Investigation of the electrode reaction of EDTA and other complexanes at the lead dioxide electrode in aqueous solutions

Summary By using an electrodeposited lead dioxide electrode as an indicator electrode, the electrode reaction of ethylenediaminetetraacetic acid (EDTA) and other complexanes was investigated in unbuffered solution covering a pH range of about 2–12. Well-defined anodic and cathodic peaks, the heights of which increase with EDTA concentration, were observed. In an anodic single-sweep process, one anodic pre-peak appeared only at a pH higher than 4. It was found that in the cathodic process lead dioxide on the electrode is reduced to lead ion which reacts with EDTA to form the complex and in the anodic process the lead complex is oxidized again and deposited onto the electrode as lead dioxide. The height of the anodic and cathodic peaks is directly proportional to the EDTA concentration. The lead dioxide electrode seems to be useful for determining a chelating agent such as the EDTA-type complexanes.

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Untersuchung der Elektrodenreaktion von EDTA und anderen Komplexanen in wäßriger Lösung an der Bleidioxidelektrode

Zusammenfassung Mit Hilfe der elektrolytisch belegten PbO₂-Elektrode wurde die Elektrodenreaktion von EDTA (sowie von IDA, NTA und DTPA) in ungepufferter Lösung im pH-Bereich 2–12 untersucht. Gut ausgebildete anodische und kathodische Peaks wurden beobachtet, deren Höhe mit der EDTA-Konzentration zunimmt. Im anodischen single-sweep-Prozeß erschien nur ein anodischer Vorpeak bei pH>4. Es wurde festgestellt, daß bei dem kathodischen Vorgang PbO₂ an der Elektrode zu Pb-Ion reduziert wird, das mit EDTA unter Komplexbildung reagiert, während an der Anode der Pb-Komplex wieder oxidiert und PbO₂ abgeschieden wird. Die Peakhöhen sind der EDTA-Konzentration direkt proportional. Die PbO₂-Elektrode erscheint daher von Nutzen für die Bestimmung von Komplexanen vom Typ des EDTA.

     

High-performance liquid chromatographic determination of clioquinol and its conjugates in biological materials

A method has been established for the determination of clioquinol (C) and its glucuronide (CG) and sulfate (CS) in biological materials. C and its internal standard were extracted with benzene-pyridine from samples. CG and CS were also hydrolyzed to C and extracted by the same method. The extracts were evaporated to dryness and redissolved in methanol. The methanol solution was subjected to HPLC using a column packed with Iatrobeads 6cp.2010 and a UV monitor (254 nm). The mobile phase was 0.1 M citric acid-methanol-n-hexane (8:86:6). The detection limit of C and 1 nmole and its recovery was above 92%.     

Simultaneous determination of iron(II), iron(III), and titanium(IV) by flow injection analysis using kinetic spectrophotometry with Tiron

Summary Two flow injection analysis systems have been worked out for the simultaneous determination of Fe(III), Fe(II), and Ti(IV) based on the kinetic spectrophotometry with Tiron. The first system uses a silver reductor column and a single detector with two flow cells aligned in the same optical path to yield two peaks corresponding to (a) Ti(IV)-Tiron and (b) Ti(IV) plus total iron(III)-Tiron complexes. An another sample injection without the silver column yields a single peak which corresponds to Ti(IV) plus Fe(III)-Tiron complexes. With the two sample aliquot injections the system permits simultaneous determinations with throughput of 30 samples/h in the g to several tens g range of each species. The second system is a multidetection system with or without the silver reductor column using the same spectrophotometry with Tiron, in which the entrapment of the sample plug into a closed system allows its repetitive passage through a single detector. With the advantage of much simpler instrumentation, the system permits 6 samples/h to be analyzed for the three metal species with somewhat lower precisions than the first system.     

A Cyclized Helix‐Loop‐Helix Peptide as a Molecular Scaffold for the Design of Inhibitors of Intracellular Protein–Protein Interactions by Epitope and Arginine Grafting

The design of inhibitors of intracellular protein–protein interactions (PPIs) remains a challenge in chemical biology and drug discovery. We propose a cyclized helix‐loop‐helix (cHLH) peptide as a scaffold for generating cell‐permeable PPI inhibitors through bifunctional grafting: epitope grafting to provide binding activity, and arginine grafting to endow cell‐permeability. To inhibit p53–HDM2 interactions, the p53 epitope was grafted onto the C‐terminal helix and six Arg residues were grafted onto another helix. The designed peptide cHLHp53‐R showed high inhibitory activity for this interaction, and computational analysis suggested a binding mode for HDM2. Confocal microscopy of cells treated with fluorescently labeled cHLHp53‐R revealed cell membrane penetration and cytosolic localization. The peptide inhibited the growth of HCT116 and LnCap cancer cells. This strategy of bifunctional grafting onto a well‐structured peptide scaffold could facilitate the generation of inhibitors for intracellular PPIs.     

Three-Ni-atom cluster formed by sulfur adsorption on Ni(1 1 1)

Sulfur adsorption on Ni(1 1 1) at room temperature has been studied by scanning tunneling microscopy. Irregularly-shaped islands, which are aggregates of small particles, appear with troughs on (1 1 1) terraces. Estimating the number of small particles in the irregular islands and that of Ni atoms ejected through the formation of troughs, we find that each small particle contains three Ni atoms. A three-Ni-atom cluster is proposed, where three S atoms are adsorbed on 4-fold hollow sites formed on the sides of the cluster. The Ni₃S₃ cluster can assume two orientations on the (1 1 1) surface. We show that the apparently-irregular distribution of small particles is well understood by assuming the alternate orientation of neighboring Ni₃S₃ clusters and the slight energy difference between the two orientations of a single Ni₃S₃ cluster. Real-time observation of a Ni(1 1 1) surface under H₂S ambience reveals that small islands composed of three or four Ni₃S₃ clusters change their positions rapidly, preventing the simple growth of islands at the initially-nucleated positions.     

Quadruple-layered perovskite (CuCl)Ca2NaNb4O13

We will present the synthesis, structure and magnetic properties of a new quadruple-layered perovskite (CuCl)Ca₂NaNb₄O₁₃. Through a topotactic ion-exchange reaction with CuCl₂, the precursor RbCa₂NaNb₄O₁₃ presumably having an incoherent octahederal tliting changes into (CuCl)Ca₂NaNb₄O₁₃ with a 2a_p×2a_p×2c_p superstructure (tetragonal; a=7.73232(5) Å, c=39.2156(4) Å). The well-defined superstructure for the ion-exchanged product should be stabilized by the inserted CuCl₄O₂ octahedral layers that firmly connect with neighboring perovskite layers. Magnetic studies show the absence of long-range magnetic ordering down to 2 K despite strong in-plane interactions. Aleksandrov′s group theory and Rietveld refinement of synchrotron X-ray diffraction data suggest the structure to be of I4/mmm space group with in-phase tilting along the a and b axes, a two-tilt system (++0).     

1.3 μm range effectively cylindrical In0.53Ga0.47As/In0.52Al0.48As quantum wires grown on (2 2 1)A InP substrates by molecular beam epitaxy

Vertically coupled quantum wires (QWRs) have been made by alternately stacking nominally 3.6 nm thick In_0.53Ga_0.47As self-organized QWR layers and 1 nm thick In_0.52Al_0.48As barrier layers on (2 2 1)A-oriented InP substrates by molecular beam epitaxy. The surface of In_0.53Ga_0.47As QWR layers was corrugated at an amplitude of 1.1 nm and period of 27 nm, and lateral confinement potential is induced by their thickness modulation. The wavelength of photoluminescence (PL) from the stacked QWRs at 15 K becomes longer from 1220 to 1327 nm with increasing total number of stacked QWR layers, N_SL, from 1 to 9, while PL full-width at half-maximum is reduced from 22 to 8.6 meV. The PL intensity with the polarization parallel to the wire direction, I, is 1.30 times larger than that with the normal polarization, I, when N_SL=1. The PL intensity ratio, I/I, reaches as large as 4 when N_SL=9, indicating successful control of relative strength between vertical confinement and lateral confinement of carriers. The value of I/I obtained for the stacked QWRs with N_SL=9 is the same value as cylindrical QWRs have. The results indicate that effectively cylindrical QWRs with the best uniformity and 1.3 μm range emission were realized by stacking of self-organized QWR layers.