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Solvation Shell (solvation + shell)
Selected AbstractsCharge and Mass Transfer Across the Metal/Solution InterfaceISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2008Eliezer Gileadi Electrode reactions are characterized by charge transfer across the interface. The charge can be carried by electrons or by ions. It is shown here that when both mass and charge cross the interface, the charge must be carried by the ionic species, not by the electrons, as a result of the very large difference in the time scale for electron and ion transfer. A prime example of charge transfer by ions is metal deposition. It is proposed that ion transfer occurs by migration of the ions across the interface, under the influence of the high electrostatic field in the double layer. The rate constants observed for metal deposition are comparable to those for outer-sphere charge transfer. These unexpectedly high rate constants for metal deposition are explained by a model in which removal of the solvation shell and reduction of the effective charge on the metal ion occur in many small steps, and a make-before-break mechanism exists, which lowers the total Gibbs energy of the system as it moves along the reaction coordinate from the initial to the final state. [source] Femtosecond dynamics of electron transfer, localization, and solvation processes at the ice,metal interfaceISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2005Uwe Bovensiepen The ultrafast dynamics of excess electrons in amorphous ice layers on single-crystal metal surfaces are investigated by femtosecond time- and angle-resolved two-photon-photoemission spectroscopy. Photoexcited electrons are injected from the metal substrate into delocalized states of the conduction band of ice and localize in the ice layer within 100 fs. Subsequently, energetic stabilization of this localized species is observed on a time scale of ,1 ps, which is attributed to electron solvation by nonadiabatic coupling to nuclear degrees of freedom of the surrounding polar molecular environment. Concomitant with this stabilization process, residual wave function overlap of the solvated electron with the metal substrate results in back-transfer by tunneling through the solvation shell. At such interfaces the correlation of electronic and molecular structure with the resulting solvation dynamics can be explored using different substrates as a template. Here we compare data on molecularly thin D2O ice layers grown on Cu(111) and Ru(001). On Ru(001) both the stabilization and back-transfer proceed about three times faster compared to Cu(111), which is attributed to different interfacial structures and the role of d-states, and projected band gaps in the electron transfer process. [source] N2O in small para -hydrogen clusters: Structures and energeticsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2009Hua Zhu Abstract We present the minimum-energy structures and energetics of clusters of the linear N2O molecule with small numbers of para -hydrogen molecules with pairwise additive potentials. Interaction energies of (p- H2),N2O and (p- H2),(p- H2) complexes were calculated by averaging the corresponding full-dimensional potentials over the H2 angular coordinates. The averaged (p- H2),N2O potential has three minima corresponding to the T-shaped and the linear (p- H2),ONN and (p- H2),NNO structures. Optimization of the minimum-energy structures was performed using a Genetic Algorithm. It was found that p- H2 molecules fill three solvation rings around the N2O axis, each of them containing up to five p- H2 molecules, followed by accumulation of two p- H2 molecules at the oxygen and nitrogen ends. The first solvation shell is completed at N = 17. The calculated chemical potential oscillates with cluster size up to the completed first solvation shell. These results are consistent with the available experimental measurements. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Supramolecular catalysis induced by polysaccharides.JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003Homogeneous hydrolysis of p -nitrobenzyl amylose xanthate Abstract p -Nitrobenzyl amylose xanthate (AmXNB) was synthesized and characterized by 13C NMR spectroscopy in solution and the solid state. The degree of substitution (DS), calculated from the sulfur content, was 7.0, and this value was similar to that obtained from solid-state 13C NMR using the signal of C-1 as internal standard. The hydrolysis of AmXNB was studied in 10% (v/v) DMSO with,µ,=,0.5 (KCl) at 25,°C. The basic hydrolysis was pseudo-first order, but the water-catalyzed hydrolysis in the pH range 7,9 showed a biphasic plot of ln (,Absorbance) vs time, as has been observed for cellulose xanthate esters, occurring through two parallel reactions with rate constants k,H2O (fast),=,5.3,×,10,5 s,1 and k,H2O (slow),=,3.3,×,10,6 s,1. The fast hydrolysis was more than three orders of magnitude faster than that of the O -ethyl analog. The activation parameters were ,H,,=,20.5,kcal,mol,1 and ,S,,=,+10 cal K,1,mol,1. They showed that the acceleration of the fast hydrolysis of AmXNB and cellulose analogs is due to an entropy of activation effect. There is a linear increase of logk,H2O (fast) with increase in the concentration of the small Li+ ion that produces an increase of the 3-D hydrogen-bond network of water while the large singly charged iodide ion has a considerable inverse effect. These results are strongly consistent with the theory that the supramolecular catalysis induced by modified polysaccharide esters is due to the 3-D hydrogen-bond network of the water in the solvation shell. Copyright © 2003 John Wiley & Sons, Ltd. [source] Probing the solvation shell of organic molecules by intermolecular 1H NOESY,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2002Alessandro Bagno Abstract The solvation of some neutral and charged organic molecules (phenol, nitroanilines, tetraalkylammonium) in binary solvent mixtures was investigated by means of intermolecular 1H-NOESY NMR spectroscopy. The solvation shell of the solute is, in most cases, selectively enriched in one of the cosolvents (preferential solvation). The origin of preferential solvation is discussed in terms of solute,solvent interactions and microheterogeneity in the solvent mixture. Copyright © 2002 John Wiley & Sons, Ltd. [source] Solvation of Uranyl(II), Europium(III) and Europium(II) Cations in "Basic" Room-Temperature Ionic Liquids: A Theoretical StudyCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2004Alain Chaumont Abstract We report a molecular dynamics study of the solvation of UO22+, Eu3+ and Eu2+ ions in two "basic" (Lewis acidity) room-temperature ionic liquids (IL) composed of the 1-ethyl-3-methylimidazolium cation (EMI+) and a mixture of AlCl4, and Cl, anions, in which the Cl,/AlCl4, ratio is about 1 and 3, respectively. The study reveals the importance of the [UO2Cl4]2, species, which spontaneously form during most simulations, and that the first solvation shell of europium is filled with Cl, and AlCl4, ions embedded in a cationic EMI+ shell. The stability of the [UO2Cl4]2, and [EuIIICl6]3, complexes is supported by quantum mechanical calculations, according to which the uranyl and europium cations intrinsically prefer Cl, to the AlCl4, ion. In the gas phase, however, [EuIIICl6]3, and [EuIICl6]4, complexes are predicted to be metastable and to lose two to three Cl, ions. This contrasts with the results of simulations of complexes in ILs, in which the "solvation" of the europium complexes increases with the number of coordinated chlorides, leading to an equilibrium between different chloro species. The behavior of the hydrated [Eu(OH2)8]3+ complex is considered in the basic liquids; the complex exchanges H2O molecules with Cl, ions to form mixed [EuCl3(OH2)4] and [EuCl4(OH2)3], complexes. The results of the simulations allow us to better understand the microscopic nature and solvation of lanthanide and actinide complexes in "basic" ionic liquids. [source] Hydration of the Calcium Dication: Direct Evidence for Second Shell Formation from Infrared SpectroscopyCHEMPHYSCHEM, Issue 15 2007Matthew F. Bush Abstract Infrared laser action spectroscopy in a Fourier-transform ion cyclotron resonance mass spectrometer is used in conjunction with ab initio calculations to investigate doubly charged, hydrated clusters of calcium formed by electrospray ionization. Six water molecules coordinate directly to the calcium dication, whereas the seventh water molecule is incorporated into a second solvation shell. Spectral features indicate the presence of multiple structures of Ca(H2O)72+ in which outer-shell water molecules accept either one (single acceptor) or two (double acceptor) hydrogen bonds from inner-shell water molecules. Double-acceptor water molecules are predominately observed in the second solvent shells of clusters containing eight or nine water molecules. Increased hydration results in spectroscopic signatures consistent with additional second-shell water molecules, particularly the appearance of inner-shell water molecules that donate two hydrogen bonds (double donor) to the second solvent shell. This is the first reported use of infrared spectroscopy to investigate shell structure of a hydrated multiply charged cation in the gas phase and illustrates the effectiveness of this method to probe the structures of hydrated ions. [source] Micro-Hydration of the MgNO3+ Cation in the Gas PhaseCHEMPHYSCHEM, Issue 11 2007Barbara Jagoda-Cwiklik Dr. Abstract Coordination complexes of the magnesium nitrate cation with water [MgNO3(H2O)n]+ up to n=7 are investigated by experiment and theory. The fragmentation patterns of [MgNO3(H2O)n]+ clusters generated via electrospray ionization indicate a considerable change in stability between n=3 and 4. Further, ion,molecule reactions of mass-selected [MgNO3(H2O)n]+ cations with D2O reveal the occurrence of consecutive replacement of water ligands by heavy water, and in this respect the complexes with n=4 and 5 are somewhat more reactive than their smaller homologs with n=1,3 as well as the larger clusters with n=6 and 7. For the latter two ions, the theory suggests the existence of isomers, such as complexes with monodentate nitrato ligands as well as solvent-separated ion pairs with a common solvation shell. The reactions observed and the ion thermochemistry are discussed in the context of ab initio calculations, which also reveal the structures of the various hydrated cation complexes. [source] Solvolysis of Some Arenediazonium Salts in Binary EtOH/H2O Mixtures under Acidic ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2003Román Pazo-Llorente Abstract We have determined the product distribution, the rate constants for dediazoniation product formation, and the solvolytic rate constants for 2-, 3-, and 4-methylbenzenediazonium ions (2-, 3-, and 4-MBD, respectively) loss in acidic ethanol/water mixtures over the whole composition range by a combination of spectrophotometric (UV/Vis) and high performance liquid chromatography (HPLC) measurements. The observed rate constants (kobs) for substrate loss are equal to those for product formation, and they remain essentially constant (2-MBD) with changing solvent composition but increase by a factor of ,2 (4MBD) on going from water to 100% EtOH. Up to four dediazoniation products , cresols (ArOH), chlorotoluene (ArCl), methylphenetole (ArOEt), and toluene (ArH) , were detected, depending on the solvent composition; the major dediazoniation products were the ArOH and ArOEt derivatives. The product selectivity (S) of the reaction towards nucleophiles is low and essentially constant with changing solvent composition, and good linear correlations between log kobs and YCl (solvent ionizing power) were observed for the three ArN2+ ions. All data are consistent with the rate-determining formation of an aryl cation, which reacts immediately with available nucleophiles. The data suggest that the distribution of neutral and anionic nucleophiles in the neighborhood of the ground state arenediazonium ion remains essentially unchanged upon dediazoniation, the observed product distribution reflecting the concentrations of nucleophiles in their immediate environment (i.e., in the first solvation shells of the arenediazonium ions). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Kinetic Study of Thermal Z to E Isomerization Reactions of Azobenzene and 4-Dimethylamino-4,-nitroazobenzene in Ionic Liquids [1-R-3-Methylimidazolium Bis(trifluoromethylsulfonyl)imide with R=Butyl, Pentyl, and Hexyl]CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2006Keita Baba Abstract Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4,-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R=butyl, pentyl, and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the viscosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4,-nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers,Grote,Hynes model or by the Agmon,Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 104,107 s,1. [source] | ||||||||||||||||||||||