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  • 1
    Electronic Resource
    Electronic Resource
    Effects of millimeter-wave radiation on monolayer cell cultures. II. Scanning and transmission electron microscopy (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 2 (1981), S. 141-150 
    Details
    ISSN: 0197-8462
    Keywords: millimeter-wave radiation ; BHK-21/C13 cells in monolayer culture ; scanning electron microscopy ; transmission electron microscopy ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Both thermal and athermal effects of millimeter-wave radiation on BHK-21/C13 cells were sought using scanning and transmission electron microscopy in conjunction with an in vitro technique that allows direct exposure of monolayer cultures to high average power densities. Culture dishes were irradiated by placing them on the open end of an E- or U-band wave guide. This technique exposes different regions of the cell monolayer lying along the longer axis of the wave guide aperture to varying power densities ranging from zero at each edge to twice the average power density at the center.Cell ultrastructure was unaffected by microwave radiation for 1 hour (41.8 or 74.0 GHz, average power densitites = 320 or 450 mW/cm2, respectively) with or without cooling by rapid recirculation of the culture medium. Temperature in recirculated cultures was held at 37.2 °C, and that in noncooled cultures never exceeded 42 °C during irradiation at either power density. In contrast, cell morphology was affected by microwave exposure whenever irradiation conditions were altered so that the temperature of the monolayer reached or exceeded 44.5 °C. Ultrastructural alterations included breakage of cell processes, progressive detachment of cells from the substrate, increased clumping of heterochromatin in the nuclei, and the appearance of large empty vesicles in the cytoplasm. Such morphological changes resulted from either application of higher average power densities or irradiation at the power densities described above at a higher ambient temperature (〉38.5°C).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250020205
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of millimeter-wave radiation on monolayer cell cultures. I. Design and validation of a novel exposure system (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 2 (1981), S. 123-140 
    Details
    ISSN: 0197-8462
    Keywords: millimeter-wave radiation ; BHK-21/C13 cells in monolayer culture ; quantitative autoradiography ; ribonucleic acid (RNA) synthesis ; protein synthesis ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A method has been devised whereby both the thermal and possible athermal biological effects resulting from microwave radiation can be assessed. Monolayer cultures of BHK-21/C13 cells were grown on microwave-transparent polystyrene coverslips, placed directly on the open end of a wave guide, and irradiated for 1 hour. In experiments seeking athermal biological effects of millimeter waves, culture medium was continuously recirculated over the cells to prevent temperature increases greater than 0.1 °C. Incorporation of 3H-uridine into RNA and of 3H-methionine into protein was quantified by measurement of optical densities of the autoradiographs in contiguous rectangular regions corresponding to portions of the cell monolayer immediately above the wave guide aperture and lying along its longer axis. Since power density was shown to vary with position along this axis according to a cosine2 relationship, it was possible to assess the extent of microwave effects on macromolecular synthesis at power densities ranging from zero at each edge to twice the average power density at the center of the waveguide.Monolayer cultures maintained at 37.2 °C by recirculation of the medium did not show microwave-induced changes in synthesis of RNA and protein (41.8 or 74.0 GHz at average power densities of 320 or 450 mW/cm2, respectively). Since macromolecular synthesis was examined both during and after irradiation, our results exclude both transient and persistent athermal biological effects of acute exposure to millimeter waves. In contrast, irradiation of cultures incubated in a small volume of nonrecirculated medium resulted in 1) marked heating of the monolayer, 2) a graded decline in macromolecular synthesis with increasing incident power, and 3), in some cases, destruction of the cell monolayer in the region immediately above the center of the waveguide aperture.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250020204
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of millimeter-wave radiation on monolayer cell cultures. III. A search for frequency-specific athermal biological effects on protein synthesis (1981)
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 2 (1981), S. 151-159 
    Details
    ISSN: 0197-8462
    Keywords: protein synthesis ; quantitative autoradiography ; BHK-21/C13 cells ; millimeter-wave radiation ; frequency-specific biological effects ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: A method recently developed in this laboratory has been used to directly expose BHK-21/C13 cells to high levels of microwave radiation without significant microwave-induced heating (≤ 0.1 °C). Monolayer cultures were grown on microwave-transparent polystyrene coverslips, placed on the open end of a wave guide, and maintained at 37.2 °C during irradiation at frequencies in both the E- and U-bands (average power densities 292 and 177 mW/cm2, respectively). Effects of microwave radiation were assessed at 0.1 GHz increments in the ranges of 38-48 GHz and 65-75 GHz. Protein synthesis was measured in quadruplicate cultures that were allowed to incorporate labeled methionine during the 15-minute period of microwave irradiation. Autoradiographs of each monolayer culture were scanned along the region corresponding to the longer axis of the wave guide aperture using a microdensitometer to quantify incorporation. Since microwave power incident on the cells was previously shown to vary along this axis according to a cosine2 relationship from zero at each edge of the wave guide to twice the average power density at the center of the wave guide, this technique should reveal biological effects that might only be manifested in narrow amplitude domains or “power windows.” Observations of protein synthesis in monolayer cultures irradiated at 202 closely spaced frequencies in the E- and U-bands failed to reveal changes associated with microwave exposure. Thus no evidence was obtained in support of the existence of frequency-specific athermal biological effects of microwaves. In addition, no support was found for the existence of amplitude-specific “power windows”.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bem.2250020206
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  • 4
    Electronic Resource
    Electronic Resource
    A simplified data treatment for dead-end and high conversion polymerization kinetics (1982)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 20 (1982), S. 241-244 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A simplified approximation method for the treatment of dead-end and high conversion polymerization kinetics is presented. The method is based on the treatment of dead-end polymerization first described by Tobolsky. In appropriate circumstances, by contrast with Tobolsky's method, this method provides measurements of kd and kp/kt1/2 without recourse to the measurement of the monomer conversion at infinite time.Kinetic studies of free radical polymerizations are normally confined to measurements of initial rates. At low conversions the predictions of the general mechanism for chain-growth polymerization involving initiation, propagation, and termination steps are generally obeyed. Thus the polymerization rate should be first order in the vinyl monomer and half-order in the initiator concentrations.At high conversions, however, large deviations which can be ascribed to various effects can occur; for example, (1) the effect of the increasing viscosity of the polymerization medium on the termination rate constant kt, and possibly also on the propagation rate constant kp, which have been considered by North1 and Cardenas and O'Driscoll,2 or (2) depletion of the initiator as the polymerization progresses. This depletion will occur in all polymerizations but its significance will depend on the magnitude of the rate constant for initiator decomposition (kd) and the period of polymerization. Appropriate conditions will lead to limiting monomer conversion even after infinite polymerization time; this phenomenon has been called dead-end polymerization by Tobolsky.3Free radical polymerizations to high conversion are particularly important in the industrial context when initial kinetics are obviously inadequate. Suitable treatment of the conversion/time relationship is highly desirable.Senogles and Woolf4 have examined the polymerization of n-lauryl methacrylate at 60°C with 2-azobisisobutyronitrile as initiator under dead-end conditions.Here we propose a modification of Tobolsky's treatment of such polymerizations by using an approximation for the exponential decay in the initiator concentration. This method permits easy manipulation of the experimental data and the estimation of values for the kinetic parameters in favorable circumstances without recourse to the measurement of the conversion at infinite time or the evaluation of complicated functions of the monomer conversion. The method thus allows the duration of the laboratory experimentation to be significantly shortened and the complexity of the subsequent data analysis to be considerably reduced.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1982.170200126
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  • 5
    Electronic Resource
    Electronic Resource
    An investigation of radiation-induced structural changes in nitrile rubber (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2439-2454 
    Details
    ISSN: 0887-624X
    Keywords: radiation ; nitrile rubber ; NMR ; ESR ; radicals ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of radiation-induced structural changes in nitrile rubber with different acrylonitrile contents were investigated by ESR, NMR, and FTIR. To investigate new structures solid-state NMR methods had to be used due to crosslinking of the irradiated rubbers, and higher probe temperatures were used to obtain better resolution. The radicals generated on the acrylonitrile groups were found to abstract hydrogen from the adjacent butadiene units resulting in the formation of allylic radicals. These allylic radicals reacted to form intermolecular crosslinks and cyclisation. Cyclisation of the butadiene units were found to occur in the initial stages of the irradiation. Radiation yields of radicals increased with acrylonitrile content from 1.42, 1.58, to 2.42 for 18, 30, and 45% acrylonitrile rubbers. The radiation yields for intermolecular crosslinking were higher in rubbers with higher acrylonitrile contents, giving G values of 17.8, 21.3, and 24.5 for 18, 30, and 45% acrylonitrile rubbers, respectively. However, the crosslink clustering was found to be less in the rubbers with a higher acrylonitrile content. © 1996 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Consistent values of rate parameters in free radical polymerization systems. II. Outstanding dilemmas and recommendations (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 851-863 
    Details
    ISSN: 0887-624X
    Keywords: polymerization ; kinetics ; free radical ; transfer ; photolysis ; propagation ; rate coefficients ; termination ; EPR ; copolymerization ; initiation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problems of determining reliable, well-characterized values of kinetic parameters in free-radical polymerizations are discussed. The origins of the fact that experimental determinations of rate coefficients of ostensibly identical systems often result in quite different values being reported can be ascribed to subtle mechanistic assumptions made in data interpretation, which are considered in detail. A series of recommendations to assist in overcoming these problems, and to highlight their origins, are presented, with emphasis placed on new techniques including those employing laser photolysis and EPR.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300516
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  • 7
    Electronic Resource
    Electronic Resource
    Consistent values of rate parameters in free radical polymerization systems (1988)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 26 (1988), S. 293-297 
    Details
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1988.140260704
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  • 8
    Electronic Resource
    Electronic Resource
    Helix-coil stability constants for the naturally occurring amino acids in water. XIII. The presence of by-products in amino-acid analysis of copolymers and their effect on the guest parameters; recomputed values of σ and s for L-serine (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 1587-1592 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previously used procedures for processing the amino acids from 6N hydrochloric acid hydrolysis of poly[N5-(4-hydroxybutyl)-L-glutamine], poly[N5-(3-hydroxypropyl)-L-glutamine], and several random copolymers derived from these, led to the formation of spurious products. These have been isolated and characterized as the γ-ester of glutamic acid and the hydroxyalkyl amine, and chloro-alkyl amine hydrochloride. The former reduces the observed values for glutamic acid, but the latter has no effect on them. A method is used to avoid formation of these artifacts in the amino-acid analysis. Of all the copolymers studied previously in this series, the compositions of only those containing L-serine are in error as a result of the formation of the γ-ester. A redetermination of the amino-acid compositions of the copolymer fractions studied earlier leads to slightly revised values for the Zimm-Bragg parameters σ and s of serine.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360160716
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  • 9
    Electronic Resource
    Electronic Resource
    Helix-coil stability constants for the naturally occuring amino acids in water. XIV. Methionine parameters from random poly(hydroxypropylglutamine,L-Methionine) (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 2447-2467 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Water-soluble, random copolymers containing L-methionine and N5-(3-hydroxypropyl)-L-glutamine have been prepared, fractionated, and characterized. The thermally induced helix-coil transitions of these copolymers in water have been investigated, and it has been found that incorporation of L-methionine increases the helix content of the polymers at all temperatures in the range of 0-60°C. The Zimm-Bragg parameters σ and s for the helix-coil transition in poly(L-methionine) in water were deduced from an analysis of the melting curves of the copolymers using the methods described in earlier papers.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360161109
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  • 10
    Electronic Resource
    Electronic Resource
    On the amino-acid-sequence distribution in benzylglutamate-methionine copolymers prepared from N-carboxyanhydrides (1977)
    New York : Wiley-Blackwell
    Biopolymers 16 (1977), S. 2469-2480 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The amino-acid-sequence distribution in poly(γ-benzyl-L-glutamate, L-methionine) prepared by polymerization of the respective N-carboxyanhydrides has been investigated. This copolymer was converted first to poly(L-glutamic acid, L-methionine), which was subsequently cleaved by treatment with cyanogen bromide. The resulting material was fractionated into oligomers of (glutamic acid)n-homoserine whose relative molar amounts were determined quantitatively. The results have been compared with those for a random incorporation of the methionine in a γ-benzylglutamate host polymer. Fairly close agreement has been found.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1977.360161110
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