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  • 1
    Digitale Medien
    Digitale Medien
    Ameloblast apoptosis and IGF-1 receptor expression in the continuously erupting rat incisor model (1999)
    Springer
    Apoptosis 4 (1999), S. 441-447 
    Details
    ISSN: 1573-675X
    Schlagwort(e): ameloblasts ; amelogenesis ; apoptosis ; insulin-like growth factor.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Enamel-producing cells (ameloblasts) pass through several phenotypic and functional stages during enamel formation. In the transition between secretory and maturation stages, about one quarter of the ameloblasts suddenly undergo apoptosis. We have studied this phenomenon using the continuously erupting rat incisor model. A special feature of this model is that all stages of ameloblast differentiation are presented within a single longitudinal section of the developing tooth. This permits investigation of the temporal sequence of gene and growth factor receptor expression during ameloblast differentiation and apoptosis. We describe the light and electron microscopic morphology of ameloblast apoptosis and the pattern of insulin-like growth factor-1 receptor expression by ameloblasts in the continuously erupting rat incisor model. In the developing rat incisor, ameloblast apoptosis is associated with downregulated expression of the insulin-like growth factor-1 receptor. These data are consistent with the hypothesis that ameloblasts are “hard wired” for apoptosis and that insulin-like growth factor-1 receptor expression is required to block the default apoptotic pathway. Possible mechanisms of insulin-like growth factor-1 inhibition of ameloblast apoptosis are presented. The rat incisor model may be useful in studies of physiological apoptosis as it presents apoptosis in a predictable pattern in adult tissues.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009600409421
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  • 2
    Digitale Medien
    Digitale Medien
    Polysalt complexes of poly(crown ethers) and sodium carboxymethylcellulose (1977)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 15 (1977), S. 1189-1197 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Insoluble polysalt complexes are formed on mixing aqueous solutions of poly(vinylbenzo-18-crown-6) (P18C6) and sodium carboxymethylcellulose (CMC) in the presence of certain salts. Potassium salts are especially effective, converting the neutral P18C6 into a polycation which then interacts with sodium CMC. Nearly quantitative precipitation can be achieved at low KCl concentration (ca. 0.005M) for a crown/carboxylate ratio of approximately 5, while for 0.1-0.2M KCl the precipitation is close to completion at a crown/CMC ratio of about 2. The precipitates solubilize again on addition of water or concentrated KCl. Precipitation also occurs with CsCl but not with NaCl. Potentiometric measurements were carried out to determine the complex formation constant of the three alkali ions to P18C6. Their values can be used to rationalize the observed phenomena. Charge equivalence appears to play an important role in the formation of the polysalt complexes.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1977.170150516
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  • 3
    Digitale Medien
    Digitale Medien
    Polysalt complexes of poly(vinylbenzo-18-crown-6) and of poly(crown acrylate)s with polyanions (1979)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 17 (1979), S. 1573-1581 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Macrocyclic polyether or crown ether ester derivatives of acrylic and methacrylic acid were synthesized and polymerized. The cation binding properties of the polymers determined by extraction of picrate salts were similar to those obtained for poly(crown ether)s derived from styrene. In the presence of a crown-complexable cation both polymers form insoluble polysalt complexes with sodium carboxymethylcellulose, potassium poly(styrene sulfonate), and potassium polyacrylate. The extent of precipitation depends on the type and concentration of cation as well as on the ratio polyanion to poly(crown ether). The precipitate appears to have an equal number of positive and negative charges. An insoluble hydrogen-bonded complex is formed in the absence of salt when poly(vinylbenzo-18-crown-6) and poly(acrylic acid) are mixed in 0.01M HCl. Organic solutes bound to the poly(crown ether)s, which occur in an aqueous mixture of poly(vinylbenzo-18-crown-6) and picrate anions, are precipitated with the poly(crown ether) when the polysalt complex is formed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1979.170170601
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  • 4
    Digitale Medien
    Digitale Medien
    Conductance studies of salt solutions in the presence of poly(vinylbenzo crown ethers) (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 14 (1976), S. 2023-2031 
    Details
    ISSN: 0360-6376
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conductance of acetone and methyl ethyl ketone solutions of tetraphenylborate salts in the presence of homopolymers and styrene copolymers of vinylbenzo-15-crown-5 and vinylbenzo-18-crown-6 was studied, and the results compared with data obtained for crown ethers. Polycations are formed on binding cations to the poly(crown ethers), and the conductance behavior of the polyelectrolytes depends on the nature of the cation-crown complex and the spacing between crown moieties which in turn determines the charge density on the polymer chain. The compositions of the crown-cation complexes were determined for crown ethers. The complex formation constants of sodium and potassium cations to poly(vinylbenzo-18-crown-6) were found to change as more cations bind to the chain. This is not the case for the copolymers where the crown ligands are spaced farther apart. A mixture of poly(vinylbenzo-15-crown-5) and 10-3M potassium tetraphenylborate in methyl ethyl ketone or acetone has a minimum conductance at a crown to cation ratio of 3.0, but the conductance rapidly increases on addition of crown ether. This was used to qualitatively determine the binding efficiency of a series of crown ethers since the rate of increase in the conductance is a measure of the binding ability of the crown ether to the cation.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.170140818
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  • 5
    Digitale Medien
    Digitale Medien
    Anionic copolymerization of styrene and 1,1-diphenylethylene (1966)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-1: Polymer Chemistry 4 (1966), S. 2219-2228 
    Details
    ISSN: 0449-296X
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Kinetics of anionic copolymerization of styrene (S) and 1,1-diphenylethylene (D) were investigated in THF. The rate constant of addition of D to living polystyrene was found to be k1,2 ± = 250 l./mole-sec. for , Na+ ion-pair, and that for the free , Na+ ion is k1,2-∼400,000 l./mole-sec. Both values refer to 25°C. The addition of styrene to —D-, Na+ was found to be reversible: and k2,1 was determined by three different methods to be ∼0.5-0.7 l./mole-sec. Studies performed in a stirred-flow reactor led to k-21 = 13 sec. -1 and K21 ∼ 5 × 10-2 l./mole. An alternating copolymer is obtained in the presence of a large excess of 1,1-diphenylethylene.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1966.150040916
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