selected by the editors in the '2017 PCCP Hot Articles' list

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Beaussart, A.; Caillet, C.; Bihannic, I.; Zimmermann, R. and Duval, J.F.L. Nanoscale 2018, 10, 3181-3190 (inner cover of the journal).


  • Colloidal properties of recombinant spider silk protein particles.

Helfricht, N.; Doblhofer, E.; Duval, J.F.L.; Scheibel, T. and Papastavrou, G. Journal of Physical Chemistry C 2016, 120, 18015-18027.

Colloidal particles have been prepared from polyanionic and polycationic recombinant spider silk protein. The amino acid sequences of these spider silk proteins are identical except for 16 residues bearing either a cationic or an anionic ionizable group. Electrophoretic titration showed that protonation of the acidic and basic amino acids had significant impact on the electrophoretic mobility of the protein particles and, in particular, on their point of zero mobility (PZM). The experimentally determined PZMs are in good agreement with the theoretical values evaluated on the basis of the relevant amino acid sequences. A comprehensive description of the electrokinetic properties of the recombinant spider silk protein particles as a function of pH and
solution ionic strength was provided from adequate application of electrokinetic theory for soft particles. Within the framework of this formalism, spider silk protein particles are viewed as porous colloids penetrable for ions and characterized by a finite penetration length for the electroosmotic flow. The differentiated electrokinetic
properties of the particles were shown to be solely governed by the electrohydro- dynamic features of their poorly charged outer peripheral layer with a thickness of about 10−20 nm. This finding was further corroborated experimentally by demonstrating that electrokinetics of particles bearing an additional outer layer consisting of oppositely charged spider silk proteins is entirely dominated thereby. The presence of a fuzzy, ion-permeable particle interface with an extension of several tenths of a nanometer was confirmed by direct measurement of the resulting steric forces using the colloidal probe atomic force microscopy (AFM) technique.

  • Coupled metal partition dynamics and toxicodynamics at biointerfaces: a theory beyond the biotic ligand model framework.

Duval, J.F.L. Physical Chemistry Chemical Physics 2016, 18, 9453-9469.

A mechanistic understanding of the processes governing metal toxicity to microorganisms (bacteria, algae) calls for an adequate formulation of metal partitioning at biointerfaces during cell exposure. This includes the account of metal transport dynamics from bulk solution to biomembrane and the kinetics of metal internalisation, both potentially controlling the intracellular and surface metal fractions that originate cell growth inhibition. A theoretical rationale is developed here for such coupled toxicodynamics and interfacial metal partitioning dynamics under non-complexing medium conditions with integration of the defining cell electrostatic properties. The formalism explicitly considers intertwined metal adsorption at the biointerface, intracellular metal excretion, cell growth and metal depletion from bulk solution. The theory is derived under relevant steady-state metal transport conditions on the basis of coupled Nernst-Planck equation and continuous logistic equation modified to include metal-induced cell growth inhibition and cell size changes. Computational examples are discussed to identify limitations of the classical Biotic Ligand Model (BLM) in evaluating metal toxicity over time. In particular, BLM is shown to severely underestimate metal toxicity depending on cell exposure time, metal internalisation kinetics, cell surface electrostatics and initial cell density. Analytical expressions are provided for the interfacial metal concentration profiles in the limit where cell-growth is completely inhibited. A rigorous relationship between time-dependent cell density and metal concentrations at the biosurface and in bulk solution is further provided, which unifies previous equations by Best and Duval formulated under constant cell density and cell size conditions. The theory is sufficiently flexible to adapt to toxicity scenarios with involved cell survival-death processes.

  • Remarkable Structure and Elasticity Relaxation Dynamics of Poly(diallyldimethylammonium chloride)-Poly(acrylic acid) Multilayer Films.

Francius, G.; Razafitianamaharavo, A.; Moussa, M.; Dossot, M.; André, E.; Bacharouche, J.; Senger, B.; Ball, V. and Duval, J.F.L.  Journal of Physical Chemistry C 2016, 120, 5599-5612.

Remarkable mechanical and structural properties of out-of-equilibrium poly(diallyldimethylammonium chloride) (PDADMAC)-poly(acrylic acid) (PAA) multilayer films are elucidated from in-situ Atomic Force Microscopy and spatially-resolved Raman spectroscopy analyses complemented by Density Functional Theory (DFT) computations. Surprisingly, fresh exponentially-grown (PDADMAC-PAA)n polyelectrolyte films behave as glassy materials with Young moduli as large as 2 MPa. Their organization is governed by a competition between PDADMAC-PAA electrostatic interactions and water-stabilization of PAA charges that limits association between polycationic and polyanionic chains. At pH 3 where PAA is weakly deprotonated, this competition leads to the formation of water-free PDADMAC-PAA polyelectrolyte complexes within well-defined donut-like structures (2-12 µm in diameter, 100-200 nm in height) that confer upon the film a mechanical rigidity comparable to that classically achieved for linearly-growing films. The relaxation of (PDADMAC-PAA)n films to equilibrium occurs over 5 days and is marked by a gradual disappearance of all donut-like structures, resulting in a three-fold decrease of the Young modulus. This mechanical softening of the film is significantly accelerated by increasing the diffusion rate of PDADMAC and PAA chains upon heating: the morphological and mechanical features of the 5-day old, naturally aged films are recovered after two hours heating treatment at 60°C. In combination, this invokes a transition from intrinsic to extrinsic film charge compensation, i.e. the tightly compacted polyelectrolyte complexes progressively change to coacervates that are loosely associated by electrostatics. It is shown that such atypical structure transition of exponentially-grown films can be used for reversible laser-assisted printing applications at microscales.

  • Evaluation of metal biouptake from the analysis of bulk metal depletion kinetics at various cell concentrations: Theory and application.

Rotureau, E.; Billard, P. and Duval, J.F.L. Environmental Science & Technology 2015, 49, 990-998.

Bioavailability of trace metals is a key parameter for assessment of toxicity on living organisms. Proper evaluation of metal bioavailability requires monitoring the various interfacial processes that control metal partitioning dynamics at the biointerface, which includes metal transport from solution to cell membrane, adsorption at the biosurface, internalization and possible excretion. In this work, a methodology is proposed to quantitatively describe the dynamics of Cd(II) uptake by Pseudomonas putida. The analysis is based on the kinetic measurement of Cd(II) depletion from bulk solution at various initial cell concentrations using electroanalytical probes. On the basis of a recent formalism on dynamics of metal uptake by complex biointerphases, cell concentration-dependent depletion timescale and plateau value reached by metal concentration at long exposure times (>3 hrs) are successfully rationalized in terms of limiting metal uptake flux, rate of excretion and metal affinity to internalization sites.
The analysis shows the limits of approximate depletion models valid in the extremes of high and weak metal affinities. The contribution of conductive diffusion transfer of metals from the solution to the cell membrane in governing the rate of Cd(II) uptake is further discussed on the basis of estimated resistances for metal membrane transfer and extracellular mass transport.


  • Remarkable electrokinetic features of charge-stratified soft nanoparticles: mobility reversal in monovalent aqueous electrolyte.

Moussa, M.; Caillet, C.; Town, R.M. and Duval, J.F.L. Langmuir 2015, 31, 5656-5666.

  • Electrokinetics as an alternative to neutron reflectivity for evaluation of segment density distribution in PEO brushes.

Zimmermann, R.; Romeis, D.;  Bihannic, I.; Cohen Stuart, M.; Sommer, J.-W.; Werner, C. and Duval, J.F.L. Soft Matter 2014,10, 7804-7809.

Unravelling details of charge, structure and molecular interactions of functional polymer coatings defines an important analytical challenge that requires the extension of current methodologies. In this article we demonstrate how streaming current measurements interpreted with combined self consistent field (SCF) and soft surface electrokinetic theories allow the evaluation of the segment distribution within poly(ethylene oxide) (PEO) brushes beyond the resolution limits of neutron reflectivity technique.

  • Chemodynamics of soft charged nanoparticles in aquatic media: fundamental concepts.

Town, R.M.; Buffle, J.; Duval, J.F.L. and van Leeuwen, H.P. Journal of Physical Chemistry A 2013, 117, 7643-7654.

A framework is presented for understanding the reactivity of nanoparticulate reactants with ions and small molecules. Without loss of generality, the formalism is developed for the case of nanoparticles in contact with environmentally relevant metal ions. In addition to reactive sites, nanoparticles generally carry indifferent electric charge distributed over either their surface (hard particles) or volume (soft particles). The ensuing structure and composition of the electric double layer formed within and/or outside the nanoparticulate reactants substantially govern the dynamics of their association and dissociation with ions in aquatic media. A defining feature of permeable nanoparticles is that their charges and reactive sites are spatially confined inside a particle body with an inner medium whose properties may be substantially different from those of the bulk solution. Consequently, the chemodynamic properties of nanoparticulate complexants may differ significantly from those of simple molecular ligands that are homogeneously dispersed in solution. The various physicochemical processes underlying the dynamic reactivity of nanoparticles toward metal ions are here identified, with a focus on the key role played by conductive-diffusion of both metal ions and nanoparticles, the partitioning of ions within the reactive nanoparticulate volume, and the dynamics of the local association/dissociation processes with the reactive sites. The nature of the rate-limiting step in the overall formation/dissociation of the nanoparticulate complexes is shown to depend on the size of the nanoparticle, its charge density, and the ionic strength of the bulk medium. The consequences of these features are further elaborated within the context of dynamics of metal partitioning at a macroscopic consuming biological interphase in the presence of metal complexing nanoparticles.

  • Understanding the extraordinary ionic reactivity of aqueous nanoparticles.

Van Leeuwen, H.P.; Buffle, J.; Duval, J.F.L.  and Town, R.M. Langmuir 2013, 29, 10297-10302.

Nanoparticles (NPs) are generally believed to derive their high reactivity from the inherently large specific surface area. Here we show that this is just the trivial part of a more involved picture. Nanoparticles that carry electric charge are able to generate chemical reaction rates that are even substantially larger than those for similar molecular reactants. This is achieved by Boltzmann accumulation of ionic reactants and the Debye acceleration of their transport. The ensuing unique reactivity features are general for all types of nanoparticles but most prominent for soft ones that exploit the accelerating mechanisms on a 3D level. These features have great potential for exploitation in the catalysis of ionic reactions: the reactivity of sites can be enhanced by increasing the indifferent charge density in the NP body.


  • X-Ray reflectivity at polarized liquid Hg/Aqueous electrolyte interface: Challenging macroscopic approaches for ion specificity issues

Duval, J.F.L.; Bera, S.; Michot, L.J.; Daillant, J.; Belloni, L.; Konovalov, O. and Pontoni, D. Physical Review Letters 2012, 108, 206102.

The interface between mercury and an electrolyte solution has been used for more than 50 years as a model system to test the applicability of theories for the electric double layer in order to quantitatively interpret ion-dependent macroscopic surface tension data for such systems. Using X-ray reflectivity, scientists have obtained an angstrom-resolved picture of the spatial distribution of ions in the vicinity of a polarised Hg surface exposed to various molar electrolyte solutions. This study highlights several peculiar features of the Hg/electrolyte interface that have been omitted by theoretical models both past and present. It also provides the first molecular view of ionic distributions in the vicinity of a charged interface since the pioneering work by Graham in 1947 on electric double layers in colloidal systems.

  • Chemodynamics and biointerfaces: Bioavailability and biological effects of chemicals in the environment.

Invited Editors : Town, R.M.; Duval, J.F.L.; Buffle, J. Journal of Physical Chemistry A 2012, vol. 116.

Schematic view of the key processes that govern the chemodynamic and biodynamic features of metal complexes in aqueous solution for the case where the free metal ion (M) is consumed or released at a biointerphase. The flux of a metal species toward the relevant sites at the plasma membrane is governed by (i) its mass transport properties (DM, DML, DMLp) connected to the concentration gradients in the diffusion layer and coupled to chemical reaction rates in the reaction layer (K, ka, kd), (ii) interactions with various electric fields (see below), and (iii) biological affinity via chemical reactions with sites of the plasma membrane(Ka, kads, kdes). Both the cell wall and colloidal ligands in solution typically carry a number of negative charges that generate a net electrostatic field (denoted by yellow shading) that may have a significant impact on local equilibrium as well as kinetic and transport parameters pertaining to metal species.

  • On the applicability of the Brinkman equation in soft surface electrokinetics

Dukhin, S.S.;  Zimmermann, R.; Duval, J.F.L. and Werner, C. Journal of Colloid and Interface Science 2010, 350, 1-4.

  • Coupled electrostatic, hydrodynamic and mechanical properties of bacterial interfaces in aqueous media.

Gaboriaud, F.; Gee, M.L.; Strugnell, R. and Duval, J.F.L. Langmuir 2008, 24, 10988-10995.