29Si CP MAS NMR Research Articles

Probing the molecular structure of antimicrobial peptide-mediated silica condensation using X-ray photoelectron spectroscopy

The antimicrobial peptide KSL (KKVVFKVKFK) mediates the rapid condensation of tetramethyl orthosilicate to form silica nanoparticles. X-ray photoelectron spectroscopy (XPS) was employed to identify the molecular interactions between protein and silica on the surface of nanoparticles containing antimicrobial peptide and silica. Comparative high resolution spectral analysis between KSL peptide and KSL-catalyzed silica nanoparticles revealed that imidates are present in the KSL peptide backbone after silica formation. Supporting evidence for the presence of an imidate is provided by FTIR spectroscopic analysis of the amide I and V bands. XPS analysis also shows that side-chain amines of lysine do not interact with the silica product and the lack of association is supported further by 15N-29Si REDOR NMR. Quantitative analysis of XPS elemental spectra determined the silica O:Si ratio is 3.6 : 1, suggesting that the nuclei (sol) particles are not highly condensed structures. Results were supported using 29Si CPMAS NMR to show that the majority of the silica is Q2 groups. A proposed mechanism of rapid silicification with involvement of a peptide imidate is presented.

Chemically modified silica gel for selective solid-phase extraction and preconcentration of heavy metal ions

This paper describes our research on the synthesis of the sorbent with chemically bonded ketoimine groups, and, furthermore, using this sorbent in the SPE technique to extract and preconcentrate trace amounts of metal ions in water samples. Surface characteristics of the sorbent were determined by elemental analysis, NMR spectra for the solid phases (29Si CP MAS NMR), and analysis of pore size distribution of the sorbent and nitrogen adsorption-desorption. The newly proposed sorbent with ketoimine groups was applied for the extraction and preconcentration of trace amounts of Cu (II), Cr (III) and Zn (II) ions from the water from a lake, post-industrial water and purified water unburdened back to the lake. The determination of the transition-metal ions was performed on an emission spectroscope with inductively coupled plasma ICP-OES. For the batch method, the optimum pH range for Cu (II) and Cr (III) extraction was equal to 5, and Zn(II)–to 8. All the metal ions can be desorbed from SPE columns with 10 mL of 0.5 mol HNO3. The detection limits of the method were found to be 0.7 µg L−1 for Cu (II), 0.08 µg L−1 for Cr (III), and 0.2 µg L−1 for Zn (II), respectively.

Characterization and boron adsorption of hydrothermally synthesised allophanes

Two hydrothermally synthesised allophanes (Si/Al = 0.5 and 1) were modified by heating at 400 °C. N-methyl- d-glucamine, a specific boron complexant, was grafted on the allophane material with Si/Al = 0.5. The surface and structural properties of the different materials were characterised by infrared spectroscopy and 29Si CP MAS NMR spectroscopy. The porous characteristics of the different allophanes (specific surface area, pore size distribution) were determined by nitrogen adsorption at 77 K using the BET equation and the BJH model. The adsorption of boron, i.e. boric acid/borate, by the modified allophanes was studied in aqueous solutions with boron contents of 1 to 100 mg L − 1 . The pH-dependence of boron adsorption of all the sorbents showed a maximum at a pH value close to the pKa value of boric acid (pKa H 3BO 3/B(OH) 4 − = 9.26). The adsorption isotherms of boron by raw and modified allophanes were fitted with a double Langmuir equation, assuming the presence of two sets of adsorption sites. The grafting of N-methyl- d-glucamine did not improve the boron adsorption of the allophanes but the structural changes by heating at 400 °C increased the adsorption.

Immobilization of carbonic anhydrase on spherical SBA-15 for hydration and sequestration of CO 2

Bovine carbonic anhydrase (BCA) was immobilized on spherical SBA-15 through various approaches, including covalent attachment (BCA-CA), adsorption (BCA-ADS), and cross-linked enzyme aggregation (BCA-CLEA). The spherical SBA-15 was characterized by XRD, BET, and FE-SEM analysis. 29Si CP-MAS NMR was used to confirm the 3-aminopropyltriethoxysilane grafting (an intermediate step in the immobilization technique), and the immobilization of BCA was confirmed by FT-IR spectrum. The catalytic activities for hydration of CO 2 were calculated for free and immobilized BCA with and without buffer. The K cat values for free BCA, BCA-CLEA, BCA-CA and BCA-ADS were 0.79, 0.78, 0.58 and 0.36 s −1, respectively, indicating that BCA-CLEA showed a comparatively higher hydration of CO 2 than BCA-CA and BCA-ADS, which was nearly the same as free BCA. The amount of CaCO 3 precipitated over free BCA, BCA-CLEA, BCA-CA and BCA-ADS were 140, 138, 135 and 130 mg, respectively. Performance studies, including assays on reusability, thermal stability and storage stability, were also carried out for BCA-CLEA. The results confirmed that BCA-CLEA is reusable, thermally stable and, withstands storage, and is thus a suitable candidate for use in hydration and sequestration of CO 2.

Capture and Sequestration of CO2 by Human Carbonic Anhydrase Covalently Immobilized onto Amine-Functionalized SBA-15

Human carbonic anhydrase (HCA) was immobilized onto mesoporous SBA-15 surfaces that had been covalently functionalized using one of three amine compounds, namely, tris(2-aminoethyl)amine (TAEA), tetraethylenepentamine (TEPA), and octa(aminophenyl)silsesquioxane (OAPS). Amine functionalization over SBA-15 was characterized by XRD, FE-SEM, BET analysis, and 29Si and 13C CP MAS NMR spectroscopy. HCA immobilization was verified by FT-IR spectroscopy. The catalytic activity toward hydrolysis of p-nitrophenylacetate (p-NPA) was calculated for free and immobilized HCA. The kcat values for HCA/TEPA/SBA-15, HCA/TAEA/SBA-15, and HCA/OAPS/SBA-15 were found to be 7182, 7368, and 7569 M–1 s–1, respectively. The activities of immobilized HCA were retained even after long-term storage, exposure to high temperatures, and reuse for 40 cycles. For comparison, CO2 hydration and sequestration were measured in the presence of both free and immobilized HCA. Importantly, the CO2 conversion efficiency was calculated using the io...

Interplay between Chemistry and Texture in Hydrophobic TiO2 Hybrids

Organic-nano-TiO2 hybrids are successfully employed in different fields, from biomaterials to self-cleaning processes and from sensing to photovoltaics. The specific wetting properties of these materials bear relevance to any application. Here, nano-TiO2 films with a multiscale roughness, as shown by AFM, are derivatized with tri- and bifunctional siloxanes, bearing either alkyl or aromatic end groups. Dynamic contact angle measurements show a marked dependence of the wettability on the siloxane nature, leading to different self-cleaning properties, as assessed by ATR-FTIR. The different behavior is rationalized on the grounds of the structure of the functionalized layer, by employing solid state 29Si CP-MAS NMR and EDX mapping. Semiempirical calculations of hybrids dipole moments in conjunction with solvent surface energy components allow us to explain the strongly different solvents wettability. This work brings attention to the importance of the hydrophobizing molecule nature and its chemical interacti...

Novel acridone-modified MCM-41 type silica: Synthesis, characterization and fluorescence tuning

A Mobil Composition of Matter (MCM)-41 type mesoporous silica material containing N-propylacridone groups has been successfully prepared by co-condensation of an appropriate organic precursor with tetraethyl orthosilicate (TEOS) under alkaline sol–gel conditions. The resulting material was fully characterized by means of X-ray diffraction (XRD), N2-adsorption–desorption, transmission electron microscopy (TEM), IR and UV–vis spectroscopy, as well as 29Si and 13C CP-MAS NMR techniques. The material features a high inner surface area and a highly ordered two-dimensional hexagonal pore structure. The fluorescence properties of the organic chromophore can be tuned via complexation of its carbonyl group with scandium triflate, which makes the material a good candidate for solid state sensors and optics. The successful synthesis of highly ordered MCM materials through co-condensation was found to be dependent on the chemical interaction of the different precursors.

Synthesis and characterization of nanostructural polymer–silica composite: Positron annihilation lifetime spectroscopy study

The swelling of poly(TRIM) spherical particles in TEOS is assessed as a potential way for obtaining polymer–silica nanocomposite materials. Silica deposition was achieved by simply stirring of swollen polymer particles in acidic hydrochloric-water solution. This procedure leads to spherical composite particles with dispersed silica gel within the polymer matrix. The resulting material exhibits the same morphology as the initial polymer. Nanocomposite particles are silica rich (about 17 wt.%). Characterization of the nanocomposites was performed using scanning electron microscopy, FT-IR spectroscopy, 29Si CP MAS NMR spectroscopy and thermogravimetry. Moreover, the use of positron annihilation lifetime spectroscopy PALS to characterize the structural properties of the nanocomposites is presented. This technique gave more realistic pieces of information about the pore structure of the investigated samples in contrast to nitrogen adsorption studies.

New mesostructured organosilica with chiral sugar derived structures: nice host for gold nanoparticles stabilisation

In this paper we describe the synthesis of functionalised mesoporous organosilicas containing a mannitol derivative in the framework. For this purpose, a bis-silylated precursor 3,4-Di-O-[3-(triethoxysilylpropyl)carbamate]-1,2:5,6-di-O-isopropylidene-D-mannitol was prepared by coupling of 1,2:5,6-di-O-isopropylidene-D-mannitol with 3-(triethoxysilylpropyl)isocyanate. The framework-functionalised materials were obtained in one step by the "direct synthesis" method which consists of a co-hydrolysis and polycondensation of a bis-silylated mannitol precursor with tetraethylorthosilicate (TEOS) in the presence of a non-ionic triblock co-polymer (P123) as structure-directing agent. Interestingly, deprotection of the 1,2,5,6 OH functional groups occurred during the material synthesis. The obtained solids were characterized by (13)C and (29)Si CP-MAS NMR, N(2) adsorption-desorption, powder X-ray diffraction, TEM and elemental analysis. We have shown that, the OH functional groups, which are released during the synthesis of the mesoporous silica, can be used for chelation of ions and stabilisation of nanoparticles. The subsequent growth of gold (0) nanoparticles in the wall has been investigated and evidenced.

Amine functionalized layered double hydroxide: a reusable catalyst for aldol condensation

Zn : Al layered double hydroxide-supported 3-aminopropyltriethoxysilane (APTES) and N-methyl 3-aminopropyltriethoxy silane (MAPTES) are found to be efficient, environmentally attractive and selective solid base catalysts for liquid phase aldol condensation reactions at room temperature. The organic functionalized solid catalysts were characterized by XRD, FT-IR, Raman, EDX, SEM, TG-DTA, 13C and 29Si CP MAS NMR techniques. The XRD pattern indicated the anti-parallel monolayer arrangements of organic moieties in the interlayer space of LDH. 29Si NMR confirmed that the linking silicon atom is fully condensed in the framework. The reusability study shows consistent activity of the heterogeneous catalyst after several cycles.

Silica hydride intermediate for octadecylsilica and phenyl bonded phase preparation via heterogeneous hydrosilation in supercritical carbon dioxide

Investigations into the preparation of silica hydride intermediate in supercritical carbon dioxide (sc-CO 2) that avoids the use of organic solvents such as toluene or dioxane are described. The effects of reaction temperature, pressure and time on the surface coverage of the supercritical fluid generated silica hydride intermediate were studied. Under optimised supercritical conditions of 120 °C, 483 bar and 3 h reaction time, silica hydride (Si–H) conversion efficiencies of ca. 40% were achieved for the hydride intermediate prepared from a monofunctional silane reagent (dimethylmethoxysilane). Si–H conversion efficiencies (as determined from 29Si CP-MAS NMR spectral analysis) for the hydride intermediate prepared from triethoxysilane (TES) in sc-CO 2 were found to be comparable to those obtained using a TES silanisation approach in an organic solvent. 13C and 29Si CP-MAS-NMR spectroscopy was employed to provide a complete structural assignment of the silica hydride intermediates. Furthermore, supercritical CO 2 was subsequently employed as a reaction medium for the heterogenous hydrosilation of silica hydride with octadecene and with styrene, in the presence of a free radical initiator. These supercritical fluid generated reversed-phase materials were prepared in a substantially reduced reaction time (3 h) compared to organic solvent based methods (100 h reaction time). Silica functionalisation in sc-CO 2 presents an efficient and clean alternative to organic solvent based methods for the preparation of important silica hydride intermediate and silica bonded stationary phases via a hydrosilation approach.

Fe(III)-salim anchored MCM-41: synthesis, characterization and catalytic activity towards liquid phase cyclohexane oxidation

A novel organic–inorganic hybrid catalyst [MCM-41-FeIII(salim)] was synthesized by covalently anchoring FeIII(salim) complex into the pore channels of MCM-41. The material was synthesized by the co-condensation of tetraethyl orthosilicate (TEOS) and the precursor of salicylaldehyde modified with 3-aminopropyl triethoxysilane in the presence of cetyltrimethyl ammonium bromide (CTAB). The Fe(III)-salicylideneimine MCM-41 mesoporous silica was generated (in situ) by taking MCM-41-salimH (I) and FeCl3 in ethanol solution. The immobilization of the complex on the functionalized silica was confirmed by small angle X-ray diffraction (XRD), N2 adsorption–desorption, electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance UV–vis spectroscopy. Solid state CP-MAS NMR spectroscopy of 29Si (29Si CP-MAS NMR) showed a highly condensed siloxane network. Catalytic activity of the supported catalyst was examined by the oxidation of cyclohexane. Cyclohexane was successfully oxidized in good conversion (68%) to cyclohexanone, as a major product with 72% selectivity using tert. butylhydroperoxide as oxidant and acetonitrile as solvent. The catalysts can be reused up to three cycles without losing much of its activity. Fe(III)-salicylideneimine immobilized MCM-41 hybrid mesoporous silica was prepared by covalent anchoring of schiffbase complex to MCM-41 host and used for liquid phase oxidation of cyclohexane.

Modification of silicalite-1 by vinyltrimethoxysilane (VTMS) and preparation of silicalite-1 filled polydimethylsiloxane (PDMS) hybrid pervaporation membranes

In preparation of inorganic particles filled polymer membranes, coupling agents can help to improve the compatibility between inorganic filler and polymer matrix. In this paper, surface modification of silicalite-1 was performed by a coupling agent, vinyltrimethoxysilane (VTMS), and hybrid pervaporation membranes were prepared by incorporating the unmodified or VTMS-modified silicalite-1 into polydimethylsiloxane (PDMS). The VTMS-modified silicalite-1 particles and hybrid membranes were characterized by FT-IR, 29Si CP MAS NMR, DSC, TGA, XRD and SEM. The results showed that the coupling agent VTMS was readily grafted on the surface of silicalite-1 by hydrolysis reaction and condensation reaction, and the chemical linking between the –CH CH 2 group on the surface-modified silicalite-1 and –Si–H on the PDMS substantially eliminated the nonselective voids inside the membrane. When used to separate acetone, butanol, ethanol (ABE) from aqueous solution, a higher selectivity was obtained with the VTMS-modified silicalite-1/PDMS hybrid membrane. Moreover, the surface modification of silicalite-1 improved its dispersion in PDMS and increased the maximal loading of silicalite-1 in membrane preparation, and thus further enhanced the separation factor of the membrane.

Solid-State NMR Characterization of Wilkinson’s Catalyst Immobilized in Mesoporous SBA-3 Silica

The Wilkinson's catalyst [RhCl(PPh(3))(3)] has been immobilized inside the pores of amine functionalized mesoporous silica material SBA-3 and The structure of the modified silica surface and the immobilized rhodium complex was determined by a combination of different solid-state NMR methods. The successful modification of the silica surface was confirmed by (29)Si CP-MAS NMR experiments. The presence of the T(n) peaks confirms the successful functionalization of the support and shows the way of binding the organic groups to the surface of the mesopores. (31)P-(31)P J-resolved 2D MAS NMR experiments were conducted in order to characterize the binding of the immobilized catalyst to the amine groups of the linkers attached to the silica surface. The pure catalyst exhibits a considerable (31)P-(31)P J-coupling, well resolvable in 2D MAS NMR experiments. This J-coupling was utilized to determine the binding mode of the catalyst to the linkers on the silica surface and the number of triphenylphosphine ligands that are replaced by coordination bonds to the amine groups. From the absence of any resolvable (31)P-(31)P J-coupling in off-magic-angle-spinning experiments, as well as slow-spinning MAS experiments, it is concluded, that two triphenylphosphine ligands are replaced and that the catalyst is bonded to the silica surface through two linker molecules.

Solid state synthesis of water-dispersible silicon nanoparticles from silica nanoparticles

A solid state synthesis for obtaining nanocrystalline silicon was performed by high temperature reduction of commercial amorphous nanosilica with magnesium powder. The obtained silicon powder contains crystalline silicon phase with lattice spacings characteristic of diamond cubic structure (according to high resolution TEM), and an amorphous phase. In 29Si CP MAS NMR a broad multicomponent peak corresponding to silicon is located at −61.28 to −69.45 ppm, i.e. between the peaks characteristic of amorphous and crystalline Si. The powder has displayed red luminescence while excited under UV illumination, due to quantum confinement within the nanocrystals. The silicon nanopowder was successfully dispersed in water containing poly(vinyl alcohol) as a stabilizing agent. The obtained dispersion was also characterized by red photoluminescence with a band maximum at 710 nm, thus enabling future functional coating applications.

Synthesis of organic–inorganic hybrid MSU-1 for separation and catalytic applications

A series of spherical hybrid MSU-1 composed of homogeneously distributed ethane groups in a silica framework was prepared via the twostep sol–gel process using 1,2-bis(triethoxysilyl)ethane (BTEE) in a nonionic alkyl polyethylene oxide (Tergitol 15-S-12) surfactant solution. Hydrolysis of BTEE was conducted in acidic condition at room temperature and condensation of silicate species was promoted by F − catalyst at 65 °C. The hybrid MSU-1 products synthesized were characterized by XRD, N 2 adsorption/desorption isotherm, TGA, SEM, and TEM after solvent extraction. The materials were made of wormhole-like mesopore structures, and surface area, pore volume, and pore diameter increased with the concentration of NaF (NaF/BTEE = 0.03–0.15) and temperature (35–65 °C). Incorporation of the organic fraction was confirmed by 29Si and 13C CP MAS NMR. The hybrid MSU-1, after C 8 grafting and end-capping, demonstrated a good performance as a stationary phase in chromatography. The hybrid MSU-1-supported palladium material also showed excellent catalytic performances in Sonogashira cross-coupling reactions of aryl iodide with phenylacetylene.

Bridged polysilsequioxane adsorption materials containing phosphonic acid residues

Reactions of hydrolytic polycondensation of bis(triethoxysilane) [(C2H5O)3Si]2C2H4 (or [(C2H5O)3Si]2C6H4) and functional agent (C2H5O)3Si(CH2)2P(O)(OC2H5)2 (alkoxysilanes molar ratio of 2: 1 and 4: 1, fluoride ion catalyst and ethanol solvent) yielded powder-like xerogels that contained phosphonic acid residues in the surface layer. Their treatment with boiling concentrated hydrochloric acid resulted in transformation of functional groups ≡Si(CH2)2P(O)(OC2H5)2 into acid groups ≡Si(CH2)2P(O)(OH)2. The methods of IR, 1H MAS NMRm and 13C, 29Si, 31P MAS NMR spectroscopy showed the following (1) The surface layer in the initial xerogels contains not only phosphorus functional groups, but also some non-hydrolyzed ethoxysilyl groups as well as silanol groups. (2) The hydrochloric acid treatment of the initial xerogels causes the hydrolysis of not only ethoxy groups in the phosphonic acid residues, but also most residual ethoxysilyl groups. (3) Vacuum drying of xerogels after acid treatment forms ≡Si(CH2)2P(O)(OH)-OSi≡ links in their surface layer (not more than 20% of phosphorus-containing groups). (4) According to 29Si CP MAS NMR spectroscopic data, boiling acid treatment relatively enriches the xerogel structure T2 and T3 units and accounts for the higher rigidity of the hybrid framework. These units also account for retention of the porous structure in these xerogels over time, while most initial xerogels have porous structures that collapse in 12–18 months of storage. The acid-treated xerogels were attributed to microporous adsorbents (having specific surface area of 620 to 760 m2/g). According to the AFM data, both initial and acid-treated xerogels contain almost spherical aggregates of the primary particles (globules).

Hybrid materials of SBA-16 functionalized by rare earth (Eu 3+, Tb 3+) complexes of modified β-diketone (TTA and DBM): Covalently bonding assembly and photophysical properties

Novel mesoporous SBA-16 type of hybrids TTA-S16 and DBM-S16 were synthesized by co-condensation of modified β-diketone (TTA-Si and DBM-Si, DBM=1,3-diphenyl-1,3- propanepione, TTA=2-thenoyltrifluoroacetone) and tetraethoxysilane (TEOS) in the presence of Pluronic F127 as template, which were confirmed by FTIR, XRD, 29Si CP-MAS NMR, and N 2 adsorption measurements. Novel organic–inorganic mesoporous luminescent hybrid containing RE 3+ (Eu 3+, Tb 3+) complexes covalently attached to the functionalized ordered mesoporous SBA-16 (TTA-S16 and DBM-S16), which were designated as bpy- RE-TTA-S16 and bpy- RE-DBM-S16, were obtained by sol–gel process. The luminescence properties of these resulting materials were characterized in detail, and the results reveal that mesoporous hybrid material bpy-Eu-TTA-S16 present stronger luminescent intensities, longer lifetimes, and higher luminescent quantum efficiencies than the corresponding DBM-containing materials bpy-Eu-DBM-S16, while bpy-Tb-DBM-S16 exhibit the stronger characteristic emission of Tb 3+ and longer lifetime than the corresponding TTA-containing materials bpy-Tb-TTA-S16.

Ta(V)-Single Site BEA Zeolite by Two-Step Postsynthesis Method: Preparation and Characterization

Ta1.0SiBEA and Ta2.0SiBEA zeolites are prepared by a two-step postsynthesis method involving first the creation of vacant T-atom sites associated with silanol groups by dealumination of TEABEA zeolite with nitric acid and then the impregnation of the resulting SiBEA zeolite with tantalum ethoxide (Ta(OC2H5)5 precursor. This postsynthesis procedure allows to incorporate Ta into the BEA framework as isolated mononuclear Ta(V) ions and to obtain Ta(V)-single site BEA zeolite as evidenced by XRD, 29Si MAS NMR, 1H–29Si CP MAS NMR, IR, 1H MAS NMR, DR UV–Vis.

Highly efficient luminescent hybrid materials covalently linking with europium(iii) complexes via a novel fluorinated β-diketonate ligand: synthesis, characterization and photophysical properties

A novel highly fluorinated beta-diketonate ligand, 1-(3,5-bis(benzyloxy)phenyl)-4,4,5,5,5-pentafluoropentane-1,3-dione (HBBPPF) and its corresponding europium(III) ternary complex, Eu(BBPPF)(3)(DDXPO) [DDXPO = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene oxide] were synthesized via a dexterously designed routine, characterized and its photophysical properties (PL) investigated. PL measurement results indicated that the europium(III) ternary complex exhibits intense red emission under UV light excitation with a solid-state quantum yield of 39%. An organic-inorganic mesoporous luminescent hybrid material was also constructed by linking the ternary europium(III) complex to the functionalized hexagonal mesoporous MCM-41 through the modified beta-diketonate ligand (SiBBPPF-Na). Beta-diketonate grafted to the coupling agent 3-(triethoxysilyl)propyl isocyanate was used as the precursor for the preparation of mesoporous materials. A modified MCM-41 mesoporous material containing ternary europium(iii) complex covalently bonded to the silica-based network, designated as Eu(BBPPF-Si)(3)(DDXPO)/MCM-41, was obtained by interacting SiBBPPF-Na with europium nitrate, DDXPO and MCM-41 via a ligand-exchange reaction. The new mesoporous hybrid material was characterized by powder X-ray diffraction, nitrogen adsorption-desorption, thermogravimetry, transmission electron microscopy, dynamic light scattering, FT-IR, (29)Si CP MAS NMR and (13)C NMR solid-state techniques, and photoluminescence spectroscopy. Eu(BBPPF-Si)(3)(DDXPO)/MCM-41 exhibits an efficient intramolecular energy transfer process from the silylated beta-diketonate to the central Eu(3+), namely, the "antenna effect", which favours a strong luminescent intensity (quantum yield = 43%). Thermogravimetric analysis on Eu(BBPPF-Si)(3)(DDXPO)/MCM-41 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous MCM-41 matrix.