On the Misleading Interpretation of the Properties of the f-Electron Elements

The aim of the paper is to elucidate the problem of the regular changes in the properties of f-elements represented by the double-double effect. It is pointed out that because of the half-filled shell and double-double effects the f-element properties cannot be plotted as a linear function of the L -quantum number, as suggested by Sinha [1][2].     

Proficiency testing of chloride content in different types of Portland cement

The accurate determination of chloride content in cement is a prerequisite for the production of high-quality concrete due to the damaging influence of free chloride ions on durability and safety of concrete constructions. The results for total chloride content in four different types of Portland cement provided by testing laboratories participating in an inter-laboratory comparison are presented. The data sets were evaluated by using different statistical methods. The laboratories exceeding critical values were signaled and sources of error were investigated. The precision parameters of the method were determined and the variance of the entire data set was apportioned among the sources of variation. The systematic differences between participating laboratories and heterogeneity of the cement samples were identified as major sources of variability of results. The ANOVA determined the intermediate precision parameters, which showed a low value for random errors resulting in good repeatability and high impact of sample and inter-laboratory difference on reproducibility of the method.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Interpreting conformational effects in protein nano-ESI-MS spectra

Nano-electrospray-ionization mass spectrometry (nano-ESI-MS) is employed here to describe equilibrium protein conformational transitions and to analyze the influence of instrumental settings, pH, and solvent surface tension on the charge-state distributions (CSD). A first set of experiments shows that high flow rates of N₂ as curtain gas can induce unfolding of cytochrome c (cyt c) and myoglobin (Mb), under conditions in which the stability of the native protein structure has already been reduced by acidification. However, it is possible to identify conditions under which the instrumental settings are not limiting factors for the conformational stability of the protein inside ESI droplets. Under such conditions, equilibrium unfolding transitions described by ESI-MS are comparable with those obtained by other established biophysical methods. Experiments with the very stable proteins ubiquitin (Ubq) and lysozyme (Lyz) enable testing of the influence of extreme pH changes on the ESI process, uncoupled from acid-induced unfolding. When HCl is used for acidification, Ubq and Lyz mass spectra do not change between pH~7 and pH 2.2, indicating that the CSD is highly characteristic of a given protein conformation and not directly affected by even large pH changes. Use of formic or acetic acid for acidification of Ubq solutions results in major spectral changes that can be interpreted in terms of protein unfolding as a result of the increased hydrophobicity of the solvent. On the other hand, Lyz, cyt c, and Mb enable direct comparison of protein CSD (corresponding to either the folded or the unfolded protein) in HCl or acetic acid solutions at low pH. The values of surface tension for these solutions differ significantly. Confirming indications already present in the literature, we observe very similar CSD under these solvent conditions for several proteins in either compact or disordered conformations. The same is true for comparison between water and water–acetic acid for folded cyt c and Lyz. Thus, protein CSD from water–acetic solutions do not seem to be limited by the low surface tension of acetic acid as previously suggested. This result could reflect a general lack of dependence of protein CSD on the surface tension of the solvent. However, it is also possible that the effect of acetic acid on the precursor ESI droplets is smaller than generally assumed.     

Prospect of determining copper sulfide nanoparticles by voltammetry: A potential artifact in supersaturated solutions

Certain natural waters appear to contain copper sulfide (Cu_xS) nanoparticles in nanomolar concentrations (as Cu). These nanoparticles have been tentatively identified by the characteristic pH below which they deposit sulfide onto Hg electrodes. A proposed alternate approach to studying Cu_xS nanoparticles relies on their hydrophobicity, which causes them to sorb to Hg electrodes; there they can undergo reduction at −0.9 to −1.1 V vs. Ag/AgCl. However, solutions supersaturated with respect to Cu sulfide phases also form Cu_xS directly at Hg electrode surfaces. The voltammetric reduction peaks obtained from these deposits are not clearly distinguishable from those obtained from sorbed nanoparticles. Surface formation of Cu_xS, which appears to be limited to approximately two layers, involves a reaction between Cu amalgam and electrodeposited HgS. Surface-formed Cu_xS could be problematic in studies of Cu_xS nanoparticles, but this obstacle can be avoided by conducting voltammetric accumulations at potentials too negative for HgS electrodeposition (e.g. −0.85 V). Electroreduction of surface-formed Cu_xS occurs by a two-dimensional instantaneous hole nucleation and growth process.     

Analysis of European oak bark beetle (Scolytus intricatus) extracts using hyphenated and chiral chromatography techniques

Two bioactive compounds, viz. 4-methylheptan-3-ol (I) and 4-methylheptan-3-one (II) have been identified in European oak bark beetle (Scolytus intricatus) extracts by gas chromatography coupled with mass spectrometric and electroantennographic detector systems. Further examination of these compounds using gas chromatography on chiral stationary phases, as well as a comparison with optically active standards proved the absolute configuration of the identified compounds to be (3R,4S)-I and (S)-II. The discovery of (3R,4S)-I and (S)-II as insect-produced compounds in both sexes of S. intricatus constitutes the first reported occurrence in this species.     

Synthesis,NMR, and Computational Study of 1,2-Diethyl-3-(trimethylsilyl)cyclopropenylium Hexachloroantimonate

Preparation and ¹³C NMR identification of 1,2-diethyl-3-(trimethylsilyl)cyclopropenylium hexachloroantimonate (4) is described. The assignment of the NMR data was corroborated by calculating ¹³C NMR chemical shifts of the corresponding model ion 4M. The total stabilization of the parent cyclopropenylium ion 1 substituted by the silyl and the two methyl groups is found to be only slightly lower than stabilization of the trimethyl derivative. The computed NICS(1) parameters reveal that all of the examined ions possess substantial aromatic character.     

Poly(3,3′-dimethoxy-2,2′-bithiophene): Synthesis and comparison with poly(3-methoxythiophene)

A new electroactive polymer, namely poly(3,3′-dimethoxy-2,2′-bithiophene) has been prepared by voltammetric polymerization of 3,3′-dimethoxy-2,2′-bithiophene. Due to a different coupling pattern (equivalent to “head-to-head,” and “tail-to-tail” coupled alkoxythiophene rings), poly(3,3′-dimethoxy-2,2′-bithiophene) exhibits different voltammetric properties than the corresponding “head-to-tail” coupled polymer, i.e., poly(3-methoxythiophene). Poly(3,3′-dimethoxy-2,2′-bithiophene) gives very sharp oxidation and reduction peaks indicating an abrupt insulator to conductor transition. This hypothesis was corroborated by the studies of relative resistance as a function of electrode potential. Sharper and better-defined redox peaks may indicate better stereoregularity of poly(3,3′-dimethoxy-2,2′-bithiophene) as compared to poly(3-methoxythiophene) since in this compound the 5,5′-coupling positions are geometrically equivalent and no coupling defects are expected. © 1992 John Wiley & Sons, Inc.     

Rotation Planar Extraction and Medium-Pressure Solid—Liquid Extraction of Onion (Allium cepa)

JPC – Journal of Planar Chromatography – Modern TLC - Extraction of onion (Allium cepa L.) with 80:20 (v/v) methanol—water in water by rotation planar extraction (RPE) and medium-...     

X-ray, 31P CP/MAS,and single-crystal NMR studies,and 31P DFT GIAO calculations of inclusion complexes of bis[6-O,6-O'-(1,2:3,4- diisopropylidene-alpha-D-galactopyranosyl)thiophosphoryl] disulfide: the importance of C-H...S=P contacts in the solid state

Bis[6-O,6-O'-(1,2:3,4-diisopropylidene-alpha-D-galactopyranosyl) thiophosphoryl] disulfide shows a strong tendency to form inclusion compounds. The crystal and molecular structure of eight different solvates was established by X-ray analysis. The results indicate three different types of disulfide arrangements in the crystal lattice. By means of 31P CP/MAS NMR experiments the principal values delta 11, delta 22, and delta 33 of the 31P chemical shift tensor were obtained for each form. The orientation of its principal axes with respect to a molecular frame was investigated by means of 31P CP and single-crystal NMR for the complex with propan-2-ol. The principal axis 1 of both chemically equivalent phosphorus atoms is nearly parallel to the P-S bond and the principal axis 3 is very close to the P=S bond. DFT GIAO calculations of the model compound (EtO)2(S)P1SSP2(S)-(OEt)2 allowed assignment of the experimental chemical shift curves to the magnetically nonequivalent atoms P1 and P2. The maximum difference between calculated angles [symbol: see text] i-P-X)calcd and experimental angles [symbol: see text] i-P-X)exptl is 8.3 degrees and the rms distance 3.8 degrees (i = principal axes 1, 2, 3; X = S, -S-, -O1-, -O2-). The influence of C-H...S weak hydrogen bonding on phosphorus shielding was tested theoretically (31P DFT GIAO) employing the dimethoxythiophosphoryl disulfide.CH4 complex as a model compound. The sensitivity of 31P delta ii parameters to intermolecular forces is demonstrated.     

Thermoresponsive poly(N-isopropylacrylamide) copolymers: contact angles and surface energies of polymer films

Surface properties of poly(N-isopropylacrylamide) (PNIPAM) copolymer films were studied by contact angle measurements and optical and atomic force microscopy. We prepared a series of copolymers of N-isopropylacrylamide with N-tert-butylacrylamide (NtBA) in order of increasing hydrophobicity. The measurements of the advancing contact angle of water at 37 degrees C were hampered by the observation of a distinct stick/slip pattern on all polymers in the series with the exception of poly(NtBA) (PNtBA). We attributed this behavior to the film deformation by the vertical component of liquid surface tension leading to the pinning of the moving contact line. This was confirmed by the observation of a ridge formed at the pinned contact line by optical microscopy. However, meaningful contact (without the stick/slip pattern and with a time-independent advancing contact angle) angles for this thermoresponsive polymer series could be obtained with carefully selected organic liquids. We used the Li and Neumann equation of state to calculate the surface energy and contact angles of water for all polymers in the series of copolymers and van Oss, Chaudhury, and Good (vOCG) acid-base theory for PNtBA. The surface energies of the thermoresponsive polymers were in the range of 38.9 mJ/m2 (PNIPAM) to 31 mJ/m2 (PNtBA) from the equation of state approach. The surface energy of PNtBA calculated using vOCG theory was 29.0 mJ/m2. The calculated contact angle for PNIPAM (74.5 +/- 0.2 degrees ) is compared with previously reported contact angles obtained for PNIPAM-modified surfaces.