Nucleoside conformations: XIII - Circular dichroïsm of guanosine gels and the conformation of GpG and poly (G)(∘)

Summary The CD spectra of eighteen guanosine derivatives in the gel form have been measured. The amplitudes of the B 1u exciton band appear to increase with sin γ (γ being the turn angle between the tetramer stacks obtained from x-ray work). On this plot the « unknowngels fit reasonably well, especially those of GpG and its 5′-5′ analogue. From a comparison of the gel CD spectrum of GpG with that of poly(G) it is concluded that the latter is a four-stranded helix with similar structural parameters as the GpG gel.