affinity

1. In chemistry, the force that impels certain atoms to bind to or unite with certain others to form complexes or compounds; chemical attraction. 2. Selective staining of a tissue by a dye or the selective uptake of a dye, chemical, or other substance by a tissue. [L. affinis, neighboring, fr. ad, to, + finis, end, boundary]

- residual a. secondary forces that enable apparently saturated atoms, ions, or molecules to attract other atoms or groups, causing such phenomena as complex formation, hydration, adsorption, etc.

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af·fin·i·ty ə-'fin-ət-ē n, pl -ties

1) an attractive force between substances or particles that causes them to enter into and remain in chemical combination

2) a relation between biological groups involving resemblance in structural plan and indicating a common origin

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af·fin·i·ty (ə-finґĭ-te) [L. affinitas relationship] 1. a special attraction for a specific element, organ, or structure. 2. chemical a. in immunology, a thermodynamic expression of the strength of interaction between a single antigen-binding site and a single antigenic determinant (and thus of the stereochemical compatibility between them), most accurately applied to interactions among simple, uniform antigenic determinants such as haptens. Expressed as the association constant (K liters mole⁻¹), which, owing to the heterogeneity of affinities in a population of antibody molecules of a given specificity, actually represents an average value (mean intrinsic association constant). Cf. avidity.