Underwater Electrical Discharges: Temperature,Density and Basic Instability Features with Different Anode Materials

Plasma Chemistry and Plasma Processing - Plasma temperature, density and arc dynamics have been investigated in underwater arc discharges under different anodic environments. Distinct differences...     

Contributions to cytochrome c inner- and outer-sphere reorganization energy

Cytochromes c are small water-soluble proteins that catalyze electron transfer in metabolism and energy conversion processes. Hydrogenobacter thermophilus cytochrome c₅₅₂ presents a curious case in displaying fluxionality of its heme axial methionine ligand; this behavior is altered by single point mutation of the Q64 residue to N64 or V64, which fixes the ligand in a single configuration. The reorganization energy (λ) of these cytochrome c₅₅₂ variants is experimentally determined using a combination of rotating disc electrochemistry, chronoamperometry and cyclic voltammetry. The differences between the λ determined from these complementary techniques helps to deconvolute the contribution of the active site and its immediate environment to the overall λ (λ_Total). The experimentally determined λ values in conjunction with DFT calculations indicate that the differences in λ among the protein variants are mainly due to the differences in contributions from the protein environment and not just inner-sphere λ. DFT calculations indicate that the position of residue 64, responsible for the orientation of the axial methionine, determines the geometric relaxation of the redox active molecular orbital (RAMO). The orientation of the RAMO with respect to the heme is key to determining electron transfer coupling (H_AB) which results in higher ET rates in the wild-type protein relative to the Q64V mutant despite a 150 mV higher λ_Total in the former.

Efficient delocalization of the redox-active molecular orbital (RAMO) in HtWT results in an increase in H_AB value which in turn accelerates the electron transfer (ET) rate in spite of the higher reorganization energy (λ) than the HtQ64V mutant.     

Curve reconstruction: Connecting dots with good reason

Curve reconstruction algorithms are supposed to reconstruct curves from point samples. Recent papers present algorithms that come with a guarantee: Given a sufficiently dense sample of a closed smooth curve, the algorithms construct the correct polygonal reconstruction. Nothing is claimed about the output of the algorithms, if the input is not a dense sample of a closed smooth curve, e.g., a sample of a curve with endpoints. We present an algorithm that comes with a guarantee for any set P of input points. The algorithm constructs a polygonal reconstruction G and a smooth curve Γ that justifies G as the reconstruction from P.     

Measurement of quadrupole moment of the 134 keV level in <Superscript>131</Superscript>Cs

The time differential as well as time integral perturbed angular correlations of the 486-134 keV cascade in ¹³¹Cs have been studied in a polycrystalline BaSO₄ powder source using a HPGe-BaF₂ detector system. The fundamental quadrupole frequency for the 134 keV level has been found to be ω₀= (4.4 ± 0.4) × 10⁷ rad/s. From a comparison of the quadrupole frequencies of this level and that of the 81 keV level in ¹³³Cs, measured earlier in the same crystalline environment of the source, the absolute value of the quadrupole moment of the 134 keV level in ¹³¹Cs has been found to be 0.022 ± 0.002 b. This value of the quadrupole moment is reported for the first time and compared with the value predicted theoretically within the unified nuclear model with intermediate coupling. Received: 21 October 1999 / Revised version: 22 December 1999     

(1S*,2S*,4S*,5S*)‐Cyclo­hexa­ne‐1,2,4,5‐tetrol monohydrate

In the title compound, C₆H₁₂O₄·H₂O, 1,4/2,5‐cyclo­hexane­tetrol and water mol­ecules are seen to possess twofold symmetry. All four hydrox­yl groups of the tetrol participate in extensive inter­molecular O—H⋯O hydrogen bonding to form mol­ecular tapes propagating along the a axis. Translationally related tapes along the c axis are held together by four coordinated water mol­ecules.     

Electrometric studies on the precipitation of thorium hydroxide

Summary On the ageing of thorium hydroxide, there is considerable change in the p_H of the system. Increase of p_H is a result of release of hydroxyl ions and decrease of p_H indicates the release of hydrogen ions from the adsorbent. Ageing before inflexion point especially with larger alkali leads to the coagulation of thorium hydroxide which eventually increases the p_H of the medium.

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Zusammenfassung Mit Alterung von Thoriumoxid treten betr?chtliche ?nderungen im p_H der Systeme auf. Der Anstieg des p_H ist ein Ergebnis des Freiwerdens von HydroxylIonen, die Abnahme zeigt das Freiwerden von Wasserstoff-Ionen vom Adsorbenten an. Alterung unterhalb des Inflexionspunktes, besonders mit gr?\erem Alkali-Gehalt, führt zur Koagulation des Thoriumhydroxids, was schlie\lich das p_H des Mediums vergr?\ert.

     

Synthesis and metal ion uptake studies of chelating resins derived from formaldehyde-furfuraldehyde condensed phenolic Schiff bases of 4,4'-diaminodiphenylether and o-hydroxyacetophenone

Two new chelating resins (o-HAP-DDE-HCHO and o-HAP-DDE-FFD), having multiple functional groups are synthesised by condensing the Schiff base of o-hydroxyacetophenone-4,4′-diaminodiphenylether (o-HAP-DDE) with formaldehyde and furfuraldehyde, respectively. The extent of loading of metal ions Cu(II) and Ni(II) was studied in both competitive and non-competitive conditions varying the time of contact, metal ion concentration and the pH of the reaction medium. Both the resins are able to preferentially remove Cu(II) from the mixture of Cu(II) and Ni(II) at a pH 5.89 in the batch operation, maximum % uptake being 76.8 and 84.1, respectively, for o-HAP-DDE-HCHO and o-HAP-DDE-FFD. The furfuraldehyde condensed resin was found to be more effective in removing Cu(II) ions than the formaldehyde condensed resins in batch technique. The resins exhibited little affinity for alkali and alkaline earth metal ions. Further, the furfuraldehyde condensed resin was utilised in column operation for removing Cu(II) ions. Elution study with HCl (>1.0 mol l⁻¹) resulted in removal of nearly 40–50% of loaded Cu(II) from the resin column.     

Nature of transient species formed during pulse radiolysis of 4-mercaptopyridine in aqueous solutions: Formation of a dimer radical species by one-electron reduction reaction

Reactions of one-electron reducing as well as oxidizing radicals with 4-mercaptopyridine (4-MPy) were studied in aqueous solutions at different pH values. One-electron oxidizing radicals such as N₃ and Br₂ ^–, react with 4-MPy by electron transfer reaction at pH 11 to give 4-pyridylthiyl radical. The reduction potential for the couple 4-PyS /4-PyS^– was estimated to be 0.93V vs. NHE by equilibrium reaction with I₂ ^– /2I^– couple. At pH 6.8, where the compound is predominantly present in the thione form, the transient species formed is a cation radical. OH radicals react with 4-MPy by addition to the pyridine ring at pH 6.8 and 11. At pH 0, OH radicals as well as one-electron oxidants like Cl₂ ^– and Br₂ ^– radicals react with 4-MPy to produce the protonated form of 4-pyridylthiyl radical. At pH 6.8 and 11, e_aq ^– reaction with 4-MPy gave an initial adducts which reacted with the parent molecule to give dimer radicals. Acetone ketyl radicals were unable to reduce 4-MPy at neutral pH. Reducing radicals like H-atoms and acetone ketyl radicals reacted with 4-MPy at acidic pH by H-abstraction reaction to give the same species as produced by oxidizing radicals.     

A scheme of separation of common inorganic cations and identification by filter paper strip chromatography

Summary The filter paper strip Chromatographic separation of the individual members of various groups of the qualitative analysis chart has been described. Use has been made of the ascending method, using 60% aqueous ethanol as solvent. The migrated ions are detected after their separation by the use of organic reagents.

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Zusammenfassung Die einzelnen Gruppen des qualitativen Kationentrennungsganges werden mit 60%igem Äthanol als Lösungsmittel papierchromatographisch nach der aufsteigenden Methode getrennt. Zum Nachweis der getrennten Ionen werden organische Reagentien benutzt.