The Structures and Properties of Poly-5-methylcytidylic Acid

The optical rotatory dispersion properties of poly 5MeC, poly diMeC, and 5MeCMP‐(5′) in 0.1M Na+ have been studied at various pH values and temperatures. Poly 5MeC and poly diMeC have optical properties which are similar to those for poly C; however, poly 5MeC has a biphasic melting profile in the pH range from 3.8 to 5.4 similar to that observed for poly 51C. Using titration, ionic strength, and pH dependence measuements, the data for poly 5MeC are interpreted in terms of the following scheme at pH 4.0 and 0.1 ionic strength: triple‐strand helix 37°C double‐strand helix 79°C single‐strand coil. Support for this scheme is discussed. The effect of the methyl group is discussed in terms of similar structural possibilities for other polymers of cytidylic acid.