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.     

Selective separation of Th(IV) from its solutions using amine modified silica gel produced from leached zircon

A solution of sodium silicate produced as a waste from the alkali fusion of Egyptian Rosetta zircon mineral was used for preparation of a silica gel in the pH range 6–7. A silica gel modified with tetraethylenepentamine (TEP) and diethylenetriamine (DET) functionalities were prepared. The success of immobilization process was confirmed by means of FT-IR, energy dispersive X-ray spectrometric analysis (EDX) and elemental analysis. The surface properties of the modified silica obtained were investigated by means of nitrogen surface area. The uptake behaviour of the modified silica towards Th(IV) ions at different experimental conditions of pH, time, concentration and temperature using batch method was studied. Kinetics and thermodynamics studies showed an endothermic pseudo-second order adsorption process. Regeneration of the loaded silica was performed using 1 M HNO₃. The investigated silicas have successfully been applied for separating of Th(IV) from U(VI) in nitric acid solution obtained from alkaline leaching of Egyptian monazite sand.     

Surface modification to improve the sorption property of U(VI) on mesoporous silica

Polyoxometalates K₇[α-PW₁₁O₃₉]·14H₂O (PW11) modified mesoporous silica (MCM-48) with cubic structure, was prepared by impregnation and calcination methods. The modified mesoporous silica sorbent (PW11/MCM-48) was studied as a potential adsorbent for U(VI) from aqueous solutions. MCM-48 and PW11/MCM-48 were confirmed by X-ray diffraction and nitrogen physisorption techniques. The results indicate the original keggin structure of PW11 and mesoporous structure of MCM-48 are maintained after supporting PW11 on mesoporous silica MCM-48. The effects of contact time, solid-to-liquid ratio (m/V), solution pH and ionic strength on U(VI) sorption behaviors of the pure and modified mesoporous silicas were also studied. Typical sorption isotherms such as Langmuir and Freundlich isotherms were determined for sorption process. The results suggest that the sorption of U(VI) on MCM-48 or PW11/MCM-48 are strongly dependent on pH values but independent of ionic strength. The sorption capacity of PW11/MCM-48 for U(VI) is about ten times more than that of MCM-48.     

Functionalized bimodal mesoporous silicas as carriers for controlled aspirin delivery

The bimodal mesoporous silica modified with 3-aminopropyltriethoxysilane was performed as the aspirin carrier. The samples’ structure, drug loading and release profiles were characterized with X-ray diffraction, scanning electron microscopy, N₂ adsorption and desorption, Fourier transform infrared spectroscopy, TG analysis, elemental analysis and UV-spectrophotometer. For further exploring the effects of the bimodal mesopores on the drug delivery behavior, the unimodal mesoporous material MCM-41 was also modified as the aspirin carrier. Meantime, Korsmeyer-Peppas equation f_t=ktⁿ was employed to analyze the dissolution data in details. It is indicated that the bimodal mesopores are beneficial for unrestricted drug molecules diffusing and therefore lead to a higher loading and faster releasing than that of MCM-41. The results show that the aspirin delivery properties are influenced considerably by the mesoporous matrix, whereas the large pore of bimodal mesoporous silica is the key point for the improved controlled-release properties.     

Tailoring pore properties of MCM-48 silica for selective adsorption of CO2

Four different types of amine-attached MCM-48 silicas were prepared and investigated for CO(2) separation from N(2). Monomeric and polymeric hindered and unhindered amines were attached to the pore surface of the MCM-48 silica and characterized with respect to their CO(2) sorption properties. The pore structures and amino group content in these modified silicas were investigated by XRD, FT-IR, TGA, N(2) adsorption/desorption at 77 K and CHN/Si analysis, which confirmed that in all cases the amino groups were attached to the pore surface of MCM-48 at 1.5-5.2 mmol/g. The N(2) adsorption/desorption analysis showed a considerable decrease of the pore volume and surface area for the MCM-48 silica containing a polymeric amine (e.g., polyethyleneimine). The CO(2) adsorption rates and capacities of the amine-attached MCM-48 samples were studied employing a sorption microbalance. The results obtained indicated that in addition to the concentration of surface-attached amino groups, specific interactions between CO(2) and the surface amino groups, and the resultant pore structure after amine group attachment have a significant impact on CO(2) adsorption properties of these promising adsorbent materials.     

Thermogravimetric studies of benzoylthiourea-modified MCM-41 after adsorption of mercury ions from aqueous solutions

High-resolution thermogravimetry (HR TG) was used to study the adsorption of mercury(II) ions by modified MCM-41 material and regeneration of the loaded adsorbent with mercury ions by using different eluents. The weight change curves were measured for MCM-41 samples modified with 1-benzoyl-3-propylthiourea ligand loaded with mercury ions. The differential thermogravimetric (DTG) curves were analyzed to investigate the adsorption of mercury ions by the aforementioned multifunctional ligand and to monitor the decomposition of the metal-ligand complexes. A series of experiments performed for different Hg(2+):ligand ratios allowed us to correlate the adsorption data for mercury ions measured by means of UV spectrophotometry with those obtained by HR TG analysis. The DTG results provided additional information about mercury-ligand interactions as well as the thermal stability of mercury-ligand complexes. This study shows that HR TG is a very attractive technique for studying the adsorption of mercury ions on modified nanoporous silicas and monitoring their regeneration. Since the samples used are small, this method seems to be promising for studying adsorption systems of environmental significance.     

Nanoporous silica films containing aluminum and titanium

By utilizing surfactant aggregates as supramolecular templates, mesoporous and mesostructured silicas with highly ordered structures became available. The resulting mesoporous silicas are promising candidates to host various photo- and electro-active species along with catalytically active species, due to their large and controllable pore sizes, highly ordered pore arrangements with low dimensional geometries, and reactive surfaces. We have developed the rapid solvent evaporation method, which is a modified sol-gel process, for synthesizing the mesostructured silica-surfactant films as well as the mesoporous silica films. Supported thin films, self-standing films and bubbles of mesoporous silicas have been synthesized by the rapid solvent evaporation method. The microstructures of the films have also been successfully controlled by changing the synthetic conditions. Taking advantage of the ease of synthetic operation and the transparency and homogeneity of the resulting materials, we have been interested in the introduction of functional units into the mesostructured materials. This paper reports the synthesis of transparent films of titanium- and aluminum-containing nanoporous silicas to modify the surface properties (such as adsorptive and catalytic) of nanoporous silicas. The incorporation of Al led to the formation of cation exchange or acidic sites on the mesopore surface, as revealed by the cationic dye adsorption experiments. The photocatalytic reactions of the Ti-containing nanoporous silica films were also examined.     

Novel modified nanoporous silica for oral drug delivery: loading and release of clarithromycin

Nanoporous silica SBA-15 was prepared to evaluate its application as an oral drug delivery system. A series of surface-functionalized nanopore materials as efficient clarithromycin delivery carriers was investigated. An efficient pH-responsive carrier system was constructed by hydrogen bond interaction between carboxyl and hydroxyl groups in the clarithromycin and the amine group in modified SBA-15. HPLC analyses of clarithromycin were run on a C₁₈ column using a mobile phase comprised of potassium dihydrogen phosphate, acetonitrile and methanol (30:40:30, v/v/v). Active molecules such as clarithromycin could be stored and released from the pore voids of SBA-15 by changing the pH. The amount of clarithromycin stored in the pores of nanoporous silica based on TREN [tris(2-aminoethyl) amine]-modified SBA-15 rods was up to 46 ± 4.8 wt% at pH 8. In addition, when the pH was below 4, clarithromycin was steadily released from the pores of SBA-15 (up to 97 wt% in simulated gastric medium).     

Silica from rice husks employed as drug delivery for folic acid

Silica was obtained from rice husk, this type of silica is also known as SiO₂-rice, was investigated as drug delivery for the folic acid. The SiO₂-rice was obtained from calcinations at 600 °C and its textural properties were compared with mesoporous silica (MS). The maximum folic acid adsorption on SiO₂-rice was at the 18 % weight, while MS adsorbs 19 % weight. An important pH effect on the drug released was observed; both silicas released around 35 % of acid folic at pH 7, while at pH 3 only 3 % of the drug was released. Differential Thermal Analyzer analysis suggests that the folic acid was not crystallized into the porous of the silica; therefore, it is possible that the drug was trapped within the complex network of pores preventing their full release. However, the drug released for 400 μg of folic acid, a commercial dose, indicated that until 93 % of drug could be released for the silicas at pH of 5.5; a minor desorption was observed by commercial tablet.     

Immobilization of Keggin and Preyssler tungsten heteropolyacids on various functionalized silica

The Keggin and Preyssler tungsten heteropolyacids, H3PW12O40 and H15P5W30O110, have been immobilized on the inner surface of mesoporous MCM-41, fume silica and silica-gel by means of chemical bonding to aminosilane groups. The materials were characterized by FT-IR spectroscopy, low-angle XRD and BET surface area analysis. The tendencies of heteropolyacids adsorption in solution on functionalized silicas have been investigated by UV-vis. Among the functionalized silica materials, MCM-41 showed the largest amine to silica and the least heteropolyacid to silica ratios. The BET surface area revealed that in all three cases the surface area decreased after grafting amine group and anchoring of the HPAs clusters. Low-angle XRD analysis showed that by introducing HPA into functionalized MCM-41 the intensity of the main reflection decreased significantly.     

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.     

Effect of pseudohalogen groups on the optical properties and the structures of diorganotin coordination compounds based on the flexible ligand 1,2,3,4‐tetra‐(4‐pyridyl)‐butane

To investigate the effect of pseudo‐halogen groups on the structure and optical properties of diorganotin(IV) coordination compounds the reaction of dimethyltin diisothiocyanate and dimethyltin dichloride with 1,2,3,4‐tetra‐ (4‐pyridyl)‐butane (TPB) were studied. The results of spectroscopic data and structural analyses of prepared compounds showed that the reaction of Me₂SnCl₂ with TPB ligand leads to the formation of a 2D organotin(IV) coordination polymer, while the replacement of chloride ions with thiocyanate ions as pseudohalogen groups in the structure of Me₂SnCl₂ results in the development of a salt with an anion complex and a dimeric stannoxane as a side product. The results showed that the use of pseudo‐halogen groups instead of halogen groups in the structure of diorganotin(IV) dihalogen compounds could be as a suitable factor in the control of the structure of diorganotin(IV) coordination compounds. The investigation of optical properties of prepared compounds demonstrated that the use of pseudo‐halogen groups in the structure of diorganotin(IV) coordination compounds have an influence on their photoluminescence behavior.     

Comparison of novel pyridine-functionalized mesoporous silicas for Au(III) extraction from natural samples

A technique for solid-phase extraction utilizing pyridine-functionalized nanoporous silica (MCM-41, MCM-48 and SBA-15) was developed for the determination of gold in different samples using flame atomic absorption spectrometry. The effects of concentration and volume of eluent, pH of the solution, flow rate of extraction, sample volume and of potentially interfering ions on the efficiency of preconcentration and recovery was investigated. The limit of detection is lower than 45 pg mL^?1. Under optimal conditions, the accuracy and precision (RSD%) of the method were calculated to be >99.5% and <0.7% for the two MCMs (41 and 48) and >89.5%, and <1.5% for SBA-15, respectively. The SPE technique was used to determine the concentration of gold in natural and industrial wastewater with satisfactory results.

Modification of MCM-48-, SBA-15-, MCF-, and MSU-type mesoporous silicas with transition metal oxides using the molecular designed dispersion method

Four various mesoporous silicas (MCM-48, SBA-15, MCF, and MSU) were modified by the molecular designed dispersion method using Fe(acac)3, Cr(acac)3, and Cu(acac)2 complexes. The deposition was performed at the same concentration of the metal acetylacetonate (acac) complex in a toluene solution. All as-synthesized samples were investigated by diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared photoacoustic spectroscopy, and thermogravimetric analysis. The calcined materials were studied with respect to their textural properties (Brunauer-Emmett-Teller adsorption isotherm) and chemical composition (electron microprobe analysis). It allowed elucidation of the mechanism of interaction between the acac complex and the silanol groups. For the MCM-48, SBA-15, and MCF materials, the formation of hydrogen bonding was found for the chromium- and copper-modified samples, whereas the Fe-containing materials showed the ligand exchange mechanism. The strong interaction of the MSU support and the different acetylacetonate complexes, resulting in a loss of at least one acac ligand, was observed. The mesoporous silicas modified with transition metal oxides were studied by UV-vis-DR spectroscopy. The different metal dispersions were found for the samples containing various transition metal oxides.     

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.     

Evaluation of Stability of Mesoporous Silica Nanoparticles and Their Further Formulation in Tablet Form

Mesoporous silica nanoparticles have been widely investigated as drug delivery systems. The present study evaluated physical stability of indomethacin loaded mesoporous MCM-41 nanoparticles. The size, polydispersity index, zeta-potential, and drug loading degree of nanoparticles were determined immediately after their preparation and after 6 months storage at 25°C in dry state. The results showed insignificant changes in these parameters, suggesting high stability of nanoparticles and loaded indomethacin. The nanoparticles were formulated in tablets by direct compression. The low friability indicated good resistance during handling and storage. The formulation of the nanoparticles into tablets decreased the initial release of indomethacin.     

Adsorption of diazinon and fenitothion on MCM-41 and MCM-48 mesoporous silicas from non-polar solvent

The adsorption of two common organophosphorus pesticides, diethoxy-[(2-isopropyl-6-methyl-4-pyrimidinyl)oxy]-thioxophosphorane (diazinon) and dimethoxy-(3-methyl-4-nitrophenoxy)-thioxophosphorane (fenitrothion), by MCM-41 and MCM-48 mesoporous silicas at room temperature was investigated. UVvis and IR spectroscopy, small-angle X-ray diffraction, and the specific surface area analysis (S _BET) were used to study the adsorption behavior of diazinon and fenitrothion. The results show that the MCM-41 and MCM-48 mesoporous silicas adsorb diazinon more efficiently than fenitrothion. The extraction of adsorbed materials from the adsorbents with polar solvents and subsequent analysis by ³¹P NMR showed that the adsorption of diazinon and fenitrothion on mesoporous silicas is destructive and non-destructive, respectively. Nitrogen adsorption measurements showed that the specific surface area of both silicas decreases after the adsorption of pesticides, and the larger effect is observed for diazinon. The article is published in the original.     

锌锡双金属掺杂MCM-41的合成及表征

以硅酸钠为硅源, 锡酸钠，硝酸锌为金属源，十六烷基三甲基溴化铵为模板剂，采用直接水热合成法合成出了锌锡双金属同时掺杂的介孔MCM-41。通过ICP﹑XRD、TG-DTA﹑FTIR﹑HRTEM以及BET等技术对材料的结构和性质进行了表征。结果表明，合成的材料具有典型的六方介孔结构，比表面高，孔分布窄，热稳定性较高，且锌锡可能进入介孔MCM-41骨架中。该材料对苯酚羟基化反应具有良好的催化性能，双金属修饰MCM-41催化活性明显优于单组分掺杂。     

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.     

Structural and conformational analysis of neutral dinuclear diorganotin(IV) complexes derived from hexadentate Schiff base ligands

The synthesis of three hexadentate Schiff base ligands has been carried out, which contain two sets of ONO donor atoms. These were reacted with diorganotin(IV) dichloride derivatives (R = Me, nBu, Ph) to prepare seven dinuclear diorganotin(IV) complexes in moderate yields. Aside from IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopic studies, mass spectrometry and elemental analysis, four tin complexes were characterized by X-ray diffraction analysis. The spectroscopic analyses showed that in solution the tin atoms have five-coordinate environments with a distorted trigonal bipyramidal geometry. Each tin atom is coordinated to the nitrogen atom and forms covalent bonds with two oxygen atoms and two carbon atoms. Due to the presence of a methylene group as bridge between the two ONO chelates, the overall molecular structures can have cis or trans conformation, having either mirror or C₂-symmetry. While in solution a fast equilibrium can be supposed, in the solid state different intermediate conformations have been detected. Furthermore, for the dialkyltin derivatives Sn?O intermolecular interactions were found allowing for a dimeric or crinkled polymeric organization, whereas for the diphenyltin derivatives no such interactions were observed.