Mesoporous silica as a carrier for topical application: the Trolox case study

As part of a recent research effort aimed at employing mesoporous materials for controlled drug delivery, this paper presents MCM-41 as a carrier for topical application, using Trolox as a model unstable guest molecule. The complexes between Trolox and MCM-41 were prepared by employing different inclusion procedures, varying solvent, method and pretreatment of the silica matrix. The objectives of this study were to determine Trolox loading, analyze its integrity and availability after immobilization on mesoporous silica, evaluate MCM-41 influence on Trolox photodegradation and establish whether the preparation method significantly influences complex properties. The characterization analyses (XRD, TGA, DSC and FTIR) confirmed the hydrogen-bonding interaction and Trolox structure preservation. Gas-volumetric analysis showed a consistent decrease in surface area and in pore volume and diameter with respect to bare MCM-41 indicating that Trolox was mainly located within mesopores. In vitro diffusion tests showed a slower release of Trolox after inclusion in the MCM-41 matrix; at the same time UV irradiation studies highlighted an increased photostability for the complex particularly in O/W emulsion. Moreover the radical scavenging activity of Trolox was maintained after immobilization. In all cases, differences were observed in all tested samples, suggesting that results could be optimized by modifying the inclusion procedure and by improving the guest loading.     

介孔分子筛孔道结构对药物巯甲丙脯酸释放性能的影响

以巯甲丙脯酸为药物模型, 研究了不同孔道结构的介孔分子筛载体的药物释放性能.     

MCM-41介孔分子筛共价键联钴酞菁的制备，表征及性质

采用两种方法将钴酞菁配合物共价联接到介孔分子筛MCM-41的表面：(1) 在MCM-41表面联接含伯胺的有机侧链；(2) 是在MCM-41表面联接含仲胺的有机侧链。含氯磺酸基的钴酞菁与胺反应形成磺酰胺。对得到的主客体化合物用多种物化手段和催化反应进行了表征。结果表明，钴酞菁以单体形式固定在介孔分子筛MCM-41的孔道壁上，在反应条件下固载后的钴酞菁具有高催化活性，同时表现出良好的稳定性，多次重复使用活性没有明显的改变。     

Amine decorated 2d hexagonal and 3d cubic mesoporous silica nanoparticles: A comprehensive dissolution kinetic study in simulated and biorelevant media

Highly ordered Bexarotene (BXR) encapsulated mesoporous silica nanoparticles in particular bare and amine functionalized MCM-41 and MCM-48 were designed employing a novel impregnation solvent evaporation strategy. The outcomes unveiled successful synthesis of mesoporous assembly having 2?D hexagonal and 3?D cubic framework for MCM-41 and MCM-48 respectively withholding large surface area, optimum pore size, pore volume along with uniform particle size distribution. Additionally, SXRD and TEM findings divulged retention of characteristic mesoporous features regardless of surface modification and drug incorporation. Eventually the release profile and release kinetics results in different dissolution media demonstrated complete drug release in simulated intestinal fluid (SIF) within 75?min and 45?min from BXR-41 and BXR-48 along with 3.33 and 5 fold increment in dissolution profile. Furthermore, lack of any interaction between gelatin of hard capsule shell and amine group in presence of enzyme were justified from the indistinguishable release pattern in enzyme free and enzyme enriched SIF media. The divergent release pattern in fed and fasted state condition having a higher release in former media strongly directs towards taking medicine after meal. Finally the release kinetics study exhibited Weibull and Higuchi model as a best fit models for bare and amine coated BXR nanoparticles respectively.     

Synthesis of pH-responsive mesoporous silica nanotubes for controlled release

A novel mesoporous silica tubes (MMT) which possessed pH-sensitive controlled release ability had been fabricated and synthesized by using carbon nanotubes (CNTs) as template. The sample replicated the morphologies of the CNTs successfully. The Brunauer–Emmett–Teller surface area of the materials can reach 1,017 m² g^?1 with the pore size of 3.8 nm. As a model drug, metformin HCl was applied to study the drug loading and control release ability of the materials. MMT possesses higher drug loading ratio (36 %) than that of MCM-41 (27.5 %). The release kinetics were studied in simulated gastric fluid (pH = 1.2) and in simulated proximal intestine fluid (pH = 7. 4), respectively. The result shows that the delivery systems exhibit well pH-sensitive control release ability and the as-synthesized materials have potential application in biomedical field.     

Effect of amine functionalization of spherical MCM-41 and SBA-15 on controlled drug release

MCM-41 and SBA-15 silica materials with spherical morphology and different particle sizes were synthesized and modified by post-synthesis method with 3-aminopropyltriethoxysilane (APTES). A comparative study of the adsorption and release of a model drug, ibuprofen, were carried out. The modified and drug loaded mesoporous materials were characterized by XRD, TEM, N₂ physisorption, thermal analysis, elemental analysis and FT-IR spectroscopy. Surface modification with amino groups resulted in high degree of ibuprofen loading and slow rate of release for MCM-41, whereas it was the opposite for SBA-15. The adsorbed drug content and the delivery rate can be predetermined by the choice of mesoporous material with the appropriate structural characteristics and surface functionality.     

Bright photoluminescent hybrid mesostructured silica nanoparticles

Bright photoluminescent mesostructured silica nanoparticles were synthesized by the incorporation of fluorescent cyanine dyes into the channels of MCM-41 mesoporous silica. Cyanine molecules were introduced into MCM-41 nanoparticles by physical adsorption and covalent grafting. Several photoluminescent nanoparticles with different organic loadings have been synthesized and characterized by X-ray powder diffraction, high resolution transmission electron microscopy and nitrogen physisorption porosimetry. A detailed photoluminescence study with the analysis of fluorescence lifetimes was carried out to elucidate the cyanine molecules distribution within the pores of MCM-41 nanoparticles and the influence of the encapsulation on the photoemission properties of the guests. The results show that highly stable photoluminescent hybrid materials with interesting potential applications as photoluminescent probes for diagnostics and imaging can be prepared by both methods.     

NSAID naproxen in mesoporous matrix MCM-41: drug uptake and release properties

Hexagonally ordered mesoporous silica material MCM-41 (S_BET?=?1090?m²/g, pore size?=?31.2 ?) was synthesized and modified by 3-aminopropyl ligands. The differences in an uptake and subsequent release of anti-inflammatory drug naproxen from unmodified and amino modified MCM-41 samples were studied. The prepared materials were characterized by high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM), nitrogen adsorption/desorption, Fourier-Transform Infrared Spectroscopy (FT-IR), Small-angle X-ray scattering (SAXS), thermoanalytical methods (TG/DTA) and elemental analysis. The amount of the drug released was monitored with thin layer chromatography (TLC) with densitometric detection in defined time intervals. The amounts of the released naproxen from mesoporous silica MCM-41/napro and amine-modified silica sample A-MCM-41/napro were 95 and 90% of naproxen after 72?h. In this study we compare the differences of release profiles from mesoporous silica MCM-41 and mesoporous silica SBA-15.     

Preparation, characterization and optical properties of lanthanum-(nanometer MCM-41) composite material

Nanometer MCM-41 molecular sieve was prepared under a base condition by using cetyltrimethylammonium bromide as template and tetraethyl orthosilicate as silica source by means of hydrothermal method. Lanthanum(III) was incorporated into the nanometer MCM-41 by a liquid phase grafting method. The prepared nanocomposite materials were characterized by means of powder X-ray diffraction, spectrophotometric anaylsis, Fourier transform infrared spectroscopy, low temperature nitrogen adsorption-desorption technique, solid diffuse reflectance absorption spectra and luminescence. The powder X-ray diffraction studies show that the nanometer MCM-41 molecular sieve is successfully prepared. The highly ordered mesoporous two-dimensional hexagonal channel structure and framework of the support MCM-41 is retained intact in the prepared composite material La-(nanometer MCM-41). The spectrophotometric anaylsis indicates that lanthanum exists in the prepared nanocomposite materials. The Fourier transform infrared spectra indicate that the framework of the MCM-41 molecular sieve still remains in the prepared nanocomposite materials and some framework vibration peaks show blue shifts relative to those of the MCM-41 molecular sieve. The low temperature nitrogen adsorption-desorption indicates that the guest locates in the channel of the molecular sieve. Compared with bulk lanthanum oxide, the guest in the channel of the molecular sieve has smaller particle size and shows a significant blue shift of optical absorption band in solid diffuse reflectance absorption spectra. The observed blue shift in the solid state diffuse reflectance absorption spectra of the lanthanum-(nanometer MCM-41) sample show the obvious stereoscopic confinement effect of the channel of the host on the guest, which further indicates the successful encapsulation of the guest in the host. The La-(nanometer MCM-41) sample shows luminescence.     

Construction of a pH-driven supramolecular nanovalve

[Structure: see text] The versatility of supramolecular chemistry has been exploited in constructing nanovalves based on mesoporous silica MCM-41 and the mutual recognition between secondary dialkylammonium ions and dibenzo[24]crown-8 (DB24C8). Naphthalene-containing dialkylammonium threads were tethered to the MCM-41, followed by loading with coumarin 460 and capping with DB24C8. Controlled release of coumarin 460 from the pores of MCM-41 was demonstrated using different bases. The rate of release of coumarin 460 from the nanovalves depends on the size of the base.     

疏水改性MCM-41对甲草胺缓释性能的影响

采用浸渍法将甲草胺吸附到纯硅MCM-41(M41)介孔材料中, 以六甲基二硅氮烷(HMDS)为表面改性剂, 通过气-固反应对吸附了甲草胺的M41材料(Ach/M41)进行疏水改性, 得到了既具有高载药性又能有效延缓甲草胺释放的缓释体系Ach/TMS-M41. XRD、低温N₂吸附/脱附、FT-IR和TG等分析结果表明, 甲草胺在M41中的吸附量高达0.381 g·g^-1(质量分数为27.6%), 此时M41仍保持原有的孔道结构, 且甲草胺能完全分散于M41孔道中. 分别对Ach/M41和Ach/TMS-M41在水中的缓释性能进行了测试, 甲草胺释放率分别为62%和38.1%, 表明疏水改性对延缓甲草胺释放有较好的效果. 而且, 介孔材料孔壁对甲草胺具有明显的紫外屏蔽保护作用.     

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH₂ (“C16-NH₂”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG _ads, of each chromatographed probe on the basis its specific retention volume. These ΔG _ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K _A) and donors (parameter: K _D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.     

Tailored doxycycline delivery from MCM-41-type silica carriers

Doxycycline, an antibiotic from the tetracycline class with a broad spectrum of activity, was used to prepare drug delivery systems based on pristine and functionalized mesostructured silica supports. MCM-41-type materials with different textural, structural, and surface properties were used to assess their influence on the drug release kinetics. Small- and wide-angle XRD, FTIR spectroscopy and N₂ adsorption/desorption isotherms were used to characterize the carriers before and after doxycycline loading. The drug release experiments were performed in vitro in 0.2 M phosphate buffer solution at 37 °C, and the slowest drug release kinetics was obtained for magnesium-modified MCM-41 carrier. All drug-loaded materials exhibited good antibacterial activity against Klebsiella pneumoniae ATCC 10031 strain, similar to the drug alone.     

H3PW12O40/MCM-41 nanoparticles as efficient and reusable solid acid catalyst for the synthesis of quinoxalines

The condensation reaction of 1,2-diketones and o-phenylenediamines was investigated in the presence of nano-sized mesoporous silica (MCM-41) supported 12-tungstophosphoric acid (TPA) as solid acid catalyst. Nano-sized MCM-41 was synthesized and the catalysts with different loading amounts of TPA (5–15 wt.%) were prepared and characterized by XRD, FT-IR and SEM techniques. The results confirm good dispersion of TPA on the solid support. The catalyst is reusable many times without loss in its activity.     

Synthesis of OMS Materials and Investigation of Their Acceptor–Donor Characteristics

Three ordered mesoporous siliceous (OMS) materials known as MCM41s—unmodified MCM-41C16 (“C16”), and two MCM41s with different surface functionalities: MCM-41C16-SH (“C16-SH”) and MCM-41C16-NH₂ (“C16-NH₂”)—were synthesized and studied by inverse gas chromatography in order to determine their acceptor–donor properties. The specific retention volumes of nonpolar and polar probes that were chromatographed on these ordered mesoporous silica adsorbents were evaluated under infinite dilution conditions. Two methods were employed to calculate the standard free energy of adsorption, ΔG _ads, of each chromatographed probe on the basis its specific retention volume. These ΔG _ads values were then employed to estimate the van der Waals contribution and the specific contribution of the free surface energy for each MCM41. DN values (donor numbers, based on the Gutmann scale) and AN* values (acceptor numbers, based on the Riddle–Fowkes scale) were employed to determine the values of parameters that characterize the ability of the MCM41s to act as electron acceptors (parameter: K _A) and donors (parameter: K _D). Considering the different compositions of the probes, each of which has different acceptor–donor properties, a new chromatographic test to supplement the Grob test is suggested.

     

Influence of the pore structure of MCM-41 and SBA-15 silica fibers on atomic layer chemical vapor deposition of cobalt carbonyl

Mesoporous high surface area MCM-41 and SBA-15 type silica materials with fibrous morphology were synthesized and used as support materials for the ALCVD (atomic layer chemical vapor deposition) preparation of Co/MCM-41 and Co/SBA-15 catalysts. Co/MCM-41 and Co/SBA-15 catalysts were prepared by deposition of Co2(CO)8 from the gas phase onto the surfaces of preheated support materials in a fluidized bed reactor. For both silica materials, two different kinds of preparation methods, direct deposition and a pulse deposition method, were used. Pure silica supports as well as supported cobalt catalysts were characterized by various spectroscopic (IR) and analytical (X-ray diffraction, Brunauer-Emmett-Teller, elemental analysis) methods. MCM-41 and SBA-15 fibers showed considerable ability to adsorb Co2(CO)8 from the gas phase. For MCM-41 and SBA-15 silicas, cobalt loadings of 13.7 and 12.1 wt % were obtained using the direct deposition method. The cobalt loadings increased to 23.0 and 20.7 wt % for MCM-41 and SBA-15 silicas, respectively, when the pulse deposition method was used. The reduction behavior of silica-supported cobalt catalysts was found to depend on the catalyst preparation method and on the mesoporous structure of the support material. Almost identical reduction properties of SBA-15-supported catalysts prepared by different deposition methods are explained by the structural properties of the mesoporous support and, in particular, by the chemical structure of the inner surfaces and walls of the mesopores. Pulse O2/H2 chemisorption experiments showed catalytically promising redox properties and surface stability of the prepared MCM-41- and SBA-15-supported cobalt catalysts.     

Thermogravimetry applied to characterization of fly ash-based MCM-41 mesoporous materials

The thermogravimetry (TG) was used for characterization of the fly ash (FA)-based MCM-41 mesoporous materials. MCM-41 mesoporous materials were synthesized using silica extracts from different FA. The synthesis of MCM-41 from FA was carried out by the hydrothermal method using the supernatants of coal FA (in the form of sodium silicate) and cationic cetyltrimethylammonium bromide (CTAB) surfactants as the structure-directing agents. On the basis of the data obtained from the TG analysis, thermal behaviour of FA-based MCM-41 mesoporous materials was assessed. This study has established the range of temperatures corresponding to the desorption of water, decomposition of the surfactant and condensation of silanol, thereby making the overall quality assessment of FA-based MCM-41 mesoporous materials.     

Synthesis and characterization of MCM-41@XA@Ni(II) as versatile and heterogeneous catalyst for efficient oxidation of sulfides and acetylation of alcohols under solvent-free conditions

Herein, Ni(II) immobilized on modified mesoporous silica MCM-41 was designed and synthesized via a facile sequential strategy. The structure of the catalyst was characterized by X-ray diffraction. The thermal property of the as-synthesized materials was studied using thermogravimetric-differential thermal analysis. The average particles size and morphology of MCM-41@XA@Ni(II) were investigated using scanning electron microscopy and transmission electron microscopy. This nanostructure catalyst was effective for the selective oxidation of sulfides and acetylation of alcohols in solvent-free conditions. The easy recyclability of the catalyst and their complete chemoselectivity toward the sulfur group of substrates in the oxidation of sulfides are important “green” attributes of this catalyst.     

A novel pH-responsive controlled release system based on mesoporous silica coated with hydroxyapatite

With well bioactive and nontoxic, hydroxyapatite (HAp) was employed to seal the nanopores of mesoporous silica (MCM-41) to realize the pH-responsive controlled release. First, MCM-41 was modified with cationic polymer, poly-(diallyldimethylammoniumchloride) (PA). And after the addition of Ca²⁺/PO₄ ^3?, HAp precipitation can take place based on the cationic sites derived from PA. It is a simple and effective way to obtain HAp coating MCM-41 system (MHAs). The structure of the system was characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, N₂ adsorption–desorption and so on. Metformin hydrochloride was used as the model drug, and the drug release performance and the release kinetics of the system were investigated in detail. Because of the degradation of HAp under acid condition, the drug loading MHAs showed a well pH-sensitive controlled release behavior. From above investigation, MHAs is a promising platform to construct a pH-responsive controlled drug delivery system, especially for some low pH tissues, such as inflammatory and tumor.     

Preparation and Optical Properties of (Nanometer MCM-41)-CdS Composite Materials

The nanometer and micrometer molecular sieves MCM-41 were prepared by a hydrothermal method. Cadmium (II) was exchanged into the molecular sieves by ion-exchange, and thioacetamide was then used as a precursor of hydrogen sulfide for sulphidizing the (MCM-41)-cadmium samples to prepare the host-guest composite materials (MCM-41)-CdS. By means of chemical analysis, powder X-ray diffraction, infrared spectroscopy, low temperature nitrogen adsorption-desorption technique, solid state diffuse reflectance absorption spectroscopy and luminescence, the prepared materials were characterized. The chemical analysis shows that the guest is successfully trapped in the molecular sieves. The powder X-ray diffraction suggests that the frameworks of the molecular sieves in the prepared host-guest composite materials are retained during the preparative process. They are intact and the degrees of crystallinity are still very high. The infrared spectra show that the frameworks of the prepared host-guest materials keep intact. The low temperature nitrogen adsorption-desorption studies indicate that the pore volumes, the pore sizes and the surface areas of the prepared composite materials decrease relative to those of the MCM-41 molecular sieve hosts. This shows that the guests are successfully encapsulated in the channels of the molecular sieves. The solid state diffuse reflectance absorption spectra of the prepared host-guest composites show some blue-shifts relative to that of bulk cadmium sulfide, indicating that the guests are trapped in the channels of the molecular sieves. This shows the obvious stereoscopic confinement effect of the molecular sieve host on the nanometer cadmium sulfide guest. The (nanometer MCM-41)-CdS and (micrometer MCM-41)-CdS samples show obvious luminescence.