A conformational study of adenylyl-(3', 5')-adenosine and adenylyl-(2', 5')-adenosine in aqueous solution by carbon-13 magnetic resonance spectroscopy.

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Abstract
The solution conformation of adenylyl-(3′,5′)-adenosine and adenylyl-(2′,5′)-adenosine in both the stacked and unstacked states was studied by carbon-13 magnetic resonance spectroscopy. Large chemical shift differences between the base carbons in the dimers and those in the corresponding monomers are attributed in part to the influence of base-base interaction. Carbon-phosphorus couplings across three bonds revealed the preferred populations for certain backbone rotamers, demonstrating that significant changes in conformation about the C(3′)-0 and C(5′)-0 bonds do not occur in the temperature or salt-induced unstacking of adenylyl-(3′,5′)- adenosine. However, rotations about the C(2′)-0 and C(5′)-0 bonds occur in the temperature-mediated unstacking of adenylyl- (2′,5′)-adenosine.