Nonporous Particles Research Articles

Evaluation of biodiesel production using lipase immobilized on magnetic silica nanocomposite particles of various structures

Nonporous and mesoporous silica-coated magnetite cluster nanocomposites particles were fabricated with various silica structures in order to develop a desired carrier for the lipase immobilization and subsequent biodiesel production. Lipase from Pseudomonas cepacia was covalently bound to the amino-functionalized particles using glutaraldehyde as a coupling agent. The hybrid systems that were obtained exhibited high stability and easy recovery regardless of the silica structure, following the application of an external magnetic field. The immobilized lipases were then used as the recoverable biocatalyst in a transesterification reaction to convert the soybean oil to biodiesel with methanol. Enzyme immobilization led to higher stabilities and conversion values as compared to what was obtained by the free enzyme. Furthermore, the silica structure had a significant effect on stability and catalytic performance of immobilized enzymes. In examining the reusability of the biocatalysts, the immobilized lipases still retained approximately 55% of their initial conversion capability following 5 times of reuse.

Reversible entrapment of plasmid deoxyribonucleic acid on different chromatographic supports

HPLC based analytical assay is a powerful technique that can be used to efficiently monitor plasmid DNA (pDNA) purity and quantity throughout the entire purification process. Anion exchange monolithic and non-porous particle based stationary phases were used to study the recovery of the different pDNA isoforms from the analytical column. Three differently sized pDNA molecules of 3.0kbp, 5.2kbp and 14.0kbp were used. Plasmid DNA was injected onto columns under the binding conditions and the separation of the isoforms took place by increasing the ionic strength of the elution buffer. While there was no substantial decrease of the recovered supercoiled and linear isoforms of the pDNA with the increase of the plasmid size and with the increase of the flow rate (recoveries in all cases larger than 75%), a pronounced decrease of the oc isoform recovery was observed. The entrapment of the oc pDNA isoform occurred under non-binding conditions as well. The partial oc isoform elution from the column could be achieved by decreasing the flow rate of the elution mobile phase. The results suggested a reversible entrapment of the oc isoform in the restrictions within the pores of the monolithic material as well as within the intra-particle space of the non-porous particles. This phenomenon was observed on both types of the stationary phase morphologies and could only be connected to the size of a void space through which the pDNA needs to migrate. A prediction of reversible pDNA entrapment was successfully estimated with the calculation of Peclet numbers, Pe, which defines the ratio between a convective and diffusive mass transport.

Inclusion of fenofibrate in a series of mesoporous silicas using microwave irradiation

A selection of porous silicas were combined with a model drug using a recently developed, controlled microwave heating process to determine if the application of microwave irradiation could enhance subsequent drug release. Five mesoporous silica types were investigated (core shell, core shell rehydrox, SBA-15, silica gel, SYLOID®) and, for comparison, one non-porous silica (stober). These were formulated using a tailored microwave heating method at drug/excipient ratios of 1:1, 1:3 and 1:5. In addition, all experiments were performed both in the presence and absence of water, used as a fluidising media to aid interaction between drug and support, and compared with results obtained using more traditional heating methods. All formulations were then characterised using differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transformation infrared spectroscopy (FT-IR). Pharmaceutical performance was investigated using in vitro drug release studies. A significant enhancement in the release profile of fenofibrate was observed for formulations prepared using microwave heating in the absence of water for five of the six silica based formulations. Of all the formulations analysed, the greatest extent of drug release within the experimental 30min was the 1:5 core shell rehydrox achieving a total of 86.6±2.8%. The non-porous (stober) particles did not exhibit an increased release of the drug under any experimental conditions studied. This anomaly is thought to be a result of the comparatively small surface area of the silica particles, thus preventing the adsorption of drug molecules.

Core shell stationary phases for a novel separation of triglycerides in plant oils by high performance liquid chromatography with electrospray-quadrupole-time of flight mass spectrometer

A new method for the analysis of triglycerides (TAGs) in vegetable oils was developed using a Poroshell 120 EC-C18 column (3.0mm×50mm, 2.7μm) with a high resolution ESI-Q-ToF tandem mass spectrometer as detection system. We used an Agilent Poroshell column, which is characterized by a recently developed stationary phase based on non-porous core particles. The results highlighted the advantages of this column in terms of the dramatic improvement in the number of theoretical plates and in low column backpressure. The developed method enabled us to analyze complex mixtures of more than 40 TAGs within less than 25min and with a low backpressure (lower than 100bar), and represents the first application of a core-shell stationary phase in reverse phase HPLC using an ESI-Q-ToF as detection system. The method was optimized on standards of TAGs, validated and applied to several plant oils. By a quantitative point of view, the method showed a very good linearity (r2>0.999) in the range 0.1–2.4μg/g; high intra- and inter-day precision both in terms of retention times (RSD%<0.04%) and peak areas (RSD%<0.3%). Limits of detection and quantitation were lower than 0.03μg/g and 0.10μg/g, respectively.

Structural features of resorcinol–formaldehyde resin chars and interfacial behavior of water co-adsorbed with low-molecular weight organics

Products of resorcinol–formaldehyde resin carbonization (chars) are characterized by different morphology (particle shape and sizes) and texture (specific surface area, pore volume and pore size distribution) depending on water content during resin polymerization. At a low amount of water (Cw=37.8wt.%) during synthesis resulting in strongly cross-linked polymers, carbonization gives nonporous particles. An increase in the water content to 62.7wt.% results in a nano/mesoporous char, but if Cw=73.3wt.%, a char is purely nanoporous. Despite these textural differences, the Raman spectra of all the chars are similar because of the similarity in the structure of their carbon sheets with a significant contribution of sp3 C atoms. However, the difference in the spatial organization of the carbon sheet stacks in the particles results in the significant differences in the textural and morphological characteristics and in the adsorption properties of chars with respect to water, methane, benzene, hydrogen, methylene chloride, and dimethylsulfoxide.

Polyacrylamide brush layer for hydrophilic interaction liquid chromatography of intact glycoproteins

A chromatographic column of nonporous silica particles with a bonded phase of linear polyacrylamide chains is evaluated for hydrophilic interaction liquid chromatography (HILIC) of intact glycoproteins. The column is shown to retain glycoproteins significantly more strongly than non-glycoproteins. A particle diameter of 700nm gives two-fold higher resolution than does a 1.4μm particle diameter, and the column efficiency is found to be mostly limited by packing heterogeneity. LCMS is able to resolve the five glycoforms of ribonuclease B and give high quality mass spectra, but there is loss of resolution of the isomers of glycoforms due to the lower amount of TFA. Compared to two leading commercial HILIC columns operated at 60°C, the polyacrylamide column operated at 30°C provided at least two-fold higher resolution for intact ribonuclease B, and showed peaks for glycoforms of prostate specific antigen, although not resolved.

Nanostructured Composite Adsorber Membranes for the Reduction of Trace Substances in Water: The Example of Bisphenol A

The increasing contamination of water with biopersistent substances is considered to become one of the key environmental problems in the next decades. These so-called micropollutants show considerable toxic or otherwise negative effects even at concentrations in the ppt level or ppb level. For the experimental proof-of-concept study we chose 2,2-bis(4-hydroxyphenyl)-propane known under the name bisphenol A (BPA). The extensive use of BPA-based polymers has led to widespread environmental distribution of BPA. BPA is an endocrine disrupting compound which has an impact on the hormonal system (endocrine system) of humans and animals even at low concentrations. To tackle the problem of the micropollutants in the aquatic environment, efforts are being made to develop new adsorber materials with specific properties for extracting these various substances in one step with one membrane. For this reason cross-linked polymer nanoparticles were synthesized by miniemulsion polymerization and their adsorption properties were characterized. The properties of the polymer particles were adjusted for BPA by variation of the monomer, cross-linker and the stoichiometric ratio. Comparative adsorption tests were carried out with silica gel, commercial adsorber material (RP-C18), activated carbon, and the adjusted adsorber material P(4-VP-co-EGDMA). The advantage of the nanoscale, nonporous polymer particles compared with commercial adsorber material is the relatively large and rapidly accessible external surface. The adjusted adsorber material P(4-VP-co-EGDMA) and the activated carbon absorbed almost the complete quantity of BPA supplied. The advantage of the polymer adsorber material compared with activated carbon is the greater ease of regenerability. The BPA can be extracted from the polymer by means of ethanol or can be desorbed by means of a pH value shift. The adsorptive polymer particles were incorporated into a porous polymer matrix by an immersion phase separation process to build an affinity membrane. The production process for the membrane is controlled in such a way as to create an inner sponge-like structure in which the polymer nanoparticles are firmly embedded and nevertheless are easily accessible to the adsorbate. The sponge-like-structured membrane has the higher flux compared with a commercial UF membrane. The polymer particles were deposited in the pores of the sponge-like membrane structure during the membrane formation process and so are freely accessible to BPA. Tests were carried out in which the retained quantity of BPA of a commercially available UF membrane was compared with the retained quantity of BPA of a particle loaded membrane. This allows the construction of membranes for specific requirements in order to extract micropollutants ideally in one step with a functional membrane.

Magnetic Porous Sugar-Functionalized PEG Microgels for Efficient Isolation and Removal of Bacteria from Solution

Here, we present a new microparticle system for the selective detection and magnetic removal of bacteria from contaminated solutions. The novelty of this system lies in the combination of a biocompatible scaffold reducing unspecific interactions with high capacity for bacteria binding. We apply highly porous poly(ethylene glycol) (PEG) microparticles and functionalize them, introducing both sugar ligands for specific bacteria targeting and cationic moieties for electrostatic loading of superparamagnetic iron oxide nanoparticles. The resulting magnetic, porous, sugar-functionalized (MaPoS) PEG microgels are able to selectively bind and discriminate between different strains of bacteria Escherichia coli . Furthermore, they allow for a highly efficient removal of bacteria from solution as their increased surface area can bind three times more bacteria than nonporous particles. All in all, MaPoS particles represent a novel generation of magnetic beads introducing for the first time a porous, biocompatible and easy to functionalize scaffold and show great potential for various biotechnological applications.

QCM-D as a method for monitoring enzyme immobilization in mesoporous silica particles

Enzyme immobilization in mesoporous materials is a field of great interest, with applications in biocatalysis and biosensing. However, the actual immobilization process is not well understood and has mainly been studied by indirect measurements. The present work demonstrates a direct method for real time study of enzyme immobilization in mesoporous silica particles using quartz crystal microbalance with dissipation monitoring (QCM-D). Silica-coated sensors were grafted with amine groups followed by adsorption of small (40nm), spherical mesoporous silica particles, after which the enzyme immobilization into the mesoporous particles could be studied in real time. The influence of pH on the immobilization efficiency was studied using two different enzymes; lipase from Rhizopus oryzae and feruloyl esterase from Fusarium oxysporum. The results showed that the silica particles adsorbed readily to the amine-grafted surface. The QCM-D measurements indicated that considerably more enzyme was immobilized into mesoporous silica particles than to non-porous silica particles and to a flat silica surface. The viscoelastic effect of the immobilized enzymes was visualized by plotting the frequency shift against the corresponding dissipation. It was observed that the immobilization into the porous particles can be divided into two regimes where the first regime is suggested to represent adsorption to the outer surface and pore openings and the second regime represents further adsorption inside the pores. In summary, we demonstrated QCM-D as a novel method for understanding enzyme immobilization in mesoporous particles in real time and the approach may be of general use for studies of entrapment of molecules into porous particles.

Analysis of the Dynamic Interaction Between SVOCs and Airborne Particles

A proper quantitative understanding of the dynamic interaction between gas-phase semivolatile organic compounds (SVOCs) and airborne particles is important for human exposure assessment and risk evaluation. Questions regarding how to properly address gas/particle interactions have introduced uncertainty when predicting SVOC concentrations and assessing exposures to these compounds. In this study, we have developed a dimensionless description for the dynamic interaction between SVOCs and organic particles. A better criterion to judge whether the internal resistance (diffusion in and out of aerosols) is negligible compared with the external one (from bulk air to aerosol surfaces) is presented. The analysis is applicable regardless of the phase state of particles (either liquid or amorphous semisolid/solid). It is found that for both porous and nonporous particles, the internal resistance can be reasonably neglected for particles with diameters between 0.01 and 10 μm if the particulate organic matter is in t...

Covalent Immobilization of β-Glucosidase on Magnetic Particles for Lignocellulose Hydrolysis

β-Glucosidase hydrolyzes cellobiose to glucose and is an important enzyme in the consortium used for hydrolysis of cellulosic and lignocellulosic feedstocks. In the present work, β-glucosidase was covalently immobilized on non-porous magnetic particles to enable re-use of the enzyme. It was found that particles activated with cyanuric chloride and polyglutaraldehyde gave the highest bead-related immobilized enzyme activity when tested with p-nitrophenyl-β-D-glucopyranoside (104.7 and 82.2 U/g particles, respectively). Furthermore, the purified β-glucosidase preparation from Megazyme gave higher bead-related enzyme activities compared to Novozym 188 (79.0 and 9.8 U/g particles, respectively). A significant improvement in thermal stability was observed for immobilized enzyme compared to free enzyme; after 5 h (at 65 °C), 36 % of activity remained for the former, while there was no activity in the latter. The performance and recyclability of immobilized β-glucosidase on more complex substrate (pretreated spruce) was also studied. It was shown that adding immobilized β-glucosidase (16 U/g dry matter) to free cellulases (8 FPU/g dry matter) increased the hydrolysis yield of pretreated spruce from ca. 44 % to ca. 65 %. In addition, it was possible to re-use the immobilized β-glucosidase in the spruce and retain activity for at least four cycles. The immobilized enzyme thus shows promise for lignocellulose hydrolysis.

High-performance liquid chromatography separation of monoclonal IgG2 isoforms on a column packed with nonporous particles

The IgG2 subclass of antibodies has emerged as an attractive therapeutic framework. However, a method for sufficiently separating the three IgG2 disulfide isoforms has not been developed. Here, we report a method for efficient separation of monoclonal IgG2 isoforms by means of high-performance liquid chromatography on a column packed with 2 μm nonporous ODS silica particles. Under optimized conditions, the isoforms were separated with high resolution because mass transfer resistance in the stationary phase was reduced by the use of the small, nonporous particles. The number of separated peaks was more than twice that reported previously. The run-to-run repeatability of the IgG2 separation pattern was satisfactory, and the day-to-day repeatability of the retention time of the main peak was good (relative standard deviation 0.9%). The separation pattern can be expected to be useful for monitoring quality consistency of therapeutic antibodies.

How changing the particle structure can speed up protein mass transfer kinetics in liquid chromatography

The mass transfer kinetics of a few compounds (uracil, 112Da), insulin (5.5kDa), lysozyme (13.4kDa), and bovine serum albumin (BSA, 67kDa) in columns packed with several types of spherical particles was investigated under non-retained conditions, in order to eliminate the poorly known contribution of surface diffusion to overall sample diffusivity across the porous particles in RPLC. Diffusivity across particles is then minimum. Based on the porosity of the particles accessible to analytes, it was accurately estimated from the elution times, the internal obstruction factor (using Pismen correlation), and the hindrance diffusion factor (using Renkin correlation). The columns used were packed with fully porous particles 2.5μm Luna-C18 100Å, core–shell particles 2.6μm Kinetex-C18 100Å, 3.6μm Aeris Widepore-C18 200Å, and prototype 2.7μm core–shell particles (made of two concentric porous shells with 100 and 300Å average pore size, respectively), and with 3.3μm non-porous silica particles. The results demonstrate that the porous particle structure and the solid–liquid mass transfer resistance have practically no effect on the column efficiency for small molecules. For them, the column performance depends principally on eddy dispersion (packing homogeneity), to a lesser degree on longitudinal diffusion (effective sample diffusivity along the packed bed), and only slightly on the solid–liquid mass transfer resistance (sample diffusivity across the particle). In contrast, for proteins, this third HETP contribution, hence the porous particle structure, together with eddy dispersion govern the kinetic performance of columns. Mass transfer kinetics of proteins was observed to be fastest for columns packed with core–shell particles having either a large core-to-particle ratio or having a second, external, shell made of a thin porous layer with large mesopores (200–300Å) and a high porosity (≃0.5–0.7). The structure of this external shell seems to speed up the penetration of proteins into the particles. A stochastic model of the penetration of bulky proteins driven by a concentration gradient across an infinitely thin membrane of known porosity and pore size is suggested to explain this mechanism. Yet, under retained conditions, surface diffusion speeds up the mass transfer into the mesopores and levels the kinetic performance of particles built with either one or two porous shells.

Efficient removal of heavy metal from aqueous solution by sulfonic acid functionalized nonporous silica microspheres

Nonporous thiol-functionalized silica spheres (SiO2SH) were prepared by hydrolysis of 3-mercaptopropyltrimethoxysilane. Then, sulfonic acid functionalized silica microspheres (SiO2SO3H) were prepared through direct oxidization of SiO2SH by H2O2 and used as adsorbent. The structure and surface of the adsorbent were investigated by field emission scanning electron microscopy, N2 adsorption–desorption isotherm, Fourier transform infrared spectroscopy and electron diffraction spectroscope. The BET surface area of the particles is only 1.58m2/g. However, the content of thiol group on particle surface was as high as 36% (wt%). It was found that the SiO2SO3H could effectively remove heavy metal ions (Pb2+, Cd2+, and Cu2+) in solution through electrostatic interaction. When SiO2SO3H with the particle size of 0.95μm was used as adsorbent, the adsorption capacity for Pb2+, Cd2+, and Cu2+ reaches 635, 499, and 260mg/g, respectively. The strong adsorption ability of SiO2SO3H can be attributed to the nonporous particles with rich sulfonic group facilitating the mass transport of metal ions to the active sites. The adsorption isotherm data obey the Freundlich model. Kinetics of the metal ions removal was found to follow pseudo-second-order rate equation. pH values have only small influence on the adsorption capacity in the studied pH range. Consecutive adsorption–desorption experiments showed that SiO2SO3H could be reused with only a slight loss in the adsorption capacity.

Poly-lactide-co-glycolide nanoparticles containing voriconazole for pulmonary delivery: in vitro and in vivo study

Poly-lactide-co-glycolide nanoparticles (207–605 nm) containing voriconazole (VNPs) were developed using a multiple-emulsification technique and were also made porous during preparation in presence of an effervescent mixture for improved pulmonary delivery. Pulmonary deposition of the particles was studied using a customized inhalation chamber. VNPs had a maximum of 30% (w/w) drug loading and a zeta potential (ZP) value around −20 mV. In the initial 2 hours, 20% of the drug was released from VNPs, followed by sustained release for 15 days. Porous particles had a lower mass median aerodynamic diameter (MMAD) than nonporous particles. Porous particles produced the highest initial drug deposition (~120 μg/g of tissue). The drug was detectable in lungs until 7 days and 5 days after administration, for porous and nonporous particles, respectively. VNPs with improved drug loading were successfully delivered to murine lungs. Porous nanoparticles with lower MMADs showed better pulmonary deposition and sustained presence in lungs. From the Clinical EditorIn this paper, voriconazole-containing porous nanoparticles were studied for inhalational delivery to lung infections in a murine model, demonstrating prolonged half-life and improved pulmonary deposition.

Electrical conductivity relaxation in PVOH+LiH2PO4+Al2O3 polymer composites

Low-frequency conductivity measurements have been performed in solid polymer electrolyte composites based on the anhydrous PVOH–LiH2PO4–Al2O3 system. A typical power law dependency in the real part of the conductivity, at higher frequencies, of the form ωn is observed, with an exponent n that depends on the alumina content and nearly independent of temperature. An analysis of the frequency dependence of the electrical susceptibility is conducted to obtain relaxation functions of the form exp[−(t/τ)β], with an exponent β ≈ n − 1. Correlation times, τ, and parameters characterizing the electrical relaxation in time and frequency domains are compared to show the equivalence of these representations. The anhydrous dc conductivity of the electrolytes increases with increasing lithium salt content, becoming of the order of 10−5 S/cm for a salt molar fraction of x = 0.14. This conductivity value increased by about one order of magnitude by addition of nanoporous particles of Al2O3. The temperature dependence of the samples conductivity was well described by the Vogel–Tammann–Fulcher’s equation indicating the effect of the polymer chains flexibility on ion migration. Although all membranes exhibited a “universal dynamic response” associated to the random hopping of the mobile carriers, variations in the measured relaxation parameters with alumina content indicate an increase of ionic correlations when adding the nonporous particles to the polyelectrolyte.

Long-term fate of silica nanoparticles interacting with human dermal fibroblasts

The long-term fate of fluorescent non-porous FITC-SiO2 nanoparticles of various sizes (10–200 nm) and charge is studied in the presence of human dermal fibroblasts. Particle aggregates are formed in the culture medium and uptaken, at least partially, by macropinocytosis. The smallest particles have a strong impact on cell viability and genotoxic effects can be observed for negatively-charged colloids 10 nm in size. Largest particles do not impact on cellular activity and can be monitored in cellulo via fluorescence and transmission electron microscopy studies over two weeks. These observations reveal a significant decrease in the size of silica particles located in endocytic vesicles. The dissolution process is confirmed by monitoring the cell culture medium that contains both colloidal and soluble silica species. Such dissolution can be explained on the sole basis of silica solubility and has great implication for the use of non-porous silica particles as intra-cellular drug release systems.

Superior hydrogen production rate by catalytic hydrolysis of ammonia borane using Co-B nanoparticles supported over mesoporous silica particles

Catalyst in the form of Co-B nanoparticles supported on mesoporous silica particles (MSP) was synthesized by chemical impregnation–reduction method. This catalyst powder was used for hydrogen production by hydrolysis of Ammonia Borane (AB) and was compared with Co-B catalyst supported on non-porous silica particles (NSP) and unsupported Co-B powder. It was found that the MSPs synthesized in the present studies have average pore size of about 3.1 nm which were efficient to anchor the Co-B particles with average size of ~ 8 nm on the surface to provide high active surface area and improved degree of dispersion. MSP-supported Co-B catalyst was able to produce expected amount of H2 gas from hydrolysis of AB with significantly superior generation rate, about 3 times higher than that produced by unsupported and NSP-supported Co-B catalyst. Availability of a large number of under-coordinated Co active atoms owing to the size of nanoparticles, better dispersion, high surface area and good stability against agglomeration during the reaction are the main features acquired by the Co-B nanoparticles supported on MSP that exhibit high catalytic efficiency.

Adsorption of direct yellow 27 from water by poorly crystalline hydroxyapatite prepared via precipitation method

In the present study, hydroxyapatite powders were prepared by modified precipitation method and characterized by XRD, FT-IR and N2 adsorption–desorption techniques. The prepared nonporous particles were organized to agglomerate with mesoporous structure and consisted of low crystallinity Ca-deficient hydroxyapatite and in amorphous phase. The commercial direct yellow 27 was selected as a model dye in order to examine the adsorption capacity of hydroxyapatite at room temperature. The adsorption isotherms are transformed from L-type to S-type curve, in Giles classification, by increasing the pH values. Equilibrium data fitted very well to the Langmuir model, signifying the energetic homogeneity of hydroxyapatite surface adsorption sites. The dye sorption kinetics was fairly described by the pseudo-first-order kinetic model.

Engineered silica nanocarriers as a high-payload delivery vehicle for antioxidant enzymes

Antioxidant enzymes for the treatment of oxidative stress-related diseases remain a highly promising therapeutic approach. As poor localization and stability have been the greatest challenges to their clinical translation, a variety of nanocarrier systems have been developed to directly address these limitations. In most cases, there has been a trade-off between the delivered mass of enzyme loaded and the carrier’s ability to protect the enzyme from proteolytic degradation. One potential method of overcoming this limitation is the use of ordered mesoporous silica materials as potential antioxidant enzyme nanocarriers. The present study compared the loading, activity and retention activity of an anti-oxidant enzyme, catalase, on four engineered mesoporous silica types: non-porous silica particles, spherical silica particles with radially oriented pores and hollow spherical silica particles with pores oriented either parallel to the hollow core or expanded, interconnected bimodal pores. All these silica types, except non-porous silica, displayed potential for effective catalase loading and protection against the proteolytic enzyme, pronase. Hollow particles with interconnected pores exhibit protein loading of up to 50wt.% carrier mass, while still maintaining significant protection against proteolysis.