Behavior of Highly Diluted Electrolytes in Strong Electric Fields—Prevention of Alumina Deposition on Grading Electrodes in HVDC Transmission Modules by CO2‐induced pH‐Control

Alumina deposition on platinum grading electrodes in high voltage direct current (HVDC) transmission modules is an unsolved problem that has been around for more than three decades. This is due to the unavoidable corrosion of aluminum heat sinks that causes severe damage to electrical power plants and losses in the range of a million Euro range per day in power outage. Simple experiments in a representative HV test setup showed that aluminates at concentrations even below 10^?8 mol L^?1 can deposit on anodes through neutralization by protons produced in de‐ionized water (κ≤0.15 μS cm^?1) at 20–35 kV (8 mA) per electrode. In this otherwise electrolyte‐poor aqueous environment, the depositions are formed three orders of magnitude below the critical precipitation concentration at pH 7! In the presence of an inert electrolyte such as TMAT (tetramethylammonium‐p‐toluenesulfonate), at a concentration level just above that of the total dissolved aluminum, no deposition was observed. Deposition can be also prevented by doping with CO₂ gas at a concentration level that is magnitudes lower than that of the dissolved aluminum. From an overview of aqueous aluminum chemistry, the mystery of the alumina deposition process and its inhibition by CO₂ is experimentally resolved and fully explained by field accumulation and repulsion models in synergism with acid–base equilibria. The extraordinary size of the alumina depositions is accounted for in terms of proton tunneling through “hydrated” alumina, which is supported by quantum chemical calculations. As a consequence, pulse‐purging with pure CO₂ gas is presented as a technical solution to prevent the deposition of alumina.     

Ein Gesamtschrittverfahren zur Berechnung der Nullstellen von Polynomen

Ohne Zusammenfassung     

Analysis of methyl and ethyl esters of hydroxybenzoic and hydroxycinnamic acids in plant material

A method is described for the extraction and purification of methyl and ethyl esters of hydroxybenzoic and hydroxycinnamic acids from plant material. The esters were analyzed as trimethylsilyl derivatives by glass capillary gas chromatography (OV-1, OV-73, Dexsil 300) and gas chromatography-mass spectrometry. The method has been applied to analysis of methyl and ethyl esters of hydroxybenzoic and hydroxycinnamic acids in vegetables and potato peels.     

Über 3,6-Dihydro-2H-1,2-thiaphosphorin-2-sulfide

Zusammenfassung Dithiophosphonsäureanhydride (1) addieren sich an 1,3-Diene zu 3,6-Dihydro-2H-1,2-thiaphosphorin-sulfiden (2). Bei der Umsetzung mit unsymmetrischen 1,3-Dienen entspricht die Additionsrichtung einem Ablauf über das stabilste Diradikal. Metallierung der 3,6-Dihydro-2H-1,2-thiaphosphorin-sulfide führte unter Ringöffnung zu Salzen der Diendithiophosphinsäure (3), die mit Alkylierungsmitteln in die entsprechenden Dithiophosphinsäureester (4) übergeführt werden können.

---

3.6-Dihydro-2H-1.2-thiaphosphorin-2-sulfides

Addition of dithiophosphonic acid anhydrides (1) to 1.3-dienes affords 3.6-dihydro-2H-1.2-thiaphosphorin-2-sulfides (2). The course of this addition reaction in the case of unsymmetrical 1.3-dienes appears to be consistent with a mechanism involving the most stable biradical intermediate. Metallation of the resulting 3.6-dihydro-2H-1.2-thiaphosphorin-2-sulfides leads to ring opening forming salts of the diene-dithiophosphinic acid (3) which are converted via alkylation to the esters of the corresponding dithiophosphinic acid (4).

---

---

Mit 2 Abbildungen

---

Herrn Professor Dr.Erich Ziegler mit herzlichen Grüßen zum 60. Geburtstag gewidmet.

---

Korrespondenz an Ulrich Schmidt.     

Rhodamine 101 Conjugates of Triterpenoic Amides Are of Comparable Cytotoxicity as Their Rhodamine B Analogs

Pentacyclic triterpenoic acids (betulinic, oleanolic, ursolic, and platanic acid) were selected and subjected to acetylation followed by the formation of amides derived from either piperazine or homopiperazine. These amides were coupled with either rhodamine B or rhodamine 101. All of these compounds were screened for their cytotoxic activity in SRB assays. As a result, the cytotoxicity of the parent acids was low but increased slightly upon their acetylation while a significant increase in cytotoxicity was observed for piperazinyl and homopiperazinyl amides. A tremendous improvement in cytotoxicity was observed; however, for the rhodamine B and rhodamine 101 conjugates, and compound 27, an ursolic acid derived homopiperazinyl amide holding a rhodamine 101 residue showed an EC₅₀ = 0.05 µM for A2780 ovarian cancer cells while being less cytotoxic for non-malignant fibroblasts. To date, the rhodamine 101 derivatives presented here are the first examples of triterpene derivatives holding a rhodamine residue different from rhodamine B.     

Mitocanic Di- and Triterpenoid Rhodamine B Conjugates

The combination of the “correct” triterpenoid, the “correct” spacer and rhodamine B (RhoB) seems to be decisive for the ability of the conjugate to accumulate in mitochondria. So far, several triterpenoid rhodamine B conjugates have been prepared and screened for their cytotoxic activity. To obtain cytotoxic compounds with EC₅₀ values in a low nano-molar range combined with good tumor/non-tumor selectivity, the Rho B unit has to be attached via an amine spacer to the terpenoid skeleton. To avoid spirolactamization, secondary amines have to be used. First results indicate that a homopiperazinyl spacer is superior to a piperazinyl spacer. Hybrids derived from maslinic acid or tormentic acid are superior to those from oleanolic, ursolic, glycyrrhetinic or euscaphic acid. Thus, a tormentic acid-derived RhoB conjugate 32, holding a homopiperazinyl spacer can be regarded, at present, as the most promising candidate for further biological studies.     

Cascadic Multigrid in a Spectral-Element Context

Current research in computational fluid dynamics focuses on high-order methods, which offer a significant reduction of the computational effort for a given error bound. In low-order methods optimal complexity solvers for elliptic equations, e.g. the Helmholtz equation, are readily available, but for high-order methods these are still an area of research. This work evaluates the effectiveness of the Cascadic Multigrid Method in the context of spectral elements, comparing it to a standard Krylov subspace solver. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Eine acidimetrische Bestimmung des Theobromins im Diuretin, im Calcium-Diuretin und in sonstigen Theobrominpr?paraten, sowie in Mischungen und Zubereitungen

Ohne Zusammenfassung     

Crystal structures of (?)-(SS, 1R, 2S, 5R)-menthyl p-tolyl sulfinate and (+)-(SS)-[(p-tolyl)sulfinyl]ferrocene

The absolute configuration at the chiral sulfurs centers of (−)-(S _S , 1R, 2S, 5R)-menthyl-p-tolylsulfinate (1) and (S _S )-[(p-tolyl)sulfinyl]ferrocene (2) were determined by single crystal X-ray diffraction with anomalous dispersion effects and the corresponding calculation of Flack’s absolute structure parameters. Both compounds crystallize in the monoclinic crystal system in space group P2₁ (no. 4); chiral sulfinate ester 1: a = 8.2868(6), b = 6.1399(3), c = 16.366(2) ?, β = 91.816(6)°, V = 832.3(2) ?³, Z = 2 and absolute structure parameter −0.03(7); chiral ferrocenyl sulfoxide 2: a = 5.8371(3), b = 15.390(2), c = 16.143(2) ?, β = 97.748(6)°, V = 1436.9(3) ?³, Z = 4 and absolute structure parameter +0.01(1). The trigonal pyramidal geometry at the chiral sulfur atom of 2 is close to expected values while the one of 1 is slightly distorted. With direct determination of the absolute configuration at the chiral sulfur centers an important gap concerning the widely used precursors 1 and 2 for the syntheses of chiral sulfoxides and 1,2-disubstituted planar chiral ferrocenyl ligands is now closed. The latter substance class is playing a key role in enantioselective catalysis.