Multicyclic polyethers derived from 1,1,1‐tris(4‐hydroxyphenyl)ethane and 2,6‐dihalopyridines

Poly(pyridine ether)s were prepared in two ways: the polycondensation of silylated 1,1,1‐tris(4‐hydroxyphenyl)ethane (THPE) with 2,6‐difluoropyridine (method A) and the polycondensation of free THPE with 2,6‐dichloropyridine (method B). With method A, the THPE/difluoropyridine feed ratio was varied from 1.0:1.0 to 1.0:1.6. Cycles, bicycles, and multicycles were the main reaction products, and crosslinking was never observed. When ideal stoichiometry was used exclusively, multicycles free of functional groups were obtained. These multicycles were detectable in matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectra up to B₃₈C₇₆ with a mass of approximately 32,000 Da. With method B, the reaction conditions were varied at a fixed feed ratio to achieve an optimum for the preparation of multicyclic polyethers, but because of the lower reactivity of 2,6‐dichloropyridine, a quantitative conversion was not achieved. The reaction products were characterized with MALDI‐TOF mass spectrometry, viscosity measurements, and size exclusion chromatography. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5725–5735, 2004     

Cyclic and telechelic ladder polymers derived from tetrahydroxytetramethylspirobisindane and 1,4‐dicyanotetrafluorobenzene

5,5′,6,6′‐Tetrahydroxy‐3,3,3′,3′‐tetramethylspirobisindane was polycondensed with 1,4‐dicyanotetrafluorobenzene in four different solvents at 70 °C. In dimethylformamide, N‐methylpyrrolidone, and sulfolane exclusively, cyclic polymers were detectable by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry up to masses around 13,000 Da. In dimethyl sulfoxide, linear byproducts were also found. Higher temperatures caused degradation reactions catalyzed by potassium carbonate. Polycondensations performed with the addition of 4‐tert‐butyl catechol or 2,2′‐dihydroxy binaphthyl yielded linear telechelic oligomers. Equimolar mixtures of linear and cyclic ladder polymers were examined by MALDI‐TOF mass spectra to determine how the end groups and the cyclic structure influenced the signal‐to‐noise ratio. The results suggested a preferential detection of the linear chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5344–5352, 2006     

A fast,sensitive determination of doxorubicin in rat plasma by solid-phase extraction and reversed-phase ion-pair chromatography

A very selective method is described for the determination of doxorubicin in rat plasma. Doxorubicin is extracted from the plasma on a pretreated octadecyl silane column and eluted with phosphate buffer pH 2.6/methanol (25/75, v/v) containing sodium 1-heptanesulfonate as ion-pairing agent. The extraction procedure is suitable for samples which contain doxorubicin encapsulated in liposomes if Triton X-100 is added. A portion of the evaporated eluate is used for high-performance reversed-phase chromatography with the same eluent and a fluorescence detector. Daunorubicin is used as internal standard. Extraction of doxorubicin from plasma is quantitative. The calibration graph is linear for 0.2-100 μg l^?1 doxorubicin with a limit of detection of 0.2 μg l^?1 for 0.5 ml of plasma. The relative standard error of estimate of the calibration was typically 3%.     

Die Zahl der Spitzen und die Jacobi-Algebra einer isolierten Hyperflächensingularität

Let f{x_o,...,x_n} define a germ of a complex analytic hypersurface (X_o,0) with isolated singularity. We show that the number of cusps of the unfolded discriminant curve is an invariant of the Jacobian algebra {x,_o},...,x_n/(f/x_o,...,f/x_n) of f. Moreover we show that this number + 1 equals the sum of the Milnor numbers of (X_o,0) and of the polar curve of (X_o,0). Our result generalizes formulas of Iversen and Lê for plane curves to arbitrary dimensions.     

Possibilities of nitric acid preparation of powder cellulose forms

For preparation of various modified forms of microcrystalline cellulose, an optional combination is proposed of hydrolytic activity with other properties of nitric acid such as, adduct forming ability (manifested as Knecht compound formation), oxidizing, bleaching and nitrating. The manifestation of a chosen acid function is reached by variation of the reaction conditions: concentration, temperature, time, etc. The sole-reagent continuous procedure involving several operations made in a predetermined sequence allows the use of a more simple technological scheme and saves energy, time and materials. The features of transformation of fibrous and microcrystalline forms of native cellulose into cellulose-II through the Knecht compound are discussed. Purely acidic transformation schemes of native cellulose into microcrystalline cellulose hydrate and amorphous low-nitrate powder cellulose according to the above scheme are considered. Morphological features as well as distinguishing properties — enhanced hydrophilicity, sorption activity and degree of whiteness — of the prepared materials are pointed out. The possibility of obtaining uniformly oxidized forms of powder cellulose according to this scheme and the outlook for the use of nitrogen(IV) oxide as a multifunctional reagent are discussed.     

Aqueous Solution Chemistry of the Mo(3)PdS(4) Cube: Substitution Reactions and the Double to Single Cube Interconversion Induced by CO, Two Phosphines, Cl(-), Br(-), and NCS(-)

The kinetics of conversion of an edge-linked double cube, in this case [{Mo(3)PdS(4)(H(2)O)(9)}(2)](8+), to the corresponding single cube [Mo(3)(PdX)S(4)(H(2)O)(9)](4+), has been studied for the first time. Reaction is induced by six reagents X = CO, two water-soluble phosphines, Cl(-), Br(-), and NCS(-), which complex at the tetrahedral Pd. The first stage of reaction is fast and is accompanied by color changes, e.g. purple to dark blue in the case of Cl(-), assigned as double to single cube conversion. With X = CO and the two phosphines, when absorbance changes are intense enough for stopped-flow monitoring with reactants at Pd-SCN. On removal of e.g. Cl(-) by chromatography or addition of Ag(+), the double cube re-forms.     

Wasserstoffumlagerungen bei der elektronenstoßinduzierten Fragmentierung von Aminoäthern

Due to neighbouring group effects the behaviour under electron impact of amino ethers of the type RO(CH₂)_nNR₁R₂ is distinctly different from that of both simple ethers and amines. In addition to α-cleavages two further primary fragmentations can often be observed, one leading to [M–aldehyde]^+. or [M–ketone]^+. ions, the other (with n≥3) giving [M–R]⁺ ions. Both processes involve hydrogen rearrangements which were investigated by means of deuterium labelling. Their importance is strongly dependent upon the nature of the substituents R, R₁, R₂ and upon the length (n) of the carbon chain between the heteroatoms. This dependence can easily be explained by the fragmentation mechanisms put forward.     

Structure determination of gas-phase niobium and tantalum carbide nanocrystals via infrared spectroscopy

Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals.