“Co-Binding of Pharmaceutical Compounds at Mineral Surfaces: Molecular Investigations of Dimer Formation at Goethite/Water Interfaces”
in Environmental Science and Technology, http://pubs.acs.org/doi/abs/10.1021/acs.est.7b02835
Jing Xu, Rémi Marsac, Dominique Costa , Wei Cheng, Feng Wu, Jean-François Boily, and Khalil Hanna
The emergence of antibiotic and anti-inflammatory agents in aquatic and terrestrial systems is becoming a serious threat to human and animal health worldwide. Because pharmaceutical compounds rarely exist individually in nature, interactions between various compounds can have unforeseen effects on their binding to mineral surfaces. This work demonstrates this important possibility for the case of two typical antibiotic and anti-inflammatory agents (nalidixic acid (NA) and niflumic acid (NFA)) bound at goethite (α-FeOOH) used as a model mineral surface. Our multidisciplinary study, which makes use of batch sorption experiments, vibration spectroscopy and periodic density functional theory calculations, reveals enhanced binding of the otherwise weakly bound NFA caused by unforeseen intermolecular interactions with mineral-bound NA. This enhancement is ascribed to the formation of a NFA–NA dimer whose energetically favored formation (−0.5 eV compared to free molecules) is predominantly driven by van der Waals interactions. A parallel set of efforts also showed that no cobinding occurred with sulfamethoxazole (SMX) because of the lack of molecular interactions with coexisting contaminants. As such, this article raises the importance of recognizing drug cobinding, and lack of cobinding, for predicting and developing policies on the fate of complex mixtures of antibiotics and anti-inflammatory agents in nature.
“Atomistic simulations of cation hydration in sodium and calcium montmorillonite nanopores”
in The Journal of Chemical Physics, http://aip.scitation.org/doi/10.1063/1.4992001
Guomin Yang, Ivars Neretnieks, and Michael Holmboe
During the last four decades, numerous studies have been directed to the swelling smectite-rich clays in the context of high-level radioactive waste applications and waste-liners for contaminated sites. The swelling properties of clay mineral particles arise due to hydration of the interlayer cations and the diffuse double layers formed near the negatively charged montmorillonite (MMT) surfaces. To accurately study the cation hydration in the interlayer nanopores of MMT, solvent-solute and solvent-clay surface interactions (i.e., the solvation effects and the shape effects) on the atomic level should be taken into account, in contrast to many recent electric double layer based methodologies using continuum models. Therefore, in this research we employed fully atomistic simulations using classical molecular dynamics (MD) simulations, the software package GROMACS along with the CLAYFF forcefield and the SPC/E water model. We present the ion distributions and the deformation of the hydrated coordination structures, i.e., the hydration shells of Na+ and Ca2+ in the interlayer, respectively, for MMT in the first-layer, the second-layer, the third-layer, the fourth-layer, and the fifth-layer (1W, 2W, 3W, 4W, and 5W) hydrate states. Our MD simulations show that Na+ in Na-MMT nanopores have an affinity to the ditrigonal cavities of the clay layers and form transient inner-sphere complexes at about 3.8 Å from clay midplane at water contents less than the 5W hydration state. However, these phenomena are not observed in Ca-MMT regardless of swelling states. For Na-MMT, each Na+ is coordinated to four water molecules and one oxygen atom of the clay basal-plane in the first hydration shell at the 1W hydration state, and with five to six water molecules in the first hydration shell within a radius of 3.1 Å at all higher water contents. In Ca-MMT, however each Ca2+ is coordinated to approximately seven water molecules in the first hydration shell at the 1W hydration state and about eight water molecules in the first hydration shell within a radius of 3.3 Å at all higher hydration states. Moreover, the MD results show that the complete hydration shells are nearly spherical with an orthogonal coordination sphere. They could only be formed when the basal spacing d001 ≥ 18.7 Å, i.e., approximately, the interlayer separation h ≥ 10 Å. Comparison between DFT and MD simulations shows that DFT failed to reproduce the outer-sphere complexes in the Stern-layer (within ∼5.0 Å from the clay basal-plane), observed in the MD simulations.
“Surface chemistry of carbon dioxide revisited”
in Surface Chemistry, https://doi.org/10.1016/j.surfrep.2016.09.001
Taifan, William; Boily, Jean-François; Baltrusaitis, Jonas.
This review discusses modern developments in CO2 surface chemistry by focusing on the work published since the original review by H.J. Freund and M.W. Roberts two decades ago (Surface Science Reports 25 (1996) 225–273). It includes relevant fundamentals pertaining to the topics covered in that earlier review, such as conventional metal and metal oxide surfaces and CO2 interactions thereon. While UHV spectroscopy has routinely been applied for CO2 gas–solid interface analysis, the present work goes further by describing surface–CO2 interactions under elevated CO2 pressure on non-oxide surfaces, such as zeolites, sulfides, carbides and nitrides. Furthermore, it describes additional salient in situ techniques relevant to the resolution of the interfacial chemistry of CO2, notably infrared spectroscopy and state-of-the-art theoretical methods, currently used in the resolution of solid and soluble carbonate species in liquid–water vapor, liquid–solid and liquid–liquid interfaces. These techniques are directly relevant to fundamental, natural and technological settings, such as heterogeneous and environmental catalysis and CO2 sequestration.
“Diverse composites of metal-complexes and PEDOT facilitated by metal-free vapour phase polymerization”
in Reactive and Functional Polymers, 2017, 116, 101-106.
Acharya, Shravan S.; Eastone, Christopher D.; McCoy, Thomas M.; Spiccia, Leone; Ohlin, C. André; Winther-Jensen, Bjorn
Abstract: Oxidative polymerization for the manufacture of conducting polymers such as poly(3,4-ethylenedioxy- thiophene) has traditionally employed iron(III) salts. Demonstrated in this study is vapour phase polymerization of 3,4-ethylenedio-xythiophene using a metal-free oxidant, ammonium persulfate, leading to films with an estimated conductivity of 75 S/cm. Additionally, a route for embedding active transition metal complexes into these poly(3,4-ethylenedioxythiophene)-poly(styrene-4-sulfonate) (PEDOT/PSS) films via vapour assisted complexation is outlined. Here, the vapour pressure of solid ligands around their melting temperatures was exploited to ensure complexation to metal ions added into the oxidant mixture prior to polymerization of PEDOT. Four composite systems are discussed, viz. PEDOT/PSS embedded with tris(8-hydroxyquinolinato)cobalt(III), tris(2,2-bipyridine)cobalt(II), tris(1,10- phenanthroline)cobalt(II) and tris(8-hydroxyquinolinato)aluminium(III). Using these composites, electrochemical reduction of nitrite to ammonia with a faradaic efficiency of 61% was reported.
“Rates of water exchange in 2,2′-bipyridine and 1,10-phenanthroline complexes of Co(II) and Mn(II)”
in Australian Journal of Chemistry, 2017, 70, 751-754,
Acharya, Shravan S.; Winther-Jensen, Bjorn; Spiccia, Leone; Ohlin, C. André
Abstract: The rates and activation parameters of water exchange at pH 3.0 have been determined using variable temperature 17O NMR for four Co(II) complexes and one Mn(II) complex, viz. [Co(bpy)(H2O)4]2+, [Co(bpy)2(H2O)2]2+, [Co(phen)- (H2O)4]2+, [Co(phen)2(H2O)2]2+, and [Mn(bpy)(H2O)4]2+. Substitution of 1,10-phenanthroline or 2,2′-bipyridyl for aquo ligands leads to an increase in the rate of exchange in the manganese complexes, from k 298 (1.8 ± 0.1) · 10 7 for [Mn(H2O)6]2+ to (7.2 ± 0.3) · 10 7 s -1 for [Mn(phen)2(H2O)2]2+ , whereas the trends are more complex for the cobalt complexes. We have used the new data in conjunction with literature data for similar complexes to analyse the impact of M-OH2 distance and degree of substitution.
“27Al MQMAS of the δ-Al13-Keggin”
in Dalton Transactions, 2017, 46, 2249-2254.
Pilgrim, Corey D.; Callahan, Joseph R.; Christopher A. Colla; Ohlin, C. André; Harris E., Mason; Casey, William H.
Abstract: One-dimensional 27Al, 23Na, Magic-Angle-Spinning (MAS) NMR and 27Al Multiple-Quantum Magic-Angle-Spinning NMR (MQMAS) measurements are reported for the δ-isomer of the Al13 Keggin structure at high spinning speed and 14.1 T field. Values for the CQ and η parameters are on the same scale as those seen in other isomers of the Al13 structure. Density functional theory (DFT) calculations are performed for comparison to the experimental fits using the B3PW91/6-31+G* and PBE0/6-31+G* levels of theory, with the Polarizable Continuum Model (PCM).
“A Non-Aqueous Microwave Assisted Protocol for Accessing Molybdovanadates”
in Angewandte Chemie, International Edition, 2017, 56(29), 8568–8572.
Spillane, Samuel; Sharma, Rupali; Zavras, Athanasios; Mulder, Roger; Ohlin, C. André; Goerigk, Lars; Best, Stephen P.; O’Hair, Richard A. J.; Ritchie, Chris
Abstract: We report a novel approach for the synthesis of heterohexa- and heterodecametalates via the use of non-aqueous, microwave assisted reaction conditions. The two novel molybdovanadates have been isolated and characterized in the solid and solution states using single-crystal X-ray diffraction, FT-IR, UV/Vis, multinuclear NMR, and ESI-MS. The relative stabilities of the possible structural isomers were probed using DFT calculations for both polyoxometalate systems.