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  • 1
    Electronic Resource
    Electronic Resource
    Crystal growth of calcium apatites in dilute solutions containing fluoride (1981)
    Springer
    Calcified tissue international 33 (1981), S. 431-439 
    Details
    ISSN: 1432-0827
    Keywords: Apatite ; Fluorhydroxyapatite ; Crystal growth ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The kinetics of seeded crystal growth of calcium apatites were studied in dilute supersaturated solutions at various levels of fluoride concentrations. Initial precipitation rates were enhanced by fluoride concentrations higher than 0.05 ppm. The analytical results are consistent with the precipitation of fluoridated hydroxyapatites, Ca5Fx-(OH)1−x(PO4)3, FHA. The degree of fluoridation, X, appears to be determined by the activity of HF in solution, which varies for the various initial fluoride levels but remains fairly constant during precipitation. Thus the composition of the precipitating phase was the same for a given solution whether 25 or 10 mg of hydroxyapatite was added as seeds. All the experimental results are consistent with the BCF theory, which relates the mean linear rate of growth, RL, to the supersaturation, DS, by the expression RL=C1T(DS-1)1n(DS)tanh(C2/T 1n DS), in which DS is the supersaturation defined by mean molar activities with respect to the precipitating FHA, T the absolute temperature, and C1 and C2 are constants calculated from the experimental results. Consequently, the crystal growth appears to take place in surface kinks and to be controlled by surface diffusion. Since crystal growth in most biological systems takes place at fluoride concentrations within the experimental range used, it seems probable that it occurs along the model advanced in the present investigation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02409467
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  • 2
    Electronic Resource
    Electronic Resource
    Adsorption of molecules of biological interest onto hydroxyapatite (1984)
    Springer
    Calcified tissue international 36 (1984), S. 48-59 
    Details
    ISSN: 1432-0827
    Keywords: Salivary proteins ; Adsorption ; Thermodynamics ; Kinetics ; Hydroxyapatite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Equilibrium and kinetic experiments were conducted to investigate the factors determining the adsorption of salivary macromolecules onto hydroxyapatite. Using amino acids and other small adsorbates, it was determined that the carboxyl attached to the α carbon does not appear to adsorb onto HA and the affinities of side-chain carboxyls are much smaller than that of the phosphate group (phosphoserine). Hydroxyl (serine) displays an extremely high affinity, but its adsorption site on HA is different and the number of such sites is much smaller than found for the rest of the functional groups investigated. It is shown that the information obtained from small molecules cannot be readily applied to prediction of the adsorption behavior of salivary macromolecules and polypeptides. The kinetics of adsorption of the salivary phosphopeptide statherin, a polyaspartate, and the salivary prolinerich phosphoprotein PRP3 are consistent with the reversibility of the adsorption process; no conclusion was possible in the case of the protein PRP1. Apparent irreversibility cannot be explained on the basis of multipoint binding or the properties of the carboxyl versus phosphate group; it appears that secondary structure determines to a significant extent the adsorption properties of the macromolecules. Calculation of the thermodynamic molar quantities of adsorption of PRP1, PRP3, andl-ASP onto HA showed that the process is entropically driven. The functional relationship between partial molar entropy and adsorption coverage is similar for the two proteins, but quite different from that for aspartate. Explanations for these results are advanced on the bases of changes in structure configurations and displacement of water from the adsorbate and the adsorbent surface, the second factor being the dominant one in the adsorption of a small molecule such asl-ASP.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405293
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  • 3
    Electronic Resource
    Electronic Resource
    Comparative kinetic light-scattering and -absorption photometry (1981)
    Springer
    European biophysics journal 8 (1981), S. 23-34 
    Details
    ISSN: 1432-1017
    Keywords: Light-scattering ; Flash photometry ; Kinetics ; Visual transduction ; Biomembranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A recent development of kinetic light-scattering and -absorption photometry is described. Essential points are: 1) In the scattering experiment, amplitude resolution of 2 · 10−5 (single flash) by application of a differential detector, stability of the same magnitude due to optical compensation, high intensity at the detector due to special optics for the scattered light and semiconductor sources. 2) In the absorption measurement, elimination of scattering contributions by the dual wavelength-method and by high aperture optics. 3) Simultaneous measurement of absorption and scattering. The application of the method is described in using signals from isolated bovine rod outer segments. A reliable procedure is described by the use of which the originally measured light-scattering effects can be split up into single signals. The method allows comparative kinetic analysis of absorption and scattering signals. The possible causal connections between pigment and membrane structure processes can be selected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01047103
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and function of viroids (1983)
    Springer
    European biophysics journal 9 (1983), S. 145-170 
    Details
    ISSN: 1432-1017
    Keywords: Viroids ; Thermodynamics ; Kinetics ; Hydrodynamics ; Function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Viroids are an independent class of plant pathogens which are distinguished from viruses by the absence of a protein coat and by their unusually small size. They are single-stranded circular RNAs composed of about 360 nucleotide residues. Sequence analysis and physicochemical studies of the potato spindle tuber viroid (PSTV) have shown that, as a result of intra-molecular base pairing, viroids form a unique rod-like secondary structure which is characterized by a serial arrangement of double-helical sections and internal loops. There is no indication for an additional tertiary structure because all parts of the molecule are freely accessible to ligand interaction. During the denaturation all of the native base pairs of viroids are dissociated in one highly cooperative transition, and in the same process very stable hairpins which are not present in the native structure are newly formed. Most of the properties of the structure and structural transitions of PSTV have been found also in citrus exocortis viroid, chrysanthemum stunt viroid and four different viroid-like RNAs associated with the cadang-cadang disease. The close similarity between these viroids is more expressed in the overall structure and in thermodynamic and functional domains than in the primary sequence. The stiffness of all viroids can be described by an unique persistence length of 300 å. Characteristically, regions of premelting, regions of stable hairpins, and the sequence UACUACCCGGUGG which is opposite to one of the stable hairpins, are the most conservative sequences in the molecules. Current hypotheses about the function of viroids are discussed on the basis of their structural and thermodynamic features. The suggestion that viroid RNA has features similar to DNA has been supported by the finding that they are replicated in vitro by the DNA-dependent RNA polymerase II of the host plant. The highly conserved sequence in viroids mentioned above corresponds very closely to a segment at the 5′-end of the small nuclear RNA U1 of eukaryotes. Because this segment is discussed in recent models, to be involved in the splicing process, a hypothesis is proposed in which viroids interfere with the splicing process leading to a pathogenic misregulation of mRNA processing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00537813
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetics of nucleation in a lattice gas model: Microscopic theory and simulation compared (1983)
    Springer
    Journal of statistical physics 30 (1983), S. 219-241 
    Details
    ISSN: 1572-9613
    Keywords: Kinetics ; phase transitions ; nucleation ; lattice gas ; Becker-Doring equations ; clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method is described for calculating from first principles the coefficients in the Becker-Döring equations for the rate of change of the distribution of cluster sizes in a low-density lattice gas with Kawasaki dynamics. The method depends on solving a diffusion problem for the concentration of particles near a given cluster. The coefficients are calculated for cluster sizes up to 6, on a simple cubic lattice at a temperature 0.59 times the critical temperatures, and extrapolated to larger sizes. The resulting version of the Becker-Doring equations is then solved numerically. Comparison with the results of a computer simulation (at overall concentration 0.075) carried out by Kalos and others indicates that the method gives quite good predictions of the dependence of the cluster distribution on the critical cluster size (usually denoted by l*) but that the predicted rate of change of critical cluster size with time is too small, at this overall concentration, by a factor of about 0.3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01010876
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetics of a first-order phase transition: computer simulations and theory (1984)
    Springer
    Journal of statistical physics 34 (1984), S. 399-426 
    Details
    ISSN: 1572-9613
    Keywords: Kinetics ; Becker-Doring equations ; clusters ; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We make a quantitative comparison between the predictions of the Becker-Döring equations and computer simulations on a model of a quenched binary A-B alloy. The atoms are confined to the vertices of a simple cubic lattice, interact through attractive nearest neighbor interactions, and move by interchanges of nearest neighbor pairs (Kawasaki dynamics). We study in particular the time evolution of the number of clusters of A atoms of each size, at four different concentrations: ρA=0.035, 0.05, 0.075, and 0.1 atoms per lattice site. The temperature is 0.59 times the critical temperature. At this temperature the equilibrium concentration of A atoms in the B-rich phase is ρ A eq =0.0145 atoms/lattice site. The coefficients entering the Becker-Döring equations are obtained by extrapolation from previously published low-density calculations, leaving the time scale as the only adjustable parameter. We find good agreement at the three lower densities. At 10% density the agreement is, as might be expected, less satisfactory but still fairly good-indicating a quite wide range of utility for the Becker-Döring equations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01018552
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