Polymorphic transformation of indomethacin in precirol solid dispersion system

The polymorphic transformation of indomethacin (IMC) in the presence of Precirol during heating was investigated by differential scanning calorimetry (DSC), infrared (IR) spectroscopy, microscopic Fourier transform infrared (FT-IR)/DSC system, and powder X-ray diffractometry with heating. The results indicate that in the presence of Precirol the original γ form of IMC was first transformed to a transition state, and then to a new polymorph by heating or exposure to IR radiation. The transition state of the melted sample gave three endothermic peaks, at 34, 48 and 127°C, and one exothermic peak, at 54°C. The stable melted sample exhibited two endothermic peaks, at 58 and 127°C, which were due to the fusion of Precirol and the new polymorph of IMC, respectively. This new polymorph of IMC also exhibited two specific IR absorption peaks, at 1693 and 1675 cm^?1. Microscopic FT-IR/DSC was used to examine the correlation between the structural transformation and its thermal response, and demonstrated the existence of the transition state of the melted sample. X-ray diffractometry with heating confirmed the appearance of the new polymorph of IMC in the presence of Precirol after heating.     

Chemical functionalization of silica and alumina particles for dispersion in carbon dioxide

The steric stabilization and flocculation of modified silica and alumina particle suspensions in condensed CO(2) were studied. Silica particles (average diameters of 7 and 12 nm) were functionalized using chlorosilanes of the form C(n)F(2n+1)CH(2)CH(2)Si(CH(3))(2)Cl (n = 8, 4, or 1) to give C(n)F(2n+1)-silica. Alumina particles (diameter of 8-14 nm) were grafted with C(8)F(17)CH(2)CH(2)Si(OEt)(3) and chemically modified with perfluorononanoic acid to yield C(8)F(17)-alumina and C(8)F(17)COOH-alumina, respectively. Elemental analysis and thermogravimetric analysis on the derivatized particles were carried out, and surface coverage was calculated. The stabilization of these modified particles in condensed CO(2) was quantified using turbidimetry. Particle stability was found to increase with increasing fluorinated tail length, temperature, and CO(2) density. Unmodified particles and those modified with only -CF(3) tails were unstable in condensed CO(2). Stabilization in supercritical CO(2) is continuous up to 24 h for the C(n)F(2n+1)-silica (n >/= 4) particles and 96 h for the C(8)F(17)-alumina particles. The C(8)F(17)COOH-alumina particles gave a significantly higher graft density than the C(8)F(17)-alumina particles but are not as stable in CO(2). The C(8)F(17)-alumina particles were stable at lower CO(2) densities than the modified silica particles. This stability difference may be attributed to the precursor organosilanes being monofunctional (modified silica) versus trifunctional (modified alumina), producing different structures on the surface.     

Modification of porous silica particles with poly(acrylic acid)

The surface of porous silica particles was modified with poly(acrylic acid) by reacting the carboxyl groups on poly(acrylic acid) with the amino groups of pregrafted aminopropyltriethoxysilane (APS). The chemical modifications by APS and polymer were characterized by infrared spectroscopy and the amount of APS and poly(acrylic acid) grafted to the surface were determined by thermal gravimetric analyses. The wettability of the modified silica particles, based on the rate of water penetration, was pH‐dependent with PAA; at pH 1.5 the wettability increased but at pH 5.5 it decreased dramatically. The pore size and size distribution of the silica particles decreased with APS and polymer grafting. Copyright © 2000 John Wiley & Sons, Ltd.     

A facile two-step etching method to fabricate porous hollow silica particles

We report here the fabrication of hollow silica particles with mesopores larger than 10 nm on their wall via a facile two-step etching method. Different from the conventional template method, the new method uses the silica particles as starting materials, which were synthesized using the well-known Stöber method. In the hollow silica preparation, first, we gently etch the silica particles with a NaOH solution without using template molecules to make them porous. Then, we coat the porous silica particles with poly-dimethyldiallylammonium chloride (PDDA) and treat the PDDA-coated porous silica with an ammonia solution to form the hollow silica nanospheres. In this study, we found that the NaOH dosage and ammonia concentration have significant impact on the morphology of the final products. Adsorption was also studied and results show that the hollow nanospheres can effectively uptake protein-based biomolecules (hemoglobin).     

Monodispersed submicron porous silica particles functionalized with CD derivatives for chiral CEC

Rapid and efficient enantioseparation of halogen aryl alcohols and β‐blockers propranolol and pindolol in packed bed CEC (p‐CEC) using as‐prepared submicron porous silica chiral stationary phases (CSPs) has been achieved. Monodispersed 0.66 and 0.81 μm chiral submicron porous silica spheres were prepared using tetramethoxysilane and hexadecyltrimethylammonium bromide, followed by a hydrothermal treatment method with ammonia–ethanol to expand the pore of silica spheres without changing their spherical morphology. A proper specific surface of ca. 230 m²/g and pore sizes average of 6–8 nm were obtained by this method. The submicron porous silica spheres were modified with mono‐6‐phenylcarbamoylated β‐CD via thiol‐en radical addition. They were packed into 9 cm 50 μm id capillary columns with photopolymerized monolithic frits. These submicron CSPs showed greater column efficiency (about 476 000 plates/m for 4‐iodophenyl‐1‐ethanol) and higher resolution than the corresponding 3 μm CSP.     

Evaluation of the compaction properties of a solid dispersion of indomethacin with crospovidone by tableting process analyzer

A powder solid dispersion system (SD) of indomethacin (IM) with crospovidone (CrosPVP) possesses good fluidity and can be used for tablet formulation. Tablets of SD can be prepared by direct compression and have adequate hardness and a small variation in weight. Forces during the tableting process were measured with a tableting process analyzer (TabAll) equipped with a single-punch. The pressure transmission ratio (PTR) from the upper to the lower punch and the die wall force (DWF) were examined during the tableting process. Ejection force (EF) and scraper pressure (SP) were measured for determining the capping and sticking properties during the tableting process. Adding 1% magnesium stearate (MS) to the SD resulted in high PTR and DWF values and a low EF value. PTR and DWF values increased and EF value decreased when MS and microcrystalline cellulose (MCC) were added to the SD. A thousand tablets could be manufactured without problems such as sticking or capping when 1% MS and 50% MCC were added to the SD containing 25% IM.     

Synthesis of biofuel via levulinic acid esterification over porous solid acid consisting of tungstophosphoric acid and reduced graphene oxide

Research on Chemical Intermediates - Reduced graphene oxide (rGO) was synthesized by chemical reduction of graphene oxide with hydrazine hydrate and used as supports to prepare a series of...     

Adsorption of cationic polyelectrolyte at the solid/liquid interface and dispersion of nanosized silica in water

Adsorption of cationic polyelectrolyte, a homopolymer of maleimide propyl trimethylammonium chloride (MPTMAC), on silica nanoparticles from aqueous solution was studied. The adsorbed amount of MPTMAC and the adsorption layer thickness from solutions of different pH, polyelectrolyte concentration, salt type, and salt concentration were measured. The adsorbed amount exhibited a maximum as a function of the electrolyte concentration. The onset of the decline in the adsorbed amount depended on the type of counterions. The thickness of the adsorption layer increased gradually with increased of electrolyte concentration and leveled off at high electrolyte concentration. The enhanced adsorption in the presence of Na2SO4 can be explained by the bivalent SO4(2-) causing a better shielding effect. With increasing pH the adsorbed amount of MPTMAC increased, whereas the thickness of an adsorbed layer of MPTMAC decreased. At low polyelectrolyte concentrations unstable silica suspensions were observed from a stability test. At high polyelectrolyte concentrations the higher particle coverage caused electrosteric stabilization of the dispersion. However, further increase in MPTMAC concentration after saturated adsorption would flocculate the dispersed system. At low pH, MPTMAC tending to create a loops or tails conformation stabilized the suspension.     

Diffusion-based deprotection in mesoporous materials: a strategy for differential functionalization of porous silica particles

A monodisperse, spherical mesoporous silica (Acid-Prepared Mesoporous Spheres, APMS) was prepared and then functionalized with two types of Fmoc (9-fluorenylmethyloxycarbonyl) terminated silanes with variable chain lengths. N2 physisorption experiments indicated that, under some conditions, the pores of the solid were completely filled by the Fmoc-protected organosilanes. These blocked pores were then "reopened" by the cleavage of Fmoc groups with a piperidine solution. In contrast to the solution reaction, this deprotection reaction was much slower within the pores. The rate of deprotection was followed by UV/visible spectroscopy, and a plot of Fmoc released versus time showed a sigmoidal shape. An empirical model was applied to the data, which indicated that the reaction was influenced by the concentration and temperature of the piperidine solution as well as the number of Fmoc moieties within the pores. Using this information, we show that the location of the deprotection reaction in the pores of the silica can be empirically controlled. Our work provides a method by which the surface of the porous silica can be functionalized in a well-defined manner. This method can be used to produce materials for catalysis or drug delivery.     

Antimicrobial porous hybrids consisting of bacterial nanocellulose and silver nanoparticles

The increasing resistance of pathogens and bacteria is a serious problem in the medical treatment of wounds and injuries. Therefore, new therapeutic agents are not solely based on antibiotics, but also on the use of antimicrobial metal nanoparticles. In this paper we present an innovative method to prepare porous hybrids consisting of bacterial nanocellulose (BNC) and silver nanoparticles (AgNPs). The stepwise modification is based on fairly simple chemical reactions already described for two-dimensional cellulose films. We transferred this method to the three-dimensional, porous network of BNC leading to an antimicrobial activation of its surface. Compared to former approaches, the ultrafine network structure of BNC is less damaged by using mild chemicals. The amount and distribution of the AgNPs on the modified BNC was investigated using scanning electron microscopy. The AgNPs are firmly immobilized on the top and bottom surface of the BNC by chemical interactions. Their size and quantity increase with an increasing concentration of AgNO₃ and extended reaction time in the AgNO₃ solution. A strong antimicrobial activity of the BNC-AgNP hybrids against Escherichia coli was detected. Furthermore, agar diffusion tests confirmed that this activity is restricted to the modified dressing itself, avoiding a release of NPs into the wound. Therefore, the produced hybrids could be potentially suited as novel antimicrobial wound dressings.     

Preparation and evaluation of solid dispersions of nitrendipine prepared with fine silica particles using the melt-mixing method

Solid dispersions (SD) of nitrendipine (NTD), a poorly water-soluble drug, were prepared using the melt-mixing method with hydrophilic silica particles (Aerosil and Sylysia) with different particle size and specific surface areas as carriers. Powder X-ray diffraction and differential scanning calorimetry evaluation showed that NTD in the SDs treated with the melt-mixing method was dispersed in the amorphous state. FT-IR spectroscopy obtained with the SDs indicated the presence of hydrogen bonding between the secondary amine groups of NTD and silanol groups of silica particles. The dissolution property of NTD in the SDs was remarkably improved regardless of the grade of silica. At the end of the dissolution test (60 min) the concentrations of NTD for the SDs with Aerosil 200 and Sylysia 350 were 8.88 and 10.09 microg/ml, corresponding to 28 and 31 times that of the original NTD crystals, respectively. The specific surface area and the adsorbed water amount of the SDs were also significantly improved. The rapid dissolution rate from the SDs was attributed to the amorphization of drug, improved specific surface area and wettability than the original drug crystals. In the stability test, powder X-ray diffraction pattern indicated that amorphous NTD in the SD with Aerosil 200 was stable for at least 1 month under the humid conditions (40 degrees C/75% RH).     

Preparation and evaluation of Ibuprofen solid dispersion systems with kollidon particles using a pulse combustion dryer system

Solid dispersions (SDs) of ibuprofen (IBU) were prepared with four carriers: Kollidon 25, Kollidon 30, Kollidon VA64, and Kollidon CL, using a newly developed pulse combustion dryer system, HYPULCON. Physicochemical properties of the SDs obtained were investigated by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), scanning electron microscope (SEM), and Fourier transformation IR spectroscopy (FT-IR). Powder X-ray diffraction (PXRD) showed that the crystal diffraction peaks of IBU in SDs disappeared completely, and in differential scanning calorimetry (DSC) curves, the endothermic peaks of IBU in SDs were not observed. Fourier transformation IR spectroscopy (FT-IR) proved that interactions between the drug and carrier existed. These findings demonstrated that IBU changed to an amorphous form in the SDs with the four carriers using the pulse combustion dryer system. The dissolution property of IBU in the SDs was markedly enhanced. The dissolution test showed that after 5 min of dissolution, the concentrations of IBU in the SDs with Kollidon CL as the carrier was 43.81 mug/ml, corresponding to 13.0 times that of pure IBU. So, it is demonstrated that the pulse combustion dryer system is very useful for preparing SDs of IBU with Kollidon of different grades as carriers.     

Three-dimensional porous metal-metalloporphyrin framework consisting of nanoscopic polyhedral cages

An unprecedented nanoscopic polyhedral cage-containing metal-metalloporphyrin framework, MMPF-1, has been constructed from a custom-designed porphyrin ligand, 5,15-bis(3,5-dicarboxyphenyl)porphine, that links Cu(2)(carboxylate)(4) moieties. A high density of 16 open copper sites confined within a nanoscopic polyhedral cage has been achieved, and the packing of the porphyrin cages via an "ABAB" pattern affords MMPF-1 ultramicropores which render it selective toward adsorption of H(2) and O(2) over N(2), and CO(2) over CH(4).     

Analysis of gas–solid noncatalytic reactions in porous particles: Finite volume method

Gas–solid noncatalytic (GSNC) reactions in porous particles are analyzed employing volume reaction model (VRM). Both single‐stage and two‐stage models have been used in the work. Earlier analysis for such reactions was mostly restricted to the first‐order reactions with respect to the gaseous component. The present work has used a range of reaction orders with respect to both gaseous and solid reactants. Front tracking method was employed for solving the moving boundary problem. Finite volume method (FVM) has been used for the first time for the analysis of GSNC reactions in porous particles, based on moving boundary zone models. The discretized equations are solved by tridiagonal matrix algorithm. The results for the first‐order reaction agree well with the analytical solution. FVM solution compares well with other numerical method (integral transformation followed by orthogonal collocation). Numerical results have also been validated with reported experimental data for reduction of Magnetite by CO. FVM is thus established to be a suitable numerical method to solve GSNC reactions in porous particles employing VRM. The effects of different process parameters on the progress of reaction have also been assessed.© 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 1–11, 2003     

The size and shape of silica particles

Negatively charged silica particles were investigated at pH 10.0. They were found to be rod-shaped (cylinder) with a diameter of 5–5.5 nm and a full length of 44–67 nm depending on the rod model used. Moreover, the particles were found to be stable against aggregation in the region 0.4–50 mM NaCl. Received: 2 December 1998 Accepted in revised form: 2 February 1999     

On the optimization of the solid core radius of superficially porous particles for finite adsorption rate

Packed chromatographic columns with the superficially porous particles (porous shell particles) guarantee higher efficiency. The theoretical equation of the Height Equivalent to a Theoretical Plate (HETP), for columns packed with spherical superficially porous particles, was used for the analysis of the column efficiency for finite rate of adsorption-desorption process. The HETP equation was calculated by the application of the moment analysis to elution peaks evaluated with the General Rate (GR) model. The optimal solid core radius for maximum column efficiency was estimated for a wide spectrum of internal and external mass transfer resistances, adsorption kinetic rate and axial dispersion. The separation power of the shell adsorbent for two component mixture, in analytical and preparative chromatography, was discussed. The conditions of the equivalence between the solutions of the General Rate model with slow adsorption kinetic and the Lumped Kinetic Model (LKM) or the Equilibrium Dispersive (ED) model were formulated.     

A solid homogeneous zirconocene catalyst from Cp2ZrCl2 supported on porous polymer particles

Monodisperse cyano‐functionalized porous polymeric beads were synthesized by seeded polymerization; these microparticles were further used as support for zirconocene catalyst, which performed as a solid homogeneous catalyst in ethylene polymerization. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Dispersity of platinium on porous glasses and silica

Hydrogen adsorption has been investigated in order to determine the dispersity of platinum supported on different silicon-containing materials, such as porous glasses, silica and acid treated silica. The acid treatment of silica results in more dispersed platinum as compared with silica and porous glasses. The influence of pore size distribution as a further important factor on Pt-crystallite distribution and dispersity is discussed.

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Network structure of fine silica particles

The network structure of silica aerogels heated at 300, 400 and 500°C in dried air have been determined by neutron total scattering measurements using a pulsed spallation neutron source. SANS experiments were also performed to obtain the particle size of the silica constituting aerogel. The elementary particle size obtained is about 13Å in diameter. The distances of the Si-O and O-O interactions in such fine silica particles are 1.61 and 2.64 Å, respectively, which are the same as those of fused silica. The coordination numbers of these pairs are found to be less evident than those of fused silica. In addition, the distances of the Si-Si pairs in the aerogels are slightly longer than that of fused silica. According to the heat treatment temperature, the coordination numbers of the Si-O and O-O interactions increase and the distance of the Si-Si pair decreases. These results indicate that although the network structure of fine silica particles treated at lower temperature is loose and imperfect, such structure can be changed by heating at relatively low temperature. The Raman spectra and the skeletal density measurements of the aerogels support also these results.