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  • Wiley  (76)
  • Wiley-Blackwell  (41)
  • 1985-1989  (117)
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  • 1
    Publication Date: 1987-09-15
    Print ISSN: 0008-543X
    Electronic ISSN: 1097-0142
    Topics: Biology , Medicine
    Published by Wiley on behalf of American Cancer Society.
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The enthalpy of hydrogen-bond formation between guanine (G) and cytosine (C) in o-dichlorobenzene and in chloroform at 25°C has been determined by direct calorimetric measurement. We derivatized 2′-deoxyguanosine and 2′-deoxycytidine at the 5′- and 3′-hydroxyls with triisopropylsilyl groups; these groups increase the solubility of the nucleic acid bases in nonaqueous solvents. Such derivatization also prevents the ribose hydroxyls from forming hydrogen bonds. Consequently, hydrogen-bond formation in our system is primarily between the bases, and to a lesser extent, between base and solvent, and can be measured directly with calorimetry. To obtain the data on base-pair formation, we first took into account the contributions from self-association of each base, and where possible, have determined the ΔH of self-association. From isoperibolic titration calorimetry, our measured ΔH of C2 formation in chloroform is -1.7 kcal/mol of C. Our measured ΔH of C:G base-pair formation in o-dichlorobenzene is -6.65 ± 0.32 kcal/mol. Since o-dichlorobenzene does not form hydrogen bonds, the ΔH of C:G base-pair formation in this solvent represents the ΔH of the hydrogen-bonding interaction of C with G in a nonassociating solvent. In contrast, our measured ΔH of C:G base-pair formation in chloroform is -5.77 ± 0.20 kcal/mol; thus, the absolute value of the enthalpy of hydrogen bonding in the C:G base pair is greater in o-dichlorobenzene than in chloroform. Since chloroform is a solvent known to form hydrogen bonds, the decrease in enthalpic contribution to C:G base pairing in chloroform is due to the formation of hydrogen bonds between the bases and the solvent. The ΔH of hydrogen bonding of G with C reported here differs from previous indirect estimates: Our measurements indicate the ΔH is 50% less in magnitude than the ΔH based on spectroscopic measurements of the extent of interaction. We have also observed that the enthalpy of hydrogen bonding of C with G in chloroform is greater when G is in excess than when C is in excess. This increased heat is due to the formation of C:Gn 〉 1 complexes that we have observed using 1H-nmr. Although C:G2 structures have previously been observed in triple-stranded polymeric nucleic acids, higher order structures have not been observed between C and G monomers in nonaqueous solvents until now. By using monomers as a model system to investigate hydrogen-bonding interactions in DNA and RNA, we have obtained the following results: A direct measurement of the ΔH of hydrogen bonding in the C:G complex in two nonaqueous solvents, and the first observation of C:Gn 〉 1 complexes between monomers. These results reinforce the importance of hydrogen bonding in the stabilization of various nucleic acid secondary and tertiary structures.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 190 (1989), S. 1407-1412 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effects of the purification of thermotropic liquid-crystalline siloxane oligomer with supercritical carbon dioxide were investigated. It was found that low-molar-mass contaminants, presumably the two alkene precursors, can be effectively removed at 80°C and carbon dioxide pressures up to 31,0 MPa. In support of this observation is the fact that glass transition temperature goes up as a result of purification. In addition, the selective reflection wavelength was found to increase at increasing purity level, as achieved by extraction at increasing carbon dioxide pressure.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 186 (1985), S. 2557-2567 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The infrared spectrum of polydiacetylene with side chains containing urethane functions (1) was analyzed. Based on the polarization data and the changes observed as a function of temperature, the multiple bands in the Amide I region observed for the film sample were attributed to the transition dipole coupling mechanism. The consequences of this new assignment illustrate the difficulty in using vibrational spectroscopy as a definitive tool to characterize the relationship between structural reorganization of the side chain and the chromic transition at high temperature.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 2311-2316 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The chromic transition observed for polydiacetylene CHCl3/CCl4 solutions was found to be concentration dependent suggesting a need to reconsider the hypothesis that this transition is a single chain phenomenon. We also found that for some polydiacetylene solutions this chromic transition exhibits a significant amount of hysteresis for the cooling and heating cycles.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 2679-2686 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: From optical absorption and infrared data, we have been able to establish the existence of a direct relationship between the weakening of the hydrogen-bonding properties of the side-chain and the chromic transition of the main chain for poly{1,2-bis{4-[N-(butoxycarbonylmethyl)-carbamoyloxy]butyl}-1-buten-3-ynediyl} (poly4BCMU), a family of soluble polydiacetylenes disubstituted with 4-[N-(butoxycarbonylmethyl)carbamoyloxy]butyl side chains. This observation is in contrast to the lack of correlation found for polydiacetylene film. Our data also show that this chromic transition is unaffected by the gelation process found for this family of polydiacetylenes.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 27 (1989), S. 3211-3225 
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal degradation mechanisms of alkyl isocyanate homo- and copolymers were studied using TGA and DP-MS. Both analyses showed that these polymers begin decomposing at around 190°C under inert or vacuum conditions. DP-MS analysis showed the formation of trace quantities of monomer from poly(butyl isocyanate) only and none from higher homologs. All polymers studied produced trimers as their principal decomposition product, implying that intramolecular cyclization is the dominant mechanism of decomposition.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0886-1544
    Keywords: nuclear migration ; microtubules ; F-actin ; root hairs ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A prominent feature of tip growth in filamentous plant cells is that the nucleus often migrates in step with the tip as it extends. We have studied this long-recognized but unexplained relationship in root hairs of the legume Vicia hirsuta by a variety of microscopic techniques. Using rhodaminyl lysine phallotoxin, and antitubulin antibodies, root hairs are shown to contain axial bundles of F-actin and a complex microtubular system. To the basal side of the nucleus the microtubules are cortical and net axial but in the region between nucleus and tip the arrangement is more complicated. Electron microscopic thin sections demonstrate that internal bundles of microtubles exist in addition to the plasma membrane-associated kind. Computerized deblurring of through-focal series of antitubulin stained hairs clarifies the three-dimensional organization: bundles of endoplasmic microtubules progress from the nuclear region toward the apical dome where they can be seen to fountain out upon the cortex.The relationship between nucleus and tip can be uncoupled with antimicrotubule herbicides. Time lapse video microscopy shows that these agents cause the nucleus to migrate toward the base. This contrary migration can be inhibited by adding cytochalasin D, which fragments the F-actin bundles.It is concluded that microtubules connect the nucleus to the tip but that F-actin is involved in basipetal migration as is known to occur when symbiotic bacteria uncouple the nucleus from the tip.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 648-651 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: β-D(+)-Glucose pentaacetate was hydrolyzed both chemically and enzymatically. In contrast to the alkaline hydrolysis, esterase-catalyzed deacetylations afforded significant accumulation of intermediate glucose esters at different degrees of substrate conversion. Aspergillus niger lipase, the most suitable of the four enzymes tested, was used for preparative hydrolysis of glucose pentaacetate. As a result, gram quantities of pure glucose-2,3,4,6-tetraacetate, glucose triacetate (a mixture of two positional isomers, 2,4,6- and 3,4,6-), and glucose-4,6-diacetate were prepared.
    Additional Material: 1 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 31 (1988), S. 628-633 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 7 Ill.
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