A comparison of the association of spermine with duplex and quadruplex DNA by NMR

The association of [1′,1″-¹³C₂]spermine ([1′,1″-¹³C₂]N,N′-bis(3- aminopropyl)-1,4-butanediamine) with duplex and quadruplex DNA has been studied by nuclear magnetic resonance spectroscopy. 1D NOESY experiments using two-way selective cross-polarization (ISI-SCP-NOESY) showed spermine intramolecular NOEs are either weakly positive or weakly negative when spermine is complexed to duplex B-DNA and linear four-stranded quadruplex DNA. In contrast, large negative intramolecular NOEs are observed when spermine is complexed to two distinct forms of folded quadruplex DNA suggesting greater immobilization of spermine on these folded DNA quadruplexes. No changes in the quadruplex stem structure are observed but there are minor changes to the loop structure of a two-stranded folded quadruplex on binding spermine.