| zero-order reaction | A reaction that proceeds at a particular rate independently of the concentration of the reactant or reactants. (05 Mar 2000) |
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| Zimmermann reaction | A chemical reaction between an alkaline solution of meta-dinitrobenzene and an active methylene group (carbon-16) of 17-ketosteroids; it is the basis of the 17-ketosteroid assay t.; more generally, a reaction between methylene ketones and aromatic polynitro compounds in alkaline solutions. Synonym: Zimmermann test. (05 Mar 2000) |
| unimolecular reaction | A reaction involving a single molecule (e.g., decomposition, intramolecular rearrangement, intramolecular oxidation or reduction), even if a catalytic agent, such as acid or alkali, is present in large excess, on a molecular basis, or is not rate-determining; such reaction's are usually first-order reaction's. Compare: molecularity. Synonym: unimolecular reaction. (05 Mar 2000) |
| Fenton reaction | The use of H2O2 and ferrous salts (Fenton's reagent) to oxidise alpha-hydroxy acids to alpha-keto acids or to convert 1,2-glycols to alpha-hydroxy aldehydes, the formation of OH-, OH-, and Fe3+ from the nonenzymatic reaction of Fe2+ with H2O2; a reaction of importance in the oxidative stress in blood cells and various tissues. (05 Mar 2000) |
| Fernandez reaction | A delayed hypersensitivity lepromin reaction, similar to a tuberculin reaction, at the site of intradermal injection of Dharmendra antigen in a lepromin test. (05 Mar 2000) |
| ferric chloride reaction of epinephrine | An intense emerald green colour in a neutral or slightly acid solution of epinephrine when ferric chloride is added to it; a reaction typical of catechols. (05 Mar 2000) |
| Feulgen reaction | <procedure> A specific staining procedure for DNA: mild acid hydrolysis makes the aldehyde group of deoxyribose available to react with Schiff's reagent to give a purple colour. (18 Nov 1997) |
| fight or flight reaction | The theory advanced by Walter Cannon, that in the autonomic nervous system and the effectors connected with it, the organism in situations of danger requiring either fight or flight is provided with a check-and-drive mechanism that puts it in readiness to meet emergencies with undivided energy output. Also known as the emergency theory. (05 Mar 2000) |
| first-order reaction | A reaction the rate of which is proportional to the concentration of the single substance undergoing change; radioactive decay is a first-order process, defined by the equation -(dN/dt)=kN, where N is the number of atoms subject to decay (reaction), t is time, and k is the first-order decay (reaction) constant, i.e., the fraction of all atoms decaying per unit of time. See: decay constant, order. (05 Mar 2000) |
| fixation reaction | <immunology> Binding of complement as a result of its interaction with immune complexes (the classical pathway) or particular surfaces (alternative pathway). (18 Nov 1997) |
| flocculation reaction | A form of precipitin reaction in which precipitation occurs over a narrow range of antigen-antibody ratio, due chiefly to peculiarities of the antibody (precipitin). (05 Mar 2000) |
| focal reaction | A reaction which occurs at the point of entrance of an infecting organism or of an injection, as in the Arthus phenomenon. Synonym: local reaction. (05 Mar 2000) |
| Folin's reaction | The reaction of amino acids in alkaline solution with 1,2-naphthoquinone-4-sulfonate (Folin's reagent) to yield a red colour; useful for quantitative assay. Synonym: Folin's reagent. (05 Mar 2000) |
| foreign-body reaction | Chronic inflammation and granuloma formation around irritating foreign bodies. (12 Dec 1998) |
| Forssman antigen-antibody reaction | The combination of Forssman antibody with heterogenetic antigen of the Forssman type, as in the agglutination of sheep erythrocytes (which contain Forssman antigen) by serum from a person with infectious mononucleosis which contains Forssman antibody. Synonym: Forssman reaction. (05 Mar 2000) |