Solvation

About: Solvation is a research topic. Over the lifetime, 21552 publications have been published within this topic receiving 746525 citations.

Evaluation of Solvent Effects in Isotropic and Anisotropic Dielectrics and in Ionic Solutions with a Unified Integral Equation Method: Theoretical Bases, Computational Implementation, and Numerical Applications

Abstract: We present the full implementation of the integral equation formalism (IEF) we have recently formulated to treat solvent effects. The method exploits a single common approach for dielectrics of very different nature: standard isotropic liquids, intrinsically anisotropic media like liquid crystals, and ionic solutions. We report here an analysis of its both formal and technical details as well as some numerical applications addressed to state the achieved generalization to all kinds of molecular solutes and to show the equally reliable performances in treating such different environmental systems. In particular, we report, for isotropic liquids, data of solvation free energies and static (hyper)polarizabilities of various molecular solutes in water, for anisotropic dielectrics, a study of an SN2 reaction, and finally, for ionic solution, a study of some structural aspects of ion pairing.

Thermodynamics of solvation of ions. Part 5.—Gibbs free energy of hydration at 298.15 K

Abstract: The standard molar Gibbs free energies of hydration, ΔhydG°, of 109 (mainly inorganic) ions ranging in their charges from –3 to +4 have been compiled and interpreted in terms of a model used previously for other thermodynamic quantities of hydration. The main contributions to ΔhydG° are the electrostatic effects, resulting in solvent immobilization, electrostriction, and dielectric saturation in a hydration shell of specified thickness, and further such effects on the water that surrounds this shell. Other effects contribute to ΔhydG° to a minor extent only.

The nature of the hydrated excess proton in water

Abstract: Explanations for the anomalously high mobility of protons in liquid water began with Grotthuss's idea1, 2 of ‘structural diffusion’ nearly two centuries ago Subsequent explanations have refined this concept by invoking thermal hopping3, 4, proton tunnelling5, 6 or solvation effects7 More recently, two main structural models have emerged for the hydrated proton Eigen8, 9 proposed the formation of an H9O4+ complex in which an H3O+ core is strongly hydrogen-bonded to three H2O molecules Zundel10, 11, meanwhile, supported the notion of an H5O2+ complex in which the proton isshared between two H2O molecules Here we use ab initio path integral12,13,14 simulations to address this question These simulations include time-independent equilibrium thermal and quantum fluctuations of all nuclei, and determine interatomic interactions from the electronic structure We find that the hydrated proton forms a fluxional defect in the hydrogen-bonded network, with both H9O4+ and H5O2+ occurring only in thesense of ‘limiting’ or ‘ideal’ structures The defect can become delocalized over several hydrogen bonds owing to quantum fluctuations Solvent polarization induces a small barrier to proton transfer, which is washed out by zero-point motion The proton can consequently be considered part of a ‘low-barrier hydrogen bond’15, 16, in which tunnelling is negligible and the simplest concepts of transition-state theory do not apply The rate of proton diffusion is determined by thermally induced hydrogen-bond breaking in the second solvation shell

The Hofmeister effect and the behaviour of water at interfaces.

Abstract: Starting from known properties of non-specific salt effects on the surface tension at an air–water interface, we propose the first general, detailed qualitative molecular mechanism for the origins of ion-specific (Hofmeister) effects on the surface potential difference at an air–water interface; this mechanism suggests a simple model for the behaviour of water at all interfaces (including water–solute interfaces), regardless of whether the non-aqueous component is neutral or charged, polar or non-polar Specifically, water near an isolated interface is conceptually divided into three layers, each layer being 1 water-molecule thick We propose that the solute determines the behaviour of the adjacent first interfacial water layer ( I 1 ); that the bulk solution determines the behaviour of the third interfacial water layer ( I 3 ), and that both I 1 and I 3 compete for hydrogen-bonding interactions with the intervening water layer ( I 2 ), which can be thought of as a transition layer The model requires that a polar kosmotrope (polar water-structure maker) interact with I 1 more strongly than would bulk water in its place; that a chaotrope (water-structure breaker) interact with I 1 somewhat less strongly than would bulk water in its place; and that a non-polar kosmotrope (non-polar water-structure maker) interact with I 1 much less strongly than would bulk water in its place We introduce two simple new postulates to describe the behaviour of I 1 water molecules in aqueous solution The first, the ‘relative competition’ postulate, states that an I 1 water molecule, in maximizing its free energy (—δG), will favour those of its highly directional polar (hydrogen-bonding) interactions with its immediate neighbours for which the maximum pairwise enthalpy of interaction (—δ H ) is greatest; that is, it will favour the strongest interactions We describe such behaviour as ‘compliant’, since an I 1 water molecule will continually adjust its position to maximize these strong interactions Its behaviour towards its remaining immediate neighbours, with whom it interacts relatively weakly (but still favourably), we describe as ‘recalcitrant’, since it will be unable to adjust its position to maximize simultaneously these interactions The second, the ‘charge transfer’ postulate, states that the strong polar kosmotrope–water interaction has at least a small amount of covalent character, resulting in significant transfer of charge from polar kosmotropes to water–especially of negative charge from Lewis bases (both neutral and anionic); and that the water-structuring effect of polar kosmotropes is caused not only by the tight binding (partial immobilization) of the immediately adjacent ( I 1 ) water molecules, but also by an attempt to distribute among several water molecules the charge transferred from the solute When extensive, cumulative charge transfer to solvent occurs, as with macromolecular polyphosphates, the solvation layer (the layer of solvent whose behaviour is determined by the solute) can become up to 5- or 6-water-molecules thick We then use the ‘relative competition’ postulate, which lends itself to simple diagramming, in conjunction with the ‘charge transfer’ postulate to provide a new, startlingly simple and direct qualitative explanation for the heat of dilution of neutral polar solutes and the temperature dependence of relative viscosity of neutral polar solutes in aqueous solution This explanation also requires the new and intriguing general conclusion that as the temperature of aqueous solutions is lowered towards o °C, solutes tend to acquire a non-uniform distribution in the solution, becoming increasingly likely to cluster 2 water molecules away from other solutes and surfaces (the driving force for this process being the conversion of transition layer water to bulk water) The implications of these conclusions for understanding the mechanism of action of general (gaseous) anaesthetics and other important interfacial phenomena are then addressed

Implicit solvation model for density-functional study of nanocrystal surfaces and reaction pathways.

Abstract: Solid-liquid interfaces are at the heart of many modern-day technologies and provide a challenge to many materials simulation methods. A realistic first-principles computational study of such systems entails the inclusion of solvent effects. In this work, we implement an implicit solvation model that has a firm theoretical foundation into the widely used density-functional code Vienna ab initio Software Package. The implicit solvation model follows the framework of joint density functional theory. We describe the framework, our algorithm and implementation, and benchmarks for small molecular systems. We apply the solvation model to study the surface energies of different facets of semiconducting and metallic nanocrystals and the SN2 reaction pathway. We find that solvation reduces the surface energies of the nanocrystals, especially for the semiconducting ones and increases the energy barrier of the SN2 reaction.