The applicability of the magnetization-transfer NMR technique to determine chemical exchange rates in extreme cases. The importance of complementary experiments

Led, Jens J.; Gesmar, Henrik

doi:10.1016/0022-2364(82)90257-8

Cited by 74 publications

(66 citation statements)

References 13 publications

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“…Magnetization transfer experiments were performed by using the selective inversion-exchange/recovery monitoring scheme according to the literature. [45] Selective inversion of one resonance in the 31 P { 1 H} NMR spectrum was achieved using Gaussianshaped pulses of 10 ms duration.…”

Section: Resultsmentioning

confidence: 99%

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML₄ Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d⁸, d⁹ and d¹⁰ Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Breher

Rüegger

Mlakar

et al. 2004

Chemistry A European J

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The formation of adducts of the square-planar 16-electron complexes trans-[M(tropp(ph))(2)](+) and cis-[M(tropp(ph))(2)](+) (M=Rh, Ir; tropp(Ph)=5-diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl(-), and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV-visible spectroscopy, square-wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans/cis isomerization cannot be detected for [M(tropp(ph))(2)](+) in non-coordinating solvents. However, both isomers are connected through equilibria of the type trans-[M(tropp(ph))(2)](+)+L<==>[ML(tropp(ph))(2)](n)<==>cis-[M(tropp(ph))(2)](+)+L, involving five-coordinate intermediates [ML(tropp(ph))(2)](n) (L=acn, n=+1; L=Cl(-), n=0). Values for K(d) (K(f)), that is, the dissociation (formation) equilibrium constant, and k(d) (k(f)), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers (k(f)>1x10(5) m(-1) s(-1)). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five-coordinate complexes [ML(tropp(ph))(2)](n) increases with Ir>Rh and Cl(-)>acn. The dissociation reaction has a pronounced influence on the square-wave (SW) voltammograms of trans/cis-[Ir(tropp(ph))(2)](+). With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans/cis isomerization is a process with a low activation barrier for the four-coordinate 17-electron complexes [M(tropp(ph))(2)](0) and especially that a disproportionation reaction 2 trans/cis-[M(tropp(ph))(2)](0)-->[M(tropp(ph))(2)](+)+[M(tropp(ph))(2)](-) may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners.

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Section: Resultsmentioning

confidence: 99%

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML₄ Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d⁸, d⁹ and d¹⁰ Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Breher

Rüegger

Mlakar

et al. 2004

Chemistry A European J

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“…[57][58][59] Experiments were performed on a Bruker AM500 instrument ( 13 C 125.68 MHz) using a 5 mm broadband probe, 1 H bandpass filter, and 13 C lowpass filter; or a Bruker AM400 instrument ( 19 F 376.48 MHz) using a 5 mm 19 F probe, 1 H bandpass filter, 19 The rate of prolyl peptide bond isomerization cannot be detected by this method at room temperature. Experiments were therefore conducted at elevated temperatures, 310-360 K. Temperature settings of the spectrometer were calibrated to within 1 °C by reference to a glycol standard.…”

Section: Kineticsmentioning

confidence: 99%

Inductive Effects on the Energetics of Prolyl Peptide Bond Isomerization: Implications for Collagen Folding and Stability

1996

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The hydroxylation of proline residues in collagen enhances the stability of the collagen triple helix. Previous X-ray diffraction analyses had demonstrated that the presence of an electronwithdrawing substituent on the pyrrolidine ring of proline residues has significant structural consequences [Panasik, N., Jr.; Eberhardt, E. S.; Edison, A. S.; Powell, D. R.; Raines, R. T. Int. J. Pept. Protein Res. 1994, 44, 262-269]. Here, NMR and FTIR spectroscopy were used to ascertain kinetic and thermodynamic properties ofThe pK a 's of the nitrogen atom in the parent amino acids decrease in the order: proline (10.8) > 4(R)-hydroxy-L-proline (9.68) > 4(R)-fluoro-L-proline (9.23). In water or dioxane, amide I vibrational modes decrease in the order: 1 > 2 > 3. At 37 °C in dioxane, the rate constants for amide bond isomerization are greater for 3 than 1. Each of these results is consistent with the traditional picture of amide resonance coupled with an inductive effect that results in a higher bond order in the amide C=O bond and a lower bond order in the amide C-N bond. Further, at 37 °C in water or dioxane equilibrium concentrations of the trans isomer increase in the order: 1 < 2 < 3. Inductive effects may therefore have a significant impact on the folding and stability of collagen, which has a preponderance of hydroxyproline residues, all with peptide bonds in the trans conformation.

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“…of ligands without and with metal cation by using the well-known inversionrecovery method [22] 4. Magnetization Transfer Experiments [23]. Cf.…”

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confidence: 99%

Coordination Mode and Kinetic Behavior of the Tetracarbonatozirconate Ion

Veyland

Rimbault

Dupont

et al. 1999

HCA

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The applicability of the magnetization-transfer NMR technique to determine chemical exchange rates in extreme cases. The importance of complementary experiments

Cited by 74 publications

References 13 publications

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML₄ Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d⁸, d⁹ and d¹⁰ Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML₄ Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d⁸, d⁹ and d¹⁰ Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Inductive Effects on the Energetics of Prolyl Peptide Bond Isomerization: Implications for Collagen Folding and Stability

Coordination Mode and Kinetic Behavior of the Tetracarbonatozirconate Ion

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The applicability of the magnetization-transfer NMR technique to determine chemical exchange rates in extreme cases. The importance of complementary experiments

Cited by 74 publications

References 13 publications

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML4 Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d8, d9 and d10 Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML4 Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d8, d9 and d10 Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Inductive Effects on the Energetics of Prolyl Peptide Bond Isomerization: Implications for Collagen Folding and Stability

Coordination Mode and Kinetic Behavior of the Tetracarbonatozirconate Ion

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Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML₄ Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d⁸, d⁹ and d¹⁰ Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)

Thermodynamic and Kinetic Data for Adduct Formation, cis–trans Isomerization and Redox Reactions of ML₄ Complexes: A Case study with Rhodium– and Iridium–tropp Complexes in d⁸, d⁹ and d¹⁰ Valence Electron Configurations (tropp= Dibenzotropylidene Phosphanes)