Adsorption of duplex DNA on mesoporous silicas: possibility of inclusion of DNA into their mesopores

It is well known that a silica surface cannot adsorb duplex DNA in common aqueous solution (not chaotropic solution) because of the electrostatic repulsion of the silica surface and polyanionic DNA. However, we recently found that when duplex DNA in phosphoric acid form (or in acidic solution) was used, DNA was successfully adsorbed into mesoporous silicas even in low-salt aqueous solution. The adsorption behaviors of DNA into mesoporous silicas were influenced by the pore diameter sizes. Mesoporous silicas with 2.80- or 3.82-nm peak pore diameters adsorbed DNA the best in diluted NaCl solution. Formation of the hydrogen bond between P(O)OH groups in DNA and adsorbed water, SiOH groups, or both on silica surfaces is regarded as a main factor in this adsorption. The coincidence of the pore sizes and DNA diameter realizes this unique adsorption promoted by the effect of encompassing DNA with the inner surface of mesoporous silica. Although there is no clear direct evidence for including duplex DNA in the mesopores yet, this adsorption technique is expected to provide a new tool for DNA science, because DNA in the pore size 2-5 nm in diameter has to be in unusual disentangled thread form.     

A sol-gel method using acetic anhydride in the presence of cholesterol in organic solution media: preparation of silicas that recognize steroid hormones

Silicas were prepared by a sol-gel method from tetraethoxysilane and acetic anhydride in the presence of cholesterol in organic solution media. Some silicas had higher pore volumes than silicas obtained in the absence of cholesterol. The adsorption abilities by these silicas were compared using various compounds in benzene solution. Although no clear difference among their adsorptions of cholesterol was observed, progesterone and other analogous steroid hormones were well adsorbed by silicas prepared in the presence of cholesterol, especially, prepared with n-heptane as an additional solvent. This silica adsorbed steroid hormones more selectively than other analogous compounds such as bisphenol A and hexestrol. On the other hand, a silica prepared by the usual aqueous sol-gel method with cholesterol had no clear adsorption selectivity to steroid hormones. Furthermore, no selective adsorption of steroid hormones was observed in the case of a common silica gel for column chromatography. This unique property of adsorption observed in silicas prepared using acetic anhydride in the presence of cholesterol is likely to be induced by the imprinting effect of the steroid skeleton part of cholesterol in silica matrix.     

2-Mercaptothiazoline modified mesoporous silica for mercury removal from aqueous media

Mesoporous silicas (SBA-15 and MCM-41) have been functionalized by two different methods. Using the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the mesoporous silica surface to give the chlorinated mesoporous silica Cl-SBA-15 or Cl-MCM-41. In a second step a multifunctionalized N, S donor compound (2-mercaptothiazoline, MTZ) was incorporated to obtain the functionalized silicas denoted as MTZ-SBA-15-Het or MTZ-MCM-41-Het. Using the homogeneous route, the functionalization was achieved via the one step reaction of the mesoporous silica with an organic ligand containing the chelating functions, to give the modified mesoporous silicas denoted as MTZ-SBA-15-Hom or MTZ-MCM-41-Hom. The functionalized mesoporous silicas were employed as adsorbents for the regeneration of aqueous solutions contaminated with Hg (II) at room temperature. SBA-15 and MCM-41 functionalized with MTZ by the homogeneous method present good mercury adsorption values (1.10 and 0.7mmolHg (II)/g of silica, respectively). This fact suggests a better applicability of such mesoporous silica supports to extract Hg (II) from aqueous solutions. In addition, it was observed the existence of a correlation between mercury adsorption with pore size and volume since, SBA-15 with lower areas and higher pore sizes functionalized with sterically demanding ligands, show better adsorption capacities than functionalized MCM-41.     

Feasibility study of silica sol as the carrier of a hydrophobic drug in aqueous solution using enrofloxacin as the model

The aim of this study was to determine the feasibility of using silica sol to carry a hydrophobic drug in aqueous solution. Enrofloxacin, which was selected as the model drug because it is a broad-spectrum antibiotic drug with poor solubility in water, was adsorbed onto silica sol in aqueous solution during cooling from 60 °C to room temperature. The drug-loaded silica sol was characterized by transmission electron microscopy, Fourier transform infrared spectrum, thermal gravimetric analysis and ultraviolet–visible light spectroscopy. The results showed that enrofloxacin was adsorbed by silica sol without degradation at a loading of 15.23 wt.%. In contrast to the rapid release from pure enrofloxacin, the drug-loaded silica sol showed a slower release over a longer time. Kinetics analysis suggested the drug release from silica sol was mainly a diffusion-controlled process. Therefore, silica sol can be used to carry a hydrophobic drug in aqueous solution for controlled drug delivery.     

Human Low Density Lipoprotein (LDL) and Human Serum Albumin (HSA) Co‐Adsorption Onto the C18‐Silica Gradient Surface

Co‐adsorption kinetics of human low density lipoprotein (LDL) and serum albumin (HSA) on hydrophilic/hydrophobic gradient silica surface were studied using Total Internal Reflection Fluorescence (TIRF) and autoradiography. Two experimental systems were examined: (1) fluorescein‐labeled LDL (FITC‐LDL) adsorption from a FITC‐LDL + HSA solution mixture onto the octadecyldimethylsilyl (C18)‐silica gradient surface, and (2) the FITC‐LDL adsorption onto the HSA pre‐adsorbed on the C18‐silica gradient surface. Experiments with fluorescein‐labeled albumin (FITC‐HSA) and unlabeled LDL have been performed in parallel. The adsorption kinetics of FITC‐LDL onto the hydrophilic silica was found to be transport‐limited and not affected by co‐adsorption of HSA. A slower adsorption kinetics of lipoprotein onto the silica with pre‐adsorbed HSA layer resulted from a slow appearance of LDL binding sites exposed by the process of HSA desorption. In the region of increasing surface density of C18 groups, the FITC‐LDL adsorption rate fell below the transport‐limited adsorption rate, except in the very early adsorption times. Pre‐adsorption of HSA onto the C18‐silica gradient region resulted in a significant decrease of both the FITC‐LDL adsorption rate and adsorbed amount. The lowest FITC‐LDL adsorption was found in the region of C18 self‐assembled monolayer, where the pre‐adsorbed HSA layer almost completely eliminated lipoprotein binding.     

Phase Characterization of Indomethacin in Adsorbates Onto Hydroxyethylcellulose

The phase state and solubility of indomethacin in adsorbates onto hydroxyethylcellulose have been studied. The characterization of the adsorbates and their relevant physical mixtures was made by the use of DSC, X-ray diffractometry, FT-IR spectrometry, and solubility analysis. The drug-to-polymer ratio determines either a partial crystallization of the metastable alpha-form onto hydroxyethylcellulose surface or complete inhibition of indomethacin crystallization. Significantly improved drug aqueous solubility was achieved. A stable immobilization of indomethacin molecules onto hydroxyethylcellulose due to drug/polymer interactions can be assumed. The changed indomethacin phase state in the adsorbates remains stable for one-year storage at ambient conditions. These results could be of practical importance.     

Phase characterization of indomethacin in adsorbates onto hydroxyethylcellulose

The phase state and solubility of indomethacin in adsorbates onto hydroxyethylcellulose have been studied. The characterization of the adsorbates and their relevant physical mixtures was made by the use of DSC, X-ray diffractometry, FT-IR spectrometry, and solubility analysis. The drug-to-polymer ratio determines either a partial crystallization of the metastable alpha-form onto hydroxyethylcellulose surface or complete inhibition of indomethacin crystallization. Significantly improved drug aqueous solubility was achieved. A stable immobilization of indomethacin molecules onto hydroxyethylcellulose due to drug/polymer interactions can be assumed. The changed indomethacin phase state in the adsorbates remains stable for one-year storage at ambient conditions. These results could be of practical importance.     

Adsorption of Some 1. 4-Benzodiazepines on Insoluble Tablet Excipients and Charcoal

Abstract

The adsorption of five widely used 1. 4-benzodiazepines on talc, calcium phosphate, magnesium stearate, microcrystalline celluloses, ethyl cellulose and starch was studied. Adsorption of these compounds on charcoal was also investigated for comparison. Diazepam was found not to be adsorbed on talc, calcium phosphate and magnesium stearate. A relatively low adsorption of the drug by cellulose and starch was measured. The amount of diazepam adsorbed per unit weight of ethyl cellulose was high in water and in phosphate buffer, while no adsorption could be measured in 0.1 N HCL. The drug interact with ethyl cellulose at higher concentrations (100-180 mcg/ml). The UV and IR of the reactants and products were studied.

The adsorption of nordiazepam, nitrazepam, flunitrazepam and chlordiazepoxide onto ethyl cellulose and charcoal from their aqueous solutions was also studied. Diazepam and nordiazepam showed the highest adsorption on ethyl cellulose. The desorption of benzodiazepines from ethyl cellulose in 0.1 N HC1 was at the following decreasing rate: flunitrazepam, chlordiazepoxide, nitrazepam, diazepam, nordiazepam.     

Adsorption effect of aqueous bichlorobiphenyls onto UV-illuminated titanium dioxide

Bichlorobiphenyls were adsorbed onto TiO(2) (Degussa P25) in batch equilibrium experiments. The results demonstrated that a triple-layer model (TLM) surface complex formation model described the adsorption of chlorobiphenyls onto the surface of the TiO(2) solid. The surface complex configuration and the adsorption reaction may have followed the equation derived from the TLM, involving the loss of a proton during the adsorption process. This dependence indicates that the oxidation reaction between surface-adsorbed substrates and photogenerated oxidants dominates. Both sorbed and dissolved components contribute to the observed degradation rate, that is, the 4,4'-CBP degradation rates might be stated as linear functions of the sorbed and dissolved concentrations. The contribution of the concentration of solution phase in degradation pathways is not negligible.     

Adsorption performance of VOCs in ordered mesoporous silicas with different pore structures and surface chemistry

Ordered mesoporous silicas with different pore structures, including SBA-15, MCM-41, MCM-48 and KIT-6, were functionalized with phenyltriethoxysilane by a post-synthesis grafting approach. It was found that phenyl groups were covalently anchored onto the surface of mesoporous silicas, and the long-range ordering of the mesoporous channels was well retained after the surface functionalization. The static adsorption of benzene and the dynamic adsorption of single component (benzene) and bicomponent (benzene and cyclohexane) on the original and functionalized materials were investigated. As indicated by the adsorption study, the functionalized silicas exhibit improvement in the surface hydrophobicity and affinity for aromatic compounds as compared with the original silicas. Furthermore, the pore structure and the surface chemistry of materials can significantly influence adsorption performance. A larger pore diameter and cubic pore structure are favorable to surface functionalization and adsorption performance. In particular, the best adsorption performance observed with phenyl-grafted KIT-6 is probably related to the highest degree of surface functionalization, arising from the relatively large mesopores and bi-continuous cubic pore structure which allow great accessibility for the functional groups. In contrast, functionalized MCM-41 exhibits the lowest adsorption efficiency, probably owing to the small size of mesopores and 1D mesoporous channels.     

Increasing Dissolution Rates of Poorly Soluble Drugs by Adsorption to Montnorillonith

The surface adsorption of griseofulvin, indomethacin and prednisone to colloidal magnesium aluminum silicate was shown to markedly improve the dissolution rates of there hydrophobic and party soluble drugs. The rapid release of drug from the surface of the clay was due to the weak physical bonding between the two materials and to the swelling of the clay in aqueous media. The hydrophilic and swelling properties of the montmorillonite clay in aqueous media also helped to facilitate the wetting of hydro-phobic drug substances. The equilibrating solvents employed in the preparation of the griseofulvin-clay adsorbates caused a significant variance in the dissolution profiles of griseofulvin. This did not occur with indomethacin. Dramatic increases in dissolution rates were seen with the prednisone adsorbates and 100 percent of the drug was present in solution from the 1:4 ad-sorbate after four minutes.     

Poly(L-lysine)-poly(ethylene glycol) layers with different structure and their influence on silica suspension stability

The effects of the structure of di- and triblock copolymers of poly(L-lysine) – LYS with poly(ethylene glycol) – PEG as well as the length of nonionic fragment in the LYS-PEG macromolecule on the copolymer chains conformation in the adsorption layer formed on the colloidal silica (SiO2) surface were examined. Spectrophotometry and turbidimetry were applied for the determination of copolymer adsorbed amounts and stability coefficients of silica aqueous suspensions. The electrokinetic parameters such as solid surface charge density and zeta potential were also estimated. The adsorption of LYS-PEG was proved to be the highest at pH 10 whereas the lowest adsorption on the solid surface was found for the triblock copolymer with long fragments of LYS at the same pH value.     

壳聚糖包覆二氧化硅纳米粒及其作为蛋白载体的研究

通过壳聚糖在二氧化硅纳米粒表面的沉积制备了壳聚糖包覆的二氧硅（CS@SiO2）。采用BSA作为模型蛋白,研究了CS@SiO2作为蛋白载体的可能性。结果表明,CS@SiO2可有效吸附BSA且可控释放被吸附的BSA。     

Preparation and characterization of thermosensitive submicron particles for gene delivery

In this study, a new thermosensitive material was proposed as a carrier for gene delivery. The thermosensitive submicron particles were synthesized by the dispersion copolymerization of N-isopropylacylamide (NIPA) with a relatively new, cationic comonomer, N-3-dimethylaminopropylmethacrylamide (DMAPM) with higher ionization ability with respect to the commonly used cationic comonomers. To achieve particle sizes smaller than 1 microm, suitable for gene delivery, the total monomer concentration in the dispersion copolymerization was kept at a sufficiently low level. The size of poly(NIPA-co-DMAPM) particles was determined as 454 nm, by AFM in dry state. The poly(NIPA-co-DMAPM) particles showed both temperature and pH sensitivity in the aqueous media.The plasmid DNA adsorption onto the thermosensitive cationic particles was investigated at different temperatures and pHs. The adsorbed amount of plasmid DNA onto the particles was significantly increased by the introduction of cationic comonomer. The equilibrium plasmid DNA adsorptions up to 13 mg/g dry particles were achieved at physiological pH. Approximately 36% w/w of adsorbed plasmid could be desorbed from the cationic nanolatex. The results of biocompatibility studies performed with mouse fibroblast cells showed the suitability of thermosensitive cationic particles for intended application.     

Application of electrostatic pull-in instability on sensing adsorbate stiffness in nanomechanical resonators

Recent theoretical and experimental research showed that the response of micro/nanocantilevers to detect materials is not always simply related to extra mass. Stiffness of adsorbates and surface stress-induced changes in the stiffness, arising from adsorption, can produce frequency shifts that are several times greater in magnitude than those induced by mass loading. Consequently, the calculated adsorbed mass does not fully represent the real adsorbed mass, making the measurements qualitative. Therefore, a proper method for measuring the stiffness of adsorbed layers has to be combined with resonance frequency measurement to quantitatively analyze changes in both the mass and the stiffness. This letter presents the theory for application of electrostatic pull-in instability for measuring the stiffness of adsorbates at the surface of cantilever resonators.     

In situ adsorption studies at silica/solution interfaces by attenuated total internal reflection fourier transform infrared spectroscopy: examination of adsorption models in normal-phase liquid chromatography

ATR-FT-IR spectroscopy was employed to the study the adsorption of ethyl acetate and 2-propanol to the surface of thin silica sol-gel films in contact with n-heptane solutions. In situ vibrational spectra of silica-adsorbed species provided information regarding the mechanisms of solute retention and elution in normal-phase chromatography. Previous normal-phase chromatographic studies of ethyl acetate adsorption revealed nonlinear isotherms which were explained by both bilayer and adsorbate delocalization models. Infrared spectra of ethyl acetate at the silica surface versus concentration showed that nonlinear adsorption can be attributed to site heterogeneity, where adsorption to free silanols and surface-adsorbed water can be distinguished. Least-squares modeling of the data produced resolved spectra for the two sites and adsorption equilibrium constants that differed by about an order of magnitude. Adsorption of 2-propanol was best modeled by a single Langmuir isotherm showing no significant difference in adsorption energy for the two sites; 2-propanol was shown to easily displace ethyl acetate from the silica surface. Ethyl acetate could also displace 2-propanol from the silica, and least-squares modeling again revealed two-adsorbed-component spectra for ethyl acetate that were indistinguishable from spectra obtained when ethyl acetate adsorbed directly onto the surface.     

Conformational stability of adsorbed insulin studied with mass spectrometry and hydrogen exchange.

A new method is described for direct monitoring of the conformational stability of proteins that are physically adsorbed from solution onto a solid substrate. The adsorption-induced conformational changes of insulin are studied using a combination of hydrogen/deuterium (H/D) exchange and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The effect of the surface hydrophobicity on the adsorption-induced conformational changes in the insulin structure is probed by adsorbing insulin on a hydrophilic silica and a hydrophobic methylated silica surface before subjecting the insulin molecules to the isotopic exchange process. The present study describes the experimental procedure of this new application of MALDI. Results show that insulin is more highly and more irreversibly adsorbed to a hydrophobic methylated silica surface than to a hydrophilic silica surface. Hydrogen-exchange experiments clearly demonstrate that the strong interaction of insulin with the hydrophobic surface is accompanied by a strong increase in the H/D-exchange rates and thus in a reduction in the insulin native structural stability. In contrast, H/D-exchange rates of insulin are somewhat reduced upon adsorption on silica from solution.     

Adsorption of methylene blue onto silylated silica surfaces, studied using visible attenuated total reflection spectroscopy with a slab optical waveguide

The behavior of methylene blue (MB) molecules at silica/water and silylated silica/water interfaces was examined using visible attenuated total reflection spectroscopy with a slab optical waveguide (SOWG). An alkyl silane coating changed the adsorbed form of MB on the surface from a dimer (lambda max = 600 nm, bare silica surface) to a monomer (lambda max = 670 nm), and the carbon number of the silylation reagent influenced the amount of adsorption and the orientation of the molecule. Moreover, the addition of an anionic surfactant, dodecylbenzenesulfonate (DBS), caused the deposition of MB/DBS ion pairs, which gave an identical attenuated total reflection (ATR) spectrum to that of the dimer. Linear dichroism measurements revealed that the ion pairs were adsorbed onto the silylated silica surface randomly in terms of the orientation angle of MB, while the MB monomer was strongly oriented, i.e., the direction of the transition moment of MB roughly parallels the surface plane. This difference in the orientation angles of the adsorbed species can be utilized for their selective detection using polarization SOWG measurements.     

Devazipide (MK-329) Adsorption on Microcrystalline Cellulose

Abstract

An in-depth evaluation of the adsorption of Devazipide onto microcrystalline cellulose, formulation and/or process optimization procedures to minimize this adsorption are reported. This adsorption was more evident in the 1 mg compared to the 10 mg strength tablet and could be completely eliminated if the microcrystalline cellulose was reduced to <10%. This adsorption followed the Langmuir Isotherm and was dependent on pH with insignificant amount of adsorption occurring at pH 2.0. At this particular pH, adsorbed drug is easily released.     

Drug Release from Coadsorbates of Nonionic Surfactants with Parabenes on Porous Silica Supports

Abstract

Parabenes are coadsorbed from aqueous solutions with nonionic surfactants (polyoxyethylene-nonyl-phenols) on silica surfaces. Rate and extend of para-bene desorption from corresponding coadsorbates on porous silica were shown to be dependent on the influence of structure and pore size (in the mesopore range 2–10 nm) of the silica supports, the alkyl chain length of the parabenes, the structure of the POE-surfactant, and the adsorption equilibria established during the drug loading of the supports. The consequences of coadsorption on drug release modification are discussed.