On the homo- and heteroassociation of hypericin

Summary Hypericin exhibits rather complicated homo- and heteroassociation behavior. Whereas in common polar solvents hypericin dissolves monomolecularly up to concentrations of 10^–3 mol/l, the presence of water in these solvents leads to homoassociation. As derived by spectroscopic measurements, these homoassociates exhibit a stacking pattern similar to the one observed for the crystalline material. Tetrahydrofuran seems to be an exception, as it is the only solvent which results in 1,6-dioxo tautomer formation. Heteroassociation of hypericin involves two distinct types of behavior. In the majority of cases, hypericin forms homoassociates which then heteroassociate with the co-solvate to yield stabilized solutions of these homoassociates. Only with human serum albumin a specific heteroassociate is formed. By means of competition experiments it could be established that hypericin is binding to the active site of the IIIA subdomain of the protein.Dedicated to Prof. Dr.Karl Schlöpl on the occasion of his 70th birthday     

Neue arsinidenverbrückte Mehrkern-Clusterkomplexe des Ag und Au. Die Kristallstrukturen von [Ag14(AsPh)6Cl2(PR3)8], (PR3 = PEt3, PMenPr2, PnPr3), [M4(As4Ph4)2(PR3)4], (M = Ag,PR3 = PEt3, PnPr3; M = Au,PR3 = PnPr3), [Au10(AsPh)4(PhAsSiMe3)2(PnPr3)6]

New Arsinidene-bridged Multinuclear Cluster Complexes of Ag and Au. The Crystal Structures of [Ag₁₄(AsPh)₆Cl₂(PR₃)₈], (PR₃ = PEt₃, PMeⁿPr₂, PⁿPr₃), [M₄(As₄Ph₄)₂(PR₃)₄], (M = Ag, PR₃ = PEt₃, PⁿPr₃; M = Au, PR₃ = PⁿPr₃), [Au₁₀(AsPh)₄(PhAsSiMe₃)₂(PⁿPr₃)₆] The reaction of AgCl with PhAs(SiMe₃)₂ in presence of tertiary phosphines (PR₃) leads to arsinidene-bridged silver clusters with the composition [Ag₁₄(AsPh)₆Cl₂(PR₃)₈], (PR₃ = PEt₃ 1 , PMeⁿPr₂ 2 , PⁿPr₃ 3 ). Further it is possible to obtain the multinuclear complexes [Ag₄(As₄Ph₄)₂(PR₃)₄], (PR₃ = PEt₃ 4 , PMeⁿPr₂ 5 ). In analogy to that [PMe₃AuCl] reacts with PhAs(SiMe₃)₂ and PⁿPr₃ to form the compound [Au₄(As₄Ph₄)₂(PⁿPr₃)₄] 6 , which is isostructurell to 4 and 5 . The gold cluster [Au₁₀(AsPh)₄(PhAsSiMe₃)₂(PⁿPr₃)₆] 7 was obtained from the same solution. The structures were characterized by X-ray single crystal structure analysis. (Crystallographic data see “Inhaltsübersicht”)     

Evidence for the Generation of Singlet Oxygen (<Superscript>1</Superscript>O<Subscript>2</Subscript>, <Superscript>1</Superscript>Δ<Subscript>g</Subscript>) from Ozone Promoted by Inorganic Salts

Summary.  Evidence for novel chemical sources of singlet oxygen based on the conversion of ozone by tin(II) in acetic acid or nitrite ions in water was found by screening a selection of inorganic salts by means of a sensitive detector for exothermic processes (SEDEX) and a N₂-cooled Ge-diode for singlet oxygen luminescence measurements. Corresponding author. E-mail: heinz.falk@jku.at Received July 18, 2002; accepted August 23, 2002     

Photocatalytic effects of Fe(III) compounds on the hydroxylation of benzoic acid by hydrogen peroxide initiated by UV-radiation

The addition of FeCl₃ and Na₂[Fe(CN)₅NO] increases the quantum yields of photochemical hydroxylation of benzoic acid by hydrogen peroxide. The photocatalytic effects operate especially when the radiation is absorbed by benzoic acid. When hydrogen peroxide is excited, the catalytic effects in the hydroxylation are small.

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FeCl₃ Na₂[Fe(CN)₅NO] , . , . .

     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Intramolecularly Friedel-Crafts Acylated Emodin Derivatives. An Access to the Cores of Angucyclinones, Anthracyclinones, and to Hypericin Analogues

Summary. Intramolecularly emodin based Friedel-Crafts acylation provided a new route for the synthesis of the angucyclinone and anthracyclinone core as well as access to a new class of cyclopentanone condensed anthraquinones. In addition, the anthracyclinone may serve as a synthon for bathochromically shifted hypericin derivatives.     

Untersuchungen über ein „Kriterium für die Aromatizität”: Die Konzentrationsabhängigkeit der molaren magnetischen Drehung

Zusammenfassung Es wurde der Versuch unternommen, ein für die Aromatizität angegebenes Kriterium (4.Labarresches Kriterium), nämlich den Verlauf der Konzentrationsabhängigkeit der molaren magnetischen Drehung, auf Metallocene anzuwenden. Die dabei und bei anderen aromatischen Systemen erhaltenen Ergebnisse führen zu dem Schluß, daß diese Konzentrations-abhängigkeit nicht auf diamagnetische Effekte eines induzierten Ringstromes zurückzuführen ist, sondern von der konzentrationsbedingten Änderung des inneren Feldes herrührt. Sie spiegelt also nicht die Aromatizität eines Systems wider.

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Investigations on a Criterion of aromaticity: The concentration dependence of the molar magnetic rotation

It was attempted to determine the relative aromaticities of metallocenes by means of a recently stated criterion (Labarre's 4th criterion), which is based on the concentration dependence of the molar magnetic rotation. The results of the investigation of these and other aromatic systems lead to the conclusion that this concentration dependence does not correlate with diamagnetic effects of an induced ring current; it rather is associated with the concentration dependent change of the internal field of the solute. Consequently, it does not reflect the aromaticity of a system.

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Mit 1 Abbildung     

Die Chloride Na3xM2–xCl6 (M = La?Sm) und NaM2Cl6 (M = Nd,Sm): Derivate des UCl3-Typs. Synthese,Kristallstruktur und Röntgenabsorptionsspektroskopie (XANES)

The Chlorides Na_3xM_2–xCl₆ (M = La? Sm) and NaM₂Cl₆ (M = Nd, Sm): Derivatives of the UCl₃-Type of Structure. Synthesis, Crystal Structure and X-Ray Absorption Spectroscopy (XANES) Single crystals of the derivatives of the UCl₃-type structure Na_3xM_2–xCl₆ (M = La/x = 0.364(4); Ce/0.349(5); Pr/0.318(8); Nd/0.305(5); Sm/0.246(4)) and NaSm₂Cl₆ were grown by different methods generally under reducing conditions. They are addition [Na(Sm₂)Cl₆] and addition/substitution variants [Na_2x(Na_xM_2–x)Cl₆] of the UCl₃ structure type [□(U₂)Cl₆]. X-Ray Absorption Spectroscopy (XANES) at the L_III edge characterizes NaSm₂Cl₆ and NaNd₂Cl₆ as mixed-valence compounds with valences of +2 and +3 in statistical distribution (approximately 1:1) for Sm and Nd, respectively.     

An FT-IR demonstration of the occurrence of satellite bands in the spectra of hydrogen bonds in crystals

OH stretching fundamentals in the spectra of hydrogen-bonded crystals are accompanied by satellite bands due to sum and difference transitions involving one quantum of the OH stretching vibration and one or more quanta of the low-frequency vibration of the hydrogen bond. Such satellites were detected in the FT-IR spectra of two hydrogen-bonded crystals, ice and methanol.NRCC No. 29006     

Infinitely constrained optimization problems

A generalized cutting-plane algorithm designed to solve problems of the form min{f(x) :x X andg(x,y) 0 for ally Y} is described. Convergence is established in the general case (f,g continuous,X andY compact). Constraint dropping is allowed in a special case [f,g(·,y) convex functions,X a convex set]. Applications are made to a variety of max-min problems. Computational considerations are discussed.Dr. Falk's research was supported by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under AFOSR Contract No. 73–2504.