DNA Amphiphilic Molecules Self-assembly And Studies On Mechanisms Of The Effects On I-Motif Structure

Recently,DNA has been perceived as one of the most versatile building blocks in constucting self-assembly systems,because of the base pairing and ease of sequence definition.DNA amphiphilic molecules,whose hydrophilic headgroups are oligonucleotides,make the versatile property of DNA combine with the self-assembly ability of amphiphilic molecules.The potential application of biomaterials generated by novel synthetic DNA amphiphilic molecules include targeted drug delivery,gene therapy,DNA detection,and so on.I-motif is a four-stranded structure,which is sensitive with pH.Human telomeric i-motif DNA has been considered as specific drug targets for cancer therapy.We can design new self-assemblied pH-responsive systems with introduction of i-motif structure.Moreover,the self-assembly of DNA amphiphilic molecules has effects on the formation and stability of i-motif.This study provides new approaches into the stability of i-motif and cancer therapy.Herein,we reported three new kinds of i-motif-based amphiphilic molecules,including tetramer i-motif amphiphilic molecule,dimer i-motif amphiphilic molecule and unimer i-motif amphiphilic molecule.Their critical micelle concentrations were determined through surface tension measurement and fluroscent probe method.The CMCs of these amphiphilic molecules at pH 4.5 were different from those at pH 9.0.At pH 4.5,the formation of i-motif structure induced the increase of the charge density and CMC.The self-assembly structures and sizes were determined through AFM,cryo-TEM and DLS.C18-imotif-11 bp self-assembled into multi-layer spherical aggregates at pH 4.5 and multi-micelle aggregates at pH 9.0.Lipid-imotif-21 bp self-assembled into spherical micelles at pH 4.5 and fibers at pH 9.0.In addition,we discovered the transformation processes of different self-assemblied structures between pH 4.5 and 9.0.Though detecting the change of aggregate structure with time,we proposed the mechanism of multi-layer assembly and multi-micelle aggregation in C18-imotif-11 bp self-assembly,and clarified the key role of i-motif forming in lipid-imotif-21 bp self-assembly.On the other hand,the thermal stabilities of i-motif structures in these i-motif amphiphilic molecules were determined with circular dichroism spectra.We found the self-assembly of i-motif amphiphilic molecules had signficant effects on intermolecular i-motif but weak effects on intramolecular i-motif.Hydrophobic interactions and the arrangement of amphiphilic molecules control the formation and stability of i-motif.C18 alkyl chain was able to induce CCC to form the i-motif tetraplex structure,but C10 was not able to.In the DNA amphiphilic molecule aggregates,the small curvatures are benefit for the stability of i-motif stucture.The small curvature of C18-imotif-11 bp arrangement facilitated the intermolecular hydrogen bond formation.The melting point was higher than that of lipid-imotif-11 bp,which has stronger hydrophobic force.Our work provided new insights into understanding the factors of i-motif stability.Furthermore,we explored the thermal stabilities of unimer i-motif and dimer i-motif in crowded enviroments.The melting points were determined in different PEG solution with different concentrations.The crowding environments of PEGs with different molecular weights had different effects on the stabilities of i-motif.PEGs with low molecular weight reduced the stability of i-motif,which was strengthened by increasing the concentrations of PEGs.Meanwhile,PEGs with high molecular weights increased the stability of i-motif,which was mantained at high concentrations of PEGs.In short,we systematically studied the mechanisms of interplay between DNA amphiphilic molecules self-assembly and i-motif structure.We discovered the new self-assemly structures of multi-micelle aggregate and multi-layer spherical structure and clarified the new mechanisms of multi-micelle aggregation and multi-layer self-assembly.At the same time,the thermal stability of i-motif in DNA amphiphilic molecules self-assembly was discussed.Our results on the formation and stablity of i-motif provide experimental basis for the new methods of tuning the i-motif formation and stability,as well as the new approaches of inhibiting cancer cell proliferation.