Synthesis of chiral mesoporous silica and its potential application to asymmetric separation

Recent advances of optically active helical polymers as adsorbents and chiral stationary phases for chiral resolution

Chiral resolution is very important and still a big challenge due to different biological activity and same physicochemical property of one pair (R)- and (S)-isomer. There is no doubt that chiral selectors are essentially needed for chiral resolution, which can stereoselectively interact with a pair of isomers. To date, a large amount of optically active helical polymers as chiral selectors have been synthesized via two strategies. First, the target helical polymers are derived from natural polysaccharide such as cellulose and amylose. Second, they can be synthesized by polymerization of chiral monomers. Alternatively, an achiral polymer is prepared first followed by static or dynamic chiral induction. Furthermore, a part of them is harnessed as chiral stationary phases for chromatographic chiral separation and as chiral adsorbents for enantioselective adsorption/crystallization, resulting in good enantioseparation efficiency. In summary, the present review will focus on recent progress of the polymers with optical activity for chiral resolution, especially the literature published in the past 10 years. In addition, development prospects and future challenges of optically active helical polymers will be discussed in detail.

Chiral mesoporous silica synthesized by a facile strategy for loading and releasing poorly water-soluble drug

Most of the mesoporous chiral mesoporous silica (CMS) was synthesized by the chiral surfactant-directing method. In this study, a facile method was designed to synthesize CMS. In this method, achiral amphiphile was used as templating agents, and dilute ammonia solution was applied to induce the chirality of the CMS. Meanwhile, its morphology can be controlled by changing the concentration of the aqueous ammonia solution. The obtained CMS was characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The results showed that all of the CMS possessed highly ordered mesostructures, and as the concentration of ammonia decreases, the chirality of the CMS becomes more obvious. Water-insoluble drug curcumin (Cur) was used as a model drug. The characteristics of CMS before and after drug loading were further detected by Fourier transform infrared spectrometer (FT-IR), N₂ adsorption-desorption and differential scanning calorimetry (DSC). The result showed that Cur was successfully loaded inside the pores of the CMS and remained an amorphous state due to steric inhibition. Additionally, CMS could significantly increase the release rate of Cur under different pH conditions.

Chirality induction on non-chiral dye-linked polysilsesquioxane in nanohelical structures

Chirally arranged organic dye-linked polysilsesquioxane was prepared, through a sol–gel transcription using its non-chiral precursor with a chiral supramolecular template, and its chiroptical properties were investigated.

Imprinting of Stöber particles for chirally-resolved adsorption of target monosaccharides and disaccharides

Soft imprinting of silica particles using sugar surfactants targets chirally resolved binding of saccharides.

Direct Observation of Siloxane Chirality on Twisted and Helical Nanometric Amorphous Silica

Synthesis of chiral inorganic or hybrid nanomaterials through sol-gel transcription of chiral organic templates has attracted a great deal of interest for more than a decade. However, the chiral nature of these inorganic matrices has never been directly observed. For the first time, we report a direct evaluation of chirality on noncrystalline silica chiral nanoribbons by vibrational circular dichroism (VCD) measurements. Strong Cotton effect around 1150-1000 cm^-1 from Si-O-Si asymmetric stretching vibration was observed. Surprisingly, calcination of these hybrid nanoribbons doubled the intensity of Cotton effects. On the basis of transmission electron microscopy observations, IR, VCD, NMR, and Raman spectroscopies, we demonstrate that the silica chirality originates from twisted siloxane network composed of chiral arrangement of the Si-O-Si bonds. Our findings clearly prove the presence of chiral organization of amorphous silica network, making them very promising chiral platforms for chiral recognition, optical applications, or asymmetric catalysis.

Helical mesoporous silica as an inorganic heterogeneous chiral trigger for asymmetric autocatalysis with amplification of enantiomeric excess

P and M-Helical mesoporous silica was found to act as a chiral inorganic trigger for asymmetric autocatalysis to afford (S) and (R)-pyrimidyl alkanol with up to >99.5% ee, respectively.