has variations on a small length-scale, quantum phenomena become important. Then asymptotic methods are less accurate. The two classes of methods perform well in different parameter regimes. This opens for hybrid methods, using Gaussian beams where we can and finite differences where we have to. We propose a new method for treating the coupling between the finite difference method and Gaussian beams. The new method reduces the needed amount of overlap regions considerably compared to previous methods, which improves the efficiency.     

Use of Liquid Precursors for Diamond Chemical Vapor Deposition--The Effects of Mass Transport and Oxygen

Thermal plasma chemical vapor deposition of diamond-utilizing liquidfeedstock injection has been shown to yield higher mass deposition rates,larger crystal size, and thicker films when compared to the use of gaseousfeedstock for equivalent operating conditions. Increased mass transport ofthe activated precursor species across the substrate diffusion boundarylayer and the presence of oxygen in liquid precursors are investigated aspotential reasons for the observed results. Comparisons of the variousprecursor systems investigated in this study are based on crystal size andfilm thickness as a function of radial postion, area of deposit, totalmass deposition rate, and the observed liquid precursor droplet trajectorieswithin the deposition chamber using a laser strobe video system. The resultsindicate that the mass transport in both the liquid and gaseous precursorsystems is greatly improved by the use of an inert carrier gas. Further, theuse of a liquid versus a gaseous precursor does not seem toresult in higher total deposition rates when the operating conditions forboth have been optimized. Finally, the presence of oxygen in the liquidfeedstock system is found to be at least partly responsible for theincreased growth rate, which is observed when comparing the plainhydrocarbon precursor cases with the oxygenated liquid precursorcase.