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Isoionic Point
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. It is different from the isoelectric point (p''I'') in that p''I'' is the pH value at which the net charge of the molecule, ''including'' bound ions is zero. Whereas the isoionic point is at net charge zero in a deionized solution. Thus, the isoelectric and isoionic points are equal when the concentration of charged species is zero. For a diprotic acid, the hydrogen ion concentration can be found at the isoionic point using the following equation ^+\sqrt * ^+hydrogen ion concentration * K_1=first acid dissociation constant * K_2=second acid dissociation constant * K_w=dissociation constant for water * C=concentration of the acid Note that if K_1 K_2 C \gg K_1 K_w then K_1 K_2 C + K_ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zwitterion
In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively- and negatively-charged functional groups. : With amino acids, for example, in solution a chemical equilibrium will be established between the "parent" molecule and the zwitterion. Betaines are zwitterions that cannot isomerize to an all-neutral form, such as when the positive charge is located on a quaternary ammonium group. Similarly, a molecule containing a phosphonium group and a carboxylate group cannot isomerize. Amino acids The equilibrium is established in two stages. In the first stage, a proton is transferred from the carboxyl group to a water molecule: :H2N(R)CO2H + H2O H2N(R)CO2- + H3O+ In the second stage, a proton is transferred from the hydronium ion to the amine group: :H2N(R)CO2- + H3O+ H3N+ (R)CO2- + H2O Overall, the reaction is an isomerization reaction :H2N(R)CO2H H3N+ (R)CO2- The ratio of the concentrations of the two spec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and ''molecule'' is often used when referring to polyatomic ions. A molecule may be homonuclear, that is, it consists of atoms of one chemical element, e.g. two atoms in the oxygen molecule (O2); or it may be heteronuclear, a chemical compound composed of more than one element, e.g. water (two hydrogen atoms and one oxygen atom; H2O). In the kinetic theory of gases, the term ''molecule'' is often used for any gaseous particle regardless of its composition. This relaxes the requirement that a molecule contains two or more atoms, since the noble gases are individual atoms. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are typically not consid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kaj Ulrik Linderstrøm-Lang
Kaj Ulrik Linderstrøm-Lang (29 November 1896 – 25 May 1959) was a Danish protein scientist, who was the director of the Carlsberg Laboratory from 1939 until his death. His most notable scientific contributions were the development of sundry physical techniques to study protein structure and function (especially hydrogen–deuterium exchange), and his definitions of protein primary, secondary, tertiary and quaternary structure. Linderstrøm-Lang devoted himself unstintingly to protein science and trained a whole generation of eminent protein scientists, Linderstrøm-Lang maintained a fun atmosphere in his laboratory and a happy spirit that expressed itself in wonderful Christmas parties and frequent trips to the Tivoli amusement park in Copenhagen. Linderstrøm-Lang was also a writer, musician and story-teller, and was active in the resistance movement against the Nazi occupation of Denmark. Research and career Early work Linderstrøm-Lang began as a physicist. Only a year a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ellen Lund
Ellen is a female given name, a diminutive of Elizabeth, Eleanor, Elena and Helen. Ellen was the 609th most popular name in the U.S. and the 17th in Sweden in 2004. People named Ellen include: *Ellen Adarna (born 1988), Filipino actress *Ellen Alaküla (1927–2011), Estonian actress *Ellen Palmer Allerton (1835–1893), American poet * Ellen Allien (born 1969), German electronic musician and music producer *Ellen Anckarsvärd (1833-1898), Swedish feminist *Ellen Andersen (1898–1989), Danish museum curator * Ellen Anderson (born 1959), American politician *Ellen Auerbach (1906–2004), German-born American photographer *Ellen Baake (born 1961), German mathematical biologist *Ellen S. Baker (born 1953), American physician and astronaut *Ellen Barkin (born 1954), American actress * Ellen Bass (born 1947), American poet and author *Ellen A. Dayton Blair (1837–1926), social reformer and art teacher *Ellen Bontje (born 1958), Dutch equestrian *Ellen Burka (1921–2016), Dutch an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, providing structure to cells and organisms, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in protein folding into a specific 3D structure that determines its activity. A linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide. Short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides. The individual amino acid residues are bonded together by peptide bonds and adjacent amino acid residues. The sequence of amino acid residue ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isoelectric Point
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). However, pI is also used. 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+). 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 function ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
