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Two-Dimensional Packing of Short DNA with Non-Pairing Overhangs in Cationic Liposome–DNA Complexes: From Onsager Nematics to Columnar Nematics With Finite-Length Columns

机译:短DNa二维包装与非配对出挑的阳离子脂质体DNa复合物:从昂萨格向列列式向列随着有限长度列

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摘要

We report the formation of liquid crystalline (LC) phases of short double-stranded DNA with non-pairing (non-sticky) overhangs, confined between two-dimensional (2D) lipid bilayers of cationic liposome–DNA complexes. In a landmark study (Science 2007, 318, 1276), Nakata et al. reported on the discovery of strong end-to-end stacking interactions between short DNAs (sDNAs) with blunt ends leading to the formation of 3D nematic (N) and columnar LC phases. Employing synchrotron small-angle X-ray scattering, we have studied the interplay between shape anisotropy-induced and DNA end-to-end interaction-induced N ordering for 11 bp, 24 bp, and 48 bp sDNA rods with single-stranded oligo-thymine (T) overhangs modulating the end-to-end interactions. For suppressed stacking interactions with 10-T overhangs, the volume fraction of sDNA at which the 2D isotropic (I) to N transition occurs for 24 bp and 48 bp sDNA rods depended on their length to width (L/D) shape anisotropy, qualitatively consistent with Onsager's theory for the entropic alignment of rigid rods. As the overhang length is reduced from 10 T to 5 T and 2 T for 24 bp and 48 bp sDNA, the N to I transition occurs at lower volume fractions, indicating the onset of some degree of end-to-end stacking interactions. The 11 bp sDNA rods with 5-T and 10-T overhangs remain in the I phase, consistent with their small shape anisotropy (L/D ≈ 1.9) below the limit for Onsager LC ordering. Unexpectedly, in contrast to the behavior of 24 bp and 48 bp sDNA, the end-to-end interactions between 11 bp sDNA rods with 2-T overhangs set in dramatically and a novel 2D columnar N phase (NC) with finite-length columns formed. The building blocks of this phase are comprised of 1D stacks of (on average) four 11bp DNA-2T rods with an effective LSTACKED/D ≈ 8.2. Our findings have implications for the DNA-directed assembly of nanoparticles on 2D platforms via end-to-end interactions and in designing optimally packed LC phases of short anisotropic biomolecules (such as peptides and short-interfering RNAs) on nanoparticle membranes, which are used in gene silencing and chemical delivery.

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