Search results for "Counterion"

Atomistic Simulations of Functional Au_{144}(SR)_{60} Gold Nanoparticles in Aqueous Environment

2012

Charged monolayer-protected gold nanoparticles (AuNPs) have been studied in aqueous solution by performing atomistic molecular dynamics simulations at physiological temperature (310 K). Particular attention has been paid to electrostatic properties that modulate the formation of a complex comprised of the nanoparticle together with surrounding ions and water. We focus on Au-144 nanoparticles that comprise a nearly spherical Au core (diameter similar to 2 nm), a passivating Au-S interface, and functionalized alkanethiol chains. Cationic and anionic AuNPs have been modeled with amine and carboxyl terminal groups and Cl-/Na+ counterions, respectively. The radial distribution functions show tha…

Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran

1997

The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between -20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M w /M n < 1.1). The dependence of the measured rate constants on the active center concentratio…

Front Cover: Magnetic Bistability in Macrocycle‐Based Fe II Spin‐Crossover Complexes: Counter Ion and Solvent Effects (Eur. J. Inorg. Chem. 34/2016)

2016

DNA nucleobase properties and photoreactivity: Modeling environmental effects

2009

Abstract The accurate ab initio quantum chemical (QM) method multiconfigurational second-order perturbation (CASSPT2)/complete active space self-consistent field (CASSCF) has been used in conjunction with molecular mechanics (MM) procedures to compute molecular properties and photoinduced reactivity of DNA/RNA nucleobases (NABs) in isolation and within a realistic environment, in which the double helix strand, the aqueous media, and the external counterions are included. It is illustrated that the use of an MM model is helpful both to account for short- and long-range effects of the system surrounding the QM molecular core and to provide the proper structural constraints that allow more acc…

FT-IR investigation of the state of iron (III) chloride clusters confined in AOT reverse micelles dispersed in carbon tetrachloride

2007

The state of the water-soluble salt iron(III) chloride in AOT reverse micelles dispersed in carbon tetrachloride has been investigated by FT-IR spectroscopy. Interestingly, while the entrapment of a lot of water-soluble inorganic salts in AOT reverse micelles requires preliminarily the presence of significant amounts of water within the micellar core, solubilization of FeCl3 occurs without the need to add water in the micellar solution reaching the very high solubility value, expressed as the maximum salt-to-surfactant molar ratio, of 1.30. The analysis of the spectral features of the investigated samples leads to hypothesize that iron(III) chloride is confined within the reverse micellar c…

Counterion's Effect on the Catalytic Activity of Zn-Prolinamide Complexes in Aldol Condensations

2012

The catalytic activity of complexes involving organic ligands and Lewis acids can be modulated by changing any of their components. In this work we have studied the influence on the stereoselectivity and catalytic activity exerted by the counterion of zinc salts employed as cocatalysts of L-prolinamide in aldol condensations. The structures of the complexes have been determined both in solution and in the solid state.

Synthesis, Spectroscopic, and Structural Investigation of the Cyclic [N(PR2E)2]+ Cations (E = Se, Te; R = iPr, Ph):  the Effect of Anion and R-Group …

2006

Two-electron oxidation of the [N(PiPr2E)2]- anion with iodine produces the cyclic [N(PiPr2E)2]+ (E =Se, Te) cations, which exhibit long E-E bonds in the iodide salts [N(PiPr2Se)2]I (4) and [N(PiPr2Te)2]I (5). The iodide salts 4 and 5 are converted to the ion-separated salts [N(PiPr2Se)2]SbF6 (6) and [N(PiPr2Te)2]SbF6 (7) upon treatment with AgSbF6. Compounds 4-7 were characterized in solution by multinuclear NMR, vibrational, and UV-visible spectroscopy supported by DFT calculations. A structural comparison of salts 4-7 and [N(PiPr2Te)2]Cl (8) confirms that the long E-E bonds in 4, 5, and 8 can be attributed primarily to the donation of electron density from a lone pair of the halide counte…

2,2’Bipyrimidine: A Useful Tool in Designing Polynuclear Complexes of Controlled Nuclearity

1996

The versatility of a simple ligand such as 2,2’-bipyrimidine (bpym) which can adopt chelating and bis(chelating) coordination modes facilitates the preparation of both mononuclear and polynuclear complexes whose nuclearity can be controlled by playing with the metal to bpym molar ratio, the nature of the counterion and the presence of additional ligands. In this work, we summarize our results dealing with the preparation and the structural and magnetic characterization of complexes between first-row transition metal ions and bpym. Examples of orbital reversal and tunable exchange in bpym-containing copper(II) complexes are presented and discussed. The influence of the number of unpaired ele…

Morphology and local organization of water-containing (1R,2S)-Dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide reverse micelles disp…

2014

The structure of (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) reverse micelles, at various water-to-surfactant molar ratio (R-w, R-w = [water]/[DMEB]) and DMEB concentrations, has been investigated by small angle X-ray scattering (SAXS) and extended X-ray absorption fine structure spectroscopy (EXAFS). SAXS data of dry reverse micelles are consistent with a model of spherical hydrophilic core surrounded by DMEB alkyl chains whose polydispersity decreases significantly with surfactant concentration. By adding water, a sphere to cylinder transition occurs leading to a one-dimensional growth of reverse micellar cores with R-w and surfactant concentration. Th…

N,N,N-Alkyloctyldimethylammonium Chlorides in Water: A Thermodynamic Investigation

1993

Abstract Specific conductivities, densities, heat capacities and enthalpies of dilution at 298 K and osmotic coefficients at 310 K were measured for N,N,N -octylbutyldimethylammonium, N,N,N -octylpentyldimethylammonium, and N,N -dioctyldimethylammonium chlorides in water as functions of concentration. From the specific conductivity data, the CMC and the degree of the counterion dissociation have been calculated. It is shown that additional CH 2 groups in the variable alkyl chain affect both CMC and β less than they do in the single chain surfactants. The partial molar volumes, heat capacities, relative enthalpies, nonideal free energies, and entropies at 298 K were derived as functions of t…