Sugar phosphate backbone, conformational states

As RNA molecules are highly negatively charged due to their sugar-phosphate backbone, the conformational state of these molecules is strongly dependent on the concentration of positively charged counterions. In the absence of Mg2+ or other polyvalent counterions, and in low monovalent salt concentrations, RNA becomes denatured as a result of ineffective Debye screening of the repulsive forces between different parts of the polymer. 

Figure 2 Sugar phosphate backbone in Bj and Bu conformational states.

The effect of packing forces and hydrogen bonds upon the observed puckered conformations of nucleosides in the solid state is well-known [56, 57]. [the anomeric effect across the 3 O-P-O-ester fragment in the sugar-phosphate backbone see references cited therein]. Solution and solid-state conformations of pentofuranose differ dramatically for some nucleosides adenosine [58] crystallizes as the N-type conformer, whereas its hydrochloride salt crystallizes as the S-type conformer [59]. 

Plavec J, Thibaudeau C, Viswanadham G, Sund C, Sandstrran A, Chattopadhyaya J (1995) The interaction of the 2 -OH group with the vicinal phosphate in ribonucleoside 3 -(ethylphosphate) drives the sugar phosphate backbone into unique (S, e) conformational state. Tetrahedron 51 11775-11792... 

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