The structure and phase behavior of oppositely charged macroions in solution have been studied with Monte Carlo simulations using the primitive model where the macroions and small ions are described as charged hard spheres. Size and charge symmetric, size asymmetric, and charge asymmetric macroions at different electrostatic coupling strengths are considered, and the properties of the solutions have been examined using cluster size distribution functions, structure factors, and radial distribution functions. At increasing electrostatic coupling, the macroions form clusters and eventually the system displays a phase instability, in analogy to that of simple electrolyte solutions. The relation to the similar cluster formation and phase instability occurring in solutions containing oppositely charged polymers is also discussed.

The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed Ag(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P-OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra.

The kinetic shift that exists between two competing unimolecular fragmentation processes has been used to establish whether or not gas-phase Mn 2ϩ exhibits preferential solvation when forming mixed clusters with water and methanol. Supported by molecular orbital calculations, these first results for a metal dication demonstrate that Mn 2ϩ prefers to be solvated by methanol in the primary solvation shell. (J Am Soc Mass Spectrom 2008, 19, 520 -530 [4 -9], but equally important is behavior in many-component solvents, where competing interactions may be dominated by differences in molecular properties [10 -12]. In general, a condensed phase solution containing solvents with very similar pure-state properties might be expected to behave in a manner that reflects the composition of the solvent mixture [13]. There have been several attempts to simulate the behavior of metal dications in mixed solvent systems, [14 -18], and of particular significance to the work discussed here are the molecular dynamics studies of Day and Patey [14,15]. From simulations of an ion in the presence of water and methanol they concluded that a positively charged solute exhibits a pronounced preference for water. If there are large differences in the solvating abilities of the components, selective or preferential solvation may occur [11,12]; however, the degree of averaging present in a typical condensed phase system means that subtle effects due to small differences in free energy are unlikely to make their presence felt [13]. In contrast, the consequences of small, individual differences in molecular properties can be amplified in the gas phase because of the influence they may have on establishing equilibria or determining fragmentation pathways [10, 19 -21]. Presented here are the results of a study designed to see if an established technique for generating multiply charged metal/solvent complexes in the gas phase can yield useful information on behavior in mixed solvent systems. From this first study, the experimental results demonstrate that for water and methanol as solvents, gas-phase Mn 2ϩ does exhibit preferential solvation. This conclusion is supported by detailed molecular orbital calculations on a wide range of mixed [Mn(MeOH) 2ϩ complexes, which show that small differences in the binding energies of methanol and water are sufficient to account for the experimental results. ExperimentalThe experimental apparatus used for the generation and detection of gas-phase multiply charged metalligand complexes has been described extensively in previous publications [22]. Briefly, mixed neutral argon/ligand clusters are produced by the adiabatic expansion of solvent vapor mixed with argon through a pulsed supersonic nozzle. Previous work on the preferential solvation of hydrogen ions in clusters composed of methanol and water showed that the composition of ionized clusters depended quite significantly on the composition of the coexpansion mixture [19]. In this study, several mixtures were evaluated, but it was found that a ratio of 5:1,...

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Under considerations in the current study are reactions of the type ½Mn LOH ðwhere the ligand LOH represents water or/and methanol. Preferential proton transfer reactions and loss of any ligand fragments are discussed in the light of ligand polarizability, dipole moment, dissociation energy, proton affinity, differences in ligand-ion ionization energy, and ion radii. The results indicate the proton affinity and dissociation energy of the O-H bond are more important for the overall proton transfer reaction than differences in the first ionization energy of the ligand and the second ionization energy of the metal ion.