Chromatographic study of metal ammines

Summary The movement of metal ammines through filter paper strips has been studied. Mixtures of solutions of the metal salts with NH₄Cl and NH₄OH were prepared and spotted on strips. 50% ethanol was used as the solvent. It was noted that excess of NH₄Cl when present, gave better chromatograms. Increase of NH₃ concentration resulted in a change of R_f values. In the case of Cu^II and Ni^II the R_f value decreases, while in the case of Ag^I, Cd^II and Co^II it increases with increasing concentrations of NH₄OH added. With progressive increase in the concentration of NH₄OH the R_f values finally tend to become constant.     

An efficient synthesis of pyrroles by a one-pot, three-component condensation of a carbonyl compound, an amine and a nitroalkene in a molten ammonium salt

A one-pot, three-component condensation of a carbonyl compound, an amine and a nitroalkene leading to an efficient synthesis of alkyl-substituted pyrroles has been carried out in molten tetrabutylammonium bromide. Neither a catalyst nor an organic solvent is required for this reaction and the molten ammonium salt is recyclable.     

Microdetermination of scandium,yttrium and lanthanum: Use of Chrome Azurol S as a chromogenic reagent

Summary Optimum conditions for the spectrophotometric determination of scandium, yttrium and lanthanum using Chrome Azurol S as a chromogenic reagent are described. The studies include the determination of the range for adherence toBeer's law, p_H range of stability of the chelates, sensitivity and the influence of foreign ions.

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Zusammenfassung Eine Arbeitsweise für die spektrophotometrische Bestimmung von So, Y und La mit Chromazurol S als Farbreagens wurde angegeben. Die Gültigkeit des Beerschen Gesetzes, die Stabilität der Chelate in Abhängigkeit vom P_h, die Empfindlichkeit der Reaktion und der Einfluß von Fremdionen wurden untersucht.

     

Microdetermination of calcium, strontium and barium using the ring-oven method

Summary The ring-oven technique is recommended for the identification and determination of Ca, Sr and Ba in the micro scale. The elements are first converted into their nitrates and Ca is washed out by a mixture of absolute alcohol and ether. Sr is then separated from Ba as soluble diethyldithiocarbamidate in alcohol-ether. The rings obtained are developed by rhodizonate (Sr, Ba) and pyrogallol (Ca). Quantitative determinations are possible by comparison with standard rings. 0.60 g of Ca, 1.31 g of Sr and 8.24 g of Ba can be determined with an error lower than 6%.

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Zusammenfassung Zur Trennung und Bestimmung von Ca, Sr und Ba im Mikromaßstab wird die Ringofen-Technik empfohlen. Die drei Elemente werden dabei zunächst in die Nitrate übergeführt und Ca mit Äther-Alkohol ausgewaschen. Sr und Ba werden anschließend mit Diäthyldithiocarbamidat behandelt und Sr mit Äther-Alkohol abgetrennt. Die Identifizierung erfolgt mit Pyrogallol (Ca) bzw. Rhodizonat (Sr, Ba). Durch Vergleich mit Standardproben ist eine quantitative Bestimmung möglich. Hierbei können noch 0,60 g Ca, 1,31 g Sr und 8,24 g Ba mit einem Fehler < 6% erfaßt werden.

     

Conductometric studies on the precipitation of thorium hydroxide

This paper presents the effect of age on the conductance of hydroxide precipitated from thorium chloride with progressive addition of alkali. The effect of age on reverse titration has also been studied. Conductance study on the aged samples reveals that in every case there is at first a decrease in the electrical conductance of mixture and then an increase on prolonged ageing. This phenomenon is more marked with the concentrated solutions where it is presumed that adsorption of ions is more marked resulting in the diminution of electrical conductance. With dilute solutions, the precipitated mass being very small in amount does not adsorb appreciable amount of electrolytes from the system. On prolonged ageing there is a decrease of the surface reactivity of the precipitated mass, resulting in the release of adsorbed electrolytes and hence the increase in conductance of the system.

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Zusammenfassung Diese Arbeit behandelt die Wirkung der Alterung auf die Leitfähigkeit von Hydroxid, ausgefällt aus Thoriumchlorid mit fortschreitender Zufügung von Alkali. Auch der Alterungseinfluß auf den umgekehrten Vorgang: Zufügung von Thoriumchlorid zu Alkali, wurde untersucht. Die Leitfähigkeitsmessungen an gealterten Proben zeigen, daß zunächst stets eine Abnahme der elektrischen Leitfähigkeit der Mischungen und später eine Zunahme mit fortschreitender Alterung stattfindet. Dieses Phänomen ist für konzentriertere Lösungen ausgeprägter, bei denen ja wohl auch die Adsorption der Ionen stärker ist und damit die Abnahme der elektrischen Leitfähigkeit. Bei verdünnten Lösungen adsorbiert die dem Betrag nach sehr kleine ausgefällte Masse keine wesentlichen Beträge von Elektrolyten aus dem System. Mit verlängerter Alterung findet eine Abnahme der Oberflächenreaktivität des Fällproduktes statt, was die Freigabe von adsorbierten Elektrolyten und damit eine Zunahme der Leitfähigkeit des Systems zur Folge hat.

     

Design of Peptides with α,β-Dehydro Residues: Synthesis,Crystal Structure and Molecular Conformation of a Peptide N-Boc-Phe-ΔPhe-Ile-OCH<Subscript>3</Subscript>

To develop a complete set of design rules with α,β-dehydro residues, a tripeptide N-Boc-Phe-ΔPhe-Ile-OCH₃ was synthesized. The synthesis was carried out in solution phase using azlactone procedure. The three-dimensional structure of the peptide was determined by X-ray diffraction method and refined to an R-factor of 0.085. The structure contains three peptide molecules in the asymmetric unit. In all the three crystallographically independent molecules ΔPhe residue adopts one of the three conformations that have been reported for a ΔPhe residue. The overall conformations of three peptide molecules in the asymmetric unit are not similar. Two out of three crystallographically independent molecules adopt type II β-turn conformations whereas the third molecule is found having the characteristic S-shaped conformation in which the values of dihedral angles φ, ψ have opposite signs alternately. One of these two types of conformations has been observed when a ΔPhe is introduced at (i+2) position of a tetrapeptide. The β-turn conformation is stabilized by a 4→1 hydrogen bond where the hydrophobic side chains of residues at (i+1) and (i+3) positions stabilized the unfolded conformation with van der Waals interactions. The three independent molecules are locked together by three hydrogen bonds between molecules A and B and two hydrogen bonds between molecules B and C.     

Chromatographic study of anionic complexes

Summary In this paper the variation of diffusion, through a filter paper strip by the ascending method, of cuprioxalate complex has been studied. Various mixtures of Cu+^2üC₂O ₄ ^2– ions have been investigated. It has been noted that till there is a precipitation, the R_f values tend to decrease and finally reach nearly to zero, when the oxalate precipitates completely. With redissolution of the precipitate to form the complex anion, R_f values increase again to a maximum and then have a slight tendency to diminish. No tailing occurs in the chromatograms in cases where the copper has passed into the anion.     

An NMR and quantum mechanical investigation of solvent effects on conformational equilibria of butanedinitrile

Vicinal proton-proton NMR couplings and ab initio quantum mechanics have been used to investigate solvent effects on conformational equilibria of butanedinitrile. The trans and gauche conformations are about equally favored at room temperature in solvents of low dielectric constant while the equilibrium is essentially the statistical proportions of one-third trans and two-thirds gauche in water with a high dielectric constant. The coupling assignments were confirmed with the aid of stereospecific deuterium-labeled (R,R or S,S)-1,2-dideuteriobutanedinitrile. The calculations support the observed trends. Similar results were observed for 1,2-dibromo- and dichloroethanes.     

A modified ring electrographic method for the non-destructive analysis of metallic artefacts

Summary The utility of the ring electrographic technique as a non-destructive method of analysis of metallic artefacts of archeological importance is sufficiently accurate to give archeological meaningful results The electrographic sampling technique has been modified to give easier and more reliable sampling. The method is of particular value in the analysis of copper and silver coins.

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Eine modifizierte elektrograpbische Ring-Methode zur Analyse metallischer Kunstgegenstände ohne deren Verletzung

Zusammenfassung Die Verwendbarkeit der elektrographischen Ring-Technik für die Analyse metallischer Gegenstände von archäologischem Interesse wurde erwiesen. Die elektrographische Probenahme wurde modifiziert. Das Verfahren ist für die Analyse von Kupfer- und Silbermünzen von besonderem Wert.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Synthesis of Some Octahedral Nickel(II) Complexes of One Isomer of Isomeric Me8[14]anes: X-ray Structure of Diisothiocyanato(3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane, LC)nickel(II), [NiLC(NCS)2]

One isomer, L_C of the isomeric Me₈[14]anes, L_A, L_B and L_C; on reaction with Ni(NCS)₂ produces a six coordinate octahedral diisothiocyanato complex, [NiL_C(NCS)₂]. This complex undergoes axial substitution reactions with the small ligands to yield corresponding monosubstituted derivatives having general formula [NiL_C(NCS)X] whereas X = Cl, Br, I, NO₂ or NO₃. The complexes have been characterized on the basis of analytical, spectroscopic, magnetic and conductance data. The structure of [NiL_C(NCS)₂] (triclinic, space group P?1, α = 8.0421(17) Å, β = 8.9085(18) Å, χ = 9.687(2) Å, α = 67.561(3) Å, β = 82,896(4) Å, ζ = 598.7(2) Å³, Z = 2, Dc = 1.352 mg/m³, μ(Mo Kα) = 1.003 mm^?1) was confirmed by X-ray crystallography.