Molecular dynamics study of the hydration of lanthanum(III) and europium(III) including many-body effects

Lanthanides complexes are widely used as contrast agents in magnetic resonance imaging (MRI) and are involved in many fields such as organic synthesis, catalysis, and nuclear waste management. The complexation of the ion by the solvent or an organic ligand and the resulting properties (for example the relaxivity in MRI) are mainly governed by the structure and dynamics of the coordination shells. All of the MD approachs already carried out for the lanthanide(III) hydration failed due to the lack of accurate representation of many-body effects. We present the first molecular dynamics simulation including these effects that accounts for the experimental results from a structural and dynamic (water exchange rate) point of view

Gd(III) polyaminocarboxylate chelate: realistic manybody molecular dynamics simulations for molecular imaging applications

Realistic molecular dynamics simulations of polyaminocarboxylate complexes of gadolinium (III) ion in water are performed, providing coordination numbers and average residence times in quantitative agreement with available experimental data. A theoretical analysis, based on fitting a fluctuating charges model on ab initio data, also indicates that charge transfer between the ion and the ligand is significant

Stepwise Hydration of 2-Aminooxazole: Theoretical Insight into the Structure, Finite Temperature Behavior and Proton-Induced Charge Transfer

International audienceIt was recently suggested that 2-aminooxazole (AO) could contribute to the formation of RNA nucleotides on primitive earth. In this article we have considered by means of computational modeling the influence of microhydration on the structural and spectral properties of this potential prebiotic molecule. The stable structures of AO(H2O)n were obtained first by sampling the potential energy landscapes of clusters containing up to n = 20 water molecules, using a simple but reasonably accurate force field and replica-exchange molecular dynamics simulations. Through reoptimization using an explicit description of electronic structure at the level of density functional theory with the M06-2X functional, the formation energies, ionization energies and electron affinities were determined in the vertical and adiabatic treatments, as well as vibrational and optical spectra covering the far-IR, mid-IR, and lower part of the UV ranges. The results generally show a clear segregation between the aminooxazole solute and the water molecules, a water cluster being formed near the nitrogen and amino group side leaving the hydrocarbon side dry even at temperatures corresponding to the liquid state. The spectral signatures generally concur and show distinct contributions of the solute and solvent, spectral shifts to lower energies being in agreement with earlier calculations in bulk solvent. We have also investigated the importance of microhydration on the charge transfer cross section upon collision with a proton, thereby extending an earlier investigation on the bare AO molecule. The presence of water molecules generally reduces the propensity for charge transfer at small sizes, but the influence of the solvent steadily decreases in larger droplets

Calculation of harmonic and anharmonic vibrational wavenumbers for triatomic uranium compounds XUY

cited By 31International audienceThe performance of nine different variants of density functional theory (DFT) for the calculation of the vibrational frequencies of the triatomic compounds UO22+, NUN, NUO+ and CUO is investigated and compared with the predictions obtained with the CASPT2 method [Chem. Phys. Lett. 331 (2000) 229]. Vibrational anharmonicity is calculated for UO22+ and for CUO and is shown to be small for these systems. A detailed comparison of experimental data obtained in rare-gas matrices with the DFT predictions shows that while the performance of hybrid DFT is uneven, the more "elementary" GGA versions such as PW91 perform extremely well, as the estimated unsigned (signed) average errors are only 11 (-2) cm-1 for the five observed IR bands. Overall, the DFT/GGA results for the closed-shell compounds considered here are at least as good as those yielded by the CASPT2 method, which is computationally much more demanding. Calculated IR intensities are in at least semi-quantitative agreement with experiment. We suggest that the vibrational data becoming available for actinide compounds could and should be used to obtain more reliable parameters in hybrid versions of DFT. The calculated harmonic stretching force constants are shown to depend critically on the U-X bond length, but they are almost insensitive to the method used for their calculation, at a given distance. Observed vibrational spectra can therefore be used to infer reliable bond lengths. © 2004 Elsevier B.V. All rights reserved