Layered assemblies composed of sulfonated cyclodextrin and poly(allylamine)

Layered assemblies containing cyclodextrin (CD) have been prepared by layer-by-layer deposition of poly(allylamine) and sulfonated α-CD or β-CD on a solid surface. A quartz crystal microbalance study revealed that α-CD and β-CD form multilayers in the films upon each deposition. The sulfonated-α-CD-containing film bound methyl orange (MO) by forming an inclusion complex, resulting in the isolation of MO as a monomer in the film, whereas MO formed aggregates in the sulfonated-β-CD and CD-free films.     

Electro- and photochemical properties of a (mu-alkoxo)bis(mu-carboxylato)diruthenium complex having two tetraphenylporphinato zinc(II) moieties

The novel (mu-alkoxo)bis(mu-carboxylato)diruthenium complex K[Ru(2)(dhpta)(mu-O(2)C-p-ZnTPP)(2)] 3 was prepared by simple ligand substitution reaction. Strong antiferromagnetic interaction between two Ru(III) ions of 3 was observed with a coupling constant of -425 approximately -404 cm(-1). The cyclic voltammogram of 3 can be explained in terms of superposition of those of ZnTPP-p-CO(2)H and K[Ru(2)(dhpta)(mu-O(2)CPh)(2)] 2, indicating no significant electrochemical interaction. The large conproportionation constant estimated from the reduction potentials for Ru(III)Ru(III) and Ru(II)Ru(III) indicates great stability of the mixed-valence state. The mixed-valence species [Ru(II)Ru(III)(dhpta)(mu-O(2)C-p-ZnTPP)(2)](2-) 4 was prepared by controlled potential electrolysis. The electronic absorption spectrum of 4 was quite similar to that of [Ru(II)Ru(III)(dhpta)(mu-O(2)CCH(3))(2)](2-) which is a typical Class II complex. The fluorescence from the S(2) state of the ZnTPP unit of 3 was significantly (78%) quenched. The electron transfer from the ZnTPP unit to Ru(III) ions in 3 is a plausible mechanism, even though energy transfer could not be ruled out completely. The free energy change for electron transfer, Delta G(CS), was estimated to be ca.-1.1 eV, which is similar to typical values for the reorganization energy lambda in polar solvents. Hence, the electron transfer scheme is situated almost at the top of the Marcus parabola, enabling ultrafast electron transfer.     

Absolute helical arrangement of sulfonamide in the crystal

[reaction: see text] 1,2-Bis(N-benzenesulfonyl-N-methylamino)benzene (2), which has no fixed asymmetric element, was crystallized from ethyl acetate as chiral crystals belonging to space group P4(1)2(1)2 (No. 92) or P4(3)2(1)2 (No. 96). The array of molecules built by the CH-pi interaction along the c-axis forms an enantiomeric helical superstructure in each individual crystal. The absolute configurations of the chiral crystals of 2 were determined by X-ray crystal structure analysis using the Flack parameter method. The solid-state CD spectra of the chiral crystals in KBr were mirror images. The equilibrium between the two enantiomers in solution is fast during crystallization at ambient temperature, and the energy barrier (DeltaG()) is estimated to be 11.7 +/- 0.3 kcal/mol (233 K).     

Reduction of isocyanates and carbodiimides via hydrosilylation

The hydrosilylation of isocyanates is promoted by palladium catalysts and affords N-silylformamides or C-silylamides. The orientation of the reaction depended upon the structure of isocyanates. The reaction of carbodiimides with silicon hydrides, catalyzed by PdCl₂ or (Ph₃P)₃RhCl, required higher temperatures to give N-silylformamidines. The adducts obtained in these reactions are precursors to formamides, formamidines, and their N-acetyl derivatives.     

Determination of phosphorus in silicate rocks by flow injection method of analysis

Summary A flow injection spectrophotometric method has been developed for the determination of phosphorus in silicate rocks. A rock solution is prepared by fusion with a mixture of lithium carbonate and boric acid and subsequent dissolution with l M hydrochloric acid. An aliquot of the sample solution is injected directly into the flow system, which consists of formation of heteropolyacids of molybdenum and antimony, reduction with ascorbic acid, and subsequent measurement of the absorbance of blue species. It permits semi-automated analysis of a variety of silicate rocks for phosphorus. Results obtained for standard rocks were in good agreement with the recommended values. The throughput comes out 20 samples per h.

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Bestimmung des Phosphors in Silikatgestein durch Flie-Injektions-Analyse

Zusammenfassung Ein Verfahren zur spektrophotometrischen Phosphorbestimmung in Silikatgestein mittels Fließinjektion wurde entwickelt. Das Gestein wird mit einer Mischung aus Lithiumcarbonat und Borsäure aufgeschlossen und in 1 M Salzsäure gelöst. Ein aliquoter Teil der Lösung wird unmittelbar in das fließende System injiziert, worin Heteropolysäuren aus Molybdän und Antimon gebildet, mit Askorbinsäure reduziert und die Absorbanz der blauen Farbe gemessen wird. Dies ermöglicht die halbautomatische Analyse verschiedener Silikatgesteine zur Phosphorbestimmung. Die Resultate von Standardproben stimmen mit den vorgeschriebenen Werten gut überein. In der Stunde können 20 Proben durchgesetzt werden.

     

Novel 2-pyridone synthesis via nucleophilic addition of malonic esters to alkynyl imines

[reaction: see text] A novel 2-pyridone synthesis via nucleophilic addition of malonic esters to alkynyl imines has been developed. The reaction of dialkylalkyl sodiomalonates with alkynyl imines provided 2-pyridones in good to excellent yields.     

Synthesis of chiral oligopeptides by means of catalytic asymmetric hydrogenation of dehydropeptides

Asymmetric hydrogenations of Ac-ΔTyr(Ac)-(S)-Ala-Gly-OMe (6), Ac-ΔTyr(Ac)-(R)-AlaGly-(S)-Phe-OMe (7), Ac-ΔPhe-NH-CH(R) CH₂-OCH₂Ph (10), HCO-ΔPhe-(S)-Leu-OMe (16), X-AA-ΔPhe-AA'-OMe (5: X ^tBOC, CBZ, CF₃CO; AA, AA' = α-amino acid), and ^tBOC-AA-ΔPhe-AA'-NH-Y (21: Y=H, NH-AA'-ΔPhe-AA-^tBOC, NHPh), catalyzed by cationic Rh complexes, [L*Rh(NBD)]⁺ClO₄ (L* = chiral diphosphine), were performed to give the corresponding chiral oligopeptides with high stereoselectivities. It was found that the nature of the N-protecting group of dehydrotripeptides (5) exerted a significant influence on the asymmetric induction as well as catalyst efficiency. The chiral centers in AA' and AA' amino acid residues in 5 were also found to have some influence on the catalytic asymmetric induction. Possible mechanism which can accommodate these effects are discussed. Asymmetric reduction of RCOCO-AA-OMe (13) via hydrosilylation was carried out to give chiral depsipeptide units. The asymmetric hydrogenation of dehydropeptides was successfully applied to the synthesis of enkephalin analogs, Ac-(R)Tyr-(R) -Ala-Gly-(S)-Phe-(S)-Leu-OMe (23) and Ac-(S)Tyr-(R) -Ala-Gly-(S)-Phe-(S)- Leu-OMe (29)     

Preparation of soluble ternary heteroazo dye complexes for the spectrophotometric determination of trace uranium(VI)

The complexing ability of typical pyridylazo, quinolylazo and thiazolylazo dyes with uranium(VI) in aqueous ethanol media are investigated in the presence and absence of aromatic carboxylic acid. Uranium(VI) forms solubilized ternary complexes with PAN, PAR, TAM, 5-Br-PADAP, 3,5-diBr-PADAP and QADAP in 48% ethanol solution containing sufficient amounts of sulfosalicylic acid and triethanolamine buffer (pH 7.8). Aromatic carboxylic acids contribute to expel the coordinated water molecules from the uranium (VI) moiety and their chelating effects have been explained by ternary complex formation. An increase in molar absorptivity and no shift in the wavelength of maximum absorbance are observed for all uranium(VI) complexes investigated. The 11 stoichiometry of uranuim(VI) and heteroazo dye in the binary complex does not change through ternary complex formation. The molar absorptivity of the uranium(VI)-3,5-diBr-PADAP-sulfosalicylic acid ternary complex at 595 nm is 8.4×10⁴l mol^–1 cm^–1 and Beer's law is valid up to 2.5gmg ml^–1 of uranium(VI). The interferences due to coexisting metal ions can be effectively masked by addition of CyDTA or Ca-CyDTA.     

Assignment of the 1H- and 13C-NMR spectra of phenanthro[1,2-b]thiophene through the concerted application of two-dimensional NMR spectroscopic techniques

Two-dimensional nmr spectroscopy, by virtue of its second frequency domain which permits the segregation of spectral information along two frequency axes, considerably simplifies many assignment problems and facilitates others which may be impossible using conventional nmr methodology. A compound which falls into the latter category of assignment problem is phenanthro[1,2-b]thiophene. The assignment of the ¹H- and ¹³C-nmr spectra of phenanthro[1,2-b]thiophene are, however, reported through the concerted application of two-dimensional nmr techniques. Experiments utilized in making the assignments included: auto-correlated homonuclear (COSY) two-dimensional spectroscopy; heteronuclear two-dimensional J-resolved spectroscopy; proton-carbon chemical shift correlation two-dimensional spectroscopy; and two-dimensional ¹³C-¹³C double quantum coherence spectroscopy.     

Fast and slow fluorescence emissions from pyrimidine vapor

The pressure and excitation-energy dependence of the fluorescence quantum yield and lifetime of pyrimidine vapor has been investigated in the pressure range 10^?3-10 torr. The results indicate that in conformity to the intermediate case the fluorescence of the isolated pyrimidine molecule consists of fast and slow components with lifetimes of the order of 1 ns and 10 μs, respectively. The total fluorescence quantum yield amounts to as high as 0.045. The yield of the slow fluorescence component decreases significantly with increasing excitation energy; this observation is interpreted as being due mainly to the lengthening of the radiative lifetime of that component.