Conformational analysis of polynucleotides. I. The favorable left-handed helical model for the poly(8,2'-S-cycloadenylic acid) with high anti conformation.

1) Energy calculations have shown that poly (8,2'-S-cycloadenylic aicd) can form left-handed helices owing to the high anti conformation. 2) Two favorable left-handed helices are characterized by axial translation per residue (Z=4.3 and 3.6A) and by rotations per residue (theta= 40 degrees and -25 degrees). 3) The proposed helical models might be stable in aqueous solution and is well explicable of the optical property of this compound.