NA-23 NMR-STUDY OF THE EFFECT OF ORGANIC OSMOLYTES ON DNA COUNTERION ATMOSPHERE

The effect of different organic osmolytes on the DNA counterion conden sation layer has been investigated by Na-23 NMR relaxation measurement s. The zwitterionic compounds glycine, beta-alanine, 4-aminobutyric ac id, and 6-aminocaproic acid have shown an increasing capacity to decre ase the amount of sodium ions in the vicinity of the macromolecule. Th e experimental data have been correlated with the dielectric constant increase in their corresponding solutions and have been compared with the prediction of counterion condensation theory. Polyols (sorbitol an d mannitol) did not display the same effect. These compounds largely i ncrease the relaxation rate of sodium ions in the proximity of DNA, un like the zwitterionic compounds. This probably results from a perturba tion of the water dynamic around the macromolecule, of the primary or secondary hydration shell of the sodium nuclei involved, or both.