| hydrogen acceptor | A molecule that, in conjunction with a tissue enzyme system, carries hydrogen from one metabolite (oxidant) to another (reductant) or to molecular oxygen to form H2O. Synonym: hydrogen acceptor. (05 Mar 2000) |
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| hydrogen bomb | <physics> An extremely powerful type of atomic bomb based on nuclear fusion. The atoms of heavy isotopes of hydrogen (deuterium and tritium) undergo fusion when subjected to the immense heat and pressure generated by the explosion of a nuclear fission unit in the bomb. (09 Oct 1997) |
| hydrogen bond | <chemistry> A weak electrostatic link between an electronegative atom (such asoxygen) and a hydrogen atom which is linked covalently to anotherelectronegative atom, hydrogen bonding is what makes water stick toitself. (09 Oct 1997) |
| hydrogen bonding | A low-energy attractive force between hydrogen and another element. It plays a major role in determining the properties of water, proteins, and other compounds. (12 Dec 1998) |
| hydrogen bromide | HBr;a colourless gas that has a very irritating odour and fumes in moist air; in aqueous solution, it is hydrobromic acid. Hydrogen chloride, HCl;a very soluble gas which, in solution, forms hydrochloric acid. (05 Mar 2000) |
| hydrogen carrier | A molecule that, in conjunction with a tissue enzyme system, carries hydrogen from one metabolite (oxidant) to another (reductant) or to molecular oxygen to form H2O. Synonym: hydrogen acceptor. (05 Mar 2000) |
| hydrogen cyanide | <chemical> Hydrogen cyanide (hcn). A toxic liquid or colourless gas. It is found in the smoke of various tobacco products and released by combustion of nitrogen-containing organic materials. Pharmacological action: poisons. Chemical name: Hydrocyanic acid (12 Dec 1998) |
| hydrogen dehydrogenase | <enzyme> Hoxf, hoxh, hoxu, and hoxy from rhodococcus opacus encode the alpha-, beta-, gamma-, and delta-subunits, respectively Registry number: EC 1.12.1.2 Synonym: hydrogen-nad+ oxidoreductase, nad-reducing hydrogenase, hoxf gene product, hoxu gene product, hoxy gene product, hoxh gene product (26 Jun 1999) |
| hydrogen dioxide | <chemical> Hydrogen peroxide is produced by vertebrate phagocytes and is used in bacterial killing (the myeloperoxidase halide system). (05 May 1997) |
| hydrogen donor | A metabolite from which hydrogen is removed (by a dehydrogenase system) and transferred by a hydrogen carrier to another metabolite, which is thus reduced. (05 Mar 2000) |
| hydrogen electrode | The ultimate standard of reference in all pH determinations, limited and technically difficult to use, consisting of a piece of spongy platinum black partly immersed in a solution in a small glass tube; the tube above the solution is filled with hydrogen gas that is bubbled through the solution and absorbed by the platinum; the electrode thus measures the potential between H2 and H+, the "standard" potential of which (1 atmosphere, 1 molar) is taken as zero; hence, the hydrogen electrode potential measures [H+] or pH. (05 Mar 2000) |
| hydrogen embrittlement | <physics> A decrease in the fracture strength of metals (embrittlement) due to the incorporation of hydrogen within the metal lattice. (09 Oct 1997) |
| hydrogen exponent | The logarithm of the hydrogen ion concentration in blood or other fluid; its negative is the pH of that fluid. (05 Mar 2000) |
| hydrogen ion | A hydrogen atom minus its electron and therefore carrying a unit positive charge (i.e., a proton); in water, it combines with a water molecule to form hydronium ion, H3O+. (05 Mar 2000) |
| hydrogen number | The quantity of hydrogen that 1 g of fat will absorb; it is a measurement of the amount of unsaturated fatty acids in the fat. See: iodine number. (05 Mar 2000) |