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  • Articles  (86)
  • Chemistry
  • Humans
  • Polymer and Materials Science
  • kinetics
  • Springer  (86)
  • 1985-1989  (86)
  • 1
    Electronic Resource
    Electronic Resource
    Human vitamin C requirements (1987)
    Springer
    European journal of nutrition 26 (1987), S. 125-137 
    Details
    ISSN: 1436-6215
    Keywords: vitamin C ; functions ; kinetics ; pool ; saturation ; requirements ; RDA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Medicine
    Description / Table of Contents: Zusammenfassung Die Bedeutung von Vitamin C für den menschlichen Organismus wird aus den wichtigen Funktionen ersichtlich, an denen das Vitamin beteiligt ist, wie zum Beispiel Kollagen- und Karnitinsynthesen. In neuerer Zeit entdeckt wurde seine Rolle bei der Noradrenalinsynthese, der Inaktivierung von freien Radikalen sowie der Verhinderung der Nitrosaminbildung. Die Vielfalt dieser Vitamin-C-abhängigen Funktionen läßt erkennen, daß die Bedarfsfestsetzung für Vitamin C nicht nur die Verhütung der Mangelkrankheit Skorbut anvisieren, sondern auch berücksichtigen sollte, daß alle diese Funktionen jederzeit genügend Vitamin C zur Verfügung haben müßten, um optimal reagieren zu können. Das Konzept der Gewebesättigung kommt diesem Ziel am nächsten. Studien mit einem kinetischen Modell haben ergeben, daß eine Sättigung mit täglicher Einnahme von 100 mg Vitamin C bei Nichtrauchern und von 140 mg bei Rauchern eintritt, Mengen, die als optimale Werte gelten können. Bei verschiedenen Krankheiten dürfte der Bedarf höher sein; die genauen Mengen müssen jedoch erst noch ermittelt werden.
    Notes: Summary The importance of vitamin C is reflected in its multifunctional roles which include participation in collagen and carnitine syntheses, promotion of iron absorption and the more recently discovered participation in noradrenaline synthesis, inactivation of free radical chain reactions, prevention of N-nitroso compound formation and more. Given the many extra-antiscorbutic functions of the vitamin, the Recommended Dietary Allowances (RDA) should not just prevent deficiency disease but should aim at providing sufficient amounts for all vitamin C-dependent functions to operate at full capacity. The concept of vitamin C tissue saturation is best able to meet this demand. The use of kinetic models has shown that the body pool is saturated with a daily intake of 100 mg vitamin C in non-smokers and 140 mg in smokers, amounts that may be regarded as optimal RDA values. Certain disease states may be accompanied by still higher vitamin C requirements but the exact amounts are not yet known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02019608
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  • 2
    Electronic Resource
    Electronic Resource
    On the theory of photoadsorption kinetics of a-Se colloids: The thermal activation energy and compensation effect (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 958-964 
    Details
    ISSN: 1435-1536
    Keywords: a-Se colloids ; photoadsorption ; kinetics ; activation energy ; compensation effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this study, a model is developed to explain in microscopic terms the results obtained from thermally activated photoadsorption experiments in a-Se colloids. The observed compensation effect can be described for two different cases. At low efficiency adsorption, the process is controlled by the potential at the boundary layer. In the high efficiency adsorption case, the process is controlled by diffusion transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410853
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  • 3
    Electronic Resource
    Electronic Resource
    Laser temperature jump experiments with fluorescence polarization and turbidity detection on the phase transition of single shell vesicles of dimyristoylphosphatidylcholine (1985)
    Springer
    Colloid & polymer science 263 (1985), S. 484-493 
    Details
    ISSN: 1435-1536
    Keywords: Phospholipid bilayer ; kinetics ; laser temperature jump ; phase transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The iodine-laser temperature-jump technique has been used to investigate the main phase transition in single shell vesicles of dimyristoylphosphatidylcholine. The probe molecules DPH and TMA-DPH were incorporated into the lipid bilayer and laserT-jump experiments with turbidity and flourescence polarization detection were performed. We found three well separated relaxation processes between 5 μs and 10 ms. The relaxation signals showed strong cooperativity in the relaxation times as well as in their corresponding amplituedes. We attributed the relaxation to the formation and dissolution of clusters of different order inside the bilayer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01458339
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  • 4
    Electronic Resource
    Electronic Resource
    Radical desorption in the emulsion polymerisation of vinyl monomers (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 58-64 
    Details
    ISSN: 1435-1536
    Keywords: Polymerisation ; emulsion ; styrene ; methylmethacrylate ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The dependence of emulsion polymerisation rates on a number of important parameters is considered. Attention is paid to the use of seeded emulsion systems for the evaluation of radical desorption coefficients (k o). Experimental conditions are shown to be important. When the average number of radicals per particle is low, large changes in the rate coefficient for chain termination do not have a large effect on the kinetics. With styrene and methylmethacrylate, radical re-absorption by the polymer particles is shown to be important and radical capture efficiences can be high. Consistency is established between the results of a number of workers and values fork o are shown to be lower than those calculated from chain transfer rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01422665
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrasonic absorption of the oxyethylene group in aqueous nonelectrolyte solutions (1986)
    Springer
    Journal of solution chemistry 15 (1986), S. 221-229 
    Details
    ISSN: 1572-8927
    Keywords: Ultrasonics ; kinetics ; aqueous solution ; triethylene glycol monobutyl ether
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The ultrasonic absorption from 6.5 to 220 MHz and velocities at 2.5 MHz have been measured in aqueous solution of triethylene glycol monobutyl ether as a function of concentration at 25°C. A single relaxational excess absorption, observed from 0.60 to 2.5 mol-dm−3, is attributed to a perturbation of an equilibrium associated with solute-solvent interaction. Rate constants for the forward and reverse processes have been determined from the concentration dependence of the relaxation frequency, and the influence on the water structure by an addition of the solute has been considered. Solution densities were also measured in order to obtain the expansivity of the solution. The standard volume and enthalpy changes of the reaction have been estimated from the concentration dependence of the maximum excess absorption per wave length. A linear relationship between the number of oxyethylene groups and the free energy change between bonded water and nonbonded water is established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00646689
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  • 6
    Electronic Resource
    Electronic Resource
    The compositional distribution of coding sequences and DNA molecules in humans and murids (1988)
    Springer
    Journal of molecular evolution 27 (1988), S. 311-320 
    Details
    ISSN: 1432-1432
    Keywords: Genome composition ; Coding sequences ; Isochores ; Humans ; Murids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The compositional distributions of coding sequences and DNA molecules (in the 50-100-kb range) are remarkably narrower in murids (rat and mouse) compared to humans (as well as to all other mammals explored so far). In murids, both distributions begin at higher and end at lower GC values. A comparison of homologous coding sequences from murids and humans revealed that their different compositional distributions are due to differences in GC levels in all three codon positions, particularly of genes located at both ends of the distribution. In turn, these differences are responsible for differences in both codon usage and amino acids. When GC levels at first+second codon positions and third codon positions, respectively, of murid genes are plotted against corresponding GC levels of homologous human genes, linear relationships (with very high correlation coefficients and slopes of about 0.78 and 0.60, respectively) are found. This indicates a conservation of the order of GC levels in homologous genes from humans and murids. (The same comparison for mouse and rat genes indicates a conservation of GC levels of homologous genes.) A similar linear relationship was observed when plotting GC levels of corresponding DNA fractions (as obtained by density gradient centrifugation in the presence of a sequence-specific ligand) from mouse and human. These findings indicate that orderly compositional changes affecting not only coding sequences but also noncoding sequences took place since the divergence of murids. Such directional fixations of mutations point to the existence of selective pressures affecting the genome as a whole.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02101193
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  • 7
    Electronic Resource
    Electronic Resource
    Temperature-jump FT-IR time-resolved spectrometry (1988)
    Springer
    Microchimica acta 94 (1988), S. 277-278 
    Details
    ISSN: 1436-5073
    Keywords: kinetics ; FT-IR ; temporal resolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A system for performing gas-phase rapid scanning Fourier transform infrared time-resolved Spectrometry (FT-IR/TRS) has been evaluated. This technique can be applied to the study of the lifetimes and reactivity of transient species and can provide detailed information regarding reaction rate constants. Temperature-jump experiments have been initiated and preliminary results are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01205888
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamic Fourier transform infrared spectroscopy in polymer research (1988)
    Springer
    Microchimica acta 94 (1988), S. 323-328 
    Details
    ISSN: 1436-5073
    Keywords: FTIR spectroscopy ; kinetics ; polymers ; rheo-optics ; variable-temperature measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rapid-scanning capability of FTIR instrumentation has revitalized the field of vibrational spectroscopy in polymer research and will be discussed with reference to the study of polyurethane kinetics, the temperature dependence of hydrogen bonding in polyamide 6 and strain-induced crystallization in a polydimethylsiloxane elastomer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01205899
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of pyrophosphate and orotidine monophosphate on cytosine deaminase regulatory properties (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1563-1564 
    Details
    ISSN: 1420-9071
    Keywords: Cytosine deaminase ; kinetics ; pyrophosphate ; orotidine monophosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The maximal velocity of the reaction (Vmax) and the half-saturation constant (K0.5) values of theS. typhimurium cytosine deaminase were altered in the presence of its effectors, pyrophosphate and orotidine monophosphate. From the kinetics of orotidine monophosphate inhibition of cytosine deaminase, it was characterized as a mixed-type noncompetitive inhibitor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01964808
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  • 10
    Electronic Resource
    Electronic Resource
    Chemistry of high mountain lakes in siliceous chatchments of the Central Eastern Alps (1989)
    Springer
    Aquatic sciences 51 (1989), S. 108-128 
    Details
    ISSN: 1420-9055
    Keywords: Chemistry ; mountain lakes ; silica ; acidity ; sediment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Alpine lakes in siliceous catchments of Tyrol and Carinthia (Austria) show signs of acidification. About 9% of the studied lakes have no alkalinity, more than 20% are below pH 6. About two thirds of all lakes have acid neutralizing capacities below 100 μeq 1−1. In spite of moderate precipitation acidity, some lakes show considerable concentrations of dissolved reactive aluminum during or shortly after snowmelt. High altitude lakes of the Alps are definitely more acidic than high mountain lakes in remote areas. Large differences in water and soil chemistry of nearby situated lakes were attributed to heterogeneities of bedrock geology. Paleolimnological investigations on former pH values of five lakes, based on diatom assemblages in the sediment, showed different developments: recent and past acidification, stable conditions, and alkalinization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879298
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  • 11
    Electronic Resource
    Electronic Resource
    Effect of two antacids on the bioavailability of paracetamol (1985)
    Springer
    European journal of clinical pharmacology 29 (1985), S. 251-253 
    Details
    ISSN: 1432-1041
    Keywords: paracetamol ; antacids ; acetaminophen ; bioavailability ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary The effect of two antacids on the bioavailability of paracetamol has been investigated in 12 young healthy volunteers. Following a random cross over design, each subject swallowed, on three separate occasions, one weak apart, 500 mg paracetamol alone, or together with two different aluminium hydroxide, magnesium hydroxide preparations (Dimalan and Maalox). Plasma paracetamol levels were measured by HPLC. The bioavailability of paracetamol was not altered by either antacid, but they both delayed the time to peak plasma concentration (0.85 h; 1.43 h; 1.25 h, without antacid, with Dimalan and with Maalox respectively). The peak plasma concentration was not affected by concurrent antacid administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00547432
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  • 12
    Electronic Resource
    Electronic Resource
    Sodium channel opening as a precursor to inactivation (1989)
    Springer
    European biophysics journal 16 (1989), S. 321-325 
    Details
    ISSN: 1432-1017
    Keywords: Sodium currents ; inactivation ; kinetics ; channel gating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The time constant of the process producing the delay in Na inactivation development as determined by the two pulse method (τdelay) was extracted and compared to that of the slowest Na activation process τ3 for the I Na during the conditioning pulse of that same determination. τdelay and two pulse inactivation τc values were computer generated using a nonlinear least squares algorithm. τh and single pulse inactivation τh values were independently generated for each determination also with the aid of the computer using the same non-linear least squares algorithm. In one determination at 2 mV, τc was 4.68 and τdelay 0.494 ms while τh was 4.70 and τ3 0.491 ms for a τc/τh of 0.996 and a τdelay/τ3 of 1.006. Mean τdelay/τ3 from five determinations in four axons, both Cs and K perfused, and spanning a potential range of-27 to 2mV was 1.068. The precursor process to inactivation is channel opening. Some fraction of channels presumably inactivate via another route where prior channel opening is not required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00257880
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  • 13
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    Arachidonic acid — Induced platelet aggregation and prostanoid formation in whole blood in relation to plasma concentration of indomethacin (1985)
    Springer
    European journal of clinical pharmacology 28 (1985), S. 163-169 
    Details
    ISSN: 1432-1041
    Keywords: indomethacin ; platelet aggregation ; prostanoids ; plasma concentration ; arachidonic acid ; thromboxane B2 ; 6-keto-prostaglandin F1α ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary A single oral dose of indomethacin 1 mg/kg was given to 6 male and 6 female volunteers. The formation of thromboxane B2 (TXB2) and 6-ketoprostaglandin F1α (6-keto-PGF1α) in clotting whole blood was measured by radioimmunoassay, and platelet aggregation induced by archidonic acid (AA) was measured with a plasma aggregometer. The results were related to the concomitant plasma concentration of indomethacin. The maximum plasma concentration ranged between 3.24 and 8.11 µg/ml and the elimination half-life between 4 and 11 h. Formation of the prostanoids was reversibly inhibited, with maximum suppression when the drug concentration in plasma exceeded 0.5–1.0 µg/ml; the IC50 was approximately 0.1 µg/ml. Platelet aggregation was also reversibly inhibited. The correlation between the formation of prostanoids and the different phases of the aggregatory response to exogenous AA is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00609686
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  • 14
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    Electronic Resource
    Extradural and parenteral pethidine as analgesia after total hip replacement: Effects and kinetics. A controlled clinical study (1986)
    Springer
    European journal of clinical pharmacology 29 (1986), S. 529-534 
    Details
    ISSN: 1432-1041
    Keywords: pethidine ; epidural injections ; pain scores ; kinetics ; spinal cord
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Twenty-one patients who had undergone total hip replacement were randomly assigned to one of three groups in order to compare a single dose of 1 mg/kg of pethidine im (I) and 20 mg (II) or 60 mg of extradural pethidine (III) in a double-blind design. The degree of analgesia, the adverse effects, and the kinetics were studied for 18 h. Pain was monitored using a visual analogue scale (VAS). Supplementary doses of oxycodone if required were given no earlier than 0.75 h after pethidine. Plasma concentrations of pethidine were measured with gas chromatography mass spectrometry (GCMS). Hypoalgesia to pin prick test was evaluated. Low pain scores were observed in the extradural groups between 0.25 and 1.5 h after the dose. A significant difference in pain score compared with the im group was found after the higher extradural dose only between 0.5 and 1 h (p〈0.05). The area under the curve (AUC) of pain score versus time (0–18 h) was not significantly different between groups. The recorded adverse effects were minor in all three groups. The terminal half-lives and plasma clearances of pethidine, and the time to peak concentration were not different between the groups. Single patients in the extradural groups showed hypoalgesia to pin prick in parallel to the effect. The present study shows that extradural pethidine produces shortlived analgesia, in contrast to the long-lasting effect of morphine found in other studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00635888
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  • 15
    Electronic Resource
    Electronic Resource
    Dimyristoylphosphatidic acid/cholesterol bilayers (1986)
    Springer
    European biophysics journal 13 (1986), S. 343-353 
    Details
    ISSN: 1432-1017
    Keywords: Lipid/cholesterol ; phase transition ; kinetics ; second order transition ; pressure jump relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Lipid bilayers and monolayers composed of dimyristoylphosphatidic acid (DMPA) and cholesterol were characterized by differential scanning calorimetry and film balance measurements. Increasing cholesterol content decreases the bilayer phase transition temperature and enthalpy in a manner similar to that observed before for other lipid/cholesterol systems. In monomolecular films at the air-water interface cholesterol exhibits the well known condensing effect in the liquid-expanded phase, while the liquid-condensed phase is less affected. As with the bilayer phase transition, the transition temperature and change in area at the liquid-condensed to liquid-expanded phase transition, as measured from isobars at 25 dynes/cm, decreases with increasing cholesterol content. The kinetics of the phase transition of DMPA/cholesterol bilayers were measured using the pressure jump relaxation technique with optical detection. Three relaxation times were observed. The relaxation times and amplitudes pass through maximum values at the transition midpoint. With increasing cholesterol content the maximum values of the relaxation times decrease but not in a linear fashion. The time constants display an intermediate maximum at ca. 10% to 12 mol% cholesterol. This observation is discussed in terms of a possible change in the nature of the phase transition from first-order with phase separation to a continuous second-order transition. The dependence of the relaxation amplitudes on cholesterol content gave evidence for nucleation being the rate limiting step for the transition in this particular system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00265670
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  • 16
    Electronic Resource
    Electronic Resource
    Plasma-chemical reactions in weakly decomposed CCl4 (1985)
    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 293-316 
    Details
    ISSN: 1572-8986
    Keywords: Plasma chemistry ; halocarbon decomposition ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract For the case of weak feed gas decomposition, where the concentration of CCl4 exceeds those of decomposition and built-up products, the emission of CCl* is shown to originate from dissociative excitation of CCl4. With electron concentration measured independently, the kinetics of CCl4 decomposition has been extracted from the time dependence of the CCl* intensity. Supported by EPR determinations of radical concentrations in rapidly flowing CCl4 and CCl4/O2 afterglows, the primary decomposition reaction is shown to be the electron impact dissociation into CCl3 and Cl. Its rate constant (k 1=4×10−8 cm3s−1) indicates strongly that dissociative electron attachment is the main reaction channel at least at r.f. power densities just above the threshold of a self-maintaining discharge. At extremely low mean electron energies the emission of a continuum is observed, which is tentatively ascribed to the radiative CCl3-Cl recombination.
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    URL: http://dx.doi.org/10.1007/BF00566006
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  • 17
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    Dynamics of the formation and decay of C2(a 3II u ,v″=0) radical in a pulse discharge in methane (1986)
    Springer
    Plasma chemistry and plasma processing 6 (1986), S. 429-436 
    Details
    ISSN: 1572-8986
    Keywords: Plasma ; laser ; diagnostics ; free radicals ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The plasma of a pulse discharge (0.05 J/cm3) in methane at low pressure (200 Pa) is studied. The dynamics of formation and decay of C2(a3IIu, v″=0) is monitored using a stroboscopic laser absorption method. It was found that substantial amounts of C2, 1015 cm−3, arise with a 1-µs delay after the current pulse.
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    URL: http://dx.doi.org/10.1007/BF00565554
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  • 18
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    Dynamics of the formation of excited hydrogen, H(n=2,3,4), during a pulse discharge in methane (1988)
    Springer
    Plasma chemistry and plasma processing 8 (1988), S. 101-110 
    Details
    ISSN: 1572-8986
    Keywords: Plasma ; laser ; diagnostics ; hydrocarbons ; free radicals ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract The dynamics of the formation and decay of excited hydrogen during a pulse discharge in methane at a pressure of 200 Pa and energy density of 0.05 J/cm3 has been studied. The population of hydrogen in the n=2 state was monitored by the laser absorption method. The time constant of the decay of the excited hydrogen was measured to be 95±15 ns. The concentration of free electrons reached a maximum value of 7×1014 cm−3, and the time constant of their recombination was 220±50 ns. The formation of appreciable amounts of atomic hydrogen in the ground state during the discharge, H(n=1)〉1016 cm−3, was estimated on the basis of a kinetic model.
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    URL: http://dx.doi.org/10.1007/BF01016934
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  • 19
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    Plasma-chemical methane conversion under nonthermal and thermal conditions: An attempt toward uniform kinetic modeling (1985)
    Springer
    Plasma chemistry and plasma processing 5 (1985), S. 283-291 
    Details
    ISSN: 1572-8986
    Keywords: Methane ; acetylene ; kinetics ; modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract It is shown that it is basically possible to model plasma-chemical methane conversion using a kinetic concept regardless of the kind of plasma, i.e., the kind of activation. While the temporal plasma-chemical decomposition of methane is controlled by a first-order rate equation, the temporal product formation can be described by a set of first-order consecutive reactions. Prolonged portions of constant product concentrations in the temporal product formation curves were explained by the assumption of an equilibrium between forward and reverse reactions. The modeling revealed the special role of the re-formation of dissociated molecules.
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    URL: http://dx.doi.org/10.1007/BF00615127
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  • 20
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    Kinetics and thermodynamic transitions of N-acetyl-β-D-glucosaminidase A and B in free and bound forms: Role of cellulose ion-exchangers (1989)
    Springer
    Molecular and cellular biochemistry 86 (1989), S. 65-70 
    Details
    ISSN: 1573-4919
    Keywords: Hex A ; Hex B ; N-acetyl-glucosaminidases ; kinetics ; thermodynamic transitions ; ion-exchangers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary The kinetic and thermodynamic properties of N-acetyl-β-D-glucosaminidase A (Hex A) and N-acetyl-β-D-D-glucosaminidase β (Hex B) from goat testes were investigated in free and bound (after binding them on ion-exchangers such as DEAE- or CM-cellulose respectively) forms. The optimum pH of free Hex A and Hex B was at 4.2 and 5.4, whereas the bound forms showed the optimum pH at 4.0 and 5.2 respectively. While apparent Km of free and bound Hex A (0.8 and 1.0 mM respectively) did not differ, the Km of Hex B increased when bound on CM-cellulose (Km of free Hex B = 0.96 mM versus bound Hex B = 1.6 mM). Though the free Hex A was more thermo-labile than the free Hex B, both isozymes, on insoluble matrices decayed at faster rates on heating. Activation analysis revealed that the energy of activation (E infa supo ) for transition state of free Hex B (81 Kcal deg−1 mole−1) did not differ from E infa supo of bound Hex B. On the other hand, E infa supo of free Hex A declined from 77.2 to 71.1 Kcal deg−1 mole−1 when heat transitions were carried out in free and bound state respectively. Thermodynamic analysis suggested a change in entropy of activation (ΔS*) of free Hex A and Hex B as 200 and 211 eu respectively. While ΔS* of Hex B did not change after heat transitions, ΔS* of Hex A was 182.5 eu.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231690
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  • 21
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    Properties of allelic variants of phosphoglucomutase from the sea anemone Metridium senile (1985)
    Springer
    Biochemical genetics 23 (1985), S. 859-876 
    Details
    ISSN: 1573-4927
    Keywords: allozyme ; Cnidaria ; cline ; isozyme ; kinetics ; Metridium senile ; phosphoglucomutase ; polymorphism ; variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The phosphoglucomutase (Pgm) locus from populations of the sea anemone Metridium senile has three alleles in natural populations from the northeastern coast of North America. Two of the alleles exhibit clinal variation north of Cape Cod, suggesting a possible association of allele frequency with environmental temperature. This clinal pattern is reproducible and stable over at least brief periods of time. The allozymes encoded by each of the six Pgm genotypes have been partially purified and characterized. The symmetrical pH optimum for V max is pH 7.5; the apparent K m (K m app ) of glucose-1-phosphate declines monotonically as the pH increases from 6.5 to 8.5. There are no pronounced differences in heat stabilities of PGM produced by various genotypes, nor are there significant differences in specific activities. There are no differences in the sensitivity of V max to temperature. K m app values are very low for all genotypes, ranging from about 2 to 12 µm, depending upon the temperature. K m app of glucose-1-phosphate declines as the temperature is raised for all genotypes, whether the pH is held constant or allowed to vary with the temperature. Under certain conditions, there are small significant differences among genotypes in K m app values, but there is no systematic pattern to these differences. The present data provide no biochemical explanation for the maintenance of the Pgm cline by selection for functional differences under different thermal regimes.
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    The oxidation of cobalt-chromium-titanium alloys at 1000°C (1986)
    Springer
    Oxidation of metals 26 (1986), S. 139-155 
    Details
    ISSN: 1573-4889
    Keywords: oxidation ; Co-Cr-Ti alloys ; kinetics ; scale morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Cobalt-based alloys containing 3,5,10,15, and 20% Cr with 1 and 3% Ti were oxidized at 1000°C in slowly flowing oxygen gas. In general, titanium additions decreased the oxidation rate with the most pronounced effect being observed at the 10% Cr level. Titanium accelerated the formation of Cr2O3 layers at the metal-oxide interface. Faceted CrxTiyOz spinel particles were found at the metal-oxide interface which varied in composition according to microprobe results. There was no evidence of spalling on the Co-Cr-Ti alloys studied in contrast to the severe spalling normally encountered in Ni-Cr-Ti alloys. Distinct morphological differences existed on the outer CoO layer of the 1% Ti alloys in comparison to the O and 3% Ti alloys.
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    URL: http://dx.doi.org/10.1007/BF00664278
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    Effect of scale constitution on the carburization of heat resistant steels (1986)
    Springer
    Oxidation of metals 26 (1986), S. 417-430 
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    ISSN: 1573-4889
    Keywords: cyclic carburization-oxidation ; carbides ; austenite ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Several austenitic heat-resistant steels were exposed to alternating periods of carburization at 1273 K [a c= 1,po2〈10−28 atm] and oxidation at 973°K [a c≈ O,po2 = 0.2 atm]. In all cases the depth of internal carbide precipitation increased with cumulative carburization time. It was found that the carburization rates of high nickel content alloys were unaffected by intermittent oxidation cycles, whereas the low nickel, high iron content alloys experienced a reduction in carburization rate subsequent to oxidation treatment. The latter group of alloys formed external scales of chromium-rich M7C3 which were shown by sulfur tracing experiments to be gas permeable. It was concluded, therefore, that oxidation of these materials led to blockage of cracks and holes in the scales, thereby decreasing the surface carbon activity and hence the carburization rate. High nickel, low iron alloys formed external scales of chromium-rich M7C3 covered by Cr3C2. These scales were shown to have very low gas permeabilities. It was concluded that the carbon activity at the surface of these alloys was controlled by scale-alloy equilibration, and was therefore not affected by brief periods of oxidation. The pattern of carbide scale formation is qualitatively consistent with the thermodynamics of the Fe-Cr-C system.
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    URL: http://dx.doi.org/10.1007/BF00659345
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  • 24
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    The regulatory kinetic properties of porcine hepatic glucokinase (1989)
    Springer
    Molecular and cellular biochemistry 86 (1989), S. 171-179 
    Details
    ISSN: 1573-4919
    Keywords: porcine glucokinase ; purification ; kinetics ; sulfhydryl-related states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Porcine hepatic glucokinase (ATP: D-hexose 6-phosphotransferase EC 2.7.1.1) has been purified by a modification of the procedure for its purification from rats. However, difficulties were encountered with endogenous proteases and the reliability of a source for porcine livers. The molecular weight has been determined to be 60 400 ± 1400 by sodium dodecyl sulfate, polyacrylamide gel electrophoresis. The enzyme has been characterized kinetically. The parameter values, S 0.5 (glucose) and Hill coefficient (nH) are 2.4 mM and 1.9 respectively under sulfhydryl-reducing conditions. The enzyme undergoes the two sulfhydryl-related decays of its activity previously observed in the enzyme isolated from rat (Tippett PS, Neet KE: Arch Biochem Biophys 222:285–298, 1983). The enzyme is inhibited by palmitoyl-CoA, K i (apparent) = 1.0 µM, nH = 1.8; this concentration of inhibitor is significantly below its critical micelle concentration. Physically and kinetically glucokinase isolated from pig is similar to the enzyme isolated from rat. The porcine system provides a second source for isolation and further characterization of this important and unusual enzyme.
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    URL: http://dx.doi.org/10.1007/BF00222617
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  • 25
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    Effect of yttrium on the sulfidation behavior of Ni-Cr-Al alloys at 700°C (1986)
    Springer
    Oxidation of metals 25 (1986), S. 1-28 
    Details
    ISSN: 1573-4889
    Keywords: sulfidation ; yttrium ; duplex-sulfide scales ; lamellar sulfides ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The sulfidation of Ni-10Cr-5Al, Ni-20Cr-5Al, and Ni-50Cr-5Al, and of the same alloys containing 1% Y, was studied in 0.1 atm sulfur vapor at 700°C. The sulfidation process followed linear kinetics for all the alloys except Ni-50Cr-5Al-1Y, and possibly Ni-50Cr-5Al, which followed the parabolic law. The reaction rates decreased with increasing chromium content in alloys without yttrium, and the addition of yttrium reduced the rates by at least a factor of two for the alloys containing 10 and 20% Cr and by an order of magnitude for Ni-50Cr-5Al. Alloys containing 10 and 20% Cr (with and without yttrium) formed duplex scales consisting of an outer layer of NiS1.03 and an inner lamellar layer of a very fine mixture of Cr2S3 and A12O3 in a matrix of NiS1.03. The two alloys containing 50% Cr formed only a compact layer of Cr2S3, which was brittle and spalled during cooling. The lamellae in the duplex scales were parallel to the specimen surface and bent around corners. The lamellae were thicker than those on Ni-Al binary alloys. The lamellae were also thicker in scales on the 20% Cr alloy than on the 10% Cr alloy. The presence of yttrium refined the lamellae and increased the lamellae density near the scale/metal interface in the 10% alloy, but in the 20% Cr alloy the lammellae were thicker and more closely spaced. Platinum markers were found in the inner portion of the exterior NiS1.03 layer close to the lamellar zone. A counter-current diffusion mechanism is proposed involving outward cation diffusion and inward sulfur diffusion, although diffusion was not rate controlling for alloys containing 10 and 20% Cr. Auger analysis of scales formed on Ni-50Cr-1Y showed an even distribution of yttrium throughout the layer of Cr2S3, suggesting that some yttrium dissolved in the sulfide. The reduced sulfidation rate of samples containing yttrium is explained by the possible dissolution of yttrium as a donor. The presence of Y4+ would then decrease the concentration of interstitial chromium ions in the N-type layer of Cr2S3, which would decrease the reaction rate.
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    URL: http://dx.doi.org/10.1007/BF00807994
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    Formation and growth of spinel and Cr2O3 oxides on 20% Cr-25% Ni-Nb stainless steel in CO2 environments (1985)
    Springer
    Oxidation of metals 23 (1985), S. 207-235 
    Details
    ISSN: 1573-4889
    Keywords: stainless steel ; duplex oxide ; kinetics ; growth rates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The nature of the first-formed oxide on 20% Cr/25% Ni/Nb stabilized steel during exposure to CO2 at high and low temperatures has been determined by surface analytical techniques. These results together with a consideration of gas/solid interactions show that the oxide produced may be determined by kinetics or thermodynamic factors, and a diagram is presented to show that rhombohedral Cr2O3 or spinel may be the oxide first formed. Under most standard conditions, a mixed spinel oxide is formed initially, and the subsequent growth of a duplex oxide is analyzed in terms of a solid-state reaction in which the spinel oxide is reduced to Cr2O3 at the metal/oxide interface. Diffusion control of growth by either spinel or Cr2O3 is incorporated in new equations describing the kinetics of oxidation, and weight-gain predictions are tested against experimental observations.
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    URL: http://dx.doi.org/10.1007/BF00659904
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  • 27
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    Molten carbonate-induced hot corrosion of nickel (1989)
    Springer
    Oxidation of metals 32 (1989), S. 225-240 
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    ISSN: 1573-4889
    Keywords: Hot corrosion ; nickel ; TGA ; kinetics ; mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The accelerated oxidation of pure nickel in the presence of a molten carbonate mixture has been studied in O2 and CO2-containing atmospheres. The oxidation rate of nickel with carbonate coatings was at least four orders of magnitude faster than that without salt coatings. The extent of oxidation, in terms of unit area weight gain, depended on both the amount of carbonate mixture coatings and the gas atmosphere. The unit area weight gain due to oxidation increased with increasing amounts of salt coatings up to a certain value. These observations suggest that the termination of nickel oxidation results from the exhaustion of either the salt coatings or metallic nickel. Porous and particulate oxide products were observed from scanning electron microscopic (SEM) examinations. The energy-dispersive analysis of x-rays (EDAX) shows that no salt remains on the specimen surface after the oxidation experiment.
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    URL: http://dx.doi.org/10.1007/BF00664800
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    Kinetic mechanisms and interaction of rat liver DNA methyltransferase with defined DNA substrates (1987)
    Springer
    Molecular and cellular biochemistry 76 (1987), S. 45-54 
    Details
    ISSN: 1573-4919
    Keywords: DNA methyltransferase ; hemimethylated DNA ; kinetics ; affinity chromatography ; (rat liver)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract DNA substrate analogs were constructed from poly(dC-dG), M13, and XP12 DNA which do not contain a mixture of types of methylation sites. These were used to distinguish different kinetic mechanisms for maintenance and de novo methylation using a highly purified rat liver DNA (cytosine-5)-methyltransferase (DMase−) preparation. De novo methylation on single (ss) and double-stranded (ds) DNA was found to obey Michaelis-Menten kinetics while methylation of hemimethylated sites showed differences depending on size of the hemimethylated region. On long stretches analogous to maintenance methylation of newly replicated DNA, saturation could not be achieved and the kinetics showed non-ideal positive cooperative kinetics, while short stretches showed non-Michaelis-Menten kinetics and rapid saturation. Two types of DMase-DNA complexes could be distinguished by means of affinity chromatography on DNA-agarose matrices and in preincubation assays. The later complex, which is engaged in methyl group turnover, exhibited enhanced stability. The competitiveness of variously configured DNAs was found to parallel the stability of complex formation, e.g., ss, hemi- and ds DNA, respectively. In studies utilizing 5-bromodeoxyuridine, the thymine analog left the basic reaction mechanisms unchanged but increased the km and S0.5 while reducing the velocity of these reactions.
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    URL: http://dx.doi.org/10.1007/BF00219397
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    Kinetics of oxidation of ferrous alloys by super-heated steam (1987)
    Springer
    Oxidation of metals 28 (1987), S. 237-258 
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    ISSN: 1573-4889
    Keywords: Steel oxidation ; duplex scale ; steam ; activation energy ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The kinetics of the oxidation of ferrous alloys in steam (10–60 kPa) at 450–550°C have been studied by measuring both the rate of hydrogen emission and the amount of metal oxidized. Excellent agreement has been found between the amount of metal oxidized calculated from both the total mass of hydrogen produced in the reaction and the thickness of the oxide layer formed; rate constants calculated from the rate of hydrogen emission, the mass of hydrogen produced as the reaction proceeds, and the oxide formed agree within experimental error. The rate of oxidation of a 9%Cr-1%Mo alloy at 501°C was found to be independent of the partial pressure of the steam. For this alloy, the activation energy agreed with literature values obtained at higher temperatures and pressures. The effect of the chromium and silicon content on the oxidation rates is compared. The rate constants are compared with theoretical calculations, assuming that the rate is determined by diffusion of iron in the magnetite lattice. For the 9%Cr-1%Mo alloy, the parabolic rate constant and activation energy are in excellent agreement with values calculated using Wagner's theory. The experimental rate constants are greater for the alloys containing smaller amounts of chromium; diffusion of iron along magnetite grain boundaries may be the dominant mechanism.
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    URL: http://dx.doi.org/10.1007/BF00666721
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    Mechanisms of high-temperature corrosion in helium containing small amounts of impurities. II. Corrosion of the nickel-base alloy inconel 617 (1988)
    Springer
    Oxidation of metals 30 (1988), S. 27-51 
    Details
    ISSN: 1573-4889
    Keywords: Ni-base alloy IN 617 ; reactor helium ; oxidation ; carburization ; decarburization ; kinetics ; mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Application of the technical nickel-base alloy IN 617 in the primary circuit of the high-temperature gas-cooled reactor is limited essentially by the chemical reactions with the impurities (CO, CO2, H2, CH4, H2O) in the helium coolant. The interactions of the alloy with the reactive impurities in different helium-base gases were investigated by thermogravimetry in a gas-tight microbalance and by simultaneous measurement of the changes in gas composition by a continuous sensitive mass spectrometric analysis. The results demonstrate that the set of six reaction equations deduced in part 1 can be applied to describe the corrosion of the alloy. The occurrence of the various reactions is determined essentially by temperature. For the case of a standardized helium gas (HHT-He), three temperature regions can be distinguished. Below a critical temperature (about 1105 K), the presence of CO can cause simultaneous oxidation and carburization. Above this temperature, this reaction does not reverse itself. Rather, oxidation by CO2 and H2O takes place that shows, after a transient period, the same kinetics observed in undiluted oxygen-containing gases. At temperatures above about 1205 K, decarburization of the alloy accompanied by the production of CO takes place, leading to severe destruction of the carbide microstructure and, therefore, limiting the applicability of the material.
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    URL: http://dx.doi.org/10.1007/BF00656643
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    Oxidation of high-aluminum austenitic stainless steels (1988)
    Springer
    Oxidation of metals 30 (1988), S. 185-200 
    Details
    ISSN: 1573-4889
    Keywords: austenitic steels ; oxidation resistance ; protective αA12O3 film ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The cyclical oxidation behavior of an austenitic stainless steel (24% Ni, 10% Cr, 5% Al, and balance Fe) has been evaluated in the temperature range 800–1300°C. The effects of trace elements such as S, Y, Zr, and Ti on the oxidation of the austenitic stainless steel have also been evaluated. The results indicate that Fe-Ni-Cr-Al stainless steels exhibit superior oxidation resistance up to 1300°C due to the formation of a very adherent and thin film of α-Al2O3.
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    URL: http://dx.doi.org/10.1007/BF00666596
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    Effect of acidicpH on the protein carmin from safflower seed (Carthamus tinctorius) (1989)
    Springer
    The protein journal 8 (1989), S. 529-548 
    Details
    ISSN: 1573-4943
    Keywords: carmin ; association-dissociation ; denaturation ; reaggregation ; kinetics ; reversibility ; hydrophobic interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of a decrease inpH on the structural integrity of carmin has been monitored by a variety of biophysical techniques. The protein undergoes initial dissociation up topH 3.5–4.0 without any significant denaturation. Below thispH the process of dissociation and denaturation appears to be simultaneous. Further, in thepH range of 2.5–1.6 the protein reassociates to probably a different polymer resulting from possibly, an entropically driven hydrophobic interaction. The process of dissociation appears to be reversible to a large extent. The process of denaturation appears to be governed by the kinetic path that the denatured protein molecule follows either by a sudden decrease inpH or through a gradual decrease inpH. These results are interpreted while keeping in view the oligomeric and globular structure of carmin at neutralpH. The results would help in understanding of structure-function relationship of the protein and its role in hydrogen ion bindingin vivo.
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    URL: http://dx.doi.org/10.1007/BF01026437
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    Kinetic studies on human lactate dehydrogenase isoenzyme-catalyzed lactate-to-pyruvate reaction (1987)
    Springer
    The protein journal 6 (1987), S. 413-429 
    Details
    ISSN: 1573-4943
    Keywords: lactate dehydrogenase isoenzymes ; lactate-to-pyruvate reaction ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to evaluate the functional differences that may exist in human lactate dehydrogenase (LDH) isoenzymes widely used for clinical examination the kinetic and thermodynamic properties of the lactate to pyruvate reaction that they catalize were examined. Small but significant differences in the kinetic properties of the three isoenzymes were observed. The difference in the rate constants might affect the activity measurement of the individual isoenzyme as the initial velocity for the L-P reaction catalyzed will not be the same for an equal amount of enzyme. Equilibrium constants for the overall reaction in the presence and absence of pyruvate have been determined. On the basis of transition-state theory, the standard enthalpy and free-energy changes for formation of ternary activated complex were positive, while the standard entropy change was negative. Although the standard free-energy change was the same for activation by the three isoenzymes, the enthalpy and entropy changes for the LDH-3-catalyzed reaction were different from the respective values for others. A large positive value for the free-energy change and a negative value for the entropy change indicated unfavorable production of the activated complex (K infeq. sup╪ =1.89×10-16). The enzyme appears to stabilize and retain the activated complex until it dissociates into the products.
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    Generalized kinetic analysis of ion-driven cotransport systems: II. Random ligand binding as a simple explanation for non-Michaelian kinetics (1986)
    Springer
    The journal of membrane biology 90 (1986), S. 67-87 
    Details
    ISSN: 1432-1424
    Keywords: cotransport ; kinetics ; reaction kinetic model ; dual isotherm ; random binding ; slip
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Solute uptake in many cells is characterized by a series of additive Michaelis-Menten functions. Several explanations for these kinetics have been advanced: unstirred layers, transport across more than one membrane, effects of solute concentration on membrane potential, numerous carrier systems. Although each of these explanations might suffice for individual cases, none provides a comprehensive basis for interpretation of the kinetics. The most common mechanism of solute absorption involves cotransport of solute with a driver ion. A model is developed in which solute and driver ion bind randomly to a membrane-bound carrier which provides a single transmembrane pathway for transport. The kinetic properties of the model are explored with particular reference to its capacity to generate additive Michaelian functions for initial rate measurements of isotopic solute influx. In accord with previous analysis of ordered binding models (Sanders, D., Hansen, U.-P., Gradmann, D., Slayman, C.L. (1984)J. Membrane Biol. 77:123), the conventional assumption that transmembrane transit rate-limits transport has not been applied. Random binding carriers can exhibit single or multiple Michaelian kinetics in response to changing substrate concentration. These kinetics include high affinity/low velocity and low affinity/high velocity phases (so-called “dual isotherms”) which are commonly observed in plant cells. Other combinations of the Michaelis parameters can result incis-(substrate) inhibition. Despite the generality of the random binding scheme and the complexity of the underlying rate equation, a number of predictive and testable features emerge. If external driver ion concentration is saturating, single Michaelian functions always result and increasing internal substrate concentration causes uncompetitive inhibition of transport. Numerical analysis of the model in conditions thought to resemble those in many experiments demonstrates that small relative differences in a few key component rate constants of the carrier reaction cycle are instrumental in generation of dual isotherms. The random binding model makes the important prediction that the contributions of the two isotherms show opposing dependence on external concentration of driver ion as this approaches saturation. In the one case in which this dependence has been examined experimentally, the model provides a good description of the data. Charge translocation characteristics of the carrier can be determined from steady-state kinetic data on the basis of the response of substrate flux to modulation of internal driver ion concentration. The application of the model to dual isotherm kinetics is discussed in relation to “slip” models of cotransport, in which the carrier is assumed to have the capability to transport substrate alone or with the driver ion. A method for distinguishing between the two models is suggested on the basis of measurement of charge/solute transport stoichiometry as a function of external driver ion concentration.
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    Characterization of sodium and pyruvate interactions of the two carrier systems specific of mono- and di- or tricarboxylic acids by renal brush-border membrane vesicles (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 197-205 
    Details
    ISSN: 1432-1424
    Keywords: sodium ; pyruvate ; transport ; proximal tubule ; kinetics ; kidney
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The experiments reported in this paper aim at characterizing the carboxylic acid transport, the interactions of pyruvate and citrate with their transport sites and specificity. The study of these carriers was performed using isotopic solutes for the influx measurements in brush-border membrane vesicles under zerotrans conditions where the membrane potential was abolished with KCl preloading with valinomycin or equilibrium exchange conditions and Δψ=0. Under zerotrans condition and Δψ=0, the influence of pyruvate concentrations on its initial rates of transport revealed the existence of two families of pyruvate transport sites, one with a high affinity for pyruvate (K t =88 μm) and a low affinity for sodium (K t =57.7mm) (site I), the second one with a low affinity for pyruvate (K t =6.1mm) and a high affinity for sodium (K t =23.9mm) (site II). The coupling factor [Na]/[pyruvate] stoichiometry were determined at 0.25mm and 8mm pyruvate and estimated at 1.8 for site I, and 3 when the first and the second sites transport simultaneously. Under chemical equilibrium (Δψ≅0) single isotopic labeling, transport kinetics of pyruvate carrier systems have shown a double interaction of pyruvate with the transporter; the sodium/pyruvate stoichiometry also expressed according to a Hill plot representation wasn=1.7. The direct method of measuring Na+/pyruvate stoichiometry from double labeling kinetics and isotopic exchange, for a time course, gives an=1.67. Studies of transport specificity, indicate that the absence of inhibition of lactate transport by citrate and the existence of competitive inhibition of lactate and citrate transports by pyruvate leads to the conclusion that the low pyruvate affinity site can be attributed to the citrate carrier (tricarboxylate) and the high pyruvate affinity site to the lactate carrier (monocarboxylate).
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    URL: http://dx.doi.org/10.1007/BF01871734
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    Kinetic response of H+-coupled transport to extracellular pH: Critical role of cytosolic pH as a regulator (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 253-261 
    Details
    ISSN: 1432-1424
    Keywords: Chara ; Cl− ; cotransport ; reaction kinetic model ; pH ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary H+-coupled transport in plant and fungal cells is relatively insensitive to external pH (pH o ). H+-coupled Cl− transport at the plasma membrane ofChara corallina was studied to explore the phenomena responsible for this insensitivity. Raising pH o from a control value of 7.5 to 9.0 results in a modest (2.5-fold) decline inJ max and increase inK m . Further increase in pH o results in a selective increase inJ max, in accordance with predictions from a reaction kinetic model of the transport system (Sanders, D., Hansen, U.-P., 1981.J. Membrane Biol. 58:139–153). Increase in cytosolic Cl− concentration ([Cl−] c ) also results in a selective decrease inJ max at pH o =7.5. Quantitative kinetic modeling of the results is not possible if it is assumed that the sole effect of pH o isvia mass action on the binding of external H+ to a transport site. If, instead, the dependence of cytosolic pH (pH c ) on pH o (Smith, F.A., 1984,J. Exp. Bot. 35:1525–1536) is taken into account along with the dependence of Cl− influx on pH c (Sanders, D., 1980,J. Membrane Biol. 53:129–141), then the observed modest changes in Michaelis parameters can be accommodated by a reaction kinetic model. The quantitative parameters of the model yield respective pK a s of the internal and external H+-binding sites=7.85 and 7.2, respective dissociation constants of the internal and external Cl−-binding sites=160 and 40 μm, and an additional, kinetically transparent, H+-binding site with a pK a 〉8.0. The quantitative model independently predicts the response ofJ max andK m to acidic conditions. The results are discussed in terms of the general physiological requirement that fluxes through H+-coupled transport systems are relatively insensitive to environmental variation in pH o . It is proposed that (i) the weak (but finite) dependence of pH c on pH o , coupled with (ii) the strong dependence of H+-coupled transport on pH c are instrumental in endowing H+-coupled transport systems with a relative insensitivity to variation in pH o . This hypothesis might also explain why pH c in plants and fungi is not acutely controlled with respect to variation of pH o .
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    Pre-steady-state analysis of the turn-on and turn-off of water permeability in the kidney collecting tubule (1989)
    Springer
    The journal of membrane biology 110 (1989), S. 57-65 
    Details
    ISSN: 1432-1424
    Keywords: fluorescence ; water transport ; vasopressin ; kidney collecting tubule ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Water transport across the mammalian collecting tubule is regulated by vasopressin-dependent water channel insertion into and retrieval from the cell apical membrane. The time course of osmotic water permeability (P f ) following addition and removal of vasopressin (VP) and 8-Br-cAMP was measured continuously by quantitative fluorescence microscopy using an impermeant fluorophore perfused in the lumen. Cortical collecting tubules were subjected to a 120 mOsm bath-to-lumen osmotic gradient at 37°C with 10–15 nl/min lumen perfusion and 10–20 ml/min bath exchange rate. With addition of VP (250 μU/ml), there was a 23±3 sec (sem,n=16) lag in whichP f did not change, followed by a rise inP f (initial rate 1.4±0.2×10−4 cm/sec2) to a maximum of 265±10×10−4 cm/sec. With addition of 8-Br-cAMP (0.01–1mm) there was an 11±2 sec lag. For [8-Br-cAMP]=0.01, 0.1 and 1mm, the initial rate ofP f increase following the lag was (units 10−4 cm/sec2): 1.1±0.1, 1.2±0.1 and 1.7±0.3. MaximumP f was (units 10−4 cm/sec): 64±4, 199±9 and 285±11. With removal of VP,P f decreased to baseline (12×10−4 cm/sec) with aT 1/2 of 18 min; removal of 0.1 and 1mm 8-Br-cAMP gaveT 1/2 of 4 and 8.5 min. These results demonstrate (i) a brief lag in theP f response, longer for stimulation by VP than by 8-Br-cAMP, representing the transient build-up of biochemical intermediates proximal to the water channel insertion step, (ii) similar initialdP f /dt (water channel insertion) over a wide range of [8-Br-cAMP] and steady-stateP f values, and (iii) more rapidP f decrease with removal of 8-Br-cAMP than with VP. These pre-steady-state results define the detailed kinetics of the turn-on and turn-off of tubuleP f and provide kinetic evidence that the rate-limiting step for turn-on ofP f is not the step at which VP regulates steady-stateP f . If water channel insertion is assumed to be the rate-limiting step in the turn-on ofP f , these results raise the possibility that water channels must be activated following insertion into the apical membrane.
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    Analysis of the blocking activity of charybdotoxin homologs and iodinated derivatives against Ca2+-Activated K+ channels (1989)
    Springer
    The journal of membrane biology 109 (1989), S. 269-281 
    Details
    ISSN: 1432-1424
    Keywords: charybdotoxin ; erythrocytes ; iodination ; kinetics ; peptides ; potassium channels ; scorpions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Two charybdotoxin peptides were purified from venom of the Israeli scorpion,Leiurus quinquestriatus hebraeus. Microsequencing of the most abundant toxin, ChTX-Lq1, revealed identity with the 37-residue peptide previously sequenced by Gimenez-Gallego et al. [Gimenez-Gallego, G., et al.,Proc. Natl. Acad. Sci. USA 85:3329–3333 (1988)]. Sequence data on the minor peptide, ChTX-Lq2, showed substantial homology to ChTX-Lq1 with differences observed at eight positions. These two charybdotoxin sequences, along with that of noxiustoxin, define a distinct family of scorpion peptide toxins with activity against K+ channels. Both charybdotoxin homologs inhibited Ca2+-dependent K+ efflux from human erythrocytes with similar potency,K 0.5∼-40nm. In planar bilayer assays of single K(Ca) channels from rat muscle, ChTX-Lq1 and ChTX-Lq2 blocked with intrinsicK d's of 1.3 and 43nm, respectively, in the presence of 50mm external KCl. A new application of dwell-time histogram analysis of single-channel blocking events was used to characterize the kinetic homogeneity of toxin samples and the blocking kinetics of ChTX derivatives. The lower blocking affinity of ChTX-Lq2 was the combined result of a faster dissociation rate and a slower association rate as compared to ChTX-Lq1. The blocking activity of two mono-iodinated derivatives of ChTX-Lq1 was also analyzed. Blocked dwell-time histograms of the iodinated peptides were characterized by predominately brief (0.2–2 sec) blocking events in comparison to the native toxin (20 sec). Histogram analysis revealed that mono-iodination of ChTX-Lq1 impairs blocking activity by adverse effects on both dissociation and association rate constants. Frequency density histograms of single channel blocking events provide a sensitive assay of toxin purity suitable for quantitating structure-activity relationships of charybdotoxin derivatives.
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    Protonophore anion permeability of the human red cell membrane determined in the presence of valinomycin (1988)
    Springer
    The journal of membrane biology 102 (1988), S. 225-234 
    Details
    ISSN: 1432-1424
    Keywords: erythrocytes ; valinomycin ; protonophore ; CCCP ; permeability ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A transport model for translocation of the protonophore CCCP across the red cell membrane has been established and cellular CCCP binding parameters have been determined. The time course of the CCCP redistribution across the red cell membrane, following a jump in membrane potential induced by valinomycin addition, has been characterized by fitting values of preequilibrium extracellular pHvs. time to the transport model. It is demonstrated, that even in the presence of valinomycin, the CCCP-anion is “well behaved,” in that the translocation can be described by simple electrodiffusion. The translocation kinetics conform to an Eyring transport model, with a single activation energy barrier, contrary to translocation across lipid bilayers, that is reported to follow a transport model with a plateau in the activation energy barrier. The CCCP anion permeability across the red cell membrane has been calculated to be close to 2.0×10−4 cm/sec at 37°C with small variations between donors. Thus the permeability of CCCP in the human red cell membrane deviates from that found in black lipid membranes, in which the permeability is found to be a factor of 10 higher.
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    Implementation of periodic acid-thiosemicarbazide-silver proteinate staining for ultrastructural assessment of muscle glycogen utilization during exercise (1985)
    Springer
    Cell & tissue research 242 (1985), S. 229-232 
    Details
    ISSN: 1432-0878
    Keywords: Skeletal muscles ; Ultrastructure ; Exercise ; Glycogen ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Distribution of glycogen particles in semithin and ultrathin sections of biopsy samples from human muscles subjected to either short- or long-term running were investigated using PAS and Periodic Acid-ThioSemiCarbazide-Silver Proteinate (PA-TSC-SP) staining methods. Glycogen particles were predominantly found immediately under the sarcolemma or aligned along the myofibrillar Iband. After long-term exhaustive exercise type-1 fibers with a few or no glycogen particles in the core of the fibers were frequently observed. The subsarcolemmal glycogen stores of these “depleted” type-1 fibers were about three times as large as after exhaustive short-time exercise. Another indication of utilization of subsarcolemmal glycogen stores during anaerobic exercise was that many particles displayed a pale, rudimentary shape. This observation suggests fragmental metabolization of glycogen. Thus, depending on type of exercise and type of fiber differential and sequential glycogen utilization patterns can be observed.
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    Folinic acid modulation of fluorouracil: tissue kinetics of bolus administration (1989)
    Springer
    Investigational new drugs 7 (1989), S. 27-36 
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    ISSN: 1573-0646
    Keywords: kinetics ; fluorouracil ; bolics ; administration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Summary Thymidylate synthase (TS) is the enzyme target of 5-fluorouracil (FUra) that recent laboratory and clinical studies with folinic acid (calcium leucovorin) suggest may mediate important antitumor cytotoxicity. Measurement in carcinoma tissue of parameters related to TS inhibition by 5-fluorodeoxyuridylate (FdUMP), by analogy to hormone receptor analysis, should be useful to determine which patients should receive fluoropyrimidine drug therapy and to evaluate folinic acid requirements. Folinic acid is metabolized to 5,10-methylenetetrahydropteroylglutamine (CH2FH4), which must be present in large excess to effect desired levels of maximal inhibition of TS, by promoting formation and stabilization of TS-FdUMP-CH2FH4 ternary complexes. In patients with metastatic disease, serial biopsies of tumor and normal tissues for studies of pharmacodynamic responses to test-dose FUra or folinic acid are shown to be easily added to routine intraoperative management. A suitable methodologic approach is described and examples given of assays of free TS, FdUMP, dUMP, and CH2FH4 levels after FUra or folinic acid, that may be useful in future studies aimed at improving the cost-effectiveness of FUra-folinic acid combinations.
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    Heterogeneous survival and cell kinetics responses of human astrocytoma clones to α-difluoromethylornithine in vitro (1989)
    Springer
    Investigational new drugs 7 (1989), S. 155-161 
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    ISSN: 1573-0646
    Keywords: heterogeneity ; polyamines ; cell killing ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Medicine
    Notes: Abstract The effects of α-difluoromethylornithine (DFMO) on survival, cell kinetics and polyamine levels were studied on two clones of human astrocytoma in vitro. The survival responses were dose and time dependent; and treatments with DFMO which lasted for 72 h resulted in heterogeneous responses with one clone being up to 6 times more sensitive than the other. Shorter treatments produced more uniform killing in the clones. A continuous exposure of the cells to 5 mM DFMO resulted in a rapid decrease in putrescine values in both clones, followed by decreases in the spermidine levels. These effects were closely followed by 148% to 170% increases in cell population doubling times, and a lowering of saturation densities. No clear correlations could be established among baseline polyamine levels and cell kinetics or survival responses to DFMO treatments.
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    Effect of dose of injected hematopoietic cells on number of daughter CFU-S in splenic colonies (1986)
    Springer
    Bulletin of experimental biology and medicine 101 (1986), S. 365-366 
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    ISSN: 1573-8221
    Keywords: hematopoietic stem cells ; CFU-S ; self-maintenance ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00835948
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    Biotransformation of a14C-hydrogenated phenazepam analog in inbred micein vivo (1987)
    Springer
    Bulletin of experimental biology and medicine 103 (1987), S. 660-662 
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    ISSN: 1573-8221
    Keywords: hydrogenated phenazepam analog ; metabolism ; kinetics ; excretion ; differences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00841831
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    Influence of food on the intravenous and oral dose kinetics of propranolol in the dog (1985)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 13 (1985), S. 229-241 
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    ISSN: 1573-8744
    Keywords: food effects ; propranolol ; kinetics ; dogs ; oral and intravenous doses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The intravenous and oral dose kinetics of propranolol were studied in the dog both in a fasted state and immediately after a meal consisting of 100 g of cooked beef liver. Fifty ΜCi of3H-propranolol was administered intravenously simultaneously with a 40-mg oral dose of unlabeled propranolol. Plasma3H-propranolol was measured by specific extraction and liquid scintillation spectrometry, and unlabeled plasma propranolol was determined by gas chromatography-mass spectrometry. Feeding significantly reduced (25%) the elimination half-life and increased (52%) the systemic clearance of intravenous propranolol. The increase in the systemic clearance of propranolol after feeding was mostly due to an increase (60%) in apparent hepatic blood flow, which appeared to remain elevated for 5–7 hr. The meal had no influence on the apparent volume of distribution or plasma binding. Feeding did not affect the area under the concentration-time curve of oral propranolol, but significantly delayed the rate of oral propranolol absorption, shifting the time to reach peak plasma levels from 60 to 158 min. The results of this study suggest that feeding alters the disposition of propranolol in the dog by producing a sustained increase in hepatic blood flow.
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    The population pharmacokinetics of theophylline in neonates and young infants (1989)
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    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 47-66 
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    ISSN: 1573-8744
    Keywords: theophyliine ; population analysis ; methylxanthines ; neonatal apnea ; kinetics ; NONMEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The population pharmacokinetics of theophylline were evaluated using 391 theophylline serum concentration measurements from 108 neonates and young infants (postnatal age 0–26 weeks), who received theophylline for the treatment of neonatal apnea. A one-compartment pharmacokinetic model with first-order elimination was used, with intravenous aminophylline and oral theophylline administration modeled as zero-order infusions. The effect of a variety of developmental and demographic factors on clearance (CL) and volume (V) were investigated. Hypothesis testing to evaluate potentially significant factors produced a final model in which clearance was based on weight (kg) raised to an exponential power and postnatal age (weeks), with CL (ml/hr)=17.5 (weight)1.28 + 1.17 (postnatal age). Clearance was reduced by 12% for patients receiving parenteral nutrition. Volume of distribution in this population was adequately described using only weight, with V (L)=0.858 L/kg. Bioavailability of orally administered drug was not significantly less than unity. Interindividual variability in clearance was modest, with a coefficient of variation for clearance of 16%. An estimate of interindividual variability in volume could not be obtained. As a measure of residual variability in theophylline serum concentrations, the coefficients of variation for theophylline serum concentrations of 5.0, 10.0, and 13.0 mg/L were found to be approximately, 25, 12, and 9%, respectively. The identification of influential patient factors and the quantification of their influence on theophylline disposition allow for a priori estimates of theophylline pharmacokinetic parameters in these patients.
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    Abstracts of Dutch doctoral theses (1988)
    Springer
    Pharmacy world & science 10 (1988), S. 93-95 
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    ISSN: 1573-739X
    Keywords: Anthracyclines ; Chemistry ; Drug stability ; Mitomycins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1007/BF01962686
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    Etoposide and teniposide (1988)
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    Pharmacy world & science 10 (1988), S. 101-116 
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    ISSN: 1573-739X
    Keywords: Chemistry ; Chromatography ; Etoposide ; Immunoassay ; Metabolism ; Podophyllotoxin ; Pharmacokinetics ; Teniposide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Etoposide (VP 16-213) and teniposide (VM 26) are semisynthetic epipodophyllotoxin derivatives active against a variety of tumours. The clinical efficacy has led to an increasing interest in these compounds. This review presents information on the mechanism of action, biochemical pharmacology, bioanalysis, metabolism and pharmacokinetics of etoposide and teniposide.
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    Eupatorium cannabinum L. (1986)
    Springer
    Pharmacy world & science 8 (1986), S. 245-251 
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    ISSN: 1573-739X
    Keywords: Analysis ; Antineoplastic agents ; Biosynthesis ; Botany ; Chemistry ; Cytotoxins ; Eupatorium cannabium ; Sesquiterpenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A review onEupatorium cannabinum L. is given, including botany, history and constituents. The sesquiterpene lactones are discussed in more detail, covering their biosynthesis, isolation, analysis and biological activity. Special attention is paid to the cytotoxic and antitumour activities of the sesquiterpene lactones.
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    Atrial natriuretic factor: a hormone secreted by the heart (1987)
    Springer
    Pharmacy world & science 9 (1987), S. 305-314 
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    ISSN: 1573-739X
    Keywords: Atrial natriuretic factor ; Blood pressure ; Chemistry ; Diuresis ; Homeostasis ; Kidney ; Muscle, smooth ; Natriuresis ; Receptors, endogenous compounds ; Renin-angiotensin system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is now known that cardiac atria play an important role in blood pressure and volume regulation. Mechanical distension of the atria results in the release of a potent diuretic and natriuretic agent or agents termed the atrial natriuretic factor (ANF). Several structurally related forms of ANF exist in man and it is thought that these represent precursory forms of a single optimally active molecule and/or the presence of more than one form of active ANF. The chemical structure of ANF between different mammalian species is similar. ANF receptors have been identified in kidney, brain, vascular endothelial and smooth muscle cells, tracheal and bronchial smooth muscle and the adrenal glands of many mammalian species, including man. This would suggest that ANF influences blood pressure and volume homoeostasis by affecting any one of a number of biochemical or physiological mechanisms via different target tissues. ANF is now considered a potentially valuable therapeutic agent for the treatment of hypertension and congestive heart failure. Synthesis of potent receptor antagonists could be extremely useful in the treatment of various clinical situations which are produced or complicated by endogenously produced ANF, such as chronic orthostatic hypotension.
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    Kinetic analysis of acetylcholine-induced chloride current in isolated snail neurons (1988)
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 293-305 
    Details
    ISSN: 1573-6830
    Keywords: isolated snail neuron ; acetylcholine ; chloride current ; kinetics ; noise analysis ; concentration clamp technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Kinetics of activation and desensitization phases of the acetylcholine (ACh)-induced chloride current (I Cl) were studied using isolated single neurons of Japanese land snail and the “concentration clamp” technique. 2. The dose-response curve for the peakI Cl gave a dissociation constant of 7.1 × 10−6 M and a Hill coefficient of 1.8. 3. The current-voltage relationship was linear in the voltage range examined (−60 to +10 mV) and the reversal potential (E ACh) was −7.2 ± 1.5 mV (N = 10). The value was close to the calculated equilibrium potential for chloride ions (E Cl). 4. Both activation and desensitization phases of the ACh-inducedI Cl consisted of a single exponential at concentrations less than 3 × 10−6 M and a double exponential at higher concentrations. The time constants of both phases decreased with increasing ACh concentrations but showed no potential dependency. 5. The recovery from desensitization of theI Cl induced by 5 × 10−6 M ACh proceeded double exponentially, with time constants of 11 and 114 sec at a holding potential of −30 mV. 6. Noise analysis was performed on a steady-state current induced by 3 × 10−7 to 2 × 10−6 M ACh. The mean open time was about 60 msec at 10−6 M ACh and the single-channel conductance was 14 PS. 7. These results suggest that the ACh receptor-Cl channel complex in snail neurons has two binding sites with the dissociation constant of 7.1 × 10−6 M and is rapidly activated and desensitized to a steady level in the presence of the agonist.
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    Diketopiperazine Formation, Hydrolysis, and Epimerization of the New Dipeptide Angiotensin-Converting Enzyme Inhibitor RS-10085 (1987)
    Springer
    Pharmaceutical research 4 (1987), S. 392-397 
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    ISSN: 1573-904X
    Keywords: angiotensin-converting enzyme (ACE) inhibitor ; RS-10085 ; degradation ; kinetics ; products ; diketopiperazine ; peptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The degradation kinetics, products, and mechanisms of RS-10085(1), 2-[2-(l-ethoxycarbonyl)-3-phenylpropyl]amino-l-oxopropyl]-6,7-dimethoxy-l,2,3,4-tetrahydroisoquinoline-3-carboxylic acid(S,S,S), in aqueous solution were investigated at 40, 60, and 80°C from pH 1 to pH 13. Pseudo-first-order kinetics were observed throughout the pH range studied and the log(rate)−pH profiles reflected four kinetic processes (k o, k′o, k″o, and k OH) as well as the two pKa's of 1. Excellent (〉98%) mass balance was obtained through products 2–5. At pH 4 or below, intramolecular cyclization leading to diketopiperazine 5 accounted for greater than 93% of the observed neutral- or water-catalyzed processes (k o and k′o). At pH levels greater than 5, hydrolysis giving 2 predominated and was responsible for the observed neutral- or water-catalyzed (k″o) and specific base-catalyzed (k OH) kinetic processes. Some epimerization leading to the S,S,R drug isomer (4) was also observed at pH levels greater than 7. The relative acidity of the protons at the three chiral centers of 1 was qualitatively compared and was used to explain the observed specificity in epimerization.
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    Development of Acute Tolerance to Bumetanide: Bolus Injection Studies (1987)
    Springer
    Pharmaceutical research 4 (1987), S. 379-384 
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    ISSN: 1573-904X
    Keywords: acute tolerance ; bumetanide ; kinetics ; dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bumetanide was administered intravenously to four mongrel dogs, in a random crossover fashion, at doses of 0.05 mg/kg (I), 0.15 mg/kg (II), and 0.5 mg/kg (III) where urinary losses were replaced with lactated Ringer's solution at 1.5 ml/min (hydropenic conditions) or at a dose of 0.5 mg/kg (IV) where urinary losses were replaced with lactated Ringer's solution isovolumetrically (euvolemic conditions). Serial plasma and urine samples were assayed for bumetanide by high-performance liquid chromatography (HPLC) and for sodium by flame photometry. There were no significant differences in the pharmacokinetic parameters of bumetanide among Treatments I–IV. The dynamic parameters E max (maximum effect attributable to the drug) and s (slope factor) were not different between treatments. However, a consistent, demonstrable increase in ER50 (urinary excretion rate of drug producing 50% of E max) was observed among Treatments I (2.34 µg/min), II (3.92 µg/min), and III (6.54 µg/min); also, a significant decrease in ER50 was observed between Treatment III (6.54 µg/min) and Treatment IV (2.66 µg/min). These results show that hydration status has a marked effect on natriuretic and diuretic response and that tolerance can rapidly develop within a single intravenous dose of bumetanide.
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    In situ SAXS investigations of isothermal crystallization in poly(TMPS) fractions (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 193-205 
    Details
    ISSN: 1435-1536
    Keywords: Poly(TMPS) ; in situ ; SAXS ; crystallization ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The isothermal crystallization kinetics of poly(TMPS) has been measured by ISSAXS and results obtained for a molecular weight fraction (21,000) below the critical entanglement molecular weight (25,000) and another one above it (371,000). The SAXS intensity vs. time curves suggest that a single transformation mechanism exists. The SAXS long period is independent of crystallization time for both poly(TMPS) fractions. However the interlamellar thickness contribution to the long period is dependent upon molecular weight and crystallization temperature, increasing with temperature and molecular weight. The crystallite contribution also increases over the range studied. Both fractions exhibit a significant, but reversible decrease in thickness on cooling the sample from the crystallization temperature to room temperature and recyling again. The change is more pronounced for 371,000 specimen in keeping with its lower crystallinity. The path dependence of lamellar dimensions has significant implications in the morphological characterization of polymers annealed or crystallized at one temperature and then measured at another one.
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    On Tanaka-Fillmore's kinetics swelling of gels (1989)
    Springer
    Colloid & polymer science 267 (1989), S. 179-183 
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    ISSN: 1435-1536
    Keywords: Gel ; swelling ; kinetics ; diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Tanaka and Fillmore treated the swelling of a gel as a process where a crosslinked polymer network having been initially under uniform stress is expanded by osmotic pressure, sucking up the surrounding fluid medium. We point out that their physical reasoning is unnatural and leads to an unacceptable conclusion; we propose a more sound approach to the same problem. Our treatment assumes that the gel network is extended not by the osmotic pressure of the gel, but rather by the swelling pressure which is generated by the excess fluid penetrating in against the real nature of a polymer network that tends to shrink. The diffusion equation of the fluid, hence, plays a dominant role and gives the distribution of fluid concentration in contrast to Tanaka-Fillmore's scheme. The expression for the distribution of local strain in a spherical gel is deduced from the relation of mechanical balance between two forces, the one is due to the elasticity of the network and the other due to the gradient in the chemical potential of the fluid. The results obtained have forms analytically similar to Tanaka-Fillmore's, but are differ in the physical meanings.
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    Diffusion of protons in silica hydrogel (1989)
    Springer
    Colloid & polymer science 267 (1989), S. 460-464 
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    ISSN: 1435-1536
    Keywords: Diffusion ; silica gel ; kinetics ; surface area ; proton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The effect of preparation pH of silica hydrogel on the effective diffusion coefficient of protons in silica hydrogel (D e , m2/s), on surface area of silica gel (S, m2/s) and on particle size of silica gel (D p , mm) was studied. Silica hydrosols were obtained by adding water glass to sulfuric acid. The effective diffusion coefficient of proton in silica hydrogel was determined by the method of diffusion from silica hydrogel plane sheet to a stirred solution of a limited volume. A numerical solution was obtained for the diffusion equation using the Regula Falsi method. Regression analyses of experimental data were conducted. Diffusion of protons in silica hydrogel is a complicated process due to a decelerating effect of the porous structure of silica hydrogel and to the accelerating effects of slow ions such as Na+ and surface diffusion. The effective diffusion coefficient increased with surface area of silica gel, indicating the diffusion of protons on the surface of the silica particles.
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    URL: http://dx.doi.org/10.1007/BF01410194
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    Migration of small hydrophobic molecules between micelles in aqueous solution (1987)
    Springer
    Colloid & polymer science 74 (1987), S. 55-63 
    Details
    ISSN: 1435-1536
    Keywords: Triplet energy transfer ; micelle ; solubilization ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Triplet energy transfer from 9-methylanthracene to azulene or guajazulene has been used to probe the migration of azulenes between micelles in aqueous solution. The migration of the hydrophobic solutes between small ionic and nonionic micelles had the temperature dependence expected for a process controlled by diffusion through the intermicellar solution, although the rate in some cases was substantially less than calculated from the Smoluchowski equation. Under conditions in which the micelles grow into large, probably rod-like structures, there are severe difficulties in separating the inter- and intramicellar deactivation processes. The intermicellar migration was enhanced under these conditions, in cetyltrimethylammonium surfactants on addition of chlorate ions, and in hexaethylene glycol dodecylether at temperatures approaching the cloud-point. The mechanism of this migration is discussed and compared with pertinent results from micelle relaxation kinetics and surfactant self-diffusion measurements.
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    URL: http://dx.doi.org/10.1007/BF01191012
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    How rapid are the internal reactions of the ubiquinol:cytochrome c 2 oxidoreductase? (1989)
    Springer
    Photosynthesis research 22 (1989), S. 69-87 
    Details
    ISSN: 1573-5079
    Keywords: electron transport ; kinetics ; Q-cycle ; Rb. sphaeroides ; thermodynamics ; ubiquinol:cytochrome c 2 oxidoreductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The temperature dependence of the partial reactions leading to turn-over of the UQH2:cyt c 2 oxidoreductase of Rhodobacter sphaeroides have been studied. The redox properties of the cytochrome components show a weak temperature dependence over the range 280–330 K, with coefficients of about 1 m V per degree; our results suggest that the other components show similar dependencies, so that no significant change in the gradient of standard free-energy between components occurs over this temperature range. The rates of the reactions of the high potential chain (the Rieske iron sulfur center, cytochromes c 1 and c 2, reaction center primary donor) show a weak temperature dependence, indicating an activation energy 〈 8 kJ per mole for electron transfer in this chain. The oxidation of ubiquinol at the Qz-site of the complex showed a strong temperature dependence, with an activation energy of about 32 kJ mole−1. The electron transfer from cytochrome b-566 to cytochrome b-561 was not rate determining at any temperature, and did not contribute to the energy barrier. The activation energy of 32 kJ mole−1 for quinol oxidation was the same for all states of the quinone pool (fully oxidized, partially reduced, or fully reduced before the flash). We suggest that the activation barrier is in the reaction by which ubiquinol at the catalytic site is oxidized to semiquinone. The most economical scheme for this reaction would have the semiquinone intermediate at the energy level indicated by the activation barrier. We discuss the plausibility of this simple model, and the values for rate constants, stability constant, the redox potentials of the intermediate couples, and the binding constant for the semiquinone, which are pertinent to the mechanism of the ubiquinol oxidizing site.
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    URL: http://dx.doi.org/10.1007/BF00114768
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    Nitrogen mineralization rates in salinevs. salt-amended soils (1987)
    Springer
    Plant and soil 104 (1987), S. 13-21 
    Details
    ISSN: 1573-5036
    Keywords: ammonification ; kinetics ; nitrification ; osmotic potentials ; soluble salts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Studies were conducted to compare N mineralization rates in salt-amended nonsaline soils to naturally-occurring saline soils. NaCl, CaCl2, and Na2SO4 were added to nonsaline soils at rates that produced electrical conductivities of the saturation extracts (ECe) of 5, 10, 15, and 20 dS m−1. Saline soils with similar properties were leached to the same ECc levels. N mineralization in the Chino soil was inhibited by salt addition, particularly with sodium and calcium chlorides. In the Domino soil there was some inhibition of N mineralization with the chloride salts, but enhancement with Na2SO4 was observed. Nitrification in both soils was more sensitive to salt addition than ammonification. N mineralization occurred more slowly in both leached saline soils compared to the salt-amended soils. Leached saline soils often accumulated greater amounts of inorganic N compared to their native saline counterparts, particularly with the 5 dS m−1 Chino soil (native, 44 dS m−1) and with the 5, 10, 15 and 20 dS m−1 Domino soils (native, 32 dS m−1). Kinetic parameters were estimated by the linear least squares (LLS) and the nonlinear least squares (NLLS) methods. Generally, the LLS transformation estimated greater values of potentially mineralizable N (No) and lower rate constants (k). With the NLLS equation, No values for the leached saline soils were usually lower, and k values usually higher than in the salt-amended soils. The nonsaline controls generally had the highest No and lowest k estimates. Average LLS rate constants for the salt-amended and leached saline soils were 0.055 and 0.083 for the Chino, and 0.104 and 0.137 week−1, respectively, for the Domino soils. With the NLLS equation, average k values for the salt-amended and leached saline soils were 0.087 and 0.089 for the Chino, and 0.181 and 0.387 week−1, respectively, for the Domino soils. These results suggest that N mineralization rates obtained in salt-amended nonsaline soils may not be representative of those in naturally-occurring saline soils.
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    A Monte Carlo method for the simulation of kinetie models (1986)
    Springer
    Photosynthesis research 9 (1986), S. 273-283 
    Details
    ISSN: 1573-5079
    Keywords: Monte Carlo ; kinetics ; simulation ; model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The purpose of this note is to illustrate the feasibility of simulating kinetic systems, such as commonly encountered in photosynthesis research, using the Monte Carlo (MC) method. In this approach, chemical events are considered at the molecular level where they occur randomly and the macroscopic kinetic evolution results from averaging a large number of such events. Their repeated simulation is easily accomplished using digital computing. It is shown that the MC approach is well suited to the capabilities and resources of modern microcomputers. A software package is briefly described and discussed, allowing a simple programming of any kinetic model system and its resolution. The execution is reasonably fast and accurate; it is not subject to such instabilities as found with the conventional analytical approach.
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    Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa) (1989)
    Springer
    Hydrobiologia 183 (1989), S. 87-95 
    Details
    ISSN: 1573-5117
    Keywords: phosphorus ; Hartbeespoort Dam ; algal uptake ; abiotic effects ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The role of biotic processes in a warm, monomictic, hypertrophic African impoundment (Hartbeespoort Dam) is examined using 32P radiobioassays. Phosphorus demand is assessed by phosphorus turnover times, alkaline phosphatase activity, cellular phosphorus status and the phosphorus deficiency index. Long turnover times indicative of an enriched system were recorded, ranging from 9 h to 1992 h, with no evidence of phosphorus stress being present. These turnover times support the hypothesis that the phosphorus cycle in Hartbeespoort Dam is dominated by the algal community which is shown to play an important role in phosphorus cycling within the water column. However, hydrological processes remain the driving force in phosphorus seasonality in the lake.
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    Microbial manganese(II) oxidation in the marine environment: a quantitative study (1986)
    Springer
    Biogeochemistry 2 (1986), S. 149-161 
    Details
    ISSN: 1573-515X
    Keywords: Microbial manganese(II) oxidation ; manganese(II) oxidation ; kinetics ; bacteria ; O2H2S interface 04
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A great number of important chemical reactions that occur in the environment are microbially mediated. In order to understand the kinetics of these reactions it is necessary to develop methods to directly measure in situ reaction rates and to develop models to help elucidate the mechanisms of microbial catalysis. The oxidation of Mn(II) in a zone above the O2/H2S interface in Saanich Inlet, B.C., Canada is one such reaction. We present here a method by which in situ rates of microbial Mn(II) oxidation are measured and a model based on our experimental results to describe the general mechanism of Mn(H) oxidation. We propose a two step process in which Mn(II) is first bound by a site on the bacterial surface and then oxidized. The model is analogous to the Langmuir isotherm model for surface catalyzed gas reactions or the Michaelis-Menten model for enzyme kinetics. In situ Mn(II) oxidation rates were measured during five cruises to Saanich Inlet during the summers of 1983 and 1984. We use the model to calculate the apparent equilibrium binding constant (Ks ≈ 0.18 μM), the apparent half saturation constant for biological Mn(H) oxidation (Km = 0.22 to 0.89 μM), the maximum rate of Mn(II) oxidation (Vmax = 3.5 to 12.1 nM·h-1) and the total microbial surface binding site concentration (Σ E ≈ 51 nM). Vmax for Mn(II) oxidation agrees with the rates calculated from the value of the flux of Mn(II) to the oxidizing zone using the Mn(II) gradient and estimates of the eddy diffusion coefficient. This consistancy verifies our methodology and indicates that the rate of Mn(II) oxidation is nearly equal to the (Vmax for the reaction. We conclude that in this environment the Mn(II) oxidation rate is more a function of the total number of surface binding sites than the Mn(H) concentration.
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    Characteristics of NO 3 − uptake in lemna and pisum (1988)
    Springer
    Plant and soil 111 (1988), S. 203-205 
    Details
    ISSN: 1573-5036
    Keywords: efflux ; influx ; kinetics ; net uptake ; nitrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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    URL: http://dx.doi.org/10.1007/BF02139939
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    Plasma kinetics of injected recombinant chicken somatotropin in juvenile coho salmon (Oncorhynchus kisutch) using a homologous radioimmunoassay (1988)
    Springer
    Fish physiology and biochemistry 5 (1988), S. 49-57 
    Details
    ISSN: 1573-5168
    Keywords: recombinant somatotropin ; radioimmunoassay ; kinetics ; half-life ; salmon ; Oncorhynchus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Although somatotropins are potent growth promoters in salmonids, there is little information on how these proteins are metabolized by poikilotherms. In the present study, the plasma uptake and clearance rates of recombinant chicken somatotropin (rcGH) were investigated in juvenile coho salmon (Oncorhynchus kisutch). Two doses of rcGH were administered by intraperitoneal (ip) or intramuscular (im) injection and blood samples were collected over a period of 32 days. A specific radioimmunoassay was validated and used to discriminate rcGH from endogenous somatotropin. Plasma rcGH concentration was proportional to the dose delivered, but uptake and clearance rates were found to be independent of dose (between 0.5 and 5.0 μg/g). Absorption of rcGH into the plasma was faster from the im site, but the peak levels attained were similar after im or ip treatment (using the same dose) as was area under the curve. Plasma half-life was calculated from the declining phase of the uptake/clearance profile but the results were biased by the concurrent uptake of rcGH from the ip or im reservoir of material, resulting in an over-estimation of the true half-life value. Effective treatment doses and intervals are discussed.
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    Cytochromec oxidase ofEuglena gracilis: Purification, characterization, and identification of mitochondrially synthesized subunits (1989)
    Springer
    Journal of bioenergetics and biomembranes 21 (1989), S. 359-373 
    Details
    ISSN: 1573-6881
    Keywords: Cyrochromec oxidase ; kinetics ; subunit composition ; mitochondrially synthesized polypeptides ; Euglena gracilis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Cytochromec oxidase was purified from mitochondria ofEuglena gracilis and separated into 15 different polypeptide subunits by polyacrylamide gel electrophoresis. All 15 subunits copurify through various purification procedures, and the subunit composition of the isolated enzyme is identical to that of the immunoprecipitated one. Therefore, the 15 protein subunits represent integral components of theEuglena oxidase. In anin vitro protein-synthesizing system using isolated mitochondria, polypeptides 1–3 were radioactive labeled in the presence of [35S]methionine. This further identifies these polypeptides with the three largest subunits of cytochromec oxidse encoded by mitochondrial DNA in other eukaryotic organisms. By subtraction, the other 12 subunits can be assigned to nuclear genes. The isolatedEuglena oxidase was highly active withEuglena cytochromec 558 and has monophasic kinetics. Using horse cytochromec 550 as a substrate, activity of the isolated oxidase was rather low. These findings correlate with the oxidase activity of mitochondrial membranes. Again, reactivity was low with cytochromec 550 and 35-fold higher with theEuglena cytochromec 558. The data show that the cytochromec oxidase of the protistEuglena is different from other eukaryotic cytochromec oxidases in number and size of subunits, and also with regard to kinetic properties and substrate specificity.
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    Effect of trypsin on the kinetic properties of reconstituted beef heart cytochromec oxidase (1985)
    Springer
    Journal of bioenergetics and biomembranes 17 (1985), S. 375-384 
    Details
    ISSN: 1573-6881
    Keywords: Cytochromec oxidase ; kinetics ; trypsin digestion ; reconstitution ; proteoliposomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Isolated beef heart cytochromec oxidase was reconstituted in liposomes by the cholate dialysis method with 85% of the binding site for cytochromec oriented to the outside. Trypsin cleaved specifically subunit VIa and half of subunit IV from the reconstituted enzyme. The kinetic properties of the reconstituted enzyme were changed by trypsin treatment if measured by the spectrophotometric assay but not by the polarographic assay. It is concluded that subunit VIa and/or subunit IV participate in the electron transport activity of cytochromec oxidase.
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    “Exchange diffusion”: Rate equations for the influx of α-aminoisobutyric acid into mouse cerebrum slices containing this amino acid (1985)
    Springer
    Journal of bioenergetics and biomembranes 17 (1985), S. 305-326 
    Details
    ISSN: 1573-6881
    Keywords: α-Aminoisobutyric acid ; amino acids ; brain slices ; exchange diffusion ; kinetics ; membrane transitions ; rate equations ; transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Rate equations for the gross influx of α-aminoisobutyric acid (AIB) into mouse cerebrum slices containing AIB have a first-order term for unsaturable concentrative influx, identical to the corresponding term for unloaded slices, and a modified Michaelis-Menten term,V′max/(1+K t /S), for saturable concentrative influx. [V′max ≡v′ L (1+K t /S), wherev′ L =saturable component of influx,S=AIB concentration in medium, andK t =Michaelis constant for unloaded slices.] Below a tissue AIB (T) of 19 µmol/g final wet weight,V′max increases linearly followingV′max=V 1+m 1 T; above that value,V max is virtually constant. The transition is sharp. This equation is consistent with a carrier model for active transport. At the transition, intracellular AIB is about 1 molecule for every 70 amino acid residues of tissue protein, vastly more than could be accommodated by AIB-binding sites in cell membranes. The transition may come from a slow process that does not fill all sites when the tissue AIB is below the transition concentration, or from an AIB-induced phase transition in the membrane.
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    Phospholipid transfer proteins: Mechanism of action (1986)
    Springer
    Journal of bioenergetics and biomembranes 18 (1986), S. 71-91 
    Details
    ISSN: 1573-6881
    Keywords: Phospholipid transfer protein ; phosphatidylcholine ; phosphatidyllinositol ; exchange ; net transfer ; lipid-protein interactions ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Phospholipid transfer proteins are generally localized in the cytosolic fraction of cells and are capable of catalyzing the flux of phospholipid molecules among membranes. Artificial membranes also participate in protein-catalyzed phospholipid movements. In this review the major phospholipid transfer proteins are discussed with respect to their phospholipid substrate specificity and the contributions of membrane physical properties to this process. The phenomenon of net transfer of phospholipids is described. The use of various kinetic approaches to the study of these catalysts is reviewed. A detailed consideration of the distinct phospholipid binding and membrane interaction domains of one phospholipid transfer protein is presented. Finally, some recent applications of phospholipid transfer proteins to the examination of membrane structure and function and further directions for the continued research activity with this class of proteins are summarized.
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    Synthesis of molecular sieve AlPO4-12 (1986)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 4 (1986), S. 325-331 
    Details
    ISSN: 1573-1111
    Keywords: Aluminophosphate ; molecular sieves ; crystallization ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A member of the novel family of crystalline microporous aluminophosphates, AlPO4-12, was synthesized by hydrothermal crystallization using different aluminum-containing compounds. Three new crystalline phases were obtained by varying the composition of the reaction mixture. The effect of the synthesis conditions on the hudrothermal process and the kinetics of crystallization are discussed. The apparent activation energies obtained for AlPO4-12 are 20.9 and 14.6 kcal/mol for nucleation and crystallization, respectively. The adsorption isotherms of one AlPO4-12 product were measured.
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    ESR spectroscopic study and kinetic discussion of the disproportionation reaction of nitrogen monoxide on CaHY-type zeolite (1987)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 5 (1987), S. 385-395 
    Details
    ISSN: 1573-1111
    Keywords: Nitrogen monoxide ; ESR spectroscopy ; disproportionation reaction ; CaHY-type zeclite ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An ESR spectroscopic study of adsorbed NO on CaHY-type zeolite was carried out and the kinetics are discussed on the basis of a mechanistic model of the disproportionation reaction. An amount of NO less than the amount of Ca2+ distributed in Site II of the faujasite structure was admitted onto the sample maintained at 373 K. ESR spectra were recorded at room temperature. The spectra consisted of well-resolved signals. It is proposed that NO molecules on CaHY-type zeolite have two kinds of adsorption patterns. The initial formation of N2O may be expressed by the following reactions: $$[ ] + NO\mathop \rightleftharpoons \limits_{}^{K_1 } [NO],[NO] + NO\mathop \rightleftarrows \limits_{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftharpoonup}$}} {k} _2 }^{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {K} _2 } [N_2 O_2 ],[N_2 O_2 ] + NO\mathop \to \limits_{}^{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {K} _3 } [NO_2 ] + N_2 O,$$ where [], [NO] and [N2O2] denote vacant adsorption, NO adsorption, and N2O2 adsorption sites, respectively. A rate equation for N2O appearance (α) has been derived by a steady state approximation: $$\alpha = \frac{{\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {k} _3 K_1 K_2 P^3 }}{{1 + (K_1 + \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {k} _3 /\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftharpoonup}$}} {k} _2 )P + K_1 (K_2 + \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {k} _3 /\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftharpoonup}$}} {k} _2 )P^2 }},$$ WhereP is the pressure of NO. The rate equation was used to explain the kinetic results of the disproportionation of NO.
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    Inclusion of rhodamine B byβ-cyclodextrin. An equilibrium and kinetic spectrophotometric study (1987)
    Springer
    Journal of inclusion phenomena and macrocyclic chemistry 5 (1987), S. 709-716 
    Details
    ISSN: 1573-1111
    Keywords: Cyclodextrin ; rhodamine B ; equilibrium ; kinetics ; temperature-jump
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A UV/visible spectrophotometric temperature-jump study of the inclusion of the rhodamine B zwitterion (RB) by β-cyclodextrin (βCD) to form a 1:1 complex (RB·βCD) in aqueous 1.00 mol dm−3 NaCl at pH 6.40 and 298.2 K yields:k 1=(1.3±0.2)×108 dm3 mol−1 s−1,k −1=(2.2±0.5)×104 s−1, andK 1=(5.9±2.3)×103 dm3 mol−1 for the equilibrium: $${\text{RB + }}\beta {\text{CD}}{\text{RB}} \cdot \beta {\text{CD}} K_1 $$ Under the same conditions the dimerization of RB: $${\text{2}} {\text{RB}}({\text{RB}})_2 K_d $$ is characterized byK d =(1.8±1.0)×103 dm3 mol−1. The interaction of RB with αCD and γCD is weaker than with βCD, and is discussed in terms of the relative sizes of RB and the cyclodextrin annulus. Comparisons are made with the inclusions of other dyes by cyclodextrins.
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    Capillaries as controlled release devices for insect pheromones and other volatile substances—A reevaluation (1985)
    Springer
    Journal of chemical ecology 11 (1985), S. 953-965 
    Details
    ISSN: 1573-1561
    Keywords: Controlled release ; capillaries ; volatile substances ; pheromones ; release rates ; kinetics ; predictive model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Controlled release formulations are required for the dissemination of behavior-modifying chemicals in insect control strategies. Among the types of formulations that have been used for some time are glass and plastic capillaries. Erratic release rates on field use of such capillaries prompted us to reexamine the release of volatile materials with regard to (1) kinetics of the release, (2) the effect of the vapor-air column above the liquid, and (3) developing a predictive model. Results indicate that the release is not zero order, and that the length of the vapor-air column is a critical factor of the system; a predictive model has been developed that will allow better design of capillary controlled-release formulations.
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    Rate of opening of a population of Na channels in frog skeletal muscle fibers (1989)
    Springer
    Journal of biological physics 17 (1989), S. 75-94 
    Details
    ISSN: 1573-0689
    Keywords: Na channels ; skeletal muscle ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Linear Systems convolution analysis of muscle sodium currents was used to predict the opening rate of sodium channels as a function of time during voltage clamp pulses. If open sodium channel lifetimes are exponentially distributed, the channel opening rate corresponding to a sodium current obtained at any particular voltage, can be analytically obtained using a simple equation, given single channel information about the mean open-channel lifetime and current. Predictions of channel opening rate during voltage clamp pulses show that sodium channel inactivation arises coincident with a decline in channel opening rate. Sodium currents pharmacologically modified with Chloramine-T treatment so that they do not inactivate, show a predicted sustained channel opening rate. Large depolarizing voltage clamp pulses produce channel opening rate functions that resemble gating currents. The predicted channel opening rate functions are best described by kinetic models for Na channels which confer most of the charge movement to transitions between closed states. Comparisons of channel opening rate functions with gating currents suggests that there may be subtypes of Na channel with some contributing more charge movement per channel opening than others. Na channels open on average, only once during the transient period of Na activation and inactivation. After transiently opening during the activation period and then closing by entering the inactivated state, Na channels reopen if the voltage pulse is long enough and contribute to steady-state currents. The convolution model overestimates the opening rate of channels contributing to the steady-state currents that remain after the transient early Na current has subsided.
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    Dynamics of hydrogen bond complexes in polymer melts (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 1102-1109 
    Details
    ISSN: 1435-1536
    Keywords: Hydrogenbonds ; reversiblenetworks ; complexformation ; complexdecomplexation ; kinetics ; viscoelasticity ; influence oftemperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The dynamics of hydrogen bond complex formation between functional groups which are attached to a polymer chain, is studied in the molten state. The concentration of complexes in the thermodynamic equilibrium is distorted by the application of a large oscillatory strain in the nonlinear viscoelastic regime. The relaxation back to the thermodynamic equilibrium is studied as a function of the temperature in the linear viscoelastic regime. From the mechanical response the kinetic analysis can be performed using a modified Doi-Edwards theory. Using the equilibrium constants obtained from IR-spectroscopy, the rate constants for complex formation and decomplexation are obtained. The temperature dependence is equivalent to the temperature dependence of the zero shear viscosity which implies that complex formation is a diffusion-controlled process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01414400
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    Methoxy formation in the reaction of CH3O2 radicals with NO (1986)
    Springer
    Journal of atmospheric chemistry 4 (1986), S. 241-251 
    Details
    ISSN: 1573-0662
    Keywords: Free radical reactions ; kinetics ; product distribution ; methane oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Formation of methoxy (CH3O) radicals in the reaction (1) CH3O2+NO→CH3O+NO2 at 298 K has been observed directly using time resolved LIF. The branching ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqOXdyMaae% 4qaiaabIeadaWgaaWcbaGaae4maaqabaGccaqGpbGaaeiiaiaabIca% ieqacaWF9aGaa8hiaiaa-nbicaWFGaGaeuiLdqKaai4waiaaboeaca% qGibWaaSbaaSqaaiaabodaaeqaaOGaae4taiaac2facaWFVaGaeuiL% dqKaai4waiaaboeacaqGibWaaSbaaSqaaiaabodaaeqaaOGaae4tam% aaBaaaleaacaqGYaaabeaakiaac2facaqGPaaaaa!4E31!\[\phi {\rm{CH}}_{\rm{3}} {\rm{O (}} = -- \Delta [{\rm{CH}}_{\rm{3}} {\rm{O}}]/\Delta [{\rm{CH}}_{\rm{3}} {\rm{O}}_{\rm{2}} ]{\rm{)}}\] has been determined by quantitative cw-UV-laser absorption at 257 nm of CH3O2 and CH3ONO, the product of the consecutive methoxy trapping reaction (2) % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4qaiaabI% eadaWgaaWcbaGaae4maaqabaGccaqGpbacbeGaa83kaiaa-bcaieaa% caGFobGaa43taiaa+bcacaGFOaGaa83kaiaa+1eacaGFPaGaa4hiai% abgkziUkaabccacaqGdbGaaeisamaaBaaaleaacaqGZaaabeaakiaa% b+eacaqGGaGaaeOtaiaab+eacaqGGaGaa4hkaiaa-TcacaGFnbGaa4% xkaiaa+5cacaGFGaGaa4hiaiabeA8aMnaaBaaajqwaacqaaiaaboea% caqGibWaaSbaaKazcaiabaGaae4maaqabaqcKfaGaiaab+eaaSqaba% aaaa!55AC!\[{\rm{CH}}_{\rm{3}} {\rm{O}} + NO ( + M) \to {\rm{ CH}}_{\rm{3}} {\rm{O NO }}( + M). \phi _{{\rm{CH}}_{\rm{3}} {\rm{O}}} \] is found to be (1.0±0.2). The rate constant k 1 is (7±2) 10-12 cm3/molecule · s in good agreement with previous results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00052003
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  • 76
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    Oxygen and nitrate reduction kinetics of a nonflocculating strain of Zoogloea ramigera (1988)
    Springer
    Antonie van Leeuwenhoek 54 (1988), S. 245-255 
    Details
    ISSN: 1572-9699
    Keywords: denitrification ; aerobic ; Zoogloea ramigera ; oxygen ; nitrate ; kinetics ; inhibition ; nitrate reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The oxygen and nitrate reduction kinetics of a nonflocculating strain of Zoogloea ramigera were determined. Axenic, nitrate-reducing bacterial suspensions were acclimated to various oxygen levels in a chemostat while measuring nitrate reduction in the presence of high ammonium nitrogen concentrations. Significant nitrate reduction was observed at oxygen concentrations up to 8 mg L−1. Oxygen consumption was inhibited by oxygen concentrations in excess of 2 mg L−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00443583
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  • 77
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    Photochemical aspects of tropospheric iodine behaviour (1985)
    Springer
    Journal of atmospheric chemistry 2 (1985), S. 359-375 
    Details
    ISSN: 1573-0662
    Keywords: Photochemistry ; kinetics ; ozone decomposition ; iodine atoms ; IO radicals ; iodine oxides ; atmospheric iodine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The I-atom sensitised decomposition of ozone in air at 1 atm pressure and ambient temperature has been investigated. Iodine atoms were produced by photolysis of I2 using visible light or of CH3I using ultraviolet light. In both cases, the quantum yield for O3 decomposition was 1.25 (±0.11) per I atom. An important role is proposed for the self-reaction of IO radicals leading to higher oxides of iodine, IO+IO(+M)→I2O2(+M)→higher oxides, which predominated over the bimolecular reaction leading to regeneration of I atoms, IO+IO→2I+O2, with k 2a/k 2b≥4. Simple computer modelling calculations indicate that reaction (2a) may be important in determining the fate of photolabile iodine species in the atmosphere. The consequences for the behaviour of radioiodine releases are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00130748
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  • 78
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    Quantum field methods in the theory of diffusion-controlled reactions (1985)
    Springer
    Journal of statistical physics 38 (1985), S. 347-359 
    Details
    ISSN: 1572-9613
    Keywords: Diffusion ; reaction ; kinetics ; master equation ; perturbation methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The diagrammatic perturbation technique for the kinetic theory of classical reacting systems with diffusion is developed. It is further applied to investigation of recombination-type reactions in media of one, two, and three dimensions. The effective rates of this reaction are calculated, covering the whole range from the slow to the fast (diffusion-controlled) regimes.
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    URL: http://dx.doi.org/10.1007/BF01017866
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  • 79
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    Partial characterisation of different classes of viral DNA, and kinetics of DNA synthesis in turnip protoplasts infected with cauliflower mosaic virus (1985)
    Springer
    Plant molecular biology 5 (1985), S. 25-34 
    Details
    ISSN: 1573-5028
    Keywords: cauliflower mosaic virus ; DNA synthesis ; kinetics ; protoplasts ; replication intermediates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Turnip protoplasts infected with cauliflower mosaic virus (CaMV) have been used to examine the kinetics of CaMV DNA synthesis, and the different classes of CaMV DNA found in vivo partially characterised. Differential extraction techniques for DNA from infected protoplasts has identified several distinct classes of viral DNA. The same approach applied to virus preparations revealed that while the majority of virion DNA was stably encapsidated, some small DNAs and a heterogeneous population 3.8-ca. 5.0 Kb were not. The structural relationship of sa-DNA (3) with the particle is such that only its 5′ RNA moeity is susceptible to nuclease attack. Two-dimensional gel electrophoresis of total CaMV DNA from infected protoplasts revealed all the DNA species found in virion DNA, those species representing the ‘free’ DNA class and a further class of molecules, rich in DNA of (−) polarity (24), to which the role of reverse transcription intermediates has been ascribed. ‘Free’ DNA contains 8 Kb supercoiled DNA (Form I DNA), an 8 Kb open circle (Form II), an 8 Kb linear (Form III) and a truncated molecule with an extension of the (−) strand previously observed from infected plants (10). Kinetic experiments show that the accumulation of total CaMV-DNA parallels the accumulation of progeny virions to reach a maximum around 72 h post-inoculation and that there is not a separation of CaMV-DNA synthesis into clearly defined early and late stages.
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    URL: http://dx.doi.org/10.1007/BF00017870
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  • 80
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    A simulation model of sulfur transformations in forested Spodosols (1986)
    Springer
    Biogeochemistry 2 (1986), S. 313-328 
    Details
    ISSN: 1573-515X
    Keywords: soil organic sulfur ; mineralization ; reaction rates ; kinetics ; immobilization ; soil adsorption ; sulfate ; first-order ; michaelis-menten
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Transformations of organic and inorganic S in two forested Spodosols from the Hubbard Brook Experimental Forest, New Hampshire and the Huntington Forest in the Adirondack Mts. of New York were investigated using laboratory35SO4 2- incorporation experiments. Sulfur transformations were modeled as a set of three reversible, first-order reactions in which soluble SO 4 2- is converted to adsorbed SO 4 2- , ester sulfate and carbon-bonded S. Reaction rate contants for35SO 4 2- adsorption/desorption and immobilization reactions involving ester sulfate and carbon-bonded S were determined using a fifth order Runge-Kutta-Fehlberg integration routine combined with least squares fitting. Model simulations were able to account for over 93% of the variation in the distribution of35S in S fractions. A hypothetical application of immobilization rate constants to field situations at the Hubbard Brook Experimental Forest suggests that large quantities of S cycle through organic forms in Northern Hardwood Forest Ecosystems.
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    URL: http://dx.doi.org/10.1007/BF02180323
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  • 81
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    Dextrose Adduct Formation in Aqueous Teicoplanin Solutions (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 1032-1038 
    Details
    ISSN: 1573-904X
    Keywords: kinetics ; rate constants ; antibiotics ; adduct formation ; equilibrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The interaction of Teicoplanin, a glycopeptide antibiotic, with dextrose in aqueous solution has been investigated. The equilibrium concentrations of the adduct formed by the interaction of the dextrose aldehyde and the Teicoplanin amino group is shown to be directly related to the concentration of the dextrose and is thought to be inversely proportional to the hydrogen ion concentration. It was also found that phosphate ion catalyzed the reverse reaction. Approximately 30 days were required to reach equilibrium a 4°C, while equilibrium was established in about 7 days at room temperature. The reaction is reversed with dilution and the rate of the reverse reaction is two to three times faster-than expected when phosphate ion is present at 0.05 M. From the temperature dependence of the rate constants, the activation energies for the various reactions were determined to be in the range 67–80 kjoules (16–19 kcal)/mol.
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    URL: http://dx.doi.org/10.1023/A:1015974319889
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    Dehydration Kinetics of Prostaglandin E1 in a Lipid Emulsion (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 210-215 
    Details
    ISSN: 1573-904X
    Keywords: lipid emulsion ; kinetics ; prostaglandin E1 ; interface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The overall dehydration kinetics of prostaglandin El (PGE1) in a lipid emulsion at 35°C were found to fit a model whereby the k apparent measured at each pH is simply the sum of the product of the fraction of the PGE1 at the interface,f i, and the rate constant at the interface, k i, plus the product of the fraction of the PGE1 in the aqueous phase,f aq, and the rate constant in the aqueous phase, k aq. The values for f i and f aq were reported earlier as a function of pH at 35°C. The k aq and k apparent were experimentally determined as a function of pH at 35°C. The k i was indirectly determined from the stability data in the emulsion. Microscopic rate constants for dehydration of PGE1 in the aqueous phase and interface at 35°C were estimated from the experimental data. Based on the kinetic evaluation performed, it appears that the dehydration kinetics might be manipulated by the addition of charged surface active agents.
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    URL: http://dx.doi.org/10.1023/A:1015909432300
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    The Role of Calcium Ions and Bile Salts on the Pancreatic Lipase-Catalyzed Hydrolysis of Triglyceride Emulsions Stabilized with Lecithin (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 449-457 
    Details
    ISSN: 1573-904X
    Keywords: pancreatic lipase ; lipase ; lipolysis ; triglycerides ; kinetics ; mechanism ; calcium ; bile salts ; lecithin ; emulsions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Lecithin-stabilized triglyceride emulsions are subject to hydrolysis by pancreatic lipase. The time profiles of these reactions are characterized by a lag-phase and a zero-order phase. Lag phases are more pronounced with long-chain triglycerides. Ca2+ is effective in reducing the lag-phase and activating lipase. Kinetic analysis of the reactions suggests that, like previous findings by others, taurodeoxycholate (TDC) micellar solutions combine with the lipase–colipase complex to form another catalytically active enzyme form. This enzyme form exhibits reduced activity in the absence of Ca2+. In the presence of Ca2+ the mixed micelle–lipase complex becomes more active and opens a new pathway for lipolysis. It is suggested that this enzyme form can bind more easily to interfaces with different physicochemical properties. Under these conditions, Ca2+ activates the lipolysis of short-, medium-, and long-chain triglycerides by a similar mechanism. Maximum activities were measured in the presence of approximately 6 mM TDC and 30 mM Ca2+. The experimental conditions approximate the physiological conditions in the gastrointestinal tract since all of the factors studied here have been reported to be necessary for in vivo lipolysis and/or absorption of triglycerides. A mechanistic model for lipolysis in the presence of Ca2+ and the bile salt TDC is proposed which accounts for most of the experimental observations in a quantitative manner.
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    URL: http://dx.doi.org/10.1023/A:1015956104500
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    Kinetics of Drug Decomposition by Heat Conduction Calorimetry (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 20-27 
    Details
    ISSN: 1573-904X
    Keywords: microcalorimetry ; Lovastatin ; decomposition ; thermodynamics ; oxidation ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The application of heat conduction calorimetry to the determination of decomposition mechanisms and rates for drugs is shown to be a rapid and generally useful method. The application of the method to determine the nature of the decomposition reaction, sources of systematic errors in the method, the equations relating the calorimetric signal to the kinetics of the reaction, and some examples of results are presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015851100015
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    Development of Acute Tolerance to Bumetanide: Constant-Rate Infusion Studies (1988)
    Springer
    Pharmaceutical research 5 (1988), S. 86-91 
    Details
    ISSN: 1573-904X
    Keywords: acute tolerance ; bumetanide ; kinetics ; dynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bumetanide was administered intravenously to four mongrel dogs as a bolus of 8.7 µg/kg, immediately followed by a constant-rate infusion of 0.35 µg/min/kg at 0.036 ml/min. Treatment A consisted of a 90-min equilibration period and first hour (Phase I) of study in which animals were maintained under euvolemic conditions. During the subsequent 3 hr of Treatment A (Phase II), animals were maintained under hydropenic conditions. These experiments were then repeated 1 week later (Treatment B) with the temporal aspects of hydration reversed (Phase III, hydropenia; Phase IV, euvolemia). Serial plasma and urine samples were assayed for bumetanide by high-performance liquid chromatography (HPLC) and for sodium by flame photometry. The bumetanide excretion rate was not significantly different during the 4 hr of Treatment A, although minor differences were observed between Phase III and Phase IV of Treatment B. The sodium excretion rate showed significant differences between euvolemic and hydropenic conditions of both treatments. A two- to threefold difference in the sodium excretion rate persisted even when slight differences (〈20%) in bumetanide excretion rates were taken into account. These results demonstrate that an acute tolerance does develop to constant-rate infusions of bumetanide when inadequate fluid and electrolyte replacement occurs and that this tolerance can be reversed by rehydration.
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    URL: http://dx.doi.org/10.1023/A:1015984016680
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    The attachment to human buccal epithelial cells by Candida albicans: An in vitro kinetic study using concanavalin A (1987)
    Springer
    Mycopathologia 98 (1987), S. 179-184 
    Details
    ISSN: 1573-0832
    Keywords: adhesion ; C. albicans ; kinetics ; concanavalin A
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The early in vitro kinetics of Candida albicans attachment to human buccal epithelial cells was studied with the aid of an adhesion assay and solutions of concanavalin A (Con A), a lectin which is capable of inhibiting yeast adhesion. Various saccharides and putative receptor analogues were also tested. Solutions of each single reagent were added to tubes containing aliquots of mucosal cells and germinated yeasts at the beginning of a 1-hour incubation period (time O) or at 10 minute intervals during the assay. The number of yeasts attached to 200 mucosal cells was subsequently determined microscopically. Yeast adhesion remained constant following addition of phosphate-buffered saline (PBS) at time 0 or at any time thereafter. However, addition of Con A at 0, 10 or 20 minutes of incubation decreased adhesion significantly to 38%, 45% and 63% of control values. This inhibitory effect dwindled as time of incubation prior to lectin addition increased and Con A could not inhibit adhesion significantly after twenty minutes. Results obtained with Con A using live germinated yeasts were similar to those obtained with formalin-killed C. albicans. The other reagents tested failed to decrease adhesion significantly. These included the putative receptor analogues fibronectin, N-acetyl-d-glucosamine and d-galactose, and several non-specific saccharides such as α-d-methylglucopyranoside, d-ribose and d-xylose. It is suggested that in vitro attachment to human mucosal cells by C. albicans is inhibitable up to a defined point in time by a lectin with affinity for mannosecontaining surface moieties, but becomes non-reversible thereafter. This experimentally-observed irreversibility is independent of yeast cell viability.
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    URL: http://dx.doi.org/10.1007/BF00437653
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