Electrostatic attraction between cationic-anionic assemblies with surface compositional heterogeneities

Electrostatics plays a key role in biomolecular assembly. Oppositely charged biomolecules, for instance, can co-assembled into functional units, such as DNA and histone proteins into nucleosomes and actin-binding protein complexes into cytoskeleton components, at appropriate ionic conditions. These cationic-anionic co-assemblies often have surface charge heterogeneities that result from the delicate balance between electrostatics and packing constraints. Despite their importance, the precise role of surface charge heterogeneities in the organization of cationic-anionic co-assemblies is not well understood. We show here that co-assemblies with charge heterogeneities strongly interact through polarization of the domains. We find that this leads to symmetry breaking, which is important for functional capabilities, and structural changes, which is crucial in the organization of co-assemblies. We determine the range and strength of the attraction as a function of the competition between the steric and hydrophobic constraints and electrostatic interactions.Comment: JCP June/200

Forest influence on the surface water chemistry of granitic basins receiving acid precipitation in the Vosges massif, France

This study shows the influence of acid rain on the chemistry of surface waters in two small basins. The basins present similar altitudes and climates, only one is forested, and the forest decline has been clearly established. In both basins, rain water is polluted by acids (H+, so24-,N03). This acid input is neutralized in soils but the efficiency of that neutralization varies from one basin to another: (a) in the non forested basin, the alkalinity of surface water dominates the anionic charge, (b) in the forested basin, the strong acid anions still dominate the anionic charge of a just neutralized solution. The chemistry of surface water in the forested basin cannot be explained only by the incident rainfall and its partial evaporation. There appears to be a major input of pollutant through dry deposits in throughfall

Translocating the blood-brain barrier using electrostatics

Copyright © 2012 Ribeiro,Domingues, Freire,Santos and Castanho. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.Mammalian cell membranes regulate homeostasis, protein activity, and cell signaling. The charge at the membrane surface has been correlated with these key events. Although mammalian cells are known to be slightly anionic, quantitative information on the membrane charge and the importance of electrostatic interactions in pharmacokinetics and pharmacodynamics remain elusive. Recently, we reported for the first time that brain endothelial cells (EC) are more negatively charged than human umbilical cord cells, using zeta-potential measurements by dynamic light scattering. Here, we hypothesize that anionicity is a key feature of the blood-brain barrier (BBB) and contributes to select which compounds cross into the brain. For the sake of comparison, we also studied the membrane surface charge of blood components—red blood cells (RBC), platelets, and peripheral blood mononuclear cells (PBMC).To further quantitatively correlate the negative zeta-potential values with membrane charge density, model membranes with different percentages of anionic lipids were also evaluated. From all the cells tested, brain cell membranes are the most anionic and those having their lipids mostly exposed, which explains why lipophilic cationic compounds are more prone to cross the blood-brain barrier.Fundação para a Ciência e Tecnologia — Ministério da Educação e Ciência (FCT-MEC, Portugal) is acknowledged for funding (including fellowships SFRH/BD/42158/2007 to Marta M.B. Ribeiro, SFRH/BD/41750/2007 to Marco M. Domingues and SFRH/BD/70423/2010 to João M. Freire) and project PTDC/QUI-BIQ/119509/2010. Marie Curie Industry-Academia Partnerships and Pathways (European Commission) is also acknowledged for funding (FP7-PEOPLE-2007-3-1-IAPP, Project 230654)

The ferroelectric Mott-Hubbard phase of organic (TMTTF)2X conductors

We present experimental evidences for a ferro-electric transition in the family of quasi one- dimensional conductors (TMTTF)2X. We interpret this new transition in the frame of the combined Mott-Hubbard state taking into account the double action of the spontaneous charge disproportionation on the TMTTF molecular stacks and of the X anionic potentials

A Study of Dual Polymer Retention Aids for the Retention on Titanium Dioxide Using the Dynamic Drainage Jar, Minidrinier, and Handsheets

Two types of dual polymer retention aid systems, a low molecular weight, high charge density, cationic polyamine with a high molecular weight, low charge density, cationic polyacrylamide, and the same polyamine with a high molecular weight, highly charged anionic polyacrylamide, were studied using the Dynamic Drainage Jar, the Minidrinier, and handsheets. Both systems gave higher retention than could be achieved using any of the retention aids alone, however, formation was a problem. Contact time and shear were shown to be important variables. All three testing methods were useful, the Dynamic Drainage Jar having an advantage due to its flexibility

The ferroelectric Mott-Hubbard phase of organic (TMTTF)2X conductors

We present experimental evidences for a ferro-electric transition in the family of quasi one- dimensional conductors (TMTTF)2X. We interpret this new transition in the frame of the combined Mott-Hubbard state taking into account the double action of the spontaneous charge disproportionation on the TMTTF molecular stacks and of the X anionic potentials

On the Impact of Solvation on a Au/TiO2 Nanocatalyst in Contact with Water

Water, the ubiquitous solvent, is also prominent in forming liquid solid interfaces with catalytically active surfaces, in particular with promoted oxides. We study the complex interface of a gold nanocatalyst, pinned by an F center on titania support, and water. The ab initio simulations uncover the microscopic details of solvent-induced charge rearrangements at the metal particle. Water is found to stabilize charge states differently from the gas phase as a result of structure specific charge transfer from to the solvent, thus altering surface reactivity. The metal cluster is shown to feature both cationic and anionic solvation, depending on fluctuation and polarization effects in the liquid, which creates novel active sites. These observations open up an avenue toward solvent engineering in liquid-phase heterogeneous catalysis

Complexation of DNA with Cationic Surfactant

Transfection of an anionic polynucleotide through a negatively charged membrane is an important problem in genetic engineering. The direct association of cationic surfactant to DNA decreases the effective negative charge of the nucleic acid, allowing the DNA-surfactant complex to approach a negatively charged membrane. The paper develops a theory for solutions composed of polyelectrolyte, salt, and ionic surfactant. The theoretical predictions are compared with the experimental measurements.Comment: 9 pages, 3 figure