Analysis of chlorine and other halogens by activation with photons and neutrons

The analysis of halogens in various matrices is described. Activation analysis with mainly high energy bremsstrahlung (PAA) and pile neutrons (NAA) was applied. In the case of chlorine, fast procedures were worked out requiring not more than 100 min for one determination. The particular problems of fluorine analysis are discussed. The described techniques were applied for the following cases: Determination of total chlorine resp. bromine in oil samples; determination of chlorine in wood, glasses and TiN powders; determination of iodine in ZnSe single crystals using instrumental photoactivation.The limits of detection are: (interference-free in μg/g) F: 0.03/–; Cl: 0.1/0.05; Br: 0.04/0.003 and I: 0.1/0.01 using PAA/NAA. Activation analysis, being independent upon the chemical status of the analyte and usually less affected by blank problems has been found to be a useful complement to conventional chemical analysis. Received: 28 February 199 / Revised: 14 April 1998 / Accepted: 18 April 1998     

Reduction of (imine)Pt(IV) to (imine)Pt(II) complexes with carbonyl-stabilized phosphorus ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3P=CHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4[NH=C(Me)ON=CR1R2]2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)=NOH], [PtCl4[NH=C(Me)ONR2]2] (R = Me, Et, CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5[NH=C(Me)ON=CR2]] [R2 = Me2, (CH2)4, (CH2)5] and 1 equiv of Ph3P=CHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum center. All thus prepared compounds (excluding previously described Delta4-1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C[1H], 31P[1H] and 195Pt NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2[NH=C(Me)ON=CMe2]2] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) A, c = 15.916(3) A] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) A, b = 12.486(4) A, c = 10.149(3) A]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides Ph3P=CHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV) complexes for biological studies.     

Structure and Stereochemistry of New Sesquiterpene Esters from Echinacea purpurea (L.) MOENCH. (Preliminary communication)

The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities.     

Chemical basis of DNA sugar-phosphate cleavage by low-energy electrons

DNA damage by low-energy electrons (LEE) was examined using a novel system in which thin solid films of oligonucleotide tetramers (CGTA and GCAT) were irradiated with monoenergetic electrons (10 eV) under ultrahigh vacuum. The products of irradiation were examined by HPLC. These analyses permitted the quantitation of 16 nonmodified nucleobase, nucleoside, and nucleotide fragments of each tetramer resulting from the cleavage of phosphodiester and N-glycosidic bonds. The distribution of nonmodified products suggests a mechanism of damage involving initial electron attachment to nucleobase moieties, followed by electron transfer to the sugar-phosphate backbone, and subsequent dissociation of the phosphodiester bond. Moreover, virtually all the nonmodified fragments contained a terminal phosphate group at the site of cleavage. These results demonstrate that the phosphodiester bond breaks by a distinct pathway in which the negative charge localizes on the phosphodiester bond giving rise to nonmodified fragments with an intact phosphate group. Conversely, the radical must localize on the sugar moiety to give as yet unidentified modifications. In summary, the reaction of LEE with simple tetramers involved dissociative electron attachment leading to phosphodiester bond cleavage and the formation of nonmodified fragments.     

Kristallstruktur und Konformation eines linearen Pentapyrrols

The crystal structure of the pentapyrrin1 was determined by X-ray diffraction methodes at two temperatures (298K and 97K). It is the first structure determination of a linear polypyrrole with more than four pyrrole rings. In the crystal, the molecule is located on a crystallographic two-fold axis, which passes through the central pyrrole ring. It assumes a helical overall-conformation, which is stabilized by intramolecular hydrogen bonding. The acidic proton at the nitrogen atom of the central pyrrolic ring is disordered, being observed with half occupancy at two symmetry-equivalent positions off the crystallographic diad. Attempts to remove the disorder by cooling to 97K were unsuccessful, since no indication for a phase transition was detected.

     

SENSITIVITY OF Porphyromonas AND Prevotella SPECIES IN LIQUID MEDIA TO ARGON LASER

Abstract— The phototoxicity of argon laser irradiation was studied in aqueous suspensions of Porphyromonas endodontalis (American Type Culture Collection [ATCC] 35406), Porphyromonas gingivalis (ATCC 33277), Prevotella denticola (ATCC 33184) and two strains of Prevotella intermedia (ATCC 15033 and 49046), all "black-pigmented bacteria," BPB, that accumulate cellular porphyrins. Several of these species have been implicated in the etiology of Periodontol disease. Non-black-pigmented bacteria were also studied to test the specificity of irradiation as a potential photodynamic treatment for Periodontol infections. Cell suspensions were irradiated with an argon laser at fluences of 20–200 J/cm². When cultured in hemin-supplemented media, ATCC 15033 was the most sensitive to irradiation. However, a second strain of the same species (ATCC 49046) was resistant. The photosensitivity of other species ranked ATCC 33277 > 35406 = 33184 = 35496. When hemin was replaced in media by hemoglobin, ATCC 33277 became resistant to irradiation. Protoporphyrin IX content in BPB cells was shown not to be a major factor determining photosensitivity. Oxygen was required during irradiation for BPB species to be affected. Non-black-pigmented bacteria were much less sensitive to irradiation than BPB.     

Pheromone, 3.Mitt.: Eine einfache Methode zur Steuerung der Reduktion von α-Alkoxy-carbonylverbindungen

Summary Enantiomerically pure 1,2-diols bearing optionallysyn oranti configurated secondary hydroxylic groups are synthesized from acetal-protected cyanohydrins. After resolution of the diastereomers the cyanohydrins are converted into -alkoxy-ketones by Grignard-reaction followed by reduction using common chelating or non-chelating agents. Among others syntheses of enantiomerically pure pheromones,endo-Brevicomin,exo-Brevicomin and Dispalure are given as examples.

Prof. Dr. Hans Berbalk zum 70. Geburtstag gewidmet     

IUPAC Commission on Inorganic Chemistry Nomenclature; Newsletter 1990

Inorganic Chemistry Nomenclature

IUPAC Commission on Inorganic Chemistry Nomenclature; Newsletter 1990