| 1. |
- Belorizky, Elie, et al.
(author)
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Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field
- 2008
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In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:5
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Journal article (peer-reviewed)abstract
- The enhancement of the spin-lattice relaxation rate for nuclear spins in a ligand bound to a paramagnetic metal ion [known as the paramagnetic relaxation enhancement (PRE)] arises primarily through the dipole-dipole (DD) interaction between the nuclear spins and the electron spins. In solution, the DD interaction is modulated mostly by reorientation of the nuclear spin-electron spin axis and by electron spin relaxation. Calculations of the PRE are in general complicated, mainly because the electron spin interacts so strongly with the other degrees of freedom that its relaxation cannot be described by second-order perturbation theory or the Redfield theory. Three approaches to resolve this problem exist in the literature: The so-called slow-motion theory, originating from Swedish groups [Benetis et al., Mol. Phys. 48, 329 (1983); Kowalewski et al., Adv. Inorg. Chem. 57, (2005); Larsson et al., J. Chem. Phys. 101, 1116 (1994); T. Nilsson et al., J. Magn. Reson. 154, 269 (2002)] and two different methods based on simulations of the dynamics of electron spin in time domain, developed in Grenoble [Fries and Belorizky, J. Chem. Phys. 126, 204503 (2007); Rast et al., ibid. 115, 7554 (2001)] and Ann Arbor [Abernathy and Sharp, J. Chem. Phys. 106, 9032 (1997); Schaefle and Sharp, ibid. 121, 5387 (2004); Schaefle and Sharp, J. Magn. Reson. 176, 160 (2005)], respectively. In this paper, we report a numerical comparison of the three methods for a large variety of parameter sets, meant to correspond to large and small complexes of gadolinium(III) and of nickel(II). It is found that the agreement between the Swedish and the Grenoble approaches is very good for practically all parameter sets, while the predictions of the Ann Arbor model are similar in a number of the calculations but deviate significantly in others, reflecting in part differences in the treatment of electron spin relaxation. The origins of the discrepancies are discussed briefly.
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| 2. |
- Ducommun, Yves, et al.
(author)
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1H NMR Kinetic Study of Dimethyl Sulfoxide Exchange on Tetrakis(dimethyl- sulfoxide)platinum(II) at Variable Temperature and Pressure : High-pressure NMR kinetics. 36.
- 1989
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In: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 28:2, s. 377-379
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Journal article (peer-reviewed)abstract
- The present report is a 'H NMR investigation of the dimethyl sulfoxide exchange on Pt(Me2S0)42+ as a function of temperature and pressure in CD3N02. Dimethyl sulfoxide is an ambidentate ligand, and the complex contains two 0-bonded and two S-bonded ligands that are exchanging with the free ligand at different rates. It is favorable to follow these exchanges in a non-coordinating diluent like nitromethane, since it allows variation of the ligand concentration, thus giving an opportunity to establish the rate law. The use of a diluent of high dielectric constant and of uncharged ligands minimizes the electrostriction changes along the reaction path, so that the measured volumes of activation will reflect primarily the intrinsic changes of molecular volumes on going to the transition state.
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| 3. |
- Ducommun, Yves, et al.
(author)
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Variable Pressure Oxygen-17 FTNMR and Stopped-Flow Kinetic Study of Water Exchange and DMSO Substitution on Square-Planar Tetraaqua-Palladium(II) and -Platinum(II)
- 1984
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In: Journal de Physique. Colloques. - : EDP Sciences. - 0449-1947. ; 45:C8, s. 8-224
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Journal article (peer-reviewed)abstract
- The very slow water exchange on Pt(H2O)42+ was studied in the temperature range 273 to 334 K and pressure range 0.1 to 228 MPa by 17O FTNMR, following the increase in height of the signal from bound water observed when platinum(II) solutions are mixed with 17O enriched water. The much faster water exchange on Pd(H2O)42+ was studied in the temperature range 240 to 345 K and pressure range 0.1 to 260 MPa, by measuring the 17O FTNMR line widths of the bound water resonance at 27.1 and 48.7 MHz. Complex formation between DMSO and Pd(H2O)42+ was studied by stopped-flow, in the temperature range 288 to 309 K and pressure range 0.1 to 175 MPa. In the three cases, the results are interpreted in terms of associative activation modes (a).
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| 4. |
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| 5. |
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| 6. |
- Helm, Lothar, et al.
(author)
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Water Exchange Mechanism of Tetraaquapalladium(II). A Variable Pressure and Variable Temperature Oxygen-217 NMR Study
- 1984
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In: Helvetica Chimica Acta. - : Wiley. - 0018-019X .- 1522-2675. ; 67:6, s. 1453-1460
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Journal article (peer-reviewed)abstract
- Water exchange of square-planar Pd(H2O)42+ 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 refer 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)42+ is 1.4 × 106 times faster than for Pt(H2O)42+ at 298 K. A comparison with reactions between other nucleophiles and Pd(H2O)42+ is also made.
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| 7. |
- Kowalewski, Jozef, et al.
(author)
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Comparison of different methods for calculating the paramagnetic relaxation enhancement of nuclear spins as a function of the magnetic field
- 2008
-
In: Journal of Chemical Physics. ; 128, s. 052315-
-
Journal article (peer-reviewed)abstract
- The enhancement of the spin-lattice relaxation rate for nuclear spins in a ligand bound to a paramagnetic metal ion (known as the paramagnetic relaxation enhancement, PRE) arises primarily through the dipole-dipole (DD) interaction between the nuclear spins and the electron spins. In solution, the DD interaction is modulated mostly by reorientation of the nuclear spin-electron spin axis and by electron spin relaxation. Calculations of the PRE are in a general complicated, mainly because the electron spin interacts so strongly with the other degrees of freedom that its relaxation cannot be described by second-order perturbation theory, or the Redfield theory. Three approaches to resolve this problem exist in the literature: the so-called slow-motion theory, originating from Swedish groups, and two different methods based on simulations of the dynamics of electron spin in time domain, developed in Grenoble and Ann Arbor, respectively. In this paper, we report a numerical comparison of the three methods for a large variety of parameter sets, meant to correspond to large and small complexes of gadolinium(III) and of nickel(II). It is found that the agreement between the Swedish and the Grenoble approaches is very good for practically all parameter sets, while the predictions of the Ann Arbor model are similar in a number of the calculations but deviate significantly in others, reflecting in part differences in the treatment of electron spin relaxation. The origins of the discrepancies are discussed briefly.
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