C2- and Cs-symmetric diamidodichlorotitanium complexes: Syntheses, structures and 1-hexene polymerization catalysis

The complexes l-[CMe₂{CHMeN(2-Prⁱ-C₆H₄)}₂TiCl₂] (2) and (3), C₂- and C_s-symmetric analogues, respectively, of McConville’s C_2v hexene polymerization precatalyst (1), were prepared by high-dilution salt-elimination from the lithium amides and characterized spectroscopically and crystallographically. Complex 2, though less active than 1, was a highly active catalyst of polymerization of 1-hexene when activated by MAO. Complex 3 was inactive under similar conditions. NMR analysis confirmed that there were more mmmm pentads in polymer produced by 2 than in the statistically atactic material produced by 1, though the isotacticity index was not high. The results are interpreted in terms of an isotactic/atactic block structure, caused by syn/anti fluxion of the two 2-isopropylphenyl rings in 2. Kinetic profiles and polydispersities were consistent with a slow initiation step involving monomer, followed by rapid propagation, with some chain transfer to aluminium and only a small extent of β-hydride elimination. The rubber-like polymers were indistinguishable by thermal analysis from those prepared by Ziegler-Natta catalyst systems.     

Analysis of Mammalian Cell Cytoplasm with Electrophoresis in Nanometer Inner Diameter Capillaries

Capillary electrophoresis in 770 nanometer inner diameter capillaries coupled to electrochemical detection with an etched electrode matching an etched capillary (etched electrochemical detection) has been used with ultrasmall sampling to inject subcellular samples from intact single mammalian cells. Separations of cytoplasmic samples taken from rat pheochromocytoma cells have been achieved. As little as 8% of the total volume of a single cell has been sampled and analyzed. Dopamine has been identified and quantified in these PC12 cells using this technique. The average cytoplasmic level of dopamine in rat pheochromocytoma cells has been determined to be 240 ± 60 μM. The use of electrophoresis in 770 nanometer inner diameter capillaries with electrochemical detection to monitor cytoplasmic neurotransmitters at the single cell level can provide information about complex cellular functions such as neurotransmitter storage and synthesis.     

A comparison of electrochemical and Auger analysis of the surface composition of platinum-rhodium alloys

Values of the surface composition of platinum-rhodium alloys determined electrochemically, utilizing the potential of the oxygen desorption peak on cyclic voltammograms, have been compared with those obtained by Auger electron spectroscopy (a.e.s.). This comparison confirms that the electrochemical method is applicable to analysis of the surface of cycled as well as untreated homogeneous noble metal alloys. The composition profile in the surface region of cycled electrodes was determined by sputtering of the surface followed by a.e.s. measurements. The rhodium content was found to increase linearly with depth. The depth scale was established from analyses of the metal dissolved during potential cycling. Consideration of the differences between data obtained from the electrochemical and a.e.s. studies leads to the conclusion that the surface zone involved in chemisorption extends over a few atomic layers.     

Mass spectra of doubly charged ions

The mass spectra of biological molecules, whose molecular mass exceeds 10 kDa, invariably contain multiply charged ions. For example, a survey scan of a small protein will produce singly, doubly and triply protonated molecules, the intensity of the doubly charged species often being greater than that of the singly charged entity. Although the spectra resulting from doubly charged peptides have not previously been studied, collisional activation of such doubly charged species may result in significant additional information pertaining to molecular structure. The techniques employed to study ions originating from multiply charged species were linked scanning of constant B/E and tandem mass spectrometry, namely low collision energy spectra acquired on a BEQQ hybrid instrument. The methodology was applied to model compounds whose tandem mass spectrometry characteristics are well known, e.g. gramicidin S and angiotensin I. The results for the product ions of the [M + 2H]²⁺ species of the models were obtained which highlight the methodology required for high-mass materials.     

Probe molecule spectroscopy of NaCl aerosol particle surfaces

Excited-state absorption spectroscopy and ionization threshold measurements for coumarin 314 (C314) adsorbed to the surface of NaCl aerosols characterize the chemical environment of the particle surface as a function of relative humidity (RH). An atmospheric pressure flow of aerosol passes through an ionization cell where two-photon laser ionization of the adsorbed molecules produces a net charge on the particle. Monitoring this charge as a function of the laser wavelength produces either the absorption spectrum of the S(1) <-- S(0) transition or the ionization threshold. The wavelength of maximum absorption for the S(1) excited-state shifts from 448 nm for RH < 5% to 441 nm for RH = 60%, indicating that adsorbed water decreases the polarity of the surface. Similarly, the ionization threshold increases from 5.10 to 5.27 eV over a similar range of RH. The decrease in polarity is attributable to changes in the local electric field experienced by C314, which is on the order of 1 x 10(7) V/cm, and is correlated with changes in the surface topography. Using a continuum model, we estimate the contributions to the measured thresholds of the polarization response of the surface ions and the electric field and calculate an effective dielectric constant for the adsorbed water film. For a multilayer water coverage (RH = 65%), the effective dielectric constant is approximately 2.4. These results demonstrate that the changes in surface topography with adsorbed water are as important as direct water-solute interactions in determining the solvent character of the surface.     

STUDIES OF PHOSPHAZENES. PART VI.1 THE PREPARATION OF THE ISOMERIC TETRACHLOROBIS-ISOPROPYLAMINOCYCLOTRIPHOSPHAZATRIENES

Abstract

The three isomers of N₃P₃Cl₄(NHPr¹)₂ have been prepared and separated by gas-liquid chromatography. Their structures have been assigned on the basis of ¹H and ³¹P nmr data.     

Parallel radioisotope collection and analysis in response to the Fukushima release

In order to co-recycle neptunium, uranium and plutonium using the PUREX process, numerical simulations were used to investigate the behaviors of neptunium in the first solvent extraction cycle. Counter-current extraction experiments using a miniature mixer-settler were performed to verify the simulation. Calculated results based on experiments show that the concentrations of nitric and nitrous acid, saturation of uranium, flow ratio and residence time have important effects on the pathway of neptunium, and accumulation of neptunium may appear with the presence of uranium and plutonium.