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Karamertzanis P.G.,Imperial College London | Raiteri P.,Nanochemistry Research Institute | Galindo A.,Imperial College London
Journal of Chemical Theory and Computation | Year: 2010

We propose a novel, anisotropic rigid-body intermolecular potential model to predict the properties of water and the hydration free energies of neutral organic solutes. The electrostatic interactions of water and the solutes are modeled using atomic multipole moments up to hexadecapole; these are obtained from distributed multipole analysis of the quantum mechanically computed charge densities and include average polarization effects in solution. The repulsion-dispersion water-water interactions are modeled with a three-site, exp-6 model fitted to the experimental liquid water density and oxygen-oxygen radial distribution function at ambient conditions. The proposed water model reproduces well several water properties not used in its parametrization, including vapor-liquid coexistence densities, the maximum in liquid water density at atmospheric pressure, the structure of ordered ice polymorphs, and the liquid water heat capacity. The model is used to compute the hydration free energy of 10 neutral organic solutes using explicit-solvent free energy perturbation. The solute-solute repulsion-dispersion intermolecular potential is obtained from previous parametrizations on organic crystal structures. In order to calculate the free energies of hydration, water-solute repulsion-dispersion interactions are modeled using Lorenz-Berthelot combining rules. The root-mean-square error of the predicted hydration free energies is 1.5 kcal mol-1, which is comparable to the error found using a continuum mean-field quantum mechanical approach parametrized using experimental free energy of hydration data. The results are also contrasted with explicit-solvent hydration free energies obtained with an atomic charge representation of the solutes charge density computed at the same level of theory used to compute the distributed multipoles. Replacing the multipole description of the solutes charge density with an atomic charge model changes the free energy of hydration by as much as 3 kcal mol-1 and provides an estimate for the effect of the modeling quality of the intermolecular electrostatic forces in free energy of solvation calculations. © 2010 American Chemical Society. Source

Liu Y.,Nanochemistry Research Institute | Holzinger A.,University of Ulm | Knittel P.,University of Ulm | Poltorak L.,CNRS Laboratory of Physical Chemistry and Microbiology for the Environment | And 6 more authors.
Analytical Chemistry | Year: 2016

The direct experimental characterization of diffusion processes at nanoscale remains a challenge that could help elucidate processes in biology, medicine and technology. In this report, two experimental approaches were employed to visualize ion diffusion profiles at the orifices of nanopores (radius (ra) of 86 ± 6 nm) in array format: (1) electrochemically assisted formation of silica deposits based on surfactant ion transfer across nanointerfaces between two immiscible electrolyte solutions (nanoITIES); (2) combined atomic force - scanning electrochemical microscopy (AFM-SECM) imaging of topography and redox species diffusion through the nanopores. The nature of the diffusion zones formed around the pores is directly related to the interpore distance within the array. Nanopore arrays with different ratios of pore center-to-center separation (rc) to pore radius (ra) were fabricated by focused ion beam (FIB) milling of silicon nitride (SiN) membranes, with 100 pores in a hexagonal arrangement. The ion diffusion profiles determined by the two visualization methods indicated the formation of overlapped or independent diffusion profiles at nanopore arrays with rc/ra ratios of 21 ± 2 and 91 ± 7, respectively. In particular, the silica deposition method resulted in formation of a single deposit encompassing the complete array with closer nanopore arrangement, whereas individual silica deposits were formed around each nanopore within the more widely spaced array. The methods reveal direct experimental evidence of diffusion zones at nanopore arrays and provide practical illustration that the pore-pore separation within such arrays has a significant impact on diffusional transport as the pore size is reduced to the nanoscale. These approaches to nanoscale diffusion zone visualization open up possibilities for better understanding of molecular transport processes within miniaturized systems. © 2016 American Chemical Society. Source

Silvester D.S.,Nanochemistry Research Institute | Silvester D.S.,Curtin University Australia | Uprety S.,Nanochemistry Research Institute | Uprety S.,Curtin University Australia | And 4 more authors.
Journal of Physical Chemistry C | Year: 2012

The redox properties of a rhenium-tetrazolato complex, namely fac-[Re(CO) 3(phen)L] (where L is 5-(4'-cyanophenyl)tetrazolate), have been studied by cyclic voltammetry in a range of common room temperature ionic liquids (RTILs) with different anions and cations. In all eight RTILs, one reduction and two oxidation peaks are observed. It is believed that the reduction peak corresponds to ligand reduction and the two oxidation peaks are two one-electron oxidations of the metal from Re(I) to Re(II) and Re(II) to Re(III). The redox potentials of the metal oxidations appear to be unchanged with the solvent; however, the potential for the reduction peak is more negative in RTILs containing the [P 14,6,6,6] + cation, suggesting a stabilization effect of the electrogenerated intermediate with the other RTIL cations studied (imidazolium and pyrrolidinium). Potential step chronoamperometric experiments were used to calculate diffusion coefficients of the complex in RTILs, and it was found that fac-[Re(CO) 3(phen)L] diffuses very slowly through the RTIL medium. A plot of diffusion coefficient against the inverse of viscosity of the RTIL solvent showed a linear trend, suggesting that the Stokes-Einstein relationship generally applies for this complex in RTILs, but the coefficient on the denominator is likely to be closer to 4 (the "slip"limit) than 6 (the stick limit) when taking into account the hydrodynamic radius. © 2012 American Chemical Society. Source

Van Der Pal K.J.,Nanochemistry Research Institute | Van Der Pal K.J.,Curtin University Australia | Sauzier G.,Nanochemistry Research Institute | Sauzier G.,Curtin University Australia | And 6 more authors.
Talanta | Year: 2016

This paper presents a study into the chemical changes occurring within automotive clear coats as a result of environmental weathering, and their potential effect upon the characterisation of samples using infrared spectroscopy combined with chemometric modelling. Testing of three samples, collected from separate vehicles, exposed to the outside environment revealed no changes in model predictions over a 175 day period; however, incorrect predictions were observed following 435 days of exposure. Inspection of the corresponding infrared spectra revealed that these changes were likely due to the hydrolysis and photodegradation of polymer chains present in the clear coat, which were not observed in samples stored away from the outside environment over a one-year period. Analysis of previously weathered samples using synchrotron infrared microscopy found these changes occurred in a top-down fashion rather than within the bulk of the clear coat. This indicates that although weathering may affect the surface characterisation of clear coats over time, the targeting of deeper portions of the clear coat layer may still provide useful information as to the identity of the vehicle. © 2015 Elsevier B.V. Source

Van Der Pal K.J.,Nanochemistry Research Institute | Van Der Pal K.J.,Curtin University Australia | Maric M.,Nanochemistry Research Institute | Maric M.,Curtin University Australia | And 3 more authors.
Analytical Methods | Year: 2015

Automotive window tint samples sourced from Western Australian retailers were analysed using transmission ultraviolet-visible spectroscopy. The spectra showed features characteristic of known window tint film components such as polyethylene terephthalate and cyclic imino esters. Principal component analysis showed that samples cluster by both groups of supplier and individual samples, indicating good reproducibility and sample separation. Window tint samples could be traced back to one of three countries of manufacture, Australia, USA and Israel, suggesting that different suppliers are sourcing their samples from the same manufacturer. This indicates the potential for window tint to be used as forensic evidence, as samples are able to be compared on a questioned versus known basis due to the variation in the sources. This journal is © The Royal Society of Chemistry. Source

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