Chemical assembly of a titanium oxide layer on microporous silica

Russian Journal of General Chemistry - The chemical assembly of a titanium oxide coating on a regular microporous silica surface by the atomic layer deposition method was considered. The change in...     

Characterization of vanadium and titanium oxide supported SBA-15

Supported vanadium and titanium oxide catalysts were prepared by adsorption and subsequent calcination of the vanadyl and titanyl acetylacetonate complexes, respectively, on mesoporous SBA-15 by the molecular designed dispersion (MDD) method. Liquid and gas phase depositions at different temperatures were carried out with vanadyl acetylacetonate, and the different results together with those of titanyl acetylacetonate in the liquid phase deposition were discussed. The bonding mechanism, the influence of the metal interaction with the support material, and differences due to the way of deposition and the temperature were investigated by TGA, chemical analysis, FTIR, and Raman spectroscopy. Elevated dissolving temperatures in the liquid phase led to higher final loadings on the SBA-15 without the formation of clusters, even at high loadings. The decomposition of the anchored vanadium and titanium complexes, their thermal stability, and the conversion to the covalently bound VO(x) and TiO(x) species on SBA-15 were studied and investigated by in situ transmission IR spectroscopy. In general, the titanium complex is more reactive than the vanadium complex toward the surface of SBA-15 and has a higher thermal stability. The MDD method of the VO(acac)2 and TiO(acac)2 enables to create a dispersed surface of supported VO(x) and TiO(x), respectively. The structure configurations of VO(x) and TiO(x) oxide catalysts obtained at different metal loadings were studied by Raman spectroscopy. Pore size distributions, XRD, and N2 sorption confirmed the structural stability of these materials after grafting. VO(x)/SBA-15 and TiO(x)/SBA-15 samples, with different metal loadings, were also catalytically tested for the selective catalytic reduction (SCR) of NO with ammonia.     

Visible light photoactivity from a bonding assembly of titanium oxide nanocrystals

TiO(2) nanocrystals are assembled together by interfacial Ti-Ti electronic bonding. Such nanocrystal assemblies have a narrower band gap, greatly enhanced visible light absorption, and solar photocatalysis compared with individual nanocrystals.     

Synthesis of vanadium-phosphorus oxide catalysts supported on pyrogenic silica and titanium dioxide

Various methods for the preparation of vanadium-phosphorus oxide (VPO) catalysts supported on aerosils A-300 and A-50 and TiO₂ were studied: a traditional method (in an organic solvent under varying the support addition time, the nature of the reducing agent, and the degree of reduction of vanadium oxide) and barothermal and mechanochemical syntheses. With the use of XRD analysis, it was found that the composition of the resulting VPO phase depends on the time of support addition to the synthesis and the temperature of thermal treatment. Conditions for the formation of a supported phase of VOHPO₄·0.5H₂O, the precursor of the active component (VO)₂P₂O₇, were determined. The presence of vanadium in an oxidation state of +4 was demonstrated using EPR and UV-VIS spectroscopy. The specific surface areas and pore structures of the synthesized catalysts were determined. The catalytic properties of samples in the reactions of n-butane oxidation in an excess of the hydrocarbon and oxidative ethane dehydrogenation were studied. It was found that, as compared with traditional bulk VPO catalysts, the use of the synthesized supported VPO catalysts made it possible to improve the process characteristics of n-butane oxidation and did not change these characteristics in the reaction of oxidative ethane dehydrogenation.     

Using bicellar mixtures to form supported and suspended lipid bilayers on silicon chips

Bicellar mixtures, planar lipid bilayer assemblies comprising long- and short-chain phosphatidylcholine lipids in suspension, were used to form supported lipid bilayers on flat silicon substrate and on nanotextured silicon substrates containing arrays of parallel troughs (170 nm wide, 380 nm deep, and 300 nm apart). Confocal fluorescence and atomic force microscopies were used to characterize the resulting lipid bilayer. Formation of a continuous biphasic undulating lipid bilayer membrane, where the crests and troughs corresponded to supported and suspended lipid bilayer regions, is demonstrated. The use of interferometric lithography to fabricate nanotexured substrates provides an advantage over other nanotextured substrates such as nanoporous alumina by offering flexibility in designing different geometries for suspending lipid bilayers.     

Oligomerisation of phenyl acetylene over titanium oxide supported on silica - alumina catalyst

Titanium oxide on silica-alumina support is found to be effective for oligomerisation of phenyl acetylene. Cyclic trimerisation of the acetylene leading to trisubstituted benzene was also found to occur during the oligomerisation, in addition to the formation of small quantities of a ketone by the reaction of phenyl acetylene with moisture over the catalyst surface.     

Fluid supported lipid bilayers containing monosialoganglioside GM1: a QCM-D and FRAP study

In an effort to use model fluid membranes for immunological studies, we compared the formation of planar phospholipid bilayers supported on silicon dioxide surfaces with and without incorporation of glycolipids as the antigen for in situ antibody binding. Dynamic light scattering measurements did not differentiate the hydrodynamic volumes of extruded small unilamellar vesicles (E-SUVs) containing physiologically relevant concentrations (0.5-5 mol%) of monosialoganglioside GM1 (GM1) from exclusive egg yolk L-alpha-phosphatidylcholine (egg PC) E-SUVs. However, quantifiable differences in deposition mass and dissipative energy loss emerged in the transformation of 5 mol% GM1/95 mol% egg PC E-SUVs to planar supported lipid bilayers (PSLBs) by vesicle fusion on thermally evaporated SiO2, as monitored by the quartz crystal microbalance with dissipation (QCM-D) technique. Compared to the 100 mol% egg PC bilayers on the same surface, E-SUVs containing 5 mol% GM1 reached a approximately 12% higher mass and a lower dissipative energy loss during bilayer transformation. PSLBs with 5 mol% GM1 are approximately 18% heavier than 100 mol% egg PC and approximately 11% smaller in projected area per lipid, indicating an increased rigidity and a tighter packing. Subsequent binding of polyclonal immunoglobulin G anti-GM1 to the PSLBs was performed in situ and showed specificity. The anti-GM1 to GM1 ratios at equilibrium were roughly proportional to the concentrations of anti-GM1 administered in the solution. Fluorescence recovery after photobleaching was utilized to verify the retained, albeit reduced lateral fluidity of the supported membranes. Five moles percentage of GM1 membranes (GM1 to PC ratio approximately 1:19) decorated with 1 mol% N-(Texas Red sulfonyl)-1,2-dihexadecanoyl-sn-glycerol-3-phosphoethanolamine (Texas Red DHPE) exhibited an approximately 16% lower diffusion coefficient of 1.32+/-0.06 microm2/s, compared to 1.58+/-0.04 microm2/s for egg PC membranes without GM1 (p<0.01). The changes in vesicle properties and membrane lateral fluidity are attributed to the interactions of GM1 with itself and GM1 with other membrane lipids. This system allows for molecules of interest such as GM1 to exist on a more biologically relevant surface than those used in conventional methods such as ELISA. Our analysis of rabbit serum antibodies binding to GM1 demonstrates this platform can be used to test for the presence of anti-lipid antibodies in serum.     

Chemical assembly of chromium oxide structures on the surface of disperse silicon carbide

The possibility was studied for synthesizing chromium oxide structures on the surface of K3–6 granular silicon carbide [GOST(State Standard 26327-84)] by its multiple successive treatment with chromium(VI) oxochloride, ethyl alcohol, and water vapors. The change in the chromium concentration in the modified samples was studied as a function of the number of successive treatment cycles. The samples were characterized by the X-ray phase analysis, X-ray photoelectron, IR, and electronic diffuse reflectance spectroscopies before and after the modification.     

Synthesis of titanium oxide structures on mesoporous silicon dioxide surface by molecular layering

The formation of titanium oxide structures through the repeated successive treatment of SBA-15 mesoporous silicon dioxide with vapors of TiCl₄ and H₂O at 200°C is investigated. The influence of the number of synthesis cycles on the character of the buildup of the surface titanium oxide structures and changes in the adsorption and structural characteristics of modified silica is shown.     

Homogeneous and disordered assembly of densely packed titanium oxide nanocrystals: an approach to coupled synthesis and assembly in aqueous solution

A homogeneous and disordered assembly of densely packed nanocrystals 2-3 nm in size was synthesized at room temperature in an aqueous solution without the assistance of any organic molecules. The assembled nanocrystals of titanium oxides, such as anatase titanium dioxide, sodium titanate, and a solid solution with rutile tin dioxide, formed macroscopic transparent objects 2-5 mm in size. In general, it is not easy to obtain homogeneous and disordered assembly of nanocrystals without assistance of any organic molecules for the inhibition of inhomogeneous and disordered aggregation. In the present work, the formation of the hydrated layer on the surface of nanocrystals facilitated the homogeneous and disordered assembly. The crystal phases and the compositions of the nanocrystals were controlled by the tuning of the synthetic conditions, such as the initial pH and metal source concentration. Based on the formation processes and mechanisms, this approach for the coupled synthesis and assembly can be applied to a variety of nanomaterials for preparation of homogeneous but disordered assembly.     

Palladium oxide nanoparticles supported on graphene oxide: A convenient heterogeneous catalyst for reduction of various carbonyl compounds using triethylsilane

Palladium oxide nanoparticles supported on graphene oxide ‐ triethylsilane was found to be an effective reductive system for a broad range of reduction processes, including the reduction of various carbonyl compounds such as aromatic aldehydes to their corresponding alcohols or methyl arene compounds, aromatic ketones to their respective alcohols or saturated compounds, aromatic acyl chlorides to their reduced compounds. The desired products were obtained in good to excellent yields under mild conditions. The heterogeneous environmentally friendly catalyst can be easily separated from the reaction mixture through a simple filtration, facilitating purification of the prepared compounds.     

Cationic lipid absorption on titanium: a counterion-mediated bilayer-to-lipid-tubule-network transition

By carefully tuning the screening effects of monovalent salt in solution, it is possible to control the formation of different lipid morphologies on a titanium dioxide substrate. A transition from an absorbed vesicle layer to fluid lipid bilayers is observed as a function of monovalent salt concentration in solution, and, above a threshold salt concentration, a network of lipid tubules with a fascinating distorted-hexagonal structure is formed in two dimensions on the substrate. We present fluorescence microscopy data for these different morphologies, confirming the connectivity and fluidity of the bilayers and tubules.     

A lipophilic hexaporphyrin assembly supported on a stannoxane core

Lipophilic hexaporphyrin free-base and copper-metalated assemblies supported on a Sn6O6 core have been synthesized and characterized. The nuclease activity of the copper derivative has been studied.     

Application of thin titanium/titanium oxide layers deposited on gold for infrared reflection absorption spectroscopy: structural studies of lipid bilayers

Ultrathin titanium layers when deposited on the surface of gold can be successfully applied for infrared reflection absorption spectroscopy (IRRAS) investigations. It was shown that the reflectivity, the phase shift, and the mean square electric field of the p- and s-polarized IR radiation in up to 20 nm thick titanium layers covered with a 3-4 nm thick layer of native oxide are comparable to those of the air/gold interface. The surface selection rule is fulfilled. Thus, qualitative and quantitative analysis of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers transferred in liquid expanded (LE) and liquid condensed (LC) states can be performed. Differences are found in the hydration state and molecular arrangement of the two investigated bilayers. In the DMPC bilayer in the LE state, the C-N bond in the positively charged choline moiety is inclined by approximately 70 degrees toward the surface of the negatively charged titanium substrate. In the phosphate moiety, the in-plane vector of the O-P-O group makes a small angle of approximately 15 degrees to the surface normal. This open structure of the lipid molecule corresponds to the B crystal structure of the DMPC molecule and provides space for strong hydration of the polar headgroup. In the DMPC bilayer in the LC state, the intermolecular distances are reduced; the C-N bond of the choline group makes a smaller angle to the surface normal, and the in-plane vector of the O-P-O group in the phosphate moiety displays a larger tilt. The degree of hydration is reduced. The arrangement of the polar headgroup region corresponds to the A crystal structure of the DMPC molecule.     

Lithium aluminates on a molecular titanium oxide

Lithium aluminates Li[Al(O-2,6-Me(2)C(6)H(3))R'(3)] (R' = Et, Ph) react with the μ(3)-alkylidyne oxoderivative ligands [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CR)] [R = H (1), Me (2)] to afford the aluminum-lithium-titanium cubane complexes [{R'(3)Al(μ-O-2,6-Me(2)C(6)H(3))Li}(μ(3)-O)(3){Ti(η(5)-C(5)Me(5))}(3)(μ(3)-CR)] [R = H, R' = Et (5), Ph (7); R = Me, R' = Et (6), Ph (8)]. Complex 7 evolves with the formation of a lithium dicubane species and a Li{Al(μ-O-2,6-Me(2)C(6)H(3))Ph(3)}(2)] unit.     

Electrochemical determination of sulfide at various carbon substrates: a comparative study.

The direct electrochemical oxidation of sodium sulfide has been examined at five different carbon-based electrode substrates (glassy carbon (GC), boron-doped diamond (BDD), edge-plane pyrollytic graphite (EPPG), basal-plane pyrollytic graphite (BPPG) and carbon nanotubes (CNT)). An electrocatalytic response is observed at both the EPPG and CNT electrode compared to that of the other three substrates. The higher capacitative charging currents obtained at the CNT electrode hinder its detection range and, as such, the EPPG electrode has been clearly shown to be the substrate of choice for the direct electrochemical detection of sulfide. The procedure was applied to the recovery of a sulfide spike in river water, with a recovery of 104%.     

Nitric oxide enhances the capacitance of self-assembled,supported bilayer lipid membranes

The effect of nitric oxide (NO) at biologically relevant concentrations on the electrochemical features of the membrane was investigated by cyclic voltammetry (CV) at self-assembled, stainless steel supported lipid bilayer membranes (s-BLMs) using a three-electrode system. The results showed that the membrane capacitance (C_m) of s-BLMs was dramatically enhanced by the presence of increasing NO concentration from 0 to 70 μM. For comparison, fullerene C₆₀ doped s-BLMs (C₆₀@s-BLMs) was also studied. The C_m of C₆₀@s-BLMs increased with NO concentration from 0 to 16 μM and gradually reached a plateau value when NO concentration was over 16 μM. We concluded that (i) NO accumulated inside lipid bilayer increases the C_m of s-BLMs, and (ii) C₆₀ inside s-BLMs changes the dielectric constant of lipid bilayer, thus reducing the effect of NO on the C_m of C₆₀@s-BLMs. This novel self-assembled lipid modified probe provides a simple yet interesting model to study the effect of NO on the electrical conductance of the membrane.     

Simulations of lipid transfer between a supported lipid bilayer and adsorbing vesicles

Recent experiments demonstrate transfer of lipid molecules between a charged, supported lipid membrane (SLB) and vesicles of opposite charge when the latter adsorb on the SLB. A simple phenomenological bead model has been developed to simulate this process. Beads were defined to be of three types, ‘n’, ‘p’, and ‘0’, representing POPS (negatively charged), POEPC (positively charged), and POPC (neutral but zwitterionic) lipids, respectively. Phenomenological bead–bead interaction potentials and lipid transfer rate constants were used to account for the overall interaction and transfer kinetics. Using different bead mixtures in both the adsorbing vesicle and in the SLB (representing differently composed/charged vesicles and SLBs as in the reported experiments), we clarify under which circumstances a vesicle adsorbs to the SLB, and whether it, after lipid transfer and changed composition of the SLB and vesicle, desorbs back to the bulk again or not. With this model we can reproduce and provide a conceptual picture for the experimental findings.