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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Transition metal chemistry 19 (1994), S. 477-480 
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The composition of the N-diketohydrindylidene histidinato chromium(III) complex formed by interaction of ninhydrin with the [Cr(histidine)(H2O)3]2+ complex has been determined using Job's method of continuous variations. The reaction is slow and the kinetic studies were carried out under varying conditions of pH, temperature and [ninhydrin]. The observed pseudo-first order rate constant under these conditions follow the rate equation: $${1 \mathord{\left/ {\vphantom {1 k}} \right. \kern-\nulldelimiterspace} k}_{obs} = {1 \mathord{\left/ {\vphantom {1 {\left\{ {K_t k_3 [N]} \right\} + {1 \mathord{\left/ {\vphantom {1 {k_3 }}} \right. \kern-\nulldelimiterspace} {k_3 }}}}} \right. \kern-\nulldelimiterspace} {\left\{ {K_t k_3 [N]} \right\} + {1 \mathord{\left/ {\vphantom {1 {k_3 }}} \right. \kern-\nulldelimiterspace} {k_3 }}}}$$ The reaction has the features of a template mechanism which proceeds through coordination of ninhydrin to the [Cr(histidine)]2+ complex. The reaction is expected to involve the combination of two ligands (ninhydrin and histidine) attached to the same CrIII (CLAM reaction). The CrIII ion provides a better opportunity for the reaction of ninhydrin and histidine by assembling their reactive groups together. On the basis of the observed data the probable mechanism has been proposed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The anation kinetics of the protonated dioxotetracyanomolybdate(IV) ion with 1,10-phenanthroline have been studied spectrophotometrically. The effect of the H+ ion, ionic strength and temperature on the reaction rate has been determined; the rate increases with increasing H+ ion concentration, is independent of ionic strength, and increases with temperature. The reaction follows first order kinetics with respect to [Mo(OH)2- (H2O)2(CN)4]2− and is considered to proceed through the formation of a 1,10-phenanthroline–Mo(OH)2- (H2O)2(CN)4M2− complex (outer sphere) which converts into an inner sphere complex. The formation constant (Kn) for the outer sphere complex has been calculated from the kinetic data by two different methods. Anation of Mo(OH)2-(H2O)2(CN)42− is discussed in terms of an associative interchange (Ia) mechanism. The activation parameters have been calculated using the Arrhenius equation. A substitution mechanism is proposed and the rate equation derived: kobs = kKnKa[H+] [phen] /{1 + KnKa[H+] [phen]}.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Transition metal chemistry 22 (1997), S. 350-355 
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of oxidation of l-methionine by chromic acid in acidic medium (pH=0.83–2.2) has been studied spectrophotometrically. The effect of l-methionine and chromium(VI) concentrations on the rate of the reaction was determined. The reaction rate decreases with increasing the pH of the medium. The kinetics of the formation of a chromium(III) complex conform to the rate law: with k1=7.5×10−2s−1 and Kes1=43.85 at constant [H+]=1.9×10−2moldm−3 and [l-methionine]T= 2.0×10−2moldm−3. The same values were found with [l-methionine]T variation at constant [H+]. The reaction proceeds through formation of chromium(VI)-l-methionine ester in a rapid pre-equilibrium step, followed by a slower redox reaction of the ester. The present study provides kinetic evidence for formation of a complex ion (ester). One mole of Cr2O72− oxidizes four moles of l-methionine, which acts as a monodentate ligand and binds to chromium(VI) through the sulfur atom. The coordinated sulfur atom of l-methionine–chromium(VI) ester is responsible for the oxidative degradation (breaking of the C1-C2 bond) of l-methionine. Coordinated oxygen of the carboxylate group inhibits the cleavage of the C1-C2 bond.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The reaction between hydroxopentaaquochromium(III) and octacyanomolybdate(IV) was investigated spectrophotometrically and obeyed a 2:1 reactant stoichiometry with respect to formation of the [Cr(H2O)4OH]2 Mo(CN)8 complex. Kinetic studies reveal that the reaction is first order with respect to hydroxopentaaquochromium(III) in the presence of an excess of octacyanomolybdate(IV). The reaction rate increased with an increase in the ionic strength and temperature, and decreased with an increase in hydrogen ion concentration. A mechanism has been proposed based upon ion-pair formation. The results are best accounted for by the Eigen-Tamm mechanism. Anation of [Cr(H2O)5OH]2+ is discussed in terms of an associative interchange (I a) where bond breaking and bond making are equally important. The activation parameters were calculated using Arrhenius's equation.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Transition metal chemistry 23 (1998), S. 537-540 
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of alkaline hydrolysis of Co(Asn)2, yielding Co(OH)2, NH3 and aspartic acid, have been studied spectrophotometrically, and the effects of CoII and NaOH concentrations on the reaction rate determined. The rate increases with increasing [NaOH], whereas variation of [CoII] has no significant effect. The kinetics of NH3 evolution conform to the rate law: $${\text{d[NH}}_{\text{3}} {\text{]/d}}t = k_1^\prime k_2^\prime [{\text{OH}}^ - ][{\text{Co(Asn)}}_{\text{2}} ]/(k_{ - 1}^\prime + k_2^\prime )$$ It is proposed that the reaction proceeds through formation of a dianionic tetrahedral intermediate.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics and mechanism of citric acid oxidation by CrVI; catalyzed by MnII, has been studied in H2O and in the presence of anionic and cationic surfactants. A linear correlation between k obs −1 and [MnII]−1 was found, satisfying the Michaelis–Menten kinetics. The rate-determining step is the decomposition of complex HCrO4–citric acid–MnII formed between citric acid–MnII and CrVI. Based on kinetic data, a one-step three-electron oxidation mechanism has been proposed. The rate decreased with increase in concentration of the cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB), while anionic sodium dodecyl sulphate (SDS) had no effect on the rate. The data have been interpreted in terms of reaction in the aqueous phase. The effect of added anions, such as chloride, bromide, nitrate, and sulphate, has been studied and discussed. The activation parameters (ΔH
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Transition metal chemistry 23 (1998), S. 147-150 
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of electron transfer between chromium(VI) and H3PO3, yielding chromium(III), have been investigated in HClO4 and H2SO4 media by visible spectrophotometry. The rate of reaction increased with increasing [H2SO4] and [HClO4]. A rate law based on ester formation preceding the electron transfer has been established and a possible mechanism has been proposed. The mechanism and the derived rate law are consistent with the observed kinetics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 48 (1965), S. 1957-1965 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aus den Wurzeln von Pleiocarpa mutica BENTH. wurden die quartären Alkaloide Hunterburnin-α-methochlorid (1), Hunterburnin-β-methochlorid (2), Huntrabrinmethochlorid (3), Pleiocarpamin-methochlorid (4), Kopsininsäure-methochlorid (8) und N(a), N(b)-Dimethylsarpaginchlorid (9) isoliert und charakterisiert.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 50 (1967), S. 625-627 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The following quaternary indole alkaloids have been isolated from the root bark of the Apocynaceae species Pleiocarpa tubicina Stapf: huntrabrine methochloride, kopsinic acid methochloride, N(a)-methyl-sarpagine methochloride and macusine B chloride.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: From the stem bark of Alstonia macrophylla Wall. a new quaternary alkaloid macrosalhine, C21H27O2N2+, has been isolated in small amounts as chloride or thiocyanate. On the basis of its chemical transformations and particularly its spectral properties (NMR., mass) the structure 1 has been proposed for it. Macrosalhin therefore represents a new skeletal type in the alkaloid field.
    Type of Medium: Electronic Resource
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