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1.
Chem Phys Lett ; 539-540: 24-29, 2012 Jun 29.
Artigo em Inglês | MEDLINE | ID: mdl-25540462

RESUMO

The solvation structure around the dicyanoaurate(I) anion (Au(CN)2-) in a dilute nitromethane (CH3NO2) solution is presented from X-ray diffraction measurements and molecular dynamics simulation (NVT ensemble, 460 nitromethane molecules at room temperature). The simulations are based on a new solute-solvent force-field fitted to a training set of quantum-chemically derived interaction energies. Radial distribution functions from experiment and simulation are in good agreement. The solvation structure has been further elucidated from MD data. Several shells can be identified. We obtain a solvation number of 13-17 nitromethane molecules with a strong preference to be oriented with their methyl groups towards the solute.

2.
J Chem Phys ; 132(1): 014506, 2010 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-20078171

RESUMO

Molecular dynamics simulations have been performed for liquid formamide using two different types of potential model (OPLS, Cordeiro). The structural results obtained from simulation were compared to experimental (x-ray and neutron diffraction measurements) outcomes. A generally good agreement for both models examined has been found, but in the hydrogen bonded region (2.9 A) the Cordeiro model shows a slightly better fit. Besides the evaluation of partial radial distribution functions, orientational correlation functions and energy distribution functions, describing the hydrogen bonded structure, have been calculated based on the statistical analysis of configurations, resulting into a new insight in the clustering properties and topology of hydrogen bonded network. It has been shown that in liquid formamide exists a continuous hydrogen bonded network and from the analysis of the distribution of small rings revealed the ring size distribution in liquid formamide. Our study resulted that the ring size distribution of the hydrogen bonded liquid formamide shows a broad distribution with a maximum around 11. It has been found that the topology in formamide is significantly different than in water.


Assuntos
Formamidas/química , Ligação de Hidrogênio , Modelos Químicos , Simulação de Dinâmica Molecular , Estrutura Molecular
3.
J Phys Chem B ; 113(13): 4054-64, 2009 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-19231825

RESUMO

The structure of a series of aqueous sodium nitrate solutions (1.9-7.6 M) was studied using a combination of experimental and theoretical methods. The results obtained from diffraction (X-ray, neutron) and molecular dynamics simulation have been compared and the capabilities and limitations of the methods in describing solution structure are discussed. For the solutions studied, diffraction methods were found to perform very well in description of hydration spheres of the sodium ion but do not yield detailed structural information on the anion's hydration structure. Molecular dynamics simulations proved to be a suitable tool in the detailed interpretation of the hydration sphere of ions, ion pair formation, and bulk structure of solutions.


Assuntos
Nitratos/química , Água/química , Simulação por Computador , Modelos Moleculares , Difração de Nêutrons , Oxigênio/química , Soluções/química , Difração de Raios X
4.
J Phys Chem A ; 113(16): 4022-7, 2009 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-19209921

RESUMO

Results from molecular dynamics simulations of aqueous hydroxide of varying concentrations have been compared with experimental structural data. First, the polarizable POL3 model was verified against neutron scattering using a reverse Monte Carlo fitting procedure. It was found to be competitive with other simple water models and well suited for combining with hydroxide ions. Second, a set of four polarizable models of OH- were developed by fitting against accurate ab initio calculations for small hydroxide-water clusters. All of these models were found to provide similar results that robustly agree with structural data from X-ray scattering. The present force field thus represents a significant improvement over previously tested nonpolarizable potentials. Although it cannot in principle capture proton hopping and can only approximately describe the charge delocalization within the immediate solvent shell around OH-, it provides structural data that are almost entirely consistent with data obtained from scattering experiments.


Assuntos
Modelos Moleculares , Hidróxido de Sódio/química , Água/química , Adsorção , Benchmarking , Simulação por Computador , Hidróxidos/química , Difração de Nêutrons , Óleos/química , Teoria Quântica , Análise Espectral , Tensão Superficial , Titulometria
5.
J Am Chem Soc ; 130(29): 9206-7, 2008 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-18576617

RESUMO

Wide-angle X-ray diffraction and molecular dynamics simulation has been used to perform complete structural characterization of nitromethane solution of a 16-membered gold(I) ring. The joint application of these two methods was an adequate tool to describe not only the structure of the complex but also the solvation properties of the complex in nitromethane and the effect of the solvation on the bulk structure. It has been found that a relatively diffuse slightly distorted solvation shell is formed around the complex, following the shape of the molecule. Nitromethane molecules in the solvation sphere are distributed randomly; no special orientation can be detected. The interaction energy of the complex with nitromethane molecules is attractive. In bulk, besides the antiparallel orientation of the nitromethane molecules, T-shape orientation and long-range order in antidipole orientation can also be detected.

6.
Phys Chem Chem Phys ; 10(32): 5004-11, 2008 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-18688546

RESUMO

Molecular dynamics simulation has been performed to study the structure of water-methanol mixtures. Besides the evaluation of partial radial distribution functions describing the hydrogen-bonded structure of the mixtures with different composition, the statistical analysis of configurations was introduced resulting in a new insight in the clustering properties and topology of hydrogen-bonded network. The results have shown that mixtures of methanol and water exhibit extended structures in solution. At low methanol concentration the water molecules form a percolated network, the methanol molecules are incorporated as monomers or short chains and together form a percolated system. In methanol-rich mixtures short water chains and longer methanol chains build up the hydrogen-bonded clusters in the system. On the basis of the statistical analysis of configurations obtained from molecular dynamics simulation it has been found that more methanol molecules are connected to non-cyclic entities, while more water molecules form rings that might have been predicted on the basis of the stoichiometry of the mixtures. This finding can be explained by the presence of microscopic configurational inhomogeneity in water-methanol mixtures.

7.
J Chem Phys ; 128(4): 044501, 2008 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-18247963

RESUMO

To determine the structure of aqueous sodium hydroxide solutions, results obtained from x-ray diffraction and computer simulation (molecular dynamics and Car-Parrinello) have been compared. The capabilities and limitations of the methods in describing the solution structure are discussed. For the solutions studied, diffraction methods were found to perform very well in describing the hydration spheres of the sodium ion and yield structural information on the anion's hydration structure. Classical molecular dynamics simulations were not able to correctly describe the bulk structure of these solutions. However, Car-Parrinello simulation proved to be a suitable tool in the detailed interpretation of the hydration sphere of ions and bulk structure of solutions. The results of Car-Parrinello simulations were compared with the findings of diffraction experiments.


Assuntos
Simulação por Computador , Hidróxido de Sódio/química , Soluções/química , Água/química , Ligação de Hidrogênio , Modelos Moleculares , Conformação Molecular , Oxigênio/química , Sódio/química , Difração de Raios X/métodos
8.
J Chem Phys ; 126(16): 164507, 2007 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-17477614

RESUMO

Simulation (molecular dynamics and Car-Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]) and diffraction (x-ray and neutron) studies on nitromethane are compared aiming at the determination of the liquid structure. Beyond that, the capabilities of the methods to describe liquid structure are discussed. For the studied liquid, the diffraction methods are performing very well in the determination of intramolecular structure, but they do not give detailed structural information on the intermolecular structure. The good agreement between the diffraction experiments and the results of molecular dynamics simulations justifies the use of simulations for the more detailed description of the liquid structure using partial radial distribution functions and orientational correlation functions. Liquid nitromethane is described as a molecular liquid without strong intermolecular interactions such as hydrogen bonding, but with detectable orientational correlations resulting in preferential antiparallel order of the neighboring molecules.

9.
J Am Chem Soc ; 128(39): 12668-70, 2006 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-17002359

RESUMO

We report the synthesis and solution- and solid-state characterization of gold(I) rings with short 1,9-transannular Au...Au interactions. The 9- and 16-membered gold(I) rings were prepared by reacting 9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene and (Me2S)AuCl in the presence of AgNO3 in the molar ratio of 1:0.5:1 and 1:1:1, respectively. X-ray crystallographic measurements in conjunction with solution X-ray diffraction and NMR methods have been used to determine the structure of gold(I) rings, and we also gained insight into the dynamics. The nine-membered gold(I) ring is chiral, and the crystal contains only one of the two enantiomers, either right- or left-handed. To the best of our knowledge this represents the first example of crystallization-induced spontaneous resolution of a binuclear gold(I) cycle. The 16-membered ring with 1,9-transannular Au...Au interaction is in a figure-eight conformation.

10.
J Am Chem Soc ; 127(30): 10731-8, 2005 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-16045362

RESUMO

Wide-angle X-ray scattering and diffusion NMR techniques have been used to obtain structural information on three self-assembled metallacyclic supramolecular complexes in solution: a rectangle, a triangle, and a three-diminsional cage. The low-angle region of the measured diffraction patterns and hydrodynamic radii calculations, determined from DOSY NMR experiments, suggest that the supramolecular assemblies retain their shape when dissolved in nitromethane. The experimental structure functions for the large-angle region have been analyzed, and the intramolecular contributions of the platinum-platinum interactions are discussed. These scattering measurements provide evidence that the supramolecular assemblies are not as rigid in solution as they are in the single crystal. Finally, by analysis of the radial distribution functions of the solutions, direct structural information (e.g., platinum-platinum intramolecular distances and coordination number) about the supramolecular assemblies has been obtained.


Assuntos
Espectroscopia de Ressonância Magnética/métodos , Compostos Organoplatínicos/química , Platina/química , Difração de Raios X/métodos , Modelos Moleculares , Soluções
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