Formation of impeller-like helical DNA-silica complexes by polyamines induced chiral packing

Abstract

The helicity of DNA and its long-range chiral packing are widespread phenomena; however, the packing mechanism remains poorly understood both in vivo and in vitro. Here, we report the extraordinary DNA chiral self-assembly by silica mineralization, together with circular dichroism measurements and electron microscopy studies on the structure and morphology of the products. Mg(2+) ion and diethylenetriamine were found to induce right- and left-handed chiral DNA packing with two-dimensional-square p4mm mesostructures, respectively, to give corresponding enantiomeric impeller-like helical DNA-silica complexes. Moreover, formation of macroscopic impeller-like helical architectures depends on the types of polyamines and co-structure-directing agents and pH values of reaction solution. It has been suggested that interaction strength between negatively charged DNA phosphate strands and positively charged counterions may be the key factor for the induction of DNA packing handedness.

Keywords: biomolecule; chirality; helical architecture; liquid crystal; polyamine, DNA–silica complex; self-assemble.

Figure 1.

Macroscopic morphologies of the DNA–silica complexes. Scanning electron microscopy (SEM) images the samples synthesized without any addition (a), with addition of Mg²⁺ (b) and diethylenetriamine (c). Inset of SEM images: the long-range DNA packing ordering.

Figure 2.

X-ray diffraction patterns (a), transmission electron microscopy images (b) and diffuse-reflectance circular dichroism and UV–vis spectra (c) of the samples shown in figure 1.

Scheme 1.

Schematic of the mechanism of formation of DNA packing synthesized with different pH in the presence of diethylenetriamine [17,18].

Figure 3.

Morphologies and structures of the DNA–silica complexes synthesized in the presence of various polyamines. Scanning electron microscopy images and corresponding diffuse-reflectance circular dichroism spectra of the samples synthesized with addition of (a) ethylamine, (b) ethylenediamine and (c) spermine.

Figure 4.

Scanning electron microscopy images and corresponding diffuse-reflectance circular dichroism spectra of the DNA–silica complexes synthesized under different pH values. The pH values of reaction solutions were (a) 4.97, (b) 5.80, (c) 7.91 and (d) 9.06, respectively.

Figure 5.

Morphologies of the DNA–silica complexes synthesized with various co-structure-directing agents (CSDAs). With aminopropyltrimethoxysilane as CSDAs, the samples were synthesized without any counterions addition (DNA–APS) (a) and with addition of diethylenetriamine (DNA–diethylenetriamine–APS) (b), respectively. Without the addition of any counterions, the samples were synthesized with N-(2-aminoethyl)-3-aminopropyl methyltrimethoxysilane (DNA–DAPS) (c) and (3-trimethoxysilylpropyl)diethylenetriamine (DNA–TAPS) (d) as a CSDA, respectively. The pH of synthesis solutions was 7.60.