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  • 1
    Electronic Resource
    Electronic Resource
    General theory of stationary random sequences with applications to the tacticity of polymersPaper presented at the 142nd Meeting of the American Chemical Society, Atlantic City, New Jersey, September 1962. (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 1635-1649 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When, in a poly-α-olefin, the probability that a given placement be isotactic depends upon the tacticity of only a finite number of immediate predecessors, the resulting diastereosequence distribution obeys the theory of Markoff chains. When this is not the case, one says that the resulting diastereosequence distribution is non-Markoffian. A special case of a Markoffian distribution is given by a simple Markof chain in which the tacticity of a given placement is assumed to be affected by only the tacticity of the immediately preceding placement. Another special case is, of course, the Bernoulli trial distribution in which the probability that a given placement be isotactic is independent of the tacticity of all other placements. A high resolution NMR spectrum can sometimes yield a quantitative determination of the concentrations of isotactic and syndiotactic placements and the concentrations of the three types of possible adjacent pairs of such placements (i.e., isotactic, syndiotactic, and heterotactic pairs). When this is the case, the spectrum can be used to determine whether or not a given diastereosequence distribution is Bernoullian. However, because the longest diastereosequences whose concentration can be measured by NMR spectroscopy involve only two placements, an NMR spectrum cannot check whether a given non-Bernoullian distribution be simple Markoffian or Markoffian in general. In fact, non-Markoffian distributions are compatible with existing NMR spectra on polymers prepared by anionic polymerizations. In this paper we work within the framework of Kac's theory of stationary statistical processes and point out some general results which are valid for both Markoffian and non-Markoffian processes. The results are applied to NMR spectroscopy and it is pointed out which calculations used to check the self-consistency of NMR data and to obtain the mean length of closed diastereosequences are valid for both Markoffian and non-Markoffian distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1996.838
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  • 2
    Electronic Resource
    Electronic Resource
    Erhöhung der Verschleißfestigkeit der TiAl6V4-Legierung durch Implantieren mit Stickstoff-Ionen (1996)
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 27 (1996), S. 9-13 
    Details
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Increasing of wear resistance of Ti-6Al-4V alloy by nitrogen implantationNitrogen ion implantation is used to improve the wear resistance of Ti-6Al-4V alloy. Different implantation doses up to 1 · 1018N+/cm2 and E = 170 KeV were used. The unimplanted and the implanted specimens were tested in a wear model system with oscillation loading. The results show, that the wear performance was influenced by implantation dose and also by mean pressure. It was found, that surfaces, which are produced by a high implantation dose (1 · 1018N+/cm2), exhibited greater were resistance than untreated Ti-6Al-4V alloy. The best wear behaviour was achieved by a high implantation dose (1 · 1018N+/cm2) and a low mean pressure (p =0.22 MPa) at the wear test. The difference between the wear rate of the untreated and of the implantated specimen can obtain a factor about 10. The effective depth of the implantation action is greater than the penetration depth of the nitrogen ions.
    Notes: Durch Implantation von Stickstoff-Ionen wurde die Randschicht der Ti-Al6-V4-Legierung mit dem Ziel der Verbesserung des Verschleißverhaltens modifiziert. Es wurde dazu mit unterschiedlichen Stickstoffdosen bis 1 · 1018N+/cm2 bei E = 170 keV implantiert. Die Modellverschleißuntersuchungen bei oszillierender Beanspruchung wiesen nach, daß die Implantationsdosis in Abhängigkeit von der im Tribosystem wirkenden mittleren Pressung den Verschleiß deutlich beeinflußt. Wird mit einer hohen Dosis (1 ·1018N+/cm2) implantiert und werden die Beanspruchungsbedingungen so gewählt, daß nur eine relativ geringe Pressung von p ≤ 0.22 MPa auftritt, dann ist mit einer Erhöhung der Verschleißbeständigkeit mindestens um den Faktor 10 zu rechnen. Für größere Pressungen nimmt die Erhöhung des Verschleißwiderstandes ab. Die verschleißmindernde Wirktiefe der Implantation liegt weit über der Eindringtiefe der implantierten Stickstoffionen.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mawe.19960270106
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  • 3
    Electronic Resource
    Electronic Resource
    Glycosyl Imidates, 78Part 77: Ref.[1].. An Efficient Synthesis of Galactinol and Isogalacatinol (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 859-863 
    Details
    ISSN: 0947-3440
    Keywords: myo-Inositol, racemate resolution ; Glycosylation, trichloroacetimidate method ; Tin(II) trifluoromethanesulfonate catalyst ; Oligosaccharide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2:3,4:5-Di-O-cyclohexylidene-D-/L-myo-inositol (2) could be readily converted into 6-O- and 1-O-unprotected L- and D-myo-inositol derivatives L- and D-4 and L- and D-6, respectively. Their reaction with trichloroacetimidate 7 as galactosyl donor in the presence of tin(II) trifluoromethanesulfonate as catalyst afforded the desired α(1-6)- and α(1-1)-connected galactopyranosides 8, 11 and 12. Compound 11 could be readily deprotected to afford target molecule (galactinol) 1 in high overall yield; from 12, the diastereoisomer 13 was obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970511
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  • 4
    Electronic Resource
    Electronic Resource
    Elucidation of Factors Affecting the Electronic Structures of Magnesium(II) and Zinc(II) Tetraarylporphyrin Radical Cations (1995)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 1 (1995), S. 222-231 
    Details
    ISSN: 0947-6539
    Keywords: electronic structure ; frontier orbitals ; metalloporphyrins ; radical cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of magnesium and zinc tetraarylporphyrins and their porphyrinoxidized derivatives were studied by UV/Vis, ESR, and resonance Raman spectroscopy at various temperatures. The series included tetra(meta-dichlorophenyl)porphyrinatozinc (5), tetra(ortho-dichlorophenyl)porphyrinatozinc (6), tetra(ortho-difluorophenyl)porphyrinatozinc and -magnesium (9 and 10), and tetra(pentafluorophenyl)porphyrinatozinc and -magnesium (7 and 8). The radical cations (3a-10a) were isolated by chemical one-electron oxidation of their neutral precursors (3-10). Despite the structural similarity of all these radicals, their electronic ground state varied within the series. The position of the chloro groups was found to play a key role. While the radical cation of the meta-dichloro-substituted derivative 5a exhibited A2u spectroscopic features, the ortho-dichlorophenyl derivative (6a) showed A1u spectral features. Radicals of the fluoro-substituted porphyrins, especially that of 10, were found to have state-admixed (A1u/A2u) electronic structures, and the relative contributions of the two states was found to vary with temperature and to depend on the axial ligand. The results indicate that the fluoro-substituted porphyrins are primarily A2u at low temperature, even though their room temperature spectroscopic features resemble those of A1u cations. The elucidation of factors that affect the electronic structures of the radicals in the present series is helpful in providing a greater understanding of the spin-spin interactions in the intermediates of heme-dependant enzymatic reactions and their synthetic analogues.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19950010405
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanism of interfacial mass transfer in membrane transport (1968)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 14 (1968), S. 421-425 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dialysis of binary aqueous solutions of several sugars through a cellophane membrane was studied in a stirred batch dialyzer. Sherwood numbers describing mass transfer resistance in the fluid adjacent to the membrane were determined as a function of the corresponding Reynolds and Schmidt numbers. The results establish a reproducible environment for membrane testing in which a known controllable and small interfacial resistance is placed in series with that of the membrane. The results are also shown to support, for this geometry, the postulation of a third power relationship between eddy diffusivity and dimensionless distance from the phase boundary as well as the Sherwood-Ryan nondimensionalization of this distance.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690140316
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  • 6
    Electronic Resource
    Electronic Resource
    Studies of intramembrane transport: A phenomenological approach (1968)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 14 (1968), S. 110-117 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The intramembrane transport properties of carbohydrates were investigated in cellophane. The experiments performed were the measurement of net volume transfer under a concentration and pressure gradient and the solute transfer due to a concentration difference together with the physical properties of the membrane. The matrix of phenomenological coefficients characteristic to the transport was established after the phase boundary contributions were extricated from the experimental transport data. These thermodynamic coefficients were then interpreted through the Spiegler-Kedem-Katchalsky frictional model.The analysis of the frictional coefficients clearly indicated the importance of solute-polymer interactions. The magnitude of solute-solvent frictional coefficients in the membrane were compared with the corresponding interactions in free solutions. Their differences were explained in terms of the interaction of the solute with the macromolecular network and were quantitatively expressed by introducing two reduced frictional coefficients. The tortuosity factor was shown to be related to these interactions and not a simple geometric property of the membrane. The temperature dependence of the frictional coefficients was established.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690140120
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  • 7
    Electronic Resource
    Electronic Resource
    Glycosyl Phosphatidylinositol (GPI) Anchor Synthesis Based on Versatile Building Blocks - Total Synthesis of a GPI Anchor of Yeast (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1153-1165 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Sphingosines ; Ceramides ; Ceramides-1-phosphates ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -For the design of a synthesis of target molecule 1 the retrosynthetic analysis yielded building blocks 2-5, of which ceramide 2-phosphite derivative 2 and aminoethyl phosphite derivative 5 are known. The generation of α-glucosaminyl (1→6)inositol building block 3 was based on pseudodisaccharide 6 which was selectively benzoylated at 6b-O and then selectively benzylated at 3b-O to give 3. The synthesis of tetramannosyl building block 4 started from known ortho ester derivative 8 which was transformed into versatile mannosyl donors 13 and 18 and into acceptor 22. Reaction of 13 with 22 gave α-disaccharide 23, deacetylation and then mannosylation with 18 gave trisaccharide 25; ensuing deacetylation and mannosylation with 13 gave tetrasaccharide 27; deallylation, acetylation, regioselective removal of the anomeric O-acetyl group and treatment with CCl3CN/DBU afforded 4. Glycosylation of 3 with donor 4 led to pseudohexasaccharide 31 in high yield. Replacement of the O-acyl groups by O-benzyl groups and then exchange of the menthyloxycarbonyl group by an O-acetyl group gave 36 which enabled regioselective attachment of 2 and 5. To this end, the 6e-O-silyl group was removed and then the aminoethyl phosphate residue was attached with reagent 5 to give 38 in high yield. 1a-O-Deacetylation and then reaction with 2 afforded 40 as fully protected 1 which was liberated in two steps; treatment with acid removed all acid labile protective groups and finally catalytic hydrogenation afforded the desired GPI anchor 1 which could be fully structurally assigned.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Application of the Benedict-Webb-Rubin equation of state to argon (1966)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 12 (1966), S. 577-580 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The coefficients of the Benedict-Webb-Rubin equation of state have been developed for argon. By employing these coefficients, the volumetric behavior of argon has been predicted with an average deviation of 0.241% for five hundred ninety-seven smoothed and experimental data points in the superheated region.At temperatures below the critical, two sets of Co's, one for the liquid and one for the vapor, were needed to relate the vapor pressure to the densities of saturated argon. However, consistent fugacities for the saturated vapor and liquid argon could not be predicted with these Co values. Therefore, another set of Co's was developed by equating the pure component vapor and liquid fugacities along the vapor pressure curve. These values were used to test the applicability of the equation of state to predict derived thermodynamic properties.The original BWR expression for calculating isothermal pressure effects on enthalpy was modified to include explicitly the temperature dependence of the coefficient Co. Vapor-liquid equilibrium relations for the argon-nitrogen system predicted by the standard BWR procedure were compared with experimental data.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690120333
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  • 9
    Electronic Resource
    Electronic Resource
    Modeling the heme vibrational spectrum: Normal-mode analysis of nickel (II) etioporphyrin-I from resonance raman, ft-raman, and infrared spectra of multiple isotopomers (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 1 (1995), S. 395-412 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Nearly complete vibrational assignments have been obtained for a heme model, nickel etioporphyrin-I (NiEPI), using variable-wavelength resonance Raman (RR), and FT-Raman (FT-R), as well as infrared (IR) spectroscopy, on a series of isotopomers labeled at positions in the skeleton (15N, β-13C, meso-d4, 15N-meso-d4) and in the peripheral substituents (methyl-d12, ethyl-d8, and ethyl-d12). The vibrational bands are assigned to the porphyrin skeletal and substituent modes on the basis of the mode description scheme developed for nickel octaethylporphyrin (NiOEP) with the aid of a normal-mode analysis of NiEPI, explicitly including the peripheral substituents, i.e., the methyl and ethyl groups. The previously reported NiOEP force field was refined to account for the observed isotope shifts of NiEPI isotopomers. An important result is the requirement of relatively large, long-range force constants for methine bridge bonds on opposite sides of the porphyrin ring. These 1-8 and 1-9 interaction force constants are required to reproduce the frequencies and isotope shifts of six Cα-Cm stretching modes and especially to predict the relative order of the two highest-frequency Eu modes, v(Cα-Cm) (v38, ∼ 1570 cm-1) and v(Cβ-Cβ) (v37, ∼ 1600 cm-1). Most of the substituent (methyl and ethyl) vibrations are located in the RR and IR spectra. Strong RR enhancement of some substituent modes can be attributed to hyperconjugative interaction of the aliphatic groups with the porphyrin a1u orbital, as well as vibrational mixing of substituent modes with the nearby skeletal modes. © 1995 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bspy.350010605
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  • 10
    Electronic Resource
    Electronic Resource
    Heme-protein interactions in cytochrome c peroxidase revealed by site-directed mutagenesis and resonance Raman spectra of isotopically labeled hemes (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biospectroscopy 2 (1996), S. 365-376 
    Details
    ISSN: 1075-4261
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Isotope labeling has been used to assign the resonance Raman spectra of cytochrome c peroxidase, expressed in Escherichia coli [CCP (MKT)], and of the D235N site mutant. 54Fe labeling establishes the coexistence of two separate bands (233 and 246 cm-1), arising from the stretching of the bond between the Fe atom and the proximal histidine ligand, His175. These are assigned to tautomers of the H-bond between the His175 imidazole NΓH proton and the Asp235 carboxylate side chain: In one tautomer the proton resides on the imidazole while in the other the proton is transferred to the carboxylate. When Asp235 is replaced by Asn, the H-bond is lost, and the Fe-His stretching frequency is markedly lowered. Two new RR bands are produced, at 205 and 185 cm-1, as a result of coupling between the shifted Fe-His vibration and a nearby porphyrin mode; the two bands share the 54Fe sensitivity expected for Fe-His stretching. C=C stretching and CβC=C bending vibrations have been separately assigned to the 2- and 4-vinyl groups of the protoheme prosthetic group via selective vinyl deuteration. In the acid form of the enzyme, the frequencies coincide for the two vinyl groups, at 1618 cm-1 for the C=C stretch, and at 406 cm-1 for the CβC=C bend. However, the 2-vinyl frequencies are elevated in the alkaline form of the enzyme, to 1628 cm-1 for C=C stretching, and to 418 cm-1 for CβC=C bending, while the 4-vinyl frequencies remain unshifted. Thus, the acid-alkaline transition involves a protein conformation change that specifically perturbs the 2-vinyl substituent. This perturbation might be a reorientation of the vinyl group, or an alteration of the porphyrin geometry that affects the porphyrin-vinyl coupling. The perturbation is attenuated when CO is bound to the enzyme; the C=C frequency is then unaffected in the alkaline form, while the CβC=C bending frequency is shifted to a smaller extent (412 cm-1). This attenuation is probably linked to inhibition of distal histidine binding to the heme Fe in the alkaline form when the CO is bound. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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