CHAPTER 14 



Optical Properties of Nucleic Acids and Their Components 

 Cx. H. BEAVEN, E. R. HOLIDAY, AND E. A. JOHNSON 



1. Introduction 493 



II. Bases, Nucleosides, and Mononucleotides 495 



1. Bases 498 



2. Nucleosides 504 



3. Nucleotides 511 



III. Nucleic Acids and Polynucleotides 514 



1. General 514 



2. The Absorption Spectra of Nucleic Acids 516 



3. Effect of pH on the e (P) of DNA 522 



4. Effect of Salts on the Absorptivity of DNA 525 



5. Effect of Other Agents on the e(P) of DNA 529 



6. Spectrophotometric Estimation of Nucleic Acids 529 



7. Nucleoproteins 530 



IV. Ultraviolet Dichroism 532 



1. General Theory 533 



2. Form Dichroism 534 



3. Definitions and Equations 535 



4. Dichroism of Simple Compounds 537 



5. Dichroism of Nucleic Acid 538 



6. Influence of Dichroism on the Microspectrographic Estimation of Nucleic 

 Acid in Intact Cells 542 



7. Dichroism of Stained Nucleic Acids 544 



V. Infrared Absorption Spectra 545 



I. Introduction 



Although ultraviolet absorption spectroscopy has been employed for the 

 characterization of nucleic acids and their derivatives for more than twenty 

 years, technical improvements in that period, in particular the introduction 

 of the photoelectric spectrophotometer, have reduced considerably the 

 value of most of the earlier work, which is in consequence not usually re- 

 ferred to here. Similarly, recent advances in instrumentation have stimu- 

 lated the application of infrared absorption methods to the study of nu- 

 cleic acids, although the full value of such methods for both analysis and 

 molecular structure determination has not yet been exploited. 



In the present field absorption spectroscopy fulfils two principal func- 

 tions, as an analytical tool and as a basis for deductions concerning struc- 

 ture. To date, the first of these functions has been by far the more important 

 since the hydrolysis products of nucleic acids lend themselves readily to 



493 



