The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis i... more The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis is due to the ability, called relaxivity, of these paramagnetic compounds to accelerate the relaxation of the surrounding water proton spins. A new classical force field for molecular dynamics simulations of Gd3+ polyaminocarboxylates has recently been published, which allows the study of the chelate internal mobility. We present two selected examples where such motions can affect relaxivity. Knowing the relationship between the bound water proton and oxygen mobility is important for the combined analysis of multinuclear NMR studies, and we show that they differ significantly. Next, we observe symmetry changes over time in the Gd3+ coordination polyhedron of the acyclic complexes. We propose that such rearrangements can play a role in the electron spin relaxation of Gd3+ chelates, an important result considering the uncertainty still attached to this particular factor.
The rate constants and activation parameters for solvent exchange for a series of RhIII and IrIII... more The rate constants and activation parameters for solvent exchange for a series of RhIII and IrIII complexes of the form [M(H2O)6]3+ (M = Rh or Ir) and [Cp*M(S)3]2+ (M = Rh or Ir, and S = H2O, MeCN, or Me2SO) have been determined by NMR spectroscopy as a function of free-solvent concentration, temperature, and pressure, and the mechanisms for the respective exchange processes have been inferred.
Recent proton magnetic measurements in the ternary systems HNO3–DNO3–water and HClO4–DClO4–water ... more Recent proton magnetic measurements in the ternary systems HNO3–DNO3–water and HClO4–DClO4–water partly confirm older data and furnish new information on the molecular states of the acids, on hydration and solvation of the hydrogen ion, and on the distribution of H in deuterated acids between the ion and water. The dissociation constants of HNO3 and DNO3 between 0° and 65° are derived from the measurements.
Nuclear magnetic resonance (NMR) was previously established as a reliable method for the determin... more Nuclear magnetic resonance (NMR) was previously established as a reliable method for the determination of the degree of dissociation. The proton magnetic resonance shift has been measured in the full range of the ternary system HNO3—DNO3—H2O—D2O. The two nitric acids are about equally strong at 32°C, but at 0° deuteronitric acid is weaker, at 63° stronger than HNO3.
The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis i... more The increasing use of contrast agents in magnetic resonance imaging (MRI) for medical diagnosis is due to the ability, called relaxivity, of these paramagnetic compounds to accelerate the relaxation of the surrounding water proton spins. A new classical force field for molecular dynamics simulations of Gd3+ polyaminocarboxylates has recently been published, which allows the study of the chelate internal mobility. We present two selected examples where such motions can affect relaxivity. Knowing the relationship between the bound water proton and oxygen mobility is important for the combined analysis of multinuclear NMR studies, and we show that they differ significantly. Next, we observe symmetry changes over time in the Gd3+ coordination polyhedron of the acyclic complexes. We propose that such rearrangements can play a role in the electron spin relaxation of Gd3+ chelates, an important result considering the uncertainty still attached to this particular factor.
The rate constants and activation parameters for solvent exchange for a series of RhIII and IrIII... more The rate constants and activation parameters for solvent exchange for a series of RhIII and IrIII complexes of the form [M(H2O)6]3+ (M = Rh or Ir) and [Cp*M(S)3]2+ (M = Rh or Ir, and S = H2O, MeCN, or Me2SO) have been determined by NMR spectroscopy as a function of free-solvent concentration, temperature, and pressure, and the mechanisms for the respective exchange processes have been inferred.
Recent proton magnetic measurements in the ternary systems HNO3–DNO3–water and HClO4–DClO4–water ... more Recent proton magnetic measurements in the ternary systems HNO3–DNO3–water and HClO4–DClO4–water partly confirm older data and furnish new information on the molecular states of the acids, on hydration and solvation of the hydrogen ion, and on the distribution of H in deuterated acids between the ion and water. The dissociation constants of HNO3 and DNO3 between 0° and 65° are derived from the measurements.
Nuclear magnetic resonance (NMR) was previously established as a reliable method for the determin... more Nuclear magnetic resonance (NMR) was previously established as a reliable method for the determination of the degree of dissociation. The proton magnetic resonance shift has been measured in the full range of the ternary system HNO3—DNO3—H2O—D2O. The two nitric acids are about equally strong at 32°C, but at 0° deuteronitric acid is weaker, at 63° stronger than HNO3.
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Papers by ANDRE MERBACH