A novel material of cross-linked styrylpyridinium salt intercalated montmorillonite for drug delivery
© Cui et al.; licensee Springer. 2014
Received: 17 April 2014
Accepted: 26 July 2014
Published: 3 August 2014
A facile synthesis of a styrylpyridinium salt (SbQ)/montmorillonite (MMT) via cationic exchange interactions between styrylpyridinium species (specifically SbQ) and MMT platelets is reported in this work. The SbQ-MMT solutions were irradiated under ultraviolet (UV) light for a specific time to obtain the cross-linked SbQ-MMT materials. Scanning electron microscopy and atomic force microscopy analyses revealed the structures and morphologies of MMT and modified MMT. X-ray diffraction and transmission electron microscope analyses indicated that the basal spacing increased from 1.24 to 1.53 nm compared with the pristine MMT, which proved that SbQ had interacted with MMT. Thermal gravimetric analysis curves showed that the amount of SbQ in the MMT interlayers was 35.71 meq/100 g. Fourier transform infrared spectroscopy also confirmed the intercalation of SbQ species into MMT interlayers, and UV spectroscopy was used to follow up the cross-linking of SbQ-MMT. This novel material has potential applications in drug delivery, and it can also be used as an additive to improve the mechanical properties of polymers.
KeywordsMontmorillonite Intercalation SbQ
SbQ (a styrylpyridinium salt), similar to surfactants, is an amphiphilic sensitizer of the styrylpyridinium family , and it produces a very planar stacked rod-like micelle structure. Such a structure makes it possible to stack the molecules with the hydrophobic regions one above the other, with the aldehyde and nitrogen-methyl groups alternating, and finally produces an aggregate . SbQ can react with amino groups of proteins to improve the protein stabilization . Moreover, it can be dimerized via the [2 + 2]-cycloaddition reaction under ultraviolet (UV) irradiation . According to Tao et al. , cross-linking of the hydrophobic core via dimerization reaction of the SbQ molecules induced by UV light ultimately produced cross-linked micelles because of hydrophobic interactions between SbQ molecules. Hence, the cross-linked SbQ-montmorillonite (MMT) has potential applications for hydrophobic drug delivery and can be used as an additive into polymeric composites and improve the stability and mechanical properties of polymers [6–9].
In recent years, modified MMTs have been extensively used as drug delivery carriers and for protein adsorption [10–13]. Banik et al. introduced soy flour (SF)-MMT nanoparticles cross-linked with glutaraldehyde (GA) as a carrier for isoniazid . Joshi et al. investigated the intercalation of timolol maleate (TM) into MMT as a sustained drug carrier . Sarıoğlan et al. studied the cationic pigment-intercalated MMT as the latent print development powder . Madurai et al. found an intestine-selective drug delivery system via the intercalation of captopril (CP) into the interlayers of MMT . MMT is one of the smectite group having two silica tetrahedral sheets layered between an alumia octahedral sheet. In nature, the charge imbalance in the structure is neutralized by adsorption of sodium or calcium ions in the interlayer, which makes intercalation possible by cation exchange with metallic/organic cations . MMT has attracted a great deal of attention in recent years for drug delivery applications due to its good physical and chemical properties .
In this work, a styrylpyridinium salt and MMT was used to prepare SbQ-MMT cross-linked hybrid materials by UV light irradiation. Since organic-inorganic hybrids prepared by the intercalation of organic species into layered inorganic solids contain properties of both the inorganic host and the organic guest in a single material, it is a useful and convenient route to prepare SbQ-MMT hybrids . The preparation process involved the following two steps: firstly, the cation of SbQ was exchanged with the sodium of MMT and the SbQ was intercalated into the interlayers of MMT. Secondly, the SbQ-MMT solution was irradiated under UV light to get the cross-linked hybrid materials. There were hydrophobic interactions between SbQ molecules via UV cross-linking . The aldehyde (−CHO) group of SbQ has a potential to interact with − NH2 groups of proteins and this interaction could be used for drug delivery applications. More importantly, after UV light irradiation, the cross-linked SbQ may have potential applications such as hydrophobic drug delivery , stimuli-responsive field [14, 15], and passivation layer .
1-Methyl-4-[2-(4-formylphenyl)-ethenyl]-pyridiniummethosulphate (SbQ) was purchased from Shanghai Guangyi Printing Equipment Technology Co. Ltd (Shanghai, China). Sodium montmorillonite (Na-MMT) was a kind gift from Zhejiang Fenghong Chemical Co. Ltd. (Huzhou, Zhejiang, China; the cation exchange capacity of the sodium MMT was 92 meq/100 g). Deionized water was used for the preparation of all solutions.
Synthesis of cross-linked SbQ-modified MMT
The shapes and surface morphologies of the samples were investigated by atomic force microscopy (AFM, Benyuan CSPM 4000, Shenzhen, China) with tapping mode under aqueous media and scanning electron microscopy (SEM, Hitachi SU1510; Hitachi Ltd., Beijing, China). To determine the particle size and size distribution, the AFM images were analyzed using the image analyzer software. XRD scans of the MMT and dried SbQ-MMT powder were obtained by X-ray diffraction patterns (XRD, MAC Science Co. Ltd. MXP 18 AHF, Yokohama, Japan) with Cu-Kα radiation and the results were confirmed by a transmission electron microscope (TEM, JEOL2010, Akishima-shi, Japan; Philips, Amsterdam, Netherlands). The intercalation of SbQ molecules in Na-MMT layers after cation exchange and UV irradiation were also examined by Fourier transform infrared spectroscopy (FTIR, Nicolet Nexus, Thermo Electron Corporation, Waltham, MA, USA) in the range 4,000 to 500 cm−1, using KBr-pressed method. The cross-linking of SbQ was followed by UV-vis spectroscopy.
The amount of SbQ intercalated in MMT was conducted by thermal gravimetric analysis (TGA, TGA/SDTA851e) at a heating rate of 10°C/min in a nitrogen flow.
In summary, SbQ was successfully intercalated into MMT via cationic exchange interactions and were irradiated under UV light to get the cross-linked SbQ-MMT. The present study was the first to our knowledge to use SbQ to intercalate into MMT layers. The results showed that the layered basal spacing of MMT was increased and the morphology of MMT was changed after the intercalation of SbQ. It was found that SbQ was cross-linked after UV irradiation as designed. The existence of aldehyde (−CHO) group, the hydrophobic character of cross-linked SbQ molecules and the natural properties of MMT make these novel materials to be potentially used in drug delivery or as an additive into polymeric composites to improve their mechanical properties.
JC, female, current master student, has a research direction of functional nanofibers. QW, male, professor, has a research field of functional nanofibers.
a styrylpyridinium salt
scanning electron microscopy
atomic force microscopy
transmission electron microscopy
thermal gravimetric analysis
Fourier transform infrared spectroscopy.
This research was financially supported by the National High-tech R&D Program of China (2012AA030313), National Natural Science Foundation of China (51006046, 51203064, 21201083 and 51163014), Changjiang Scholars and Innovative Research Team in University (IRT1135), the Priority Academic Program Development of Jiangsu Higher Education Institutions, Industry-Academia-Research Joint Innovation Fund of Jiangsu Province (BY2012068), Science and Technology Support Program of Jiangsu Province (SBE201201094), and the Innovation Program for Graduate Education in Jiangsu Province (CXZZ13_07).
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