Table Of Content7261tp.indd 1 10/22/09 2:22:29 PM
TThhiiss ppaaggee iinntteennttiioonnaallllyy lleefftt bbllaannkk
edited by
Werner Kunz
University of Regensburg, Germany
World Scientific
NEW JERSEY • LONDON • SINGAPORE • BEIJING • SHANGHAI • HONG KONG • TAIPEI • CHENNAI
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Published by
World Scientific Publishing Co. Pte. Ltd.
5 Toh Tuck Link, Singapore 596224
USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601
UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
Cover image from Dr. Roland Neueder.
SPECIFIC ION EFFECTS
Copyright © 2010 by World Scientific Publishing Co. Pte. Ltd.
All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means,
electronic or mechanical, including photocopying, recording or any information storage and retrieval
system now known or to be invented, without written permission from the Publisher.
For photocopying of material in this volume, please pay a copying fee through the Copyright
Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to
photocopy is not required from the publisher.
ISBN-13 978-981-4271-57-8
ISBN-10 981-4271-57-8
Typeset by Stallion Press
Email: [email protected]
Printed in Singapore.
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Contents
Foreword...................................................... vii
Preface........................................................ ix
Acknowledgements............................................. xiii
ListofContributors............................................ xv
Part A: Examples, Ion Properties and Concepts.............. 1
Chapter 1: An Attempt of a General Overview............... 3
WernerKunzandRolandNeueder
Chapter 2: Phospholipid Aggregates as Model Systems
to Understand Ion-Specific Effects:
Experiments and Models.......................... 55
EpameinondasLeontidis
Chapter 3: Modelling Specific Ion Effects
in Engineering Science............................ 85
ChristophHeldandGabrieleSadowski
Part B: Promising Experimental Techniques.................. 117
Chapter 4: Linear and Non-linear Optical Techniques
to Probe Ion Profiles at the Air–Water
Interface.......................................... 119
HubertMotschmannandPatrickKoelsch
Chapter 5: X-Ray Studies of Ion Specific Effects.............. 149
PadmanabhanViswanath,LucGirard,
JeanDaillant,LucBelloni,OlivierSpallaand
DmitriNovikov
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vi Contents
Chapter 6: The Determination of Specific Ion Structure
by Neutron Scattering and Computer
Simulation........................................ 171
GeorgeW.Neilson,PhilipE.Mason
andJohnW.Brady
Chapter 7: Specific Ion Effects at the Air–Water Interface:
Experimental Studies.............................. 191
VincentS.J.CraigandChristineL.Henry
Part C: Newest Results from Theory and Simulation......... 215
Chapter 8: Ion Binding to Biomolecules...................... 217
MikaelLund,JanHeydaandPavelJungwirth
Chapter 9: Ion-Specificity: From Solvation Thermodynamics
to Molecular Simulations and Back............... 231
JoachimDzubiella,MariaFyta,DominikHorinek,
ImmanuelKalcher,RolandR.NetzandNadine
Schwierz
Chapter 10: HNC Calculations of Specific Ion Effects........ 267
LucBelloniandIouliaChikina
Chapter 11: Modifying the Poisson–Boltzmann Approach
to Model Specific Ion Effects.................... 293
MathiasBoström,EduardoR.A.Lima,
EvaristoC.BiscaiaJr.,FredericoW.Tavares
andWernerKunz
Part D: Summary and Conclusions........................... 311
Chapter 12: An Attempt of a Summary....................... 313
WernerKunzandGordonJ.T.Tiddy
Index ......................................................... 321
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Foreword
At a symposium celebrating the 100th anniversary of the Nobel Prizes
in Chemistry, Aaron Klug, Nobel Laureate of 1982, made the remark
that it was well known to biologists that the Debye–Hückel theory, and
by implication its extensions, was limited to slightly contaminated water.
This remark on the relevance of physical chemistry to biology is widely
held. Biologists and biochemists, long familiar with specific ion effects,
havequitereasonablybeenbemusedbythefailureofphysicalchemistryto
dealwitheffectstheyknowareuniversal.Anotherbiochemistparticipant
remarked that mechanisms of enzyme action were all understood. There
wasnoneedforfurtherwork.
Thiswasnewstophysicalchemists.
Klugg’s view is fair enough, at one level. After all Hofmeister was a
pharmacologist,andthebiologistscouldclaimhimastheirown.Hofmeis-
ter’sworkonspecificioneffectsgoesbacktothe1870s.ItpredatesArrhe-
niusandvan’tHoff.ItpredatespHandbuffers.Itwasputtoonesideby
colloidscientistsandphysicalchemistsandonlycamebacktocentrestage
againadecadeorsoago.
TheoristshavebeenuneasilywellawarethatHofmeistereffectsareas
importantintheschemeofthingsasMendel’sworkwastogenetics.And
that they were not accommodated by the classical theories of colloid and
physicalchemistry.Buttheycouldnotexplaintheresults.
At another level the Kluggian view is absurdly limited. It admits no
roleforphysicalchemistryinbiology,orforthatmatterinchemicalengi-
neering.Chemistryisspecific,andthatisthat.Thisviewispre-Mendeleev.
Butbiologistsandbiochemistsdousethetoolsandconceptsofphysi-
calchemistry.Thesehavetheirrootsinthe‘slightlycontaminated’waterof
Debye–Hückeltheoryanditsextensionstoinclude‘ionsize’anddouble
layers.ThisissoforconceptslikepH,buffers,pKa’s,ionbinding,interac-
tionsofionswithsurfaces,membraneandzetapotentials,colloidalinterac-
tionsthataredeeplyembeddedinourcollectivepsyche.Thefoundations
ofthesehaveonlybeenquestionedoverthelastdecade.Thetheoriesused
vii
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viii Foreword
tointerpretthesethingsallinvolveDebye–Hückeltheoryanditsdecora-
tions. Indeed the dictum of the IUPAC commission on best practice in
pHmeasurement—thatreliesonthevalidityofextendedDebye–Hückel
theoryandtheequivalentPoissonBoltzmandistributionforchargedsur-
faces — has the unhelpful advice that it is better to restrict pH measure-
mentstopHsomewhatlessthan0.1molar.Theinterpretationofstandard
measurements generally depends on classical theory. So if the theory is
flawed, so is the meaning of the measurement. Various unknown ion-
specific mechanisms, words like hydrophobic, hydrophilic, ‘hydration’,
‘secondaryhydration’,Sternlayers,sitebindingmodels,‘waterstructure’,
have perforce substituted for ‘explanation’ of ‘non-DLVO’ forces and
disguiseourignorance.
Wehavehadhugefrustrationwiththemuddleandmishmashofunex-
plained phenomena and the lack of systemisation associated with specific
ioneffects.
The availability of powerful experimental techniques and advances
in computation and computer simulation over the last few decades have
changedmatters.AddtothesituationthefactthatKlugg’srealdirtywater
contains dissolved atmospheric gas and other solutes that strongly affect
everything else, like hydrophobic interactions in a way that is itself ion
specific.Thenwehavenewbeginning.
Somerealprogresshasbeenmade.Newinsightshaveemerged.There
are opposing views that are coming together. These problems of physical
chemistry we can hope are now well on the way to solution and a new
synthesis.
Fromthetrulyvastconfusingliterature,thisbookhasdistilledatimely,
fair,clearandusefulstatementandsummaryonthecentralproblemofion
specificity,andofprogressinunderstandingfromtheviewpointofphysical
chemists proper. It is also appropriate as Pavel Jungwirth’s laboratory is
astone’sthrowfromHofmeister’sinPragueandthatofWernerKunzin
Regensburgisafewhours’driveaway.
Barry W. Ninham
ResearchSchoolofPhysicsandEngineering
AustralianNationalUniversity
Canberra,Australia
June2009
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Preface
So many specific ion effects are described in literature in thousands of
papers since the pioneering studies by Franz Hofmeister and his group
in Prague, some 130 years ago. Theoretical work has been done over a
centurynow,yetstillthepuzzlepersists.Whatistheoriginoftheinterac-
tionsofsimpleionswithwater,otherionsandsolutes,andwithinterfaces,
beyond electrostatics? Is it only the size and charge density or do disper-
sionforcesplayamajorrole?Inwhatcasesarethechargedistributionand
the geometry of ions important? Is the size dominating or is it the size
pluspolarisability?
Can we ever predict specific ion effects quantitatively and beyond
empirical rules? Is it like long-term weather forecast or can we find some
generalprinciplesbehindit?
The fact that the so-called Hofmeister series exist is a sign that some
generalisationshouldbepossible.ButthereareseveralHofmeisterseries,
direct and reversed ones, or even bell-shaped, and they may change with
temperature and ion concentration. All this seems to be hopelessly com-
plicated,andpartoftheproblemcomesfromapparentlydivergingexper-
imentalresults.
Asanexample,wecanconsiderthesurfacepropertiesofasimpleelec-
trolyte solution as follows: the experimentally measured surface tension
can be calculated, according to Gibbs’ equation, as an integral over the
ionprofilesperpendiculartothesurfacefromzerotoinfinitedistancefrom
thesurface.However,someexperimentsmainlyprobethefirstatomicand
molecular layers near the surface. It was one of the major findings of the
last several years that locally (close to an interface) accumulation of ions
can occur, despite the fact that globally (integrated over a large distance)
depletion is detected. Therefore the old perception that small ions are
always pushed away from the interface turned out to be wrong. Ions can
beattractedtothesurfaceinthefirstlayers,althoughthesurfacetension
ofthetotalsolutionisenhanced,comparedtopurewater.
ix
