Synthetic, structural, electrochemical and solvent extraction studies of neutral trinuclear Co(II), Ni(II), Cu(II) and Zn(II) metallocycles and tetrahedral tetranuclear Fe(III) species incorporating 1,4-aryl-linked bis-beta-diketonato ligands

Uncharged complexes, formulated as trimeric metallocycles of type [M3(L(1))3(Py)6] (where M = cobalt(II), nickel(II) and zinc(II) and L(1) is the doubly deprotonated form of a 1,4-phenylene linked bis-beta-diketone ligand of type 1,4-bis(RC(O)CH2C(O))C6H4 (R = t-Bu)) have been synthesised, adding to related, previously reported complexes of these metals with L(1) (R = Ph) and copper(ii) with L(1) (R = Me, Et, Pr, t-Bu, Ph). New lipophilic ligand derivatives with R = hexyl, octyl or nonyl were also prepared for use in solvent extraction experiments. The X-ray structures of H2L(1) (R = t-Bu) and of its trinuclear (triangular) nickel(II) complex [Ni3(L(1))3(Py)6].3.5Py (R = t-Bu) are also presented. Electrochemical studies of H2L(1), [Co3(L(1))3(Py)6], [Ni3(L(1))3(Py)6], [Cu3(L(1))3], [Zn3(L(1))3(Py)6] and [Fe4(L(1))6] (all with R = t-Bu) show that oxidative processes for the complexes are predominantly irreversible, but several examples of quasireversible behaviour also occur and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as involving metal-centred oxidations. The reduction behaviour for the respective metal complexes is not simple, being irreversible in most cases. Solvent extraction studies (water/chloroform) involving the systematic variation of the metal, bis-beta-diketone and heterocyclic base concentrations have been performed for cobalt(II) and zinc(II) using a radiotracer technique in order to probe the stoichiometries of the respective extracted species. Significant extraction synergism was observed when 4-ethylpyridine was also present with the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies demonstrated a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).     

Stabiliser diffusion in long-term pressure tested polypropylene pipes analysed by IR microscopy

Pipes of random polypropylene was (PP-R) were hydrostatic pressure tested and the distribution of the primary stabiliser, Irganox 1010, was measured in the radial direction over the pipe wall by Infrared (IR) microscopy. Parabolic concentration profiles of the stabiliser develop during testing indicating a loss of stabiliser, at both the inner and outer pipe walls. Raising the temperature of the water bath leads to a uniformly accelerated loss of stabiliser. An increase of the hoop stress accelerates the stabiliser migration at the inner pipe wall.The concentrations of Irganox 1010 averaged over the pipe wall as determined by IR microscopy were in excellent agreement with those obtained from High Performance Liquid Chromatography and Oxidation Induction Time (OIT) analysis. Diffusion constants were calculated from the stabiliser concentration profiles based on the Fickian equations using appropriate initial and boundary conditions. A literature value is compared to these experimental results. The developed IR technique allows monitoring the stabiliser migration faster and more reproducibly than the conventional approach by manual abrasion of layers and measurement of the OIT. Additionally, this brings a tremendous improvement with regard to spatial resolution. As a result the impact of hoop stress and extrusion rate on the migration of stabiliser in PP-R pipes can be shown for the first time.     

Concluding the Amyloid Formation Pathway of a Coiled‐Coil‐Based Peptide from the Size of the Critical Nucleus

The size of the critical nucleus acting as intermediate in the amyloid formation of a model peptide is calculated. The theoretical approach is based on experimentally determined amyloid formation rates and gives new insights into the amyloid formation pathway.     

Basin hopping simulations for all-atom protein folding

We investigate different protocols of the basin hopping technique for de novo protein folding. Using the protein free-energy force field PFF01 we report the reproducible all-atom folding of the 20-amino-acid tryptophan-cage protein [Protein Data Bank (PDB) code: 112y] and of the recently discovered 26-amino-acid potassium channel blocker (PDB code: 1wqc), which exhibits an unusual fold. We find that simulations with increasing cycle length and random starting temperatures perform best in comparison with other parametrizations. The basin hopping technique emerges as a simple but very efficient and robust workhorse for all-atom protein folding.     

Speciation of arsenic of liquid and gaseous emissions from soil in a microcosmos experiment by liquid and gas chromatography with inductively coupled plasma mass spectrometer (ICP-MS) detection

Gas chromatography and high-performance liquid chromatography coupled to a double focusing sectorfield ICP-MS as sensitive element specific detector are used for the speciation of arsenic of liquid and gaseous emissions from soil samples, which were equilibrated in a microcosmos experiment. Speciation of liquid samples was performed by HPLC and hydride generation was used as introduction system to ICP-MS. An online prereduction step was introduced to enhance the sensitivity for As(V). A home-built and laboratory-ready transfer line from GC to ICP-MS is presented and quantification of As in gaseous emissions was performed by external calibration via hydride generation. The microcosmos experiment revealed only low production rates of organoarsenic compounds and reflected a limited capability of the biovolatilization experiment for the simulation of natural systems. Received: 2 December 1998 / Revised: 3 February 1999 / Accepted: 5 February 1999     

Furfural and 5-Hydroxymethylfurfural Production from Sugar Mixture Using Deep Eutectic Solvent/MIBK System

Choline chloride (ChCl) / glycolic acid (GA) deep eutectic solvent (DES) media with high water content but without any additional catalyst are introduced in furfural and 5-hydroxymethylfurfural (HMF) production. The effects of water content, reaction time, and reaction temperature are investigated with two feedstocks: a glucose/xylose mixture and birch sawdust. Based on the results, 10 equivalent quantities of water (32.9 wt.%) were revealed to be beneficial for conversions without rupturing the DES structure. The optimal reaction conditions were 160 °C and 10 minutes for the sugar mixture and 170 °C and 10 minutes for birch sawdust in a microwave reactor. High furfural yields were achieved, namely 62 % from the sugar mixture and 37.5 % from birch sawdust. HMF yields were low, but since the characterization of the solid residue of sawdust, after DES treatment, was revealed to contain only cellulose (49 %) and lignin (52 %), the treatment could be potentially utilized in a biorefinery concept where the main products are obtained from the cellulose fraction. Extraction of products into the organic phase (methyl isobutyl ketone, MIBK) during the reaction enabled the recycling of the DES phase, and yields remained high for three runs of recycling.     

A sulfonated calix[4]resorcinarene with α-methyl-l-prolinylmethyl groups as a water-soluble chiral NMR solvating agent

A water-soluble calix[4]resorcinarene containing α-methyl-l-prolinylmethyl groups was investigated as a chiral NMR solvating agent. Substrates form complexes by insertion of the aromatic ring into the cavity of the calix[4]resorcinarene. Amino acid derivatives with phenyl or indole rings, ammonium substrates with pyridyl, indane or dihydroindole rings, and phenyl-containing substrates with carboxylic acid and/or hydroxyl groups were studied. The effectiveness of the α-methyl-l-prolinylmethyl calix[4]resorcinarene is compared to similar reagents with proline and hydroxyproline moieties that have previously been reported. The α-methyl-l-prolinylmethyl derivative causes larger enantiomeric discrimination of one or more ¹H resonances than the previous systems for most of the substrates.     

In-field monitoring of cleaning efficiency in waste water treatment plants using two phenol-sensitive biosensors

Two amperometric biosensors based on the enzymes cellobiose dehydrogenase (CDH) and quinoprotein-dependent glucose dehydrogenase (GDH), have been applied for monitoring the phenolic content in water samples, collected at different stages of a waste water treatment process, thus representing different cleaning levels of two waste water treatment plants (WWTPs). The biosensor measurements were performed in-field, compared with the results obtained by liquid chromatography-mass spectrometry and were further correlated with the cleaning efficiencies of the WWTPs. The effect of several potentially interfering compounds on the sensor response was also studied.The general purpose of the study was to evaluate the potential use of biosensors, not as quantitative tools for phenol analysis, but rather as screening tools indicating a certain trend, i.e. compounds present or not present, and potential correlation with sample toxicity. It was found that the biosensors and LC-MS results were not quantitatively comparable, however, both sensors could follow the decrease of the phenol content from the influent, primary treated and effluent waters. In addition, the correlation between biosensor inhibition and sample toxicity is discussed.     

Chiral NMR discrimination of piperidines and piperazines using (18-crown-6)-2,3,11,12-tetracarboxylic acid

Enantiomeric discrimination is observed in the (1)H and (13)C NMR spectra of piperidines and piperazines in the presence of (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid. The amines are protonated by the carboxylic acid groups of the crown ether to produce the corresponding ammonium and carboxylate ions. Association of the ammonium ion with the crown ether likely involves two hydrogen bonds with the crown ether oxygen atoms and an ion pair with the carboxylate anion. Methyl, hydroxymethyl, phenyl, carboxyl, pyridyl, and cyclohexyl substituent groups alpha to the nitrogen atom do not inhibit binding of the ammonium ion to the crown ether. The NMR spectra of piperidines with the stereogenic center alpha or beta to the nitrogen atom exhibit substantial enantiomeric discrimination. Dibasic substrates such as the piperizines are likely converted to their diprotonated form in the presence of the crown ether, and both nitrogen atoms appear to associate with the crown ether moiety.