| hydronium ion | <chemistry> A positively charged ion that is water with an additional hydrogen atom (H3O). (09 Oct 1997) |
|---|---|
| spectrometry, mass, secondary ion | A mass-spectrometric technique that is used for microscopic chemical analysis. A beam of primary ions with an energy of 5-20 kiloelectronvolts (kev) bombards a small spot on the surface of the sample under ultra-high vacuum conditions. Positive and negative secondary ions sputtered from the surface are analyzed in a mass spectrometer in regards to their mass-to-charge ratio. (12 Dec 1998) |
| sulfonium ion | A compound in which a sulfur atom has three single covalent bonds and therefore has a positive charge analogous to the nitrogen of an ammonium compound; e.g., S-adenosyl-l-methionine. (05 Mar 2000) |
| sulfur-ferric ion oxidoreductase | <enzyme> From thiobacillus ferrooxidans; catalyses the production of sulfite and fe(2+) from elemental sulfur and fe(3+) Registry number: EC 1.8.99.- Synonym: sf oxidoreductase, sulfite-ferric ion oxidoreductase (26 Jun 1999) |
| ion | <chemistry, radiobiology> Atomic particle, atom or chemical radical bearing an electric charge, either negative or positive. (16 Dec 1997) |
| ion channel | <cell biology> A transmembrane pore that presents a hydrophilic channel for ions to cross a lipid bilayer down their electrochemical gradients. Some degree of ion specificity is usually observed and typically a million ions per second may flow. Channels may be permanently open, like the potassium leak channel or they may be voltage gated, like the sodium channel or ligand gated like the acetylcholine receptor. (27 Oct 1998) |
| ion channel gating | The opening and closing of ion channels due to a stimulus. The stimulus can be a change in membrane potential (voltage-gated), drugs or chemical transmitters (ligand-gated), or a mechanical deformation. Gating is thought to involve conformational changes of the ion channel which alters selective permeability. (12 Dec 1998) |
| ion channels | Gated, ion-selective glycoproteins that traverse membranes. The stimulus for channel gating can be a membrane potential, drug, transmitter, cytoplasmic messenger, or a mechanical deformation. Ion channels which are integral parts of ionotropic neurotransmitter receptors are not included. (12 Dec 1998) |
| ion cyclotron emission | <radiobiology> As ions gyrate around in a magnetic field (see also larmor radius or cyclotron radius), they radiate radio-frequency electromagnetic waves. This is known as ion cyclotron emission, and can be measured to help diagnose a plasma. (09 Oct 1997) |
| ion diode | <radiobiology> Device for producing and accelerating ion beams for light ion drivers for inertial confinement fusion. Ions are produced in an anode plasma, extracted as space-charge-limited ion flow, and accelerated to the cathode, composed of a confined electron swarm, by an applied electric field. Millions of amperes of current at millions of volts have been produced this way. (27 Oct 1998) |
| ion exchange | Reversible chemical reaction between a solid, often an ion exchange resin, and a fluid whereby ions may be exchanged from one substance to another. This technique is used in water purification, in research, and in industry. (12 Dec 1998) |
| ion exchange chromatography | <procedure> Separation of molecules by absorption and desorption from charged polymers. An important technique for protein purification. For small molecules the support is usually polystyrene, but for macromolecules, cellulose, acrylamide or agarose supports give less non-specific absorption and denaturation. Typical charged residues are CM carboxymethyl) or DEAE (diethylaminoethyl). (27 Oct 1998) |
| ion exchanger | See: anion exchanger, cation exchanger. (05 Mar 2000) |
| ion exchange resin | <chemistry> A resin of polymers that havefixed charged groups which is used in chromatographic columns to separate ions. (27 Oct 1998) |
| ion exchange resins | <chemistry> High molecular weight, insoluble polymers which contain functional groups that are capable of undergoing exchange reactions (ion exchange) with either cations or anions. See: ion exchange, ion exchanger. (12 Dec 1998) |