Thermal transitions in mixtures of polydeoxyribodinucleotides

Oligo d(C‐A) and oligo d(T‐G) of known average lengths, prepared by a combination of chemical and enzymatic procedures, have been mixed in 0.02 M and 0.07 M Na + , and absorbance has been studied as a function of increasing temperature. The transitions have been analyzed for the temperature of maximum slope T m , the breadth of the transition, the value of the slope at T m , and the maximum hyperchromicity. Linear expressions have been found relating the inverse of the length in nucleotide units ( n −1 ) of the shorter oligomer, irrespective of its identity, to T m and also to the transition breadth. From a difference in slope between the T m versus n −1 expressions for the two molarities, the entropy and enthalpy of melting have been calculated as a function of n −1 .