Coulometrische Wismutometrie

Zusammenfassung Durch elektrolytische Oxydation einer Bi-Anode in gesättigter NaCl-Lösung können Bi³⁺-Ionen in Lösung gebracht werden. Dieser Prozeß ermöglicht die coulometrische Bestimmung anwesender Anionen, die schwerlösliche Bi-Verbindungen bilden.Es wurden Semimikro- und Mikrobestimmungen von Phosphationen durch elektrolytisch erzeugte Bi³⁺-Ionen bei konstanter Stromstärke ausgeführt. Die Endpunktbestimmung erfolgte amperometrisch bei konstantem Potential mit einer Indikatorelektrode — tropfende Quecksilberelektrode — und mit einer gesättigten Kalomelelektrode als Bezugselektrode. Die coulometrische Wismutometrie bietet eine weitere Möglichkeit der coulometrischen Eichung volumetrischer Lösungen im Sinne des seinerzeitigen Vorschlags vonTutundi.

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Summary Bi³⁺ ions can be brought into solution through electrolytic oxidation of a Bi-anode in saturated NaCl solution. This process makes possible the coulometric determination of the anions present that yield difficulty soluble bismuth compounds.Semimicro- and micro-determinations of phosphate ions were made via Bi³⁺-ions produced electrolytically at constant current strength. The endpoint was determined amperometrically at constant potential with an indicator electrode-dropping mercury electrode-and with a saturated calomel electrode as reference electrode. The coulometric bismuthometry affords a further possibility of the coulometric standardization of volumetric solutions in the sense of the proposal previously advanced byTutundi.

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Résumé On peut utiliser les ions Bi³⁺ en solution par oxydation électrolytique d'une anode en bismuth, en solution de chlorure de sodium saturée. Ce procédé permet le dosage coulométrique des anions présents qui forment des composés peu solubles avec le bismuth.On a mis au point le dosage semimicro et micro des ions phosphates par les ions Bi³⁺ formés électrolytiquement sous intensité constante. On détermine par ampérométrie le point équivalent à potentiel constant à l'aide d'une électrode indicatrice — électrode de mercure à goutte pendante —et avec une électrode au calomel saturée comme électrode de référence. La «bismuthométrie» coulométrique offre de grandes possibilités pour l'étalonnage coulométrique de solutions volumétriques, suivant l'idée queTutundi a émise en son temps.

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Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.

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Wir danken Herrn Dipl.-Ing.Vladimir Pantovi für seine Hilfe bei unserer experimentellen Arbeit.     

Neutral pi-associated porphyrin [2]catenanes

A series of neutral porphyrin-containing catenanes has been synthesised, consisting of a zinc porphyrin strapped by a polyethylene glycol chain containing four or six ethylenoxy-units and incorporating a central naphthoquinol unit, interlinked with a naphthalene diimide macrocycle. The napthalene diimide precursor units exhibit only weak binding with the strapped porphyrins (Ka between 8 and 0.02 M(-1)), but good yields of the catenanes were obtained by Glaser coupling of the alkynyl napthalene diimide precursors in the presence of the porphyrins. Structures and solution conformations were determined by mass spectral and detailed 1H NMR studies. For the longer strapped porphyrins, the diimide macrocycle rotates around the central naphthoquinol unit at 420-450 times per second, while rotation is virtually prevented in the tighter strapped derivatives. A second dynamic process occurring in both sets of catenanes and described as 'yawing' leads to inequivalence in the naphthalene moieties. UV-Visible spectra indicate charge transfer interactions and electronic communication between the two components of the catenane.     

Partial Least-Squares Study of the Effects of Organic Modifier and Physicochemical Properties on the Retention of Some Thiazoles

JPC – Journal of Planar Chromatography – Modern TLC - Reversed-phase (RP) HPTLC with aqueous ammonia-organic modifier (acetonitrile, dioxane, acetone) mobile phases has been used to...     

Stereochemistry of cyclic ether formation—II : Intramolecular cyclisation of secondary aliphatic alcohols to tetrahydrofuran-type ethers

The mechanism and stereochemistry of δ-C atom functionalisation in the reactions of secondary straight-chain aliphatic alcohols with lead tetraacetate, ceric ammonium nitrate, and heavy metal (Pb⁴⁺, Hg²⁺, Ag⁺) salts (AcO)^?1, O^2?, CO₃^2?-halogen (I₂, Br₂, Cl₂) combinations are discussed. By demonstrating the intermediacy of 5-bromo-2-hexanol, it was confirmed that the dark silver oxidebromine induced cyclisation of 2-hexanol (and alcohols in general) involves (as the other hypohalite reactions) intramolecular 1,5-hydrogen abstraction by alkoxy radicals and formation of δ-bromohydrins. A novel and simple procedure for obtaining tetrahydrofurans from alcohols by way of the hypochlorite reaction, using silver or mercuric salts and chlorine, is described.     

Interactions of proteins with uniform colloidal hematite and chromium hydroxide particles. I. Adsorption

The adsorption of ovalbumin, -globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and -globulin was greatest at their isoelectric points and differed little at 10^–2 and 10^–3 mol dm^–3 NaNO₃. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO₃)₂ was significantly greater than that with NaNO₃ under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg²⁺ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of -globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis     

Improvement of electron capture efficiency by resonant excitation

A novel pulse sequence improving the efficiency for electron capture dissociation (ECD) of an unmodified Fourier transform ion cyclotron resonance (FTICR) mass spectrometer by more than an order of magnitude is presented. Commercially available FTICR instruments are usually equipped with a filament-based electron source producing an electron beam that has a rather small cross section. An ideal overlap between the rotating ion cloud and the electron beam appears to be a prerequisite for a high ECD efficiency. A reduced interception of the ion cloud and the electron beam is probably due to the contribution of the magnetron motion to the trajectory of the ions, resulting in a precession about the z-axis of the instrument. By increasing the kinetic energy and therefore increasing the cyclotron radii of the precursor ions by resonant excitation, the overlap of the rotating ion cloud with the electron beam is improved. By use of this protocol the efficiency of electron capture is substantially increased and consequently the acquisition time of ECD spectra is reduced significantly. The capability of resonant excitation of the precursor ions during the irradiation with electrons is demonstrated for standard peptides. This approach is particularly valuable for analysis and characterization of O-glycosylated peptides. In addition to amino acid sequence information, the attachment site of the labile glycan moiety is determined, and also radical-site-induced fragmentations of the glycosidic bonds are observed.     

Some new ring-D seco steroids

The Beckmann fragmentation product, 3-methoxy-17-oxo-16,17-secoestra-1,3,5(10)-trien-16-nitrile (2) has been reduced by LAH giving the expected 3-methoxy-17-hydroxy-16,17-secoestra-1,3,5(10-trien-16-amine hydrochloride (3) and 3-methoxy-17-oxa-D-homoestra-1,3,5(10)-trien-16-ol (4), by a presumed neighbouring group participation of 17-OH group in the intermediary formed 16-imino derivative (A). The structure of 4 has been proved by an alternative synthetic route by reducing 3-methoxy-17-oxa-D-homoestra-1,3,5(10)-trien-16-one (7) with di-iso-butylaluminium hydride.     

Benchmarking of ruthenium initiators for the ROMP of a norbornenedicarboxylic acid ester

The kinetic study of ring-opening metathesis polymerization (ROMP) of a diester functionalised norbornene derivative, (±)-exo,endo-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid diethyl ester, with a series of ruthenium benzylidene complexes revealed the applicability of these initiators for well defined polymerization reactions. Values for the rate of initiation as well as the rate of propagation of the initiators were determined and correlated to the molecular weight and polydispersity of the isolated polymers. As the only initiator providing an entry to virtually monodisperse polymers the classical “first generation Grubbs-catalyst” was identified, while N-heterocyclic carbene based initiators polymerized with a rate of propagation much higher than the rate of initiation yielding polymers with a broader molecular weight distribution.     

Circular‐Dichroism Studies on Artemisinin and Epiartemisinin and Their β‐Cyclodextrin Complexes in Solution

The circular dichroism (CD) spectra of the powerful antimalarian active principle artemisinin (ART; 1 ) from Artemisia annua, and of epiartemisinin (EPI, 2), its C(7) epimer, were studied in solution in the presence and absence of β‐cyclodextrin (β‐cd). A significant inversion of sign in the region of the second electronic transition was detected. The rotational strengths were successfully calculated within the time‐dependent density functional theory (DFT), which enabled us to establish a correlation between the molecular recognition and the biological acitivities of the two isomers.     

Study of the Retention Behavior of Newly Synthesized s-Triazine Derivatives in RP TLC Systems,and the Lipophilicity of the Compounds

JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of nine newly synthesized s-tri-azines has been studied by thin-layer chromatography on C18/UV254...