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  • Triticum aestivum  (853)
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  • 1
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    European journal of nutrition 26 (1987), S. 125-137 
    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.
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  • 2
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    Colloid & polymer science 261 (1983), S. 188-189 
    ISSN: 1435-1536
    Keywords: Polymerization ; kinetics ; redox polymerization ; acrylamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
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    Colloid & polymer science 266 (1988), S. 958-964 
    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.
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  • 4
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    Colloid & polymer science 262 (1984), S. 366-373 
    ISSN: 1435-1536
    Keywords: kinetics ; isothermal crystallization ; polymer ; spherulite ; differential scanning calorimetry
    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 the DSC technique, isothermal crystallization experiments are usually performed on thin flat specimens, but their interpretation generally uses theories developed for an unbounded volume. In this paper, isothermal crystallization of spherical entities in the volume limited by two parallel infinite planes is considered. Our model, derived from Avrami's theory, gives an analytical expression for the transformed volume fraction as a function of time. It is shown that the influence of thickness becomes important when thickness becomes of the order of or smaller than the average spherulite radius. The main effects of a decreasing thickness are a slower crystallization kinetics and a decrease in the Avrami exponent. These results can be used to interpret experimental data obtained in isothermal polymer crystallization.
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  • 5
    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.
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  • 6
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    Colloid & polymer science 265 (1987), S. 58-64 
    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.
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  • 7
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    Colloid & polymer science 261 (1983), S. 621-625 
    ISSN: 1435-1536
    Keywords: Polyamide 6 ; crystallisation ; kinetics ; titania
    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 kinetics of isothermal and nonisothermal crystallization of polyamide-6 (PA6) containing titania was studied by means of DSC. It was found thatTiO 2 causes an acceleration in the crystallization of polyamide-6 and lowers the value of the Avrami exponent,n. The presence of TiO2 does not affect equilibrium melting pointT m 0 , glass temperatureT g, or surface free energiesσ e andσ of the basal and lateral surfaces.
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  • 8
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    Entomologia experimentalis et applicata 91 (1999), S. 403-412 
    ISSN: 1570-7458
    Keywords: aphid ; Diuraphis noxia ; Triticum aestivum ; endosymbiont ; insect-plant interactions ; phloem ; amino acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The feeding behavior of Diuraphis noxia Mordvilko (Homoptera: Aphididae) on susceptible hosts causes both ultrastructural and tissue level damage which may affect phloem composition. Genetic evidence suggests that endosymbiotic bacteria in most aphids overproduce limiting amino acids to benefit hosts but that D. noxia depends less on endosymbionts for these nutrients, possibly due to an enriched diet. To determine whether D. noxia feeding damage results in higher concentrations of essential amino acids, stylet exudates were analyzed from wheat (Triticum aestivum) damaged to different degrees. Comparison of samples from undamaged and damaged susceptible wheat revealed changes in amino acid composition and an increase in levels of essential amino acids, indicating a nutritionally enhanced ingesta. The changes in stylet exudates paralleled changes in leaf exudates, indicating that the effects are systemic. Feeding damage is not observed on a resistant wheat host, var. Halt, and leaf exudates from infested Halt did not show changes in amino acid composition. Mean relative growth of nymphs was significantly lower on Halt than on susceptible Arapahoe, indicating that Halt is a less suitable host. Both varieties show similar amino acid levels in non-infested samples, suggesting that D. noxia infestation does not enhance the phloem environment in Halt. This study provides evidence that aphid feeding can generate a nutritionally enhanced phloem diet.
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  • 9
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    Fire technology 20 (1984), S. 47-63 
    ISSN: 1572-8099
    Keywords: Extinguishment ; fire modeling ; mass loss ; heat release ; char ; reflash ; sprinklers ; radiant flux ; kinetics ; reaction rate ; heat loss ; ash ; latent heat ; spray density ; extinguishing agents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying
    Notes: Abstract The Ad Hoc Mathematical Fire Modeling Working Group was organized about seven years ago to facilitate voluntary cooperation and coordination in developing mathematical fire modeling capability. The group has a steering committee of representatives of agencies that support fire modeling and related research. These include the National Bureau of Standards' Center for Fire Research, Factory Mutual Research Corp., the Naval Research Laboratory, NASA, and the Federal Aviation Agency. The Group holds plenary meetings when it seems desirable to do so (about once each 1 1/2 years), and workshops on topical subjects. Three workshops were held in 1983. Normally, Group meetings are held before or after other meetings at which a number of interested personnel would likely be present. Minutes are mailed to those who attended and to others (including European and Japanese personnel) who have indicated interest. This workshop was arranged by Ron Alpert of Factory Mutual Research Corp. and held at their facilities at Norwood, MA, in November 1983.
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  • 10
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    Entomologia experimentalis et applicata 58 (1991), S. 69-74 
    ISSN: 1570-7458
    Keywords: Rhopalosiphum padi ; antixenosis ; plant resistance ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Die Antixenose gegenüberRhopalosiphum padi (L.) in den drei Weizensorten Timmo, Moghan 2 und Ommid, von denen die zwei letzteren Sorten aus dem Iran stammen, wurde unter Verwendung des systemischen Insektizids Pirimicarb gemessen. Jeweils zwei Pflanzen aus verschiedenen Sorten wurden als Paar verwendet (in allen Kombinationen der drei Sorten), pro Paar ein Topf mit Pirimicarb gegossen, und zwanzig Blattlaüse über Blattflächen von beiden Sorten gekäfigt. Ähnliche Versuche wurden auch ohne Insektizid ausgeführt. Beide Methoden zeigten deutliche Antixenose von Moghan 2 und Ommid in Vergleich mit Timmo. Die Insektizidmethode zeigte auch eine Bevorzugung von Moghan 2 gegenüber Ommid, ein Resultat, das mit der schon bekannten relativen Antibiose dieser zwei Sorten übereinstimmte, während sich ohne Insektizid kein solcher Unterschied erwies. Die statistische Analyse solcher Versuche mit einem Insektizid, die eine Modifikation der Berechnung des erwarteten Werts mit dem χ2 Test enthält, ist beschrieben.
    Notes: Abstract Antixenosis in three wheat varieties (Timmo, Moghan 2 and Ommid) toRhopalosiphum padi (L.) was measured by pairing plants of any two varieties with one plant of each pair treated with a soil drench of the systemic insecticide pirimicarb. Aphids were then allowed access to equivalent leaf areas from the two plants in a leaf cage. The results were compared with similar choice experiments without insecticide. By either technique, the two Iranian varieties (Moghan 2 and Ommid) showed antixenosis in comparison with Timmo. The statistical analysis of the data, using a heterogeneity χ2 test, is described.
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  • 11
    ISSN: 1570-7458
    Keywords: LepidopteraEphestia kuehniella ; α-amylase ; Triticum aestivum ; endosperm ; α-amylase inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Crude α-amylase preparations from seven Lepidoptera pests were susceptible to inhibition by salt-soluble proteins of bread wheat (Triticum aestivum L.) endosperm. Protein fractions that corresponded to tetrameric, dimeric, and monomeric wheat α-amylase inhibitors, were decreasingly effective against the insect α-amylase activity. To further confirm these results, purified inhibitors were tested against an α-amylase preparation fromEphestia kuehniella (Zeller). This preparation showed decreased activity when increasing amounts of an heterotetrameric inhibitor (reconstituted from its isolated subunits WTAI-CM2, -CM3 and -CM16) were assayed. Activity was only partially inhibited by homodimeric (WDAI-1, synonym 0.53; WDAI-2, synonym 0.19) and monomeric (WMAI-1, synonym 0.28) inhibitors.
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  • 12
    ISSN: 1570-7458
    Keywords: sieve element ; salivation ; aphid ; plant resistance ; wheat ; Sitobion fragariae ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extended sieve element salivation (E1 waveform in the electrical penetration graph) is a characteristic activity during early sieve element punctures, particularly in resistant plants. In order to explore a chemically-mediated mechanism of resistance associated with sieve element salivation, we compared the pattern of feeding behaviour of the aphid, Sitobion fragariae (Walker), on two cultivars of the wheat Triticum aestivum L., with different concentrations of hydroxamic acids (Hx). During 24 h of electronic monitoring, aphids dedicated over 50% of the total time to phloem ingestion from the sieve elements. Total time allocated to E1 in the experiment, time to first E1 within the experiment, time allocated to E1 before a sustained phloem ingestion (E2) and the contribution of sieve element salivation to the phloem phase (E1/[E1+E2]) were significantly higher in the high-Hx cultivar. The increased salivation in plants with higher contents of Hx suggests the existence, at least in this system, of a chemically-mediated sieve element constraint.
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  • 13
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    Journal of solution chemistry 11 (1982), S. 339-346 
    ISSN: 1572-8927
    Keywords: Carbon dioxide ; hydrolysis ; aqueous solution ; kinetics ; activation volume
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The pressure dependence of the dehydration reaction of H2CO3 was measured in acidic aqueous solution for pressures up to 1 kbar using a high-pressure stopped-flow instrument. The corresponding volume of activation was found to be 6.4±0.4 cm3-mol−1 at 25°C and 0.5 ionic strength. Volume equation calculations result in a value of −9.9±1.9cm3-mol−1 for the volume of activation for the hydrolysis of CO2 under the same conditions. For the first time, the reaction mechanism can be interpreted in terms of dissociative and associative modes, respectively. These data are used to construct an overall reaction volume profile.
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  • 14
    ISSN: 1572-8927
    Keywords: Temperature jump ; kinetics ; thermodynamics ; TRIS ; iminodiacetic acid ; magnesium ion ; phenol red
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Equations describing the temperature jump amplitudes associated with a system of two coupled reactions (TRIS-phenol red) as well as the ternary system (Mg2+-iminodiacetic acid-phenol red) are presented. The termodynamic parameters calculated from experimentally measured temperature perturbation amplitudes using a multiparametric curve fitting procedure are found to be in good agreement with those determined from pH- and costant rate thermometric titrations. For phenol red, pK I =7.55, ΔH I =3.45 kcal, and for Mg2+ iminodiacetic acid, log K M =2.84, ΔH M =3.25 kcal, were obtained. It is shown that this method can be used to determine accurate thermodynamic enthalpy changes over a narrow temperature interval of less than 1.0°C from a single experiment requiring about 50 μl of sample solution.
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  • 15
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    Journal of solution chemistry 12 (1983), S. 771-781 
    ISSN: 1572-8927
    Keywords: Ultrasonics ; kinetics ; aqueous solution ; iso-butyl cellosolve
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ultrasonic absorption and velocity measurements in aqueous solution of iso-butyl cellosolve (ethylene glycol iso-butyl ether) as a function of the concentration are reported. The two relaxational absorptions have been attributed to the perturbation of the equilibria expressed by AB⇌A+B and Aα(1/n)An where A is the solute, B is the solvent, AB is the complex and A n is the solute aggregate. The rate constants for each step have been determined. From the concentration dependence of the maximum excess absorption per wave length, the enthalpy change and the volume change for the reaction between the solute and the solvent have been determined for aqueous solutions of butyl cellosolve (ethylene glycol n-butyl ether), iso-butyl cellosolve and propyl cellosolve (ethylene glycol n-propyl ether). The results are consistent with a hydrogen bonding reaction. The effect of the ethers on water structure are considered and it is clear that the fraction of water molecules which can hydrogen bond to the solute decreases with the increasing hydrophobicity of the solute.
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  • 16
    ISSN: 1572-8927
    Keywords: Solvolysis ; kinetics ; aqueous solvent mixtures ; Co(III) complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of the solvolysis of [Co(CN)5Cl]3− have been investigated in water +2-methoxyethanol and water + diethylene glycol mixtures. Although the addition of these linear hydrophilic cosolvent molecules to water produces curvature in the variation of log(rate constant) with the reciprocal of the dielectric constant, their effect on the enthalpy and entropy of activation is minimal, unlike the effect of hydrophobic cosolvents. The application of a Gibbs energy cycle to the solvolysis in water and in the mixtures using either solvent-sorting or TATB values for the Gibbs energy of transfer of the chloride ion between water and the mixture shows that the relative stability of the emergent solvated Co(III) ion in the transition state compared to that of Co(CN)5Cl3− in the initial state increases with increasing content of cosolvent in the mixture. By comparing the effects of other cosolvents on the solvolysis, this differential increase in the relative stabilities of the two species increases with the degree of hydrophobicity of the cosolvent.
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  • 17
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    Journal of solution chemistry 6 (1977), S. 203-216 
    ISSN: 1572-8927
    Keywords: Glucose ; kinetics ; mixed solvent ; kinetic isotope effect ; enthalpy of activation ; entropy of activation ; tetrahydrofuran ; tert-butanol ; mutarotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The mutarotation rates of glucose in aqueous mixtures of tetrahydrofuran andtert-butanol in the mole fraction (xi) range 0〈xi〈0.2 have been measured at 5° intervals in the range 5–35°C. The kinetic deuterium isotope effects have been determined for the same solvent compositions at 25 and 35°C. A statistical analysis of the Arrhenius plots indicates that the experimental errors, although small, are too large for the establishment of any compensation behavior between ΔH
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  • 18
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    Journal of applied electrochemistry 29 (1999), S. 191-200 
    ISSN: 1572-8838
    Keywords: cyclic redox reaction ; dissolution ; kinetics ; manganese dioxide ; mechanism ; pyrite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This paper describes a study of the kinetics and mechanism of MnO2 dissolution in H2SO4 in the presence of pyrite through leaching and electrochemical parameters. Manganese(iv) was found to dissolve mainly through reduction by the ferrous ion generated during oxidation of pyrite by the ferric ion. The oxidation which is slower and rate controlling may proceed through two different reactions, one producing S0 and the other SO42−. Manganese dissolution runs at the same rate as that of pyrite oxidation by maintaining ferrous ion concentration at a much lower level than that of ferric. Kinetic equations based on corrosion coupling principles are developed to explain the observed leaching behaviour.
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  • 19
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    Journal of chemical crystallography 28 (1998), S. 69-72 
    ISSN: 1572-8854
    Keywords: Co(III) complex ; crystal structure ; kinetics ; steric effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The title compound crystallizes in the orthorhombic space group Pnma, with a = 7.9209(5), b = 9.818(1), c = 16.867(2) Å, and Z = 4. The structure was solved employing 1864 independent x-ray reflections with I〉2σ(I) by Patterson and difference Fourier techniques and refined by full-matrix least-squares to R = 0.036. The trans-[CO(NH3)4(NH2CH3)Cl](ClO4)2 molecule is on a crystallographic mirror plane. The cobalt ion is in an elongated octahedral coordination with four equatorial ammonia ligands [average Co–N distance equal to 1.966(2) Å], an axial methylamine [Co–N=1.965(3)Å], and an axial chlorine ion [Co–Cl=2.2771(9)Å]. Kinetic steric effects of the complex are interpreted in terms of structural results.
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  • 20
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    Journal of solution chemistry 19 (1990), S. 1073-1084 
    ISSN: 1572-8927
    Keywords: Solvolysis ; kinetics ; mixtures of water+cosolvent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Rates of solvolysis of the complex cation [Co(4tBupy)4Cl2]+ have been determined in mixtures of water with the hydrophobic solvent, t-butyl alcohol. The solvent composition at which the extremum is found in the variation of the enthalpy ΔH* and the entropy ΔS* of activation correlates well with the extremum in the variation of the relative partial molar volume of t-butyl alcohol in the mixture and the straight line found for the variation of ΔH* with ΔS* is coincident with the same plot for water + 2-propanol mixtures. A free energy cycle is applied to the process initial state (C n+) going to the transition state [M(n+1)+...Cl−] in water and in the mixture using free energies of transfer of the individual ionic species, ΔG t o (i), from water into the mixture. Values for ΔG t o (i) are derived from the solvent sorting method and from the TATB/TPTB method: using data from either method, changes in solvent structure on going from water into the mixture are found to stabilize the cation in the transition state, M(n+1)+, more than in the initial state, C n+. This is compared with the application of the free energy cycle to the solvolysis of complexes [Co(Rpy)4Cl2]+ and [Coen2LCl]+ in mixtures of water with methanol, 2-propanol or t-butyl alcohol: the above conclusion regarding the relative stabilization of the cations holds for all these complexes in their solvolyses in water+alcohol mixtures using values of ΔG t o (Cl−) from either source.
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  • 21
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    Journal of solution chemistry 2 (1973), S. 217-238 
    ISSN: 1572-8927
    Keywords: Cation ; energies ; H. S. Frank ; M. Eigen ; R. G. Wilkins ; kinetics ; ligand substitution ; mechanism ; mixed solvents ; nonaqueous ; solvation ; solvent ; solvent structure ; solvent exchange ; transition metal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The role of the solvent in reactions involving ions is considered in relation to the structure of liquids. The rate constants and activation parameters for ligand substitutions at divalent transition metal cations in various solvents are compared with those for solvent exchanges. The differences are related to structural properties of the solvents, represented by their heats of evaporation and fluidities, and interpreted with the aid of a model developed from that of Frank and Wen. Water is not a typical solvent.
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  • 22
    ISSN: 1572-8927
    Keywords: Cu(II) ; kinetics ; reduction ; temperature dependence ; H2O2, NaCl, NaBr, NaClO4
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The rates of reduction of Cu(II) with H2O2 have been measured in NaCl and NaBr solutions and mixtures with NaClO4 as a function of pH (6 to 9), temperature (5 to 45°C) and ionic composition (0.1 to 6M). The effect of pH on the rates was found to be independent of temperature and ionic composition. The rates increased as a function of [H+] raised to the power of 1.3 to 1.6. Speciation calculations indicate that this pH dependence can be attributed to Cu(OH)2 being the reactive species. The rate constants in NaCl and NaBr and mixtures with NaClO4 were independent of ionic strength, but proportional to the halide concentration raised to the power of 2.0 (0.2 to 2.6M). These results can be attributed to Cu(OH)2Cl 2 2− being the reactive species to reduction with H2O2. The Cu(I) halide complexes formed from the reduction are not easily oxidized with O2 or H2O2. The faster rates in Br− solutions, which form stronger complexes with Cu+, support this contention. Measurements made in NaCl with added NaHCO3, NaB(OH)4 EDTA, NTA and glycine were also made. These measurements indicate that the CuL complexes (L=B(OH) 4 − , CO 3 2− , EDTA, NTA, and glycine) are not very reactive to reduction with H2O2. The addition of Mg2+ or Ca2+ caused the rates to increase due to the formation of MgL or CaL complexes and the resultant release of reactive Cu2+.
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  • 23
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    Journal of solution chemistry 23 (1994), S. 483-500 
    ISSN: 1572-8927
    Keywords: Thermodynamics ; kinetics ; chemical relaxation ; temperature-jump ; amplitudes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Amplitudes of chemical relaxation signals can provide useful information as to the thermodynamics of coupled chemical reactions. The temperature-jump technique has been used to investigate the thermodynamic behavior of the Nickel(II)-3,5-dinitrosalicylate system in buffer solution, where complex formation steps are coupled to proton transfer steps. The analysis of the relaxation curves is based on the transformation of a set of coupled elementary reactions into a set of uncoupled ‘normal reactions.’ By analogy with classical titrations, the experiments have been performed by changing the metal ion concentration at constant ligand concentration and pH. Each measured amplitude is associated in this way to a point of a ‘dynamic titration’ and a procedure is formulated by which the values of the equilibrium constants and enthalpies of the normal reactions are simultaneously obtained by simple linear plots. From the dependence of these parameters on suitable functions of the concentrations of the reactants the values of ΔG° and ΔH° of the individual steps are derived. It is shown that the addition of a buffer (instead of an indicator) influences the stoichiometric coefficients of the normal reaction in such a way that measurable amplitudes are produced in systems that, as the presently investigated, in unbuffered solution would remain insensitive to the external perturbation. The circumstances under which the dynamic method offers advantages over the classical techniques are discussed.
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  • 24
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    Journal of solution chemistry 5 (1976), S. 163-169 
    ISSN: 1572-8927
    Keywords: Solvent effects ; tetramethylurea ; hydrolysis ; hydrogen bonding ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Tetramethylurea was hydrolyzed in aqueous hydrochloric acid at temperatures of 80, 90, and 100°C. All reactions were carried out in an excess of both tetramethylurea and water, with first-order dependence on acid concentration being observed. As the concentration of water was increased, the rate of hydrolysis decreased until equimolar amounts of water and tetramethylurea were present. Subsequent addition of water had no effect on the observed rate.
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    Adsorption 1 (1995), S. 133-151 
    ISSN: 1572-8757
    Keywords: PSA process ; sensitivity ; equilibria ; kinetics ; heats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Mathematical models for pressure swing adsorption (PSA) processes essentially require the simultaneous solutions of mass, heat and momentum balance equations for each step of the process using appropriate boundary conditions for the steps. The key model input variables needed for estimating the separation performance of the process are the multicomponent adsorption equilibria, kinetics and heats of adsorption for the system of interest. A very detailed model of an adiabatic Skarstrom PSA cycle for production of high purity methane from a ethylene-methane bulk mixture is developed to study the sensitivity of the process performance to the input variables. The adsorption equilibria are described by the heterogeneous Toth model which accounts for variations of isosteric heats of adsorption of the components with adsorbate loading. A linear driving force model is used to describe the kinetics. The study shows that small errors in the heats of adsorption of the components can severely alter the overall performance of the process (methane recovery and productivity). The adsorptive mass transfer coefficients of the components also must be known fairly accurately in order to obtain precise separation performance.
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    Adsorption 2 (1996), S. 265-277 
    ISSN: 1572-8757
    Keywords: frequency response ; diffusion cell ; kinetics ; diffusion ; heat effects
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    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper deals with frequency response (FR) analysis of a closed diffusion cell system with two resonators, that is both the LHS and RHS volumes are modulated. The analysis is made for a homogeneous particle described by a single effective diffusivity as well as a biporous pellet described by macropore and micropore diffusions. It is shown that if the perturbation of the volume of the reservoir #2 is lagged behind that of the reservoir #1 by 3π/2, the pressure response in reservoir #1 is significantly enhanced with larger amplitude as well as phase angle. When the perturbations of the two reservoirs are out of phase, the heat effect is reduced and can become insignificant when the two perturbations are completely out of phase (ψ = π). Under such a condition, the pressure difference between the two reservoirs could be doubled. In the case of biporous pellets, it is shown that the FR behaviours obtained for micropore diffusion control and macropore diffusion control are well distinguished. In the former case, the FR system reduces to a traditional batch adsorber one while in the latter case, the FR behaviour is the same as for a two resonator system with homogeneous particles. This difference can be used for the discrimination of micropore and macropore diffusion processes.
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  • 27
    ISSN: 1572-8757
    Keywords: characterisation ; equilibria ; kinetics ; micropore size distribution ; n-butane ; nutshell
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    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Adsorption equilibria and dynamics ofn-butane on two activated carbon samples prepared from the physical activation of nutshell are studied in this paper. The micropore size distribution (MPSD) is considered as the main source of solid heterogeneity. Lennard-Jones' potential theory and Dubinin's theory (TVFM) are used in the equilibria data to derive the MPSD, which is well fitted by a Gamma distribution function. The adsorption energy distribution derived from the MPSD is very asymmetric for both the samples studied, and this energy distribution used in the HMSD/HMSMD kinetics models for the study of adsorption dynamics ofn-butane.
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  • 28
    ISSN: 1572-8773
    Keywords: acidophilic ; strain ; oxidation ; kinetics
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    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Recovery of metal values from sulfide ores by use of acidophilic microorganisms is gaining importance. A number of commercial/pilot plants are setup to find out the techno-economic feasibility of the overall process. The main drawback in the process is the slow kinetics of dissolution of metal values from the sulfide ores. To make the technology e attractive the kinetics should be improved considerably. There are various factors which determine the overall kinetics such as bacterial activity and concentration, iron and sulfur oxidation, oxygen consumption, reactor design and nature of ore. A brief review has been made dealing with the above parameters
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  • 29
    ISSN: 1572-879X
    Keywords: Fischer-Tropsch synthesis ; reaction activation barrier ; carbon chain growth and termination ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A method is established, by which the difference of the reaction activation barriers of carbon chain growth and termination in Fischer-Tropsch (FT) synthesis can be determined from experiments. A FT synthesis is carried out on Fe/Zn catalyst. We apply the method to analyze the experimental result and obtain the difference of reaction activation barriers of carbon chain growth and termination of α-olefins on the catalyst.
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    Catalysis letters 37 (1996), S. 167-172 
    ISSN: 1572-879X
    Keywords: dissociation ; kinetics ; Co-Mo sulphide ; H2S
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    Topics: Chemistry and Pharmacology
    Notes: Abstract In this study, a high surface area 4Co∶6Mo∶100γ-Al2O3 sulphide prepared using precipitation from homogeneous solution (PFHS) has been used for the catalytic splitting of hydrogen sulphide into H2 and elemental sulphur. The activity of this new formulation was significantly better than previously reported recipes. Kinetic data collected over a wide range of H2S partial pressures between 883 and 983 K revealed that, although the decomposition followed a first-order law, a mechanism involving H2S adsorption on co-ordinative unsaturation sites of the Co-Mo sulphide catalyst gave a Langmuir-Hinshelwood rate expression that yielded satisfactory model parameters. In particular, the scission of the surface H-S bond appeared to be the rate determining step.
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    Cellulose 1 (1994), S. 26-56 
    ISSN: 1572-882X
    Keywords: low-temperature degradation ; kinetics ; mechanisms ; electrical insulation ; transformers
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A critical review is given of the degradation of cellulose in the low-temperature region (below about 300°C) of power transformer operation. The large number of kinetic studies, under a variety of environmental conditions from Kraft paper in insulating oil, to cotton and paper in oxygen, are considered in terms of a first-order polymer chain scission model. In many cases, the data are replotted to suit the model. A common activation energy of 111±6 kjmol−1 is calculated and it is shown that the pre-exponential factor, rather than the activation energy, is sensitive to the oxidizing nature of the environment and the susceptibility to degradation of the material. The chemical mechanisms of degradation are reviewed, and conclusions and recommendations are made regarding chemical condition monitoring and life prediction of electrical insulation.
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    Adsorption 6 (2000), S. 137-147 
    ISSN: 1572-8757
    Keywords: adsorption ; kinetics ; linear driving force model ; process design
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    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The Linear Driving Force (LDF) model for gas adsorption kinetics is frequently and successfully used for analysis of adsorption column dynamic data and for adsorptive process designs because it is simple, analytic, and physically consistent. Yet, there is a substantial difference in the characteristics of isothermal batch uptake curves on adsorbent particles by the LDF and the more rigorous Fickian Diffusion (FD) model. It is demonstrated by using simple model systems that the characteristics of the adsorption kinetics at the single pore or the adsorbent particle level are lost in (a) evaluating overall uptake on a heterogeneous porous solid, (b) calculating breakthrough curves from a packed adsorbent column, and (c) establishing the efficiency of separation by an adsorptive process due to repeated averaging of the base kinetic property. That is why the LDF model works in practice.
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    Catalysis letters 37 (1996), S. 173-179 
    ISSN: 1572-879X
    Keywords: ammonia synthesis ; iron catalysts ; potassium promotion ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Measurements were performed of reaction rate in the process of ammonia synthesis (T=370–470°C) on doubly promoted (DP) (Al2O3, CaO) and triply promoted (TP) (K2O, Al2O3, CaO) iron catalysts. The latter were obtained by impregnation of the reduced and subsequently passivated DP precursors with alcoholic solution of KOH. The studies were carried out under high total pressure (10 MPa) in a wide range of ammonia partial pressure in the gas phase: from 0.25 to about 7 bar. The results are shown to be authoritative for the so-called kinetic regime. The effect of the presence of K+ cations in the catalyst was the stronger, as the temperature of the reaction was the lower and, in particular, the ammonia pressure in the gas phase the higher. The obtained results are in good accordance with the results of Somorjai's studies on activity of iron single crystal surfaces both clean and covered with (K+O) adlayer.
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    Catalysis letters 27 (1994), S. 79-90 
    ISSN: 1572-879X
    Keywords: kinetics ; carbon ; oxygen ; recombination ; rhodium ; surface characterisation ; XPS ; AES
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Different mechanisms of atomic carbon and oxygen recombination on a rhodium surface are studied with Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The kinetics of adsorbed carbidic carbon oxidation (carbon coverageθ c ≈ 0.1–0.3 ML) by gas-phase oxygen that proceeds by a Langmuir-Hinshelwood reaction mechanism, provides the value of the activation energy for recombination (E rec ⇂t ≈ 170±20 kJ/mol).E rec ⇂t depends slightly on the carbon coverage. An Eley-Rideal type of reaction was observed for adsorbed oxygen and atomic gas-phase carbon recombination which occurs in a dynamic regime. The low value found for the activation energy (near zero) is consistent with the mechanism that this exothermic reaction is too fast for energy dissipation into the substrate; the energy is mainly transferred into translational, vibrational and rotational energy of CO.
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  • 35
    ISSN: 1572-879X
    Keywords: ammonia synthesis ; kinetics ; ruthenium catalysts ; promotional effect
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of NH3 synthesis over carbon-based ruthenium catalysts promoted with barium or alkali was studied. Both the ammonia partial pressure dependencies of the reaction rates (T = 400°C, p = 63 bar, H2 : N2 = 3 : 1) and the pressure variations of the activity (T = 370°C, p= 4–63 bar, H2 : NN2 = 3 : 1) were found to be different for Ba and for the alkali (K, Cs). Ba–Ru/C proved to be more sensitive to the NH3 content and to the total pressure. The rate of synthesis over the alkali-promoted catalysts is, in turn, much stronger influenced by the ruthenium dispersion. TOFs of NH3 synthesis for the promoted samples at 370°C and 4 bar (Ba 0.085 1/s, Cs 0.05 1/s, K 0.035 1/s) are significantly higher than that for the Ru(0001) basal plane (0.0085 1/s results from the literature data at 370°C, 2 bar). The most active Ru/C samples (Ba or Cs) exceed significantly the fused iron catalyst, especially at high conversions.
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  • 36
    ISSN: 1572-882X
    Keywords: accelerated tests ; aging tests ; cellulose degradation ; durability ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Accelerated aging tests are credible and useful to predict paper permanence only if such tests can be shown to correlate with natural aging. In the first part of this study, a kinetic model was developed based on the accelerated aging results. In this report, we have shown that this kinetic model can indeed predict the natural aging results of lignin-free sheets with a statistical confidence. This is the first quantitative comparison of accelerated aging with natural aging.
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    Journal of solution chemistry 27 (1998), S. 1123-1138 
    ISSN: 1572-8927
    Keywords: Sol–gel processing ; hydrolysis ; condensation ; kinetics ; methoxydimethyloctylsilane ; copper nitrate hydrate ; phase diagram
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction rate was determined for copper nitrate hydrate with methoxydimethyloctylsilane (MDOS) in methanol. The rate constants of hydrolysis and condensation were established by quantitative measurement of the product and Karl Fischer water determination. The reaction with the hydrated copper salt resulted in the phase separation of an insoluble product from the reaction mixture. The structure of the product was determined, by Fourier Transform Infrared Spectrometry (FTIR) and Nuclear Magnetic Resonance (NMR) to be a dimer of the MDOS. The results showed the alcohol, producing condensation reaction was negligible in the formation of the dimer. contrary to the case for the well-known reaction by trialkoxysilanes and tetraalkoxysilanes.
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  • 38
    ISSN: 1572-8927
    Keywords: Enthalpies of reaction ; heats of reaction ; kinetics ; ester hydrolysis ; microcalorimetry
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The conditions under which the Picker flow microcalorimeter can be used to measure enthalpies and rates of reactions were investigated. For this purpose, systematic studies were made of the enthalpies of neutralization of HCl, HBr, HNO 3 , acetic, proprionic, and butyric acids with NaOH, enthalpies of hydrolysis of methyl and ethyl acetate with NaOH, and the reaction rates of the ester hydrolysis with NaOH. The general procedure and various sources of error are discussed and it is concluded that enthalpies of slow reactions can be measured to about 1% when the calorimeter is operated in the quasi-isothermal mode and the reaction rates to about 3% when operated in the quasi-adiabatic mode.
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    Cellulose 4 (1997), S. 1-5 
    ISSN: 1572-882X
    Keywords: paper ; degradation ; ageing ; kinetics ; modelling
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
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    Cellulose 3 (1996), S. 243-267 
    ISSN: 1572-882X
    Keywords: aging tests ; cellulose degradation ; durability ; kinetics ; paper properties
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    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The validity of accelerated aging tests to predict and rank papers on their permanence has been under question, preventing the development of performance-based standards for permanent paper. We conducted a general kinetic analysis to investigate the aging process of paper. A general kinetic model is proposed to describe the depolymerization of cellulose. Experimentally it was shown that in the case of aging, cellulose degradation follows classic first-order kinetics as a special case of our general kinetic model. The Arrhenius equation was critically re-examined for the case of a multiple reaction system. It was shown analytically that the Arrhenius equation is still applicable when certain conditions are met. This was convincingly supported by experimental results. We also analysed the dependence of the degradation rate on the moisture content and hydrogen ion concentration. By conducting systematic experiments on these two factors, a general and quantitative relationship was established to explain the contribution of each factor and their interactions. Finally, based on this kinetic analysis, the effects of storage conditions on the life expectancy of paper were estimated.
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    Journal of solution chemistry 3 (1974), S. 881-887 
    ISSN: 1572-8927
    Keywords: Binary aqueous mixtures ; solubilities ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A treatment which predicts the solubilities of gases in solvent mixtures is examined in the context of the analysis of kinetic data for reactions in aqueous mixtures. The treatment is qualitatively successful to some extent in resolving the effects of changes in the initial state of the reacting substrate in the activation parameters.
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    Journal of inorganic and organometallic polymers and materials 8 (1998), S. 111-117 
    ISSN: 1572-8870
    Keywords: Organosiloxane ; kinetics ; poly(phenylmethylsiloxane) ; catalyst ; anionic ; ring-opening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is well known that the rate of polymerization for an anionic mechanism is dependent on the ability of the bulk material or solvent system to disassociate the ion pair at the propagating chain end. In the anionic ring-opening polymerization of cyclic organosiloxanes in particular, the larger and softer the counter ion, the more rapidly the reaction proceeds. A recently developed phosphazene initiator system provides a large, soft counter ion relative to other traditional initiators used for the polymerization of poly(dimethylsiloxane) (PDMS). This novel initiator system was used in this investigation for the ring-opening polymerization of tetraphenyltetramethylcyclotetrasiloxane (P4) and the reaction kinetics under bulk and solution conditions were investigated. The new initiator system showed a dramatic increase in the rate of polymerization over the conventional potassium hydroxide-catalyzed system. Furthermore, this initiator was sufficiently reactive to be useful for the ring-opening polymerization of P4 at 293 K.
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  • 43
    ISSN: 1572-8900
    Keywords: Cellulose ; alkaline degradation ; peeling off ; degree of polymerization ; kinetics ; (gluco)isosaccharinic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The degradation of cellulosic materials, differing mainly in the degree of polymerization and the number of reducing end groups, was studied under the alkaline conditions similar to those existing in a cementitious repository for low- and intermediate-level radioactive waste (pH 13.3, T = 25°C). The kinetics of alkaline degradation (peeling-off reaction) were studied and the data analyzed by the model of Haas et al. [13]. The observed kinetic parameters for the propagation reaction and overall stopping reaction were compared with literature data. Although measured under different experimental conditions, literature data and data from this study show a consistent picture. Differences in the extent of degradation observed for the different cellulosic materials could be satisfactorily explained by differences in reducing end group content and, consequently, by differences in the degrees of polymerization. Besides the number of reducing end groups, the degree of amorphousness also plays an important role. The main degradation products formed under the experimental conditions used are α- and β-(gluco)isosaccharinic acid. This is in agreement with many other studies on alkaline degradation of cellulose. The two isomers are formed in roughly equal amounts.
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    Journal of solution chemistry 15 (1986), S. 221-229 
    ISSN: 1572-8927
    Keywords: Ultrasonics ; kinetics ; aqueous solution ; triethylene glycol monobutyl ether
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    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.
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    Topics in catalysis 5 (1998), S. 133-147 
    ISSN: 1572-9028
    Keywords: NMR ; catalysis ; high pressure ; dynamic equilibria ; magnetization transfer ; sapphire tube ; gas phase ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract High resolution NMR techniques are applicable to a variety of aspects of catalysis. Methods for studying homogeneously-catalyzed systems under high gas pressure are described along with approaches for obtaining mechanistic and dynamic information. Many of the same techniques may be applied to heterogeneous catalysis by following the reaction chemistry by gas phase NMR.
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    Entomologia experimentalis et applicata 59 (1991), S. 79-85 
    ISSN: 1570-7458
    Keywords: Wheat ; Triticum aestivum ; cereals ; Rhopalosiphum padi ; Aphididae ; barley yellow dwarf virus ; hydroxamic acids ; DIMBOA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid (Hx) occurring in wheat, was shown to deter feeding by the aphid Rhopalosiphum padi (L.), and to reduce BYDV transmission to the plant. Dual choice tests with wheat leaves showed the preferential settlement of aphids on leaves with lower levels of DIMBOA. Electric monitoring of aphid feeding behaviour showed that in seedlings with higher DIMBOA levels fewer aphids reached the phloem and they needed longer times to contact a phloem vessel than in those with lower levels. When aphids carrying BYDV were allowed to feed on wheat cultivars with different DIMBOA levels, fewer plants were infected with BYDV in the higher DIMBOA cultivars than in the lower ones. Preliminary field experiments showed a tendency for wheat cultivars with higher Hx levels to be more tolerant to infection by BYDV than lower Hx level ones.
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  • 47
    ISSN: 1572-9028
    Keywords: nonlinear temperature behavior ; Eyring plot ; modified Eyring plot ; selectivity ; selection process ; enantioselectivity ; selection level ; isoinversion principle ; isoinversion temperature ; inversion temperature ; kinetics ; catalysis ; asymmetric hydrogenation ; dihydroxylation ; cocyclization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of the temperature on selectivity is described under special consideration of nonlinearities in the corresponding modified Eyring plots. Reasons for the experimentally well-known behavior are discussed. Furthermore, the conditions for nonlinear temperature behavior are quantified and a concept is described which allows the determination of the temperature dependence of a single reaction pathway in a selection process.
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    Topics in catalysis 1 (1994), S. 305-314 
    ISSN: 1572-9028
    Keywords: non-Langmuir ; kinetics ; non-linear dynamics ; oscillations ; chaos ; self-organization
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of a catalytic reaction is frequently formulated in terms of simple concepts of the Langmuir type. Apart from limitations arising from the non-uniformity of the catalyst's surface and from the coverage dependence of the rate “constants”, several other complications may come into play. These may arise on the “quantum level” where energy flow between the various degrees of freedom may cause failure of simple transition state theory, as well as on the “continuum level” where formulation of rate equations in terms of coupled non-linear differential equations may give rise to a rich scenario of spatio-temporal self-organization, including kinetic oscillations, chaos, and formation of concentration patterns. Several of these phenomena are illustrated by selected examples.
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    Topics in catalysis 11-12 (2000), S. 327-333 
    ISSN: 1572-9028
    Keywords: hydrodenitrogenation ; toluidine ; methylcyclohexylamine ; kinetics ; nickel-promoted molybdenum sulphide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrodenitrogenation (HDN) of o-toluidine and its reaction intermediates was studied over a NiMo/γ-Al2O3 catalyst. The kinetics of the HDN of methylcyclohexylamine and of the hydrogenation of cyclohexene were also studied. Hydrogenation of o-toluidine alone produces methylcyclohexene and methylcyclohexane. When a sufficient quantity of cyclohexene is added during the HDN of toluidine, methylcyclohexylamine, the first intermediate in the hydrogenation of toluidine, becomes detectable. Because of its strong adsorption constant and high rate constant for reacting further to methylcyclohexene and methylcyclohexane, methylcyclohexylamine is not observed in the HDN of toluidine. Adding cyclohexene decreases the adsorption of methylcyclohexylamine, thus enabling its detection. The rate and adsorption constants of methylcyclohexylamine and cyclohexene in the HDN of methylcyclohexylamine were calculated by fitting the kinetic data to a Langmuir–Hinshelwood equation. A two-site model was used to describe the surface reactions, with one site for the methylcyclohexylamine reactions and the other for the cyclohexene reaction.
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    Cellular and molecular life sciences 49 (1993), S. 110-117 
    ISSN: 1420-9071
    Keywords: Polymerization ; sickle hemoglobin ; sickle cell disease ; kinetics ; thermodynamics ; polymer domains ; nucleation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The polymerization of sickle hemoglobin occurs by the same mechanisms in solutions and in cells, and involves the formation of 14 stranded fibers from hemoglobin molecules which have assumed a deoxy quaternary structure. The fibers form via two types of highly concentration-dependent nucleation processes: homogeneous nucleation in solutions with hemoglobin activity above a critical activity, and heterogeneous nucleation in similarly supersaturated solutions which also contain hemoglobin polymers. The latter pathway is dominant, and creates polymer arrays called domains. The individual polymers bend, but also cross-link, and the resulting mass behaves as a solid. The concentration of polymerized hemoglobin increases exponentially unless clamped by rate limiting effects such as oxygen delivery.
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  • 51
    ISSN: 1572-8757
    Keywords: micropore size distribution ; activated carbon ; adsorption ; desorption ; equilibrium ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract This paper deals with the prediction of adsorption equilibrium and kinetics of hydrocarbons onto activated carbon samples having different micropore size distribution (MPSD). The microporous structure of activated carbon is characterised by the distribution of slit-shaped micropores, which is assumed to be the sole source of surface heterogeneity. The interaction between adsorbate molecule and pore walls is described by the Lennard-Jones potential theory. Different adsorbates have access to different pore size range of activated carbon due to the size exclusion, a phenomenon could have a significant influence on both multicomponent equilibria and kinetics. Activated carbons with three different MPSDs are studied with ethane and propane as the two model adsorbates. The Heterogeneous Macropore Surface Diffusion model (HMSD) is employed to simulate adsorption kinetics. The simulation results show that the MPSD is an important factor affecting both the multicomponent equilibria and kinetics.
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    Adsorption 6 (2000), S. 349-357 
    ISSN: 1572-8757
    Keywords: sulfadiazene ; adsorption ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract To investigate the nature of interactive forces between sulfadiazene molecules and alumina surface the experiments were performed for the adsorption of sulfadiazene (SD) from its aqueous sulution onto the alumina surfaces at 25 ± 0.2°C and the influence of factors such as increasing concentration of SD (4.0–20.0 × 10−3 mol cm−3), the time required for adsorption equilibrium, pH (2.0–12.0) and temperature (5–45°C) of the adsorption medium, the presence of ions like Cl−, SO2− 4 and PO3− 4 (0.01–0.30 M) and organic solvents (5% v/v) were observed on the course of adsorption of SD. Various adsorption and kinetic parameters such as adsorption coefficient, the rate constants for adsorption and desorption were also evaluated. The results of the above cited studies facilitated to formulate the mechanisms of interaction between SD and alumina surfaces. From application view point the present work may be a potential tool for an effective chromatographic separation of sulfa drugs from industrial effluents.
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  • 53
    ISSN: 1572-879X
    Keywords: propane ; oxidation ; platinum ; palladium ; sulfur dioxide ; alumina ; zirconia ; activity ; acidity ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated γ-alumina or zirconia compared to γ-alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/γ-alumina, Pt/zirconia, Pd/γ-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/γ-alumina, and Pd/zirconia is less active than Pd/γ-alumina.
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  • 54
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    Catalysis letters 60 (1999), S. 51-57 
    ISSN: 1572-879X
    Keywords: furfural hydrogenation ; Cu/carbon catalysts ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Furfural hydrogenation over copper dispersed on three forms of carbon – activated carbon, diamond and graphitized fibers – were studied. Only hydrogenation of the C=O bond to form either furfuryl alcohol or 2‐methyl furan occurred at temperatures from 473 to 573 K. Reduction at 573 K gave the most active catalysts, all three catalysts had activation energies of 16 kcal/mol, and turnover frequencies were 0.018–0.032 s-1 based on the number of Cu0 + Cu+ sites, which were counted by N2O adsorption at 363 K and CO adsorption at 300 K, respectively. The Cu/activated carbon catalyst showed no deactivation during 10 h on stream, in contrast to the other two catalysts. A simple Langmuir–Hinshelwood model invoking two types of sites was able to fit all kinetic data quite satisfactorily, thus it was consistent with the presence of both Cu0 and Cu+ sites.
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  • 55
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    Catalysis letters 60 (1999), S. 167-171 
    ISSN: 1572-879X
    Keywords: ammonia decomposition ; iron catalyst ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The decomposition of ammonia is a reaction associated with the process of the nitriding of metals. The kinetics of the ammonia decomposition on iron catalysts has been studied using a differential reactor with internal mixing. The balance between the inlet and outlet ammonia quantity has been used to determine the degree of conversion. The rate of ammonia decomposition could be described by the following expression: r = k0 exp (Ea/RT)pNH3. The activation energy of the ammonia decomposition process has been found for samples with potassium as E a= 96 kJ/mol, for samples without potassium as E a= 87 kJ/mol.
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  • 56
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    Catalysis letters 64 (2000), S. 65-75 
    ISSN: 1572-879X
    Keywords: NO reduction ; CH3OH ; La2O3 ; methyl nitrite ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nitric oxide (NO) reduction by methanol was studied over La2O3 in the presence and absence of oxygen. In the absence of O2, CH3OH reduced NO to both N2O and N2, with selectivity to dinitrogen formation decreasing from around 85% at 623 K to 50–70% at 723 K. With 1% O2 in the feed, rates were 4–8 times higher, but the selectivity to N2 dropped from 50% at 623 K to 10% at 723 K. The specific activities with La2O3 for this reaction were higher than those for other reductants; for example, at 773 K with hydrogen a specific activity of 35 μmol NO/s m2 was obtained whereas that for methanol was 600 μmol NO/s m2. The Arrhenius plots were linear under differential reaction conditions, and the apparent activation energy was consistently near 14 kcal/mol with CH3OH. Linear partial pressure dependencies based on a power rate law were obtained and showed a near‐zero order in CH3OH and a near‐first order in H2. In the absence of O2, a Langmuir–Hinshelwood type model assuming a surface reaction between adsorbed CH3OH and adsorbed NO as the slow step satisfactorily fitted the data, and the model invoking two types of sites provided the best fit and gave thermodynamically consistent rate constants. In the presence of O2 a homogeneous gas‐phase reaction between O2, NO, and CH3OH occurred to yield methyl nitrite. This reaction converted more than 30% of the methanol at 300 K and continued to occur up to temperatures where methanol was fully oxidized. Quantitative kinetic studies of the heterogeneous reaction with O2 present were significantly complicated by this homogeneous reaction.
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  • 57
    ISSN: 1572-8757
    Keywords: kinetics ; isotope-exchange ; nitrogen ; adsorption ; methane ; zeolite ; equilibria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The Isotope Exchange Technique (IET) was used to simultaneously measure pure and binary gas adsorption equilibria and kinetics (self-diffusivities) of CH4 and N2 on pelletized 4A zeolite. The experiment was carried out isothermally without disturbing the adsorbed phase. CH4 was selectively adsorbed over N2 by the zeolite because of its higher polarizability. The multi-site Langmuir model described the pure gas and binary adsorption equilibria fairly well at three different temperatures. The selectivity of adsorption of CH4 over N2 increased with increasing pressure at constant gas phase composition and temperature. This curious behavior was caused by the differences in the sizes of the adsorbates. The diffusion of CH4 and N2 into the zeolite was an activated process and the Fickian diffusion model described the uptake of both pure gases and their mixtures. The self-diffusivity of N2 was an order of magnitude larger than that for CH4. The pure gas self-diffusivities for both components were constants over a large range of surface coverages (0 〈 θ 〈 0.5). The self-diffusivities of CH4 and N2 from their binary mixtures were not affected by the presence of each other, compared to their pure gas self-diffusivities at identical surface coverages.
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  • 58
    ISSN: 1572-8773
    Keywords: aromatic donor molecules ; horseradish peroxidase ; kinetics ; lactoperoxidase
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    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Based on kinetic evidence, it has been shown for the first time that the mode of binding of aromatic donor molecules is similar in horseradish peroxidase and lactoperoxidase; also that the nature of the heme plays an important role in the reaction with hydrogen peroxide, and has no effect on the reaction of the intermediate compound II with aromatic substrates.
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  • 59
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    Catalysis letters 31 (1995), S. 431-438 
    ISSN: 1572-879X
    Keywords: partial hydrogenation of benzene ; production of cyclohexene ; kinetics ; reaction mechanism ; ruthenium catalyst
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A method has been developed for direct measurement of reaction rates in a continuously operated slurry (CST-) reactor. In contrast to the usual procedure in a two-liquid-phase system the reactor contains only one liquid phase, an aqueous zinc chloride solution in which a ruthenium lanthanoxide catalyst is suspended. The selectivity of benzene hydrogenation with respect to cyclohexene is higher when the new one-liquid-phase procedure is applied. With decreasing degree of benzene conversion the selectivity with respect to cyclohexene approaches 100%. The conclusion is that cyclohexane is formed only by consecutive hydrogenation of cyclohexene.
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  • 60
    ISSN: 1572-879X
    Keywords: non-uniform surface ; kinetics ; ethanol ; oxidation ; molybdenum oxide
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Temkin's theory of rates of catalytic reactions on non-uniform surfaces is extended to the MoO3-catalyzed oxidation of ethanol to acetaldehyde. Two types of sites are assumed to be present, an oxygen atom site that can be modeled with uniform properties and a metal atom site characterized by non-uniform properties both for ethanol chemisorption to an ethoxide intermediate and the conversion of this intermediate to acetaldehyde. The rate-limiting step is the cleavage of a C-H bond in the absorbed ethoxide intermediate. Non-uniform surface kinetics leads to a kinetic rate expression of the form $$v = kP_{C_2 H_5 OH}^{1 - m} P_{O_2 }^{(1 - m)/4} P_{H_2 O}^{ - (1 - m)/2} $$ . Such a rate expression, withm=0.14, is shown to provide a good fit to kinetic data for the selective oxidation of ethanol on a silica supported molybdenum oxide catalyst.
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  • 61
    ISSN: 1572-879X
    Keywords: Ultraviolet heterogeneous photocatalysis ; oxidation ; trichloroethylene ; titania ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Kinetics of the gas/solid heterogeneous photocatalytic oxidation of dilute trichloroethylene (TCE) vapors by ultraviolet-illuminated titanium dioxide have been determined using a fixed-bed dynamic photoreactor. Reaction rate dependences on inlet TCE, oxygen and water vapor concentrations were found to consist of both reactant sensitive and insensitive regions. In the reactant sensitive regions, measured limiting apparent reaction rate orders for TCE, oxygen and water vapor are 0.8, 1.7 and — 3, respectively. Water vapor in the reactant stream lowersinitial reaction rates relative to corresponding water free conditions, but is required to sustain photocatalytic activity for extended periods of time.
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  • 62
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    Catalysis letters 36 (1996), S. 31-36 
    ISSN: 1572-879X
    Keywords: ethanol ; kinetics ; oxidation ; oxydehydrogenation ; platinum ; structure sensitivity
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of the platinum particle size was investigated for the catalytic oxidative dehydrogenation of aqueous ethanol to ethanal at a temperature of 303 K, an ethanol concentration of 260 mol m−3, a partial oxygen pressure 60 kPa, a pH of 9, and an ethanal and ethanoate concentration of 20 mol m−3. A particle size effect on the turnover frequency was observed but only for particle sizes smaller than 2 nm. Hence, the reaction shows a limited structure sensitivity.
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  • 63
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    Catalysis letters 55 (1998), S. 73-77 
    ISSN: 1572-879X
    Keywords: enantioselectivity ; hydrogenation of ethyl pyruvate ; Pt/alumina catalyst ; solvent effects ; kinetics ; solvent polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of solvent on the kinetics of enantioselective hydrogenation of ethyl pyruvate by Pt/Al2O3/dihydrocinchonidine is reported. In a non‐polar solvent, toluene, the reaction is approximately zero order in substrate at constant hydrogen pressure, while under the same conditions and at the same substrate concentration, in the polar solvents ethanol and propylene carbonate the reaction shows a first‐order substrate concentration dependence. Fits to a Michaelis–Menten rate expression show that these differences are the expression of the relative magnitudes of the adsorption term in the rate expression, which in turn reflects the influence of the solvent on the adsorption–desorption processes which take place at the catalyst surface.
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  • 64
    ISSN: 1572-879X
    Keywords: hydrogen ; desorption ; copper ; activation energy ; kinetics ; order of desorption
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of desorption of hydrogen from the copper component of an alumina-supported polycrystalline copper catalyst has been studied in detail by temperature-programmed desorption (TPD). Line-shape analysis of the hydrogen TPD spectra shows: (i) that the desorption is second order, (ii) that the desorption activation energy is in the range 64–68 kJ mol−1 in the coverage range 7–44% of a monolayer, and (iii) that the desorption pre-exponential term has a value ∼10−5 cm2 s−1 atom−1 consistent with the desorption being second order, involving mobile adsorbates and a mobile desorption transition state.
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  • 65
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    Catalysis letters 69 (2000), S. 103-107 
    ISSN: 1572-879X
    Keywords: dicyclopentadiene ; Wacker oxidation ; Pd(AcO)2 ; benzoquinone ; kinetics
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The oxidation of dicyclopentadiene catalyzed by palladium(II) acetate and benzoquinone in the presence of perchloric acid was studied. Tricyclodecenone in high selectivity (85–98%) at a conversion of dicyclopentadiene up to 76% was obtained. The kinetic model assumed the significant inhibition complexation between dicyclopentadiene and tricyclodecenone with the catalytic species.
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  • 66
    ISSN: 1432-1890
    Keywords: Key words Glomus mosseae ; Hydroponics ; Nitrate uptake ; Root respiration ; Triticum aestivum
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    Topics: Biology
    Notes: Abstract  Oxygen and CO2 fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO3 – uptake of the plants was used to estimate the amount of root respiration attributable to ion uptake. Plants were grown at 4 mM N and 10 μM P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O2 consumption and NO3 – uptake rates were similar and the CO2 release was higher in mycorrhizal than in non-mycorrhizal wheat. This resulted in a significantly higher respiratory quotient (RQ, mol CO2 mol–1 O2) in mycorrhizal (1.27±0.13) than in non-mycorrhizal (0.79±0.05) wheat. As the biomass and N and P concentrations in mycorrhizal and non-mycorrhizal wheat were the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition per se.
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  • 67
    ISSN: 1432-0789
    Keywords: Wheat ; Paddy straw compost ; N and P enrichment ; Rock phosphate ; Pyrite ; Triticum aestivum ; Nutrient uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A nutrient-rich compost from paddy straw was prepared using urea and Mussoorie rock phosphate for N and P enrichment respectively. Inorganic N was partly conserved in the compost by the addition of pyrite. Citric-acid-soluble P also increased with the addition of pyrite. Compost containing about 1.6% total N and 3.3% total P was found to be a good source of P for a wheat crop and also supplied a significant amount of N to the plants.
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  • 68
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    Biology and fertility of soils 9 (1990), S. 281-282 
    ISSN: 1432-0789
    Keywords: Surface sterilization ; Contaminants ; Sterile plant selection ; Axenic seedlings ; Triticum aestivum ; Trifolium pratense ; Trifolium repens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Sterile seedlings are required for the investigation of interactions between microorganisms and plants. The present study was designed to develop a simple and reliable method for the selection of sterile seedlings by the use of liquid nutrient media, avoiding some of the disadvantages of solid media. The method of germinating surface-sterilized seedlings on solid water agar or nutrient media was compared with our method for sterility control in nutrient broth. Sterile plant selection in liquid media was the most sensitive method for detecting bacterial and fungal contaminants. Sterile plants grow with the same vigour as unsterilized plants and can be used for sterile plant experiments.
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  • 69
    ISSN: 1432-0789
    Keywords: 15N-labelled fertilizer ; Added N interaction Fertilizer N uptake ; Soil N uptake ; Wheat ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of 15N-labelled ammonium nitrate, urea and ammonium sulphate on yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L. cv. Mexi-Pak-65) were studied in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 64.0–74.8%, 61.5–64.7% and 61.7–63.4% of the N from ammonium nitrate, urea and ammonium sulphate, respectively. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea and ammonium sulphate. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the three N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied with the method of application of fertilizer N. Ammonium nitrate, urea and ammonium sulphate gave 59.3%, 42.8% and 26.3% more added N interaction, respectively, when applied by the broadcast/worked-in method than with band placement. A highly significant correlation between soil N and grain yield, dry matter and added N interaction showed that soil N was more important than fertilizer N in wheat production. A values were not significantly correlated with added N interaction (r=0.719). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N stood proxy for unlabelled soil N.
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  • 70
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    Biology and fertility of soils 3 (1987), S. 199-204 
    ISSN: 1432-0789
    Keywords: Phosphatases ; Rhizosphere ; Organic phosphorus ; Allium cepa ; Brassica oleracea ; Triticum aestivum ; Trifolium alexandrinum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The distribution of phosphatase activity and of phosphate fractions of the soil in the proximity of roots was studied in order to evaluate the significance of phosphatases in P nutrition of various plants (Brassica oleracea, Allium cepa, Triticum aestivum, Trifolium alexandrinum). A considerable increase in both acid and alkaline phosphatase activity in all the four soil-root interfaces was observed. Maximum distances from the root surface at which activity increases were observed ranged from 2.0 mm to 3.1 mm for acid phosphatase and from 1.2 mm to 1.6 mm for alkaline phosphatase. The increase in phosphatase activity depended upon plant age, plant species and soil type. A significant correlation was noticed between the depletion of organic P and phosphatase activity in the rhizosphere soil of wheat (r = 0.99**) and clover (r = 0.97**). The maximum organic P depletion was 65% in clover and 86% in wheat, which was observed within a distance from the root of 0.8 mm in clover and 1.5 mm in wheat. Both the phosphatases in combination appear to be responsible for the depletion of organic P.
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  • 71
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    Biology and fertility of soils 23 (1996), S. 327-331 
    ISSN: 1432-0789
    Keywords: CO2 emission ; Field method ; Soil respiration ; Triticum aestivum ; Soil moisture ; Carbon reservoirs ; Greenhouse effect ; Grey forest soil ; Mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of the rate of CO2 evolution from soil in fallow and croplant under spring wheat (Triticum aestivum L.) was studied in a crop rotation in grey forest soil of the Baikal forest-steppe during the growing season and in different years. It was shown that the regional characteristics of soils and hydrothermal conditions in different years affect the rate of CO2 evolution in agroecosystems. The seasonal dynamics of CO2 is characterized by insignificant changes in the autumn to spring period and enhanced emission in hot and dry summers. CO2 evolution is assumed to increase due to enhanced mineralization and partial diffusion from the carbonate horizon at the depth of the seasonal frost. During the growing season the dynamics of CO2 evolution depends on the soil moisture regime. There was a strong correlation between the rate of CO2 emission and soil moisture in the particularly dry year of 1993 (η=0.86) and a moderate correlation in the other years (η=0.38–0.54). The effect of the previous crop and fertilizer application on the rate of CO2 emission was insignificant. In a continuous fallow the total carbon release into the atmosphere varied throughout the years studied from 558 to 1880 kg ha-1. Humus losses varied from 0.9% to 3.1%.
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  • 72
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    Biology and fertility of soils 5 (1987), S. 76-82 
    ISSN: 1432-0789
    Keywords: Biomass accumulation ; Decomposition ; Litter ; Soil organic matter ; Soil respiration ; 14C deposition ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In a field experiment with 14C-labeled winter wheat conducted in the north-central region of the United States, crop-accumulated carbon (grain excluded) returned to the soil was found to be 542 g m−2 year−1. Almost half of the carbon from the underground compartment was released in the form of CO2 during the first 3 months after harvest due to very favorable conditions for biological activity. After 18 months, no less than 80% of the carbon from the plant residues was mineralized. About 16% of straw carbon and 24% of root carbon was transferred into soil organic matter. The annual rate of soil organic matter decomposition was approximated as 1.7%.
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  • 73
    ISSN: 1432-0789
    Keywords: Triticum aestivum ; T. turgidum ; Nitrogen fixation ; Field inoculation ; Acetylene reduction assay (ARA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Eight commercial Israeli spring wheat cultivars (six Triticum aestivum and two T. turgidum) grown with 40 and 120 kg N/ha were tested for responses to inoculation with Azospirillum brasilense. At the low level of N fertilization (40 kg/ha), five cultivars showed significant increases in plant dry weight measured at the milky ripe stage; however, by maturation only the cultivar “Miriam” showed a significant increase in grain yield. Two cultivars, which had shown a positive inoculation effect at the earlier stages, had a significant decrease in grain yield. No significant effect of inoculation was found at the high N level. To confirm those results, four wheat (T. aestivum) cultivars were tested separately over 4 years in 4 different locations under varying N levels. Only Miriam showed a consistently positive effect of Azospirillum inoculation on grain yield. Inoculation increased the number of roots per plant on Miriam compared with uninoculated plants. This effect was found at all N levels. Nutrient (N, P and K) accumulation and number of fertile tillers per unit area were also enhanced by Azospirillum, but these parameters were greatly affected by the level of applied N. It is suggested that the positive response of the spring wheat cultivar “Miriam” to Azospirillum inoculation is due to its capacity to escape water stresses at the end of the growth season.
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  • 74
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    Biology and fertility of soils 23 (1996), S. 327-331 
    ISSN: 1432-0789
    Keywords: Key words CO2 emission ; Field method ; Soil respiration ; Triticum aestivum ; Soil moisture ; Carbon reservoirs ; Greenhouse effect ; Grey forest soil ; Mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of the rate of CO2 evolution from soil in fallow and cropland under spring wheat (Triticum aestivum L.) was studied in a crop rotation in grey forest soil of the Baikal forest-steppe during the growing season and in different years. It was shown that the regional characteristics of soils and hydrothermal conditions in different years affect the rate of CO2 evolution in agroecosystems. The seasonal dynamics of CO2 is characterized by insignificant changes in the autumn to spring period and enhanced emission in hot and dry summers. CO2 evolution is assumed to increase due to enhanced mineralization and partial diffusion from the carbonate horizon at the depth of the seasonal frost. During the growing season the dynamics of CO2 evolution depends on the soil moisture regime. There was a strong correlation between the rate of CO2 emission and soil moisture in the particularly dry year of 1993 (η=0.86) and a moderate correlation in the other years (η=0.38–0.54). The effect of the previous crop and fertilizer application on the rate of CO2 emission was insignificant. In a continuous fallow the total carbon release into the atmosphere varied throughout the years studied from 558 to 1880 kg ha–1. Humus losses varied from 0.9% to 3.1%.
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  • 75
    ISSN: 1432-0789
    Keywords: Key words Phosphate-solubilizing microorganisms ; Mussoorie rock phosphate ; Vesicular-arbuscular mycorrhizae ; Triticum aestivum ; Nutrient-deficient soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effect of inoculating wheat (Triticum aestivum L.) with the PO4 3–-solubilizing microorganisms (PSM) Bacillus circulans and Cladosporium herbarum and the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus sp. 88 with or without Mussoorie rock phosphate (MRP) amendment in a nutrient-deficient natural sandy soil was studied. In the sandy soil of low fertility root colonization by VAM fungi was low. Inoculation with Glomus sp. 88 improved root colonization. At maturity, grain and straw yields as well as N and P uptake improved significantly following inoculation with PSM or the VAM fungus. These increases were higher on combined inoculation of PSM and the VAM fungus with MRP amendment. In general, a larger population of PSM was maintained in the rhizosphere of wheat in treatments with VAM fungal inoculation and MRP amendment. The results suggest that combined inoculation with PSM and a VAM fungus along with MRP amendment can improve crop yields in nutrient-deficient soils.
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  • 76
    ISSN: 1432-0789
    Keywords: Azospirillum brasilense ; Triticum aestivum ; Inoculation ; N and dry matter yield ; N percentages in plant parts ; Associative N2 fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Wheat plants (Triticum aestivum) grown in pots and in the field under the Mediterranean climate of the south of France were inoculated with a strain of Azospirillum brasilense. Comparisons with non-inoculated plants grown under the same conditions showed significant responses to inoculation with an increase in the number of fertile tillers, shoot and root dry weight, and root to shoot biomass ratio. The roots of inoculated plants attracted relatively more assimilates than those of the control plants until a late stage of growth (heading stage) but the rhizosphere respiration expressed per unit of root growth was not increased by inoculation. Nitrogen yield, both total and in grains, was also enhanced; however, N percentages of all aerial parts of the plants grown in pots were always statistically lower after inoculation than in the control. At maturity, the N % in seeds was 1.81 and 2.45, respectively. The possible mechanisms of this effect of inoculation under the experimental conditions of this study are discussed.
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    Biology and fertility of soils 23 (1996), S. 273-281 
    ISSN: 1432-0789
    Keywords: Wheat ; Triticum aestivum ; Rhizosphere ; Soil microflora ; Gram-negative bacteria ; API 20 NE ; Flavobacterium spp ; Cytophaga
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We identified 161 Gram-negative bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into seven groups based on major morphological and physiological properties. Taxonomic allocation of the groups was verified by guanine+cytosine contents of DNA. Except for one group, which may be assumed to include bacteria belonging to the genera Flavobacterium and Cytophaga, the various groups were taxonomically united. The distribution of the groups changed with soil improvement. Pseudomonads predominated in unimproved soil, but Flavobacterium and Cytophaga spp. were predominant in the most improved soil. As all the strains were non-fermentative by Hugh and Leifson's test, API 20NE identification was applied. However, many strains were misidentified by this system, especially in the Flavobacterium and Cytophaga spp. group. For ecological studies, the strains were classified to species level by the API 20 NE system and by the results of a combination of guanine+cytosine (mol%) and isoprenoid quinone data. The pattern of distribution of the bacteria on the root surface of wheat varied at species level within one genus depending on soil conditions.
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  • 78
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    Biology and fertility of soils 7 (1988), S. 67-70 
    ISSN: 1432-0789
    Keywords: Root activity ; Soil C mineralization ; 14C-labelled plant material ; Decomposition stages ; Wheat ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two different soils were amended with 14C-labelled plant material and incubated under controlled laboratory conditions for 2 years. Half the samples were cropped with wheat (Triticum aestivum) 10 times in succession. At flowering, the wheat was harvested and the roots removed from the soil, and a new crop was started. Thus, the soil was continuously occupied by predominantly active root systems. The remaining samples were maintained without plants under the same conditions. The aim of the experiment was to study the effects of active roots on C-mineralization rates during different stages of decomposition and during long-term incubation. During the first 200 days, corresponding to the active decomposition stages, the roots weakly reduced 14C mineralization. With a lower level of decomposition, when more than 60% of the initial 14C was mineralized and when the available nutrients were markedly exhausted by plant uptake, the roots stimulated 14C mineralization.[/ p]
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  • 79
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    Biology and fertility of soils 7 (1988), S. 71-78 
    ISSN: 1432-0789
    Keywords: Root activity ; Rhizosphere ; C metabolism ; Microbial biomass ; Microbial activity ; Wheat ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two different soils were amended with 14C-labelled plant material and incubated under controlled laboratory conditions for 2 years. Half the samples were cropped with wheat (Triticum aestivum) 10 times in succession. At flowering, the wheat was harvested and the old roots removed from the soil, so that the soil was continuously occupied by predominantly active root systems. The remaining samples were maintained without plants under the same conditions. During the initial stages of high microbial activity, due to decomposition of the labile compounds, the size of the total microbial biomass was comparable for both treatments, and the metabolic quotient (qCO2-C = mg CO2-C·mg−1 Biomass C·h−1) was increased by the plants. During the subsequent low-activity decomposition stages, after the labile compounds had been progressively mineralized, the biomass was multiplied by a factor of 2–4 in the presence of plants compared to the bare soils. Nevertheless, qCO2-C tended to reach similar low values with both treatments. The 14C-labelled biomass was reduced by the presence of roots and qCO2-14C was increased. The significance of these results obtained from a model experiment is discussed in terms of (1) the variation in the substrate originating from the roots and controlled by the plant physiology, (2) nutrient availability for plants and microorganisms, (3) soil biotic capacities and (4) increased microbial turnover rates induced by the roots.
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  • 80
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    Biology and fertility of soils 4 (1987), S. 37-40 
    ISSN: 1432-0789
    Keywords: Azospirillum brasilense ; Azospirillum amazonense ; rate reductase ; Inoculation ; Wheat ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Three field experiments with wheat were conducted in 1983, 1984, and 1985 in Terra Roxa soil in Paraná, the major Brazilian wheat-growing region, to study inoculation effects of various strains of Azospirillum brasilense and A. amazonense. In all three experiments inoculation with A. brasilense Sp 245 isolated from surface-sterilized wheat roots in Paraná produced the highest plant dry weights and highest N% in plant tops and grain. Grain yield increases with this strain were up to 31 % but were not significant. The application of 60 or 100 kg N ha−1 to the controls increased N accumulation and produced yields less than inoculation with this strain. Another A. brasilense strain from surface-sterilized wheat roots (Sp 107st) also produced increased N assimilation at the lower N fertilizer level but reduced dry weights at the high N level, while strain Sp 7 + Cd reduced dry weights and N% in the straw at both N levels. The A. amazonense strain isolated from washed roots and a nitrate reductase negative mutant of strain Sp 245 were ineffective. Strains Sp 245 and Sp 107st showed the best establishment within roots while strain Cd established only in the soil.
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  • 81
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    Biology and fertility of soils 4 (1987), S. 41-46 
    ISSN: 1432-0789
    Keywords: Competition ; Migration ; Colonization potential ; Replica printing ; Triticum aestivum ; Pseudomonas fluorescens ; Bacillus subtilis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Colonization patterns of Pseudomonas fluorescens and Bacillus subtilis on roots of wheat seedlings growing on water agar were studied qualitatively by replica printing and quantitatively by the plate count method. The results indicated a stronger colonization potential for P. fluorescens (up to 107 cfu/cm root) than for B. subtilis (up to 105 cfu/cm root). Although the numbers of both species were lower when inoculated together, the observed colonization patterns on the roots were comparable to those found with single inoculations. For none of these bacteria was active migration along the root surface in any direction observed, indicating that distal positions are reached mainly by a passive displacement on the root tip and elongating cells. Ecological implications of the observed phenomena are discussed.
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  • 82
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    Biology and fertility of soils 5 (1987), S. 31-35 
    ISSN: 1432-0789
    Keywords: Gaeumannomyces graminis ; VegVetative growth ; Pathogenicity ; Herbicides ; Diquat+paraquat ; Glyphosate ; Dicamba ; Trifluralin ; Chlorsulfuron ; Chlorthal dimethyl ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effects of Spray Seed (diquat + paraquat), Roundup (glyphosate), Banvel-D (dicamba), Treflan (trifluralin), Glean (chlorsulfuron) and Dacthal (chlorthal dimethyl) at concentrations of 0–500 ppm product on the vegetative growth, vigour and pathogenicity of Gaeumannomyces graminis var. tritici (Ggt) on wheat were examined. All herbicides with the exception of dicamba and chlorsulfuron inhibited fungal growth on potato dextrose agar (PDA) at concentrations 10–500-fold of rates recommended for use in the field. The vegetative growth of the pathogen growing out of straw colonized on PDA supplemented with 100 ppm diquat + paraquat or glyphosate was reduced by 47.4% and 42.4%, respectively. When portions of these colonies were subcultured onto unamended PDA, their growth and the pathogenicity of straw pieces colonized by these subcultures were found to be unaltered. Straw colonized by Ggt on agar amended with concentrations of diquat + paraquat or at all concentrations of glyphosate produced less root disease in wheat seedlings in comparison to those colonized on unamended agar. It is proposed that the reduced pathogenicity of inocula prepared on agar amended with these two herbicides is due to poor colonization by the pathogen of straw on these media, and that a similar effect on saprophytic colonization in the field could lead to a reduction in the field inocula of the pathogen.
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  • 83
    ISSN: 1432-0789
    Keywords: Biopores ; Root growth ; Transpiration ; Simulations ; Mechanical impedance ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The use of vertical biopores by wheat (Triticum aestivum) seminal roots for easy access to the subsoil and the consequences for plant water supply and yield has been investigated by computer simulation. Parameters included were: biopore density and diameter, depth of cultivation and strength of the subsoil — all under a wide range of seasonal weather conditions. The model predicts that biopores add significantly to root penetration at depth, even at a density of 0.1% v/v of small, vertical pores, while 1.5% to 2.0% v/v can ensure maximum root penetration. When the growing season is shorter a larger number of biopores is needed to ensure timely root penetration to depth. With shallow tillage, biopores occur closer to the soil surface, and their importance is increased. Deeper root penetration invariably gives greater water uptake and transpiration, but may have a negative effect on grain yield, especially under the driest climatic conditions. An increase in early water use may result in less soil water being available during the grain-filling period. The effect of biopores on plant transpiration varies from year to year, depending on the amount of rain and its distribution in time, and on the amount of soil water stored at time of sowing.
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  • 84
    ISSN: 1432-0983
    Keywords: Secale cereale ; Triticum aestivum ; Ribosomal RNA genes ; Mitochondrial DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The mitochondrial 18S and 5S ribosomal RNA (rRNA) genes of rye, plus a total of about 90 kilobase pairs of flanking DNA, have been cloned and maps of restriction enzyme cleavage sites have been constructed. Like their homologs from hexaploid wheat, the rye genes are closely linked and are part of a three-copy family of recombining repeats (the “18S/5S repeat”). The rye repeat probably also contains a mitochondrial tRNAfMet gene, which the wheat repeat is known to carry. However, despite the overall organizational similarity between the wheat and rye 18S/5S repeats in the immediate vicinity of their coding regions, extensive rearrangement of flanking sequences has taken place during evolutionary divergence of the two species. Our data provide additional support for an emerging picture of plant mitochondrial genomes as evolving much more rapidly in structure than in sequence.
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  • 85
    ISSN: 1432-0983
    Keywords: Triticum aestivum ; Plant mitochondrial DNA ; Ribosomal genes ; Sequence rearrangements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nucleotide sequence of the wheat mitochondrial 26S ribosomal RNA gene and flanking regions was determined and compared with mitochondrial 26S rRNA genes from maize and Oenothera. All three genes exhibit a high degree of homology except within two variable regions. When the plant mitochondrial 26S rRNA genes are compared with Escherichia coli 23S rRNA and chloroplast 23S and 4.5S rRNA genes, a third variable region is apparent close to the 3′ end of the gene. The 5′ and 3′ ends of the wheat mitochondrial gene were determined by S1 nuclease mapping. Computer analysis of the wheat mitochondrial gene revealed several small sequences present either in the 5′ region of the 26S rRNA gene or in the 18S rRNA gene.
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  • 86
    ISSN: 1432-0983
    Keywords: Light regulation ; psbN ; Triticum aestivum ; Etioplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The nucleotide sequence of a region of wheat chloroplast DNA containing the psbB gene for the 47 kDa chlorophyll a-binding protein of photosystem II has been determined. The gene encodes a polypeptide of 508 amino acid residues which is predicted to contain six hydrophobic membrane-spanning regions. The psbB gene is located 562 bp upstream of the psbH gene for the 10 kDa phosphoprotein of photosystem II. A small open reading frame of 38 codons is located between psbB and psbH, and on the opposite strand the psbN gene, encoding a photosystem II polypeptide of 43 amino acid residues, is located between orf38 and psbH. S1 nuclease mapping indicated that the 5′ ends of transcripts were located 371 and 183 bp upstream of the psbB translation initiation codon. Predominant transcripts of 2.1 kb and 1.8 kb for psbB and 0.4 kb for psbH were present in RNA isolated from etiolated and greening wheat seedlings. Immunodecoration of Western blots indicated that the 47 kDa polypeptide was absent, or present in very low amounts, in dark-grown tissue and accumulated on greening, whereas the 10 kDa polypeptide was present in similar amounts in both dark-grown and greening seedlings. The 10 kDa polypeptide was phosphorylated in vitro by incubating wheat etioplast membranes with [γ3 2P] ATP.
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  • 87
    ISSN: 1432-0983
    Keywords: Triticum aestivum ; Genomic variability ; Mitochondrial DNA ; Somatic tissue culture ; Regeneration ability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Embryogenic and non-embryogenic long-term callus cultures of hexaploid wheat exhibit differences in the organization of their mitochondrial genome. Embryogenic and non-embryogenic fractions of callus cultures initiated from immature embryos of the wheat cultivar “Chinese Spring” have been isolated and subsequently subcultured. DNA-DNA hybridization experiments using labelled cloned wheat mitochondrial DNA fragments have shown that the mitochondrial DNA organization of embryogenic subcultures derived from embryogenic parts of “Chinese Spring” calli is closely related to that of the initial “Chinese Spring” calli, while non-embryogenic subcultures derived from non-embryogenic fragments of “Chinese Spring” calli exhibit a mitochondrial DNA organization similar to that found in non-embryogenic calli derived from cultivar “Aquila”. In addition, somatic tissue cultures initiated from three other non-embryogenic wheat cultivars (“Talent”, “Thésée” and “Capitole”) display mitochondrial DNA arrangements similar to those found in cultivar “Aquila”. These results strongly suggest that, in wheat callus cultures, a particular mitochondrial genome organization is correlated with the ability of cultured cells to regenerate whole plants.
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  • 88
    ISSN: 1432-0983
    Keywords: Triticum aestivum ; Mitochondrial DNA ; Chloroplast DNA ; ATPase alpha subunit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An internal part of the chloroplast atpA gene has been identified in the mitochondrial DNA of Triticum aestivum. It is located near the 18S-5S ribosomal genes and partially contained within a repeated sequence. Comparison of the transferred sequence with the original ct sequence reveals several nucleotide changes and shows that neither 5′ nor 3′ ends are present in the mt genome. No transcript of this region could be detected by Northern analysis. This sequence is present in mitochondrial genomes of other tetraploid and diploid species of Triticum, also in the vicinity of the 18S-5S ribosomal genes, suggesting a unique transfer event. The date of this event is discussed.
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  • 89
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    Microchimica acta 94 (1988), S. 277-278 
    ISSN: 1436-5073
    Keywords: kinetics ; FT-IR ; temporal resolution
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    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.
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    Microchimica acta 94 (1988), S. 323-328 
    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.
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  • 91
    ISSN: 1436-5073
    Keywords: flow injection analysis (FIA) ; mercury ; porphyrin ; kinetics ; spectro-photometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 5,10,15,20-tetrakis(3-chloro-4-sulfophenyl)porphine (m-Cl-TPPS4) was synthesized and used for the Spectrophotometric determination of mercury by flow injection analysis. A pseudo-first-order reaction kinetic mechanism was proposed with a rate constant of 0.8 min−1 for Hg(II) withm-Cl-TPPS4 in the presence of 8-hydroxyquinoline in a medium of 1.0M acetic acid and sodium acetate buffer solution (pH 6.22). In the optimum conditions of reaction temperature (85 ° C), stopped-flow time (60 s) and sampling volume (100 μl), the method's relative standard deviation was 0.82% (n = 12) at 5.0 μg ml−1 mercury, with a linear range of 0–12.0 μg ml−1 and an analytical frequency of 60h−1. The detection limit (3σ) was 0.025 μg ml−1. Interference studies showed that most metal ions co-existing with Hg2+ could be tolerated at 100-fold excess levels, but Zn2+, Cu2+ and Mn2+ needed to be masked. The method has been applied to the analysis of water samples with satisfactory results.
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  • 92
    ISSN: 1436-5073
    Keywords: atrazine ; terbuthylazine ; sequential binding ; kinetics ; cross-reactivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Immunoassays for triazine herbicides were tested for their reaction to the variation of the tracer incubation time. By application of a sequential technique the measuring range of atrazine could be expanded to five decades and the total duration of the test could be reduced to about 30 min. In an optimized version a lower detection limit of 9 pmol/l (2 ng/l) was achieved. The detection limit of a sensitive immunoassay for terbuthylazine is also below the concentration limit demanded of the German drinking water regulation (100 ng/l) and reaches 130 pmol/l (30 ng/l). Short tracer incubation times did not lead to increased cross-reactivities in contrast to theoretical models [1, 2]. Different mechanisms, which could cause a shift of the center point of the calibration curve, are discussed, including kinetic considerations.
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  • 93
    ISSN: 1436-5073
    Keywords: kinetics ; rates ; integrating ratemeter ; optimization ; first-order
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The integrating ratemeter is used in concert with the two-rate parameter to form the integrating ratemeter two-rate parameter. Propagation of error theory is applied to the integrating ratemeter two-rate parameter to yield expressions for the precision of rates calculated from the integrating ratemeter two-rate parameter in terms of the precision of the rates measured with the integrating ratemeter. Simulations and experimental results show that in cases where the standard deviation of the rate is relatively constant, the optimum time to make a rate measurement using the integrating ratemeter is also the optimum time to measure either of the rates in the two-rate parameter. If either of the two rates comprising the two-rate parameter is measured at the optimum time, then the precision and accuracy of concentrations measured with this technique are optimized.
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    Biodegradation 4 (1993), S. 163-170 
    ISSN: 1572-9729
    Keywords: factorial analysis ; kinetics ; methane ; methanotrophs ; nutrients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of different mineral nutrients on the kinetics of methane biodegradation by a mixed culture of methanotrophic bacteria was studied. The substrate factors examined were ammonia, iron, copper, manganese, phosphate, and sulphide. The presence of iron in the growth medium had a strong effect on the yield coefficient. Yield coefficients up to 0.49 mg protein per mg methane were observed when iron was added at concentrations of 0.10–5.0 mg/l. Iron addition also increased the maximum methane utilization rate. The same effect was observed after addition of ammonium to a medium where nitrate was the only nitrogen source. The observed Monod constant for methane utilization increased with increasing concentration of ammonia. This shows that ammonia is a weak competitive inhibitor as observed by other researchers. Relatively high levels of both ammonia (70 mg/l) and copper (300 µg/l) inhibited the methane degradation, probably due to the toxic effect of copper-amine complexes.
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    Nutrient cycling in agroecosystems 20 (1989), S. 59-66 
    ISSN: 1573-0867
    Keywords: Ammonia volatilization ; nitrogen leaching ; denitrification ; time of N application ; wheat ; Triticum aestivum ; Triticale ; irrigation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Grain yield, nitrogen (N) assimilation, ammonia (NH3) volatilization, denitrification and fertilizer N distribution were examined in three commercially grown cereal crops; two were sown into conventionally tilled fields, while the third was direct drilled into an untilled field. The crops were top dressed with urea at establishment, tillering or ear initiation. Crop yield and N assimilation were measured in 16 m by 2.5 m plots receiving 0, 35, 70, 105, 140 or 175 kg N ha−1. A mass balance micrometeorological technique was used to measure NH3 volatilization, and other fertilizer N transformations and transfers were studied using15N labelled urea in microplots. On the conventionally tilled sites application of urea increased the grain yield of wheat from 3.9 to 5.5 t ha−1, when averaged over the five application rates, three application times and two sites. There were no site or application time effects. However, on the direct drilled site, time of application had a significant effect on grain yield. When urea was applied at establishment, grain yield was not significantly increased and the mean yield (2.81 t ha−1) was less than that obtained from treatments fertilized at tillering or ear initiation (4.09 and 4.0 t ha−1, respectively). Much of the variation in grain yield at the no-till site could be ascribed to differences in NH3 volatilization. At the no-till site, NH3 losses were equivalent to 24, 12 and 1% of the N applied at establishment, tillering and ear initiation, respectively. Negligible volatilization of NH3 occurred at the other sites. The surface soil at the no-till site had the highest urease activity and the soil was covered with alkaline ash resulting from stubble burning. Plant recovery of fertilizer N did not vary with application time on conventionally tilled sites (mean 62%). However, plant recovery of15N applied to the no-till site at establishment (35% of the applied N) was significantly less than that from plots where the application was delayed (45% at tillering and 55% at ear initiation, respectively). Leaching of N to below 300 mm depth was minimal (0 to 5% of the applied N). The calculated denitrification losses ranged from 1% to 14% of the applied N. The results show that the relative importance of NH3 volatilization, leaching and denitrification varied with site and fertilization time. The importance of the various N loss mechanisms needs to be taken into account when N fertilization strategies are being developed.
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    Nutrient cycling in agroecosystems 40 (1994), S. 207-214 
    ISSN: 1573-0867
    Keywords: available P ; citrate insoluble P ; phosphorus sources ; triple superphosphate ; Triticum aestivum ; water soluble P ; wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A greenhouse study was conducted to determine if soil pH affects the requirement for water-soluble P and the tolerance of water-insoluble impurities in TSP fertilizers. Two commercial TSP fertilizers were selected to represent a range in phosphate rock sources and impurities. Phosphate fertilizer impurities were isolated as the water-washed fraction by washing whole fertilizers with deionized water. TSP fertilizers with various quantities of water-soluble P (1.2 to 99% water-soluble P) were simulated by mixing the water-washed fertilizer fractions or dicalcium phosphate (DCP) with reagent-grade monocalcium phosphate (MCP). The fertilizers were applied to supply 40 mg AOAC available P kg−1 to a Mountview silt loam (fine-silty, siliceous, thermic Typic Paleudults). Wheat (Triticum aestivum (L.)) was harvested at 49 and 84 days after planting. Soil pH values at the final forage harvest were 5.4±0.16 and 6.4±0.15. At a soil pH of 5.4, the TSP fertilizers required only 37% water-soluble P to reach maximum yields while at pH 6.4 the fertilizers required 63% water-soluble P. Results of this study show that higher levels of water -insoluble P can be tolerated in TSP fertilizers when applied to acid soils. Phosphorus uptake was not affected by soil pH, but for the mixtures containing the fertilizer residues the source having the lowest level of Fe and Al had a higher relative agronomic effectiveness.
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    Nutrient cycling in agroecosystems 51 (1998), S. 209-215 
    ISSN: 1573-0867
    Keywords: Desorption ; kinetics ; microbial transformation ; phosphate ; soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The improvement of P management in agriculture and environment requires a good understanding of residual effect of applied P in soils. The specific adsorption of P on variable charge minerals has been considered as the major mechanism that leads to a very low utilization of P fertilizer by crops within a growing season in Chinese red soils. Soil incubation and isotope tracing analysis were carried out to examine the transformation kinetics and potential availability of added specifically sorbed 32P in two pH contrasting light textured soils. The 32P recovered by 0.5 M NaHCO3 extraction and microbial biomass-P measurement from the added specifically sorbed 32P in the soils was well described by a first-order reaction and a Langmuir-type kinetic model, with correlation coefficients (R) being, on average, 0.938 and 0.959, respectively. The half-life (t1/2, from the first-order model) of the four tested mineral-P complexes ranged from 29 to 47 d in the acid sandy soil and 33 to 105 d in the neutral silty soil. Goethite-P was the most stable among the four tested mineral-P complexes. The potential availability of the mineral complex P (q m , in percent of total 32P added) obtained from the Langmuir equation ranged from 43.7 to 90.9% for the four mineral-P complexes, and decreased in the order: Al oxide-P (90.9%) 〉 montmorillonite-P (86.2%) 〉 kaolinite-P (77.5%) 〉 goethite-P (60.2%) in the acid sandy soil, whereas the order was Al oxide-P (89.3%) 〉 kaolinite-P (86.2%) 〉 montmorillonite-P (82.6%) 〉 goethite-P (43.7%) in the neutral silty soil. Based on the release rate and potential availability, kaolinite-P and Al oxide-P could be important sources for residual effect of applied P in variable-charge soils. The goethite-P has the lowest release rate and potential availability among the mineral-P complexes, implying that iron oxides may be the most important variable-charge mineral responsible for P fixation in the Chinese red soils.
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    Nutrient cycling in agroecosystems 53 (1999), S. 157-175 
    ISSN: 1573-0867
    Keywords: Brassica napus ; Cicer arietinum ; current P ; Lens culinaris ; Lupinus albus ; Lupinus angustifolius ; P concentration response ; P content response ; Pisum sativum ; previous P ; sigmoid response ; single superphosphate ; Triticum aestivum ; Vicia faba ; yield response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphorus (P) is a major deficiency of soils of south-western Australia (WA). The fertilizer P requirements are not known for grain legumes being evaluated for neutral to alkaline, fine textured soils in WA. To rectify this, glasshouse and field experiments were undertaken to compare the responses of several grain legume species, wheat and canola to applications of single superphosphate and the results are reported in this paper. The glasshouse experiments measured responses of dried tops, harvested at 26 to 42 days after sowing, to P that was freshly-applied (current P) and previously-applied (previous P). Responses in the glasshouse were measured using yield, P concentration and P content (P concentration multiplied by yield) of oven dried tops of the following: wheat (Triticum aestivum), canola (Brassica napus), faba bean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), field pea (Pisum sativum), albus lupin (Lupinus albus) and narrow leaf lupin (Lupinus angustifolius). Field experiments in 1994 and 1995 compared seed (grain) yield responses of faba bean, chickpea, lentil, albus lupin and wheat to applications of current P. The P was banded (drilled) with the seed while sowing at 5 cm depth. Canola and wheat produced very large yield responses to increasing applications of current P. Responses were much smaller for albus lupin, faba bean and chickpea. Responses for lentil, narrow leaf lupin and field pea, fell in between responses of the small and large seeded species. Similar trends for responses were obtained as measured using yield, P concentration, or P content. For soils treated with previous P, similar trends were observed as for current P, but differences in yield responses between species were much less marked and the response curves tended to become more sigmoid. In the field experiments, grain yield responses to current P of albus lupin and chickpea were less than that for wheat. Relative to wheat, faba bean was the most responsive grain legume to applications of current P, with lentil producing similar responses to wheat in one experiment at a newly cleared, P deficient site.
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    Nutrient cycling in agroecosystems 56 (2000), S. 59-68 
    ISSN: 1573-0867
    Keywords: bicarbonate-extractable potassium ; muriate of potash ; potassium ; potassium chloride ; relative effectiveness ; silicate rock powder ; Triticum aestivum ; Trifolium subterraneum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Granite (silicate) rock dust, a by-product of quarry operations, is being advocated and used as a fertilizer in the wheatbelt of south-western Australia (WA). The dust is insoluble and based on its nutrient element content (1.9% K and 0.3%P and negligible N) it is not expected to be a useful fertilizer. Previous laboratory studies and glasshouse experiments in WA suggest the dust is a slow release K fertilizer. This paper extends the previous studies to consider the dust as an NP or K fertilizer in the year of application in a field experiment on a soil deficient in N, P and K. In addition, the effectiveness of the dust as a K fertilizer was compared with the effectiveness of KCl (muriate of potash), the K fertilizer used in WA at present, in glasshouse experiments using K deficient soils. In the field experiment, compared with NP fertilizer or NPK fertilizer (urea, supplying N; superphosphate, providing P, S, Ca, Cu, Zn and Mo; KCl providing K), the dust had no effect on grain yield of wheat (Triticum aestivum); in fact dust applied at 20 t ha-1, for unknown reasons, reduced yields by about 65% compared to the nil (no fertilizer, no dust) treatment. Relative to the nil treatment, applying NPK fertilizer increased yields about threefold, from 0.54 to 1.79 t ha. The glasshouse experiments showed that, relative to KCl, the dust was from about 0.02 to 14% as effective in K deficient grey sandy soils for producing dried tops of 30-day old wheat plants or 42-day old clover (Trifolium subterraneum) plants. In soils with adequate K (yellow sands, sandy loams or clays, loamy clays, clay loams and clays), neither KCl nor the dust affected yields of 30 to 42-day old wheat or clover plants grown in the glasshouse. In the glasshouse experiments, no yield depressions were measured for the dust applied up to 17 g dust per kg soil (equivalent to 17 t dust ha-1 mixed into the top 10 cm of soil in the field). It is concluded that the dust has no value as a fertilizer.
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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    Nutrient cycling in agroecosystems 56 (2000), S. 117-123 
    ISSN: 1573-0867
    Keywords: labelled nitrogen ; Lolium perenne ; nitrogen cycling ; root biomass ; straw ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Large amounts of nitrogen (N) fertiliser (150–200 kg N/ha) are currently being applied to perennial ryegrass (Lolium perenneL.) seed crops in New Zealand. Due to increasing requirements for efficient use of N fertilisers and minimising nitrate contamination of the environment, a field experiment was established using 15N-labelled fertiliser to follow the fate of applied N. Urea-15N was applied to a perennial ryegrass seed crop in April (30 kg N/ha), August (30 kg N/ha), September (60 kg N/ha) and October (60 kg N/ha). The urea-15N was applied in solution and watered in to minimise volatilisation loss. At the time of harvest (December), 9% of the applied 15N was in the seed, 29% in the straw, 19% in the roots and 39% in the soil organic matter. Losses of 15N were minimal as the N was applied in several applications, each one at a relatively low rate, and at times when leaching was unlikely to occur. Ryegrass plants used a greater proportion of the N applied in September and October (61–65%) compared with that applied in April (44%). Consequently more N was recovered from the soil in the autumn application (57%) than from the September and October applications (28–44%). The availability of the residual fertiliser N to a subsequent wheat (Triticum aestivum L.) crop was studied in a glasshouse experiment. The residual fertiliser N was present in the soil and ryegrass roots and stubble. The wheat plants only recovered 7–9% of this residual N. Most of the N taken up by the wheat came from the soil organic N pool. Overall, applying a total of 180 kg N/ha to the ryegrass appeared to have minimal direct impact on the environment. In the short term N not used by the ryegrass plants contributed to the soil organic N pool.
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