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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms of Water Exchange between Lanthanide(III) Aqua Ions [Ln(H2O)n]3+ and bulk water: A Molecular Dynamics Simulation Approach Including High-Pressure Effects (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 285-294 
    Details
    ISSN: 0947-6539
    Keywords: computer simulations ; high-pressure chemistry ; lanthanide complexes ; ligand exchange ; mechanistic studies ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the microscopic mechanisms of the water exchange reaction between the hydration shells of lanthanide(III) ions (Ln = Nd, Sm, Yb) and bulk water by means of molecular dynamics simulations. In contrast to the residence time of a water molecule in the first hydration shell (τres (1st shell) = 1577, 170 and 410 ps for Nd3+, Sm3+ and Yb3+, respectively), that in the second hydration shell is nearly independent of the type of the cation and amounts to 12-18 ps. Along the lanthanide series a change in the coordination number from 9 to 8 is coupled to a changeover in the water exchange mechanism. The observed water exchange events on the [Nd(H2O)9]3+ aqua ion follow a dissociatively activated Id mechanism via an eightfold-coordinated transition state of square antiprismatic geometry. The lifetime of the transitory square antiprism varies between virtually 0 and 10 ps. The assignment of an Id mechanism (instead of a limiting D mechanism) is supported by the existence of a preferential arrangement between the exchanging water molecules (1800) and by the fact that the calculated average activation volume ΔV≠ = + 4.5 cm3 mol-1 is clearly smaller than the estimated activation volume ΔV≠lim ≈ΔV0 = + 7.2 cm3 mol-1 for a limiting D process. In the case of Sm3+ a ninth water molecule exchanges frequently between the first hydration shell and the bulk and maintains the coordination equilibrium between a [Sm(H2O)8]3+ and a [Sm(H2O)9]3+ aqua ion. The resulting trajectory pattern of incoming and leaving water molecules is an alternation of elimination and addition reactions and cannot be classified into the scheme of D, I or A mechanisms for substitution processes. The reaction volume ΔV0 for the coordination equilibrium [Sm(H2O)8]3+ + H2O → [Sm(H2O)9]3+ can be evaluated consistently both by a thermodynamic and a geometric approach. The observed exchange events for [Yb(H2O)8]3+ exhibit the characteristics of an Ia mechanism. The water exchange takes place via a transition-state geometry close to that of a tricapped trigonal prism and involves a slightly negative activation volume.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020309
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  • 2
    Electronic Resource
    Electronic Resource
    The Role of Water Exchange in Attaining Maximum Relaxivities for Dendrimeric MRI Contrast AgentsHigh-Pressure NMR Kinetics, Part 72; part 71, see ref. [1]. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1607-1615 
    Details
    ISSN: 0947-6539
    Keywords: contrast agents ; dendrimers ; gadolinium complexes ; ligand exchange ; magnetic resonance imaging ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Macrocyclic GdIII complexes attached to dendrimers represent a new class of potential MRI contrast agents. They have an extended lifetime in the blood pool, which is indispensable for their application in magnetic resonance angiography, and high relaxivities, which reduce the dose required to produce quality images. We performed a variable-temperature and -pressure 17O NMR study in aqueous solution and at 14.1, 9.4, and 1.4 T on the water exchange and rotational dynamics of three macrocyclic GdIII complexes based on polyamidoamine dendrimers, as well as on the GdIII complex of the monomer unit with the linker group. The water exchange rates k298ex for generation 5 [G5(N{CS}N-bz-Gd-{DO3A}{H2O})52], generation 4 [G4(N-{CS}N-bz-Gd{DO3A}{H2O})30], generation 3 [G3(N{CS}N-bz-Gd{DO3A}-{H2O})23], and the monomer [Gd(DO3A-bz-NO2)(H2O)] complexes are 1.5±0.1, 1.3±0.1, 1.0±0.1, and 1.6±0.1 × 106 s-1, respectively, and the activation volumes ΔV≢ of water exchange on the latter two compounds are + 3.1±0.2 and + 7.7±0.5 cm3 mol-1, indicating dissociatively activated exchange reactions ({CS}N-bz-{DO3A}=1-(4-isothiocyanatobenzyl)amido-4,7,10-tri(acetic acid)tetraazacyclododecane). The rotational correlation times for the dendrimers are 4 to 8 times longer than for monomeric or dimeric GdIII poly(amino carboxylates). As a consequence of the slow rotation, the proton relaxivities of these dendrimer complexes are considerably higher than those of smaller complexes. However, the low water exchange rates prevent the dendrimer proton relaxivities from attaining the values expected from the increase in the rotational correlation times. Modifications of the chelating ligand may result in a faster water exchange and thus allow the full benefit of slow rotation to be achieved.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021220
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  • 3
    Electronic Resource
    Electronic Resource
    The solution structure and reactivity of decavanadate (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1406-1420 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxygen-exchange reaction of V10O286- with bulk water has been followed by time-dependent 17O-NMR spectroscopy (buffered solutions, pH ∼ 5.5, [V10]total ∼ 0.17m, T = 298 K). It is shown that all seven structurally different sites of O-atoms are kinetically similar but, in contrast to earlier studies, not identical (6 h ≤ ‘t1/2’ ≤ 11 h). The kinetic similarity of the various structural sites implies the some (but not full) O scrambling is involved. Two possible mechanisms with a ‘half-bonded’ and an ‘open’ intermediate are discussed in detail to interpret the experimental results. A computer simulation of the exchange reaction based on these models is presented. It is shown that the ‘half-bonded-intermediate’ mechanism is consistent with the experimental data and the following parameters are calculated: formation of the intermediate: k1 = 5.8 · 10-3 s-1, k-1 = 6.7 · 10-2 s-1, [intermediate]∞ ≈ 8%; all activated O-atoms exchange within the lifetime of the intermediate (τ ∼ 15 s), and the calculated exchange rate of the intermediate (k2 ≥ 0.60 s-1) is consistent with earlier assumptions (k2 ≈ 0.5 s-1). It is shown that a simulation based on the ‘open-intermediate’ mechanism results in kinetic parameters which are not consistent with the kinetics of the formation of cyclic metavanadates ((VO3-)n, n = 4,5) from decavanadate, since the required formation rate is by a factor ∼ 102 too fast, and the equilibrium concentration of metavanadates is by a factor of ∼ 2 too large (under the conditions of the O-exchange experiments of decavanadate (T = 298 K, [V10]total ≈ 0.17m, pH ∼ 5.55) the total amount of metavanadates present is ∼ 8%, with [(VO3-)4]/[(VO3-)5] ∼ 4:1; a qualitative analysis of the kinetics of the formation of metavanadates (vo kinetics; the exact mechanism of the back-reaction (at least second-order) is not known with certainty) leads to k1 ≥ 4·10-5 s-1). O exchange of decavanadates via equilibrated metavanadates would lead to full scrambling of the O sites and is not consistent with the observed differences in the exchange rates. From the qualitative kinetic parameters of the metavanadate formation kinetics, it can be concluded that any contribution of an ‘open’ or an ‘metavanadate’ mechanism is of the order of 1-2% at most.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710605
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  • 4
    Electronic Resource
    Electronic Resource
    Intramolecular Dynamics of Five-coordinate iron Carbonyl Complexes with olefinic ligands as studied by variable-pressure 1H-NMR spectroscopy (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1458-1466 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variable-pressure 1H-NMR Spectroscopy has been used to study the fluxionality of some five-coordinated Fe complexes in solution. For [Fe(CO)2 1,3-cyclooctadiene (PPh3)], the CO site exchange is known (by analogy with [Fe(CO)3(1,3-cyclooctadiene)]) to be a non-dissociative process, and an activation volume of ca. 0 cm3.mol-1 was indeed obtained. However, for [Fe(CO2){2,3-η:O-σ-(7,7-dimethoxybicyclo[2.2.1]hept-2-ene)}(PPh3)], the activation volume of +5 cm3 mol-1 suggests that an unprecedented dissociation process is responsible for the CO site exchange. The molecular structure of [Fe(CO)2(1,3-cyclooctadiene)(PPh3)] was ascertained by single-crystal X-ray diffractometry. The crystals are triclinic, space group P1, a = 9.606(3), b = 16.795(2), c = 7.743(8) Å, α = 97.83(4), β = 109.63(4), γ = 83.37(2)°. The structure determination has shown that the complex possesses a tetragonal pyramidal coordination, with the endocyclic C=C bond and PPh3 occupying basal sites.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710609
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  • 5
    Electronic Resource
    Electronic Resource
    Multinuclear NMR Studies of Ligand-Exchange Reactions on Analogous Technetium(V) and Rhenium(V) Complexes. Relevance to nuclear medicine (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 210-217 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of pyridine exchange on trans-[MO2(py)4]+ have been followed by 1H-NMR in CD3NO2 for M = Re, Tc: k298S-1 = (5.5 ± 0.1) × 10-6, 0.04 ± 0.02; ΔH≠/kJmol-1 = 111 ± 3, 101 ± 9; ΔS≠/JK-1mol-1 = +28 ± 10, +68 ± 35. For the Rev complex, pyridine and oxygen exchanges have been measured simultaneously by 1H- and 17O-NMR in deuterated water: k298/s-1 = (8.6 ± 0.2) × 10-6 (py), (14.5 ± 0.3) × 10-6 (oxygen); ΔH≠/kJmol-1 = 111 ± 1, 91 ± 1; ΔS /JK-1mol-1 = +32 ± 3, -32 ± 4. For both complexes, the rate law for pyridine exchange is first-order in complex and zero-order in pyridine; together with the activation parameter values, and the fact that the rate does not depend significantly on the nature of the solvent, this strongly implies the operation of a dissociative mechanism. The ratio of pyridine exchange rates for the Tc and Re complexes at room temperature is ca. 8000. The consequences of these observations for radiopharmaceutical synthesis are discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750119
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  • 6
    Electronic Resource
    Electronic Resource
    Dimethylformamide-Exchange Mechanism on Some First-Row Divalent Transition-Metal IonsPart 33 of the series ‘High-Pressur NMR Study’. Part 32: [1].Taken in part from the diploma work of C. Cossy, Université de Lausanne, 1983.This work was presented in part at the 24th International Conference on Coordination Chemistry, Athens, Greece, August 1986. (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 1516-1525 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of temperature on the dimethylformamide exchange on Mn(DMF)2+6 and Fe(DMF)2+6 has been studied by 13C- and 17O-NMR, respectively, yielding the following kinetic parameters: k298 equals; (2.2±0.2). 106 S-1, ΔH≠ = 34.6 ± 1.3 kJ mol-1, ΔS≠ = -7.4 ± 4.8 J K-1mol-1 for Mn2+ and K298 = (9.7 ± 0.2).105 S-1, Delta;H≠ = 43.0 ± 0.9 kJ mol-1, ΔS≠ = + 13.8 ± 2.8 J K-1mol-1 for Fe2+. The volumes of activation, ΔV≠ in cm3mol-1, derived from high-pressure NMR on these metal ions, together with the previously published activation volumes for Co2+ and Ni2+ (+2.4 ± 0.2 (Mn2+), +8.5 ± 0.4 (Fe2+) +9.2 ± 0.3 (Co2+), + 9.1 ± 0.3 (Ni2+)) give evidence for a dissociative activation mode for DMF exchange on these high-spin first-row transition-metal divalent ions. The small positive ΔV≠ value observed for DMF exchange on Mn2+ seems to indicate that a mechanistic changeover also occurs along the series, (probably from Id to D), as for the other solvents previously studied (Ia to Id, for H2O, MeOH, MeCN). This changeover is shifted to the earlier elements of the series, due to more pronounced steric crowding for dimethylformamide hexasolvates.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700608
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  • 7
    Electronic Resource
    Electronic Resource
    Quantitative Formation in Water of [Ru(CO)(H2O)5]2+ from Hexaaquaruthenium(II) and Carbon Monoxide (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 1236-1238 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-pressure 17O- and 13C-NMR show that [Ru(H2O)6]2+ reacts quantitatively with carbon monoxide (50 bar) in water to form [Ru(CO)(H2O)5]2+.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740611
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  • 8
    Electronic Resource
    Electronic Resource
    17O-NMR, EPR and NMRD Characterization of [Gd(DTPA-BMEA)(H2O)]: A Neutral MRI Contrast Agent (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2017-2021 
    Details
    ISSN: 1434-1948
    Keywords: MRI ; GdIII complexes ; NMR spectroscopy ; NMRD ; Lanthanides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study including variable-temperature and -pressure, multiple-field 17O NMR, EPR and NMRD has been performed on the MRI contrast agent, [Gd(DTPA-BMEA)(H2O)]. The water exchange rate [kex298 = (0.39 ± 0.02) × 106 s-1] and the activation volume (ΔV≠ = +7.4 ± 0.4 cm3 mol-1), hence the mechanism, are identical to those for [Gd(DTPA-BMA)(H2O)]. The longer rotational correlation time of [Gd(DTPA-BMEA)(H2O)], as obtained from a global analysis of 17O-NMR, EPR and NMRD data, and compared to that of [Gd(DTPA-BMA)(H2O)], can be explained by water molecules hydrogen-bonded to the ether oxygen atoms of the ligand side chain.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Water-Exchange Mechanism of Tetraaquapalladium(II). A Variable-Pressure and Variable-Temperature Oxygen-17 NMR StudyPart 23 of the series ‘High-Pressure NMR Kinetics’. For part 22, see [1]. (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1453-1460 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Water exchange of square-planar Pd(H2O)24+ has been studied as a function of temperature (240 to 345 K) and pressure (0.1 to 260 MPa, at 324 K) by measuring the 17/O-FT-NMR line-widths of the resonance from coordinated water at 27.11 and 48.78 MHz. The following exchange parameters were obtained: k298ex = (560 ± 40) s-1, ΔH* = (49.5 ± 1.9) kJ mol-1, ΔS* = - (26 ± 6) J K-1 mol-1 and ΔV* = - (2.2 ± 0.2) cm3 mol-1. The values refere to an aqueous perchlorate medium with an ionic strength between 2.0 and 2.6 m and a perchloric-acid concentration between 0.8 and 1.7 m, and are interpreted in terms of an associative (a) activation for the exchange. The exchange rate for Pd(H2O)24+ is 1.4 × 106 times faster than for Pt(H2O)24+ at 298 K. A comparison with reactions between other nucleophiles and Pd(H2O)24+ is also made.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670605
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  • 10
    Electronic Resource
    Electronic Resource
    Variable-Temperature and Variable-Pressure 17O-NMR Study of Water Exchange of Hexaaquaaluminium(III)Part 25 of the series ‘High-Pressure NMR Kinetics’. Part 24: [1].These results are part of the Ph. D. thesis of D. H.-C., University of Lausanne, 1984. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 545-554 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transverse relaxation rate of H2O in Al(H2O)63+ has been measured as a function of temperature (255 to 417 K) and pressure (up to 220 MPa) using the 17O-NMR line-broadening technique, in the presence of Mn(II) as a relaxation agent. At high temperatures the relaxation rate is governed by chemical exchange with bulk H2O, whereas at low temperatures quadrupolar relaxation is prevailing. Low-temperature fast-injection 17O-NMR was used to extend the accessible kinetic domain. The samples studied contained Al3+ (0.5 m), Mn2+ (0.2-0.5 m), H+ (0.2-3.1 m) and 17O-enriched (20-40%) H2O. Non-coordinating perchlorate was used as counter ion. The following H2O exchange parameters were obtained: kex298 = (1.29 ± 0.04) s-1, ΔH* = (84.7 ± 0.3) kJ mol-1, ΔS* = +(41.6 ± 0.9) J K-1 mol-1, and ΔVex* = +(5.7 ± 0.2) cm3 mol-1, indicating a dissociative interchange, Id, mechanism. These results of H2O exchange on Al(H2O)63+ are discussed together with the available complex-formation rate data and permit also the assignment of Id mechanisms to these latter reactions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680302
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