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Resenha da obra: SACRAMENTO, Igor; MATHEUS, Letícia Cantarela (Org.). História da Comunicação: experiências e perspectivas. Rio de Janeiro: Mauad, 2014. 360 p.

The interaction between surface patches of proteins with different surface properties has a vital role to play driving conformational changes in proteins in different salt solutions. We demonstrate the existence of ion-specific attractive double-layer forces between neutral hydrophobic and hydrophilic surfaces in the presence of certain salt solutions. This is performed by solving a generalized Poisson-Boltzmann equation for two unequal surfaces. In the calculations, we utilize parametrized ion-surface potentials and dielectric-constant profiles deduced from recent non-primitive-model molecular dynamics simulations that partially account for molecular structure and hydration effects.

Specific ion effects are important in numerous fields of science and technology. They have been discussed for over 100 years, ever since the pioneering work done by Franz Hofmeister and his group in Prague. Over the last decades, hundreds of examples have been published and periodically explanations have been proposed. However, it is only recently that a profound understanding of the basic effects and their reasons could be achieved. Today, we are not far from a general explanation of specific ion effects. This book summarizes the main new ideas that have come up in the last ten years. In this book, the efforts of theoreticians are substantially supported by the experimental results stemming from new and exciting techniques. Both the new theoretical concepts and the experimental landmarks are collected and critically discussed by eminent scientists and well-known specialists in this field. Beyond the rigorous explanations, guidelines are given to non-specialists in order to help them understand the general rules governing specific ion effects in chemistry, biology, physics and engineering.

Ion-specific interactions between two colloidal particles are calculated using a modified Poisson-Boltzmann (PB) equation and Monte Carlo (MC) simulations. PB equations present good results of ionic concentration profiles around a macroion, especially for salt solutions containing monovalent ions. These equations include not only electrostatic interactions, but also dispersion potentials originated from polarizabilities of ions and proteins. This enables us to predict ion-specific properties of colloidal systems. We compared results obtained from the modified PB equation with those from MC simulations and integral equations. Phase diagrams and osmotic second virial coefficients are also presented for different salt solutions at different pH and ionic strengths, in agreement with the experimental results observed Hofmeister effects. In order to include the water structure and hydration effect, we have used an effective interaction obtained from molecular dynamics of each ion and a hydrophobic surface combined with PB equation. The method has been proved to be efficient and suitable for describing phenomena where the water structure close to the interface plays an essential role. Important thermodynamic properties related to protein aggregation, essential in biotechnology and pharmaceutical industries, can be obtained from the method shown here.

In two-phase finite volume systems of electroneutral phospholipids, the electrolyte concentration is different in the two phases. The partitioning is highly anion-specific, a phenomenon not accounted for by classical electrolyte theories. It is explained

Dependence of colloidal interactions on salt identity, observed frequently in experiments, can be accounted for once ion specific non-electrostatic forces are included in the theory. Ability to predict the effect of added salt on the phase diagram of colloid dispersions is essential for the design of processes involving nanocolloids. The Ornstein-Zernike equation with hypernetted chain closure approximation provides a viable first estimate for the potential of mean force between ionized nanoparticles like alumina aggregates in aqueous electrolytes subject to dispersion interactions with hydrated simple ions. Calculated potentials of mean force enable the prediction of osmotic second virial coefficients and phase diagrams showing a dramatic dependence on ion type. The choice of salt therefore provides an efficient, non-intrusive way to tune the phase behavior of nanoparticle dispersions.

Monte Carlo simulations are used to establish the potential of mean force between two globular proteins in an aqueous electrolyte solution. This potential includes nonelectrostatic contributions arising from dispersion forces first, between the globular proteins, and second, between ions in solution and between each ion and the globular protein. These latter contributions are missing from standard models. The potential of mean force, obtained from simulation, is fitted to an analytic equation. Using our analytic potential of mean force and Barker-Henderson perturbation theory, we obtain phase diagrams for lysozyme solutions that include stable and metastable fluid-fluid and solid-fluid phases when the electrolyte is 0.2 M NaSCN or NaI or NaCl. The nature of the electrolyte has a significant effect on the phase diagram.

Interactions between proteins are studied by calculating the potential of mean force based on the Poisson-Boltzmann equation. We define a parameter that allows a comparison between the osmotic second virial coefficients obtained from different experimental analytical techniques and provides information about both protein-protein or protein-surface interactions. It can be related to the protein solubility and be used to determine favorable conditions for protein adsorption on a specific surface or protein aggregation. The calculations show reasonable agreement with the experimental second virial coefficient. They also reveal that it is possible to predict different Hofmeister effects observed experimentally in protein solutions. We demonstrate that the effect of including many-body ion-protein dispersion potentials originating from polarizabilities of ions and proteins may offer an explanation for the Hofmeister series. In particular, we give evidence for the inversion of Hofmeister series as function of pH for a given protein.

Protein solubility, protein charge and acid-base titration in protein solutions depend strongly on the choice of background salt solution. Hofmeister effects, or sequences, refer to the relative effectiveness of anions or cations on a wide range of phenomena. Understanding this ion specificity is vital for biology, biotechnology, and colloid chemistry but the reason has, until very recently, not been clear. We present calculations using the Poisson-Boltzmann equation that includes not only electrostatic interactions but also many-body ion-protein dispersion potentials, originated from polarizabilities of ions and proteins. These calculations reveal that is possible to qualitatively predict different Hofmeister effects observed in protein solutions. Our results enable us to give an explanation for the Hofmeister series observed in the measured pH in protein and buffer solutions, protein charge and ion adsorption on protein surface.

Monte Carlo simulations have been performed for ion distributions outside a single globular macroion and for a pair of macroions, in different salt solutions. The model that we use includes both electrostatic and van der Waals interactions between ions and between ions and macroions. Simulation results are compared with the predictions of the Ornstein-Zernike equation with the hypernetted chain closure approximation and the nonlinear Poisson-Boltzmann equation, both augmented by pertinent van der Waals terms. Ion distributions from analytical approximations are generally very close to the simulation results. This demonstrates that properties that are related to ion distributions in the double layer outside a single interface can to a good approximation be obtained from the Poisson-Boltzmann equation. We also present simulation and integral equation results for the mean force between two globular macroions (with properties corresponding to those of hen-egg-white lysozyme protein at pH 4.3) in different salt solutions. The mean force and potential of mean force between the macroions become more attractive upon increasing the polarizability of the counterions (anions), in qualitative agreement with experiments. We finally show that the deduced second virial coefficients agree quite well with experimental results.

The relative effectiveness of different anions in crystallizing proteins follows a reversed Hofmeister sequence for pH < pI and a direct Hofmeister sequence for pH > pI. The phenomenon has been known almost since Hofmeister's original work but it has not