Nonporous Particles Research Articles

Rapid Analysis of Cyclic Peptide Cyclosporine A by HPLC Using a Column Packed with Nonporous Particles.

We developed a rapid and efficient analytical technique for cyclosporine A using HPLC on a column packed with 2-µm nonporous octadecylsilyl silica particles. Under optimized conditions, cyclosporine A was separated with high resolution from other cyclic peptides within 3 min, because the mass transfer resistance in the stationary phase was reduced by the use of the small, nonporous particles. Although the plate number increased greatly with the increase in the column temperature, the retention times were not affected. This behavior is different from other cyclic peptides or linear peptides. Based on its physicochemical characteristics, cyclosporine A is a poor hydrogen bond donor, and has a small topological polar surface area, low rotatable bond count, and high log P value. These results show that cyclosporine A is structurally rigid and undergoes poor water solvation even at high temperature. In the context of the rapid development of cyclic peptides with similar physicochemical characteristics to cyclosporine A, our developed method is useful for the development of cyclic peptide therapeutics.

INFLUENCE OF SURFACE HEATING TEMPERATURE ON EXTERNAL HEAT-EXCHANGE IN WET VIBRO-FLUIDIZED BED

Experimental data are given on the influence of the temperature of the heating surface, placed to a wet vibro-fluidized bed of non-porous particles, and higher that the saturation temperatures on the external heat-transfer coefficient at conductive supply of the heat.

Biosorption of cationic dyes by Pará chestnut husk (Bertholletia excelsa).

Pará chestnut husk (Bertholletia excelsa) (PCH), an agro-industrial waste largely generated in Brazil, was employed as a low-cost and efficient biosorbent to remove the cationic dyes Crystal Violet (CV) and Methylene Blue (MB) from aqueous media. PCH presented an amorphous structure containing carboxylic acids, esters, ketones and aldehydes on the surface. Non-porous and irregular particles were also observed. For both dyes, the biosorption capacity was favored under acid conditions. Equilibrium was attained within 40 min at 25 °C with a PCH dosage of 0.5 g L-1. The biosorption kinetic curves were satisfactory explained by the pseudo-first-order model. The Freundlich model was best for representing the equilibrium curves. The maximum biosorption capacities were 83.6 and 83.8 mg g-1 for CV and MB, respectively. PCH was efficient for treating a simulated textile effluent containing several dyes and chemicals, achieving a color removal of 90%. In this way, PCH can be considered as an option for treating colored effluents containing textile dyes.

Preparation of Ultraviolet Curing Type Silicone Rubbers Containing Mesoporous Silica Fillers.

Here we have been focusing on mesoporous silica (MPS) as inorganic filler material to improve the mechanical strength of silicone rubbers. The MPS particles are more effective in reducing the coefficient of thermal expansion (CTE) and hardening silicone rubber composites when compared to commercially available nonporous silica particles. In this study, we utilize ultraviolet curing type silicone rubbers and prepare MPS composites according to a simple single-step method. From an industrial viewpoint, simplifying the fabrication processes is critical. The thermal stability and mechanical strength are examined in detail in order to showcase the effectiveness of MPS particles as filler materials.

Drug transport mechanisms and in vitro release kinetics of vancomycin encapsulated chitosan-alginate polyelectrolyte microparticles as a controlled drug delivery system

In this study, chitosan-alginate polyelectrolyte microparticles containing the antibiotic, vancomycin chloride were prepared using the ionotropic gelation (coacervation) technique. In vitro release and drug transport mechanisms were studied concerning the chitosan only and alginate only microparticles as a control group. Further, the effect of porosity on the drug transport mechanism was also studied for chitosan-alginate mixed particles produced by lyophilizing in contrast to the air-dried non-porous particles. According to the in vitro release data, alginate only and chitosan only microparticles showed burst release and prolonged release respectively. Chitosan-alginate lyophilized microparticles showed the best-controlled release of vancomycin with the average release of 22μg per day for 14days. Also, when increasing alginate concentration there was no increase in the release rate of vancomycin. The release data of all the microparticles were treated with Ritger-Peppas, Higuchi, Peppas-Sahlin, zero-order, and first-order kinetic models. The best fit was observed with Peppas-Sahlin model, indicating the drug transport mechanism was controlled by both Fickian diffusion and case II relaxations. Also, Fickian diffusion dominates the drug transport mechanism of all air-dried samples during the study period. However, the Fickian contribution was gradually reducing with time. Porosity significantly effects the drug transport mechanism as case II relaxation dominates after day 10 of the lyophilized microparticles.

High-resolution separation of neodymium and dysprosium ions utilizing extractant-impregnated graft-type particles

An efficient method for rare metal recovery from environmental water and urban mines is in high demand. Toward rapid and high-resolution rare metal ion separation, a novel bis(2-ethylhexyl) phosphate (HDEHP)-impregnated graft-type particle as a filler for a chromatography column is proposed. To achieve rapid and high-resolution separation, a convection-flow-aided elution mode is required. The combination of 35μm non-porous particles and a polymer-brush-rich particle structure minimizes the distance from metal ion binding sites to the convection flow in the column, resulting in minimized diffusional mass transfer resistance and the convection-flow-aided elution mode. The HDEHP-impregnated graft-type non-porous-particle-packed cartridge developed in this study exhibited a higher separation performance for model rare metals, neodymium (III) and dysprosium (III) ions, and a narrower peak at a higher linear velocity, than those of previous HDEHP-impregnated fiber-packed and commercially available Lewatit® VP OC 1026-packed cartridges.

Core-shell microspheres with porous nanostructured shells for liquid chromatography.

The development of new stationary phases has been the key aspect for fast and efficient high-performance liquid chromatography separation with relatively low backpressure. Core-shell particles, with a solid core and porous shell, have been extensively investigated and commercially manufactured in the last decade. The excellent performance of core-shell particles columns has been recorded for a wide range of analytes, covering small and large molecules, neutral and ionic (acidic and basic), biomolecules and metabolites. In this review, we first introduce the advance and advantages of core-shell particles (or more widely known as superficially porous particles) against non-porous particles and fully porous particles. This is followed by the detailed description of various methods used to fabricate core-shell particles. We then discuss the applications of common silica core-shell particles (mostly commercially manufactured), spheres-on-sphere particles and core-shell particles with a non-silica shell. This review concludes with a summary and perspective on the development of stationary phase materials for high-performance liquid chromatography applications.

Adsorption and Recovery of Polyphenolic Flavonoids Using TiO2-Functionalized Mesoporous Silica Nanoparticles.

Exploiting specific interactions with titania (TiO2) has been proposed for the separation and recovery of a broad range of biomolecules and natural products, including therapeutic polyphenolic flavonoids which are susceptible to degradation, such as quercetin. Functionalizing mesoporous silica with TiO2 has many potential advantages over bulk and mesoporous TiO2 as an adsorbent for natural products, including robust synthetic approaches leading to high surface area, and stable separation platforms. Here, TiO2-surface-functionalized mesoporous silica nanoparticles (MSNPs) are synthesized and characterized as a function of TiO2 content (up to 636 mg TiO2/g). The adsorption isotherms of two polyphenolic flavonoids, quercetin and rutin, were determined (0.05-10 mg/mL in ethanol), and a 100-fold increase in the adsorption capacity was observed relative to functionalized nonporous particles with similar TiO2 surface coverage. An optimum extent of functionalization (approximately 440 mg TiO2/g particles) is interpreted from characterization techniques including grazing incidence X-ray scattering (GIXS), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption, which examined the interplay between the extent of TiO2 functionalization and the accessibility of the porous structures. The recovery of flavonoids is demonstrated using ligand displacement in ethanolic citric acid solution (20% w/v), in which greater than 90% recovery can be achieved in a multistep extraction process. The radical scavenging activity (RSA) of the recovered and particle-bound quercetin as measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrates greater than 80% retention of antioxidant activity by both particle-bound and recovered quercetin. These mesoporous titanosilicate materials can serve as a synthetic platform to isolate, recover, and potentially deliver degradation-sensitive natural products to biological systems.

Rationally Turning the Interface Activity of Mesoporous Silicas for Preparing Pickering Foam and "Dry Water".

We develop a novel protocol to prepare smart, gas/water interface-active, mesoporous silica particles. This protocol involves modification of highly mesoporous silicas with a mixture of hydrophobic octyl organosilane and hydrophilic triamine organosilane. Their structure and compositions are characterized by transmission electron microscopy (TEM), N2 sorption, solid state NMR, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FT-IR), thermogravimetric analysis (TGA), and elemental analysis. It is demonstrated that our protocol enables the interface activity of mesoporous silica particles to be facilely tuned, so that the stable gas-water interfaces ranging from air bubbles dispersed in water (Pickering foam) and water droplets dispersed in air ("dry water") can be achieved, depending on the molar ratio of these two organosilanes. The "dry water" is not otherwise attainable for the analogous nonporous silica particles, indicting the uniqueness of the chosen mesoporous structures. Moreover, these particle-stabilized Pickering foams and "dry waters" can be disassembled in response to pH. Interestingly, it was found that aqueous potassium carbonate droplets stabilized by these interface-active mesoporous silica particles ("dry K2CO3-containing water") could automatically capture CO2 from a simulated flue gas with enhanced adsorption rate and adsorption capacity when compared to the aqueous potassium carbonate bulk solution. This study not only supplies a novel type of efficient, smart, gas/water interface-active mesoporous silica particles but also demonstrates an innovative application of mesoporous materials in gas adsorption.

Direct wet deposition of zeolite FAU thin films using stabilized colloidal suspensions

Seeded growth is the most popular approach to the preparation of zeolite thin films and membranes. Herein, we report a simplified method of fabricating zeolite Faujasite (FAU) thin films through the direct wet deposition of zeolite FAU thin films using stabilized colloidal suspensions. Zeolite FAU suspensions are stabilized by adjusting the pH values and the suspensions are spin-coated on a silicon wafer substrate to form dense zeolite FAU thin films. Dynamic light scattering (DLS) was used to investigate the colloidal properties of the zeolite FAU suspensions. The time-dependent hydrodynamic radius Rh was derived from DLS measurements for use as a quantitative measure of colloidal stability. It was found that high pH values destabilize the colloidal suspensions. Thin film samples cast using the relatively stable zeolite FAU suspensions yielded thin films with uniform morphology. In thin films formed from suspensions with a high pH value, the zeolite FAU crystals transformed into a dense phase. We also measured the relative permittivity (εr) of the thin film samples cast from various suspensions. At a low frequency (<100 kHz), thin films that compose zeolite FAU crystals presented higher εr values than did those possessing nonporous particles. The high εr values of the zeolite FAU thin films can probably be attributed to the physical adsorption of water. At a high frequency (1000 kHz), water had far less effect on εr values and thin films with a zeolite FAU structure presented εr values characteristic of low-dielectric constant (low-k) thin films.

Heterogeneous Crystallization Inside Microporous Polymer Particles as a Process Intensification Technology for the Manufacture of Drug Formulations

Current pharmaceutical manufacturing practices lack the type of rapid advancements achieved through the quick adoption of technical innovations as has been done in other manufacturing sectors. There is significant interest from both academia and the pharmaceutical industry in developing new technologies that accelerate process optimization in a cost-effective manner. Process intensification technologies (PITs) improve efficiency and reduce costs by reducing the number of unit operations required to manufacture a drug formulation. Recent studies have shown the potential of directly crystallizing drug compounds inside porous excipients as a PIT for pharmaceutical manufacturing. However, these studies have primarily focused on developing techniques for crystallizing the drug inside the excipients and maximizing drug loading. There is little understanding of how the excipient particles themselves influence the crystallization process or how this technology compares with other drug encapsulation processes. This investigation considers two other drug encapsulation processes, direct crystallization onto nonporous particles and molecular adsorption of the drug. We discuss the direct crystallization of acetaminophen and sulfathiazole inside microporous particles of alginate and carboxymethyl cellulose. The polymer chemistry and available surface area have a significant impact on drug loading and secondary nucleation in the bulk solution. Direct crystallization offers higher drug loadings compared to other drug encapsulation technologies. This study highlights the potential of direct crystallization inside excipients as a PIT for pharmaceutical manufacturing.

Enhanced Acrylate Production from 2-Acetoxypropanoic Acid Esters

Reaction conditions and reactor geometry for producing acrylates in high yield from lactic acid-derived 2-acetoxypropanoic acid (APA) esters are presented. An acrylate ester yield of 75% is achieved from methyl and benzyl APA esters at 550 °C in a fixed bed reactor filled with nonporous silica particles, carbon dioxide as a diluent gas, and acetic acid as a co-feed with the APA ester. The yield from methyl and benzyl APA esters is remarkably higher than from ethyl or butyl esters of APA, which have hydrogen atoms on the β-carbon of the ester functional group and thus can undergo alkene elimination, leading to reduced acrylate yield. Under optimum conditions, APA conversion to acrylates is stable over 30 h of continuous operation with little carbon deposition on the contact material.

Fabrication of Hierarchical Layer-by-Layer Assembled Diamond-based Core-Shell Nanocomposites as Highly Efficient Dye Absorbents for Wastewater Treatment

The effective chemical modification and self-assembly of diamond-based hierarchical composite materials are of key importance for a broad range of diamond applications. Herein, we report the preparation of novel core-shell diamond-based nanocomposites for dye adsorption toward wastewater treatment through a layer-by-layer (LbL) assembled strategy. The synthesis of the reported composites began with the carboxyl functionalization of microdiamond by the chemical modification of diamond@graphene oxide composite through the oxidation of diamond@graphite. The carboxyl-terminated microdiamond was then alternatively immersed in the aqueous solution of amine-containing polyethylenimine and carboxyl-containing poly acrylic acid, which led to the formation of adsorption layer on diamond surface. Alternating (self-limiting) immersions in the solutions of the amine-containing and carboxyl-containing polymers were continued until the desired number of shell layers were formed around the microdiamond. The obtained core-shell nanocomposites were successfully synthesized and characterized by morphological and spectral techniques, demonstrating higher surface areas and mesoporous structures for good dye adsorption capacities than nonporous solid diamond particles. The LbL-assembled core-shell nanocomposites thus obtained demonstrated great adsorption capacity by using two model dyes as pollutants for wastewater treatment. Therefore, the present work on LbL-assembled diamond-based composites provides new alternatives for developing diamond hybrids as well as nanomaterials towards wastewater treatment applications.

Discussion about the use of the volume specific surface area (VSSA) as a criterion to identify nanomaterials according to the EU definition. Part two: experimental approach.

The first part of this study was dedicated to the modelling of the influence of particle shape, porosity and particle size distribution on the volume specific surface area (VSSA) values in order to check the applicability of this concept to the identification of nanomaterials according to the European Commission Recommendation. In this second part, experimental VSSA values are obtained for various samples from nitrogen adsorption isotherms and these values were used as a screening tool to identify and classify nanomaterials. These identification results are compared to the identification based on the 50% of particles with a size below 100 nm criterion applied to the experimental particle size distributions obtained by analysis of electron microscopy images on the same materials. It is concluded that the experimental VSSA values are able to identify nanomaterials, without false negative identification, if they have a mono-modal particle size, if the adsorption data cover the relative pressure range from 0.001 to 0.65 and if a simple, qualitative image of the particles by transmission or scanning electron microscopy is available to define their shape. The experimental conditions to obtain reliable adsorption data as well as the way to analyze the adsorption isotherms are described and discussed in some detail in order to help the reader in using the experimental VSSA criterion. To obtain the experimental VSSA values, the BET surface area can be used for non-porous particles, but for porous, nanostructured or coated nanoparticles, only the external surface of the particles, obtained by a modified t-plot approach, should be considered to determine the experimental VSSA and to avoid false positive identification of nanomaterials, only the external surface area being related to the particle size. Finally, the availability of experimental VSSA values together with particle size distributions obtained by electron microscopy gave the opportunity to check the representativeness of the two models described in the first part of this study. They were also used to calculate the VSSA values and these calculated values were compared to the experimental results. For narrow particle size distributions, both models give similar VSSA values quite comparable to the experimental ones. But when the particle size distribution broadens or is of multi-bimodal shape, as theoretically predicted, one model leads to VSSA values higher than the experimental ones while the other most often leads to VSSA values lower than the experimental ones. The experimental VSSA approach then appears as a reliable, simple screening tool to identify nano and non-nano-materials. The modelling approach cannot be used as a formal identification tool but could be useful to screen for potential effects of shape, polydispersity and size, for example to compare various possible nanoforms.

Liquid transport rates during binary collisions of unequally-sized particles

In this paper, we study the liquid transport between particles of different sizes, as well as build a dynamic liquid bridge model to predict liquid transport between these two particles. Specifically, the drainage process of liquid adhering to two unequally-sized, non-porous wet particles is simulated using direct numerical simulations (DNS). Same as in our previous work (Wu et al., AIChE Journal, 2016, 62:1877–1897), we first provide an analytical solution of a proposed dynamic liquid bridge model. We find that such an analytical solution also describes liquid transport during collisions of unequally-sized particles very well. Finally, we show that our proposed model structure is sufficient to collapse all our direct numerical simulation data. Our model is hence able to predict liquid transport rates in size-polydisperse systems for a wide range of parameters.

Corundum dissolution in concentrated sodium hydroxide solution

The corundum (α-alumina) core has been considered as a suitable candidate for investment casting of hollow, high pressure turbine engine airfoils due to its excellent properties. However, the efficiency of removing alumina cores in concentrated caustic solution cannot meet the needs of industrial production. In this paper, the effects of temperature and initial solution concentration on dissolution of α-alumina were studied by the classical weight-loss method. The fractal kinetic model was developed in order to describe α-alumina dissolution, assuming that the nonporous particles shrank during reaction process. The results show that the dissolution rate increases with increasing reaction temperature and initial solution concentration. Especially, the initial solution concentration has a significant influence on α-alumina dissolution rate at a higher reaction temperature. The activation energies decrease with increasing initial solution concentration, and the chemical reaction is the rate-controlling step.

Aerosolizable modified-release particles of montelukast improve retention and availability of the drug in the lungs

Montelukast, a cysteinyl leukotriene receptor antagonist available as oral tablets, is used as a second-line therapy in asthma. In this study, we sought to enhance the availability of montelukast in the lungs by encapsulating the drug in poly (lactide-co-glycolic acid)-based (PLGA) respirable large porous particles. We determined the oral and lung specific availability of montelukast by assessing metabolic stability of the drug in the lung and liver homogenates, respectively. We similarly measured the oral and inhalational bioavailability by monitoring the pharmacokinetics and disposition of the drug in live animals. After preparing montelukast-loaded particles with various polymers, in the absence or presence of polyethylenimine (PEI-1), we characterized the particles for physical-chemical properties, entrapment efficiency, in vitro release, uptake by alveolar macrophages, deposition in the lungs, and safety after pulmonary administration. When incubated in lung or liver homogenates, the amount of intact drug in the lung homogenates was greater than that in the liver homogenates. Likewise, the extent of montelukast absorption via the lungs was greater than that via the oral route. Compared with smaller non-porous particles, large porous particles (PEI-1) were taken up by the alveolar macrophages at a lesser extent but deposited in the lungs at a greater extent. The levels of injury markers in the bronchoalveolar lavage fluid (BALF), collected from rat lungs treated with PEI-1, were no different from that in BALF collected from saline treated rats. Overall, the retention time and concentration of montelukast in the lungs can be increased by formulating the drug in large porous particles of PLGA.

Contact properties determination of macroscopic fine disperse glass particles via compression tests in normal direction

The paper describes the deformation behavior of spherical, dry and non-porous particles during a single particle compression test in normal direction. Therefore a compression tester was built. Industrial used soda lime glass particles with two macroscopic fine disperse sizes (d1,50,3=284.30μmand d2,50,3=513.20μm) were applied as model material to investigate the micromechanical contact behavior. In order to influence the elastic-plastic contact properties of particles, the surfaces were altered with chemical modification by means of silanization.The determination of various micromechanical contact properties (e.g. adhesion force, modulus of elasticity and contact stiffness) was carried out model-based with the contact model ‘stiff particles with soft contacts’ by means of a back-calculation.It could be shown that the model-based determination of material properties was a good alternative compared to the comprehensive tensile tests and pull-off force measurements.In addition to the gained normal force-displacement data in normal direction, the friction limits for tangential loading and rolling with the load-dependent adhesion force were model-based determined.

Bulk- and Powder Surface Exchange Coefficients of (La,Sr)CoO3-d

1. Introduction La0.6Sr0.4CoO3-δ (LSC64) has been recognized as a promising cathode for SOFC, which has high mixed conductivity of electron hole and oxide ion. Its high mixed conductivity makes oxygen reduction reaction (ORR) possible to take place not only at triple-phase boundary but also on two-phase boundary of electrode surface and gas phase. This two-phase boundary reaction proceeds: oxygen gas diffusion to the electrode surface, adsorption, dissociation of the oxygen atom, incorporation into the electrode, then bulk diffusion. In the case of LSC64 thin film, the rate limiting step is the surface reaction [1]. It is necessary to understand the surface reaction kinetics to improve ORR on LSC64 cathode. Surface exchange coefficients of LSC64 bulk are reported in several papers including ref. 1. However ORR kinetics of LSC64 porous cathode can’t be explained by the reported values. In this study, therefore, surface exchange coefficients of LSC64 powder are determined, which is better to simulate surface reaction kinetics of porous electrode. 2. Experimental Surface exchange coefficients, k, of LSC64 powder were determined by a pulse isotope exchange (PIE) method [2]. The measurements were performed in oxygen partial pressure range from 10-3to 10-2 bar at 573-773 K. Sample powder was loaded at the center of a quartz tubular micro reactor (ϕ2 mm). Typical values of the powder mass and length of the powder bed were 0.03-0.05 g and 13-15 mm, respectively. A 16O2-N2 gas mixture was used as the carrier gas. A six-port valve was used for injection of the 18O2/He pulse gas (500 μL) into the 16O2/N2 carrier gas. The response to an 18O2-enriched pulse gas was analyzed by an on-line mass spectrometry (OmniStar TM GSD320, Pfeiffer-Vacuum). The pulse experiments are carried out under following conditions. (i) The number of 18O atoms is negligibly small compared to that of the exchangeable oxygens in the oxide, hence f(O18) ≈ 0. (ii)There is a large diffusion length of 18O in the non-porous oxide particle. Under these conditions, mass balance analysis yields a simple equation for surface exchange coefficients [2]: k = nV m/t r*ln(f(18g.i)/f(18g.e)) where f(g.i18) and f(g.e18) are the 18O isotope molar fractions in the pulse at the inlet and exit of the reactor, respectively; n is the total number of oxygen atoms in the free volume of the packed bed; V m is molecular volume; t r is the average residence time of the labeled gas in the reactor. 3. Results and discussion Temperature dependence of k for LSC64 powder are shown in Fig. 1. Surface exchange coeffiicients k of LSC64 powder showed temperature dependence at 300-400℃. In comparison to LSC64 bulk, surface exchange coefficients, k, has different tendency. This suggests that surface reaction kinetics of LSC powder (or porous LSC64) might be different.

A modelling framework for bulk particles dissolving in turbulent regime

A mixing-tank model combining CFD simulation and Noyes–Whitney equation has been demonstrated for predicting dissolution of spray-dried detergent powder. The dissolution behaviour of bulk particles has been directly linked to the input power of the mixing system which is highly desired by industry with the aim of reducing testing when extrapolating particle dissolution performance from bench scale measurements to any washing system/condition. Initial particle parameters such as density, solubility, size distribution and diffusivity were considered. The model was first validated with experiment of non-porous single-ingredient particle Na2CO3 granules. Later, porous multi-ingredients particles from spray-drying pilot were used to validate the model with dissolution experiment data. The good agreements between experiment and simulation at different agitating speeds and temperatures illustrated that the model can be used for predicting bulk particles dissolving in a turbulent regime where they are well suspended in the mixing system. The CFD simulation results revealed detail information about energy dissipation rate across the vessel which explained the phenomena that when non-porous Na2CO3 granules were not well mixed in the system, dissolution predicted by modelling was much faster than experiment, indicating that local energy dissipation rate could be one solution to improve the modelling accuracy of this case.