212 WALDO E. COHN 



2. Polyphosphonucleosides 230 



a. Diphosphates 230 



b. Polyphosphates 232 



3. Polynucleotides 233 



a. Ionic Properties and Molecular Size 233 



b. The Ribonuclease Digest 234 



c. The Deoxyribonuclease Digest 235 



IV. Separations Involving Sugar-Borate Complexing 235 



1. Sugars (Borate Exchanger and Solution) 235 



2. Sugar Phosphates (Borate in Solution Only) 236 



a. Nucleosides 236 



b. Sugar Phosphates and the Isomeric Ribose Phosphates 236 



c. Nucleotides 241 



V. Related Reviews 241 



I. Ion Exchange 

 Ion-Exchange Resins^ 



The basic principles of ion exchange were first observed in clays and 

 minerals, in particular the zeolites (hydrated aluminum silicates), and led 

 to the use of synthetic zeolites to remove calcium ion from water in exchange 

 for sodium ("water softening"). These synthetic zeolites expanded the 

 limited range of usefulness of the natural materials, the first analytical 

 application being to remove armnonia from urine for colorimetric determi- 

 nation. It remained for the recent rapid developments of resin technology 

 to produce the synthetic ion-exchange materials which have made possible 

 the spectacular separations of the closely related members of such families 

 as the rare earths,' the amino acids,* and the isomeric nucleotides (Sect. 

 Ill.l.e). Significant among the properties of these newer materials in this 

 connection are: (1) strength of functional group (strong-acid cation ex- 

 changers or strong-base anion exchangers); (2) single functional species 

 (e.g., nuclear sulfonic acid devoid of phenoUc or other acid groups); (3) 

 use of the chemically stable polystyrene resins as the supporting matrix 

 (reducing side reactions of the matrix essentially to zero); (4) ability to 

 produce the exchangers in the form of spherical particles (with improve- 

 ment in hydrodynamic properties) ; and (5) control of the degree of cross- 

 linking (divinylbenzene) allowing the exchange of substances of high mo- 

 lecular weight. 



Not all of these advances in technology occurred at once; hence, some 

 of the earlier separations of rare earths and amino acids were performed on 



2 O. Samuelson, "Ion-Exchangers in Analytical Chemistry." John Wiley & Sons, 

 New York, 1953. 



3 E. R. Tompkins, J. X. Khym, and W. E. Cohn, J. Am. Chem. Soc. 69, 2769 (1947); 

 B. Ketelle and G. E. Boyd, ibid. 2800. 



" W. H. Stein and S. Moore, /. Biol. Chem. 192, 663 (1951); et ante. 



