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  • Chemistry  (25)
  • Cayley tree  (3)
  • N-(2-hydroxy-4-methoxybenzyl)  (2)
  • 1
    Electronic Resource
    Electronic Resource
    On mean field equations for spin glasses (1982)
    Springer
    Journal of statistical physics 27 (1982), S. 457-472 
    Details
    ISSN: 1572-9613
    Keywords: Cayley tree ; iteration ; fixed point ; spin glass ; Gaussian distribution ; local mean-field theory ; SK equations ; TAP equations.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we study rigorously the random Ising model on a Cayley tree in the limit of infinite coordination numberz → 8. An iterative scheme is developed relating mean magnetizations and mean square magnetizations of successive shells far removed from the surface of the lattice. In this way we obtain local properties of the model in the (thermodynamic) limit of an infinite number of shells. When the coupling constants are independent Gaussian random variables the SK expressions emerge as stable fixed points of our scheme and provide a valid local mean-field theory of spin glasses in which negative local entropy (at low temperatures) while perfectly possible mathematically may still perhaps be physically undesirable. Finally we examine the TAP equations and show that if the average over bond disorder and the limitz → 8 are actually performed, one recovers our iterative scheme and hence the SK equations also in the thermodynamic limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01011086
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  • 2
    Electronic Resource
    Electronic Resource
    Local properties of an Ising model on a Cayley tree (1982)
    Springer
    Journal of statistical physics 27 (1982), S. 441-456 
    Details
    ISSN: 1572-9613
    Keywords: Ising model ; Cayley tree ; phase transition ; iteration ; fixed point ; bifurcation ; ferromagnetic ; antiferromagnetic.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Ising model on a Cayley tree displays a peculiar (continuous order) phase transition with zero long-range order at all finite temperatures. When one studies expection values of spins far removed from the surface (which contains a finite fraction of the total number of spins in the thermodynamic limit), however, one obtains the so-called Bethe approximation. Here we study such a local description by setting up a simple recurrence relation for successive shell magnetizations far removed from the surface. In the ferromagnetic case the local magnetization is a fixed point of the iterative transformation, while in the antiferromagnetic case the fixed point bifurcates to a two-cycle of the transformation (for low temperatures and fields) giving rise to local sublattice magnetizations. In both cases, local thermodynamical properties are obtained by integration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01011085
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  • 3
    Electronic Resource
    Electronic Resource
    Ising model with competing interactions on a Cayley tree (1983)
    Springer
    Journal of statistical physics 33 (1983), S. 419-436 
    Details
    ISSN: 1572-9613
    Keywords: Cayley tree ; iteration ; fixed points ; cycles ; attractors ; chaos ; spin glass ; frequency locking ; devil's staircase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An iterative scheme is developed for a renormalized effective nearest-neighbor couplingK r and effective field per siteK r for spins in therth shell of a Cayley tree with nearest neighborJ, and next nearest neighborJ′, interactions between Ising spins on the lattice. In addition to the expected paramagnetic, ferromagnetic, and antiferromagnetic phases, we find an intermediate range ofJ'/J 〈 0 values whereX r, and Kr iterate to a continuous or quasicontinuous attractor in theX-K plane. In this range the local magnetization is mainly chaotic with oscillatory glasslike behavior. Embedded in the chaos, however, are regions of periodic and commensurate phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01009804
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  • 4
    Electronic Resource
    Electronic Resource
    Models for hemoglobin and allosteric enzymes (1968)
    New York : Wiley-Blackwell
    Biopolymers 6 (1968), S. 1101-1118 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for hemoglobin is proposed and its application to allosteric enzymes is discussed with particular reference to asparate transcarbamylase. The main assumptions made are that the molecule is composed of subunits and that occupation of a sub-unit produces a conformational change which affects the occupational probability of neighboring subunits. The results compare favorably with experiment and a number of specific predictions are made for aspartate transcarbamylase.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1968.360060806
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  • 5
    Electronic Resource
    Electronic Resource
    Time dependent model for hemoglobin and allosteric enzymes. II. (1971)
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 1331-1349 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The time-dependent theory developed in Part I is specialized to treat tetrameric hemoglobin, and the results of the theory for dimeric-and tetrameric hemoglobin are compared with data on the kinetics of the reactions of hemoglobin with carbon monoxide and oxygen at various salt concentrations for the case of large concentration of ligand relative to that of hemoglobin. The fit of the theoretical results to the data suggests that hemoglobin at a 2 M salt concentration is predominantly dimeric and that the tetramer should be taken as the functional unit to explain the kinetics of the reactions of normal hemoglobin. A relationship is established between the time-dependent theory arid Adair's Intermediate Compound Hypothesis (I.C.H.) for hemoglobin, as brought to its present state by Gibson and Roughton. A generalization (G.I.C.H.) of the I.C.H. is presented and is shown to be equivalent to the time-dependent theory in the limit of infinite ligand concentration. The I.C.H. is shown to be an excellent approximation to the centralized theory (G.I.C.H.) in this limit.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360100807
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  • 6
    Electronic Resource
    Electronic Resource
    Time-dependent model for hemoglobin and allosteric enzymes. I. General formulation (1971)
    New York : Wiley-Blackwell
    Biopolymers 10 (1971), S. 961-972 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A previous equilibrium model is generalized to study time-dependent behavior of hemoglobin and allosteric enzymes. An exact solution for two interacting subunits (e.g., diheme) is given, and a general method for solving the resulting set of differential equations is outlined. At half saturation (equilibrium) concentration, the model takes a particularly simple form which suggests an experiment to determine the number of subunits of an allosteric enzyme, or in particular to distinguish diheme from ordinary hemoglobin. The relation between the present model and other kinetic models is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360100603
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  • 7
    Electronic Resource
    Electronic Resource
    The synthesis and spectroscopic analysis of the neurotoxic prion peptide 106–126: Comparative use of manual Boc and Fmoc chemistry (1999)
    Springer
    International journal of peptide research and therapeutics 6 (1999), S. 129-134 
    Details
    ISSN: 1573-3904
    Keywords: amyloid ; circular dichroism ; ‘difficult sequence’ ; in situ neutralisation ; N-(2-hydroxy-4-methoxybenzyl) ; tetramethylfluoroformamidinium hexafluorophosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A peptide corresponding to residues 106–126 of the human prion protein (PrP) possesses the neurotoxic and amyloidogenic properties of the infectious form of the parental protein. This peptide is now identified as a ‘difficult sequence’ and synthesis using conventional manual Fmoc chemistry was unsuccessful with acylation terminating at a central core of hydrophobic amino acids. The use of tetramethylfluoroformamidinium hexafluorophosphate and 1-methyl-2-pyrrolidone as anti-aggregatory agents in the coupling steps improved the synthesis but still resulted in an incomplete peptide. The incorporation ofN-(2-hydroxy-4-methoxybenzyl)protection at glycine residues 119 and 124 enabled synthesis of the full length peptide in low yield. Synthesis using Boc chemistry within situ neutralisation gave the full length peptide in high yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02443627
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  • 8
    Electronic Resource
    Electronic Resource
    The synthesis and spectroscopic analysis of the neurotoxic prion peptide 106-126: Comparative use of manual Boc and Fmoc chemistry (1999)
    Springer
    International journal of peptide research and therapeutics 6 (1999), S. 129-134 
    Details
    ISSN: 1573-3904
    Keywords: amyloid ; circular dichroism ; 'difficult sequence' ; in situ neutralisation ; N-(2-hydroxy-4-methoxybenzyl) ; tetramethylfluoroformamidinium hexafluorophosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A peptide corresponding to residues 106-126 of the human prion protein (PrP) possesses the neurotoxic and amyloidogenic properties of the infectious form of the parental protein. This peptide is now identified as a 'difficult sequence' and synthesis using conventional manual Fmoc chemistry was unsuccessful with acylation terminating at a central core of hydrophobic amino acids. The use of tetramethylfluoroformamidinium hexafluorophosphate and 1-methyl-2- pyrrolidone as anti-aggregatory agents in the coupling steps improved the synthesis but still resulted in an incomplete peptide. The incorporation of N-(2-hydroxy-4-methoxybenzyl) protection at glycine residues 119 and 124 enabled synthesis of the full length peptide in low yield. Synthesis using Boc chemistry with in situ neutralisation gave the full length peptide in high yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008808607811
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  • 9
    Electronic Resource
    Electronic Resource
    Solvent effects on biocatalysis in organic systems: Equilibrium position and rates of lipase catalyzed esterification (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1137-1143 
    Details
    ISSN: 0006-3592
    Keywords: organic-phase biocatalysis ; equillibrium ; reaction rates ; log P ; solvent choice ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381004
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  • 10
    Electronic Resource
    Electronic Resource
    Automatic simulated distillation of heavy petroleum fractions up to 800°C TBP by capillary gas chromatography. Part I: Possibilities and limits of the method (1985)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 8 (1985), S. 771-781 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary columns ; Simulated distillation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The characterization of heavy petroleum fractions is essential for the design and improvement of cracking plants converting heavy feedstock into valuable “white” products. Conventional simulated distillation methods using packed columns are unsuitable for this purposes, being limited to boiling points up to about 600°C. The method presented is able to cover a boiling points interval ranging from about 150°C up to around 800°C. It employs a short, nonpolar, highly thermostable capillary column routinely operated at temperatures around 430°C. The analytical system is based on a high temperature versions of a fully automatic, capillary dedicated gas chromatograph. The experimental data demonstrate that cold on-column injection is the sole sampling system suitable for such heavy compounds. The conversion of the retention times into boiling points, based on the use of low molecular weight polyethylenes, is extremely reliable, as demonstrated by the excellent retention time reproducibilities. The lower part (up to 550-600°C TBP) of the boiling point distribution curves of heavy petroleum fractions obtained on capillary columns fits well with the corresponding distribution curves based on packed column data. For the petroleum fractions fully eluted from the column the quantitative results obtained either using internal standards or by direct processing of the elution curves are in excellent agreement (less than 0.3 weight% differences). The method has been applied to the determination of the true boiling points corresponding to short path vacuum distillation (DISTACT) cut points over 300°C.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240081113
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