Analysis of polyethylenimine by spectrophotometry of its copper chelate

Polyethylenimine (PEI) forms a copper chelate with a N/Cu ratio of about 5 and with extinction coefficients of about 175 at 6350 A. and 4250 at 2694 A. Solutions of PEI-copper chelate obey Lambert's and Beer's laws and show increased optical density in the presence of chloride ion. Above pH 4.25, hydrogen ion has little effect. A comparison with the copper chelate of polyvinylamine suggests that PEI has a highly, branched structure. Analysis of PEI via its copper chelate is described.     

Conductance of a cobalt(II) terpyridine complex based molecular transistor: a computational analysis

A recent experiment, in which a molecular transistor based on the coordination chemistry of cobalt(II) and organic self-assembled monolayers is formed by means of self-aligned lithography,2 is analyzed with a computational approach. The calculations reveal that a complex involving two cobalt(II) ions bridged by acetate ions can effectively span the nanogap. This bridged complex is shown to be both more flexible and more conductive than the alternative structure involving a single cobalt(II) ion. The single cobalt(II) ion complex is the more stable structure in a nonconfined environment (i.e., in solution) but is found to be less effective at connecting the leads of the fabricated gap and is less likely to result in a conductive device.     

New methodological approach for the vanadium K-edge X-ray absorption near-edge structure interpretation: application to the speciation of vanadium in oxide phases from steel slag

This paper presents a comparison between several methods dedicated to the interpretation of V K-edge X-ray absorption near-edge structure (XANES) features. V K-edge XANES spectra of several V-bearing standard compounds were measured in an effort to evaluate advantages and limits of each method. The standard compounds include natural minerals and synthetic compounds containing vanadium at various oxidation state (from +3 to +5) and in different symmetry (octahedral, tetrahedral, and square pyramidal). Correlations between normalized pre-edge peak area and its centroid position have been identified as the most reliable method for determining quantitative and accurate redox and symmetry information for vanadium. This methodology has been previously developed for the Fe K edge. It is also well adapted for the V K edge and is less influenced by the standard choice than other methods. This methodology was applied on an "environmental sample," i.e., a well-crystallized leached steel slag containing vanadium as traces. Micro-XANES measurements allowed elucidating the microdistribution of vanadium speciation in leached steel slag. The vanadium exhibits an important evolution from the unaltered to the altered phases. Its oxidation state increases from +3 to +5 together with the decrease of its symmetry (from octahedral to tetrahedral).     

Relative intensity noise and frequency noise of a compact Brillouin laser made of As38Se62 suspended-core chalcogenide fiber

Relative intensity noise and frequency noise have been measured for the first time for a single-frequency Brillouin chalcogenide As38Se62 fiber laser. This is also the first demonstration of a compact suspended-core fiber Brillouin laser, which exhibits a low threshold power of 22 mW and a slope efficiency of 26% for nonresonant pumping.     

Core–Shell Structured Chitosan-Polyethylenimine Nanoparticles for Gene Delivery: Improved Stability,Cellular Uptake,and Transfection Efficiency

The delivery of nucleic acids relies on vectors that condense and encapsulate their cargo. Especially nonviral gene delivery systems are of increasing interest. However, low transgene expression levels and limited tolerability of these systems remain a challenge. The improvement of nucleic acid delivery using depolymerized chitosan–polyethylenimine DNA complexes (dCS-PEI/DNA) is investigated. The secore complexes are further combined with chitosan-based shells and functionalized with polyethylene glycol (PEG) and cell penetrating peptides. This modular approach allows to evaluate the effect of functional shell components on physicochemical particle characteristics and biological effects. The optimized ternary complex combines a core-dCS-linear PEI/DNA complex with a shell consisting of dCS-PEG-COOH, which results in improved nucleic acid encapsulation, cellular uptake and transfection potency in human hepatoma HuH-7cells and murine primary hepatocytes. Effects on transgene expression are confirmed in wild-type mice following retrograde intrabiliary infusion. After administration of only 100 ng complexed DNA, ternary complexes induced a high reporter gene signal for three days. It is concluded that ternary coreshell structured nanoparticles comprising functionalized chitosan can be used for in vitro andin vivo gene delivery.     

Cracking study of pentakis(dimethylamino)tantalum vapors by Knudsen cell mass spectrometry

Organometallic molecules are commonly used as gaseous precursors in Atomic Layer Deposition/Chemical Vapor Deposition (ALD/CVD) processes. However, the use of these molecules, which are generally thermally unstable at temperatures close to the deposition temperature, requires an understanding of their gas‐phase chemical behavior. The thermal cracking of the gaseous precursor, pentakis(dimethylamino) tantalum (PDMAT), generally adopted in the ALD/CVD TaN deposition processes, has been studied in the temperature range from 343 to 723K using a specific reactor coupled with a high‐temperature mass spectrometer. This reactor – built as tandem Knudsen cells – consists of two superimposed cells. The first stage reactor – an evaporation cell – provides an input saturated vapor flow operating from room temperature to 333K. The second stage cell, named the cracking cell, operated from 333 to 723K in the present study. Experiments showed the appearance of many gaseous species when the cracking temperature increased and, in particular, dimethylamine, corresponding to the saturated organic branches of PDMAT. Decomposition products of the HNC₂H₆ branch were observed at relatively high temperature, namely above 633K. This gas‐phase study – as for the preceding saturated one – shows the presence of oxygen‐containing molecules in PDMAT cracked vapor. Thus, it explains the systematic presence of oxygen contamination in the deposited TaN films observed in ALD/CVD industrial processes. Copyright © 2010 John Wiley & Sons, Ltd.     

Structural Studies of Two Isoelectronic Tetrakis Isocyano Complexes

Abstract  

Two isoelectronic tetrakis isocyano compounds, tetra(p-isocyanoanisole)nickel(0) and tetra(p-isocyanoanisole)copper(I) hexafluorophosphate were synthesized from nickel bis cyclooctadiene and copper (I) tetra acetonitrile hexafluorophosphate and the isonitrile, respectively, and their structures were determined. The nickel complex crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 9.6709(8), b = 15.2324(13), c = 19.0955(16) ? and Z = 4. The copper salt forms crystals with a tetragonal setting in P4/n with a = b = 15.8206(5), c = 6.5848(4) ? and Z = 2. Both complexes exhibit the approximate tetrahedral coordination environment expected for 18 valence electron complexes with soft σ-donor π-acceptor ligands. Packing in the nickel complex is dominated by weak π–π stacking, C–H···π_phenyl, and C–H···π interactions towards the isonitrile carbon and nitrogen atoms, and several slightly stronger C–H···O interactions. In the copper complex the presence of the PF₆ anion allows for the formation of stronger C–H···F interactions, and these in combination with π–π stacking and C–H···O hydrogen bonds dominate the packing.