Physicochemical Characterization and Drug Release Properties of Methyl-Substituted Silica Xerogels Made Using Sol-Gel Process.

In this work, a multi-analytical approach involving nitrogen porosimetry, small angle neutron and X-ray scattering, Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies, X-ray diffraction, thermal analysis and electron microscopy was applied to organically modified silica-based xerogels obtained through the sol-gel process. Starting from a tetraethoxysilane (TEOS) precursor, methyltriethoxysilane (MTES) was added to the reaction mixture at two different pH values (2.0 and 4.5) producing hybrid xerogels with different TEOS/MTES molar ratios. Significant differences in the structure were revealed in terms of the chemical composition of the silica network, hydrophilic/hydrophobic profile, particle dimension, pore shape/size and surface characteristics. The combined use of structural characterization methods allowed us to reveal a relation between the cavity dimensions, the synthesis pH value and the grade of methyl substitution. The effect of the structural properties on the controlled Captopril release efficiency has also been tested. This knowledge facilitates tailoring the pore network for specific usage in biological/medical applications. Knowledge on structural aspects, as reported in this work, represents a key starting point for the production of high-performance silica-based hybrid materials showing enhanced efficacy compared to bare silica prepared using only TEOS.

Synthesis of polyethylene glycol functional bonded silica gel for selective recognition and separation of α-cyclodextrin.

In this work, we for the first time synthesized the polyethylene glycol (PEG) bonded silica gel via KH-560 as a silane coupling reagent for column chromatography by a solid/liquid surface continuous reaction method. The molecular interaction, structure, morphology, and thermostability was characterized by fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), scanning electronic microscope (SEM) and thermogravimetric analysis (TGA). Given that PEG is capable to self-assemble with α-CD, the PEG bonded silica gel was used as packing of column chromatography to achieve the selective separation of α-cyclodextrin (α-CD) at room temperature and atmospheric pressure. The bonded silica gel column could realize the effective separation of α-CD in the enzymatic hydrolysis mixture, which provides support for industrial separation of α-CD.

Enhanced photocatalytic degradation of acephate pesticide over MCM-41/Co3O4 nanocomposite synthesized from rice husk silica gel and Peach leaves.

Novel green nanocomposite from mesoporous MCM-41 and Co3O4 was synthesized from rice husk based silica gel and using the green extract of Peach leaves as reducing reagent. The composite was labeled as RH-MCM-41/Co3O4 and characterized by different techniques as green photocatalyst in the degradation of Acephate pesticide under visible light illumination. The composite showed well developed spherical MCM-41 particles decorated by nano Co3O4 nanoparticles with stunning surface area and low bandgap energy (1.51 eV). The composite displayed superior photocatalytic activities in the oxidation of Acephate which reflected in a complete degradation of different concentrations of it after 40 min (50 mg/L), 60 min (100 mg/L), 100 min (150 mg/L) and 140 min (200 mg/L) using 0.25 g of the composite. The complete removal of the present TOC for treatment of 100 mg/L acephate was achieved using 0.25 g after 70 min reflecting the formation of intermediate compounds during the oxidation steps. The reported intermediate compounds are CH3C(O)NH2, CH3O(CH3S)P(O)NH2, (CH3O)2P(O)SCH3, CH3OP(O)(OH)2, CH3SS(O)2CH3, and (COOH)2. All the formed intermediate compounds were degraded under the visible light photocatalytic activity of RH-MCM-41/Co3O4 into NO3-, SO42-, PO43-, and CO2 as final products.

Multi-element determination in some foods and beverages using silica gel modified with 1-phenylthiosemicarbazide.

1-Phenylthiosemicarbazide bonded modified silica gel (PTC-SG) was synthesised and characterised by FTIR, SEM and elemental analysis for a novel separation/preconcentration of multiple elements based on solid phase extraction. The analytical parameters including pH of solutions, amounts of PTC-SG, flow rates of sample, eluent type and sample volume were optimised. The adsorption capacities of PTC-SG were found to be 7.9, 6.4, 6.3, 8.3, 7.2, 8.9 and 6.6 mg/g for Cu(II), Cd(II), Pb(II), Co(II), Cr(III), Ni(II) and Mn(II), respectively. The limit of detection (LOD) was calculated as 3x the standard deviation(s) of the reagent blank (k = 3, N = 21) and the LOD values were obtained to be 0.98 µg L-1 (Cu), 0.65 µg L-1 (Cd), 0.57 µg L-1 (Pb), 1.12 µg L-1 (Co), 1.82 µL-1 (Cr), 1.67 µg L-1 (Ni) and 0.55 µg L-1 (Mn). Certified reference materials were used to test the validation of the present method. The new solid phase extraction method was successfully applied to determination of the amount of multiple elements in food and beverage samples.

A Dual Ligand Sol⁻Gel Organic-Silica Hybrid Monolithic Capillary for In-Tube SPME-MS/MS to Determine Amino Acids in Plasma Samples.

This work describes the direct coupling of the in-tube solid-phase microextraction (in-tube SPME) technique to a tandem mass spectrometry system (MS/MS) to determine amino acids (AA) and neurotransmitters (NT) (alanine, serine, isoleucine, leucine, aspartic acid, glutamic acid, lysine, methionine, tyrosine, and tryptophan) in plasma samples from schizophrenic patients. An innovative organic-silica hybrid monolithic capillary with bifunctional groups (amino and cyano) was developed and evaluated as an extraction device for in-tube SPME. The morphological and structural aspects of the monolithic phase were evaluated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen sorption experiments, X-ray diffraction (XRD) analyses, and adsorption experiments. In-tube SPME-MS/MS conditions were established to remove matrix, enrich analytes (monolithic capillary) and improve the sensitivity of the MS/MS system. The proposed method was linear from 45 to 360 ng mL-1 for alanine, from 15 to 300 ng mL-1 for leucine and isoleucine, from 12 to 102 ng mL-1 for methionine, from 10 to 102 ng mL-1 for tyrosine, from 9 to 96 ng mL-1 for tryptophan, from 12 to 210 ng mL-1 for serine, from 12 to 90 ng mL-1 for glutamic acid, from 12 to 102 ng mL-1 for lysine, and from 6 to 36 ng mL-1 for aspartic acid. The precision of intra-assays and inter-assays presented CV values ranged from 1.6% to 14.0%. The accuracy of intra-assays and inter-assays presented RSE values from -11.0% to 13.8%, with the exception of the lower limit of quantification (LLOQ) values. The in-tube SPME-MS/MS method was successfully applied to determine the target AA and NT in plasma samples from schizophrenic patients.

Sol-gel Silica Nanoparticles in Medicine: A Natural Choice. Design, Synthesis and Products.

Silica is one of the most abundant minerals in the Earth's crust, and over time it has been introduced first into human life and later into engineering. Silica is present in the food chain and in the human body. As a biomaterial, silica is widely used in dentistry, orthopedics, and dermatology. Recently amorphous sol-gel SiO2 nanoparticles (NPs) have appeared as nanocarriers in a wide range of medical applications, namely in drug/gene target delivery and imaging diagnosis, where they stand out for their high biocompatibility, hydrophilicity, enormous flexibility for surface modification with a high payload capacity, and prolonged blood circulation time. The sol-gel process is an extremely versatile bottom-up methodology used in the synthesis of silica NPs, offering a great variety of chemical possibilities, such as high homogeneity and purity, along with full scale pH processing. By introducing organic functional groups or surfactants during the sol-gel process, ORMOSIL NPs or mesoporous NPs are produced. Colloidal route, biomimetic synthesis, solution route and template synthesis (the main sol-gel methods to produce monosized silica nanoparticles) are compared and discussed. This short review goes over some of the emerging approaches in the field of non-porous sol-gel silica NPs aiming at medical applications, centered on the syntheses processes used.

Adsorption and recognition characteristics of surface molecularly imprinted polymethacrylic acid/silica toward genistein.

In this paper, on the basis of surface-initiated graft polymerization, a new surface molecular imprinting technique is established by molecular design. And molecularly imprinted polymer MIP-PMAA/SiO2 is successfully prepared with genistein as template. The adsorption and recognition characteristics of MIP-PMAA/SiO2 for genistein are studied in depth by using static method, dynamic method and competitive adsorption experiment. The experimental results show that MIP-PMAA/SiO2 possesses very strong adsorption affinity and specific recognition for genistein. The saturated adsorption capacity could reach to 0.36mmolg(-1). The selectivity coefficients relative to quercetin and rutin are 5.4 and 11.8, respectively. Besides, MIP-PMAA/SiO2 is regenerated easily and exhibits excellent reusability.

Biomimetic synthesized nanoporous silica@poly(ethyleneimine)s xerogel as drug carrier: characteristics and controlled release effect.

The purpose of this study was to prepare and characterize nanoporous silica@poly(ethyleneimine)s (NS@P) xerogel and methanol modified NS@P xerogel synthesized with biomimetic method, and investigate controlled release behavior of propranolol hydrochloride (PNH) loaded carrier materials in vitro and in vivo. Preparation was conducted at ambient conditions, and NS@P xerogel as well as PNH loaded NS@P xerogel were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential scanning calorimeter (DSC). Investigations on morphology and porous characteristics of NS@P xerogel and methanol modified NS@P xerogel were evaluated with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption. The results showed that the order of morphology compactness was NS@P xerogel>25%NS@P xerogel>75%NS@P xerogel because PEIs scaffold ability for silica condensation and forming hydrogen bond weakened with increasing volume ratio of methanol modification. Moreover, SBET decreased and uniformity of pore size distribution was interrupted after methanol modification. PNH loaded carrier materials displayed controlled release, and release effect was related with pore size of materials and PEIs scaffold ability. In vivo pharmacokinetic study demonstrated that release of PNH was delayed due to the PNH incorporated inside carrier materials and controlled release effect was in accordance with in vitro results.

Synthesis and properties of a newly obtained sorbent based on silica gel coated with a polyaniline film as the stationary phase for non-suppressed ion chromatography.

The new sorbent for non-suppressed ion chromatography based on silica gel coated with a film of polyaniline (PANI) was obtained in a process of in situ polymerization of aniline by oxidation with ammonium peroxydisulfate. Raman analyses performed using a Thermo Scientific DXR confocal Raman Microscope equipped with the Omnic 8 software from Thermo Fisher Scientific have proved a uniform distribution of PANI on the surface of chromatographic beads and in the pores of the particle. The obtained stationary phase was packed into a stainless steel HPLC column. The quality of the prepared column was verified on the basis of hydrodynamic parameters such as column efficiency index (Ip) and separation impedance (E). The potential application of silica gel modified with polyaniline for separation and determination of selected anions using non-suppressed ion chromatography was also investigated. Chromatographic analyses were performed using of the ion chromatograph Dionex DX-500. The best results were obtained for the mobile phase consisting of an aqueous or methanolic solution of hydrochloric acid. The tested column and optimized chromatographic system were successfully used for the analysis of nitrate, bromide and iodide in waters samples.

Photopolymerized sol-gel monoliths for separations of glycosylated proteins and peptides in microfluidic chips.

Photopolymerized silica sol-gel monoliths, functionalized with boronic acid ligands, have been developed for protein and peptide separations in polydimethylsiloxane microfluidic devices. Pore size characterization of the monoliths was carried out with SEM, image analysis, and differential scanning calorimetry to evaluate both the micron-sized macropores and the nanometer-sized mesopores. Monoliths were functionalized with boronic acid using three different immobilization techniques. Batch experiments were conducted to determine the capacity of the monoliths and selectivity toward cis-diol-containing compounds. Conalbumin was used as a model glycoprotein, and a tryptic digest of the glycoprotein horseradish peroxidase was used as a peptide mixture to demonstrate proof-of-concept extraction of glycoproteins and glycopeptides by the monoliths formulated in polydimethylsiloxane microfluidic chips. For proteins, fluorescence detection was used, whereas the peptide separations employed off-line analysis using MALDI-MS.

Synthesis of poly(N-[tris(hydroxymethyl)methyl]acrylamide) functionalized porous silica for application in hydrophilic interaction chromatography.

Porous silica coated by a highly hydrophilic and nonionic tentacle-type polymeric layer was synthesized by free radical "grafting from" polymerization of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]-2-propenamide (TRIS-acrylamide) in partly aqueous solutions. The radical initiator sites were incorporated on the silica surfaces via a two-step reaction comprising thionyl chloride activation and subsequent reaction with tert-butyl hydroperoxide. The surface-bound tert-butylperoxy groups were then used as thermally triggered initiators for graft polymerization of TRIS-acrylamide. The synthesized materials were characterized by diffusive reflectance Fourier transform infrared specotroscopy, X-ray photoelectron spectroscopy, and CHN elemental analysis. Photon correlation spectroscopy was used to determine changes in ζ-potentials resulting from grafting, (29)Si magic angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) spectroscopy was used to assess the ratio of silanol to siloxane groups in the substrate and the grafted material, and the changes in surface area and mesopore distribution were determined by nitrogen cryosorption. Chromatographic evaluation in hydrophilic interaction chromatography (HILIC) mode showed that the materials were suitable for use as stationary phases, featuring good separation efficiency, a comparatively high retention, and a selectivity that differed from most commercially available HILIC phases. A comparison of this neutral phase with a previously reported N-(2-hydroxypropyl)-linked TRIS-type hydrophilic tentacle phase with weak anion exchange functionality revealed substantial differences in retention patterns.

A novel chiral mesoporous binaphthyl-silicas: preparation, characterization, and application in HPLC.

Mesoporous organosilicas with both R-(+)-1,1'-binaphthyl-2,2'-diamine and ethane moieties bridging in the framework were synthesized. This mesoporous material was prepared via the one-step co-condensation of N,N'-bis-[(triethoxysilyl)propyl]-(R)-bis-(ureido)-binaphthyl (Si-DABN) with 1,2-bis(triethoxysilyl)ethane (BTSE) using octadecyltrimethylammonium chloride (C(18) TMACl) as a structural directing agent with the aid of a co-solvent (ethanol) in basic medium. The morphology of these bifunctionalized mesoporous organosilicas is sensitive to the Si-DABN mole fraction and the base concentration. And the mesostructure becomes less ordered as the mole fraction of Si-DABN in the initial mixture increases from 10 to 40%. Elemental analysis and Fourier transform infrared (FT-IR) spectrometer indicate that the binaphthyl diamine was successfully introduced to the mesoporous organosilicas. Acidic conditions are more suitable than basic ones for the hydrolysis and condensation of (R)-2,2'-dicyanomethoxy-6,6'-di[(2-triethoxysilyl)ethenyl]-1,1'-binaphthyl, a chiral silane precursors with a short silane side chain on the binaphthyl group. A column packed with these bifunctionalized mesoporous organosilica spheres exhibits greater selectivity for R/S-1,1'-bi-2,2'-naphthol than one packed with commercial SiO(2) grafted with N,N'-bis-[(triethoxysilyl)propyl]-(R)-bis-(ureido)-binaphthyl. Binaphthol and bromosubstituted binaphthol were fully resolved, but two ether derivatives were only partially enantioseparated and the other three ester derivatives were no fully resolved on the column via co-condensation method.

A novel click lysine zwitterionic stationary phase for hydrophilic interaction liquid chromatography.

A novel type of zwitterionic HILIC stationary phase was prepared by covalently bonding the l-azido lysine on silica gel via click chemistry. The key intermediate azido lysine was synthesized by transformation the amino group in l-Boc-lysine to corresponding azido group and subsequent removal of the N-protected group (Boc). Finally, the azido lysine was covalently bonded to silica beads by click chemistry to get click lysine. Its structure was confirmed by FT-IR and elemental analysis. The new stationary phase showed good HILIC characteristics, when it was applied to separate polar and hydrophilic compounds, such as organic acids, cephalosporins and carbapenems. Compared with the commercial stationary phases, such as Atlantics HILIC and ZIC-HILIC, click lysine displayed better or similar chromatographic behaviors.

Preparation and complex characterization of silica holmium sol-gel monoliths.

Amorphous, sol-gel derived SiO(2) are known to biocompatible and bioresorbable materials. Biodegradable and inert materials containing radioactive isotopes have potential application as delivery vehicles of the beta radiation to the cancer tumors inside the body. Incorporation of holmium in the sol-gel derived SiO(2) could lead to the formation of a biodegradable material which could be used as carrier biomaterial for the radiation of radioactive holmium to the various cancer sites. The homogeneity of the prepared sol-gel silica holmium monoliths was investigated by Back Scattered Electron Imaging of Scanning Electron Microscope equipped with Energy Dispersive X-ray Analysis, X-ray Induced Photoelectron Spectroscopy and Nuclear Magnetic Resonance Spectroscopy. The biodegradation of the monoliths was investigated in Simulated Body Fluid and TRIS (Trizma pre-set Crystals) solution. The results show that by suitable tailoring of the sol-gel processing parameters holmium can be homogeneously incorporated in the silica matrix with a controlled biodegradation rate.

Solid phase extraction of trace Hg(II) on silica gel modified with 2-(2-oxoethyl)hydrazine carbothioamide and determination by ICP-AES.

In this work, a new 2-(2-oxoethyl)hydrazine carbothioamide modified silica gel (SG-OHC) sorbent was prepared and applied for preconcentration of trace mercury(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The optimization of some analytical parameters affecting the adsorption of the analyte such as acidity, shaking time, sample flow rate and volume, eluent condition, and interfering substances were investigated. At pH 3, the maximum static adsorption capacity of Hg(II) onto the SG-OHC was 37.5 mg g(-1). The quantitative recovery (>95%) of Hg(II) could be obtained using 2 mL of 0.5 mol L(-1)HCl and 1% CS(NH(2))(2) solution as eluent. Common coexisting substances did not interfere with the separation of mercury(II) under optimal conditions. The detection limit of present method was 0.10 ng mL(-1), and the relative standard deviation (RSD) was lower than 4.0% (n=8). The prepared sorbent was successfully applied for the preconcentration of trace Hg(II) in certified and water samples with satisfactory results.