Chiral Mesoporous Silicas Research Articles

Design of chiral mesoporous silica nanorods using ursodeoxycholic acid/chenodeoxycholic acid and CTAB as templates for chiral-selective release of achiral drugs

Twisted rod-like structured chiral mesoporous silicas (CMSs) have been firstly synthesized with the novel template systems from ursodeoxycholic acid (UDCA)/chenodeoxycholic acid (CDCA) and CTAB. CMSs were characterized by various instrumental techniques, demonstrating highly ordered hexagonal mesoscopic phase and twisted rod-like morphology. Induced circular dichroism (ICD) indicated the preferential optical activity of the CMSs with involving phenol as a probe. Besides, CMSs exhibited chiral-selective delivery of achiral drug indometacin (IMC) and nimesulide (NMS) in simulated chiral environment. We believe that the novel synthesized CMSs were expected to be desirable carriers for drug delivery in the pharmaceutical field to extend the applications of inorganic nanomaterials.

Chiral mesoporous silica based LOFL delivery systems using achiral alcohols as co-structure-directing agents: Construction, characterization, sustained release and antibacterial activity

The present work reported two synthesized chiral mesoporous silicas (CMSs) with opposite chirality for loading, release, and antibacterial activities of levofloxacin (LOFL). Herein, helical CMS nanorods were prepared by the sol-gel method using CTAB as a template and either n-heptanol or n-nonanol as a co-structure-directing agent (CSDA). The synthesized CMSs were characterised by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), induced circular dichroism (ICD), and nitrogen adsorption/desorption. X-ray diffraction (XRD) was applied to confirm amorphous state transformation after drug loading, and thermal gravimetric analysis (TGA) was used to quantify the LOFL loading capacity. In vitro drug release studies from the loaded CMSs showed significant differences in the release behaviour for LOFL. Moreover, LOFL-loaded CMSs significantly sustained LOFL release with Fickian diffusion mechanism. Both the drug-loaded CMSs inhibited bacterial growth successfully when tested with strains of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Therefore, the prepared CMSs could find application as suitable vehicles for drug delivery systems to exert the therapeutic effects of LOFL and achieve different release behaviours.

Design and preparation of mesoporous silica carriers with chiral structures for drug release differentiation

In this study, twisted rod-like chiral mesoporous silicas (CMSs) with discriminating chiral characteristics (D/L) were designed and biomimetic synthesized by using L- and d-alanine derivatives as templates, and employed as poorly water-soluble chiral drug ibuprofen (IBU) carriers. The morphology and mesoscopic characteristics of CMSs were determined by transmission electron microscope (TEM) and small-angle X-ray scattering (SAXS). Meanwhile, the physicochemical properties of CMSs before and after drug loading were systematically characterized by infrared spectroscopy (IR), nitrogen adsorption, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and induced circular dichroism (ICD). The results suggested that, the CMSs exhibited local chiral characteristics, which were successfully endowed by the alanine-derivative surfactants templates with a reversal of chirality. The crystalline state of IBU was effectively converted to amorphous state after being incorporated into CMSs, and the drug delivery systems shared the chiral characteristic of carriers. Besides, in vitro drug release experiments were respectively performed in simulated gastric fluid (SGF, pH 1) and simulated intestinal fluid (SIF, pH 6.8) medium, and the results demonstrated that both l-CMS and d-CMS could improve the dissolution of IBU in SGF medium, which could be explained by the amorphization of IBU. Particularly, due to the different pore geometry of these two materials, CMSs with different chirality (D/L) could be applied as carriers to accomplish drug release differentiation.

Synthesis of chiral mesoporous silicas with oligo(saccharide) surfaces and their use in separation of stereoisomers

Novel chiral mesoporous silicas (SBA-15 motif) with chemically bonded oligo(saccharides) (1, 3, and 7 glucose units) were obtained through the cocondensation of organosilicon derivatives of the oligo(saccharides) and silica precursors in the presence of polymer surfactant template under mild acidic conditions. The pore order and structure of the materials prepared were characterized by transmission electron microscopy and nitrogen adsorption. The direct application of the oligo(saccharide)-grafted SBA-15 stationary phases in the HPLC separations of stereoisomers was demonstrated for the first time.

Chiral mesoporous silica synthesized with the presence of different anionic acids

We report that chiral mesoporous silicas (CMSs) with highly ordered helical nano-sized channels were successfully synthesized by using chiral anionic amphiphilic molecules ( N-acyl- l-alanine) as template upon a co-structural-directing-agent (CSDA) method. The effect of anionic in the solution on the pore size, mesostructure and morphology of the CMSs has been studied in details. We observed that: (1) in different inorganic acids reaction system, chiral mesoporous silica materials were achieved; (2) the pore size at a range of 2.40–2.95 can be adjusted by changing the species of inorganic acids in reaction system; (3) the pitch length and rod diameter maintained a linear relationship, as the acids changed from HCl, HBr and HNO 3 to H 2SO 4.

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

Chiral mesoporous silica (CMS) has been successfully synthesized in the presence of basic amino acids; the use of basic amino acids in combination with the chiral anionic surfactant is advantageous for the formation of CMS in terms of uniformity in the twisted morphology. We first demonstrate that thus obtained chiral mesoporous silicas can be used for the enantioselective separation of racemic compounds; the helical rod-shaped CMS is found to be capable of asymmetric separation of racemic N-trifluoroacetylalanine ethyl ester (CF3CO-Ala-OEt). The left handedness-rich CMS shows asymmetric preferential adsorption of the L isomer and vice versa.

Understanding the Mechanism of Chirality Transfer in the Formation of a Chiral MCM-41 Mesoporous Silica

Recently, a series of chiral mesoporous silicas with various pore sizes and nanostructures (including chiral MCM-41, chiral SBA-15, and chiral SBA-16) have been successfully synthesized in our group by using achiral templates and a chiral cobalt complex as cotemplate. Enantioselective discrimination ability of these chiral materials was observed when they were applied on the controlled release of a chiral drug. The enantioselectivity of these silica materials was attributed to the local chirality at a molecular level on the pore wall surfaces. Nevertheless, the formation mechanism of local chirality, i.e., the chirality transferring from chiral cobalt complex to inorganic mesoporous silica matrix, remains indeterminate at this juncture. In this report, by tuning the synthesis parameters based on the previously reported method, chiral MCM-41 with left-handed enantiomeric excess in twisted hexagonal particle morphology was obtained. Enantioselective adsorption of racemic valine corroborated the general chir...

Supramolecular Chiral Transcription and Recognition by Mesoporous Silica Prepared by Chiral Imprinting of a Helical Micelle

Let's twist again: The chirality of a helical propeller-like micelle has been memorized by functional groups on the mesopore surface of chiral mesoporous silicas. Such imprinted supramolecular chirality can be transcripted to poly(propiolic acid) sodium salt and tetraphenylporphine tetrasulfonic acid (see picture), and recognized by B-DNA.

Synthesis of chiral mesoporous silica by using chiral anionic surfactants

Recently, the use of a chiral anionic surfactant derived from amino acid, N-myristoyl- l-alanine sodium salt, has enabled us to obtain a chiral mesoporous silica. In this study, chiral mesoporous silicas with helical particles were successfully synthesized by using the chiral anionic surfactants N-miristoyl- d-alanine as well as N-miristoyl- l-alanine. The left-/right-handed ratios for the helical particles synthesized with C 14- l-AlaA and C 14- d-AlaA proved to be 75/25 and 25/75, respectively, suggesting that the predominant handedness of helices was directed by the handedness of the surfactants. The optimization of the synthesis conditions for obtaining a chiral mesoporous silica were conducted. We found that the macroscopic morphology as well as the mesostructure of the chiral mesoporous silica was extremely sensitive to the synthetic conditions. The influence of the stereoisomerism of the chiral surfactant on the mesostructure and morphology of chiral AMS was investigated by using a mixture of C 14- l-AlaA and C 14- d-AlaA.

Factors affecting the efficiency of hybrid chiral mesoporous silicas used as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

Chiral hybrid organic–inorganic materials were prepared by anchoring optically active β-aminoalcohols such as (−)-ephedrine on MCM-41 type silica as a member of micelle-templated silicas (MTS). Silylation of the surface was performed with halogenopropyltrimethoxysilane. Then, (−)-ephedrine was anchored through halogen substitution. These materials were used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the various factors such as accessibility to the catalytic sites and coverage of the inorganic surface, which affect their efficiency (activity, selectivity and enantioselectivity).

Chiral mesoporous templated silicas as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

New mesoporous templated silicas of the MCM-41 family covalently linked to chiral ephedrine are used as heterogeneous chiral auxiliaries in the enantioselective alkylation of benzaldehyde by diethylzinc. Promising results are obtained with these inorganic–organic catalysts. Various factors which may affect the activity, selectivity and enantioselectivity are studied. Comparison with homogeneous catalysis is carried out.