DOCSLIB.ORG

Protein±Protein Interactions in Concentrated Electrolyte Solutions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Protein±Protein Interactions in Concentrated Electrolyte Solutions Protein±Protein Interactions in Concentrated Electrolyte Solutions Hofmeister-Series Effects R. A. Curtis,1 J. Ulrich,3 A. Montaser,1 J. M. Prausnitz,1,2 H. W. Blanch1* 1Chemical Engineering Department, University of California, Berkeley, California 94720; telephone:(510) 642-1387; fax:(510) 643-1228; e-mail:[email protected] 2Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 3Automatic Control Laboratory, Swiss Federal Institute of Technology, ETH-Z, ETL I 22, CH-8092 Zurich, Switzerland Received 12 November 2000; accepted 4 July 2001 DOI:10.1002/bit.10342 Abstract: Protein±protein interactions were measured precipitate a target protein is dicult. Protein solubility for ovalbumin and for lysozyme in aqueous salt solu- is governed by many factors, including pH, surface tions. Protein±protein interactions are correlated with a proposed potential of mean force equal to the free en- hydrophobicity, surface-charge distribution, size, salt- ergy to desolvate the protein surface that is made inac- type, and salt concentration (Rothstein, 1994). The goal cessible to the solvent due to the protein±protein of this work is to understand how these factors in¯uence interaction. This energy is calculated from the surface protein solubility. The ®rst step is to determine the in- free energy of the protein that is determined from pro- teractions between the protein molecules, salt ions, and tein±salt preferential-interaction parameter measure- ments. In classical salting-out behavior, the protein±salt water; these interactions, described quantitatively, are preferential interaction is unfavorable. Because addition then used to predict conditions for optimal separation of of salt raises the surface free energy of the protein ac- a mixture of proteins. However, generating a phase cording to the surface-tension increment of the salt, diagram from knowledge of the intermolecular potentials protein±protein attraction increases, leading to a reduc- between the proteins, salt, and water is impossible with- tion in solubility. When the surface chemistry of proteins is altered by binding of a speci®c ion, salting-in is ob- out adopting physically realistic simplifying assump- served when the interactions between (kosmotrope) ion± tions. In general, most models of protein precipitation protein complexes are more repulsive than those be- are based on an eective protein±protein interaction tween the uncomplexed proteins. However, salting-out (Chiew et al., 1995; Fornaseiro et al., 1999; Malfois et al., is observed when interactions between (chaotrope) ion± 1996; Piazza, 1999; Poon, 1997; Rosenbaum et al., 1996) protein complexes are more attractive than those of the that is mediated by salt ions and water. At the present uncomplexed proteins. ã 2002 Wiley Periodicals, Inc. Bio- technol Bioeng 79: 367±380, 2002. time, eective protein±protein interactions in solutions Keywords: Hofmeister-series; protein interactions; hy- of concentrated electrolytes are not well understood. drophobic effect; protein salting-out Because protein solubility usually decreases with rising salt concentration (salting-out) (Cohn, 1943), we simi- larly expect that as salt concentration rises the eective INTRODUCTION protein±protein interactions become more attractive. However, it is not clear whether these interactions are Salt-induced precipitation/crystallization provides an related to solvation forces between proteins or possibly extensively used method in biotechnology for obtaining to speci®c short-range forces that stabilize protein crys- high-quality crystals and for separating target proteins tals, such as van der Waals contacts, salt bridges, or from multicomponent protein solutions as the ®rst pu- hydrogen bonds (Neal et al., 1999; Asthagiri et al., 1999). ri®cation step. However, because protein phase behavior In this work, we focus on determining these eective is not well understood, selecting optimum conditions to protein±protein interactions; from these we develop speci®c criteria for choosing conditions favorable for *Correspondence to: H. W. Blanch selective protein precipitation or protein crystallization. Contract grant sponsors: the Oce for Basic Energy Sciences of the U.S. Department of Energy, the National Science Foundation In concentrated salt solutions, protein solubility de- Contract grant number: CTS-9530793 pends on the anion's or cation's position in the lyotropic ã 2002 Wiley Periodicals, Inc. series (Hofmeister, 1888), but this dependence cannot be work to transfer a protein molecule from a hypothetical explained by considering salt ions as charged hard ideal gas into the aqueous salt solution. This work is the spheres. It is well known that salting-out eectiveness is protein solvation free energy; it is given by the product related to the water-structure-making or water-struc- of the surface free energy, r, and the solvent-accessible ture-breaking ability of the salt (Collins and Washa- surface area of the protein molecule A: baugh, 1985). To predict protein solubility, this eect needs to be incorporated into models for eective pro- h ig l2 l2 NavAr 1b tein±protein interactions. Presently, the only theories that account for these ion-speci®c eects are based on where Nav is Avogadro's number (Ben-Naim, 1978). the approach originally proposed by Melander and Substituting Eq. (1a) into (1b) and taking the derivative Horvath (1977), where protein solubility is determined with respect to molality of salt, m3, gives: by the preferential interactions between the protein and salt (Arakawa and Timashe, 1985). To incorporate d ln S2 dr RT NavA : 1c these theories into a statistical-mechanical model based dm3 dm3 on eective protein±protein interactions, we need to The problem of determining protein solubility as a formulate eective protein±protein interactions in terms function of salt concentration is reduced to solving for of protein±salt interactions. the surface free energy of the protein molecule. The For this reason, we summarize the salting-out theory dependence of the surface free energy of the protein on of Melander and Horvath and present a brief discussion salt molality can be determined from preferential inter- of protein±salt interactions. The following section dis- action-parameter measurements (Casassa and Eisen- cusses current models for eective protein±protein in- berg, 1964): teractions and proposes a simple form for the potential of mean force that can be used in protein phase equi- or o om 1 ol o A À 3 3 2 librium models for predicting protein solubility and for om3 T;p om2 T;l ;l om3 T;p determining conditions favorable for protein crystalli- o 1 3 o zation. Ion-speci®c eects are included in the model by Here, m3 and m2 are salt and protein molality and l1 relating the protein±protein potential of mean force to and l3 are the chemical potential of water and salt, re- the experimentally determinable protein±salt preferen- spectively. Superscript o denotes that the property is tial interaction parameter. PROTEIN±SALT INTERACTIONS Salting-Out Theory The important result of Melander and Horvath (1977) is that protein solubility can be expressed in terms of the solvation free energy of the protein molecule in the equilibrated ¯uid phase. When the solubility is small, we can neglect ¯uid-phase protein±protein interactions. The phase-equilibrium criterion (the chemical potential of the protein in the crystal is equal to that in the ¯uid) at a given salt concentration reduces to: S ls À lh RT ln 2 1a 2 2 h S2 s h where l2 and l2 are the chemical potential of the protein in the solid phase and the in®nite-dilution standard-state chemical potential of the protein, respectively, and S2/ h S2 is protein solubility relative to a standard state sol- ubility. The major assumption of the salting-out theory is that the protein crystal is a pure phase; in that event, the salting-out behavior is determined from the depen- dence of the standard-state chemical potential on salt concentration. The standard-state chemical potential can be further decomposed into a hypothetical ideal-gas contribution and a contribution from the reversible vorable interactions between the salt and the nonpolar water due to interaction with the peptide group, whereas surface of the protein and by favorable weak ion-bind- kosmotropic anions were not retarded due to unfavor- ing interactions between the salt and either the charged able interaction with the nonpolar backbone of poly- surface groups or the surface peptide groups of the acrylamide. protein. In most cases, because the unfavorable hydro- Anion binding to the positively charged surface phobic interactions are greater than the attractive weak groups of protein molecules has been observed in studies ion-binding interactions, salting-out is observed. concerning stabilization of folded structures of protein molecules at low pH (Goto et al., 1990). The strength of this interaction is related to the ion's position in the Surface-Tension-Increment Effect electroselectivity series (Gjerde et al., 1980), as measured The surface free energy of a nonpolar surface in contact by the anity of an ion for an anion-exchange resin. The with a solvent is related to the surface tension of the series depends on the resin employed, but the general 2) ) ) ) ) solvent. Because all salts increase the surface tension of trend is in the order SO4 > SCN >I >Br >Cl . water, they similarly increase the surface free energy of For monovalent anions the electroselectivity series is the
Load more

Recommended publications
  • Protein Precipitation Using Ammonium Sulfate
    HHS Public Access Author manuscript Author ManuscriptAuthor Manuscript Author Curr Protoc Manuscript Author Protein Sci. Manuscript Author Author manuscript; available in PMC 2016 April 01. Published in final edited form as: Curr Protoc Protein Sci. 2001 May ; APPENDIX 3: Appendix–3F. doi:10.1002/0471140864.psa03fs13. Protein Precipitation Using Ammonium Sulfate Paul T. Wingfield Protein Expression Laboratory (HNB-27), National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) - NIH, Bldg 6B, Room 1B130, 6 Center Drive, Bethesda MD 20814, Tel: 301-594-1313 Paul T. Wingfield: [email protected] Abstract The basic theory of protein precipitation by addition of ammonium sulfate is presented and the most common applications are listed, Tables are provided for calculating the appropriate amount of ammonium sulfate to add to a particular protein solution. Key terms for indexing Ammonium sulfate; ammonium sulfate tables; protein concentration; protein purification BASIC THEORY The solubility of globular proteins increases upon the addition of salt (<0.15 M), an effect termed salting-in. At higher salt concentrations, protein solubility usually decreases, leading to precipitation; this effect is termed salting-out ((Green and Hughes, 1955). Salts that reduce the solubility of proteins also tend to enhance the stability of the native conformation. In contrast, salting-in ions are usually denaturants. The mechanism of salting-out is based on preferential solvation due to exclusion of the cosolvent (salt) from the layer of water closely associated with the surface of the protein (hydration layer). The hydration layer, typically 0.3 to 0.4 g water per gram protein (Rupley et al., 1983), plays a critical role in maintaining solubility and the correctly folded native conformation.
    [Show full text]
  • Salting in and Salting out of Proteins BCH 332 Lecture 3 and 4
    Salting in and salting out of proteins BCH 332 lecture 3 and 4 1 • Proteins show a variation in solubility depending on their solution ionic environments. • These frequently complex effects may involve either specific interactions between charged side chains and solution ions, particularly at high salt concentration. 2 Salting in • The effects of salts such as sodium chloride on increasing the solubility of proteins is often referred to as salting in. The salting in effect is related to the nonspecific effect the salt has on the ionic strength. When low concentrations of salt is added to a protein solution, the solubility increases. This could be explained by the following: • Salt molecules stabilize protein molecules by decreasing the electrostatic energy between the protein molecules which increase the solubility of proteins. 3 Salting out • When the ionic strength of a protein solution is increased by adding salt, the solubility decreases, and protein precipitates. This could be explained by the following: • The salt molecules compete with the protein molecules in binding with water. • Many globular proteins precipitate out at very low ionic strengths or in pure water. This happens because different proteins are able to interact favorably leading to formation of a complex. When this complex formation is extended between many protein molecules, it can lead to protein precipitation. 4 • Some salts, such as high concentrations of ammonium sulfate, have general effects on solvent structure that lead to decreased protein solubility and salting out. In this case, the protein molecules tend to associate with each other because protein-protein interactions become energetically more favorable than protein-solvent interaction.
    [Show full text]
  • Biochemistry 06 Salt Fractionation of Proteins
    . 1 Biochemical Techniques Biochemistry 06 Salt Fractionation of Proteins Description of Module Subject Name Biochemistry Paper Name 12 Biochemical Techniques Module Name/Title 06 Salt Fractionation of Proteins 2 Biochemical Techniques Biochemistry 06 Salt Fractionation of Proteins 1. Objectives Understanding the concept of protein fractionation Understanding protein fractionation with salt 2. Concept Map 3. Description 3.1 Protein purification Protein purification is vital for the characterization of protein structure, function and interactions, for example conformational alterations, substrate specificities, specific activities as well as interaction with other ligands. Further, for applications in the food and pharmaceutical industry, a high level of protein purity is 3 Biochemical Techniques Biochemistry 06 Salt Fractionation of Proteins essential and the desired protein must be purified over a number of steps. This is thus achieved through methods of protein purification. Purification is a multistep procedure. The various steps in the purification process are aimed removing non- protein components and impurities to finally separating out the desired protein in its pure form. 3.2 Fractionation of proteins The first step in purifying intracellular proteins is preparing a crude extract. The extract will contain a complex mixture of proteins from cell cytoplasm, and additional components such as macromolecules, cofactors and nutrients. The debris are removed by centrifugation and supernatant (crude protein extract) recovered. Crude preparations of extracellular proteins may be obtained by removing cells by centrifugation. The extract can be subjected to treatments that separate proteins into different fractions based on several properties such as size, charge etc. This process is known as fractionation. Fractionation helps in the removal of any other contaminating material and also in the enrichment of the desired protein fraction.
    [Show full text]
  • Protein Analytics
    Part I Protein Analytics Protein Purification Friedrich Lottspeich 1 Peter-Dörfler-Straße 4a, 82131 Stockdorf, Germany Investigation of the structure and function of proteins has already kept scientists busy for over 200 years. In 1777 the French chemist Pierre J. Macquer subsumed under the term Albumins all substances that showed the peculiar phenomenon of change from a liquid to a solid state upon warming. Chicken egg white, casein, and the blood component globulin already belonged to this class of substances. Already as early as 1787 (i.e., about the time of the French Revolution) the purification of egg white-like (coagulating) substances from plants was reported. In the early nineteenth century many proteins like albumin, fibrin, or casein were purified and analyzed. It soon became apparent that these compounds were considerably more complicated than other organic molecules known at that time. The word protein was most probably introduced by the Swedish chemist Jöns J. von Berzelius in about 1838 and was then published by the Dutch Gerardus J. Mulder. Mulder also suggested a chemical formula, which at that time was regarded as universally valid for all egg white-like materials. The homogeneity and purity of these purified proteins did not correspond of course to today’s demands. However, it became clear that proteins are different and distinct molecules. At that time purification could succeed only if one could use very simple steps, such as extraction for enrichment, acidification for precipitation, and spontaneous crystallization. Already in 1889 Hofmeister had obtained chicken albumin in crystalline form. Although Sumner in 1926 could already crystallize enzymatically active urease, the structure and the The molar mass (M) – often wrongly construction of proteins remained unknown up to the middle of the twentieth century.
    [Show full text]
  • Workshop 7B Protein Isolation and Purification
    Workshop 7B Protein Isolation and Purification Part I--Fractionation and dialysis Introduction page 2 Concentration and partial fractionation of a protein “extract” page 3 Ammonium sulfate table page 5 Dialysis page 6 References and useful books page 7 Part II--Liquid Chromatography and MALDI Mass Analysis Introduction page 8 Size exclusion chromatography page 10 Desalting using gel filtration chromatography page 10 Normal phase chromatography page 11 Ion-exchange chromatography page 12 Reversed-phase chromatography page 12 HPLC instructions page 14 MALDI instructions page 17 Principle of MALDI page 21 MALDI sample preparation page 23 Mass Spectrometry Terms page 24 Resolution page 24 Mass accuracy page 26 Common matrices used for MALDI page 27 MALDI spectrums page 29 References and useful books page 32 Equipment List page 33 Spring 2016 Workshop 7B- Protein Isolation and purification Part I- Fractionation and dialysis Instructors Joel Nott, Margie Carter, 1182 Mol. Biol. Bldg., Phone 294-3267, [email protected], http://www.protein.iastate.edu Introduction The first step in protein purification involves a cell disruption step. The method of choice depends on the type of cell. In general, animal cells are easier to disrupt than bacteria, yeast or plant cells. The table below summarizes some of the methods. This list is by no means complete, as there are as many methods of disruption as there are types of cells. Cell Type Method Comment Bacteria French press Shearing forces disrupt cell wall as the cells Plant cells are forced through a small opening under very high pressure. Not practical for large volumes. Bacteria Sonication Disruption of cell walls by shearing and cavitation.
    [Show full text]
  • Lehninger Principles of Biochemistry Fourth Edition
    David L. Nelson and Michael M. Cox Lehninger Principles of Biochemistry Fourth Edition Chapter 3: Working with Proteins: Protein Isolation and Characterization Reading material: p. 89 – 95, Lehninger Chapter 3 [1] Protein Source: 1. Tissue 2. Microbial cells. If we isolate a protein from a tissue or cell, we might first need to isolate a particular part of the cell i.e. organelle. We can do this by differential centrifugation, where the spin speed determines what remains in the pellet.. 1. Grind tissue (blender/homogenizer) 2. Centrifuge – the speed determines which organelles appear in the pellet and this is based on density (which ones will pellet first?) (Fig 1-8) [2] Solubilization 1.Osmotic lysis: simple and gentle - place cells in a hypotonic solution 2. Mechanical: good if cells have cell wall crushing or grinding of cells, French press (pressure), sonication (sound) 3. Detergents: used if protein is in lipid membrane • pH: use an appropriate buffer. Figure 2-16; p.13, H(3) • Temperature: 0-4 °C – can be unstable once outside of cell • Proteases: must be inhibited (Proteases (proteinases) cut amide bonds of protein) • Adsorption: keep concentrated (denatures at surfaces) minimize foaming/exposure to air (reduce unfolding) • Storage: store under inert gas, frozen at -80 °C or -196 °C [3] Stabilization Proteins are most stable under pH and ionic strength close to physiological conditions. pH: 7.4, (lysosomal enzymes, pH 5) I (ionic strength) = 0.15 M How is Ionic Strength determined? 2 I = ½ciZi where ci is the concentration (mol/L) of ionic species, and Zi is the net charge of the species.
    [Show full text]
  • Investigation of the Salting out of Methane from Aqueous Electrolyte Solutions Using Computer Simulations
    J. Phys. Chem. B 2007, 111, 8993-9000 8993 Investigation of the Salting Out of Methane from Aqueous Electrolyte Solutions Using Computer Simulations H. Docherty and A. Galindo* Department of Chemical Engineering, Imperial College London, South Kensington Campus London SW7 2AZ, United Kingdom E. Sanz† and C. Vega Departamento de Quı´mica Fı´sica, Facultad de Ciencias Quı´micas, UniVersidad Complutense de Madrid, Ciudad UniVersitaria 28040 Madrid, Spain ReceiVed: NoVember 24, 2006; In Final Form: February 12, 2007 We calculate the excess chemical potential of methane in aqueous electrolyte solutions of NaCl using Monte Carlo computer simulations. In a recent work [Docherty et al. J. Chem. Phys. 2006, 125, 074510], we presented a new potential model for methane in water which is capable of describing accurately the excess chemical potential of methane in pure water over a range of temperatures, a quantity that can be related to the solubility and which is commonly used to study the hydrophobic effect. Here, we use the same potential model for the water-methane interactions and investigate the effect of added salt on the chemical potential of methane in the solution. The methane molecules are modeled as single Lennard-Jones (LJ) interaction sites, and the water molecules are modeled with the TIP4P/2005 model. A correcting factor of ø ) 1.07 for the energetic Berthelot (geometric) combining rule of the methane-water interaction is also used, which mimics the polarization of methane in water. We consider NaCl as the salt and treat the ions with the Smith and Dang model (i.e., as charged LJ interaction sites).
    [Show full text]
  • Protein Precipitation for the Purification of Therapeutic Proteins
    Protein Precipitation for the Purification of Therapeutic Proteins by Christopher W Morris A thesis submitted for the degree of Doctor of Engineering in The Department of Biochemical Engineering, UCL 1 Abstract This thesis documents the application of precipitant scouting and analytical tools for the development of a precipitation process for the purification of therapeutic proteins in biopharmaceuticals. Precipitation has the potential to bypass the bottlenecks in productivity experienced with packed bed chromatographic separations, offering a fast, robust first purification step with volume reduction at low cost. In order to evaluate a large number of precipitation candidates, microscale investigations aided by automated liquid handling robotics were chosen, which conferred precision, speed, and complex experimental design with microliter material requirements and in-line analytics. A precipitation screening methodology was successfully built onto a Tecan liquid handling platform including product recovery and techniques for measuring soluble protein, liquid volumes, and recovered protein precipitate. The protocol was supplemented with a custom- build Excel VBA driven Tecan control tool. This accelerated progress by freeing up the potential of the liquid handling arm, which was curtailed by system software. These techniques were then used to characterise effective precipitants for the purification of monoclonal antibodies. Optimal conditions were identified on pure protein models, which were the bridged to process relevant cell culture fluid. Process performance, notably recovery yield and product quality were the investigated on the precipitant conditions brought forward. Process integration aspects were explored, by linking precipitation with an anion exchange chromatography step. This led to discussion on future work and process scale up considerations. 2 Impact Statement This impact statement serves as a suitable place to reflect on the work presented in this thesis and how it relates to academic and industrial applications.
    [Show full text]
  • Hofmeister Series
    Hofmeister Series Rationale Thermodynamic properties Effect on physical properties Effect on solubility Stabilization of proteins Hydrophobic and hydrophilic associations The effects of ions on biological and chemical processes in solution usually depend on the particular ions involved. These specific ion effects make up the Hofmeister phenomena [1827]. The Hofmeister series [85], below, originates from the ranking of various ions toward their ability to precipitate a mixture of hen egg white proteins.a 2- 2 - - - - Anions: SO4 > HPO4 > acetate > Cl > NO3 2+ + + + + Cations: Mg > Li > Na = K > NH4 Simplistically, this protein precipitation can be explained in terms of the extent of the ions binding to water (see also salting-out).b Thus the effective concentration of the proteins increases (in the remaining 'free' water) and they precipitate, so releasing low entropy surface water. The series has been shown to have a much more general utility with at least 38 observed phenomena (given in the comprehensive review [139], with the current state of play recently reviewed [671,1132]) including showing the graduated effects on the structuring or denaturation of biological macromolecules, effects on interfacial hydration [1302] and affecting pH measurements [481]. Nowadays the Hofmeister series are usually given in terms of the ability of the ions to stabilize the structure of proteins. A similar effect has been found with the salt-induced activation of lyophilized enzymes [204]. They show opposite correlations for anions and cations with their degree of strong hydration. The relative positions (mostly corresponding to the degree of strong hydration [250]) in the series should be thought of as indicative only as there will be variation with protein, pH and temperature, with acetate ions showing pronounced cation-specific effects.
    [Show full text]
  • The Role of Counter-Ions in Peptides—An Overview
    pharmaceuticals Review The Role of Counter-Ions in Peptides—An Overview Karol Sikora * , Maciej Ja´skiewicz , Damian Neubauer , Dorian Migo ´n and Wojciech Kamysz Department of Inorganic Chemistry, Faculty of Pharmacy, Medical University of Gda´nsk,80-210 Gda´nsk,Poland; [email protected] (M.J.); [email protected] (D.N.); [email protected] (D.M.); [email protected] (W.K.) * Correspondence: [email protected] Received: 2 November 2020; Accepted: 1 December 2020; Published: 3 December 2020 Abstract: Peptides and proteins constitute a large group of molecules that play multiple functions in living organisms. In conjunction with their important role in biological processes and advances in chemical approaches of synthesis, the interest in peptide-based drugs is still growing. As the side chains of amino acids can be basic, acidic, or neutral, the peptide drugs often occur in the form of salts with different counter-ions. This review focuses on the role of counter-ions in peptides. To date, over 60 peptide-based drugs have been approved by the FDA. Based on their area of application, biological activity, and results of preliminary tests they are characterized by different counter-ions. Moreover, the impact of counter-ions on structure, physicochemical properties, and drug formulation is analyzed. Additionally, the application of salts as mobile phase additives in chromatographic analyses and analytical techniques is highlighted. Keywords: peptides; counter-ions; drug formulation; analytical techniques; physicochemical; counter-ion exchange; peptide drugs; peptide synthesis 1. Introduction Peptides along with proteins constitute the largest group of mediators of cellular processes making them pivotal for the functioning of many organisms.
    [Show full text]
  • Interactions Between Macromolecules and Ions: the Hofmeister Series Yanjie Zhang and Paul S Cremer
    COCHBI-389; NO OF PAGES 6 Interactions between macromolecules and ions: the Hofmeister series Yanjie Zhang and Paul S Cremer The Hofmeister series, first noted in 1888, ranks the relative [4–7], protein stability [8], protein–protein interactions influence of ions on the physical behavior of a wide variety of [9,10], protein crystallization [11], optical rotation of sugar aqueous processes ranging from colloidal assembly to protein and amino acids [12], as well as bacterial growth [13]. folding. Originally, it was thought that an ion’s influence on Although Hofmeister effects for macromolecules in aqu- macromolecular properties was caused at least in part by eous solution are ubiquitous, the molecular-level mechan- ‘making’ or ‘breaking’ bulk water structure. Recent time- isms by which ions operate are only beginning to be resolved and thermodynamic studies of water molecules in salt unraveled [14]. solutions, however, demonstrate that bulk water structure is not central to the Hofmeister effect. Instead, models are being In this short review we first examine several recent experi- developed that depend upon direct ion–macromolecule ments which cast doubt on the notion that water structure interactions as well as interactions with water molecules in the making and breaking by salts is central to the Hofmeister first hydration shell of the macromolecule. series. This leads to the hypothesis that direct ion–macro- molecule interactions are largely responsible for most Addresses Department of Chemistry, Texas A&M University, College Station, TX aspects of this phenomenon (Figure 2b). Second, we look 77843, USA at the inclusion of dispersion forces in theoretical calcula- tions of specific ion effects.
    [Show full text]
  • The Inverse and Direct Hofmeister Series for Lysozyme
    The inverse and direct Hofmeister series for lysozyme Yanjie Zhang and Paul S. Cremer1 Department of Chemistry, Texas A&M University, College Station, TX 77843 Communicated by Gabor A. Somorjai, University of California, Berkeley, CA, July 15, 2009 (received for review June 2, 2009) Anion effects on the cloud-point temperature for the liquid؊liquid Perhaps the quintessential example of an inverse Hofmeister phase transition of lysozyme were investigated by temperature series is the precipitation of lysozyme from solution (8, 17–24). gradient microfluidics under a dark field microscope. It was found Herein, we show that lysozyme actually displays an inverse that protein aggregation in salt solutions followed 2 distinct Hofmeister series only at low salt concentration when studied at Hofmeister series depending on salt concentration. Namely, under pH 9.4. As the concentration of monovalent salts is raised, the low salt conditions the association of anions with the positively order reverts back to a direct Hofmeister series. Indeed, the charged lysozyme surface dominated the process and the phase charge screening effects that lead to the inverse series are only transition temperature followed an inverse Hofmeister series. This dominant below Ϸ200 or 300 mM salt. Above this concentration, inverse series could be directly correlated to the size and hydration the physical properties follow a direct series. Moreover, we build thermodynamics of the anions. At higher salt concentrations, the a simple model based on charge screening and surface tension liquid–liquid phase transition displayed a direct Hofmeister series effects, which can completely account for the hydrophobic that correlated with the polarizability of the anions.
    [Show full text]