Heats of the helix–coil transitions of the poly A–poly U complexes

The heats of the conformational transitions of poly (A + U) and poly(A + 2U) were determined in a twin‐cell differential thermal analysis microcalorimeter capable of measuring heat effects of 25–35 meal, in reactions of this type, with a precision of about 3%. The dependence of these heats on the concentration of Na + and K + was studied and was found to be interpretable with fair success by a simple phenomenological argument which employs the concept of binding of counterions to polyelectrolytes.