Artigos | equerj

A theoretical study of colloidal forces near amphiphilic polymer brushes

(Lima, Eduardo R.A. ; Jiang, Tao ; Wu, Jianzhong)

A B S T R A C T

Polymer-based “non-stick” coatings are promising as the next generation of effective, environmentally friendly marine antifouling systems that minimize non-speciﬁc adsorption of extracellular polymeric substances (EPS). However, design and development of such systems are impeded by the poor knowledge of polymer-mediated interactions of biomacromolecules with the protected substrate. In this work, a polymer density functional theory (DFT) is used to predict the potential of mean force between spherical biomacromolecules and amphiphilic copolymer brushes within a coarse-grained model that captures essential non-speciﬁc interactions such as the molecular excluded volume effects and the hydrophobic energies. The relevance of theoretical results for practical control of the EPS adsorption is discussed in terms of the efﬁciency of different brush conﬁgurations to prevent biofouling. It is shown that the most effective antifouling surface may be accomplished by a good balance of the polymer chain length and the grafting density.

http://www.sciencedirect.com/science/article/pii/S0927775711001956

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Artigos Publicados por Eduardo Lima

A B S T R A C T

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.

http://link.aps.org/doi/10.1103/PhysRevE.84.061903

A B S T R A C T

Ion-specific interactions between two colloidal particles are calculated using a modified Poisson-Boltzmann (PB)equationandMonteCarlo(MC)simulations. PBequationspresentgoodresultsofionicconcentration 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.

http://dx.doi.org/10.1590/S0001-37652010000100010

Ion-specific thermodynamical properties of aqueous proteins

(LIMA, E. R. A. ; BISCAIA , E. C.,JR. ; BOSTROM, M. ; TAVAVES, F. W.)

A B S T R A C T

Franz Hofmeister established in 1888 that different salt solutions with the same ionic charges have different efficiencies in precipitating proteins from whole egg white. We will discuss how this can be understood from the modified Poisson–Boltzmann equation that accounts for ion specificity via the ion-surface non-electrostatic potential of mean force (NE-PMF) from molecular dynamics simulations. Using this approach, it is at least in principle possible to capture the important physics of the system due to the inclusion of ion-surface van der Waals forces, short range hydration, image potential and different solvent-mediated forces. 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. As an illustrative example, we demonstrate why the double layer force between two gold electrodes coated with hydrophobic self-assembled monolayers in different electrolytes can be highly ion specific. Important thermodynamic properties related to protein aggregation, essential in biotechnology and pharmaceutical industries, can be obtained from the method shown here.

http://www.sciencedirect.com/science/article/pii/S0378381210001068

Ion-specific thermodynamic properties of colloids and proteins

(TAVAVES, F. W. ; BOSTROM, M. ; LIMA, E. R. A. ; BISCAIA , E. C.,JR.)

A B S T R A C T

We recently investigated specific ion effects near a single charged self-assembled monolayer (SAM) in a salt solution by exploiting a modified Poisson–Boltzmann equation that accounts for both water profile and ion-surface potential profiles inferred from molecular dynamics simulations. In the present contribution we extend this work to consider two charged SAMs interacting across different salt solution. Our results demonstrate one important reason why the double layer force between charged colloidal surfaces in electrolytes could be highly ion specific.

http://www.sciencedirect.com/science/article/pii/S0927775709003148

Ion specific forces between charged self-assembled monolayers explained by modified DLVO theory

(LIMA, E. R. A. ; Boström, M. ; Biscaia Jr., E.C. ; Tavares, F.W. ; KUNZ, W.)

A B S T R A C T

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 if ionic dispersion forces that lead to specific ion binding are taken into account. The mechanism provides a contribution to active ion pumps not previously considered.

http://pubs.acs.org/doi/abs/10.1021/jp809051j

Anion-Specific Partitioning in Two-Phase Finite Volume Systems: Possible Implications for Mechanisms of Ion Pumps

(BOSTROM, M. ; LIMA, E. R. A. ; BISCAIA , E. C.,JR. ; TAVAVES, F. W. ; LO NOSTRO, P. ; PARSONS, D. F. ; DENIZ, V. ; NINHAM, B. W.)

A B S T R A C T

Mean-field theories that include nonelectrostatic interactions acting on ions near interfaces have been found to accommodate many experimentally observed ion specific effects. However, it is clear that this approach does not fully account for the liquid molecular structure and hydration effects. This is now improved by using parametrized ionic potentials deduced from recent nonprimitive model molecular dynamics (MD) simulations in a generalized Poisson−Boltzmann equation. We investigate how ion distributions and double layer forces depend on the choice of background salt. There is a strong ion specific double layer force set up due to unequal ion specific short-range potentials acting between ions and surfaces.

http://pubs.acs.org/doi/abs/10.1021/jp7098174

Specific Ion Adsorption and Surface Forces in Colloid Science

(LIMA, E. R. A. ; HORINEK, D. ; NETZ, R. R. ; BISCAIA , E. C.,JR. ; TAVAVES, F. W. ; KUNZ, W. ; BOSTROM, M.)

A B S T R A C T

We consider within a modified Poisson−Boltzmann theory an electrolyte, with different mixtures of NaCl and NaI, near uncharged and charged solid hydrophobic surfaces. The parametrized potentials of mean force acting on Na+, Cl-, and I- near an uncharged self-assembled monolayer were deduced from molecular simulations with polarizable force fields. We study what happens when the surface presents negative charges. At moderately charged surfaces, we observe strong co-ion adsorption and clear specific ion effects at biological concentrations. At high surface charge densities, the co-ions are pushed away from the interface. We predict that Cl- ions can also be excluded from the surface by increasing the concentration of NaI. This ion competition effect (I- versus Cl-) may be relevant for ion-specific partitioning in multiphase systems where polarizable ions accumulate in phases with large surface areas.

http://pubs.acs.org/doi/abs/10.1021/la7037069

Co-Ion and Ion Competition Effects: Ion Distributions Close to a Hydrophobic Solid Surface in Mixed Electrolyte Solutions

(LIMA, E. R. A. ; BOSTROM, M. ; HORINEK, D. ; BISCAIA , E. C.,JR. ; KUNZ, W. ; TAVAVES, F. W.)

The influence of ion binding and ion specific potentials on the double layer pressure between charged bilayers at low salt concentrations

(BOSTROM, M. ; LIMA, E. R. A. ; TAVAVES, F. W. ; NINHAM, B. W.)

A B S T R A C T

Measurements of surface forces between double-chained cationic bilayers adsorbed onto molecularly smooth mica surfaces across different millimolar salt solutions have revealed a large degree of ion specificity [ Pashley et al., J. Phys. Chem. 90, 1637 (1986) ]. This has been interpreted in terms of highly specific anion binding to the adsorbed bilayers. We show here that inclusion in the double layer theory of nonspecific ion binding and ion specific nonelectrostatic potentials acting between ions and the two surfaces can account for the phenomenon. It also gives the right Hofmeister series for the double layer pressure.

http://jcp.aip.org/resource/1/jcpsa6/v128/i13/p135104_s1?isAuthorized=no

A B S T R A C T

Ion specificity plays a key role in solution chemistry and many biological processes. However, the classical DLVO theory has not been able to explain the experimentally observed ion specific forces acting between air-bubbles in electrolyte solutions. We resolve this problem by using a generalized Poisson–Boltzmann equation. We demonstrate that inclusion of both short-range potentials obtained from simulation (acting between ions and the air–water interface) and the spatial variation of the local dielectric constant near the air–water interface may be essential to obtain correct results.

http://www.sciencedirect.com/science/article/pii/S000926140800612X

Forces between air-bubbles in electrolyte solution

(LIMA, E. R. A. ; BOSTROM, M. ; SERNELIUS, B. E. ; HORINEK, D. ; NETZ, R. R. ; BISCAIA , E. C.,JR. ; KUNZ, W. ; TAVAVES, F. W.)

http://pubs.acs.org/doi/abs/10.1021/jp802983f

Correction: Osmotic Second Virial Coefficients and Phase Diagrams for Aqueous Proteins from a Much-Improved Poisson−Boltzmann Equation

(LIMA, E. R. A. ; BISCAIA , E. C.,JR. ; BOSTROM, M. ; TAVAVES, F. W. ; PRAUSNITZ, J. M.)

Differential-Algebraic Approach to Dynamic Simulations of Flash Drums with Rigorous Evaluation of Physical Properties

(LIMA, E. R. A. ; CASTIER, M. ; BISCAIA , E. C.,JR.)

A B S T R A C T

The dynamics of flash drums is simulated with rigorous physical properties calculations using an equation of state to model each phase present. The formulation results in a set of differential-algebraic equations (DAE), whose differential equations describe the material and energy balances and the algebraic equations result from the conditions for thermodynamic equilibrium inside the drum. PSIDE (Parallel Software for Implicit Differential Equations) [Lioen et al., 1998] is used to solve the set of DAE with an efficient differential–algebraic approach. In this approach, the equations are solved simultaneously, with direct iterations in temperature, phase volumes and mole number of each component in each phase. The results show the efficiency of this methodology for the simulation of flash drums.

http://dx.doi.org/10.2516/ogst:2008019

Finite volume solution of the modified Poisson–Boltzmann equation for two colloidal particles

(LIMA, E. R. A. ; TAVAVES, F. W. ; BISCAIA , E. C.,JR.)

A B S T R A C T

The double layer forces between spherical colloidal particles, according to the Poisson–Boltzmann (PB) equation, have been accurately calculated in the literature. The classical PB equation takes into account only the electrostatic interactions, which play a significant role in colloid science. However, there are at, and above, biological salt concentrations other non-electrostatic ion specific forces acting that are ignored in such modelling. In this paper, the electrostatic potential profile and the concentration profile of co-ions and counterions near charged surfaces are calculated. These results are obtained by solving the classical PB equation and a modified PB equation in bispherical coordinates, taking into account the van der Waals dispersion interactions between the ions and both surfaces. Once the electrostatic potential is known we calculate the double layer force between two charged spheres. This is the first paper that solves the modified PB equation in bispherical coordinates. It is also the first time that the finite volume method is used to solve the PB equation in bispherical coordinates. This method divides the calculation domain into a certain number of sub-domains, where the physical law of conservation is valid, and can be readily implemented. The finite volume method is implemented for several geometries and when it is applied to solve PB equations presents low computational cost. The proposed method was validated by comparing the numerical results for the classical PB calculations with previous results reported in the literature. New numerical results using the modified PB equation successfully predicted the ion specificity commonly observed experimentally.

http://pubs.rsc.org/en/Content/ArticleLanding/2007/CP/b701170a#!divAbstract

A B S T R A C T

We investigate the effect of ion-specific potentials on the force between a nanoprobe attached to a cantilever tip, and a charged surface. The probe is treated as a spherical nanoparticle with constant charge. A modified Poisson−Boltzmann equation in bispherical coordinates is used to address this problem in a more quantitative way. We predict that the ion-specific series of measured forces depend on the sign and magnitude of surface charge densities.

http://pubs.acs.org/doi/abs/10.1021/la700690g

Ion-Specific Forces between a Colloidal Nanoprobe and a Charged Surface

(LIMA, E. R. A. ; BISCAIA , E. C.,JR. ; BOSTROM, M. ; TAVAVES, F. W.)

A B S T R A C T

A much-improved Poisson−Boltzmann equation for two globular proteins using bispherical coordinates is used to establish the potential of mean force (PMF) between two globular lysozyme particles. Calculations presented here include previously ignored ion−protein nonelectrostatic potentials. The lysozyme−lysozyme PMF is used to calculate osmotic second virial coeffiencients. The theoretical PMF curve as a function of sodium chloride concentration is successfully compared with that from experiment. Our theoretical PMF shows how the second virial coefficient and the phase diagram depends on salt concentration, pH and, most notably, on the choice of salt in the aquous solution.

http://pubs.acs.org/doi/abs/10.1021/jp074807q

Osmotic Second Virial Coefficients and Phase Diagrams for Aqueous Proteins from a Much-Improved Poisson−Boltzmann Equation

(LIMA, E. R. A. ; BISCAIA , E. C.,JR. ; BOSTROM, M. ; TAVAVES, F. W. ; PRAUSNITZ, J. M.)

Attractive double-layer forces between neutral hydrophobic and neutral hydrophilic surfaces

(Lima, Eduardo R. ; Boström, Mathias ; Schwierz, Nadine ; Sernelius, Bo ; Tavares, Frederico)