等電点

関: isoelectric、pI

WordNet

mark with diacritics; "point the letter"
a very small circular shape; "a row of points"; "draw lines between the dots" (同)dot
an instant of time; "at that point I had to leave" (同)point in time
repair the joints of bricks; "point a chimney" (同)repoint
a V shape; "the cannibals teeth were filed to sharp points" (同)tip, peak
a linear unit used to measure the size of type; approximately 1/72 inch
a style in speech or writing that arrests attention and has a penetrating or convincing quality or effect
one percent of the total principal of a loan; it is paid at the time the loan is made and is independent of the interest on the loan
the unit of counting in scoring a game or contest; "he scored 20 points in the first half"; "a touchdown counts 6 points"
the gun muzzles direction; "he held me up at the point of a gun" (同)gunpoint
the property of a shape that tapers to a sharp tip (同)pointedness
a wall socket (同)power_point
an outstanding characteristic; "his acting was one of the high points of the movie" (同)spot
a distinguishing or individuating characteristic; "he knows my bad points as well as my good points"
sharp end; "he stuck the point of the knife into a tree"; "he broke the point of his pencil"
a V-shaped mark at one end of an arrow pointer; "the point of the arrow was due north" (同)head
a brief version of the essential meaning of something; "get to the point"; "he missed the point of the joke"; "life has lost its point"
a geometric element that has position but no extension; "a point is defined by its coordinates"
a promontory extending out into a large body of water; "they sailed south around the point"
the object of an activity; "what is the point of discussing it?"
the precise location of something; a spatially limited location; "she walked to a point where she could survey the whole street"
be positionable in a specified manner; "The gun points with ease"
indicate the presence of (game) by standing and pointing with the muzzle; "the dog pointed the dead duck"
mark (a psalm text) to indicate the points at which the music changes
mark (Hebrew words) with diacritics
having a point
direct and obvious in meaning or reference; often unpleasant; "a pointed critique"; "a pointed allusion to what was going on"; "another pointed look in their direction"
Hawaiian dish of taro root pounded to a paste and often allowed to ferment

PrepTutorEJDIC

〈C〉(針・鉛筆・剣などの)『とがった先』,(…の)先端《+『of』+『名』》 / 〈C〉岬(みさき) / 〈C〉(小数点・句読点などの)点 / 〈C〉(図形上の)点 / 〈C〉(ある特定の)『地点』(spot),場所(place) / 〈C〉(計器の目盛りなどの)『点』,『度』 / 〈C〉時点,瞬間 / 〈C〉《単数形で》(物語・議論などの)『要点』,核心《+『of』(『in』)+『名』》 / 〈U〉(…の)『目的』,『意義』,ねらっている点《+『of』(『in』)+『名』(do『ing』)》 / 〈C〉(全体の中の)個々の項目,細目(item),細部(detail) / 〈C〉特徴(characteristic),特質(trait) / 〈C〉(競技・学校の成績などの)得点 / 〈C〉ポイント(活字の大きさの単位;約1/72インチの大きさ) / (…に)〈銃・指など〉‘を'『向ける』《+『名』+『at』(『to, toward』)+『名』》 / …‘に'『指し示す』《point+名+to+名…に…をさし示す》 / …‘の'先をとがらせる,‘に'先を付ける / …‘に'点を打つ;…‘に'小数点を付ける;…‘に'句読点を付ける / 〈猟犬が〉〈獲物〉‘を'指し示す / (…を)(指などで)『示す』,指し示す《+『at』(『to, toward』)+『名』(do『ing』)》 / 〈猟犬が〉獲物の位置を示す
『先のとがった』,鋭い / (皮肉など)痛烈な,しんらつな / (ある目標に)向けられた,(はっきりと特定の人に)向けられた,当てこすりの

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/01/18 13:00:04」(JST)

wiki en

[Wiki en表示]

The isoelectric point (pI, pH(I), IEP), is the pH at which a particular molecule carries no net electrical charge. The standard nomenclature to represent the isoelectric point is pH(I),^[1] although pI is also commonly seen,^[2] and is used in this article for brevity. 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⁺).

Surfaces naturally charge to form a double layer. In the common case when the surface charge-determining ions are H⁺/OH⁻, 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 QPNC-PAGE 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.

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.^[3]

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 pK = 2.72, 9.60	adenosine monophosphate pK = 0.9, 3.8, 6.1

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

H₂NCH₂CO₂H H₃N⁺CH₂CO₂⁻

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)H₃²⁺ is negligible at the isoelectric point in this case. If the pI is greater than the pH, the molecule will have a positive charge.

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^[4] 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⁻, while at pH values below the IEP, M-OH₂⁺ species predominate. Some approximate values of common ceramics are listed below (Haruta^[5] and Brunelle,^[6] 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.

Examples of isoelectric points

The following list gives the pH_25 °C of isoelectric point at 25 °C for selected materials in water:

Note: The list is ordered by increasing pH values.

tungsten(VI) oxide WO₃: 0.2-0.5^[7]
antimony(V) oxide Sb₂O₅: <0.4 to 1.9^[7]
vanadium(V) oxide (vanadia) V₂O₅: 1-2^[8] (3^[7])
silicon dioxide (silica) SiO₂: 1.7-3.5^[7]
silicon carbide (alpha) SiC: 2-3.5^[9]
tantalum(V) oxide, Ta₂O₅: 2.7-3.0^[7]
tin(IV) oxide SnO₂: 4-5.5 (7.3^[10])
zirconium(IV) oxide (zirconia) ZrO₂: 4-11^[7]
manganese(IV) oxide MnO₂: 4-5
indium tin oxide ITO: 6^[11]
delta-MnO₂ 1.5, beta-MnO₂ 7.3^[8]
titanium(IV) oxide (titania) (rutile or anatase) TiO₂: 3.9-8.2^[7]
silicon nitride Si₃N₄: 6-7
iron (II, III) oxide (magnetite) Fe₃O₄: 6.5-6.8^[7]
gamma iron (III) oxide (maghemite) Fe₂O₃: 3.3-6.7^[7]
cerium(IV) oxide (ceria) CeO₂: 6.7-8.6^[7]
chromium(III) oxide (chromia) Cr₂O₃: 7^[8] (6.2-8.1^[7])
gamma aluminium oxide (gamma alumina) Al₂O₃: 7-8
thallium(I) oxide Tl₂O: 8^[12]
alpha iron (III) oxide (hematite) Fe₂O₃: 8.4-8.5^[7]
alpha aluminium oxide (alpha alumina, corundum) Al₂O₃: 8-9
silicon nitride Si₃N₄: 9^[10]
yttrium(III) oxide (yttria) Y₂O₃: 7.15-8.95^[7]
copper(II) oxide CuO: 9.5^[10]
zinc oxide ZnO: 8.7-10.3^[7]
lanthanum(III) oxide La₂O₃: 10
nickel(II) oxide NiO: 10-11^[10] (9.9-11.3^[7])
lead(II) oxide PbO: 10.7-11.6^[7]
magnesium oxide (magnesia) MgO: 12-13 (9.8-12.7^[7])

Mixed oxides may exhibit isoelectric point values that are intermediate to those of the corresponding pure oxides. For example, Jara et al.^[13] measured an IEP of 4.5 for a synthetically prepared amorphous aluminosilicate (Al₂O₃-SiO₂). 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 3Al₂O₃-2SiO₂ by others (see Lewis^[10]). Lewis^[10] also lists the IEP of barium titanate, BaTiO₃ as being between pH 5 and 6, while Vamvakaki et al.^[14] 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 TiO₂-rich surfaces.

The farther the pH of an Amino Acid solution is from its pl the greater the electric charge on that population of molecules.

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.

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.^[15] 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 specifically adsorbed positive or negative charges.^[4] 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,^[8] 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.

References

^ Acceptable variants on pH(I) would include pH_I, pH_IEP, etc; the main point is that one cannot take the 'power' of I, rather one measures the pH subject to a nominated condition.
^ IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook. Last update: 2014-02-24; version: 2.3.3. DOI of this term: doi:10.1351/goldbook.I03275.
^ For derivation of this expression see acid dissociation constant
^ ^a ^b 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. doi:10.1016/j.jeurceramsoc.2011.08.015.
^ Haruta M (2004). 'Nanoparticulate Gold Catalysts for Low-Temperature CO Oxidation', Journal of New Materials for Electrochemical Systems, vol. 7, pp 163–172.
^ Brunelle JP (1978). 'Preparation of Catalysts by Metallic Complex Adsorption on Mineral Oxides'. Pure and Applied Chemistry vol. 50, pp. 1211-1229.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Marek Kosmulski, "Chemical Properties of Material Surfaces", Marcel Dekker, 2001.
^ ^a ^b ^c ^d 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).
^ U.S. Patent 5,165,996
^ ^a ^b ^c ^d ^e ^f Lewis, JA (2000). 'Colloidal Processing of Ceramics', Journal of the American Ceramic Society vol. 83, no. 10, pp.2341–2359.
^ 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.
^ 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.
^ 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.
^ 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.
^ A.W. Adamson, A.P. Gast, "Physical Chemistry of Surfaces", John Wiley and Sons, 1997.

External links

Calculation of protein isoelectric point — free online and offline program to calculation pI and more theoretical information about this subject.
prot pi - protein isoelectric point — free online program for calculating pI of proteins, also allowing for multiple subunits and posttranslational modifications. Prot pi also shows a plot of protein charge versus pH.
Isoelectric point determination and Charge versus pH plot of amphoteric molecules (e.g., amino acids) by a free suite of spreadsheets for computing acid-base equilibria.

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 異常ヘモグロビン症の検査室診断 laboratory diagnosis of the hemoglobinopathies
2. 心電図チュートリアル：心電図分析の基本原則 ecg tutorial basic principles of ecg analysis
3. QT間隔のばらつき：測定および解釈 qt dispersion measurement and interpretation
4. 2本鎖（ds）DNA、Sm、およびU1 RNPに対する抗体 antibodies to double stranded ds dna sm and u1 rnp
5. 環境中のアレルゲンサンプリング allergen sampling in the environment

English Journal

Physicochemical properties of whey protein, lactoferrin and Tween 20 stabilised nanoemulsions: Effect of temperature, pH and salt.

Teo A1, Goh KK2, Wen J3, Oey I4, Ko S5, Kwak HS5, Lee SJ6.
Food chemistry.Food Chem.2016 Apr 15;197(Pt A):297-306. doi: 10.1016/j.foodchem.2015.10.086. Epub 2015 Oct 19.
Oil-in-water nanoemulsions were prepared by emulsification and solvent evaporation using whey protein isolate (WPI), lactoferrin and Tween 20 as emulsifiers. Protein-stabilised nanoemulsions showed a decrease in particle size with increasing protein concentration from 0.25% to 1% (w/w) level with Z-
PMID 26616953

The chitosan-gelatin (bio)polyelectrolyte complexes formation in an acidic medium.

Voron'ko NG1, Derkach SR2, Kuchina YA3, Sokolan NI4.
Carbohydrate polymers.Carbohydr Polym.2016 Mar 15;138:265-72. doi: 10.1016/j.carbpol.2015.11.059. Epub 2015 Nov 26.
The interaction of cationic polysaccharide chitosan and gelatin accompanied by the stoichiometric (bio)polyelectrolyte complexes formation has been studied by the methods of capillary viscometry, UV and FTIR spectroscopy and dispersion of light scattering. Complexes were formed in the aqueous phase,
PMID 26794762

Synthesis, characteristics and sonocatalytic activities of calcined γ-Fe2O3 and TiO2 nanotubes/γ-Fe2O3 magnetic catalysts in the degradation of Orange G.

Pang YL1, Lim S2, Ong HC3, Chong WT3.
Ultrasonics sonochemistry.Ultrason Sonochem.2016 Mar;29:317-27. doi: 10.1016/j.ultsonch.2015.10.003. Epub 2015 Oct 9.
In this work, γ-Fe2O3 and TiO2 NTs/γ-Fe2O3 composites with good magnetism and sonocatalytic activity were prepared by a facile polyol method and utilize the principle of isoelectric point method, respectively. The structural and magnetic features of the prepared calcined γ-Fe2O3 and composite cat
PMID 26585012

Japanese Journal

Preparation of Aqueous Dispersion of Titanium Dioxide Nanoparticles using Plasma on Liquid Surface

Ito Michiko,Hayakawa Masahiro,Takashima Seigo,Asami Etsuo,Aoki Takeshi,Oka Masato,Asano Hiroyuki,Kitahara Michiro,Nakata Satoru,Yamaguchi Koichi,Murase Yoshiaki
Jpn J Appl Phys 51(11), 116201-116201-4, 2012-11-25
… Although the pH of the dispersion prepared by Ar plasma treatment was fairly close to the isoelectric point of TiO2, the dispersion maintained a finely dispersed state. …
NAID 150000105237

Engineering of novel tamavidin 2 muteins with lowered isoelectric points and lowered non-specific binding properties

Takakura Yoshimitsu,Oka Naomi,Kajiwara Hitomi 他
Journal of bioscience and bioengineering 114(5), 485-489, 2012-11-00
NAID 40019498505

Related Pictures

★リンクテーブル★

リンク元	「等電点」
関連記事	「point」「pointing」「isoelectric」

「等電点」

　　[★]

英: isoelectric point pI

分子全体の電荷の総和が0となるpHを指す
該当するpHはpIで表す

	塩基性タンパク質	酸性タンパク質
優勢なアミノ酸	塩基性アミノ酸	酸性アミノ酸
想定される側鎖の末端	NH2	COOH
等電点(pI)	<7.4 酸性側	>7.4 アルカリ性側
pH7.4での電荷	-	+
代表的な蛋白質	アルブミン	ヒストン

「point」

　　[★]

vt.
vi.

指さす、示す(at,to)
(ある方向に)向いている(to,toward)
傾向にある(to)

n.

関: dictate、direct、dot、indicate、indication、instruct、instruction、spot

「pointing」

　　[★]

n.

とがり付け、ポインティング，照準，目地仕上，先付け

「isoelectric」

　　[★]

等電点の、等電の

関: isoelectric point、pI

[1] Acceptable variants on pH(I) would include pH_I, pH_IEP, 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"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook. Last update: 2014-02-24; version: 2.3.3. DOI of this term: doi:10.1351/goldbook.I03275.

[3] For derivation of this expression see acid dissociation constant

[ref2pineapple-4] 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. doi:10.1016/j.jeurceramsoc.2011.08.015.

[5] Haruta M (2004). 'Nanoparticulate Gold Catalysts for Low-Temperature CO Oxidation', Journal of New Materials for Electrochemical Systems, vol. 7, pp 163–172.

[6] Brunelle JP (1978). 'Preparation of Catalysts by Metallic Complex Adsorption on Mineral Oxides'. Pure and Applied Chemistry vol. 50, pp. 1211-1229.

[Kosmulski-7] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Marek Kosmulski, "Chemical Properties of Material Surfaces", Marcel Dekker, 2001.

[Jolivet-8] 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).

[9] U.S. Patent 5,165,996

[Lewis-10] ^ ^a ^b ^c ^d ^e ^f Lewis, JA (2000). 'Colloidal Processing of Ceramics', Journal of the American Ceramic Society vol. 83, no. 10, pp.2341–2359.

[11] 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.

[12] 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.

[13] 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.

[14] 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.

[15] A.W. Adamson, A.P. Gast, "Physical Chemistry of Surfaces", John Wiley and Sons, 1997.

匿名

検索

案内

案内

isoelectric point