Solid-state 29Si MAS Research Articles

Silsesquioxane-based porous polymer derived from organic chromophore with AIE characteristics for selective detection of 2,4-dinitrophenol and Ru3+

A novel silsesquioxane-based polymers (PCS-DPB) was prepared by the Friedel-Crafts reaction of octavinylsilsesquioxane (OVS) with AIE-active 4-[1-cyano-2-[4-(diphenylamino)phenyl]ethenyl]-α-[[4-(diphenylamino)phenyl]methylene]benzeneea-cetonitrile (CN-DPB). FTIR, solid state 29Si MAS and 13C CP MAS NMR spectroscopy analyses are performed to confirm its chemical structure and the presence of silsesquioxane units in the cross-linked network. XRD and TEM results prove its amorphous feature of the PCS-DPB material. TGA shows a high thermal stability of PCS-DPB with 5% mass loss temperature about 438 °C due to the highly cross-linking density and the presence of the inorganic silsesquioxane cage. The CN-DPB unit endows PCS-DPB with an excellent luminescence and a large red shift of 120 nm, which makes it to act as a probe to detect 2,4-dinitrophenol (DNP) and Ru3+ with high selectivity and sensitivity.

Hydrophobic Mesoporous Silica Particles Modified With Nonfluorinated Alkyl Silanes.

This work reports the preparation of hydrophobic mesoporous silica particles (MSPs) modified with nonfluorinated alkyl silanes. Alkyl silanes were grafted onto the surface of the MSPs as a function of the length of nonfluorinated alkyl chains such as propyltriethoxysilane (C3), octyltriethoxysilane (C8), dodecyltriethoxysilane (C12), and octadecyltriethoxysilane (C18). Moreover, the grafting of the different alkyl silanes onto the surface of MSPs to make them hydrophobic was demonstrated using different conditions such as by changing the pH (0, 4, 6, 8, and 13), solvent type (protic and aprotic), concentration of silanes (0, 0.12, 0.24, 0.36, 0.48, and 0.60 M), reaction time (1, 2, 3, and 4 days), and reaction temperature (25 and 40 °C). The contact angles of the alkyl silane-modified MSPs were increased as a function of the alkyl chain lengths in the order of C18 > C12 > C8 > C3, and the contact angle of C18-modified MSPs was 4 times wider than that of unmodified MSPs. The unmodified MSPs had a contact angle of 25.3°, but C18-modified MSPs had a contact angle of 102.1°. Furthermore, the hydrophobicity of the nonfluorinated alkyl silane-modified MSPs was also demonstrated by the adsorption of a hydrophobic lecithin compound, which showed the increase of lecithin adsorption as a function of the alkyl chain lengths. The cross-linking ratios of the modified silanes on the MSPs were confirmed by solid-state 29Si-MAS nuclear magnetic resonance (NMR) measurement. Consequently, the hydrophobic modification on MSPs using nonfluorinated alkyl silanes was best preferred in a protic solvent, with a reaction time of ∼24 h at 25 °C and at a high concentration of silanes.

Solid-state MAS NMR investigations for pentavalent cation-replaced pollucite compounds with a negative thermal expansion coefficient

Pollucite compounds with an aluminosilicate structure, V-replaced pollucite, Cs0.7V0.1Al0.8Si2.1O6 (CVAS), P-replaced pollucite, Cs0.7P0.1Al0.8Si2.1O6 (CPAS), and Nb-replaced pollucite, Cs0.7Nb0.1Al0.8Si2.1O6 (CNbAS), were synthesized by a multistep heat treatment of 550–1200 °C. CVAS exhibited the superior thermal expansion with thermal expansion coefficients of 0.9 × 10−6 °C−1 (30–500 °C), −0.9 × 10−6 °C−1 (30–150 °C), and −0.4 × 10−6 °C−1 (30–100 °C). Solid-state 29Si MAS NMR spectroscopy clarified that the number of Si–O–Si bonds of tetrahedra in the framework of CVAS was larger than those of CPAS and CNbAS. The chemical shift for peaks of the 29Si MAS NMR spectrum of CVAS was larger than those of CPAS and CNbAS, suggesting that the bond angle of tetrahedra was enlarged by the V replacement. Solid-state 27Al MAS NMR spectroscopy implied that CVAS had a small amount of sixfold coordinated Al species, which resulted in an increase in the number of Si–O–Si bonds of tetrahedra of CVAS.

Borophosphosilicate glass � Polycaprolactone hybrid scaffolds for bone tissue engineering

Event Abstract Back to Event Borophosphosilicate glass – Polycaprolactone hybrid scaffolds for bone tissue engineering Dibakar Mondal1, 2, Kibret Mequanint1 and Amin S. Rizkalla1, 2, 3 1 The University of Western Ontario, Chemical and Biochemical Engineering, Canada 2 The University of Western Ontario, Bone and Joint Institute, Canada 3 The University of Western Ontario, Dentistry, Schulich School of Medicine & Dentistry, Canada Introduction: Scaffold materials for bone tissue engineering applications should be osteoconductive and osteoinductive while exhibiting suitable porosity to allow cell infiltration, tissue growth and metabolic waste removal. Their rate of degradation must match the rate of tissue formation [1]-[3]. Conventional bioactive composite materials have been proposed to be a solution to this problem [4]-[5]. However, these materials possess micro-scale domain sizes leading to distinct phases. This, in turn, results in their non-uniform physical, chemical, mechanical and biological properties at the nano or molecular level making them unsuitable for bone biomaterials [6]. The main objective was to synthesize and characterize a range of bioactive organic-inorganic class II hybrid biomaterials via a non-aqueous sol-gel process with poly (ԑ-caprolactone) diol (PCL) as the organic component and SiO2-P2O5-B2O3 based ternary Borophosphosilicate glass (BPSG) as the inorganic component. Materials and methods: PCL diol was end-capped with 3-Glycidoxypropyl trimethoxysilane then reacted with metal alkoxides in a non-aqueous sol-gel process to produce PCL-BPSG hybrid biomaterials. Fibrous scaffolds of the synthesized hybrids biomaterials were electrospun from the viscous sol. Results and discussion: To study organic-inorganic bridging, solid-state 29Si-MAS NMR was conducted for BPSG and 50 wt% PCL-50 wt% BPSG (50H) hybrid biomaterials (Figure 1A). In silica networks, if the silicon atom is bonded to four oxygen atoms, then the resultant structure is designated as Q network. However, if a silicon atom is bonded to three oxygen atoms and one carbon atom, then the structure is designated as T network. Both of BPSG and 50H exhibited quaternary Si-O-Si bridging networks, which is denoted as Q4 (superscript indicates the number of Si-O-Si framework connections with respect to the silicon atom). Chemical shifts at δ= -92, -100 and -109 ppm were associated with Q2, Q3 and Q4 structures respectively. Chemical shifts at δ= -57 and -64 ppm denoted as T2 and T3 were attributed to the Si-O-Si bridging networks with Si-C at one end. The control BPSG did not have any peak for T networks because it has no Si-C bonding associated with Si-O-Si bridging network. In contrast, 50H spectrum showed a T3 network since Si-C bond from PCL-Si is covalently bonded with the inorganic glass network and resulted in a class II hybrid. In the FTIR spectra of PCL-BPSG hybrids (Figure 1B), characteristic peak at 1072 cm-1 is attributed to Si-O-Si stretching and the peaks at 920 and 670 cm-1 are attributed to Si-O-B stretching vibration. SEM images of BPSG and 50H surface before and after incubation in simulated body fluid (SBF) for 7 days are shown in Figure 2. Before incubation in SBF, BPSG and PCL-BPSG hybrid exhibited smooth surfaces. After incubation for 7 days both BPSG and PCL-BPSG surfaces were covered by spherical hydroxyapatite particles. From EDX spectrum (inset of Figures 2C and 2D) the Ca/P ratio were 1.7±0.6. The fibrous scaffolds from hybrid biomaterials produced by electrospinning had diameter ranged between 100 -150 nm (figure not shown). Conclusion: PCL-BPSG class II hybrid biomaterials were successfully synthesized via a non-aqueous sol-gel process. Fibrous scaffolds of the synthesized hybrids were successfully produced by electrospinning. Hydroxyapatite deposition was observed on the hybrid materials following incubation in SBF. The synthesized hybrid biomaterials could be potential candidates for bone tissue engineering. Vanier Canada Graduate Scholarship; Natural Sciences and Engineering Research Council of Canada

Fast, selective adsorption of Cu2+ from aqueous mixed metal ions solution using 1,4,7-triazacyclononane modified SBA-15 silica adsorbent (SBA-TACN)

A new SBA-15 supported 1,4,7-triazacyclononane modified mesoporous silica adsorbent (SBA-TACN) has been synthesized using post grafting route and has thoroughly been characterized by small angle X-ray scattering (SAXS), N2 adsorption–desorption measurements, Fourier-transform infrared (FT-IR), solid-state 29Si MAS and 13C CP MAS NMR spectroscopy, transmission electron (TEM) and scanning electron microscopy (SEM), elemental analysis (EA) and thermogravimetric analysis (TGA). The synthesized material shows excellent copper (II) ion adsorption selectivity at pH 5 in mixed metal ion solution containing Cu2+, Cr3+, Ni2+, Co2+ and Li+. The copper ion adsorption capacity of the SBA-TACN can reach a maximum value of 0.67mmol/g. Possible adsorption mechanism of metal ions on SBA-TACN has been discussed. The adsorbent can be readily regenerated by HNO3–NH3 treatment.

Periodic mesoporous organosilicas with co-existence of diurea and sulfanilamide as an effective drug delivery carrier

In this article we report the synthesis of new periodic mesoporous organosilicas (PMOs) with the co-existence of diurea and sulfanilamide-bridged organosilica that are potentially useful for controlled drug release system. The materials possess hexagonal pores with a high degree of uniformity and show long-range order as confirmed by the measurements of small-angle X-ray scattering (SAXS), N 2 adsorption isotherms, and transmission electron microscopy(TEM). FT-IR and solid state 29Si MAS and 13C CP MAS NMR spectroscopic analyses proved that the bridging groups in the framework are not cleaved and covalently attached in the walls of the PMOs. It was found that the organic functionality could be introduced in a maximum of 10 mol% with respect to the total silicon content and be thermally stable up to 230 °C. The synthesized materials were shown to be particularly suitable for adsorption and desorption of hydrophilic/hydrophobic drugs from a phosphate buffer solution at pH 7.4.

Formation of Single-Walled Aluminosilicate Nanotubes from Molecular Precursors and Curved Nanoscale Intermediates

We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles.

N, N′-diureylenepiperazine-bridged periodic mesoporous organosilica for controlled drug delivery

N, N′-diureylenepiperazine-bridged periodic mesoporous organosilicas (PDPMOs) have been successfully synthesized through co-condensation of bissilylated N, N′-diureylenepiperazine (BPDU) and tetraethyl orthosilicate (TEOS), using a triblock copolymer (Pluronic P123) as a structure-directing agent in acidic conditions with various BPDU to TEOS ratios. These PMOs were characterized by small angle X-ray scattering (SAXS), N 2 adsorption–desorption measurements, Fourier-transform infrared (FT-IR), solid-state 29Si MAS and 13C CP-MAS NMR spectroscopy, transmission electron (TEM) and scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). It was found that the organic functionalities could be introduced at a maximum of 30 mol% in the wall structure of the diureylenepiperazine-bridged periodic mesoporous organosilica (PDPMO-30) with respect to the total silicon content. The PDPMO-30 was thermally stable up to 230 °C. The PDPMOs have an ordered mesostructure, a high surface area (ranging from 663 to 316 m 2 g −1), a medium pore volume (1.26–0.66 cm 3 g −1), and uniform pore sizes (7.7–5.4 nm). To test a potential application of the PDPMO, in vitro assays of captopril or 5-flurouracil adsorption and delivery were carried out at pH 7.4. Due to the presence of hydrophilic urea moieties within the wall structure, the materials were shown to be particularly suitable for adsorption and desorption of drugs and could be utilized for controlled drug delivery.

Synthesis of a ferrocene-containing ordered mesoporous organosilica and its catalytic activity

A new ordered mesoporous organosilica has been synthesized through co-condensation of 1,1′-bis[2-(triethoxylsilyl)ethyl]ferrocene and tetraethyl orthosilicate under basic conditions using supramolecular templates of cetyltrimethylammonium bromide as structure directing agents. The templates were removed through solvent extraction to yield the ferrocene-containing ordered mesoporous organosilicas. The pore diameter, BET surface area, and pore volume of the extracted material were 2.2 nm, 1,085 m2/g and 0.67 cm3/g, respectively. The material also has been characterized by XRD, TEM, FT-IR, UV–Vis DRS, solid state 29Si MAS NMR and 13C CP-MAS NMR etc. In the reaction of benzene hydroxylation to phenol, the ferrocene-containing ordered mesoporous materials show a comparable activity with the homogeneous ferrocene catalyst, giving 20.2% of yield and 65.3% of selectivity for phenol.

Nuclear magnetic resonance techniques for the structural characterization of siloxane–oxide hybrid materials

The objective of this paper is to discuss the appropriateness of various solution and solid state NMR techniques to describe structural aspects of siloxane–oxide hybrid systems prepared by sol-gel processes. Co-hydrolysis of organosilanes and metallic alkoxides can promote either self-condensation or co-condensation reactions between the different precursors, and this will control the structural homogeneity of the final network. Solution state 29Si and 17O NMR can give unique information on the formation and stability of co-condensing species. In the final gels, solid state 29Si MAS used in conjunction with cross-polarization (CP) and related two-dimensional 29Si– 1H heteronuclear NMR correlation techniques, provides detailed information on dipole–dipole coupled 29Si and 1H species among different molecular moieties. Finally, the use of 17O MAS NMR with the newly developed MQ MAS sequence that provides a direct identification of the various oxo bridges will be discussed.

The silicalite(MFI)/p-nitroaniline system. I. Location of the sorbed molecules at medium and high pore-fillings. A study by X-ray powder diffraction, 29Si mas NMR and energy minimization calculations

Structural investigation of the silicalite(MFI)/np-nitroaniline system by X-ray powder diffraction, establishes the existence of two single phased host/guest complexes corresponding to n=4 and 8 at medium and high pore-fillings respectively. Predictive studies by molecular mechanics simulations indicate that the pNAN molecules are located at the channel-intersections (for n=4) or in the elliptic channel-sections of the MFI topology (for n=8). 29 Si solid-state mas NMR measurements show that the actual MFI framework symmetry of the silicalite.4pNAN complex is acentric Pn2 1 a. Interpretation of the XRD pattern corresponding to the saturated silicalite. 8pNAN complex by Rietveld type structure refinements shows that two independent pNAN molecules are located on sites II (zig-zag channel sections) and sites III (straight channel sections). The van der Waals type interactions between the sorbed molecules take place at the channel-intersections (sites I). These sites are not occupied by extra-framework species. This is in agreement with the commensurability criterion already observed in several MFI/sorbate systems.

Formation at low surfactant concentrations and characterization of mesoporous MCM-41

At low concentrations of cetyltrimethylammonium bromide, all silica-based mesoporous materials with hexagonal phase have been synthesized via interactions between self-assembled surfactant molecule aggregates and anionic silicate polymers. The resulting materials are characterized by XRD, FT-IR, solid state29Si MAS NMR, ther-mal analysis and N2 adsorption-desorption measurements. After soluble ions are removed, the interactors between sur-factant micelles and silicate polymers are reorganized and then form mesostructures. The hexagonal framework is con-sistent with amorphous silica gel. The structures of materials depend on the synthesis conditions. Hydrothermal pro-cess improves the interact~ons between molecules and increases the degree of framework silicon atom polymerization. The surface area and the mesopore volume of the material prepared at l000C increase by 87% and 71 %, respectively, compared with those obtained at room temperature.

Strukturuntersuchungen an den Produkten aus der Reaktion des Tris(trimethylsilyl)silyllithiums mit Aceton

The reaction of (Me 3Si) 3SiLi ( 1) with acetone has been clarified with the aid of crystal structure and 29Si NMR investigations of H(Me 3Si) 2Si(Me 3Si) 2SiCMe 2SiMe 3 ( 3) and (Me 3Si) 3Si(Me 3Si) 2SiCMe 2SiMe 3 ( 4). The chemically but not crystallographically equivalent silicon atoms in 3 and 4 and the two crystallographically independent molecules of 4 all gave rise to separate signals in the solid state 29Si-MAS NMR spectra. The 1 J( 29Si, 29Si) couplings observed in solution facilitated the assignment of 29Si resonances.

Solid-state high-resolution 29Si mas MAR of silicates with sixfold coordinated silicon

A correlation between isotropic 29chemical shifts and mean Si-O bond length is presented for ten silicates containing sixfold coordinated silicon. The 29Si chemical shift data afford a measure of the cationic, neutral or anionic character of the octahedral silicon.