Direct visual proof for the micellar solubilization of RNA models during its transesterification

In this study, the micellar effects on the transesterification of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP^-) - a classic RNA model-were evaluated in the presence of three dinuclear copper(II) complexes (Cu₂L¹Cl₄, Cu₂L²Cl₄, Cu₂L³Cl₄) with new bidentate 'NNO' ligands. In both nonmicellar and micellar systems, bromine-bearing Cu₂L¹Cl₄ displayed the best activity in contrast to the other analogues due to the positive electron-withdrawing ability of bromine. The introduction of cationic micelles resulted in a significant rate enhancement of the HPNP^- transesterification, achieving improvements of one order of magnitude (upping to 45 times) in contrast with nonmicellar system. In addition, in cationic micelles an observed change in activity trend shall be contributed to the combined influence of electronic effects of substituents and solubilization of the as-screened complexes. Controlled experiments confirmed a notable solubilization of the substrate HPNP^- inside cationic micelles. Importantly, the first visual evidence was obtained from the TEM-based element mappings, demonstrating the distinct solubilization behaviour of both anionic HPNP^- and neutral HPNP. Anionic HPNP^- underwent more rapid transesterification against its neutral analogue (HPNP) by about 3.22- or 4.70-fold in 16-6-16 micelles. Moreover, it strongly supports the previously reported 'Sandwich Adsorptive Mode'.