Organization of nucleosides supported by boronic-acid-appended poly(L-lysine): Creation of a novel RNA mimic

Boronic-acid-appended poly(L-lysine) (1) can form anionic boronate esters w ith diol derivatives in aqueous solution. One can thus expect that when nuc leosides are mixed with 1, the resultant complexes will satisfy the basic s tructural characteristics of RNA, viz., one-dimensionally organized nucleic bases and anionic charges. To obtain insights into this novel RNA mimic, t he solution properties of adenosine (Ad) were estimated in the absence and the presence of 1. The large absorption and CD spectral changes were observ ed at pH 6-10 where the poly(L-lysine) main chain tends to adopt an a-helix -rich conformation. On the basis of the fact that the magnitude of the spec tral changes is much larger than the fraction of complexed Ad molecules, th e polymer-supported organization mode was proposed: that is, Ad molecules c omplexed by covalent bonds with I act as clusters to induce further organiz ation of uncomplexed Ad molecules by noncovalent interactions. The proposal was further confirmed by H-1 NMR spectroscopy and dynamic light scattering , On the other hand, none of these spectral changes were observed for 2 ' - deoxyadenosine. The I-Ad complex thus formed can interact with complementar y poly(U) but not with noncomplementary poly(C), indicating that it can act as a novel RNA mimic.