Die Koordinationszahl von Lanthaniden: Thermodynamik der LnIIIEDTA-Mischkomplexe mit den Anionen der 8-Hydroxychinolin-5-sulfonsäure,Iminodiessigsäure und Nitrilotriessigsäure

The values of ΔG, ΔH and ΔS for the formation of the mixed 1:1:1 lanthanide EDTA complexes with the anions of 8-hydroxyquinoline-5-sulfonic acid, iminodiacetic acid and nitrilotriacetic acid were determined by pH-titrations and a direct calorimetric method. These thermodynamic data are discussed and compared with those for the formation of the Ln(III)EDTA complexes. Contrary to current opinion it is concluded that all trivalent lanthanide aquoions have the same coordination number in dilute solution. However, in the series of the lanthanide EDTA complexes the coordination number changes between Sm and Tb. In this region, equilibria occur between two types of EDTA complexes with different numbers of coordinated water molecules: The corresponding equilibrium constants could be evaluated. The coordination number changes also in many other Ln complexes along the lanthanide series, and similar equilibria occur.     

Konformationen von 1,3-dioxanen nach der kraftfeldmethode. nichtbindende wechselwirkungen von sauerstoff

The treatment of oxygen lone pairs in force field calculations is discussed. The geometries of 1,3-dioxanes can be calculated well without explicit account of lone pairs. For the calculation of conformational energies in 5-alkyl-1,3-dioxanes electrostatic interactions between point charges taken from quantum mechanical calculations must be included. Addition of van der Waals interactions of lone pairs as weak potentials further improves the calculated conformational energies.     

An electrochemical study of redox indicators : Part I. Substituted chrysoidines

The electrochemical oxidation of various substituted chrysoidines was studied by cyclic voltammetry, to determine which have stable oxidation products. Only 4-hydroxy-chrysoidine has a stable product; the apparent oxidation potential is 0.779 V vs. NHE. 4-Methoxy- and 4-ethoxy-chrysoidine rapidly lose methanol or ethanol, respectively, so that the 4-hydroxychrysoidine wave appears on subsequent scans. All the other chrysoidines studied are irreversible. The results indicate that a hydroxy group in the 4-position is necessary for stability; the 4-alkoxychrysoidines can achieve the stable quinoidal structure by cleavage of the alkoxy group after nucleophilic attack.     

A new spot test for cerium(IV)

Summary A new colour reaction for the detection of cerram(IV) which can be carried out both in a test tube and on a spot plate has been described. The test solution is treated with methylene blue in nitric acid solution (11) to form a rose-red colour. This simple procedure has an advantage over the existing tests in that it is applicable in the presence of oxidising agents like chromium(VI), vanadium(V), nitrate, perchlorate and of coloured ions like copper(II), cobalt(II), nickel(II), chromium(III), iron(III), vanadium(IV), uranium(VI).

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Zusammenfassung Eine neue, sowohl in der Eprouvette wie auf der Tüpfelplatte ausführbare Farbreaktion zum Nachweis von Cer(IV) wurde angegeben. Die Probelösung wird mit salpetersaurer Methylenblaulösung behandelt und gibt eine rosarote Färbung. Die Reaktion hat gegenüber bekannten Tests den Vorteil, in Gegenwart von Oxydationsmitteln wie Cr(VI), V(V), NO₃ ^–, ClO₄ ^– bzw. in Anwesenheit gefärbter Ionen wie Cu(II), Co(II), Ni(II), Cr(III), Fe(III), V(IV) oder U(VI) anwendbar zu sein.

     

Production of new lagochilin derivatives

The tetrahydric alcohol Lgochilin belongs to the 9,13-epoxylabdane series of diterpenoids. It is produced by many species of plants of the Lagochilus genus and can be used as the starting material for the synthesis of new compounds with a broad spectrum of physiological action [1, 2]. Many lagochilin derivatives possess hemostatic (3, 4) and antiviral properties. Lagochilin derivatives with aromatic hydroxaldehydes and naphthaldehydes have been synthesized, and the cytotoxic effects of the compounds synthesized in cell cultures have been studied.Tashkent State University, (fax (3712) 46 24. 42. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 86–88, January–February, 1995. Original article submitted October 17, 1994.     

Comparison of the structural and chemical composition of giant T-even phage heads.

A study has been made of the structure of the capsids of T4D giant phage produced from mutants in gene 23 and temperature-sensitive mutants in gene 24, and T4D and T2L giant phage formed by the addition of L-canavanine followed by an Larginine chase in the growth medium. All the giant phage capsids have been shown to be built according to the same geometrical architecture. This consists of a near-hexagonal surface net, lattice constant 129.5 A, folded into a left-handed T = 13 prolate icosahedron elongated along one of its fivefold symmetry axes. Their only apparent difference from wild-type T-even phage capsids is their abnormally elongated tubular part. A comparison of the capsomere morphologies and protein compositions of the giant phage capsids showed that all T4D giants are identical but differ from T2L: The T4D capsomere has a complex (6 + 6 + 1)-type morphology, whereas the T2L has a simple 6-type. T2L phage, however, lack two capsid proteins, "soc" and "hoc", present in T4D. The difference in capsomere morphology can therefore be related to the difference in the protein compositions of these two phage. Possible differences between the initiation and means of length regulation of giant phage heads and the aberrant polyheads are discussed.     

Die Bildungsenthalpien einiger Siliciumtetrahalogenid—Pyridin-Addukte

The enthalpies of formation of the addition compounds F₄Si(py)₂, Cl₄Si(py)₂, Br₄Si(py)₂ and I₄Si(py)₄ have been measured calorimetrically by two different ways (see table 1). It was not possible to confirm enthalpy data published in^{7, 8}. The sequence SiF₄4～SiBr₄>SiI₄(?) is proposed for the acceptor power of the silicon tetrahalides towards pyridine.     

Photophysical behaviour of azaphenanthrenes

Nitrogen position and internal heavy atom effects on the radiative and radiationless transitions from the lowest excited states of the isomeric azaphenanthrenes and some of their methyl, chlorine and bromine derivatives have been studied in E.P.A. solutions at 77 K. The nitrogen position affects the fluorescence and S₁-T₁ intersystem crossing rates more than the phosphorescence and T₁-S₀ intersystem crossing rates. Small differences in the behaviour of 9-azaphenanthrene are enhanced in non-hydroxylic solvents and at room temperature, and it is inferred that (n, π*) states play a more important role in the photophysical behaviour of this isomer. Halogen, substitution in all the isomers increases the phosphorescence rate, induces a smaller increase in the T₁-S₀ intersystem crossing rates and has a negligible effect on the fluorescence rate.     

Zum Mechanismus der Hydrogenolyse aromatisch gebundenen Halogens

The selective chlorination of a m/p-xylene mixture, followed by distillation of the unreacted p-xylene, leaves a residue containing up to 90% of monochlorinated m-xylenes. m-Xylene is recovered from the latter by heterogeneous catalytic hydrogenolysis in the gas-phase. It was found that the hydrogenolysis on certain noble metal catalysts proceeds according to an ionic reaction mechanism at temperatures below a definite temperature range. At temperatures above this range hydrogenolysis follows a radical reaction mechanism.     

Lifetime measurements of two-photon excited vibronic levels in the low pressure limit: naphthalene

Single vibronic lifetimes of two-photon excited states are measured in the low pressure limit for naphthalene. The two-photon spectrum, besides yielding new states in S₁, is also free of the interference from the neighborhood of the S₂, known from one-photon experiments, and hence unperturbed lifetimes can be measured to higher excess energies. The overall pattern of lifetimes with excess energy including both one-photon and two-photon states shows that the vibronic structure is subordinate to an overall monotonic decrease, much as found earlier for β-naphthylamine. This indicates, at least for naphthalene, that radiationless processes into triplets are dominated by Franck—Condon factors and not by vibronic inductions and promoting modes.