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  • Chemistry  (68)
  • General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.  (7)
  • 1
    ISSN: 1434-193X
    Keywords: Zeolites ; Electron transfer ; Proton transfer ; Radical ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Incorporation of N,N′-diphenylhydrazine into HZSM-5 led to the formation of azobenzene and aniline (70-80 mol-% mass balance). The formation of azobenzene can be followed by the appearance in diffuse reflectance UV/Vis spectroscopy of a characteristic band (λmax = 420 nm). IR spectra of the extracted solids indicate that some aniline is retained in the zeolite, probably due to acid-base interaction with active sites. The products are rationalized by two competing mechanisms: the formation of azobenzene by electron transfer to an oxidizing site, the generation of aniline by proton transfer from a Brønsted acid site. A long-wavelength diffuse-reflectance band (λmax = 800 nm) in the initial stages of the reaction supports the intermediacy of a radical cation. These results show that acid zeolites can exhibit a dual behavior against basic substrates with low oxidation potential, serving simultaneously as electron acceptor and Brønsted acid.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 15 (1992), S. 124-130 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The adsorption of p-nitrophenol (PNP) from an NaOH, H3PO4-buffered, aqueous solution on activated carbon was studied at pH 2, 7, and 8.5. Comparative studies were then carried out on ozonized carbon and ozonized PNP solution. In the latter case, PNP adsorption was performed from an ozonized solution, and also after exposing the activated carbon to the ozonized PNP solution for 24 h. At acid pH, PNP adsorption was found to be markedly higher than at neutral and weakly basic pH's. Ozonization of carbon affects the results only at pH 7 and 8.5. Ozonization of PNP led to a small decrease in adsorption, irrespective of the method of contect between carbon and ozonization reaction products. The rate was faster at acid than at basic pH, and the ozonization speeded up the adsorption slightly but only at pH 8.5. Application of a mathematical model indicated that mass transfer in bulk solution controls the rate of adsorption.
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 684-694 
    ISSN: 0006-3592
    Keywords: immobilized enzymes ; organic solvents ; mechanism ; kinetic studies ; microscopic rate constants ; rate-limiting step ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics of the immobilized lipase B from Candida antarctica have been studied in organic solvents. This enzyme has been shown to be slightly affected by the water content of the organic media, and it does not seem to be subject to mass transfer limitations. On the other hand, some evidence indicates that the catalytic mechanism of reactions catalyzed by this lipase proceeds through the acyl-enzyme intermediate. Moreover, despite the fact that the immobilization support dramatically enhances the catalytic power of the enzyme, it does not interfere with the intrinsic solvent effect. Consequently, this enzyme preparation becomes optimum for studying the role played by the organic solvent in catalysis. To this end, we have measured the acylation and deacylation individual rate constants, and the binding equilibrium constant for the ester, in several organic environments. Data obtained show that the major effect of the organic solvent is on substrate binding, and that the catalytic steps are almost unaffected by the solvent, indicating the desolvation of the transition state. However, the strong decrease in binding for hydrophilic solvents such as THF and dioxane, compared to the rest of solvents, cannot be easily explained by means of thermodynamic arguments (desolvation of the ester substrate). For this reason, data have been considered as an indication of the existence of an unknown step in the catalytic pathway occurring prior to formation of the acyl-enzyme intermediate. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:684-694, 1998.
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 44 (1992), S. 1371-1376 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of iron oxides particles mixed in natural rubber (NR) or aged natural rubber (ANR) from Manihot glaziovii were investigated. IR spectroscopy showed that α-Fe2O3 inhibits or retards the thermal degradation (200°C) of ANR, but it does not inhibit or retard the thermal degradation of NR. A retardation effect is observed using iron (III) oxide in both ANR and NR. Using both oxides, longer autoxidation induction periods of ANR and NR are observed (150°C). The periods were extended for a higher content of rubber hydroperoxide concentration. The inhibition or retardation of autoxidation using Fe3O4 in both ANR and NR is not evident. We suggest an interaction between hydroxyl groups of hydroperoxide, mainly present in aged natural rubber, and the iron oxide surface.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 51 (1996), S. 673-678 
    ISSN: 0006-3592
    Keywords: image analysis ; Saccharomyces cerevisiae floc ; floc counting ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A standardized image analysis method has been developed permitting determination of the number of yeast flocs and their size distribution. The method includes image grabbing, image enhancement, automatic determination of the appropriate threshold, curve fitting of the areahistogram, determination of the mean single floc area and its standard deviation, and floc counting. The extension of the method to other applications is immediate and straightforward. Two Saccharomyces cerevisiae floc Populations (with ages of 48 and 72 h) were analyzed. The results showed a variation around the mean of 9%-12% for the single floc mean area, 6%-7% for the number of single flocs, and 5%-6% for the total number of flocs. Aggregates of two flocs (doublets) and three flocs (triplets) were enumerated. The correctness of the method was checked by analyzing the parameters of interest as a function of the threshold. The constant correlation between the parameters and the threshold showed the validity and consistency of the method. © 1996 John Wiley & Sons, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 11 (1998), S. 25-30 
    ISSN: 0894-3230
    Keywords: 1,ω-bis(2-bromopyridinium)alkanes ; hydroxide ion ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reaction of OH- ion with 1,ω-bis(2-bromopyridinium)alkanes, where the reaction centers are separated by a varying number of methylene groups, was investigated to model the increased velocity of OH- attack on premicellar aggregated N-alkylpyridinium compounds. 1,ω-Bis(2-bromopyridinium)alkanes (RPBr) [R  =  propane (I), butane (II), pentane (III), hexane (IV) and octane (V)] were synthesized and characterized by standard procedures. The kinetics of I-V with OH- ion fitted two consecutive first-order reactions. The intermediate products, 1-(2-pyridone)-ω-(2-bromopyridinium)alkane, and also the final products 1,ω-bis(2-pyridone)alkanes, were isolated. Deuterium isotope effects, activation parameters and salt effects on the reaction rates suggest that OH- attack is rate limiting and there is a through-space acceleration of the initial attack due to the proximity of the positive charges. These results place an upper limit of 20-fold for the electrostatic acceleration in OH- attack in premicellar aggregates. © 1998 John Wiley & Sons, Ltd.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 33 (1987), S. 2107-2115 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A natural polymer in a commercially available form (chitosan) has been tested using a factorial design of experiments for its application to cobalt recovery either in hydrometallurgy and in analytical separations. A simple mechanically stirred system has been used, evaluating the influence of the contact time, iron(II), cobalt (II), chitosan concentration, salinity, and pH in the separation. The pH value has a dramatic influence on the metal recovery from a negligible amount of metals at pH = 1.0 to a quantitative sorption at pH = 3.0. Linear relationships between sorbed metal and the variables have been determined at constant pH value and a quantitative evaluation of the metal recovery at different pH values can be performed using the maximum sorption capacity of the chitosan (a0) and the selectivity for both metals. The obtained results allow the evaluation of the recovery of metals using chitosan as solid phase.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 169-174 
    ISSN: 0935-6304
    Keywords: Experimental design optimization ; Supercritical fluid chromatography ; Aromatic content ; Petroleum cuts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A experimental design optimization method is demonstrated for evaluation of the resolution of the performance mixture used in the proposed ASTM test to determine the aromatic content of aviation fuels. The method uses a Doehlert experimental matrix test to optimize the resolution and analysis time by varying the pressure and temperature of the supercritical carbon dioxide mobile phase. The separation between saturated and aromatic compounds was optimized using only seven experiments. With this procedure, the analysis time required for determination of the total aromatic content of more complex samples can be reduced to less than 10 min.
    Additional Material: 9 Ill.
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  • 9
    ISSN: 1434-1948
    Keywords: Metal complexes ; Template synthesis ; Schiff bases ; Oxaazamacrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New series of macrocyclic Schiff-base lanthanide(III), yttrium(III), and cadmium(II) complexes, [M(1)]Xn (X = NO3-, M = Y, Ln = La-Yb except Pm and Dy; X = ClO4-, M = Cd, La, Ce, Pr, Sm, Gd, or Er) and [M(3)]Xn (X = NO3-, M = Dy; X = ClO4-, M = Er and Cd), have been prepared by cyclocondensation of O1,O7-bis(2-formylphenyl)-1,4,7-trioxaheptane with O1,O7-bis(2-aninyl)-1,4,7-trioxaheptane (1) or tris(2-aminoethyl)amine (3) in the presence of the appropriate metal salt as a template agent. The Schiff-base macrocycles 1 and 3 are also formed in the absence of a metal ion. Treatment of 1 with NaBH4 in methanol gives the diamine macrocycle 2. The reactions of LnIII, CdII, and YIII ions with 2 have also been investigated. The crystal structures of the monoprotonated ligand 2 and of the complex [Cd(3)](ClO4)2 have been determined by X-ray diffraction analysis.Supporting information for this article is available on the WWW under -//_/_http://www.wiley-vch.de/contents/jc_2005/2000/99352_s.pdf or from the author.
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  • 10
    ISSN: 1434-1948
    Keywords: Gold(I) ; Silver(I) ; S-donor and N-donor ligand ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ligand properties of 2-(phenacylthio)pyridine towards gold(I) and silver(I) have been investigated. From the reactions of the ligand with acetone solutions of [M(PPh3)(acetone)]ClO4 (M = Ag, Au) under various experimental conditions, complexes [(AuPPh3)n{py{SCH2C(O)Ph}-2}](ClO)n, and [(AgPPh3)n(OClO3)n{py{SCH2C(O)Ph}-2}](n = 1-3) have been obtained. The crystal structures of the complexes [(AuPPh3){py{SCH2C(O)Ph}-2}]ClO4 and [(AgPPh3)(OClO3){py{SCH2C(O)Ph}-2}] have been determined by X-ray diffraction. In the cationic gold complex the metal is linearly coordinated to nitrogen and phosphorus, whereas the corresponding silver complex displays a trigonal planar geometry with pyridine, phosphane and perchlorato ligands.
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