Hydration Structure and Dynamic Properties of the Square Planar Pt(II) Aquaion Compared to the Pd(II) Case

Unraveling the Hydration Shell Structure and Dynamics of Group 10 Aqua Ions

We present ab initio simulations based on subsystem DFT of group 10 aqua ions accurately compared against experimental data on hydration structure. Our simulations provide insights into the molecular structures and dynamics of hydration shells, offering recalibrated interpretations of experimental results. We observe a soft, but distinct second hydration shell in Palladium (Pd) due to a balance between thermal fluctuations, metal-water interactions, and hydrogen bonding. Nickel (Ni) and platinum (Pt) exhibit more rigid hydration shells. Notably, our simulations align with experimental findings for Pd, showing axial hydration marked by a broad peak at about 3 Å in the Pd-O radial distribution function, revising the previously sharp "mesoshell" prediction. We introduce the "hydrogen bond dome" concept to describe a resilient network of hydrogen-bonded water molecules around the metal, which plays a critical role in the axial hydration dynamics.

Hydration of Heavy Alkaline-Earth Cations Studied by Molecular Dynamics Simulations and X-ray Absorption Spectroscopy

The physicochemical properties of the three heaviest alkaline-earth cations, Sr²⁺, Ba²⁺, and Ra²⁺ in water have been studied by means of classical molecular dynamics (MD) simulations. A specific set of cation-water intermolecular potentials based on ab initio potential energy surfaces has been built on the basis of the hydrated ion concept. The polarizable and flexible model of water MCDHO2 was adopted. The theoretical-experimental comparison of structural, dynamical, energetic, and spectroscopical properties of Sr²⁺ and Ba²⁺ aqueous solutions is satisfactory, which supports the methodology developed. This good behavior allows a reasonable reliability for the predicted Ra²⁺ physicochemical data not experimentally determined yet. Simulated extended X-ray absorption fine-structure (EXAFS) and X-ray absorption near-edge spectroscopy spectra have been computed from the snapshots of the MD simulations and compared with the experimental information available for Sr²⁺ and Ba²⁺. For the Ra²⁺ case, the Ra L₃-edge EXAFS spectrum is proposed. Structural and dynamical properties of the aqua ions for the three cations have been obtained and analyzed. Along the [M(H₂O)_n]^m+ series, the M-O distance for the first-hydration shell is 2.57, 2.81, and 2.93 Å for Sr²⁺, Ba²⁺, and Ra²⁺, respectively. The hydration number also increases when one is going down along the group: 8.1, 9.4, and 9.8 for Sr²⁺, Ba²⁺, and Ra²⁺, respectively. Whereas [Sr(H₂O)₈]²⁺ is a typical aqua ion with a well-defined structure, the Ba²⁺ and Ra²⁺ hydration provides a picture exhibiting an average between the ennea- and the deca-hydration. These results show a similar chemical behavior of Ba²⁺ and Ra²⁺ aqueous solutions and support experimental studies on the removal of Ra-226 of aquifers by different techniques, where Ra²⁺ is replaced by Ba²⁺. A comparison of the heavy alkaline ions, Rb⁺ and Cs⁺, with the heavy alkaline-earth ions is made.

Palladium Oxide Nanoparticles: Preparation, Characterization and Catalytic Activity Evaluation

Stable palladium oxide nanoparticles were prepared in aqueous suspension with a very simple procedure, by dissolving palladium nitrate in water at a concentration around 10−4 M. UV-visible absorption spectroscopy was adopted to follow the formation of these nanoparticles, which were characterized by TEM microscopy, along with XRD, XPS and Raman measurements. DFT calculations allowed to interpret the Raman data and to clarify the species present at the surface of the nanoparticles. The catalytic activity of the latter was evaluated by monitoring the reduction of p-nitrophenol to p-aminophenol. This investigation paves the way to the use of these colloidal nanoparticles in processes of heterogeneous catalysis, in particular those concerning the catalytic degradation of aromatic derivatives that represent a serious danger for the environment as pollutants, as in the case of p-nitrophenol.

Fate of cisplatin and its main hydrolysed forms in the presence of thiolates: a comprehensive computational and experimental study

Thiolations and bidentations drive the chemical fate of cisplatin compounds in intracellular medium.

Square planar or octahedral after all? The indistinct solvation of platinum(ii)

The solvation structures of Pd(ii) and Pt(ii) are typically reduced to the well-known square-planar structural motif, although it has been shown, in both experimental and theoretical investigations, that these solutes demonstrate the affinity to bind ligand molecules at elongated distance in axial coordination sites.

Metal Ion Modeling Using Classical Mechanics

Metal ions play significant roles in numerous fields including chemistry, geochemistry, biochemistry, and materials science. With computational tools increasingly becoming important in chemical research, methods have emerged to effectively face the challenge of modeling metal ions in the gas, aqueous, and solid phases. Herein, we review both quantum and classical modeling strategies for metal ion-containing systems that have been developed over the past few decades. This Review focuses on classical metal ion modeling based on unpolarized models (including the nonbonded, bonded, cationic dummy atom, and combined models), polarizable models (e.g., the fluctuating charge, Drude oscillator, and the induced dipole models), the angular overlap model, and valence bond-based models. Quantum mechanical studies of metal ion-containing systems at the semiempirical, ab initio, and density functional levels of theory are reviewed as well with a particular focus on how these methods inform classical modeling efforts. Finally, conclusions and future prospects and directions are offered that will further enhance the classical modeling of metal ion-containing systems.

The hydration structure of the heavy-alkalines Rb+ and Cs+ through molecular dynamics and X-ray absorption spectroscopy: surface clusters and eccentricity

Hydration shells around Rb⁺ and Cs⁺ are not symmetric; the cation and the 1st-shell water mass center are separated by ∼0.4 Å, and this is supported by agreement between the theoretical and experimental EXAFS spectrum.

Modeling the interactions of phthalocyanines in water: from the Cu(II)-tetrasulphonate to the metal-free phthalocyanine

A quantum and statistical study on the effects of the ions Cu(2+) and SO(3)(-) in the solvent structure around the metal-free phthalocyanine (H(2)Pc) is presented. We developed an ab initio interaction potential for the system CuPc-H(2)O based on quantum chemical calculations and studied its transferability to the H(2)Pc-H(2)O and [CuPc(SO(3))(4)](4-)-H(2)O interactions. The use of the molecular dynamics technique allows the determination of energetic and structural properties of CuPc, H(2)Pc, and [CuPc(SO(3))(4)](4-) in water and the understanding of the keys for the different behaviors of the three phthalocyanine (Pc) derivatives in water. The inclusion of the Cu(2+) cation in the Pc structure reinforces the appearance of two axial water molecules and second-shell water molecules in the solvent structure, whereas the presence of SO(3)(-) anions implies a well defined hydration shell of about eight water molecules around them making the macrocycle soluble in water. Debye-Waller factors for axial water molecules have been obtained in order to examine the potential sensitivity of the extended x-ray absorption fine structure technique to detect the axial water molecules.

Characterizing Pt-derived anticancer drugs from first principles: the case of oxaliplatin in aqueous solution

The molecular compound ethyldiamine-oxalatoplatinum(II), EDO-Pt, is used as a model to study the oxaliplatin anticancer drug in aqueous solution by means of ab initio computer simulation. Gas-phase structure optimizations have been performed for both oxaliplatin and its EDO-Pt mimic along with Car-Parrinello molecular dynamics simulations of EDO-Pt in gas phase and in aqueous solution. The coordination of Pt(II) is square-planar on average, with Pt-N and Pt-O(I) distances of 2.04 A in solution. The diamine ligand has a bent structure, while the oxalate ligand is planar on average. The complex features a very rigid structure during the simulation and the charge distribution describes a dipole with its negative pole on the oxalate ligand and the positive pole on the Pt-diamine side. The solvation pattern of EDO-Pt is most well-defined around the amine and oxalate groups and is quantified by means of radial and spatial distribution functions of water molecules around the complex. Decomposition of radial distribution functions into their contributions from different regions (axial and equatorial) reveals an "anionic hydration" pattern of the metal cation by the solvent, which is analogous in nature to the bare Pt(II) aqua ion. A qualitative prediction on the kinetics of ligand exchange in oxaliplatin is derived based on its axial hydration pattern.

Dendrimer−Tetrachloroplatinate Precursor Interactions. 1. Hydration of Pt(II) Species and PAMAM Outer Pockets

Density functional theory is used to investigate the structure and energetics of the tetrachloroplatinate anion and its hydrolysis products at several degrees of hydration, as well as those of outer dendrimer pockets hosting such species. The number of water molecules able to saturate an unprotonated outer dendrimer pocket is found to be two, as inferred from calculated thermodynamic data. However, such a number could not be established for a protonated pocket where the dendrimer adopts a more open configuration. An analysis of possible pocket configurations is done on the basis of the orientations of the amide O atoms in the outer pockets. The effect of explicit water on the infrared spectra of the dendrimer pockets is reported and compared to experimental values.

Monte Carlo Simulation of Cisplatin Molecule in Aqueous Solution

The Lennard-Jones (12-6) parameters were obtained for all atoms of cisplatin molecule using the ab initio quantum mechanical potential energy surface for the water-cisplatin interaction as reference data. The parameters found were (epsilon/kcal.mol(-1) and sigma/angstroms) 1.0550, 3.6590 (Pt); 0.0381, 4.6272 (Cl); 0.0455, 3.3783 (N); and 0.0185, 0.0936 (H) and provided very good results for the description of the aqueous solution of cisplatin through Monte Carlo simulation. From statistical analysis of solute-solvent interactions, we observed that the NH3 groups are involved in 53% of the calculated hydrogen bonds with a significant contribution from chlorides (41%) and only 6% involving the Pt center. This is in agreement with the expected behavior for such molecules. Two hydration shells with 22 and 81 water molecules, respectively, centered around 4.6 and 7.3 angstroms were found from the center of mass pair correlation function analysis. The cisplatin atomic Lennard-Jones parameters are reported for the first time, and they might be useful for studying the structure, properties, and processes of cisplatin-like molecules in aqueous solution, including explicitly the solvent effect.