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| The '''isoelectric point''' ('''pI'''), sometimes abbreviated to '''IEP''', is the [[pH]] at which a particular [[molecule]] or surface carries no net [[electric charge|electrical charge]].
| | == 秦ゆうぶら下げ体は述べています == |
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| [[Amphoteric]] molecules called [[zwitterion]]s contain both positive and negative charges depending on the [[functional groups]] present in the molecule. 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#In Physics and biochemistry|protons]] (H<sup>+</sup>). The pI is the pH value at which the molecule carries no electrical charge or the negative and positive charges are equal. | | この土地は非常に密接に守られている。しかし蘭シュウは、後でいくつかの知人に語った。私の息子が生まれた。神とそれを考えて、小さな贈り物にの多くを与えた王のすべて。 '<br><br>'贈り物？'秦のSi目は秦ゆうネックを保持している、秦ゆうを自沈サルのように、ライトアップ。秦ゆうぶら下げ体は述べています。 「お父さん、何贈り物？ '<br><br>'あなたは最初にダウンして、私はあなたを与える。'秦ゆうは言った [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_10.php クリスチャンルブタン 銀座]。<br><br>秦Siは秦ゆう本体から飛び降り、突然、非常に迅速に応答した。アニーリング工程は、その後秦ゆうを見た [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_6.php クリスチャンルブタン 中古]。すぐに秦ゆうHuixiu [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_4.php クリスチャンルブタン セール]。私は秦の前で見たが、すぐに多くの奇妙なガジェットがあったと思います。<br>与えるために贈り物を考えて<br>秦。小説楽しい場所のほとんどは [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_10.php クリスチャンルブタン 店舗]。主にあまりにも貴重ではないし、最大3つのストリームが不分明Lingbaoのみ [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_11.php クリスチャンルブタン 偽物]。しかし、この記事では、子どもたちがであるためには実際には非常に良いです。<br>ヨーヨーの目は色の驚きでいっぱい丸みを帯びた、鳥と<br>「すごい。 '秦のSiの目が突然広い。<br><br>ごちそうで、非常に活発な。<br><br>秦ゆう江沢民李は「かわいい面と彼の息子を見て |
| | 相关的主题文章： |
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| Surfaces naturally charge to form a [[double layer (interfacial)|double layer]]. In the common case when the surface charge-determining ions are H<sup>+</sup>/OH<sup>-</sup>, the net surface charge is affected by the pH of the liquid in which the solid is submerged.
| | == 「黄金の斧の手を握りしめHuangfu水は、手を振っ保た == |
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| 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 [[protein]]s 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 according to their isoelectric point (overall charge) on a [[polyacrylamide gel]] using a technique called [[isoelectric focusing]], which uses a pH gradient to separate proteins. Isoelectric focusing is also the first step in [[Two-dimensional gel electrophoresis|2-D gel polyacrylamide gel electrophoresis]].
| | 「マスター、マスターはあなたが呼んでいるものを知らない？」Huangfu水があっても言った、「多分私はそれについて知っているよ。 '<br><br>「マスターが行ったので、私は彼の方法の名前は、私は本当に申し訳ないと言うことはできません。 '秦Yuは申し訳なさそうだ。<br><br>ファクト車侯家は、部外者の発見をさせてください、また秦ゆう、秦ゆうこの相続人へのメッセージを持っていた [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_11.php クリスチャンルブタン ブーツ]。そうでなければ。カーペンター神だけでは「後継者」アイデンティティは多くの人がスパイになります。<br>Huangfuはうなずい<br>水が、彼はまた、神が任意のトップグレードは害を生じプレーするではありませんので、に大きな世界を見られている [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_11.php クリスチャンルブタン ブーツ]。<br><br>「9虫。あなたの三愚かな牛、妹が行っているだけでなく、全く見知らぬ人でもありません、私たちはバーにこの戦争にある [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_12.php 靴 クリスチャンルブタン]。「黄金の斧の手を握りしめHuangfu水は、手を振っ保た。<br>トリオとして、相も非常に厚い、非常に複雑な、非常に山賊を<br> [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_13.php クリスチャンルブタン サンダル]。<br><br>第二子は非常に複雑うなずく大声でハム： [http://www.lamartcorp.com/modules/mod_menu/rakuten_cl_13.php クリスチャンルブタン 日本] 'や、今日は3人の兄弟とブラックドラゴンは、もともと単にムードを破壊するHuangfuはあなたの妹を水で、それについて戦いたかった、そして今、あなたの妹がなくなって、私たち |
| | | 相关的主题文章： |
| == Calculating pI values ==
| | <ul> |
| For an [[amino acid]] with only one [[amine]] and one [[carboxyl]] group, the pI can be calculated from the [[mean]] of the [[pKa]]s of this molecule.<ref>For derivation of this expression see [[acid dissociation constant#Isoelectric point|acid dissociation constant]]</ref>
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| | | <li>[http://www.childgo.cn/forum.php?mod=viewthread&tid=195338&fromuid=62769 http://www.childgo.cn/forum.php?mod=viewthread&tid=195338&fromuid=62769]</li> |
| : <math> pI = {{pKa_1} + {pKa_2} \over 2} </math>
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| | | <li>[http://ktvwz.net/home.php?mod=space&uid=8117 http://ktvwz.net/home.php?mod=space&uid=8117]</li> |
| The [[pH]] of an electrophoretic gel is determined by the [[Buffer solution|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.
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| | | <li>[http://bbs.pyshell.com/home.php?mod=space&uid=7180 http://bbs.pyshell.com/home.php?mod=space&uid=7180]</li> |
| === Examples ===
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| {|
| | </ul> |
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| |[[File:Glycine pI.png|250px]]
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| |[[File:AMP pI.png|250px]]
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| |-
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| |align=center|glycine pK = 2.72, 9.60
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| |align=center|adenosine monophosphate pK = 2.15, 9.16, 10.67
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| |}
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| In these two examples the isoelectric point is shown by the green vertical line. In [[glycine]] the pK values are separated by nearly 7 units so the concentration of the neutral species, glycine (GlyH), is effectively 100% of the analytical glycine concentration. Glycine may exist as a [[zwitterion]] at the isoelectric point, but the equilibrium constant for the isomerization reaction in solution
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| :H<sub>2</sub>NCH<sub>2</sub>CO<sub>2</sub>H {{eqm}} H<sub>3</sub>N<sup>+</sup>CH<sub>2</sub>CO<sub>2</sub><sup>-</sup>
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| is not known.
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| 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)H<sub>3</sub><sup>2+</sup> is negligible at the isoelectric point in this case.
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| If PI is greater than pH, the molecule will positively charge, and reverse is true.
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| == Ceramic materials ==
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| 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<ref name="ref2pineapple">
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| {{cite journal
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| | last1=Hanaor
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| | first1=D.A.H.
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| | last2=Michelazzi
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| | first2=M.
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| | last3=Leonelli
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| | first3=C.
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| | last4=Sorrell
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| | first4=C.C.
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| | title= The effects of carboxylic acids on the aqueous dispersion and electrophoretic deposition of ZrO<sub>2</sub>
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| | journal= Journal of the European Ceramic Society
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| | year=2012
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| | volume=32
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| | issue=1
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| | pages=235–244
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| | url=http://www.sciencedirect.com/science/article/pii/S0955221911004171
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| | doi=10.1016/j.jeurceramsoc.2011.08.015}}</ref> 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.). At pH values above the IEP, the predominate surface species is M-O<sup>-</sup>, while at pH values below the IEP, M-OH<sub>2</sub><sup>+</sup> species predominate. Some approximate values of common ceramics are listed below (Haruta<ref>Haruta M (2004). 'Nanoparticulate Gold Catalysts for Low-Temperature CO Oxidation', ''Journal of New Materials for Electrochemical Systems'', vol. 7, pp 163–172.</ref> and Brunelle,<ref>[http://www.iupac.org/publications/pac/1978/pdf/5009x1211.pdf Brunelle JP (1978). 'Preparation of Catalysts by Metallic Complex Adsorption on Mineral Oxides'. ''Pure and Applied Chemistry'' vol. 50, pp. 1211-1229.]</ref> except where noted). The exact value can vary widely, depending on material factors such as purity and phase as well as physical parameters such as temperature. In addition, precise measurement of isoelectric points is difficult and requires careful techniques, even with modern methods. Thus, many sources often cite differing values for isoelectric points of these materials.
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| === Examples of isoelectric points ===
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| The following list gives the pH<sub>25°C</sub> of isoelectric point at 25 °C for selected materials in water:
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| ''Note: The list is ordered by increasing pH values.''
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| *[[tungsten(VI) oxide]] WO<sub>3</sub>: 0.2-0.5<ref name="Kosmulski"/>
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| *[[antimony(V) oxide]] Sb<sub>2</sub>O<sub>5</sub>: <0.4 to 1.9<ref name="Kosmulski"/>
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| *[[vanadium(V) oxide]] (vanadia) V<sub>2</sub>O<sub>5</sub>: 1-2<ref name="Jolivet"/> (3<ref name="Kosmulski"/>)
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| *[[silicon dioxide]] (silica) SiO<sub>2</sub>: 1.7-3.5<ref name="Kosmulski"/>
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| *[[silicon carbide]] (alpha) SiC: 2-3.5<ref>U.S. Patent 5,165,996</ref>
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| *[[tantalum(V) oxide]], Ta<sub>2</sub>O<sub>5</sub>: 2.7-3.0<ref name="Kosmulski"/>
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| *[[tin(IV) oxide]] SnO<sub>2</sub>: 4-5.5 (7.3<ref name="Lewis">Lewis, JA (2000). 'Colloidal Processing of Ceramics', ''Journal of the American Ceramic Society'' vol. 83, no. 10, pp.2341–2359.</ref>)
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| *[[zirconium(IV) oxide]] (zirconia) ZrO<sub>2</sub>: 4-11<ref name="Kosmulski"/>
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| *[[manganese(IV) oxide]] MnO<sub>2</sub>: 4-5
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| *[[indium tin oxide]] ITO: 6<ref>Daido T and Akaike T (1993). 'Electrochemistry of cytochrome c: influence of coulombic attraction with indium tin oxide electrode', ''Journal of Electroanalytical Chemistry'' vol. 344, no. 1-2, pp. 91–106.</ref>
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| *delta-MnO<sub>2</sub> 1.5, beta-MnO<sub>2</sub> 7.3<ref name="Jolivet"/>
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| *[[titanium(IV) oxide]] (titania) ([[rutile]] or [[anatase]]) TiO<sub>2</sub>: 3.9-8.2<ref name="Kosmulski"/>
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| *[[silicon nitride]] Si<sub>3</sub>N<sub>4</sub>: 6-7
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| *[[magnetite|iron (II, III) oxide]] (magnetite) Fe<sub>3</sub>O<sub>4</sub>: 6.5-6.8<ref name="Kosmulski"/>
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| *[[maghemite|gamma iron (III) oxide]] (maghemite) Fe<sub>2</sub>O<sub>3</sub>: 3.3-6.7<ref name="Kosmulski"/>
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| *[[cerium(IV) oxide]] (ceria) CeO<sub>2</sub>: 6.7-8.6<ref name="Kosmulski"/>
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| *[[chromium(III) oxide]] (chromia) Cr<sub>2</sub>O<sub>3</sub>: 7<ref name="Jolivet"/> (6.2-8.1<ref name="Kosmulski"/>)
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| *gamma [[aluminium oxide]] (gamma alumina) Al<sub>2</sub>O<sub>3</sub>: 7-8
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| *[[thallium(I) oxide]] Tl<sub>2</sub>O: 8<ref>Kosmulski M and Saneluta C (2004). 'Point of zero charge/isoelectric point of exotic oxides: Tl2O3', ''Journal of Colloid and Interface Science'' vol. 280, no. 2, pp. 544–545.</ref>
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| *[[hematite|alpha iron (III) oxide]] (hematite) Fe<sub>2</sub>O<sub>3</sub>: 8.4-8.5<ref name="Kosmulski"/>
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| *alpha [[aluminium oxide]] (alpha alumina, corundum) Al<sub>2</sub>O<sub>3</sub>: 8-9
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| *[[silicon nitride]] Si<sub>3</sub>N<sub>4</sub>: 9<ref name="Lewis"/>
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| *[[yttrium(III) oxide]] (yttria) Y<sub>2</sub>O<sub>3</sub>: 7.15-8.95<ref name="Kosmulski"/>
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| *[[copper(II) oxide]] CuO: 9.5<ref name="Lewis"/>
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| *[[zinc oxide]] ZnO: 8.7-10.3<ref name="Kosmulski"/>
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| *[[lanthanum(III) oxide]] La<sub>2</sub>O<sub>3</sub>: 10
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| *[[nickel(II) oxide]] NiO: 10-11<ref name="Lewis"/> (9.9-11.3<ref name="Kosmulski"/>)
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| *[[lead(II) oxide]] PbO: 10.7-11.6<ref name="Kosmulski">Marek Kosmulski, "Chemical Properties of Material Surfaces", Marcel Dekker, 2001.</ref>
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| *[[magnesium oxide]] (magnesia) MgO: 12-13 (9.8-12.7<ref name="Kosmulski"/>)
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| Mixed oxides may exhibit isoelectric point values that are intermediate to those of the corresponding pure oxides. For example, Jara ''et al.''<ref>Jara, A.A., S. Goldberg and M.L. Mora (2005). 'Studies of the surface charge of amorphous aluminosilicates using surface complexation models', ''Journal of Colloid and Interface Science'', vol. 292, no. 1, pp. 160–170.</ref> measured an IEP of 4.5 for a synthetically prepared amorphous [[aluminosilicate]] (Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>). The researchers noted that the electrokinetic behavior of the surface was dominated by surface Si-OH species, thus explaining the relatively low IEP value. Significantly higher IEP values (pH 6 to 8) have been reported for 3Al<sub>2</sub>O<sub>3</sub>-2SiO<sub>2</sub> by others (see Lewis<ref name="Lewis"/>). Lewis<ref name="Lewis"/> also lists the IEP of [[barium titanate]], BaTiO<sub>3</sub> as being between pH 5 and 6, while Vamvakaki et al.<ref>[http://www.rsc.org/ej/JM/2001/b101728o.pdf Vamvakaki, M., N.C. Billingham, S.P. Armes, J.F. Watts and S.J. Greaves (2001). 'Controlled structure copolymers for the dispersion of high-performance ceramics in aqueous media', ''Journal of Materials Chemistry'', vol. 11, pp. 2437-2444.]</ref> reported a value of 3, although these authors note that a wide range of values have been reported, a result of either residual [[barium carbonate]] on the surface or TiO<sub>2</sub>-rich surfaces.
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| The farther the pH of an Amino Acid solution is from its pl the greater the electric charge on that population of molecules.
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| == Isoelectric point 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.
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| In systems in which H<sup>+</sup>/OH<sup>-</sup> 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 [[Electrical double layer|shear plane]]. This is termed the isoelectric point.<ref>A.W. Adamson, A.P. Gast, "Physical Chemistry of Surfaces", John Wiley and Sons, 1997.</ref> 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 than 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 [[adsorption|specifically adsorbed]] positive or negative charges.<ref name="ref2pineapple" /> In this context, specific adsorption is understood as adsorption occurring in a [[Double layer (interfacial)|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.
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| According to Jolivet,<ref name="Jolivet">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).</ref> 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<sup>-</sup> and pK<sup>+</sup> to define the two conditions in terms of the relative number of charged sites:
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| :<math> pK^- - pK^+ = \Delta pK = \log {\frac{\left[MOH\right]^2}{\left[MOH{_2^+}\right]\left[MO^-\right]}} </math>
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| For large ΔpK (>4 according to Jolivet), the predominate 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.
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| == See also ==
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| * [[Isoionic point]]
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| == References ==
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| {{reflist}}
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| == Further reading==
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| * Nelson DL, Cox MM (2004). ''Lehninger Principles of Biochemistry''. W. H. Freeman; 4th edition (Hardcover). ISBN 0-7167-4339-
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| * Kosmulski M. (2009). ''Surface Charging and Points of Zero Charge''. CRC Press; 1st edition (Hardcover). ISBN 978-1-4200-5188-9
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| == External links ==
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| * [http://www.embl-heidelberg.de/cgi/pi-wrapper.pl EMBL WWW Gateway to Isoelectric Point Service] — calculates the pI for an input amino acid sequence.
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| * [http://isoelectric.ovh.org Calculation of protein isoelectric point] — free online and offline program to calculation pI and more theoretical information about this subject.
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| * Isoelectric point determination and Charge versus pH plot of amphoteric molecules (e.g., amino acids) by a [http://www2.iq.usp.br/docente/gutz/Curtipot_.html free suite of spreadsheets for computing acid-base equilibria.]
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| {{DEFAULTSORT:Isoelectric Point}}
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| [[Category:Ions]]
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| [[Category:Molecular biology]]
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