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The interaction between a variety of polyamines, both naturally occurring and synthetic, and calf thymus DNA has been studied using 23Na NMR. The relaxation behaviour of 23Na reflects the extent of interaction of Na+ with DNA phosphate groups and therefore the extent of charge neutralisation of DNA phosphate groups (P) by polyamine amino and imino groups (N) in solutions of DNa, polyamine and Na+. The studies reveal that whereas spermine and spermidine are capable of expelling nearly all of the Na+ ions from DNA at N/P approximately 1, diamines such as putrescine and homologues of spermine and spermidine are capable of neutralising only roughly 50% of DNA phosphates. The results provide a challenge to current models of DNA-polyamine interactions.

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The 35C1 and 37C1 nuclear magnetic relaxation of the chloride and perchlorate ions has been investigated for simple aqueous electrolyte solutions. The infinite dilution relaxation rates obtained by extrapolation are compared with Hertz's electrostatic theory of ion quadrupole relaxation. Good agreement between experiment and theory is obtained for the chloride ion. For nuclei at symmetry sites in tetrahedral or octahedral ions a more.elaborate analysis is required. Thus distortion of the ion from tetrahedral or octahedral symmetry may create sizable electric field gradients and, furthermore, the Sternheimer antishielding terms must take into account that not only an external electric field gradient, but also an external electric field can produce field gradients at the nucleus. Indeed, the latter effect is found to be considerable for the ammonium ion. Using calculated antishielding factors, the 14N relaxation of the aqueous ammonium ion is found to agree closely with Hertz's theory. A discussion of the quadrupole relaxation of other symmetrical polyatomic ions is presented and it is found that for the case of the perchlorate ion, as well as for other ions, the electric field induced field gradient may have a marked influence on the relaxation.

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