Trilateral Seminar
(Russia-Germany-France)
Solvation in Complex Liquids: Bridging
Length Scales by Theory and Experiment
Max Planck Institute for Mathematics in the Sciences,
Inselstr. 22-26, lecture room (G10) Leipzig, Germany
Organizers:
• Maxim Fedorov Max-Planck-Institute for
Mathematics in the Sciences (MPI MIS) Leipzig, Germany
e-mail: fedorov@mis.mpg.de
web:
http://www.mis.mpg.de/scicomp/CompPhysChem/GroupMain.html
• Michael Kiselev Institute of solution Chemistry Russian Academy of Sciences Ivanovo, Russia
e-mail: mgk@isc-ras.ru web: http://www.isc-ras.ru
• Abdenacer Idrissi Univerity of Lille, France
e-mail: Nacer.Idrissi@univ-lille1.fr
web: http://www-lasir.univ-lille1.fr
Scientific secretary:
Volodymyr Sergiievskyi (MPI MIS)
Local Organizing Committee (MPI MIS):
Wolfgang Hackbusch Gennady Chuev
Ekaterina Ratkova Andrey Frolov
Anastasia Romanova Roman Saburdjajew
Sponsors:
German Research Foundation (DFG),
National Center for Scientific Research (CNRS, France), Russian Foundation for Basic Research (RFBR)
Scientific Secretary
Volodymyr Sergiievskyi
sergiiev@mis.mpg.de +49 (0)341-9959-726 +49 (0)1522365-18-71
Secretary ( TRAVEL FORMS )
Valeria Hünniger vah@mis.mpg.de +49 (0)341-9959- 752
Guest Program Manager
Heike Rackwitz gprog@mis.mpg.de +49 (0)341-9959- 671
Guest House Administrator
Theresa Petsch petsch@mis.mpg.de +49 (0)341-9959-678
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DAY 1. We
dnesday, June 23
, 2010
DAY 2. Thursday, June 24, 2010.
Mornin
DAY 2. Thursday, June 24, 2010. Evening session DA Y 2 Thursday June 24 th 2010 DAY 3. Fri d ay, June 25 th 2010.
List of Reports in the Last Name alphabet order
Name Title rep.
ID
page Frederic
Affouard
Investigation of the bioprotective properties of disaccharide/water mixtures from Molecular Dynamics simulations
O23 58
Michael
Basilevsky The implicit electrostatic solvent model with continuous dielectric permittivity function
O29 72 Philippe
Bopp r from Supercritical Fluids to Interfaces Simulations Studies of Fluctuations: O4 22 Richard
Buchner Ion solvation versus association: Insights from dielectric spectroscopy on competing processes in solutions
O16 44 Gennady
Chuev
Self-assembly in aqueous solutions treated by integral equations methods of molecular liquids
O30 74 Marina
Fedotova Ion Association and Ion Cluster Formation in Aqueous 1:1 Electrolyte Solutions under Supercritical
Conditions O31 76 Marina Fedotova On the Calculation of Thermodynamic Characteristics of Ion Hydration in the Framework of RISM Approach
P1 84
Andrey
Frolov Interactions of Alkali and Halide Ions with the Carbon Nanotube Surface in Aqueous Solutions: Understanding the Molecular Mechanisms.
O9 30
Nikolaj
Georgi In silico studies of ionic liquids at electrified interfaces O20 52 Klaus
Huber The Impact of Specifically Interacting Metal Cations on the Solution Behaviour of Long Chain Anionic Polyacrylates
O13 38
Abdenacer
Idrissi Intermolecular interactions in aqueous solutions O17 46
Name Title rep.
ID
page Noël
Jakse Combining classical and ab initio molecular dynamics. Application to the liquid-liquid transition and related problems
O25 64
Michael Kiselev
Solvation and association of polar molecules at ambient and
supercritical conditions
O2 16 Sabine
Klapp
Computer simulations and theory of spatially confined charged and dipolar systems
O3 18 Alexander
Klinov unctions for the description of The method of particle distribution ermodynamic properties and phase quilibrium in multicomponent fluids
P2 86
Ralf
Ludwig Interplay between local hydrogen bonding and long-range Coulomb interactions in Ionic Liquids
O19 50 Nobuyuki
Matubayasi Free-Energy Analysis of Solvation in the Energetic Perspective O26 66 Babak
Minofar Surface propensity and ion pair in organic solvents
O10 32 Shahbaz
Naeem pePC-SAFT - An Equation of State for Polyelectrolyte Systems O14 40 Renat
Nazmutdinov
Solvent dynamics effects in electron transfer across electrochemical interfaces
O22 56 Evgeny
Nogovitsyn A new approach within self-consistence field theory for polymer solutions.
O15 42 Alexey
Odinokov
Potential of mean force for ion pairs in aprotic organic solvents and their binary mixtures.
O11 34 Roman
Oparin A vibrational spectroscopic study of hydrogen bonding in water subsystem of ternary water-scCO2-NaCl mixture
O8 28
Yuriy
Pukhovskiy Molecular dynamics simulations of ethanol-carbon dioxide mixtures along the liquid – vapor coexistence curve
O7 26
Rosa Ramirez
Dressed molecule theory: screening and charge renormalization for ionic and molecular interactions in solution
Name Title rep. ID
page Ekaterina
Ratkova Hybrid method for accurate and fast prediction of hydration free energy of small organic solutes
O6 24 Anastasia
Romanova Selective Na+/K+ effects on α-cyclodextrin complex formation with aromatic carboxylic acids:
competition for the guest
O18 48
Anastasia
Romanova On the Calculation of Thermodynamic Characteristics of Ion Hydration in the Framework of RISM Approach
P3 88
Joshua
Sangoro Rotational and translational diffusion in ion-conducting material P4 90 Wolffram
Schröer Statistical thermodynamics of structure, dynamics and critical properties of ionic fluids
O1 14 Ilya Semenov Electrokinetics and Charge Inversion
as studied by Single Colloid Electrophoresis
P5 92 Volodymyr
Sergiievskyi Fast Multi-Grid Algorithm for Prediction of Hydration Free Energies of the Drug-Like Molecules
O27 68 Eckhard
Spohr
Molecular Dynamics of the
Discharge of Solvated Protons at the Aqueous/Metallic Interface
O21 54 Godehard
Sutmann Simulations of molecular liquids: simulation approaches, fast algorithms, parallelization and coarse graining
O28 70
Makoto
Suzuki Hydration measurement of salt ions, polyelectrolytes, and proteins in dilute solutions by high resolution dielectric relaxation spectroscopy
O12 36
Thierry
Tassaing Solvation of organic molecules in supercritical CO2 O32 78 Ivan
Vyalov Inhomogeneity in Ar in supercritical conditions: A combined molecular simulations and density based clustering approaches
O4 20
List of listeners
Name Affiliation Kathleen Kirchner Max-Planck-Institute for Mathematics in the
Sciences
Tom Kirchner Max-Planck-Institute for Mathematics in the Sciences
Georgy Kitavtsev Max-Planck-Institute for Mathematics in the Sciences
Oral Reports
Statistical thermodynamics of structure, dynamics and critical properties of ionic fluids
Wolffram Schröer
Institut für Anorganische und Physikalische Chemie Fachbereich Biologie /Chemie
Universität Bremen
The properties of ionic fluids that are molten salts and ionic solutions represent a long standing problem in statistical thermodynamics. The reason for this are the Coulomb forces, which in variance to van der Waals interactions are long-range interactions. They are also much stronger so that ion-pairs and higher associates are discussed.
Because of their perspective for applications molten salts with melting points below 100 °C, down to – 80°C, termed ionic liquids, have triggered a new interest on ionic fluids. Some ionic liquids are soluble in non-polar solvents as hydrocarbons others in polar solvents like water and vice versa. In ionic liquids and their solutions the interplay of Coulomb and van der Waals interactions provides a further challenge for the theoretical understanding.
For some solutions of ionic liquids liquid-liquid phase transitions are observable at ambient temperatures enabling investigations of the critical properties (coexistence, critical fluctuations, critical dynamics) with mK accuracy. Such research is of fundamental interest: While in nonionic systems the liquid-gas as well as liquid-liquid phase transitions are driven by short range van der Waals interactions with an r-6 -range dependence, the phase transitions in the ionic systems are
driven by long-range r-1 -Coulomb interactions. The
universality hypothesis that liquid-gas as well as liquid-liquid phase transitions all belong to the Ising universality class has been theoretically proven for r-n interactions with n>4.97, while the nature of the critical point in Coulomb systems was unknown till recently. Some experiments reported mean-field behavior for such systems. Meanwhile, experiments as well as
simulations that apply finite size scaling techniques support the conclusion that the liquid-gas and the isomorphous liquid– liquid phase transitions of Coulomb systems also belong to the Ising universality class.
The simulations concern the so called primitive model, which considers charged hard spheres in a dielectric continuum and the restricted primitive model (RPM) where the size of the ions is equal. Analytical mean-field theory that, extending the Debye –Hückel theory, includes ion-pairing and interactions not only between the ions but also between ions and ion-pairs is in reasonable agreement with standard simulations of the RPM. and provides rational for the concentration dependence of the conductivity
The critical points of the liquid-liquid phase transitions in ionic solutions in non-polar solvents are in fair agreement with the predictions of the simulations of the RPM, while the critical temperatures of solutions in polar solvents are higher varying linearly with the dielectric permittivity of the solvent. Furthermore, corresponding state analysis based on the reduced variables of the RPM reveals further differences, when comparing phase separation in aprotic solvents (hydrocarbons) with that in protic solvents (alcohols , water). In terms of the RPM-variables the phase separation in aprotic solvents, which is driven by Coulomb interactions, have an upper critical solution point, while the coexistence curves in protic solvents have a lower critical solution point, typically for phase separation caused by hydrophopic interactions.
Light scattering investigations and phase diagrams indicate the onset of crossover from asymptotic Ising behavior to mean field criticality. Theoretical estimates of the Ginzburg temperature predict that the crossover should occur at larger separation from the critical point than in nonionic fluids, which appears to be in variance to the experimental observations.
Solvation and association of polar molecules at ambient and supercritical conditions
M.G. Kiselev
Institute of Solution Chemistry, Russian Academy of Sciences, Akademicheskaya str.1, Ivanovo, Russia, 153045,
e-mail: mgk@isc-ras.ru
The study of solvation of the heterofunctional molecules provides very important clues for understanding the effects of molecules on the three dimensional hydrogen bonded network of water. The reason is that there is a delicate balance between structure-making and structure-breaking effects in these mixtures, i.e., both hydrophilic and hydrophobic effects play equally important roles in them. The process of a solute molecule dissolution in water at low concentration can be divided into three stages: (1) create a cavity in the solvent to hold the solute; (2) insert the solute molecule into the cavity and (3) reorganize the solvent structure in presence of the solute. The first and second stages have been extensively described in the literature, whereas the third stage is still a matter of controversy. In this light, the solute–solvent interactions at low concentration might be looked at as being an external perturbation on the hydrogen bond network of water. Looking at the resistance of the water hydrogen bond network to external perturbations could lead to an understanding of the reorganization of the inherent water structure in the mixture.
In the next part of this communication the role of water in association and conformational stability of the macromolecules will be discussed. Previously developed approximation of decomposition of an association free energy on contributions from individual interactions has been used for calculation of intermolecular interactions, solvation free energy and various entropies of process of macromolecular association. Using a normal modes method, it was concluded, that presence of individual water molecules on the protein - protein interface promotes magnification of the vibration entropy contribution to a
free energy of association due to magnification of flexibility of a complex. The water molecules shared in formation of protein - water-ligand hydrogen bonds change balance of system forces.
As for water influence on conformational stability of the macromolecules we consider hydration of the toxins as example. In order to understand Cry4B (one of potential-membrane-inserting proteins of Bti Cry toxins) in the early step of killing mechanism in aqueous solution, molecular dynamics simulation was performed to investigate structural dynamics, properties and the influence of water molecules. The domains movement of Cry4Aa was compared with Cry4Ba which domain I gradually separated from other domains, this showed a difference in dynamics of Cry4Aa and Cry4Ba in aqueous solution. A high root-mean-square displacement (RMSD) observed in Cry4Aa indicated a flexibility in the structure required for conformational change in prior to forming a pore in target cell membrane.
Computer simulations and theory of spatially confined charged and dipolar systems
Sabine Klapp TU Berlin, Sekr. EW 7-1
Institut für Theoretische Physik, Fakultät II Mathematik und Naturwissenschaften , Hardenbergstr. 36, 10623
BERLIN-Charlottenburg
The physics of fluids confined in pores or slits can be strongly different from that observed in three spatial dimensions. In this talk I will present recent computer simulation and theoretical results on spatially confined colloidal systems. A well-known surface effect consists of a layering of the particles which can be detected, e.g., by oscillations in the solvation forces. However, the length scales determining such forces are still under debate. Here I will discuss these issues for a film of charged colloids in solution, including an interpretation via density functional theory and a comparison with experimental (Colloidal-Probe AFM) data. Even more complex layering effects occur when the spatial confinement is supplemented by additional external fields. In particular, in films with dipolar interactions such as polar fluids and ferrofluids, external electric or magnetic fields can give rise to layer formation, layer destruction, and field-induced crystallization.
Cellobiose solvation free energy in SC CO2
with co-solvents.
Vyalov I. I.†‡, Idrissi A.†, Kiselev M. G.‡ †University of Lille, Science and Technology ‡Institute of Solution Chemistry of Russian Academy of
Science
Cellulose consists of linked repeating cellobiose units and is the most abundant natural
polymer (see Fig. 1) found on earth and is known to have very attractive properties such as
biocompatibility, biodegradability, thermal and chemical stability. Cellulose solubility is very limited due to the formation of inter- and intramolecular hydrogen bonds that stabilize its structure. That is why at present moment very special techniques for industrial cellulose treatment are used: dissolution in CS2 and
ionic liquids what is obviously environmentally hazardous. Our goal is to replace these solvents by supercritical(SC) CO2 which
has proved to be environmentally benign and attractive in industrial application.
Our first step in this direction was to calculate solvation free energy of cellobiose unit in pure SC CO2 and in mixtures of
it with water and water/ethylene glycol. Such a choice of systems was dictated by the available experimental data that indicate dramatic changes in cellulose structure when it is treated by SC CO2/water/ethylene glycol mixture.
Cellobiose solvation free energy was calculated by means of free energy perturbation method. Reliability of these data and errors arose from these calculation are discussed. It was shown that for such a large molecule as cellobiose one has to conduct at least 1 ns per lambda-window simulation.
Figure 1: Cellobiose fragment in cellulose molecule.
Simulation Studies of Fluctuations: From Supercritical Fluids to Interfaces
Philippe A. Bopp and Jean-Christophe Soetens2
1 On sabbatical leave at Materials Chemistry,
Ångström Laboratory, Uppsala University and Max Planck-Institut für Mathematik in den Naturwissenschaften, Leipzig
2 Department of Chemistry, Université Bordeaux 1
Molecular Dynamics (MD) simulations provide, among other things, information about the time evolution, at the molecular level, of the system under study. With present-day computers this evolution can be followed over times of several nanoseconds for system of average size and complexity (say: a few 10 simple solutes and a few hundred solvent molecules in the cases studied here). Time-correlation functions are usually employed for the quantitative analysis, but it is some times also instructive to simply visualize the time evolution with graphics tools.
The hydration shells of the Br−-ion in supercritical
RbBr aqueous solutions have been studied some time ago by EXAFS and MD simulations [1] and discussed in terms of the strongly fluctuating number of first water (and other) neighbors of this ion. Similar fluctuations were seen indirectly when the hydrogen bonding in sub- and supercritical alcohols was studied spectroscopically and in simulations [2,3].
The liquid-liquid interface between the two phases in a mixture of two partly miscible substances has been the object of several simulation studies, see [4]. When subject to a gradient, particular collective motions arise at these interfaces, which are thought to be of importance in chemical engineering processes. When the gradient is a temperature gradient, thermocapillary (Marangoni) convections arise. Such systems can be studied in simulations only with very simple models like Lennard-Jonesium. In particular the long-range electrostatic
interactions, which are characteristic for the systems discussed above, cannot (yet) be included.
We have been able to demonstrate the emergence of such thermocapillary flows in MD simulations of two partly miscible Lennard-Jones fluids under a thermal gradient. This work is currently in progress [5] and preliminary results will be presented.
[1] G. Ferlat, J. C. Soetens, A. San Miguel, and Ph. A. Bopp: Combining extended x-ray absorption fine structure with numerical simulations for disordered systems. J.Phys.: Condens Matter 17, 145 (2005), and references therein
[2] J.-M. Andansson, Ph. A. Bopp, and J.-C. Soetens: Relation between hydrogen bonding and intramolecular motions in liquid and supercritical methanol. J. Mol. Liq. 129, 101 (2006)
[3] J.-M. Andanson, J.-C. Soetens, T. Tassaing, and M. Besnard: Hydrogen-bonding in supercritical Tert-Butanol assessed by vibrational spectroscopies and molecular dynamics simulations. J. Chem. Phys., 2005, 122, 174512 [4] J. B. Buhn, Ph. A. Bopp, and M. B. Hampe: Structural and dynamical properties of liquid-liquid interfaces: A systematic molecular dynamics study J. Mol. Liq. 125, 187 (2006), and references therein.
[5] H. A. Maier, Ph. A. Bopp, and M. B. Hampe: Non-Equilibrium Molecular Dynamics Simulation of the Thermocapillary Effect, work in progress
Hybrid method for accurate and fast prediction of
hydration free energy of small organic solutes
Ekaterina Ratkova, Volodymyr Sergiievskyi, Maxim Fedorov
Max Planck Institute for Mathematics in the Sciences, Inselstrasse 22, Leipzig, 04103, Germany We report a novel method for the estimation of the hydration free energy of organic molecules - Structural Descriptors Correction (SDC) model. The method is based on a combination of the Reference Interaction Site Model (RISM) with several empirical corrections. The model requires only a small number of chemical descriptors associated with main features of the chemical structure of solutes: excluded volume, branch, double bond, benzene ring, hydroxyl group and phenol fragment. The optimum model was selected after testing of different RISM free energy expressions on a training set of 36 molecules. We show that the correction parameters of the SDC model are transferable between different chemical classes that allows one to cover a wide range of organic solutes. The new model substantially increases the accuracy of calculated HFEs. After parametrization of this model, the standard deviation of the error for a test set of 60 organic molecules was around 0.85 kcal/mol.
Molecular dynamics simulations of ethanol-carbon dioxide mixtures along the liquid – vapor coexistence
curve
Y. Puhovskia, A. Idrissib, M. Kiseleva
aInstitute of Solution Chemistry of the Russian Academy of Sciences,
Akademicheskaya St., 1, Ivanovo, 153045, Russia
bLaboratoire de Spectrochimie Infrarouge et Raman,
Université des Sciences et Technologies de Lille, Bâtiment C5, 59655 Villeneuve d'Ascq Cedex,- France
The green chemistry is the most perspectives topic in modern chemistry for human society developments. It uses as basis the processes that are less resource-intensive and cause less pollution than traditional industrial production and classic chemical techniques. Solvent usage in various chemical industry sectors has been linked to waste generation and associated environmental and economic burdens. The major targets to reduce environmental and cost burdens in conventional processes include significant reduction of solvent usage and replacement with benign alternatives.
The application of supercritical CO2 as a benign medium in
chemistry and reaction engineering satisfies several green chemistry and engineering principles such as pollution prevention and lower toxicity. Supercritical CO2 and CO2-expanded liquids (CXLs) are the
alternate media for performing chemical reactions. Expanded liquids combine the beneficial properties of compressed CO2 and of
traditional solvents, leading to a new class of tunable solvents that are often the ideal type of solvents for a given application while simultaneously reducing the environmental burden [1]. Supercritical CO2-expanded ethanol is an advanced medium for high selective
extraction possesses, formation of nanoparticles, nanofilms, and membranes because liquid ethanol dissolves large amounts of CO2, expands greatly and consequently undergoes significant changes in virtually every physical property.
Eleven molecular dynamics simulations have been performed for carbon dioxide - ethanol along the experimental liquid – vapor coexistence curve: two for the pure components and nine for the mixtures, containing 0.1-0.9 mole fraction x2 of ethanol. MD
simulation was carried out using the DL_POLY program [2] in a NPT ensemble. The cubic basic simulation box has contained 2048 carbon dioxide and/or ethanol molecules. The pressure of the system have been kept constant by means of the weak coupling algorithms of
Hoover in accordance with experimental values at Т=313К. Standard periodic boundary conditions have been applied. The Zhang [3] and Chen [4] potential models have been used for CO2 and ethanol,
respectively. The equations of motion have been integrated using the leap-frog algorithm, employing an integration time step of 2 fs. The systems have been equilibrated by generating 5 ns long trajectories for each mole fractions. The duration of subsequent runs was 800 ps for data collection.
The compositions and densities of the liquid phases of the binary system at equilibrium are critically compared with corresponding literature values. A satisfactory agreement was obtained between experimental [5] and calculated phase compositions and saturated densities.
Structural properties of the mixture were investigated through the radial distribution functions (RDF), hydrogen bond network properties and the statistical geometry approach. H-bond analysis and dipole correlation functions show that the local geometry of the H-bonded ethanol molecules remains nearly unchanged with varying composition of the mixture. The ethanol molecules form the ramified chains in supercritical mixture even at 0.1 mole fraction of ethanol. The solute-solvent structure reorganization and preferential solvation of the mixture components are discussed in terms the local mole fractions of the i component molecule around a reference molecule of the j component xloc
ij.
This work was supported by the Russian Foundation for Basic Research Grants RFBR- 08-07-00321 and RFBR-08-03-00439 [1] P.G. Jessop, B. Subramaniam Gas-expanded liquids, Chem. Rev., 2007, 107, 2666-2694
[2.]W. Smith, T.R. Forester, I.T. Todorov and M. Leslie, The DL_POLY_2.0 User Manual, CCLRC Daresbury Laboratory, UK [3] Z. Zhang, Z. Duan, J. Chem. Phys. 2005, 122, 214507
[4] B. Chen,† J.J. Potoff,‡ and J.I. Siepmann, J. Phys. Chem. B 2001, 105, 3093-3104
[5] I. Tsivintzelis, D. Missopolinou, K. Kalogiannis, C. Panayiotou, Fluid Phase Equil. 2004, 224, 89–96
A Vibrational Spectroscopic Study of Hydrogen Bonding in Water Subsystem of Ternary
water-scCO2-NaCl mixture
Roman Oparin
Institute of Solution Chemistry of Russian Academy of Sciences, Academicheskya str., 1, Ivanovo, 153045, Russia,
r.oparin@mail.ru
The local order of water subsystem of water-scCO2-NaCl ternary mixture for both rich phase of supercritical carbon dioxide and rich phase of water at constant pressure 250 bar as a function of temperature (T=313-633 K, ΔT=20 K) and electrolyte concentration (0; 6; 15; 23 wt.%) has been investigated using near and mid infrared as well as Raman spectroscopy.
The near IR results have allowed us to estimate the partial density of water in its sub-systems in the water and scCO2 rich phases as function of temperature and NaCl concentration. The investigation of thermal effect on the H-bond distribution in water subsystem at different salt concentration has been based on the mid-IR spectroscopic data analysis.
It has been established that in the case of rich phase of carbon dioxide at the temperatures below 373 K, water molecules dissolved in CO2 exist only under their monomeric
form irrespective of the salt concentration. However the hydrogen-bonded species, namely dimers start to appear at higher temperatures, but larger aggregates have a negligible concentration in the investigated temperature range. The analysis of obtained data allowed to estimate the concentrations of water species in the CO2 phase. Upon heating, it was found
that the concentration of dimers considerably increases at the expense of the monomers one, so that only dimers are detected in carbon dioxide at highest temperatures. Increasing the salt concentration affects significantly the concentration of monomers and reduces strongly the dimers population as the solution becomes progressively saturated in salt. Thus, at the highest electrolyte concentration and T=613 K, the dimer
concentration is at least two times smaller than in the binary water-CO2 mixture.
In the case of water rich phase the thermal effect on the average numbers of H-bonds, <nHB>, is reduced with the
increase of salt concentration. As a result, the slowdown of thermal destroying of H-bond network in water sub-system is observed. When the salt concentration is equal to 0 wt.% (binary water-scCO2 mixture), the temperature increase leads to the disappearance of water molecules having the more than three of H-bonds and to the preferential formation of water dimmers (molecules with one H-bond). However, even with small addition of salt (only 6 wt. %) the water molecules with three H-bonds remain in the system in the whole temperature range. In the case of high NaCl concentration (23 wt. %), the water molecules with two H-bonds become the main structure specie of water sub-system at the temperature above 613 K.
This work was supported by the Russian Foundation for Basic Research (grant No. 10-03-91272-РФГ_з).
Interactions of Alkali and Halide Ions with the Carbon Nanotube Surface in Aqueous Solutions: Understanding the Molecular Mechanisms.
Andrey I. Frolov1, Alex G. Rozhin2, Maxim V. Fedorov1 1 Max Planck Institute for Mathematics in the Sciences, Inselstrasse 22, 142293, Leipzig, Germany, e-mail: fedorov@mis.mpg.de
2 School of Engineering & Applied Science, Aston University, Aston Triangle, Birmingham, B4 7ET, United Kingdom
The carbon nanotube (CNT) aqueous solutions are of primary importance for such applications of CNTs as: photonics, biological and environmental sensing, drug delivery and
bioimaging.[1,2] The CNTs liquid dispersions could be used
inside of micro-fluidic devices targeting specific
biomolecules[3] or as essential components in the emerging
solvent-based molecular engineering processes, e. g. nano-ink printing of CNT functional arrays.[4] But in the applications, the CNTs are rarely dispersed in pure water - the most of technical and biological aqueous environments of CNTs contain different dissolved ions. It has been recently shown, that ions significantly affect the physical-chemical properties of single-wall CNTs (SWNTs) in water solutions.[5,6] Addition of salt into SWNT dispersions results in the quenching of photoluminescence (PL) of SWNTs.[5,6] Brege et al. revealed that the strength of PL quenching has strong correlation with the size of the quenching ions, showing the increase in quenching with increase in the size of ions.[6] Despite of these reports on significant ion effects on PL of CNTs, the molecular mechanisms of ion interactions with the CNT surface are not completely understood.
In this work we studied the molecular mechanisms of alkali halide ions interactions with the SWNT surface in water by means of fully atomistic molecular dynamics simulations.[7] We have shown that there is a strong negative correlation between the strength of ion hydration and the probability of a direct
CNT-ion contact. Ions with high surface charge density (e.g. Li+, F-) do not form direct contacts with the CNT surface. These ions are strongly hydrated and, as a result, they are unable to come closer that the size of one water molecule to the CNT surface. Large ions with low surface charge density (Cs+, Br-, I-) can make direct contacts with the CNT surface. Because of these ions are weakly hydrated, they can loose water molecule from the hydration shells while attaching the CNT surface. As a result, they do make direct contacts with the CNT surface.
We hope that these findings are interesting for the many scientists working in the field surface-specific effects in CNTs and can help in understanding the mechanisms of ion effects on CNTs photoluminescence quenching phenomena in aqueous solution.
[1] R. H. Baughman, A. A. Zakhidov, W. A. de Heer, Science 2002, 297, 787-792.
[2] a) F. Liang, B. Chen, Curr. Med. Chem. 2010, 17, 10-24; b) E. Katz, I. Willner, ChemPhysChem 2004, 5, 1084-1104.
[3] J. Berthier, P. Silberzan, Microfluidics for Biotechnology, Artech House, Boston, 2006, p. 374.
[4] P. Beecher, P. Servati, A. Rozhin, A. Colli, V. Scardaci, S. Pisana, T. Hasan, A. J. Flewitt, J. Robertson, G. W. Hsieh, F. M. Li, A. Nathan, A. C. Ferrari, W. I. Milne, J. Appl. Phys. 2007, 102, 043710.
[5] a) S. Niyogi, S. Boukhalfa, S. B. Chikkannanavar, T. J. McDonald, M. J. Heben, S. K. Doorn, J. Am. Chem. Soc. 2007, 129, 1898-1899; b) S. Niyogi, C. G. Densmore, S. K. Doom, J. Am. Chem. Soc. 2009, 131, 1144-1153. [6] a) J. J. Brege, C. Gallaway, A. R. Barron, J. Phys. Chem. C 2007, 111, 17812-17820; b) J. J. Brege, C. Gallaway, A. R. Barron, J. Phys. Chem. C 2009, 113, 4270-4276.
[7] A. I. Frolov, A. G. Rozhin, M. V. Fedorov, ChemPhysChem 2010, accepted to publication, manuscript number: cphc.201000231.
Surface propensity and ion pair in organic solvents
Babak Minofar
Institute of Systems Biology and Ecology of the Academy of Sciences of the Czech Republic and Institute of Physical Biology, University of South Bohemia, Zamek 136, Nove Hrady,
Czech Republic
Surface propensity and ion pair formation of different
inorganic salts such as NaCl, NaBr, NaI, NaSCN, NaClO4 ,
CH3COONa, CH3COONH4 in organic solvent with and
withought hydrophobic groups such as methanol, isopropanol, dimethyl sulfoxide (DMSO) , aceton, dimethylformamide,
tetrahydrofuran and 1-ethyl-3-methylimidazolium
bis-(trifluoromethanesulfonyl)amide ionic liquid were studied by
means of molecular dynamics (MD) simulations. Analysis of data showed that when the organic solvent has hydrophobic groups such as methyl groups the propensity of ions to the surface is reduced because most surface area is covered by hydrophobic methyl groups of organic solvent or ionc liquid and ions can not penetrate easily. Moreover ion pair formation is observed for many inorganic ions in organic solvents. In the case of surface propensity and observed strongly for hydrophobic ions such as Br-, I- and SCN- eventhogh DMSO has two hydrophobic methyl groups which are pointing out from liquid phase to vapor phase. Also surface propensity of ions in the case of DMSO was stronger than in methanol which has only one methyl group.
Potential of mean force for ion pairs in aprotic organic solvents and their binary mixtures.
A. V. Odinokova), I. V. Leontyevb), M. V. Basilevskya), N. Ch. Petrova).
a) Photochemistry center, RAS, 7a ul. Novatorov, Moscow, 119421, Russia
b) Department of Chemistry, University of California Davis, One Shields Avenue, Davis, California, 95616
Potentials of mean force (PMF) are calculated for two model ion pairs in two aqueous solvents. Standard non-polarizable molecular dynamics simulation (NPMD) and approximate polarizable simulation (PMD; it treats the rapidly relaxing part of the solvent electronic polarization as a dielectric continuum) are implemented and compared as tools for monitoring PMF profiles. For the polar solvent (dimethylsulfoxide, DMSO) the PMF generated in terms of the NPMD reproduces fairly well the refined PMD-PMF profile. For the nonpolar solvent (benzene) the conventional NPMD computation proves to be deficient. The validity of the correction found in terms of the approximate PMD approach is verified by its comparison with the result of the explicit PMD computation in benzene.
The shapes of the PMF profiles in DMSO and in benzene are quite different. In the DMSO, owing to strong dielectric screening, the PMF represents a flat plot with a shallow minimum positioned in the vicinity of the van der Waals contact of the ion pair. For the benzene case, the observed minimum proves to be unexpectedly deep, which manifests a formation of a tightly-binded contact ion pair. This remarkable effect arises owing to the strong electrostatic interaction which is incompletely screened by a non-polar medium. The PMFs for the binary benzene/DMSO mixtures display the intermediate behavior depending on the DMSO contents.
O11
Hydration measurement of salt ions, polyelectrolytes, and proteins in dilute solutions by
high resolution dielectric relaxation spectroscopy
Makoto Suzuki
Department of Materials Processing, Graduate School of Engineering, Tohoku Univeristy, Aoba 6-6-02, Aramaki,
Aoba-ku, endai 980-8579, Japan
msuzuki@material.tohoku.ac.jp 81-22-795-7303 (phone/fax) Interactions between an ion and surrounding water molecules have been discussed over a century. Aqueous solutions of large halogen or alkali ions, so-called chaotropic ions. were known to have higher dielectric relaxation frequencies than bulk water in the microwave frequency range. We developed a high-resolution microwave dielectric spectroscopy technique to analyze hydration states of different kinds of solute such as sodium-halides, polyelectrolyte (polyionenes), and proteins (actin filaments, globular and unfolded proteins) in dilute aqueous conditions. Using an emulsion mixture theory most of bulk solvent component is eliminated from the solution spectrum and the spatially-averaged dielectric property of the ellipsoidal volume containing a solute molecule and surrounding water molecules was extracted and decomposed into a bulk solvent component and a sum of several Debye relaxation components. These analyses on sodium halide aqueous solutions, polyionenes and actin filaments revealed an existence of higher relaxation frequency component than that of bulk solvent proportional to the solute concentrations.
[1] Suzuki et al. “Hyper-mobile water found around F-actin”, Biophys. J. 72, 18, (1997); Kabir et al. Biophys. J. 85, 3154, (2003); Suzuki et al. BBRC 322, 340, (2004); Miyazaki et al. J. Phys. Chem. A 112, 10801 (2008).
The Impact of Specifically Interacting Metal Cations on the Solution Behaviour of Long
Chain Anionic Polyacrylates
Sebastian Lages, Guenter Goerigk1, Peter Lindner2, Ralf Schweins2 and Klaus Huber
Prashant Sinha3 and Manfred Stamm3 Matthias Ballauff4
Chemsitry Department, Universität Paderborn, Warburger Str.100, D-33089 Paderborn
1Forschungszentrum Juelich, JCNS-FRMII, c/o Technische Universität München, Lichtenbergstr. 1, D-85747
Garching
2Institute Laue-Langevin, Grenoble 3Institut für Polymerforschung, Dresden 4Physikalische Chemie I, Universität Bayreuth
. Organic polyelectrolytes are highly charged water soluble polymer chains. The degree of electrical charging on one hand and the hydrophobic chain backbone on the other hand make these chains extremely sensitive to variations of solution conditions. Weak polyacids like polyacrylic acids for instance vary their degree of charge by decreasing the pH value, which causes a significant shrinkage of the coil dimensions. In this case, specific interactions between the protons and the anionic carboxylate functions neutralize charges along the backbone. Another tool to control coil dimensions of highly charged polyelectrolytes in general is the addition of a simple and thus inert salt like NaCl. The added ions screen electrostatic interactions among the charges within a single chain and hence cause a coil shrinking. In line with this impact, they also weaken inter-molecular interactions eventually leading to a precipitation if a sufficiently large excess of the inert salt has been added. Effects of such inert salts can to a large extent be captured by simple electrostatic models. This is not possible any more once specifically interacting metal cations are added to dilute solutions of
polyelectrolytes. In the case of sodium polyacrylate anions (NaPA) alkaline earth cations and transition metal cations are typical representatives of such specifically interacting counterions. Due to their tendency to bind directly to the COO -residuals, they can discharge the chains in very much the same way as protons do and hence lead to a coil shrinking and finally to a coil collapse and coil precipitation already in the presence of stoichiometric amounts of the cations. Therefore, the impact of specifically interacting counterions goes far beyond a simple electrostatic screening. The driving force of such specific binding is at least in part entropic in nature. Altogether, these specific interactions provide an additional set of tools to control the size and solubility of such chains in aqueous solutions. These tools include the variation of temperature, and the subtle interplay of inert salts and specifically interacting counterions. The present account outlines the response of dilute chains onto the variation of the respective parameters. In addition the question is addressed how the chains, decorated with a controllable amount of specifically interacting counterions, form aggregates once the precipitation threshold is crossed. The knowledge in this field is considered to be highly relevant for the development of responsive materials and the process of biomineralization.
pePC-SAFT -
An Equation of State for Polyelectrolyte Systems
Shahbaz Naeem and Gabriele Sadowski* TU Dortmund, Laboratory of Thermodynamics, 44227
Dortmund, Germany
* Corresponding author, Tel.: +49-231-7552635; Fax: +49-232-7552572, E-mail: g.sadowski@bci.tu-dortmund.de
Perturbation theories, which divide the total intermolecular interactions into a reference and perturbations terms, are often used to deliver simple approximate solutions for a given molecular model. Gross and Sadowski developed the PC-SAFT equation of state by applying perturbation theory of Barker and Henderson to a hard-chain reference fluid [1]. The chain-length dependence of the attractive (dispersion) interactions is treated as a perturbation to the reference repulsive interactions. Furthermore, association of the molecules is accounted for by a Helmholtz-energy contribution according to Chapman et al.. The PC-SAFT equation of state uses three or five pure-component parameters for non-associating and non-associating components, respectively. Description of mixtures requires an additional binary interaction parameter. The thermodynamic properties of real systems containing gases, solvents, polymers, as well as copolymers can be calculated using SAFT. Recently PC-SAFT was extended to charged compounds using a Debye-Hückel contribution term accounting for the Coulombic interactions [2].
In this work, we modify the hard-chain expression of original PC-SAFT to describe polyelectrolyte systems. In contrast to neutral polymers, thermodynamic modeling of polyelectrolyte solutions is much more challenging because of: (1) the presence of counterions and possibly other electrolytes, (2) varying charge density (degrees of neutralization) of the
polyelectrolyte, (3) the phenomenon of ion-pair formation, and most importantly (4) the influence of charge density and counterion type on polyelectrolyte structural changes.
Therefore, we replaced the reference hard-chain by the charged-hard-chain using a modified radial distribution function (rdf) as proposed by Jiang et al.[3]. The new rdf qualitatively predicts the chain unfolding with increasing charge density of the polyelectrolyte as well as the effect of counterion and ion-pair formation on chain conformation. An analytical expression for the residual Helmholtz energy is obtained and referred to as pePC-SAFT. It does not introduce any new pure-component or binary interaction parameters and reduces to the original PC-SAFT for non-polyelectrolyte systems.
pePC-SAFT is used to calculate phase equilibria of polyelectrolyte systems. A polyelectrolyte is parameterized by fitting to liquid densities and vapor pressures of aqueous solutions of the non-neutralized polyelectrolyte (neutral polymer). This unique set of parameters (e.g. for polyacrylic acid) is able to predict vapor-liquid equilibria of aqueous polyelectrolyte solutions of different molecular weights, different degrees of neutralization, with different neutralization agents like Na+, NH4+, and in the absence or presence of additional salts in good agreement with experimental data. Moreover, pePC-SAFT is successfully applied to predict aqueous two-phase systems (ATPS) containing (1) a polyelectrolyte and a non-charged polymer as well as (2) a polyelectrolyte and a salt. Predictions are performed as function of degree of neutralization, molecular weight and temperature.
[1] J. Gross, G. Sadowski, Fluid Phase Equilib. 2000, 168, 183.
[2] L. F. Cameretti, G. Sadowski, J. Mollerup, Ind. Eng. Chem. Res. 2005, 44, 3355-3362
[3] Jiang J., Feng J., Liu H., Hu Y.; J. Chem. Phys. 2006, 124, 144908(1)-144908(6)
A new self-consistence field theory approach for polymer solutions.
Nogovitsin E.
Ivanovo State University, Ermaka 37, Ivanovo, Russia Since the pioneering works of Edwards and de Gennes, it has been well acknowledged that concepts originally introduced in quantum field theory, like e.g. functional integrals or renormalization group theory, have substantially contributed to major breakthroughs in the field of polymer science.
In the report a new theoretical approach to calculation of the thermodynamic and structural functions of polymer solutions is presented. This approach bases on the method of Gaussian equivalent representation for calculation of functional integrals and goes beyond the mean-field approximation. The Gaussian equivalent representation leads to self-consistent equations for the mean-force potential.
The theoretical tools for representations of the partition functions in the form of functional integrals are discussed.
As the example the water solution of sodium poly(styrene-sulfonate) with added salt is considered.
Ion solvation versus association: Insights from dielectric spectroscopy on competing
processes in solutions
Richard Buchner
Universität Regensburg, Institut für Physikalische und Theoretische Chemie Regensburg, Germany. Email
Richard.Buchner@chemie.uni-regensburg.de Electrolyte solutions are ubiquitous, ranging from natural waters to hydrometallurgical processes to biological fluids. Understanding ion-solvent interactions is thus a
prerequisite for understanding the behaviour of such systems at a molecular level and for the optimization of associated
technological processes. The key features of ion-solvent
interactions are ion solvation and ion association. Their balance largely determines the structure, thermodynamics and dynamics of electrolyte solutions. Despite being studied for many years with a large number of techniques these effects are still intriguing. Regarding solvation, the discrepancies generally found between effective solvation numbers, as determined from thermodynamic and transport measurements, and the
coordination numbers obtained from scattering techniques and simulations, deserve further attention if we are to understand solution properties. For ion association processes, similar discrepancies between the results of different techniques exist.
The present contribution reviews what kind of information on ion hydration and association can be obtained with dielectric spectroscopy and how this information is linked to results from other methods. Possible problems associated with the interpretation of the dielectric spectra will be addressed. Examples will focus on currently studied aqueous solutions of alkali carboxylates and fluorides, as well as on choline and guanidinium salts. According to our results, in addition to weak ion pairing, all these compounds
exhibit solute-water interactions which are rather similar in
strength to water-water interactions. Intermolecular interactions in aqueous solutions
A. Idrissi
Laboratoire de Spectroschimie Infrarouge et Raman, Centre d’Etudes et de Recherches Lasers et Applications,
Université des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq Cedex, France
When theoretical interpretations are sought for the macroscopic properties of aqueous solutions, one must consider the solute-solute, solute-water and water-water interactions. Analyzing these interactions is essential to describe phenomena of fundamental and practical importance in aqueous solutions ranging from the change in the conformation of proteins (denaturation process), the bio-protection in drying and freezing processes, to hydrophobic/hydrophilic interactions and intermolecular forces.
In this communication the solute-solute interactions is analyzed through the study of the problem of demixing of mixtures of water and solute potential models by calculating the Helmholtz free energy of the two neat liquids as well as their mixtures of different compositions. Further, the composition dependence of the Helmholtz free energy provides information on whether the demixing of the system to two mixtures of different compositions would lead to a thermodynamically stable system or not.
Important information concerning the solute-water and water-water interactions is gathered from the analysis of the thermodynamic properties of the mixture. These studies provided additional information that helps one to understand and interpret the relation between the structural changes of water and the thermodynamic changes accompanying the solvation. In our approach the difference of the hydration free energy of two reasonably similar solute molecules is calculated instead of their full hydration free energies. Furthermore, the effect of the solute on water structure is quantified through the
extent to which a given water molecule and its surrounding neighbours adopt a tetrahedral arrangement. In order to understand the effect of solute on the tetrahedral arrangement of water molecules; we used the nearest neighbour approach to get information on the radial and the mutual orientation of the water molecules around a reference one. We also investigated the effect of adding the solute on the tetrahedral local structure of water molecules in the first hydration shell of the solute as well as in the vicinity of its different functional groups.
The solutes considered in this study are urea, acetone , acetamide and isopropanol.
Selective Na+/K+ effects on
α-cyclodextrin complex formation with aromatic carboxylic acids: competition for the guest
Irina V. Terekhova2, Anastasia O. Romanova1, Roman S. Kumeev2, Maxim V. Fedorov1
1 Max Planck Institute for Mathematics in the Sciences,
Inselstrasse 22, 142293, Leipzig, Germany
2 Institute of Solution Chemistry, Russian Academy of Sciences,
Akademicheskaya str.1, Ivanovo, Russia, 153045
Ions are well known to effect on structures of macromolecules in the solution[1-3]. However, ion effects on reaction in the solution are not sufficiently explored. We have investigated effects of K+ and Na+ ions on the formation of α-cyclodextrin complexes with benzoic and nicotinic acids. Using
solution calorimetry and 1H NMR we performed
thermodynamic and structural investigation of α-cyclodextrin complex formation with ionized aromatic carboxylic acids (benzoic acid and nicotinic acid) in different aqueous solutions
containing K+ and Na+ ions as well as in pure water. The
experiments show that the addition of the sodium ions results in decreasing of the binding constants of the carboxylic acids with α-cyclodextrin comparing to the potassium ions and bulk water. From another side, the effect of the potassium ions is insignificant comparing with bulk water. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. We complemented the experimental results by fully atomistic molecular dynamic simulations which show the molecular scale details of the formation of cation pairs with carboxylate groups of the carboxylic acids. The molecular simulations show that sodium ions preferentially form direct contact ion pairs with the carboxylate groups. At the same time, potassium ions practically do not form direct contacts with the carboxylate
groups and usually stay in the second solvation shell of the carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of α-cyclodextrin with aromatic carboxylic acids. We proposed a novel molecular mechanism of salt effects which is based on the competition between cations and α-cyclodextrin for binding with ionized carboxylic acid.
[1] Fedorov, M. V.; Goodman, J. M.; Schumm, S. Chem. Commun. (2009), 896 - 898.
[2] Fedorov, M. V.; Goodman, J. M.; Schumm, S. J. Amer. Chem. Soc. (2009), 131, 10854 - 10856.
[3] Vlachy, N.; Jagoda-Cwiklik, B.; Vacha, R.; Touraud, D.; Jungwirth, P.; Kunz, W. Adv. Colloid Interface Sci. (2009), 146, 42 - 47.
Interplay between local hydrogen bonding and
long-range Coulomb interactions in Ionic Liquids
Alexander Wulf,1 Koichi Fumino,1 Ralf Ludwig,1 1Universität Rostock, Institut für Chemie, Abteilung
Physikalische Chemie, Rostock/Germany
The ubiquitous properties of ionic liquids are governed by the type and strength of interaction between its constituents. Although interactions in ionic liquids are mainly dominated by Coulomb forces, it is assumed that hydrogen bonding plays an important role for their properties and reaction dynamics. The presence of hydrogen bonding in the structure of 1-alkyl-3-methylimidazolium salts was first reported by Seddon et al. in 1986.[1] Since then evidence for hydrogen bonding is coming from X-ray diffraction, mid-infrared and NMR spectroscopy.[2] However, in recent publications the authors strongly challenge the presence of H-bonds in ionic liquids.[3] For that purpose we initiated a small programme of direct spectroscopic observation of hydrogen bonds and have established clear criteria for making more positive assignments. Increasing capabilities of hydrogen bond formation in a set of well chosen imidazolium ionic liquids allow the direct observation of hydrogen bonding by far-infrared spectroscopy. The frequency shifts can be directly referred to the abilities and strength of H-bond formation. We could show that reduced mass effects are negligible and that the interactions are to large extent local and directional in nature. Additionally, it is shown that the interplay between different intermolecular forces give rise to complex phenomena. A well balanced combination of Coulomb forces, olocal and directional hydrogen bonds as well as dispersion forces enables to tune the favored properties of ionic liquids.
[1] J. A Zora, J. Chem. Soc. Chem. Comm., 1986, 1753-1754.
[2] J. D. Holbrey, W.M. Reichert, R. D. Rogers, Dalton Trans., 2004, 2267-2271; P. Bonhôte, A.-P. Dias, N. Papageorgiou, K. Kalynasundaram, M. Grätzel, Inorg. Chem. 1996, 35, 1168-1178; T. Köddermann, C. Wertz, A. Heintz, R. Ludwig, ChemPhysChem, 2006, 7, 1944-1949.
[3] J.-C. Lassègues, J. Gronding, D. Cavagnat, P. Johansson, J. Phys. Chem.
A 2009, 113, 6419.
In silico studies of ionic liquids at electrified interfaces
N. Georgi§ , A. A. Kornyshev# and M. V. Fedorov§ § Max-Planck Institute for Mathematics in the Sciences, D
04103 Leipzig, Germany
# Department of Chemistry, Imperial College London, SW7 2AZ London, UK
Ionic Liquids have recently received much attention from industry and academia due to their versatile nature as solvents. Ionic Liquids consist of charged molecules only and therefore exhibit high charge density. In addition many of them posses a large electrochemical window making them promising candidates for electrochemical applications, such as supercapacitors.
The properties of electrochemical devices crucially depend on the structure of the liquid-solid interface. Due to the large number of possible anion-cation combinations and the resulting large number of possible candidates a fundamental understanding of Ionic Liquids at solid interfaces would be helpful in advancing the rational design of electrochemical devices.
In my talk I will present results from simulations of simplified models of ionic liquids and discuss the relationship between the molecular geometry and the structure of the liquid at the electrified interface.
In experiments the structure of the liquid-solid interface is accessible measuring the differential capacitance of the Ionic liquid varying the electrode potential. The capacitance in turn can be expressed through the charge density in the liquid adjacent to the wall allowing thus to compare simulations with experimental results.
I will discuss the qualitative agreement between the experimental data of a set of ionic liquids and the simplified models.
Molecular Dynamics of the Discharge of Solvated Protons at the Aqueous/Metallic Interface
Eckhard Spohr
Lehrstuhl für Theoretische Chemie, Fakultät für Chemie, Universität Duisburg-Essen
Universitätsstr. 5, 45141 Essen, Germany eckhard.spohr@uni-due.de
Empirical valence-bond (EVB) models were developed in order to describe the transfer of a proton from aqueous solution bulk to electrocatalytically active and inactive (charged) metal electrode surfaces. Results of density functional calculations are used for parametrizing the model for the Pt(111) surface and the Ag(111) surface. The EVB models make possible large scale molecular dynamics simulations for a metal/electrolyte solution including Grotthuss style proton transport [1]. We have systematically studied the rate of proton discharge on negatively charged surfaces in the range of medium to large surface charge densities. The mean rate of transfer was analysed for proton trajectories which were started in the bulk of a water film adsorbed on the electrode. For the Pt(111) surface the results indicate a transition between a reaction-dominated regime at moderate negative charges, where the rate constant increases exponentially, to a ``diffusion controlled'' regime where the transfer rate is almost independent of the surface charge density (at more negative surface charge densities) [2]. Characteristic differences between the nonreactive Ag(111) and the reactive Pt(111) surface are discussed.
[1] A Model for Proton Transfer To Metal Electrodes, F. Wilhelm, W. Schmickler, R. R. Nazmutdinov and E. Spohr, J. Phys. Chem. C 112, 10814 (2008).
[2] Proton Transfer to Charged Platinum Electrodes. A Molecular Dynamics Trajectory Study, F. Wilhelm, W. Schmickler, and E. Spohr, J. Phys. Cond. Matt. 22, 175001 (2010)
Solvent dynamics effects in electron transfer across electrochemical interfaces
Renat R. Nazmutdinov
Kazan State Technological University
420015 Kazan, Republic Tatarstan, Russian Federation E-mail: nazmutdi@kstu.ru
Some results on the modeling of solvent dynamics (viscosity) effects on electrochemical bond-breaking electron transfer (ET) are reported. The electroreduction of a peroxodisulphate anion at a mercury electrode from mixed ethylene glycol (EG) – water solutions is considered as example. Recent experimental studies predict a challenging non-monotonous dependence of the reaction rate on the EG
content (xEG): descending and ascending plots are clearly
observed at high overpotentials when increasing xEG from 0 to
100% [1].
We made an attempt to elucidate this effect resting on modern stochastic ET theories and experimental complex dielectric spectra for EG-water mixtures [1]. The solvent was treated in terms of three different modes (slow, intermediate and fast); their characteristic times and contributions to the outersphere reorganization energy was obtained from the solvent correlation function [2] which was calculated as well. An effective coordinate was used to describe the intramolecular reorganization [3]. Some qualitative aspects of the problem are discussed using computational results obtained in the framework of Sumi-Marcus model [3]. The Langevin (Brownian) dynamics was employed to perform simulations in the five-dimensional reaction space. Model predictions give a deeper insight into the solvent dynamics effect observed experimentally, which results from a complex interplay between different solvent modes.
This work was supported in part by the RFBR-FWF (project № 09-03-91001-a).
[1] P.A. Zagrebin, R. Buchner, R.R. Nazmutdinov, G.A. Tsirlina. Dynamic solvent effects in electrochemical kinetics: indications for a switch of a relevant solvent mode. J. Phys. Chem. B, (2010), v.114, p.311-320.
[2] R.R. Nazmutdinov, G.A. Tsirlina, M.D. Bronshtein, I.R. Manyurov, N.V. Titova , Z.A. Kuz”minova. Misleading aspects of viscosity effect on heterogeneous electron transfer. Chem. Phys., 2006. v.326. p.123-137. [3] R.R. Nazmutdinov, M.D. Bronshtein, G.A. Tsirlina, N.V. Titova. Interplay between solvent effects of different nature in interfacial bond-breaking electron transfer. J. Phys. Chem. B, 2009. v.113. p.10227-10284.
Investigation of the bioprotective properties of disaccharide/water mixtures from Molecular
Dynamics simulations
F. Affouard, A. Lerbret, A. Hedoux, Y. Guinet, M. Decamps
Unité Matériaux et Transformations (UMET) - UMR CNRS 8207 - UFR de Physique - BAT P5 - Université Lille 1,
59655 Villeneuve d'Ascq, France. e-mail : frederic.affouard@univ-lille1.fr
Disaccharides have received a huge interest over the past few decades for their preservation capabilities of biosystems such as cells, vaccines, or therapeutic proteins employed in pharmaceutical industry. Indeed, disaccharides such as trehalose, maltose or sucrose can be added to biologically active solutions to overcome the limited stability range of proteins (in pH, in temperature, in salt concentration, etc.). These additives prevent the partial or even total degradation of biomolecules due to the lethal thermal or dehydration stresses encountered during industrial conservation methods (lyophilization), where trehalose has been found the most effective. However, the molecular mechanisms at the origin of the superior capabilities of trehalose and, more generally, of the biopreservation phenomenon itself still remain unclear, despite various experimental and theoretical works. Several hypotheses (glass transition temperature, water molecules replacement, hydrogen bonding destructuring effect, preferential excluded volume,…) have been proposed, but none of them can be considered as fully accepted since they have sometimes led to contradictory conclusions.
In order to better understand the biopreservative physical properties of sugars we have performed Molecular Dynamics (MD) investigations of three homologous disaccharides: trehalose, sucrose and maltose in aqueous solutions at different concentrations and temperatures. Hydration numbers clearly show that trehalose binds to a larger number of water molecules than maltose or sucrose, thus
affecting the water structure to a deeper extent. Two dimensional radial distribution functions of trehalose solutions definitely reveal that water is preferentially localized at the hydration sites found in the trehalose dihydrate crystal, this tendency being enhanced when increasing trehalose concentration. Over a rather wide concentration range (4-49 wt %), the fluctuations of the radius of gyration and of the glycosidic dihedral angles of trehalose indicate a higher flexibility with respect to maltose and sucrose. At sugar concentrations between 33 and 66 wt %, the mean sugar cluster size and the number of sugar-sugar hydrogen bonds formed within sugar clusters reveal that trehalose is able to form larger clusters than sucrose but smaller than maltose. These features suggest that trehalose-water mixtures would be more homogeneous than the two others, thus reducing both desiccation stresses and ice formation.
Dressed Molecule Theory and the renomalized charges of molecules in solution.
Rosa Ramírez.
Évry University, 91000 Évry, France
The « Dessed Molecule Theory » (DMT) is an exact statistical mechanical theory for fluid mixtures of rigid molecules with arbitrary charge distributions, sizes, and shapes. It deals with many-body effects in electrostatic interactions between molecules in fluids and can, for example, be applied to mixtures of polar molecules and to solutions of electrolytes or colloidal dispersions in polar molecular solvents. All solute and solvent molecules are treated on the same fundamental level in statistical mechanics. The exact screened Coulomb potential,
0( )r
ϕ ,for the solution, is given a general definition. A
renormalized charge distribution, 0( )
i r
ρ G ,for each molecule of
any species i is uniquely defined such that the exact total electrostatic potential from each i molecule is exactly given byϕ0with 0
i
ρ as the source. By using 0
i
ρ when calculating the
interaction between the molecule and the total electrostatic potential from any source, one includes the indirect effects from the surrounding polarizable molecular medium on the electrostatic part of the potential of mean force for the molecule. DMT can be then used to build up an implicit solvent model to describe molecular interactions in solution.
Selective Na+/K+ effects on α-cyclodextrin complex
formation with aromatic carboxylic acids: competition for the guest
Irina V. Terekhova2, Anastasia O. Romanova1, Roman S.
Kumeev2, Maxim V. Fedorov1
1 Max Planck Institute for Mathematics in the Sciences,
Inselstrasse 22, 142293, Leipzig, Germany
2 Institute of Solution Chemistry, Russian Academy of Sciences,
Akademicheskaya str.1, Ivanovo, Russia, 153045
Ions are well known to effect on structures of macromolecules in the solution[1-3]. However, ion effects on reaction in the solution are not sufficiently explored. We have investigated effects of K+ and Na+ ions on the formation of α-cyclodextrin complexes with benzoic and nicotinic acids. Using
solution calorimetry and 1H NMR we performed
thermodynamic and structural investigation of α-cyclodextrin complex formation with ionized aromatic carboxylic acids (benzoic acid and nicotinic acid) in different aqueous solutions
containing K+ and Na+ ions as well as in pure water. The
experiments show that the addition of the sodium ions results in decreasing of the binding constants of the carboxylic acids with α-cyclodextrin comparing to the potassium ions and bulk water. From another side, the effect of the potassium ions is insignificant comparing with bulk water. We suggest that the selectivity of cation pairing with carboxylates is the origin of the difference between the effects of sodium and potassium ions on complex formation. We complemented the experimental results by fully atomistic molecular dynamic simulations which show the molecular scale details of the formation of cation pairs with carboxylate groups of the carboxylic acids. The molecular simulations show that sodium ions preferentially form direct contact ion pairs with the carboxylate groups. At the same time, potassium ions practically do not form direct contacts with the carboxylate
groups and usually stay in the second solvation shell of the carboxylate groups. That confirms our hypotheses that the selective formation of ion pairs is the main cause of the difference in the observed effects of sodium and potassium salts on the guest-host complex formation of α-cyclodextrin with aromatic carboxylic acids. We proposed a novel molecular mechanism of salt effects which is based on the competition between cations and α-cyclodextrin for binding with ionized carboxylic acid.
[1] Fedorov, M. V.; Goodman, J. M.; Schumm, S. Chem. Commun. (2009), 896 - 898.
[2] Fedorov, M. V.; Goodman, J. M.; Schumm, S. J. Amer. Chem. Soc. (2009), 131, 10854 - 10856.
[3] Vlachy, N.; Jagoda-Cwiklik, B.; Vacha, R.; Touraud, D.; Jungwirth, P.; Kunz, W. Adv. Colloid Interface Sci. (2009), 146, 42 - 47.
Combining classical and ab initio molecular dynamics. Application to the liquid-liquid
transition and related problems
Noël Jakse
Science et Ingénierie des Matériaux et Procédés, Grenoble-INP, UJF-CNRS, 1130, rue de la Piscine, BP 75,
38402 Saint-Martin d’Hères Cedex, France
An overview of a recent series of hybrid simulations combining classical and ab initio molecular dynamics for the study of the liquid, supercooled and amorphous phase of different materials is presented. Various numerical strategy, depending on the system and properties under consideration, will be detailed and illustrated on two examples. First, we will consider the possible the existence of a liquid-liquid transition in silicon, still out of reach to state-of-the-art experimental facilities, for which our numerical simulations give a strong support [1, 2]. It has been possible to clarify the nature of atomic and electronic structures of both the high and low density phase more precisely than earlier classical simulations [3]. Our finding indicates the liquid-liquid transition is accompanied by an enhancement of the local tetrahedral and the appearence of a boson peak in the THz frequency range indicating a fragile-to-strong crossover across the liquid-liquid phase transition. Second, we consider the structural and dynamical properties of amorphous Cu-Zr alloys. A well defined boson peak is also found in this system in good agreement with the experimental observations for equiatomic composition. It is shown that it can be associated to low-density defective local structures around both types of atoms. A correlation of the boson peak with sound attenuation of longitudinal and transverse propagating modes as well as localization of transverse sound waves is found. Implications on the origin of the boson peak in this system are discussed.
[1] N. Jakse, S. Krishnan, E. Artacho, T. Key, L. Hennet, B. Glorieux, A. Pasturel, D. L. Price, M.-L. Saboungi, Appl. Phys. Lett. 83, 4734 (2003).
