1. In chemistry, a group of elements or atoms usually passing intact from one compound to another, but usually incapable of prolonged existence in a free state ( e.g., methyl, CH3); in chemical formulas, a r. is often distinguished by being enclosed in parentheses or brackets. 2. Thorough or extensive; relating or directed to the extirpation of the root or cause of a morbid process; e.g., a r. operation. 3. Denoting treatment by extreme, drastic, or innovative, as opposed to conservative, measures. 4. SYN: free r.. [L. radix (radic-), root]
- acid r. a r. formed from an acid by loss of one or more hydrogen ions; e.g., SO4, NO3.
- color r. SYN: chromophore.
- free r. a r. in its (usually transient) uncombined state; an atom or atom group carrying an unpaired electron and no charge; e.g., hydroxyl and methyl Free radicals may be involved as short-lived, highly active intermediates in various reactions in living tissue, notably in photosynthesis. The free r. nitric oxide, NO, plays an important role in vasodilation. SYN: r. (4).Free radicals occur naturally within the body as a result of metabolic processes and can also be introduced from without (through smoking, inhaling environmental pollutants, or exposure to UV radiation). They interact readily with nearby molecules and may cause cellular damage, including genetic alterations. It has been theorized that they are involved in plaque formation in atherosclerosis, in cancer, and in degenerative disorders such as Alzheimer dementia and parkinsonism. Natural enzymes such as superoxide dismutase and peroxidase are thought to counteract free radicals, and there is evidence that many nutrients, including vitamins C and E and β-carotene, also exert an antioxidant effect. see also antioxidant.
- oxygen-derived free radicals an atom or atom group having an unpaired electron on an oxygen atom, typically derived from molecular oxygen. For example, one-electron reduction of O2 produces the superoxide r., O2·; other examples include the hydroperoxyl r. (HOO·), the hydroxyl r. (HO·), and nitric oxide (NO·). These apparently have a role in reprofusion injury.

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rad·i·cal 'rad-i-kəl adj
1) designed to remove the root of a disease or all diseased tissue <\radical surgery>
2) involving complete removal of an organ <\radical prostatectomy> compare CONSERVATIVE
rad·i·cal·ly -i-k(ə-)lē adv
radical n FREE RADICAL also a group of atoms bonded together that is considered an entity in various kinds of reactions

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rad·i·cal (radґĭ-kəl) [L. radicalis] 1. directed to the cause; directed to the root or source of a morbid process, as radical surgery. 2. a group of atoms which enters into and goes out of chemical combination without change, and which forms one of the fundamental constituents of a molecule. Organic radicals are symbolized R.

Medical dictionary. 2011.

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  • radical — radical, ale, aux [ radikal, o ] adj. et n. • fin XVe; bas lat. radicalis, de radix « racine » I ♦ Adj. 1 ♦ Qui tient à l essence, au principe (d une chose, d un être). ⇒ foncier, fondamental; absolu. « L instinct le plus radical dans l homme, le …   Encyclopédie Universelle

  • radical — radical, ale (ra di kal, ka l ) adj. 1°   Terme de botanique. Qui appartient à la racine, qui part de la racine. Pédoncules radicaux.    Feuilles radicales, celles qui naissent si près de la racine, qu elles semblent en sortir et non de la tige.… …   Dictionnaire de la Langue Française d'Émile Littré

  • Radical — Rad i*cal (r[a^]d [i^]*kal), a. [F., fr. L. radicalis having roots, fr. radix, icis, a root. See {Radix}.] 1. Of or pertaining to the root; proceeding directly from the root. [1913 Webster] 2. Hence: Of or pertaining to the root or origin;… …   The Collaborative International Dictionary of English

  • Radical — (from Latin radicis , genitive of radix root ) can refer to many different things and concepts.Mathematics*The symbol √ used to indicate the square root or nth root *Radical of an algebraic group, a concept in algebraic group theory *Radical of… …   Wikipedia

  • radical — RADICÁL, Ă, radicali, e, adj., s.m. I. adj. 1. De bază, fundamental, esenţial. ♦ (Adverbial) Din temelie, cu desăvârşire, complet. ♦ (Despre tratamente, leacuri) Care vindecă în întregime, complet. 2. Care preconizează reforme adânci, acţiuni… …   Dicționar Român

  • Radical — Saltar a navegación, búsqueda El término radical viene del latín radix ( raíz ), significa así de raíz o de base, refiriéndose sobre todo a un punto de vista profundo, sustancial, más aún si es aplicado a alguna convicción, práctica, análisis o… …   Wikipedia Español

  • Radical — Rad i*cal (r[a^]d [i^]*kal), n. 1. (Philol.) (a) A primitive word; a radix, root, or simple, underived, uncompounded word; an etymon. (b) A primitive letter; a letter that belongs to the radix. [1913 Webster] The words we at present make use of,… …   The Collaborative International Dictionary of English

  • radical — adjetivo 1. De la raíz: El morfema radical de amar es am . 2. (antepuesto / pospuesto) Que se produce de manera total, sin ninguna limitación: cambio radical. Las radicales reformas emprendidas por el Ayuntamiento han levantado protestas. Se ha… …   Diccionario Salamanca de la Lengua Española

  • radical — [rad′i kəl] adj. [ME < LL radicalis < L radix (gen. radicis), ROOT1] 1. a) of or from the root or roots; going to the foundation or source of something; fundamental; basic [a radical principle] b) extreme; thorough [a radical change in one… …   English World dictionary

  • radical — (Del lat. radix, īcis, raíz). 1. adj. Perteneciente o relativo a la raíz. 2. Fundamental, de raíz. 3. Partidario de reformas extremas, especialmente en sentido democrático. U. t. c. s.) 4. Extremoso, tajante, intransigente. 5. Bot. Dicho de… …   Diccionario de la lengua española

  • Radical 2 — meaning vertical stroke is one of six of the 214 Kangxi radicals that are composed of only one stroke.In the Kangxi Dictionary there are only 21 characters (out of 40 000) to be found under this radical.Radical 1 (橫 héng) is one of the Eight… …   Wikipedia

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