Nanosheet‐Stacked Chiral Silica Transcribed from Metal Ion‐ and pH‐Tuned Supramolecular Crystalline Complexes of Polyamine‐D‐Glucarate

Abstract

D-glucaric acid (D-Glc) associates with linear poly(ethyleneimine) (PEI) through hydrogen bonding and electrostatic interactions in aqueous media to form nanostructured crystalline PEI/D-Glc/H2O complexes with PEI/D-Glc/H2O ratios of 2:1:2. These complexes can serve as templates for silica depositions from hydrolytic condensation of tetramethoxysilane to guide morphologically duplicated silica under very mild conditions. Their microscale morphologies are tunable by use of the crystalline complexes regulated in the different pH of the PEI/D-Glc solutions. It was also found that some metal ions added in the PEI/D-Glc complexation process could have a synergistic effect under a certain pH regimes, bringing about remarkable changes in the hierarchy of the resulting complexes. Especially, the complexes formed through fine-tuning of the complexation conditions could direct torsionally stacked silica nanosheets, in which the nanosheets are composed of orderly-bundled nanofibrils. Final elimination of organic components of the templates afforded chiral inorganic silica while retaining the morphologically higher-order structures. The chirality of the silica, which was obtained after calcination at 600 °C, was characterized by means of diffused reflectance circular dichroism (DRCD) spectroscopy with a remote confirmation of the appearance of induced-CD (ICD) signals of achiral or racemic chromophores covalently linked on the silica frames. Interestingly, the shapes and signs of these ICD signals are dramatically changed depending on the pH-tuned templates used in silicification and are strongly correlated to that of the CD signals of the complex templates, indicating that the chiral transcription proceeds accurately with imprinting the higher-order chirality of the complexes on the morphologically structured silica networks.

Chiral SiO2 and Ag@SiO2 Materials Templated by Complexes Consisting of Comblike Polyethyleneimine and Tartaric Acid

“…[27] Furthermore,w ea lso presented af acile strategy to fabricate chiral silica materials using av ery effective catalytic template component formed by crystallization-driven self-assembly of linear PEI with chiral acids such as tartaric acid and d-glucarate in water. [28,29] In this system,t he carboxyl groups of chiral acids are well associated with basic secondary amino groups of PEI polymer chain in a1 :1 molarr atio to form chiral crystalline complexes.T hese chiral complexes play ad ual role in the fur-ther silicification process. They not only direct silicad eposition as templates, but also promote the hydrolytic condensation of silica precursors withouta dditional catalyst.…”

Biomimetic Synthesis of Shaped and Chiral Silica Entities Templated by Organic Objective Materials

“…We found that PEI interacted with guest chiral tartaric acid or glucaric acid in a 1:1 molar ratio of NH/COOH to form nanoscale crystalline complexes, which exhibited evident CD activity in solid state 55. 56 We employed chiral or racemic crystalline complexes consisting of linear PEI and chiral D ‐, L ‐, and dl ‐tartaric acid as templates to deposit silica in the same way as we did in the PEI/water system. Expectedly, all templates easily produced silica hybrids SiO 2 /PEI@ D , SiO 2 /PEI@ L and SiO 2 /PEI@ dl under very mild conditions of ambient temperature, nearly neutral aqueous medium and short reaction time 55.…”

“…Replacing the chiral source of tartaric acid by D ‐glucaric acid, we also developed chiral crystalline complexes consisting of PEI and D ‐Glc (PEI/ D ‐Glc) and used this complex as catalytic template in the hydrolytic condensation of TMOS (Figure 36). Interestingly, the complex PEI/ D ‐Glc showed nanosheet structures with crystallites and promoted the silicification of TMOS to direct chiral silica with nanosheet‐stacked morphology 56. Tuning the formation conditions of the template of PEI/ D ‐Glc by pH and metal ions, such as Ca 2+ , Zn 2+ , Mg 2+ , we controlled the silica nanosheet array with spherical or twisted structures (Figure 37).…”

“… Illustration of chiral silica duplication from the complexation of D ‐glucaric acid ( D ‐Glc) with linear PEI. a) Synthesis of supramolecular complexes consisting of PEI and D ‐Glc; b) preparation of silica replicas transcribed from PEI/ D ‐Glc complexes 56. Copyright © 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”

“… SEM images of Ca 2 + ‐affected SiO 2 @PEI/ D ‐Glc‐1 hybrids. PEI/ D ‐Glc complexes were prepared from PEI/ D ‐Glc solutions of different pH values: a), b) pH 4.53; c), d) pH 3.50; e), f) pH 3.00 56. Copyright © 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.…”