PHYSICAL PROPERTIES OF NUCLEIC ACIDS 



487 



20- 



15 — 



10— 



10 15 



centipoises 



Fig. 20. Values of tan ao for a solution of sodium deoxypentose nucleate with 

 sodium chloride when viscosity is varied by addition of glycerine (Schwander and 

 Cerf'^s). 



formation of the nucleate ion, and the more detailed experimental study of 

 Horn et al}^^ confirms this view although the neutral ion in neutral solution 

 is much less deformable than the acid-treated material. 



The light-scattering results of Reichmann et alJ^ and of llo\ven et al}^^ 

 confirm the conclusion that the deoxypentose nucleate ion is deformable, 

 but the contraction on the addition of electrolyte to a water solution is much 

 less than for a typical polyelectrolyte. Thus Rowen et al}^'^ found that the 

 maximum dimension decreased from 6800 A. to 4500 A. when the ionic 

 strength was increased from to 2 X 10"^. A similar change of solvent 

 with sodium polymethacrylate would produce about a tenfold decrease in 

 the maximum dimension."^ Furthermore, Reichmann et al?^ conclude that 

 the deoxypentose nucleate ion in 0.2 M sodium chloride solution is only 

 slightly more asymmetric than that of a random coil; if this be so, the 

 streaming birefringence can only arise by a deformation of the molecule. 



Direct evidence that sodium ions are bound to the nucleate ion has been obtained 

 from determinations of the charge on the nucleate ion at various ionic strengths. 

 The charge has so far only been determined from measurements of the membrane 

 potential, and the measurements of Creeth and Jordan'^* have recently been extended 

 by Shack ei oL'" Their results are very similar in that the charge on the nucleate ion 



»" P. Horn, J. Leray, J. Pouyet, and C. Sadron, J. Polymer Sci. 9, 531 (1952). 



"^ J. W. Rowen, M. Eden, and H. Kahler, Biochim. et Biophys. Acta 10, 89 (1953). 



i« A. 0th and P. Doty, J. Phys. & Collid Chern. 56, 43 (1951). 



"« J. M. Creeth and D. O. Jordan, /. Chem. Soc. 1949, 1409. 



