Postmodification of poly(9‐alkyl‐9H‐carbazole‐2,7‐diyl)s as a route to new main‐chain‐functionalized carbazole polymers

The postmodification of poly[9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P1 ) upon its reaction with N‐bromosuccinimide affords exclusive and full bromination of the 3,6‐positions of the carbazole repeat units to yield poly[3,6‐dibromo‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P2 ). Brominated polymer P2 can be used as a precursor for further functionalization at the 3,6‐positions with the desired functional group to afford other useful polymers. Polymer P2 has hence been reacted with copper(I) cyanide to afford poly[3,6‐dicyano‐9‐(2‐hexyldecyl)‐9H‐carbazole‐2,7‐diyl] ( P3 ). Full substitution of the bromide groups with nitrile‐functional groups has been achieved. The preparation and structural characterization of polymers P2 and P3 are presented together with studies on their electronic conjugation and photoluminescence properties. Cyclic voltammetry studies on polymer P3 indicate that the new polymer is easier to reduce (n‐dope) but more difficult to oxidize than its unsubstituted counterpart ( P1 ) as a result of the introduction of the electron‐withdrawing nitrile‐functional groups at the 3,6‐positions on the carbazole repeat units on the polymer chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3336–3342, 2006     

One cannot hear orbifold isotropy type

We show that the isotropy types of the singularities of Riemannian orbifolds are not determined by the Laplace spectrum. Indeed, we construct arbitrarily large families of mutually isospectral orbifolds with different isotropy types. Finally, we show that the corresponding singular strata of two isospectral orbifolds may not be homeomorphic. Received: 6 October 2005     

Fe2P2O7 and Fe2P4O12 studied between 5–800 K

Mössbauer spectra of triclinic Fe₂P₂O₇ indicate the existence of two crystallographic metal positions in the structure. In the paramagnetic region the two Mössbauer doublets are closely overlapping. The magnetic transition takes place at ≈ 21 K and the saturated fields are around 12 tesla for the two positions. In monoclinic Fe₂P₄O₁₂ the two octahedrally coordinated metal positions give quite different quadrupole splittings (1.5 and 3 mm/s at room temperature) and hyperfine field values (42 and 12.5 Tesla at 5 K). The transition temperature is at ≈ 18.5 K.     

Heat “polynomials” for a singular differential operator on (0, ∞)

We generalize the theory of the heat polynomials introduced by P. V. Rosenbloom and D. V. Widder for a more general class of singular differential operator on (0, ). The heat polynomials associated with the Bessel operator and studied by D. T. Haimo appear as a particular case in this paper. In the special cases of second derivative and Bessel operators the heat polynomials are in fact polynomials inx andt, however, this property does not hold in general.Communicated by Tom. H. Koornwinder.     

Use of spectroscopy of gamma-radiation from the inelastic scattering of reactor fast neutrons for elemental analysis

Gamma-spectra of stainless-steel and soil samples have been measured to study the potentialities of using spectroscopy of γ-radiation from the inelastic scattering of reactor fast neutrons for element analysis of various materials. Contents of iron, chromium, nickel, manganese, silicon and titanium in stainless steel, and those of silicon, iron, aluminium, magnesium, calcium, sodium, titanium, carbon and oxygen in soil have been determined by comparing the spectra of the samples with those of specially prepared mixtures of elements. The distinguishing features, advantages, and limitations of this method are discussed.     

Membranes obtained by preirradiation grafting of acrylic acid onto poly(tetrafluoroethylene–perfluorovinyl ether)

Some properties of the membranes obtained by preirradiation grafting of acrylic acid onto poly(tetrafluoroethylene-perfluorovinyl ether) copolymer (PFA) films have been investigated. The dimensional change caused by grafting and swelling behavior, water uptake, electrical conductivity, and mechanical properties of the grafted films were found to increase as the grafting proceeds. The influence of the preparation conditions (such as preirradiation dose, monomer concentration, grafting temperature, and film thickness) on those properties was studied. These properties were found to be dependent mainly on the degree of grafting regardless of grafting conditions, except at higher monomer concentration (>40 wt %). The electric conductivity and mechanical properties for the membranes obtained at higher AAc concentrations were lower than those obtained at lower ones. Analysis by x-ray microscopy of the grafted films revealed that the grafting begins at the part close to the film surface and proceeds into the central part with progressive diffusion of monomer to give finally homogeneous distribution of the electrolytes in the whole bulk of the polymer. The membranes show good electrochemical and mechanical properties which make them acceptable for practical use as cation-exchange membranes.     

Covering pairs by quintuples with index λ  0 (mod 4)

A (v, k. λ) covering design of order v, block size k, and index λ is a collection of k-element subsets, called blocks, of a set V such that every 2-subset of V occurs in at least λ blocks. The covering problem is to determine the minimum number of blocks, α(v, k, λ), in a covering design. It is well known that $ \alpha \left({\nu,\kappa,\lambda } \right) \ge \left\lceil {\frac{\nu}{\kappa}\left\lceil {\frac{{\nu - 1}}{{\kappa - 1}}\lambda} \right\rceil} \right\rceil = \phi \left({\nu,\kappa,\lambda} \right) $, where [χ] is the smallest integer satisfying χ ≤ χ. It is shown here that α (v, 5, λ) = ?(v, 5, λ) + ? where λ ≡ 0 (mod 4) and e= 1 if λ (v?1)≡ 0(mod 4) and λv (v?1)/4 ≡ ?1 (mod 5) and e= 0 otherwise With the possible exception of (v,λ) = (28, 4). © 1993 John Wiley & Sons, Inc.     

Reductive Amination of Aldehydes and Ketones with Sodium Triacetoxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures(1)

Sodium triacetoxyborohydride is presented as a general reducing agent for the reductive amination of aldehydes and ketones. Procedures for using this mild and selective reagent have been developed for a wide variety of substrates. The scope of the reaction includes aliphatic acyclic and cyclic ketones, aliphatic and aromatic aldehydes, and primary and secondary amines including a variety of weakly basic and nonbasic amines. Limitations include reactions with aromatic and unsaturated ketones and some sterically hindered ketones and amines. 1,2-Dichloroethane (DCE) is the preferred reaction solvent, but reactions can also be carried out in tetrahydrofuran (THF) and occasionally in acetonitrile. Acetic acid may be used as catalyst with ketone reactions, but it is generally not needed with aldehydes. The procedure is carried out effectively in the presence of acid sensitive functional groups such as acetals and ketals; it can also be carried out in the presence of reducible functional groups such as C-C multiple bonds and cyano and nitro groups. Reactions are generally faster in DCE than in THF, and in both solvents, reactions are faster in the presence of AcOH. In comparison with other reductive amination procedures such as NaBH(3)CN/MeOH, borane-pyridine, and catalytic hydrogenation, NaBH(OAc)(3) gave consistently higher yields and fewer side products. In the reductive amination of some aldehydes with primary amines where dialkylation is a problem we adopted a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH(4).     

Voltammetric determination of mercury levels in tuna fish

Summary A reliable and rapid procedure for the determination of Hg in fish by differential pulse anodic-stripping voltammetry (DPASV) at the gold electrode has been developed for use in food control and marine ecotoxicology. Potentialities and performance are demonstrated by the investigation of tuna fish. Samples of 0.5–2.5 g are subjected to pressurized digestion with HNO₃/HClO₄ (71). The resulting analyte solution is irradiated in closed flasks with ultraviolet light in presence of H₂O₂ to decompose dissolved organic substances. This is followed by DPASV with two standard additions. The relative standard deviation for the lower g/g range is below 5%. Comparative determination by gas chromatography confirmed that in fish-muscle mercury exists almost completely in the form of toxic organomercurials, i. e. methyl- and dimethylmercury.

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Voltammetrische Bestimmung von Quecksilber in Thunfischen

Zusammenfassung Für die Lebensmittelkontrolle und marine Ökotoxikologie wurde eine neue spurenanalytische Alternative zur raschen und zuverlässigen Bestimmung des Quecksilbergehaltes in Fisch unter Einsatz der differentiellen Pulsinversvoltammetrie (DPIV) und Verwendung einer Goldscheibenelektrode entwickelt.Möglichkeiten und Leistungsfähigkeit der Methode werden durch die Untersuchung von Thunfisch demonstriert. Proben von 0,5 bis 2,5 g Frischgewicht werden zunächst einem Druckaufschluß mit HNO₃/HClO₄ (71) unterworfen. Die resultierende Analytlösung wird zum Abbau gelöster organischer Substanzen im geschlossenen Gefäß einer UV-Bestrahlung (70° C, 150 W Quecksilberlampe, 4 h) unter oxydierenden Bedingungen (H₂O₂) unterzogen. Anschließend erfolgt die voltammetrische Bestimmung mit DPIV unter Vornahme von zwei Eichzusätzen. Die relative Standardabweichung liegt im unteren mg/kg-Bereich unter 5%. Die Richtigkeit wurde durch Vergleichsbestimmung mit der Gaschromatographie getestet. Die Übereinstimmung der ermittelten Quecksilbergehalte bestätigt, daß im Muskelfleisch von Fisch das Quecksilber nahezu vollständig in toxischen organischen

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Taken in part from the Ph. D. Thesis of R. Ahmed. Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.