Inorganic Silica Matrix Research Articles

Synthesis, Structural, Morphological and Thermal Characterization of Five Different Silica-Polyethylene Glycol-Chlorogenic Acid Hybrid Materials

The present study investigated the structure, morphology, thermal behavior, and bacterial growth analysis of novel three-component hybrid materials synthesized by the sol-gel method. The inorganic silica matrix was weakly bonded to the network of two organic components: a well-known polymer such as polyethylene glycol (PEG, average molar mass of about 4000 g/mol), and an antioxidant constituted by chlorogenic acid (CGA). In particular, a first series was made by a 50 wt% PEG-based (CGA-free) silica hybrid along with two 50 wt% PEG-based hybrids containing 10 and 20 wt% of CGA (denoted as SP50, SP50C10 and SP50C20, respectively). A second series contained a fixed amount of CGA (20 wt%) in silica-based hybrids: one was the PEG-free material (SC20) and the other two contained 12 and 50 wt% of PEG, respectively (SP12C20 and SP50C20, respectively), being the latter already included in the first series. The X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images of freshly prepared materials confirmed that all the materials were amorphous and homogeneous regardless of the content of PEG or CGA. The thermogravimetric (TG) analysis revealed a higher water content was adsorbed into the two component hybrids (SP50 and SC20) because of the availability of a larger number of H-bonds to be formed with water with respect to those of silica/PEG/CGA (SPC), where silica matrix was involved in these bonds with both organic components. Conversely, the PEG-rich materials (SP50C10 and SP50C20, both with 50 wt% of the polymer) retained a lower content of water. Decomposition of PEG and CGA occurred in almost the same temperature interval regardless of the content of each organic component. The antibacterial properties of the SiO2/PEG/CGA hybrid materials were studied in pellets using either Escherichia coli and Enterococcus faecalis, respectively. Excellent antibacterial activity was found against both bacteria regardless of the amount of polymer in the hybrids.

Ibuprofen incorporated into unmodified and modified mesoporous silica: From matrix synthesis to drug release

Abstract Aiming to rationalize the release profile of an incorporated pharmaceutical drug in terms of its mobility, driven by guest-host interactions, the poorly water-soluble Ibuprofen drug was loaded in a mesoporous inorganic silica matrix with unmodified (MCM-41) and modified surface (MCM-41sil) by post-synthesis silylation, both having pore sizes ∼ 3 nm. The single calorimetric detection of a broad glass transition step for both ibuprofen composites indicates full drug amorphization, confirmed by the only appearance of an amorphous halo in the powder XRD patterns. Moreover, a gradient profile is disclosed by the heat flux derivative plot in the glass transition, in coherence with the thermogravimetric profile that shows a multi-step decomposition trace for confined ibuprofen in these matrixes. While identical guest dynamics, as probed by dielectric relaxation spectroscopy, were found in both dehydrated composites, a significant molecular population with faster relaxation exists in the hydrated state for the drug inside the unmodified matrix. This was rationalized as the concurrence of true confinement effects, which manifest under nanometer dimensions, and greater water affinity of the unmodified matrix, forcing the drug molecules to be placed mostly in the pore core. Finite size effects are also felt in both dehydrated composites, however guest-host interactions give origin to a dominant population with slowed down mobility that governs the overall guest dynamics. In spite of an inferior number of active sites for drug adsorption in the silylated matrix, a faster Ibuprofen delivery in phosphate buffer (pH = 6.8) was observed when the drug is released from unmodified MCM-41 in the hydrated state. Therefore, our results suggest that a relevant role is played by water molecules, which impair a strong guest adsorption in the host surface more efficiently than the limited surface modification, influence the higher ratio of a faster population in the pore core and facilitate the diffusion of the aqueous releasing media inside pores.

Structural modifications caused by the increasing MTES amount in hybrid MTES/TEOS-based silica xerogels

In this work, MTES/TEOS-based silica xerogels have been synthesized by sol-gel method from tetraethoxysilane (tetraethylorthosilicate, TEOS) and methyltriethoxysilane (MTES) using ethanol/water mixture, different MTES/TEOS molar ratios and two different pH levels.Starting with the TEOS silica precursor, the structural and dynamical variations - as a consequence of the introduction of an increasing amount of MTES from 5% to 80% of substitution - have been monitored by nitrogen porosimetry, small angle neutron scattering (SANS), electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and thermal analysis, with the aim to provide a clear picture about the relationship between the MTES/TEOS molar ratio and the induced structural variations. Knowledge on this aspect can furnish an experimental evidence of the hydrophilic/hydrophobic behavior of the whole matrix, which is strongly related to the size of the particles/pores within the investigated network. The obtained results revealed significant skeletal variations with the increase of the MTES amount, suggesting a strong influence of MTES in the inorganic silica matrix and the presence of three different structural regimes in the explored MTES substitution range. The possibility to “tune” the structural parameters varying the MTES content, represents a key point for the design of organic hybrid materials showing enhanced performances with respect to those prepared with TEOS only, particularly useful in various potential applications such as medicine and nanotechnology.

Efficient encapsulation of low dimensional particles in thin films to obtain functional coatings

The incorporation of nanoparticles into a polymeric matrix to improve the mechanical properties or add new functionalities is a very common practice in nanocomposites materials. However, the organic nature of the common matrices difficults this methodology. In this work, low dimensional particles (LDPs) are introduced in an inorganic silica matrix obtained by the sol-gel method, which provides an appropriate host to encapsulate the LDPs. The step of introducing particles with only one of their dimensions in the nanoscale, into an inorganic matrix is not defined in the literature, therefore, a study of process and efficiency of the LDPs encapsulation is carried out by means of measuring structural properties (SEM, XRD, DTA-TG, particle size) and functionalities (colorimetry and abrasion-chemical resistances) of composites in thin films.

Optimized hybrid nanospheres immobilizing Rhizomucor miehei lipase for chiral biotransformation

In this study, the immobilization of Rhizomucor miehei lipase into hybrid nanospheres containing a liposomal core was reported. Organic internal liposomal enzyme phase was protected by inorganic silica matrix, obtained with and without surfactant, that stabilizes the internal organic phase and isolates and protects the bioactive molecules. The optimized heterogeneous catalyst thus prepared was used for enantioselective esterification of (R,S)-ibuprofen. The influence of several catalytic parameters on the activity of hybrid nanospheres (type of solvent, nature of the alcohol, reaction temperature, etc.,) was investigated. The heterogeneous biocatalysts best performed at 37°C, using isooctane as solvent and 1-propanol as alcohol (with ester yield ranging between 78 and 93%). High activity and stability (up to nine reaction cycles) of enzyme-immobilized hybrid nanospheres, with respect to the free form, were observed. R. miehei lipase, both in its free and immobilized forms, reacts only with the S(+) enantiomer of (R,S)-ibuprofen, in all the tested reaction conditions.

Freeze-dried and spray-dried zinc-containing silica microparticles entrapping insulin

New approaches for oral administration of insulin are strongly related to novel insulin carriers. The aim of this study was the insulin microencapsulation in a new zinc-silica matrix for drug protection and controlled release. Zinc-silica microparticles loaded with insulin were obtained by sol-gel process via spray drying and freeze drying methods. Inorganic silica matrix isolates and constrains the movement of the biomolecules preventing their aggregation and denaturation, while the zinc oxide improves the system stability. Moreover, formation of insulin hexamers in the presence of zinc ions leads to an increased stability of the insulin three-dimensional structure during preparation, storage and release. The particles were characterized with respect to average size, specific surface area, porosity and morphology. In vitro behavior of insulin-loaded particles together with protein structural conformation was also evaluated. The release profile can be adapted by synthesis route of microparticles.

One-step synthesis of dye-incorporated porous silica particles

Fluorescent nanoparticles have a variety of biomedical applications as diagnostics and traceable drug delivery agents. Highly fluorescent porous silica nanoparticles were synthesized in a water/oil phase by a microemulsion method. What is unique about the resulting porous silica nanoparticles is the combination of a single-step, efficient synthesis and the high stability of its fluorescence emission in the resulting materials. The key of the success of this approach is the choice of a lipid dye that functions as a surrogate surfactant in the preparation. The surfactant dye was incorporated at the interface of the inorganic silica matrix and organic environment (pore template), and thus insures the stability of the dye–silica hybrid structure. The resulting fluorescent silica materials have a number of properties that make them attractive for biomedical applications: the availability of various color of the resulting nanoparticle from among a broad spectrum of commercially dyes, the controllablity of pore size (diameters of ~5 nm) and particle size (diameters of ~40 nm) by adjusting template monomer concentration and the water/oil ratio, and the stability and durability of particle fluorescence because of the deep insertion of surfactant’s tail into the silica matrix.

Composite materials based on ormosil for the construction of electrochemical sensors and biosensors

Sol-gel process has gained tremendous attention in past decades for the preparation of pure and composite material for numerous applications. Organically modified sol-gel glasses (ormosils) have hybrid properties of rigid inorganic silica matrix and organic functionalities. Ormosils provide ambient environment for bio-molecules encapsulation and such systems have been used widely for biosensor applications. Biological elements including enzymes, antibodies, antigens, DNA, whole cells, tissues, proteins, biologically derived material, and biomimetic materials provide the possibility of biological recognition to the device and transducer to detect the biological signals with the help of associated electronics and software to amplify these signals into a readable form for the user. In this review we report on the formation of sol-gel based composite materials primarily on ormosil along with carbon nano tubes, metal nano particles, mediators, inorganic complexes, polymers, ionomers and biological materials and cite the electrochemical sensor/biosensor system based on it.

Bicontinuous Cubic Mesoporous Materials with Biphasic Structures

The replication of amphiphilic systems within an inorganic silica matrix allows the study of the fundamental properties of mesostructural changes, that is, kinetic and structural parameters. Herein we report a detailed study of the transition between cubic bicontinuous mesostructure with space groups Ia ̅3d and Pn ̅3m symmetry, which are associated with the minimal G and D surfaces, respectively. The transition may be induced through micellar swelling of the anionic amphiphilic surfactant N-lauroyl alanine by trimethylbenzene. Rich kinetic behaviour is observed and has been exploited to prepare particles with biphasic structures. Transmission electron microscopy evidence indicates that there is epitaxial growth from one mesostructure to the other involving the [111] and [110] orientations of the Ia ̅3d and Pn ̅3m symmetry structures, respectively. From kinetic studies, we show that the formation of the Ia ̅3d mesophase is preceded by a hexagonal phase (plane group p6mm) and an epitaxial relationship has been observed involving the sixfold or ̅3 axis orientations of both structures. Our data suggests that the Pn ̅3m mesostructure is kinetically stable at low temperatures whereas the Ia ̅3d mesostructure is the more stable structure after prolonged periods of hydrothermal treatment. We present evidence from transmission electron microscopy and small-angle X-ray diffractograms and also electron crystallography modelling of the unit cells at particular points in the structural change.

Thermo-optic coefficient in some hybrid organic/inorganic fast sol–gel glasses

We have investigated the effect of organic content in hybrid organic/inorganic glasses prepared by the sol–gel process on the thermo-optic coefficient dn/ dT. The organic phase consisted of homogeneously dispersed methyl groups within an inorganic silica matrix. Analysis of Fresnel reflectance temperature dependence of an optically polished sample-surface yielded the desired value, with an accuracy of 10 −5/°C. A negative linear dependence of the thermo-optic coefficient on the volumetric thermal expansion coefficient β was obtained, dn/ dT[10 −4/°C] = −1.1–0.45 β[10 −4/°C]. Using Prod’homme’s model, a negative value was derived for the electronic polarizability coefficient Φ = (−1.8 ± 0.3) × 10 −4/°C. The negative sign of Φ is attributed to isolation of the silica matrix sections by the methyl groups, causing the sections to distance upon increase in temperature.

A Mesoporous 3D Hybrid Material with Dual Functionality for Hg2+ Detection and Adsorption

Dual-function hybrid material U1 was designed for simultaneous chromofluorogenic detection and removal of Hg(2+) in an aqueous environment. Mesoporous material UVM-7 (MCM41 type) with homogeneously distributed pores of about 2-3 nm in size, a large specific surface area exceeding 1000 m(2) g(-1), and nanoscale particles was used as an inorganic support. The mesoporous solid is decorated with thiol groups that were treated with squaraine dye III to give a 2,4-bis(4-dialkylaminophenyl)-3-hydroxy-4-alkylsulfanylcyclobut-2-enone (APC) derivative that is covalently anchored to the inorganic silica matrix. The solid was characterised by various techniques including X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and nitrogen adsorption. This hybrid solid is the chemodosimeter for Hg(2+) detection. Hg(2+) reacts with the APC fragment in U1 with release of the squaraine dye into the solution, which turns deep blue and fluoresces strongly. Naked-eye Hg(2+) detection is thus accomplished in an easy-to-use procedure. In contrast, U1 remains silent in the presence of other thiophilic transition metal ions, alkali and alkaline earth metal ions, or anions ubiquitously present in water such as chloride, carbonate, sulfate, and phosphate. Material U1 acts not only as chemodosimeter that signals the presence of Hg(2+) down to parts-per-billion concentrations, but at the same time is also an excellent adsorbent for the removal of mercury cations from aqueous solutions. The amount of adsorbed mercury ranges from 0.7 to 1.7 mmol g(-1), depending on the degree of functionalisation. In addition, hybrid material U1 can be regenerated for both sensing and removal purposes. As far as we know, U1 is the first example of a promising new class of polyfunctional hybrid supports that can be used as both remediation and alarm systems by selective signalling and removal of target species of environmental importance. Model compounds based on silica gel (G1), fumed silica (F1), and micrometre-sized MCM-41 scaffolds (M1) were also prepared and studied for comparative purposes.

Solid-phase assays for small molecule screening using sol-gel entrapped proteinsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Systems and Chemical Biology, and has undergone the Journal's usual peer review process.

With compound libraries exceeding one million compounds, the ability to quickly and effectively screen these compounds against relevant pharmaceutical targets has become crucial. Solid-phase assays present several advantages over solution-based methods. For example, a higher degree of miniaturization can be achieved, functional- and affinity-based studies are possible, and a variety of detection methods can be used. Unfortunately, most protein immobilization methods are either too harsh or require recombinant proteins and thus are not amenable to delicate proteins such as kinases and membrane-bound receptors. Sol-gel encapsulation of proteins in an inorganic silica matrix has emerged as a novel solid-phase assay platform. In this minireview, we discuss the development of sol-gel derived protein microarrays and sol-gel based monolithic bioaffinity columns for the high-throughput screening of small molecule libraries and mixtures.

Synthesis of propyl‐functionalized hybrid monolithic silica capillaries and evaluation of their performances in nano‐LC and CEC

During the last decade, silica monolithic capillaries have focused more and more attention on miniaturized separation techniques like CEC, nano-LC, and chip electrochromatography owing to their unique chromatographic properties and to their possible in situ synthesis. Nevertheless, the preparation of conventional silica-based individual monolithic columns is time consuming, owing to the individual steps involved, including the synthesis of the silica matrix and its subsequent on-column chemical grafting. The hybrid organic-inorganic monoliths, whose synthesis is based on the polycondensation of siloxane with organosiloxane precursors, seems to be an attractive alternative since their direct synthesis leads to silica monoliths with organic moieties covalently linked to the inorganic silica matrix through hydrolytically stable Si-C bonds. This study describes the synthesis of hybrid monoliths using propyltrimethoxysilane (C3-TriMOS) as a new kind of silica coprecursor to subsequently increase the hydrophobicity of the stationary phase. The influence of several experimental parameters (pH, gelation temperature, relative proportion of the precursors) on the textural (skeleton and macropore size) and chromatographic properties (efficiency, retention, and electroosmotic mobility) of the obtained monoliths are discussed. The results show that the optimal coprecursor incorporation is obtained after a postgelation step during which the condensation of the C3-TriMOS coprecursor is favored by an increase in the pH medium. Thermal hydrolysis of urea previously added to the polymerization mixture allows this in situ pH increase. These hybrid monoliths present hydrophobic properties and allow the separation of test mixtures in the RP mode without any further modification. Moreover, they present excellent efficiencies since reduced plate height as low as 5 and 15 microm are obtained in the electrodriven mode (CEC) and in the hydrodynamic one (nano-LC), respectively.

Optical investigation on dye-doped sol-gel glasses

We have investigated the optical properties of the 3,3′-diethyl-oxadicarbocyanine iodide (DODCI) dye incorporated in a number of sol-gel glasses in order to study the interaction between the trapped molecule and the host matrix. The differences found in both the absorption and the photoemission spectra demonstrate that the excitation processes of the dye molecule are influenced by the chemical reactivity and the degree of porosity of the surrounding network. We have found that while the molecular photoisomerization is quenched in all the matrices, for the modifications of the electronic excited states the high rigidity of the purely inorganic silica matrix is required. Conversely, the possibility of chemical attacks to the molecular conjugate chain seems to increase in the hybrid organic/inorganic ormosil matrices.

Dielectric Properties of Glass-Dispersed Liquid Crystals

Liquid crystals can be dispersed in gel-glass silica matrices by sol-gel processes. The resulting gel-glass dispersed liquid crystals (GDLCs) are similar to polymer-dispersed liquid crystals; however, the use of an inorganic silica matrix yields a material with enhanced optical and mechanical properties. Dielectric properties of these materials are highly dependent on the manufacturing conditions. Impedance spectroscopy of the isolated silica matrix and the GDLC composite has been employed to characterize the system between 200 mHz and 8 MHz. The results have been compared to theoretical results based on several equivalent circuits.

Sol-Gel-Derived Thin Films Incorporating An Organic Second-Order NLO Compound With Large βμ

ABSTRACTWe have synthesized a new second-order NLO compound containing both the highly active tricyanovinyl electron acceptor group and appropriate funtionality for covalent bonding to an inorganic silica matrix by sol-gel processing. Sub-Micron films of this material can be prepared by spin-coating, and thicker films can be prepared by casting or by spinning multiple layers. After curing at 150 °C, these films exhibit good chemical durability. The chromophores can be aligned by either corona or parallel-plate poling during the curing process. In this paper we will discuss the synthesis of the NLO compounds; sol-gel processing and thin-film preparation; optical, thermal, and chemical properties of the films; and the results of both corona and parallel-plate poling experiments.