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  • Springer  (30)
  • American Meteorological Society (AMS)
  • 1995-1999  (30)
  • 1
    Electronic Resource
    Electronic Resource
    3D-QSAR Analysis and Molecular Modeling Investigations of Piritrexim and Analogous (1997)
    Springer
    Journal of molecular modeling 3 (1997), S. 338-346 
    Details
    ISSN: 0948-5023
    Keywords: Keywords: Free-Wilson-analysis ; PLS ; genetic algorithm ; CoMFA ; piritrexim analogous
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Quantitative structure-activity relationships for piritrexim and analogues acting as inhibitors of tumour cell growth have been derived. First the Free-Wilson-method was used on a homologous training set of eight derivatives. The selection of variables important for the biological activity of the compounds was carried out with different multivariate methods as multiple linear regression, the partial least squares method und a genetic algorithm. The derivation of three-dimensional structure activity relationships started with a systematic conformational analysis of all compounds. For the conformations having minimal energy and being in agreement with the crystal structure of piritrexim charges were calculated with the AM1 hamiltonian. For the superimposition of the derivatives two methods were used: maximal similarity of the common substructure or of the molecular fields. A Comparative Molecular Field Analysis with steric and electrostastic fields identified regions important for the activity of the studied compounds independent of the chosen alignment and also correctly predicted the activity of two nonhomologous compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s008940050048
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  • 2
    Electronic Resource
    Electronic Resource
    Temperature variations in the director orientation and anchoring energy at the surface of cholesteric layers (1996)
    Springer
    JETP letters 63 (1996), S. 43-49 
    Details
    ISSN: 1090-6487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Slight changes with temperature in the director orientation at the surface of a perfect planar cholesteric liquid crystal (CLC) layer, which are precursors of a jump in the pitch of the cholesteric helix, are observed by measuring the temperature dependence of the optical transmission spectra of the layer. The observed changes in the director orientation are described in the framework of the continuum theory of CLCs, supplemented with allowance for the surface anchoring forces. In particular, the angle of deviation of the director at the surface from the alignment direction at the exact temperature of the jump in pitch is expressed in terms of the anchoring potential. The relation obtained is use to find the anchoring potential in the samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.566961
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature hysteresis of the change in the cholesteric pitch and surface anchoring in thin planar layers (1997)
    Springer
    Journal of experimental and theoretical physics 85 (1997), S. 285-291 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Hysteresis of the temperature of jumps in the cholesteric pitch in planar layers of cholesteric liquid crystals (CLCs) has been observed in the temperature dependence of the optical transmission spectra measured in a 4.8 ¼m thick specimen of a 60% chiral racemic mixture of CE6. The temperature difference for the pitch jumps during heating and cooling was equal to about 0.1°C near 40.3°C. No difference in the temperature of the pitch jumps during heating and cooling was observed for an 18 µm thick specimen. A theoretical description of this hysteresis is presented on the basis of a continuum theory of elasticity of CLCs that also takes account of the surface anchoring of the CLC. Different possible mechanisms leading to a change in the director configuration in the layer during a pitch jump and their correspondence to the jump mechanism and hysteresis which occur in the experimental specimens are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558276
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  • 4
    Electronic Resource
    Electronic Resource
    Encapsulation of the ferritin protein in sol-gel derived silica glasses (1996)
    Springer
    Journal of sol gel science and technology 7 (1996), S. 109-116 
    Details
    ISSN: 1573-4846
    Keywords: ferritin ; sol-gel ; magnetism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A significant recent development in sol-gel science has been the encapsulation of biomolecules such as proteins and enzymes in optically transparent silica glasses. This paper reports on the encapsulation of an iron (Fe) storage protein, ferritin, to develop a magnetic silica glass. Native ferritin, which has a nanometer-sized microcrystalline Fe oxide core, was encapsulated in optically transparent silica glasses using the sol-gel process. Fe could be released from ferritin but could not be reconstituted into apoferritin when the protein was trapped in the pores of the glass. Transmission electron microscopy of ferritin-doped aged silica gels indicated that crystallinity of the Fe oxide core was retained upon sol-gel encapsulation. Magnetic measurements on ferritin-doped silica gels indicated the material to be paramagnetic, but not superparamagnetic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00401890
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  • 5
    Electronic Resource
    Electronic Resource
    Enzymatic activity of oxalate oxidase and kinetic measurements by optical methods in transparent sol-gel monoliths (1996)
    Springer
    Journal of sol gel science and technology 7 (1996), S. 117-121 
    Details
    ISSN: 1573-4846
    Keywords: sol-gel monoliths ; immobilized enzyme ; oxalate oxidase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Novel synthetic techniques are used for the encapsulation of the enzymes oxalate oxidase and peroxidase in stable, optically transparent porous silica glass matrices. The large enzymes are fully immobilized in the porous glass but small molecules such as oxalate ions pass readily through the pores in the glass. The enzymes catalyze the reactions leading to the formation of a colored dye product. Upon exposure of the doped glass to oxalate solutions, a colored glass is formed. The absorption spectrum of the colored product and the changes of absorbance with time are measured within the glass matrix. The sensitivity and the time-dependence of the response are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00401891
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  • 6
    Electronic Resource
    Electronic Resource
    Encapsulation of proteins in bulk and thin film sol-gel matrices (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 629-634 
    Details
    ISSN: 1573-4846
    Keywords: protein encapsulation ; absorption spectroscopy ; thin films ; cytochrome c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper considers the nature of the interactions between the sol-gel derived inorganic matrix and a specific biomolecule, cytochrome c. Optical absorption and impedance spectroscopies are used to characterize the influence of synthesis conditions on the protein’s stability and conformation within the silica matrix. In some instances, encapsulation within the sol-gel matrix provides stabilization. For example, protein denaturation is reversible and aggregation is prevented. Moreover, the drying process does not negatively affect the protein; it is possible to regenerate the aged gel state by rehydration. The flexibility of the sol-gel process enables high quality cytochrome c-doped SiO2 thin films to be prepared. These films possess the characteristic reactivity and chemical function of cytochrome c in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436913
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  • 7
    Electronic Resource
    Electronic Resource
    Spectroscopic determination of cholinesterase activity and inhibition in sol-gel media (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 1067-1070 
    Details
    ISSN: 1573-4846
    Keywords: cholinesterase ; sol-gel ; pesticide ; THA ; enzyme activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Biological activity of cholinesterases can be determined by optically monitoring the enzymatic reaction with indophenyl acetate, (N-4′-acetoxyphenyl)-4-quinone imine. At pH 8.0 cholinesterases hydrolyze this yellow dye to yield a blue reaction product. Cholinesterase inhibitors reduce the rate of this hydrolysis. Thus, by monitoring absorbance of the hydrolysis product at its maximum (630 nm) as a function of time, reaction rates of both cholinesterase activity and cholinesterase inhibition may be quantified spectroscopically. Using this technique, we measured the enzymatic activity of butyrylcholinesterase (BuChE) molecules encapsulated in tetramethyl orthosilicate (TMOS) silicate gel-glass prepared by hydrolysis and condensation. This activity is reduced, in a concentration-dependent manner, by the reversible cholinesterase inhibitors 1,5-bis(4-allyldimethyl-ammoniumphenyl) pentan 3-one dibromide (BADAPP) and 9-amino-1,2,3,4-tetrahydroacridine (THA; tacrine, Cognex). The gel-glasses are rigid, and compact, transparent and porous enough to allow reagents to diffuse in and out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436985
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  • 8
    Electronic Resource
    Electronic Resource
    Optical Properties and Dimer Formation in Copper Phthalocyanine-Doped Sol-Gel Matrices (1998)
    Springer
    Journal of sol gel science and technology 11 (1998), S. 241-250 
    Details
    ISSN: 1573-4846
    Keywords: copper phthalocyanine ; dimer ; monomer ; optical absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dimer formation in sol-gel matrices was studied using optical absorption spectroscopy of copper phthalocyanine tetrasulfonate dopants in silicate and aluminosilicate sol-gel matrices. Changes in the optical absorption spectra of dimers and monomers were correlated with various stages of the sol-gel process. Dimerization is strongly influenced by the chemistry of the pore liquid. The primary factors that control dimerization are the quantity of solvent remaining in the pores, pore solvent alcohol/water ratio, and presence of protons which can be either from the catalyst or from silanol groups on the silicate pore surfaces. Synthesis conditions which cause dye protonation invariably lead to dimerization during the latter stages of drying when the pore liquid becomes water-rich and there is a high dye concentration. These studies also identify chemical conditions which are able to avoid dye protonation and subsequently reduce dimer formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008602111839
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  • 9
    Electronic Resource
    Electronic Resource
    Allosteric Regulation of Enzymatic Reactions in a Transparent Inorganic Sol-Gel Material (1999)
    Springer
    Journal of sol gel science and technology 15 (1999), S. 57-62 
    Details
    ISSN: 1573-4846
    Keywords: glutamate dehydrogenase ; allosteric regulators ; sol-gel ; enzyme activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Glutamate dehydrogenase is encapsulated in a transparent porous silicate matrix by using sol-gel techniques. The inorganic polymer is formed around the enzyme (MW 〉 300,000 D). The enzyme is active in the material, catalyzes the reaction of L-glutamate to 2-oxoglutarate and follows Michaelis-Menten kinetics. The allosteric regulators ADP and GTP inhibit or activate the reaction; at pH 6, GTP acts as a strong activator and ADP acts as an inhibitor. This system involves a complex series of interactions; the co-enzyme NAD+ is required for catalysis, large-scale conformational changes accompany the binding of the substrate and coenzyme to the enzyme, the activators/inhibitors must bind to the enzyme to regulate the reactions, and the substrates and products must diffuse through the matrix to and from the binding site. The influence of the unique matrix on the complex enzymatic system is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008713014152
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  • 10
    Electronic Resource
    Electronic Resource
    Encapsulation of Proteins in Bulk and Thin Film Sol-Gel Matrices (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 629-634 
    Details
    ISSN: 1573-4846
    Keywords: protein encapsulation ; absorption spectroscopy ; thin films ; cytochrome c
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This paper considers the nature of the interactions between the sol-gel derived inorganic matrix and a specific biomolecule, cytochrome c. Optical absorption and impedance spectroscopies are used to characterize the influence of synthesis conditions on the protein's stability and conformation within the silica matrix. In some instances, encapsulation within the sol-gel matrix provides stabilization. For example, protein denaturation is reversible and aggregation is prevented. Moreover, the drying process does not negatively affect the protein; it is possible to regenerate the aged gel state by rehydration. The flexibility of the sol-gel process enables high quality cytochrome c-doped SiO2 thin films to be prepared. These films possess the characteristic reactivity and chemical function of cytochrome c in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018316108875
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