Interaction des Ions Métalliques avec le DNA. II. Adsorption préférentielle de l'Ion césium par les Acides nucléiques

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Abstract
Preferential adsorption of cations occurs in the solvated shell surrounding polyanions, especially polynucleotides and nucleic acids. The solvation parameter Γ is determined from sedimentation coefficients which are considered as pienometric determinations of the specific volume of the sample. By comparing two identical concentrations (0.1M) of monovalent salts, NaCl and CsCl, and using the model of DNA described in the preceding paper, one can relate the ratio SCs/SNa to solvation parameters ΓCs, and ΓNa.On the other hand, Γ can be related to the difference of energy W, between cation and water, to be extracted from the solution and placed in the vicinity of the polyanion. One finds generally a preferential solvation of the polarizable caesium ion by means of London–van der Waals interactions with bases. With reasonable assumptions, an estimate of W can be made, and the predicted value of Γ can be compared to the experimental one. An average of six sites is found around each base in a single‐stranded polymer, but‐only one in the double‐stranded structure. The amount of secondary structure can thus be estimated from the simple measurement of the ratio of two sediment constants.

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