Ion influence on surface water dynamics and proton exchange at protein surfaces - A unified model for transverse and longitudinal NMR relaxation dispersion.

In all biologically relevant media, proteins interact in the presence of surrounding ions, and such interactions are water-mediated. Water molecules play a crucial role in the restructuring of proteins in solution and indeed in their biological activity. Surface water dynamics and proton exchange at protein surfaces is investigated here using NMR relaxometry, for two well-known globular proteins, lysozyme and bovine serum albumin, with particular attention to the role of surface ions.

Efficient method for agitation of liquids directly inside NMR spectrometer.

The objective of the method is to allow agitation and fast homogenization of liquid systems in NMR tubes, directly inside the NMR spectrometer. The setup makes it possible to record spectra of samples that are macroscopically not stable, as dispersions of large particles. It makes also possible to fasten the homogeneization of liquid during a reaction or a phase transition.

Structure-Property-Function Relationships of Iron Oxide Multicore Nanoflowers in Magnetic Hyperthermia and Photothermia.

Magnetite and maghemite multicore nanoflowers (NFs) synthesized using the modified polyol-mediated routes are to date among the most effective nanoheaters in magnetic hyperthermia (MHT). Recently, magnetite NFs have also shown high photothermal (PT) performances in the most desired second near-infrared (NIR-II) biological window, making them attractive in the field of nanoparticle-activated thermal therapies. However, what makes magnetic NFs efficient heating agents in both modalities still remains an open question.

Connecting Rheological Properties and Molecular Dynamics of Egg-Tempera Paints based on Egg Yolk.

Egg-tempera painting is a pictorial technique widely used in the Middle Ages, although poorly studied in its physico-chemical aspects until now. Here we show how NMR relaxometry and rheology can be combined to probe egg-tempera paints and shed new light on their structure and behavior. Based on recipes of the 15th century, model formulations with egg yolk and green earth have been reproduced to characterize the physicochemical properties of this paint at the mesoscopic and macroscopic scales.

Multiscale Water Dynamics on Protein Surfaces: Protein-Specific Response to Surface Ions.

Proteins function in crowded aqueous environments, interacting with a diverse range of compounds, and among them, dissolved ions. These interactions are water-mediated. In the present study, we combine field-dependent NMR relaxation (NMRD) and theory to probe water dynamics on the surface of proteins in concentrated aqueous solutions of hen egg-white lysozyme (LZM) and bovine serum albumin (BSA).

Green Earth pigments aqueous dispersions: NMR relaxation rates dataset.

The data presented here are related to the research paper entitled "Green Earth pigments dispersions: water dynamics at the interfaces". The nuclear magnetic resonance (NMR) relaxometry data are provided for various aqueous Green Earth (GE) pigments dispersions with volume fraction spanning approximately from 0.1 to 0.

Green earth pigments dispersions: Water dynamics at the interfaces.

Hypothesis: The objective is to elucidate the multiscale dynamics of water within natural mixtures of minerals, green earth pigments that are mainly composed of phyllosilicates containing large amount of iron. In particular, the interaction of water with the different kinds of surfaces has to be probed. One issue is to examine the influence of surface type, basal or edge, on the dispersion quality.

Specificity of Counterion Binding to a Conjugated Polyelectrolyte: A Combined Molecular Dynamics and NOESY Investigation.

Poly(thiophen-3-ylacetic acid) (PTAA) is a representative of conjugated polyelectrolytes which are used in many optoelectronics devices. The performance of these devices is affected by the polymer conformation, which, among others, depends on the nature of the counterion. In this study, the binding of tetrabutylammonium counterions (TBA) on PTAA was determined using a combination of nuclear Overhauser effect spectroscopy (NOESY) and molecular dynamics (MD) simulation.

Coarse-Grained Models of Aqueous Solutions of Polyelectrolytes: Significance of Explicit Charges.

The structure of polyelectrolytes is highly sensitive to small changes in interactions between their monomers. In particular, interactions mediated by counterions play a significant role and are affected by both specific molecular effects and generic concentration effects. The ability of coarse-grained models to reproduce the structural properties of an atomic model is thus a challenging task.

Ion-specificity and surface water dynamics in protein solutions.

Ion-specific effects at the protein surface are investigated here in light of the changes they infer to surface water dynamics, as observed by 1H NMR relaxation (at 20 MHz). Two well-known proteins, hen egg-white lysozyme (LZM) and bovine serum albumin (BSA), show qualitatively opposite trends in the transverse relaxation rate, R2(1H), along a series of different monovalent salt anions in the solution. Presence of salt ions increases R2(1H) in the case of lysozyme and diminishes it in the case of BSA.

Thermoelectricity and Thermodiffusion in Magnetic Nanofluids: Entropic Analysis.

An analytical model describing the thermoelectric potential production in magnetic nanofluids (dispersions of magnetic and charged colloidal particles in liquid media) is presented. The two major entropy sources, the thermogalvanic and thermodiffusion processes are considered. The thermodiffusion term is described in terms of three physical parameters; the diffusion coefficient, the Eastman entropy of transfer and the electrophoretic charge number of colloidal particles, which all depend on the particle concentration and the applied magnetic field strength and direction.

Spectral induced polarization of Na-montmorillonite dispersions.

Montmorillonite (Mt) clays have a high specific surface area and surface charge, which confer them remarkable adsorption properties. Nevertheless, their electrochemical and aggregation behavior are not completely elucidated because of the complexity of their microstructural and interfacial properties. In this work, the conductive and dispersive properties of Na-Mt suspensions of weight fractions 0.

Influence of counterions on the conformation of conjugated polyelectrolytes: the case of poly(thiophen-3-ylacetic acid).

The addition of simple salt to a solution of conjugated polyelectrolyte can lead to substantial changes in its optical properties caused by the conformational change of the polymer chain. The effect of the addition of alkali metal and tetraalkylammonium chlorides to solutions of lithium salt of poly(thiophen-3-ylacetic acid) is investigated by NMR. The fractions of free alkali metal counterions are in agreement with predictions of the cylindrical Poisson-Boltzmann cell model.

Ion association in aqueous and non-aqueous solutions probed by diffusion and electrophoretic NMR.

The results of diffusion and electrophoretic NMR (eNMR) measurements are reported for a series of tetramethylammonium (TMA) electrolytes (with sulphate, fluoride, acetate, chloride, bromide, nitrate, iodide and perchlorate as anions) in deuterated solvents such as water, dimethylsulphoxide (DMSO), acetonitrile, methanol and ethanol. In addition, similar data are presented for aqueous solutions of tetraalkylammonium salts with increasing alkyl chain length. The combination of diffusion NMR and eNMR yields the effective charge for the TMA cation.

Aqueous solutions of tetraalkylammonium halides: ion hydration, dynamics and ion-ion interactions in light of steric effects.

Molecular simulations have allowed us to probe the atomic details of aqueous solutions of tetramethylammonium (TMA) and tetrabutylammonium (TBA) bromide, across a wide range of concentrations (0.5 to 3-4 molal). We highlight the space-filling (TMA(+)) versus penetrable (TBA(+)) nature of these polyatomic cations and its consequence for ion hydration, ion dynamics and ion-ion interactions.

Salicylate isomer-specific effect on the micellization of dodecyltrimethylammonium chloride: large effects from small changes.

Specific effects of the sodium salts of m- and p-hydroxybenzoates (m-HB and p-HB) on the aggregation process of dodecyltrimethylammonium chloride have been investigated by isothermal titration calorimetry, electrical conductivity, and (1)H NMR and compared with already reported data for the sodium salt of o-hydroxybenzoate (o-HB). For p-HB, it has been found that the aggregate is only formed by spherical micelles at all p-HB concentrations. On the other side, the situation is more complex for o-HB, where two distinct states of aggregation can be involved, depending on the concentration of o-HB.

Nanoporous photocathode and photoanode made by multilayer assembly of quantum dots.

We perform in this paper a kinetic study of the photoelectrochemical responses of nanoporous thin photoactive films. The films were fabricated by by a layer-by-layer assembly of positively charged polyelectrolytes (poly-l-Lysine, pLys) and negatively charged semiconductor nanoparticles (NPs) on a carboxylic acid terminated alkanethiol-modified gold electrode. Two types of NPs were used to build uniform films: cadmium selenide (CdSe) and cadmium selenide/cadmium sulfide core/shell (CdSe@CdS).

What tunes the structural anisotropy of magnetic fluids under a magnetic field?

In the present study, the structure of monophasic ionic magnetic fluids under a static magnetic field is explored. In these aqueous electrostatically stabilized ferrofluids, we vary both the isotropic interparticle interactions and the anisotropic dipolar magnetic interaction by tuning the ionic strength and the size of the nanoparticles. Small angle neutron scattering measurements carried out on nanoparticles dispersed in light water exhibit miscellaneous 2D nuclear patterns under a magnetic field with various q-dependent anisotropies.

Liquid-liquid phase-transfer of magnetic nanoparticles in organic solvents.

We report a novel route for the preparation of well-defined colloidal dispersions of magnetic nanoparticles stabilized by steric repulsion in organic solvents. The usual methods standardly lead to the surfaction of multiparticle aggregates, incompatible with our long-term aim of studying and modeling the influence of magnetic dipolar interactions in colloidal dispersions which are free of aggregates, all other interactions being perfectly defined. A new and reproducible method based on a surfactant-mediated liquid-liquid phase transfer of individually dispersed gamma-Fe(2)O(3) nanoparticles from an aqueous colloidal dispersion to an organic phase is developed.