Isoelectric point

Last updated

The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). [1] However, pI is also used. [2] For brevity, this article uses pI. The net charge on the molecule is affected by pH of its surrounding environment and can become more positively or negatively charged due to the gain or loss, respectively, of protons (H+).

Contents

Surfaces naturally charge to form a double layer. In the common case when the surface charge-determining ions are H+/HO−, the net surface charge is affected by the pH of the liquid in which the solid is submerged.

The pI value can affect the solubility of a molecule at a given pH. Such molecules have minimum solubility in water or salt solutions at the pH that corresponds to their pI and often precipitate out of solution. Biological amphoteric molecules such as proteins contain both acidic and basic functional groups. Amino acids that make up proteins may be positive, negative, neutral, or polar in nature, and together give a protein its overall charge. At a pH below their pI, proteins carry a net positive charge; above their pI they carry a net negative charge. Proteins can, thus, be separated by net charge in a polyacrylamide gel using either preparative native PAGE, which uses a constant pH to separate proteins, or isoelectric focusing, which uses a pH gradient to separate proteins. Isoelectric focusing is also the first step in 2-D gel polyacrylamide gel electrophoresis.

In biomolecules, proteins can be separated by ion exchange chromatography. Biological proteins are made up of zwitterionic amino acid compounds; the net charge of these proteins can be positive or negative depending on the pH of the environment. The specific pI of the target protein can be used to model the process around and the compound can then be purified from the rest of the mixture. Buffers of various pH can be used for this purification process to change the pH of the environment. When a mixture containing a target protein is loaded into an ion exchanger, the stationary matrix can be either positively-charged (for mobile anions) or negatively-charged (for mobile cations). At low pH values, the net charge of most proteins in the mixture is positive – in cation exchangers, these positively-charged proteins bind to the negatively-charged matrix. At high pH values, the net charge of most proteins is negative, where they bind to the positively-charged matrix in anion exchangers. When the environment is at a pH value equal to the protein's pI, the net charge is zero, and the protein is not bound to any exchanger, and therefore, can be eluted out. [3]

Calculating pI values

For an amino acid with only one amine and one carboxyl group, the pI can be calculated from the mean of the pKas of this molecule. [4]

The pH of an electrophoretic gel is determined by the buffer used for that gel. If the pH of the buffer is above the pI of the protein being run, the protein will migrate to the positive pole (negative charge is attracted to a positive pole). If the pH of the buffer is below the pI of the protein being run, the protein will migrate to the negative pole of the gel (positive charge is attracted to the negative pole). If the protein is run with a buffer pH that is equal to the pI, it will not migrate at all. This is also true for individual amino acids.

Examples

Glycine pI-en.svg AMP pI-en.svg
glycine pK = 2.72, 9.60adenosine monophosphate pK = 0.9, 3.8, 6.1

In the two examples (on the right) the isoelectric point is shown by the green vertical line. In glycine the pK values are separated by nearly 7 units. Thus in the gas phase, the concentration of the neutral species, glycine (GlyH), is effectively 100% of the analytical glycine concentration. [5] Glycine may exist as a zwitterion at the isoelectric point, but the equilibrium constant for the isomerization reaction in solution

is not known.

The other example, adenosine monophosphate is shown to illustrate the fact that a third species may, in principle, be involved. In fact the concentration of (AMP)H2+3 is negligible at the isoelectric point in this case. If the pI is greater than the pH, the molecule will have a positive charge.

Peptides and proteins

A number of algorithms for estimating isoelectric points of peptides and proteins have been developed. Most of them use Henderson–Hasselbalch equation with different pK values. For instance, within the model proposed by Bjellqvist and co-workers, the pKs were determined between closely related immobilines by focusing the same sample in overlapping pH gradients. [6] Some improvements in the methodology (especially in the determination of the pK values for modified amino acids) have been also proposed. [7] [8] More advanced methods take into account the effect of adjacent amino acids ±3 residues away from a charged aspartic or glutamic acid, the effects on free C terminus, as well as they apply a correction term to the corresponding pK values using genetic algorithm. [9] Other recent approaches are based on a support vector machine algorithm [10] and pKa optimization against experimentally known protein/peptide isoelectric points. [11]

Moreover, experimentally measured isoelectric point of proteins were aggregated into the databases. [12] [13] Recently, a database of isoelectric points for all proteins predicted using most of the available methods had been also developed. [14]

In practice, a protein with an excess of basic aminoacids (arginine, lysine and/or histidine) will bear an isoelectric point roughly greater than 7 (basic), while a protein with an excess of acidic aminoacids (aspartic acid and/or glutamic acid) will often have an isoelectric point lower than 7 (acidic). The electrophoretic linear (horizontal) separation of proteins by Ip along a pH gradient in a polyacrylamide gel (also known as isoelectric focusing), followed by a standard molecular weight linear (vertical) separation in a second polyacrylamide gel (SDS-PAGE), constitutes the so called two-dimensional gel electrophoresis or PAGE 2D. This technique allows a thorough separation of proteins as distinct "spots", with proteins of high molecular weight and low Ip migrating to the upper-left part of the bidimensional gel, while proteins with low molecular weight and high Ip locate to the bottom-right region of the same gel.

Ceramic materials

The isoelectric points (IEP) of metal oxide ceramics are used extensively in material science in various aqueous processing steps (synthesis, modification, etc.). In the absence of chemisorbed or physisorbed species particle surfaces in aqueous suspension are generally assumed to be covered with surface hydroxyl species, M-OH (where M is a metal such as Al, Si, etc.). [15] At pH values above the IEP, the predominant surface species is M-O−, while at pH values below the IEP, M-OH2+ species predominate. Some approximate values of common ceramics are listed below: [16] [17]

MaterialIEP
WO3 [18] 0.2–0.5
Sb2O5 [18] <0.4–1.9
V2O5 [18] [19] 1–2 (3)
δ-MnO2 1.5
SiO2 [18] 1.7–3.5
SiC [20] 2–3.5
Ta2O5 [18] 2.7–3.0
TiO2 [21] 2.8–3.8
γ-Fe2O3 [18] 3.3–6.7
SnO2 [22] 4–5.5 (7.3)
ZrO2 [18] 4–11
ITO [23] 6
Cr2O3 [18] [19] 6.2–8.1 (7)
Fe3O4 [18] 6.5–6.8
CeO2 [18] 6.7–8.6
Y2O3 [18] 7.15–8.95
γ-Al2O3 7–8
β-MnO2 [19] 7.3
Tl2O [24] 8
α-Al2O3 8–9
α-Fe2O3 [18] 8.4–8.5
ZnO [18] 8.7–10.3
Si3N4 [22] 9
CuO [22] 9.5
La2O3 10
NiO [22] 10–11
PbO [18] 10.7–11.6
MgO [18] 12–13 (9.8·12.7)

Note: The following list gives the isoelectric point at 25 °C for selected materials in water. The exact value can vary widely, depending on material factors such as purity and phase as well as physical parameters such as temperature. Moreover, the precise measurement of isoelectric points can be difficult, thus many sources often cite differing values for isoelectric points of these materials.

Mixed oxides may exhibit isoelectric point values that are intermediate to those of the corresponding pure oxides. For example, a synthetically prepared amorphous aluminosilicate (Al2O3-SiO2) was initially measured as having IEP of 4.5 (the electrokinetic behavior of the surface was dominated by surface Si-OH species, thus explaining the relatively low IEP value). [25] Significantly higher IEP values (pH 6 to 8) have been reported for 3Al2O3-2SiO2 by others. [22] Similarly, also IEP of barium titanate, BaTiO3 was reported in the range 5–6 [22] while others got a value of 3. [26] Mixtures of titania (TiO2) and zirconia (ZrO2) were studied and found to have an isoelectric point between 5.3–6.9, varying non-linearly with %(ZrO2). [27] The surface charge of the mixed oxides was correlated with acidity. Greater titania content led to increased Lewis acidity, whereas zirconia-rich oxides displayed Br::onsted acidity. The different types of acidities produced differences in ion adsorption rates and capacities.

Versus point of zero charge

The terms isoelectric point (IEP) and point of zero charge (PZC) are often used interchangeably, although under certain circumstances, it may be productive to make the distinction.

In systems in which H+/OH− are the interface potential-determining ions, the point of zero charge is given in terms of pH. The pH at which the surface exhibits a neutral net electrical charge is the point of zero charge at the surface. Electrokinetic phenomena generally measure zeta potential, and a zero zeta potential is interpreted as the point of zero net charge at the shear plane. This is termed the isoelectric point. [28] Thus, the isoelectric point is the value of pH at which the colloidal particle remains stationary in an electrical field. The isoelectric point is expected to be somewhat different from the point of zero charge at the particle surface, but this difference is often ignored in practice for so-called pristine surfaces, i.e., surfaces with no specifically adsorbed positive or negative charges. [15] In this context, specific adsorption is understood as adsorption occurring in a Stern layer or chemisorption. Thus, point of zero charge at the surface is taken as equal to isoelectric point in the absence of specific adsorption on that surface.

According to Jolivet, [19] in the absence of positive or negative charges, the surface is best described by the point of zero charge. If positive and negative charges are both present in equal amounts, then this is the isoelectric point. Thus, the PZC refers to the absence of any type of surface charge, while the IEP refers to a state of neutral net surface charge. The difference between the two, therefore, is the quantity of charged sites at the point of net zero charge. Jolivet uses the intrinsic surface equilibrium constants, pK− and pK+ to define the two conditions in terms of the relative number of charged sites:

For large ΔpK (>4 according to Jolivet), the predominant species is MOH while there are relatively few charged species – so the PZC is relevant. For small values of ΔpK, there are many charged species in approximately equal numbers, so one speaks of the IEP.

See also

Related Research Articles

<span class="mw-page-title-main">Amino acid</span> Organic compounds containing amine and carboxylic groups

Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 appear in the genetic code of life.

<span class="mw-page-title-main">Agarose gel electrophoresis</span> Method for separation and analysis of biomolecules using agarose gel

Agarose gel electrophoresis is a method of gel electrophoresis used in biochemistry, molecular biology, genetics, and clinical chemistry to separate a mixed population of macromolecules such as DNA or proteins in a matrix of agarose, one of the two main components of agar. The proteins may be separated by charge and/or size, and the DNA and RNA fragments by length. Biomolecules are separated by applying an electric field to move the charged molecules through an agarose matrix, and the biomolecules are separated by size in the agarose gel matrix.

<span class="mw-page-title-main">Gel electrophoresis</span> Method for separation and analysis of biomolecules

Gel electrophoresis is a method for separation and analysis of biomacromolecules and their fragments, based on their size and charge. It is used in clinical chemistry to separate proteins by charge or size and in biochemistry and molecular biology to separate a mixed population of DNA and RNA fragments by length, to estimate the size of DNA and RNA fragments or to separate proteins by charge.

<span class="mw-page-title-main">Polyacrylamide gel electrophoresis</span> Analytical technique

Polyacrylamide gel electrophoresis (PAGE) is a technique widely used in biochemistry, forensic chemistry, genetics, molecular biology and biotechnology to separate biological macromolecules, usually proteins or nucleic acids, according to their electrophoretic mobility. Electrophoretic mobility is a function of the length, conformation, and charge of the molecule. Polyacrylamide gel electrophoresis is a powerful tool used to analyze RNA samples. When polyacrylamide gel is denatured after electrophoresis, it provides information on the sample composition of the RNA species.

<span class="mw-page-title-main">Electrophoresis</span> Motion of charged particles in electric field

In chemistry, electrophoresis is the motion of charged dispersed particles or dissolved charged molecules relative to a fluid under the influence of a spatially uniform electric field. As a rule, these are zwitterions. Electrophoresis of positively charged particles or molecules (cations) is sometimes called cataphoresis, while electrophoresis of negatively charged particles or molecules (anions) is sometimes called anaphoresis.

<span class="mw-page-title-main">Two-dimensional gel electrophoresis</span>

Two-dimensional gel electrophoresis, abbreviated as 2-DE or 2-D electrophoresis, is a form of gel electrophoresis commonly used to analyze proteins. Mixtures of proteins are separated by two properties in two dimensions on 2D gels. 2-DE was first independently introduced by O'Farrell and Klose in 1975.

<span class="mw-page-title-main">Gel electrophoresis of proteins</span> Technique for separating proteins

Protein electrophoresis is a method for analysing the proteins in a fluid or an extract. The electrophoresis may be performed with a small volume of sample in a number of alternative ways with or without a supporting medium, namely agarose or polyacrylamide. Variants of gel electrophoresis include SDS-PAGE, free-flow electrophoresis, electrofocusing, isotachophoresis, affinity electrophoresis, immunoelectrophoresis, counterelectrophoresis, and capillary electrophoresis. Each variant has many subtypes with individual advantages and limitations. Gel electrophoresis is often performed in combination with electroblotting or immunoblotting to give additional information about a specific protein.

<span class="mw-page-title-main">Coomassie brilliant blue</span> Chemical compound

Coomassie brilliant blue is the name of two similar triphenylmethane dyes that were developed for use in the textile industry but are now commonly used for staining proteins in analytical biochemistry. Coomassie brilliant blue G-250 differs from Coomassie brilliant blue R-250 by the addition of two methyl groups. The name "Coomassie" is a registered trademark of Imperial Chemical Industries.

<span class="mw-page-title-main">Isoelectric focusing</span> Type of electrophoresis

Isoelectric focusing (IEF), also known as electrofocusing, is a technique for separating different molecules by differences in their isoelectric point (pI). It is a type of zone electrophoresis usually performed on proteins in a gel that takes advantage of the fact that overall charge on the molecule of interest is a function of the pH of its surroundings.

A surface charge is an electric charge present on a two-dimensional surface. These electric charges are constrained on this 2-D surface, and surface charge density, measured in coulombs per square meter (C•m−2), is used to describe the charge distribution on the surface. The electric potential is continuous across a surface charge and the electric field is discontinuous, but not infinite; this is unless the surface charge consists of a dipole layer. In comparison, the potential and electric field both diverge at any point charge or linear charge.

Electrophoresis is the motion of charged dispersed particles or dissolved charged molecules relative to a fluid under the influence of a spatially uniform electric field.

<span class="mw-page-title-main">Point of zero charge</span> The pH value at which the surface of a colloidal solid carries no net electrical charge

The point of zero charge (pzc) is generally described as the pH at which the net electrical charge of the particle surface (i.e. adsorbent's surface) is equal to zero. This concept has been introduced in the studies dealing with colloidal flocculation to explain why pH is affecting the phenomenon.

QPNC-PAGE, or QuantitativePreparativeNativeContinuousPolyacrylamideGel Electrophoresis, is a bioanalytical, one-dimensional, high-resolution and high-precision electrophoresis technique applied in biochemistry and bioinorganic chemistry to separate proteins quantitatively by isoelectric point and by continuous elution from a gel column.

Protein precipitation is widely used in downstream processing of biological products in order to concentrate proteins and purify them from various contaminants. For example, in the biotechnology industry protein precipitation is used to eliminate contaminants commonly contained in blood. The underlying mechanism of precipitation is to alter the solvation potential of the solvent, more specifically, by lowering the solubility of the solute by addition of a reagent.

<span class="mw-page-title-main">Protein mass spectrometry</span> Application of mass spectrometry

Protein mass spectrometry refers to the application of mass spectrometry to the study of proteins. Mass spectrometry is an important method for the accurate mass determination and characterization of proteins, and a variety of methods and instrumentations have been developed for its many uses. Its applications include the identification of proteins and their post-translational modifications, the elucidation of protein complexes, their subunits and functional interactions, as well as the global measurement of proteins in proteomics. It can also be used to localize proteins to the various organelles, and determine the interactions between different proteins as well as with membrane lipids.

The isoionic point is the pH value at which a zwitterion molecule has an equal number of positive and negative charges and no adherent ionic species. It was first defined by S.P.L. Sørensen, Kaj Ulrik Linderstrøm-Lang and Ellen Lund in 1926 and is mainly a term used in protein sciences.

<span class="mw-page-title-main">Affinity electrophoresis</span>

Affinity electrophoresis is a general name for many analytical methods used in biochemistry and biotechnology. Both qualitative and quantitative information may be obtained through affinity electrophoresis. Cross electrophoresis, the first affinity electrophoresis method, was created by Nakamura et al. Enzyme-substrate complexes have been detected using cross electrophoresis. The methods include the so-called electrophoretic mobility shift assay, charge shift electrophoresis and affinity capillary electrophoresis. The methods are based on changes in the electrophoretic pattern of molecules through biospecific interaction or complex formation. The interaction or binding of a molecule, charged or uncharged, will normally change the electrophoretic properties of a molecule. Membrane proteins may be identified by a shift in mobility induced by a charged detergent. Nucleic acids or nucleic acid fragments may be characterized by their affinity to other molecules. The methods have been used for estimation of binding constants, as for instance in lectin affinity electrophoresis or characterization of molecules with specific features like glycan content or ligand binding. For enzymes and other ligand-binding proteins, one-dimensional electrophoresis similar to counter electrophoresis or to "rocket immunoelectrophoresis", affinity electrophoresis may be used as an alternative quantification of the protein. Some of the methods are similar to affinity chromatography by use of immobilized ligands.

Adsorption is the accumulation and adhesion of molecules, atoms, ions, or larger particles to a surface, but without surface penetration occurring. The adsorption of larger biomolecules such as proteins is of high physiological relevance, and as such they adsorb with different mechanisms than their molecular or atomic analogs. Some of the major driving forces behind protein adsorption include: surface energy, intermolecular forces, hydrophobicity, and ionic or electrostatic interaction. By knowing how these factors affect protein adsorption, they can then be manipulated by machining, alloying, and other engineering techniques to select for the most optimal performance in biomedical or physiological applications.

Protein adsorption refers to the adhesion of proteins to solid surfaces. This phenomenon is an important issue in the food processing industry, particularly in milk processing and wine and beer making. Excessive adsorption, or protein fouling, can lead to health and sanitation issues, as the adsorbed protein is very difficult to clean and can harbor bacteria, as is the case in biofilms. Product quality can be adversely affected if the adsorbed material interferes with processing steps, like pasteurization. However, in some cases protein adsorption is used to improve food quality, as is the case in fining of wines.

<span class="mw-page-title-main">SDS-PAGE</span> Biochemical technique

SDS-PAGE is a discontinuous electrophoretic system developed by Ulrich K. Laemmli which is commonly used as a method to separate proteins with molecular masses between 5 and 250 kDa. The combined use of sodium dodecyl sulfate and polyacrylamide gel eliminates the influence of structure and charge, and proteins are separated by differences in their size. At least up to 2012, the publication describing it was the most frequently cited paper by a single author, and the second most cited overall.

References

  1. ↑ Acceptable variants on pH(I) would include pHI, pHIEP, etc; the main point is that one cannot take the 'power' of I, rather one measures the pH subject to a nominated condition.
  2. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " isoelectric point in electrophoresis ". doi : 10.1351/goldbook.I03275
  3. ↑ Dayton, W. R. (1983). "Protein Separation Techniques" (PDF). Reciprocal Meat Conference Proceedings. 36: 98–102.
  4. ↑ For derivation of this expression see acid dissociation constant
  5. ↑ Jensen, Jan H.; Gordon, Mark S. (August 1995). "On the Number of Water Molecules Necessary To Stabilize the Glycine Zwitterion". Journal of the American Chemical Society. 117 (31): 8159–8170. doi:10.1021/ja00136a013. ISSN   0002-7863.
  6. ↑ Bjellqvist, B.; Hughes, G. J.; Pasquali, C.; Paquet, N.; Ravier, F.; Sanchez, J. C.; Frutiger, S.; Hochstrasser, D. (1993-10-01). "The focusing positions of polypeptides in immobilized pH gradients can be predicted from their amino acid sequences". Electrophoresis. 14 (10): 1023–1031. doi:10.1002/elps.11501401163. ISSN   0173-0835. PMID   8125050. S2CID   38041111.
  7. ↑ Gauci, Sharon; van Breukelen, Bas; Lemeer, Simone M.; Krijgsveld, Jeroen; Heck, Albert J. R. (2008-12-01). "A versatile peptide pI calculator for phosphorylated and N-terminal acetylated peptides experimentally tested using peptide isoelectric focusing". Proteomics. 8 (23–24): 4898–4906. doi:10.1002/pmic.200800295. ISSN   1615-9861. PMID   19003858. S2CID   21527631.
  8. ↑ Gasteiger, Elisabeth; Gattiker, Alexandre; Hoogland, Christine; Ivanyi, Ivan; Appel, Ron D.; Bairoch, Amos (2003-07-01). "ExPASy: the proteomics server for in-depth protein knowledge and analysis". Nucleic Acids Research. 31 (13): 3784–3788. doi:10.1093/nar/gkg563. ISSN   0305-1048. PMC   168970 . PMID   12824418.
  9. ↑ Cargile, Benjamin J.; Sevinsky, Joel R.; Essader, Amal S.; Eu, Jerry P.; Stephenson, James L. (2008-07-01). "Calculation of the isoelectric point of tryptic peptides in the pH 3.5–4.5 range based on adjacent amino acid effects". Electrophoresis. 29 (13): 2768–2778. doi: 10.1002/elps.200700701 . ISSN   0173-0835. PMID   18615785.
  10. ↑ Perez-Riverol, Yasset; Audain, Enrique; Millan, Aleli; Ramos, Yassel; Sanchez, Aniel; Vizcaíno, Juan Antonio; Wang, Rui; Müller, Markus; Machado, Yoan J. (2012-04-03). "Isoelectric point optimization using peptide descriptors and support vector machines". Journal of Proteomics. 75 (7): 2269–2274. doi:10.1016/j.jprot.2012.01.029. ISSN   1876-7737. PMID   22326964.
  11. ↑ Kozlowski, LP. (2016). "IPC - Isoelectric Point Calculator". Biol Direct. 11 (1): 55. doi: 10.1186/s13062-016-0159-9 . PMC   5075173 . PMID   27769290.
  12. ↑ Hoogland, C.; Mostaguir, K.; Sanchez, JC.; Hochstrasser, DF.; Appel, RD. (2004). "SWISS-2DPAGE, ten years later". Proteomics. 4 (8): 2352–6. doi:10.1002/pmic.200300830. PMID   15274128. S2CID   31933242.
  13. ↑ Bunkute, E.; Cummins, C.; Crofts, FJ.; Bunce, G.; Nabney, IT.; Flower, DR. (2015). "PIP-DB: the Protein Isoelectric Point database". Bioinformatics. 31 (2): 295–6. doi: 10.1093/bioinformatics/btu637 . PMID   25252779.
  14. ↑ Kozlowski, LP. (2016). "Proteome-pI: proteome isoelectric point database". Nucleic Acids Res. 45 (D1): D1112–D1116. doi:10.1093/nar/gkw978. PMC   5210655 . PMID   27789699.
  15. 1 2 Hanaor, D.A.H.; Michelazzi, M.; Leonelli, C.; Sorrell, C.C. (2012). "The effects of carboxylic acids on the aqueous dispersion and electrophoretic deposition of ZrO2". Journal of the European Ceramic Society. 32 (1): 235–244. arXiv: 1303.2754 . doi:10.1016/j.jeurceramsoc.2011.08.015. S2CID   98812224.
  16. ↑ Haruta, M (2004). "Nanoparticulate Gold Catalysts for Low-Temperature CO Oxidation". Journal of New Materials for Electrochemical Systems. 7: 163–172.
  17. ↑ Brunelle JP (1978). 'Preparation of Catalysts by Metallic Complex Adsorption on Mineral Oxides'. Pure and Applied Chemistry vol. 50, pp. 1211–1229.
  18. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Marek Kosmulski, "Chemical Properties of Material Surfaces", Marcel Dekker, 2001.
  19. 1 2 3 4 Jolivet J.P., Metal Oxide Chemistry and Synthesis. From Solution to Solid State, John Wiley & Sons Ltd. 2000, ISBN   0-471-97056-5 (English translation of the original French text, De la Solution à l'Oxyde, InterEditions et CNRS Editions, Paris, 1994).
  20. ↑ U.S. Patent 5,165,996
  21. ↑ Anodic Aqueous Electrophoretic Deposition of Titanium Dioxide Using Carboxylic Acids as Dispersing Agents Journal of the European Ceramic Society, 31(6), 1041-1047, 2011
  22. 1 2 3 4 5 6 Lewis, JA (2000). "Colloidal Processing of Ceramics". Journal of the American Ceramic Society. 83 (10): 2341–2359. CiteSeerX   10.1.1.514.1543 . doi:10.1111/j.1151-2916.2000.tb01560.x. S2CID   9513223.
  23. ↑ Daido, T; Akaike, T (1993). "Electrochemistry of cytochrome c: influence of coulombic attraction with indium tin oxide electrode". Journal of Electroanalytical Chemistry. 344 (1–2): 91–106. doi:10.1016/0022-0728(93)80048-m.
  24. ↑ Kosmulski, M; Saneluta, C (2004). "Point of zero charge/isoelectric point of exotic oxides: Tl2O3". Journal of Colloid and Interface Science. 280 (2): 544–545. Bibcode:2004JCIS..280..544K. doi:10.1016/j.jcis.2004.08.079. PMID   15533430.
  25. ↑ Jara, A.A.; Goldberg, S.; Mora, M.L. (2005). "Studies of the surface charge of amorphous aluminosilicates using surface complexation models". Journal of Colloid and Interface Science. 292 (1): 160–170. Bibcode:2005JCIS..292..160J. doi:10.1016/j.jcis.2005.05.083. hdl: 10533/176403 . PMID   16051258.
  26. ↑ Vamvakaki, Maria; Billingham, Norman C.; Armes, Steven P.; Watts, John F.; Greaves, Stephen J. (2001). "Controlled structure copolymers for the dispersion of high-performance ceramics in aqueous media". Journal of Materials Chemistry. 11 (10): 2437–2444. doi:10.1039/b101728o. ISSN   0959-9428.
  27. ↑ Drisko, Glenna L; Luca, Vittorio; Sizgek, Erden; Scales, Nicolas F.; Caruso, Rachel A. (2009). "Template Synthesis and Adsorption Properties of Hierarchically Porous Zirconium Titanium Oxides". Langmuir. 25 (9): 5286–5293. doi:10.1021/la804030h. ISSN   0743-7463. PMID   19397363.
  28. ↑ A.W. Adamson, A.P. Gast, "Physical Chemistry of Surfaces", John Wiley and Sons, 1997.

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.