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  • 1
    ISSN: 0021-9304
    Keywords: titanium ; dental implant ; osseointegration failure ; surface analysis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A multitechnique approach has been used to characterize the surface of nonosseointegrated titanium implants and the surrounding biological tissues. Five pure titanium dental implants were used as reference, and 25 removed implants were studied. Surface and in-depth chemical compositions of the implants (from a total of 16 patients) were investigated by X-ray photoelectron spectroscopy (XPS). Histological slides of the surrounding tissues were examined by light microscopy, XPS, and electron microprobe analysis. None of the failed implants presented the regular surface composition and depth profile of the TiO2 overlayer; foreign elements (Ca, Na, P, Si, Cl, Zn, Pb, and Al) were observed on some implants. Fibrosis, lymphocytic and plasmocytic infiltrates, and granulomatous lesions were detected in the surrounding tissues. XPS and electron microprobe analysis indicated the presence of Zn, Fe, Sn, and Ti in the tissues. As a possible scenario for implant failure, we propose and discuss a oxidoreduction mechanism, leading to a partial dissolution or the complete dissociation of the protective titanium dioxide overlayer and to ion diffusion through the surrounding tissues. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 43: 300-312, 1998
    Additional Material: 11 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 743-760 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of NO on the decomposition of CH3ONO have been investigated in the temperature range 450-520 K at a constant pressure of 710 torr using He as buffer gas. The measured time-dependent concentration profiles of CH3ONO, NO, N2O, and CH2O can be quantitatively accounted for with a general mechanism consisting of various reactions of CH3O, HNO, and (HNO)2. The results of kinetic modeling with sensitivity analyses indicate that the disappearance rate of CH3ONO is weakly affected by NO addition, whereas that of the HNO intermediate strongly altered by the added NO. In the presence of low NO concentrations, the modeling of N2O yields leads to the rate constant for the bimolecular reaction, HNO + HNO → N2O + H2O (25): \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{25} = 10^{8.93 \pm 0.30}\, \,e^{-1,550 \pm 150/{\rm T}} {\rm cm}^3 /{\rm mol}\,{\rm s} $$\end{document} In the presence of high NO concentrations (PNO 〉 50 torr), the modeling of CH2O yields gives the rate constant for the termolecular radical formation channel, HNO + 2NO → HN2O + NO2 (35): \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{35} = 10^{11.2 \pm 0.3}\, \,e^{-1050 \pm 200/{\rm T}} {\rm cm}^6 /{\rm mol}^2\,{\rm s} $$\end{document} Discussion on the mechanisms for reactions (25) and (35), and the alkyl homolog of (35), RNO + 2NO, is presented herein. © John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 25 (1993), S. 845-863 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal reaction of HNCO with NO2 has been studied in the temperature range of 623 to 773 K by FTIR spectrometry. Major products measured are CO2 and NO with a small amount of N2O. Kinetic modeling of the time resolved concentration profiles of the reactants and products, aided by the thermochemical data of various likely reactive intermediates computed by means of the BAC-MP4 method, allows us to conclude that the reaction is initiated exclusively by a new bimolecular process: with a rate constant, k1 = 2.5 × 1012e-13,100/T cm3/mols. The well-known bimolecular reaction is the only strong competitive process in this important reactive system throughout the temperature range studied. Kinetic modeling of NO formation and NO2 decay rates gave rise to values of k10 which were in close agreement with literature data. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 23 (1991), S. 1129-1149 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal reaction of HNCO has been studied in a static cell at temperatures between 873 and 1220 K and a constant pressure of 800 torr under highly diluted conditions. The reaction was measurable above 1000 K by FTIR spectrometry. The products detected include CO, CO2, HCN, NH3, and the unreacted HNCO. In this moderate temperature regime, the rates of product formation and HNCO decay cannot be accounted for by a previously established high-temperature mechanism, assuming HNCO → NH + CO (1) as the initiation process. Instead, a new bimolecular reaction, 2HNCO → CO2 + HNCNH (2), has been invoked to interpret the disappearance of HNCO as well as the formation of various products, most importantly CO2.The concentration profiles of all measured species can be quantitatively modeled, throughout the temperature range analyzed, by varying k2 using a modified mechanism. The kinetically modeled values of k2 can be effectively represented by \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm 2} = 10^{10.84 \pm 0.07} {\rm \,exp}(- 21,240 \pm 1,960/{\rm T}){\rm\, cm}^3 /{\rm mol\, s}{\rm .} $$\end{document}This result agrees closely with that computed with the conventional transition-state theory using the TST parameters predicted by the BAC-MP4 method: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 ({\rm BAC} - {\rm MP}4) = 10^{11.13} {\rm \,exp(- 21,600/T) cm}^{\rm 3} /{\rm mol s}{\rm .} $$\end{document}The bimolecular reaction takes place via a stable 4-membered ring intermediate which is isoelectronic with diketene; viz.
    Additional Material: 11 Ill.
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  • 5
    ISSN: 0749-1581
    Keywords: α-Cyclodextrin nitrate ; β-Cyclodextrin nitrate ; Hydroxylamine denitration ; 15N—O—C—1H shift correlations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hexakis(2,3,6-tri-O-nitro)-α-cyclodextrin and heptakis(2,3,6-tri-O-nitro)-β-cyclodextrin were prepared and the complete assignment of the 1H, 13C and 15N resonance signals in each case was achieved using homonuclear shift correlation experiments, one-bond 13C—1H and three-bond 15N—O—C—1H heteronuclear shift correlation measurements. The denitration of these cyclodextrin nitrates by hydroxylamine in pyridine was investigated to study its selectivity in preparing partially nitrated derivatives of these cyclodextrins. The sites of denitration were determined in each case using 13C and 15N NMR and the products were completely characterized. The results indicate that denitration of these cyclodextrin nitrates is a highly regiospecific reaction occurring at the 2-position only and giving rise to hexakis(3,6-di-O-nitro)-α-cyclodextrin and heptakis(3,6-di-O-nitro)-β-cyclodextrin, respectively.
    Additional Material: 4 Ill.
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