Ribonucleic guanidine demonstrates an unexpected marked preference for complementary DNA rather than RNA.

Replacement of the phosphodiester linkages of DNA and RNA by guanidinium linkages provides DNG and RNG. We report here the order of stability of mixed duplexes (RNG-U5.DNA-A5>>RNA-U5.RNA-A5>RNG-U5.RNA-A5>RNA-U5.DNA-A5>DNA-T5.DNA-A5). The considerable stability of RNG.DNA compared to RNG.RNA is shown to be due to the rigid backbone of RNG existing only in B-form and therefore lowering its affinity for A-RNA. RNG oligomers are putative antigene agents which are specific for DNA and would have minimal competitive binding to ncRNA.