PHYSICAL PROPERTIES OF NUCLEIC ACIDS 483 



is a cationic dye, it will be adsorbed only at negatively charged sites, and at neutral 

 pll these will be the phosphoric acid dissociations. 



A further possibility of testing these conclusions lies in the different stability of 

 the tertiary and secondary esters of phosphoric acid towards alkaline reagents. '^^ 

 The alkaline hydrolysis constants have been given by Cavalieri'^^ as being ca. 3.5 X 

 10"^ min.~i for the reaction: triester phosphate -^ diester phosphate, and ca. 2.9 X 

 10~^ min.~' for the reaction: diester phosphate — > monoester phosphate. Cavalieri's 

 results of a kinetic study''^^ of the alkaline hydrolysis of yeast ribonucleic acid again 

 suggests that there are at least two types of phosphate linkage, one more labile than the 

 other. The analysis of the kinetic data is, however, difficult in view of possible dif- 

 ferences in the rate of hydrolysis of bonds between different nucleotides, and Cavalieri 

 did not consider it justifiable to relate the two types of linkage definitely to the tri- 

 and diester phosphates. 



4. The Solution Properties of Sodium Deoxypentose 

 Nucleate 



Although studies of the properties and structure of nucleic acids and 

 their sodium salts in the solid state have yielded results of fundamental 

 importance, it is, nevertheless, the size, shape, and rigidity of the nucleate 

 ion in solution which is probably of greatest interest from the biological 

 viewpoint. In view of the very different nature of the environments, con- 

 clusions drawn from studies of the solid state may require some modifica- 

 tion when the properties in solution are considered. It has been known for 

 some time that the properties of the nucleate ion in solution are very de- 

 pendent on the pH and ionic strength of the solvent as well as upon the 

 previous treatment of the nucleic acid, and the nature of these changes 

 will now be considered. 



Owing to the difficulty in obtaining high-molecular-weight preparations 

 of pentose nucleic acids, most studies have been made on the sodium salt 

 of a deoxypentose nucleic acid and this discussion will be confined to the 

 properties of this group of acids. 



a. The Influence of Ionic Strength in Neutral Solution 



Measurements of viscosity and streaming birefringence made on solu- 

 tions of sodium deoxypentose nucleate containing no added electrolyte 

 have not been found to be reproducible (see for example Sadron'-®), par- 

 ticularly at concentrations above about 0.005 %, the actual value varying 

 with the nucleate sample, being lower for high-molecular-weight prepara- 

 tions. This lack of reproducibility will be due to the slow degradation of the 

 nucleate which occurs in aqueous solution and which is accelerated by in- 



'" G. M. Kosolapoff, "Organophosphorus Compounds," p. 232. John Wiley and Sons, 



Inc. New York, 1950. 

 "6 L. F. Cavalieri, J. Am. Chem. Soc. 73, 4899 (1951). 

 '28 C. Sadron, Prog. Biophys. and Biophys. Chem. 3, 237 (1953). 



