Photo-induced proton gradients and ATP biosynthesis produced by vesicles encapsulated in a silica matrix

Sol-gel immobilization of soluble proteins has proven to be a viable method for stabilizing a wide variety of proteins in transparent inorganic matrices. The encapsulation of membrane-bound proteins has received much less attention, although work in this area suggests potential opportunities in microarray technology and high-throughput drug screening. The present paper describes a liposome/sol-gel architecture in which the liposome provides membrane structure and protein orientation to two transmembrane proteins, bacteriorhodopsin (bR) and F(0)F(1)-ATP synthase; the sol-gel encapsulation converts the liposomal solution into a robust material without compromising the intrinsic activity of the incorporated proteins. Here we report on two different proteoliposome-doped gels (proteogels) whose properties are determined by the transmembrane proteins. Proteogels containing bR proteoliposomes exhibit a stable proton gradient when irradiated with visible light, whereas proteogels containing proteoliposomes with both bR and F(0)F(1)-ATP synthase couple the photo-induced proton gradient to the production of ATP. These results demonstrate that materials based on the liposome/sol-gel architecture are able to harness the properties of transmembrane proteins and enable a variety of applications, from power generation and energy storage to the powering of molecular motors, and represent a new technology for performing complex chemical synthesis in a solid-state matrix.     

Fluorescence switch in red-phase polydiacetylene films and vesicles upon thermal cycles

The switch phenomena of thermochromism of red-phase polymerized PCDA (10,12-pentacosadiynoic acid) Langmuir-Schaefer (LS) films and vesicles were investigated in situ during repeated heating and cooling processes between 25 degrees C and 70 degrees C. During repeated thermal cycles, the solid-supported LS films exhibited switch phenomena in both the visible and fluorescent spectra, that is, the colorimetric response (CR) of the PCDA LS films was ca. 80% at 70 degrees C but is ca. 50-60% at 25 degrees C with an increase of fluorescent intensity in the cooling process and a decrease in the heating process. On the other hand, the PCDA vesicles exhibited such phenomenon only in the fluorescent spectra, that is, the CR of the PCDA vesicles was constant as ca. 100% after being stable red form with the same trend in the fluorescent intensity. The changes in molecular configuration revealed by in situ Fourier transform infrared (FTIR) were in good agreement with the trend of fluorescence emission upon repeated thermal stimuli rather than that of visible absorption.     

Iron oxide in a silica matrix prepared by the sol-gel method

Fe_xO_y-SiO₂ nanocomposites were prepared by sol-gel method by using two SiO₂ sources and Fe(SO₄)₂·7H₂O as raw materials. The amorphous gels were thermally treated up to 1000 °C. The initial gel and the thermally treated samples were characterized by thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) and infrared spectroscopy. The presence of hematite was confirmed by the obtained Mössbauer spectra which showed the characteristic sextet. The total amount and the size distributions of the hematite nanoparticles can be controlled via the initial precursors and subsequent by annealing conditions.     

Hardness recovery of ceramic coated aluminium matrix composites using thermal-shock resistant sol-gel silica coatings

Sol-gel silica coatings increase wear and corrosion resistance of aluminium matrix composites, but a heat treatment stage at temperatures as high as 500 °C is usually required to consolidate the ceramic coating. Under these thermal conditions, sol-gel ceramic coatings tend to crack and the aluminium matrix hardness strongly reduces. Present paper describes how the combination of a certain sol-gel procedure accompanied with quenching treatment in silicone oil allows recovering most of the hardness of the substrate, while keeping undamaged the sol-gel silica coating deposited.     

A lipophilic sol-gel matrix for the development of a carbonate-selective electrode

Organic-inorganic hybrid sol-gel matrixes were used as hosts for trifluoroacetyl-p-decylbenzene (TFADB), a traditional ionophore for carbonate. The sol-gel precursor was prepared by the reaction of (3-isocyanopropyl)triethoxysilane with ethylene glycol. Hexadecyltrimethoxysilane (HDTMOS) was employed as a co-precursor. An appropriate amount of tridodecylmethylammonium chloride (TDMAC) and 2-nitrophenyloctyl ether (NPOE) were used as membrane components. On mixing with an acidic catalyst, the sol-state precursors slowly gelled, yielding a membrane in which the active components, TFADB and TDMAC, were encapsulated. Infrared, (1)H, and (29)Si MAS NMR spectrometers were employed to monitor the sol-gel process and the degree of polymerization. The performances of the sol-gel membrane-based electrodes were compared to those of TFADB-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with a molar ratio of TFADB:TDMAC (1:0.14) showed extended lifetime and stable baseline potential. The response slope toward carbonate was approximately 27 mV/decade between 10(-)(5) and 10(-)(3.5) M at 18 degrees C. Interestingly, selectivity toward carbonate over salicylate and other lipophilic anions was improved, clearly deviating from the Hofmeister selectivity pattern. Responses toward small inorganic anions including chloride and sulfate were negligible. The selectivity coefficients measured by the matched potential method in 0.1 M tris-sulfuric acid buffer, pH 8.75, were log = -0.3, log = -4.2, and log = -2.5.     

Electrochemiluminescence of ruthenium (II) tris(bipyridine) encapsulated in sol-gel glasses

The electrogenerated chemiluminescence (ECL) of Ru(bpy)3 2+ and tripropylamine, tributylamine, triethylamine, trimethylamine, or sodium oxalate encapsulated within sol-gel-derived silica monoliths have been investigated using an immobilized ultramicroelectrode assembly. The major purpose of this study was to investigate the role of the reductant on the magnitude and stability of the ECL in this solid host matrix. For gel-entrapped Ru(bpy)3 2-/tertiary amines, the shape and intensity of the ECL-potential curves were highly dependent on scan rate. At 10 mV/s, the ECL intensity was ca. 6-fold higher relative to that observed at 500 mV/s. When the ECL acquired at low scan rates was normalized by that obtained in solution under similar conditions, a value of 0.03-0.06 was obtained. In direct contrast, the ECL of the Ru(bpy)3 2+-oxalate system showed little dependence on scan rate, and the ECL was ca. 65-75% of that measured in solution. These differences can be attributed to differences in rotational and translational mobility between the reductants (amines vs oxalate) trapped in this porous solid host For both systems, the ECL was found to be stable upon continuous oxidation or upon drying the gels in a high-humidity environment for over 10 days.     

Synthesis of CuAlO2 ceramics using sol-gel

Sol-gel as a versatile method for the preparation of oxide ceramics was used to prepare the delafossite-structured p-type CuAlO₂ ceramics. The results showed that mechanical milling is necessary to prepare pure CuAlO₂ ceramics using short annealing periods, and the particle size of CuAlO₂ ceramics prepared from the powders with mechanical milling procedures was smaller than that derived from powders without mechanical milling. The prepared CuAlO₂ ceramics behaved like semiconductors and the thermally activated energy near room temperature was about 0.175 eV.     

Observation of room-temperature 5D1 luminescence of an organoeuropium complex encapsulated in sol-gel glass

In comparing emissions of the inorganic Eu3+ salts (chloride or nitrate) to organoeuropium complexes doped into optically transparent sol-gel glass, previous studies have indicated that changes in the local chemical environment by chelation or variation of the ligand or gel matrix compositions were found to leave the main spectral features of Eu3+ essentially unchanged; complexation just increases the emission intensity of europium and leads to broadening and splitting of the peaks. In all cases studied and irrespective of the excitation energy, the observable emission peaks result only from relaxations out of the 5D0 excited state of Eu3+ to the first five levels of the 7F ground manifold. The present research examines the luminescence behavior of EuCl3 and Eu-TETA (TETA is the macro cycle, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetraaceticacid) doped into a sol-gel host; in addition to emissions from the 5D0, emission from the 5D1 excited state of Eu3+ is observed for the first time.     

Amperometric detection of Escherichia coli heat-labile enterotoxin by redox diacetylenic vesicles on a sol-gel thin-film electrode

Supramolecular assemblies (bilayer vesicles) prepared from ferrocenic diacetylene lipid and the cell surface receptor ganglioside GM1 are utilized to construct an amperometric biosensor for Escherichia coli heat-labile enterotoxin on a sol-gel thin-film electrode. The bilayer vesicles adsorbed on the sol-gel film provide an open platform for molecular recognition, while the electrochemical communication between the incorporated redox lipids and the electrode is influenced by the binding of the toxin. Cyclic voltammetric studies suggest a facile redox reaction for the adsorbed supramolecular assembly, which allows the sensor to detect enterotoxin up to 3 ppm (3.6 x 10(-8) M) concentration. The apparent diffusion coefficients for the redox lipids in the assembly were observed to be in the range of 4.73 x 10(-8) -2.30 x 10(-8) cm/s2. A mechanism of lateral electron transport of redox lipids controlled by biomolecular recognition is proposed.     

Immunochemical approaches for purification and detection of TNT traces by antibodies entrapped in a sol-gel matrix

A highly sensitive immunochemical method for immunoaffinity purification (IAP) and detection of trace amounts of TNT was developed on the basis of antibodies (Abs) in a ceramic matrix (sol-gel). The study resulted in: (i) a highly sensitive and reproducible TNT ELISA (I50 and I20 values of 0.4 +/- 0.09 ppb and 0.12 +/- 0.03 ppb, respectively; n = 12), which is highly specific to TNT; and (ii) successful entrapment of the Abs that bound free analyte from solution. Binding was found to be highly reproducible, dose dependent, and only slightly (1.2-1.8-fold) lower than that in solution. The entrapped Abs did not leach from the matrix and were tolerant of absolute ethanol, acetone, and acetonitrile. Bound analytes could be easily eluted from the sol-gel matrix at high recoveries. The sol-gel-based IAP method described above introduces a simple one-step procedure that has a high potential to serve as a suitable and convenient immunochromatographic device for cleanup and concentration of TNT from "real field" samples in a manner that complies with both chemical and immunochemical residue analysis methods.     

Optically transparent magnetic nanocomposites based on encapsulated Fe(3)O(4) nanoparticles in a sol-gel silica network

Composite Fe(3)O(4)-SiO(2) materials were prepared by the sol-gel method with tetraethoxysilane and aqueous-based Fe(3)O(4) ferrofluids as precursors. The monoliths obtained were crack free and showed both optical and magnetic properties. The structural properties were determined by infrared spectroscopy, x-ray diffractometry and transmission electron microscopy. Fe(3)O(4) particles of 20?nm size lie within the pores of the matrix without any strong Si-O-Fe bonding. The well established silica network provides effective confinement to these nanoparticles. The composites were transparent in the 600-800?nm regime and the field dependent magnetization curves suggest that the composite exhibits superparamagnetic characteristics.     

Synthesis and characterization of sol-gel derived ZnS : Mn2+ nanocrystallites embedded in a silica matrix

Synthesis and characterization of undoped and Mn²⁺ doped ZnS nanocrystallites (radius 2–3 nm) embedded in a partially densified silica gel matrix are presented. Optical transmittance, photoluminescence (PL), ellipsometric and electron spin resonance measurements revealed manifestation of quantum size effect. PL spectra recorded at room temperature revealed broad blue emission signal centred at ∼ 420 nm and Mn²⁺ related yellow-orange band centred at ∼ 590 nm while ESR indicated that Mn in ZnS was present as dispersed impurity rather than Mn cluster.     

LaCoO3 nanosystems by a hybrid CVD/sol-gel approach

LaCoO3 nanosystems are receiving increasing attention for the development of innovative fuel cells and heterogeneous catalysts. In this report, we describe the synthesis of nanophasic LaCoO3 thin films by a hybrid chemical vapor deposition (CVD)/sol-gel (SG) approach. The adopted strategy consists in the CVD of La-O-based systems on SG cobalt oxide xerogels CoOx(OH)y at temperatures as low as 200 degrees C and in the subsequent thermal treatment in air (400-800 degrees C, 2-8 h). In this context, particular attention is devoted to achieving an intimate La/Co intermixing already in the as-prepared systems, in order to favor reactions yielding a single La-Co-O phase with uniform composition. The obtained results point out to the formation of pure and structurally homogeneous LaCoO3 nanosystems after annealing at 700 degrees C, 2 h, with a typical grain-like morphology. More severe thermal treatment resulted in the thermal decomposition of LaCoO3 nanocrystallites.     

Preparation of porous titania sol-gel matrix for immobilization of horseradish peroxidase by a vapor deposition method

A new and facile vapor deposition method has been developed for the preparation of sol-gel matrix. This method was used to form a titania sol-gel thin film and to immobilize horseradish peroxidase (HRP) on a glassy carbon electrode surface for the production of an amperometric hydrogen peroxide biosensor. This process prevented the cracking of conventional sol-gel-derived glasses. The morphologies of both titania sol-gel and the enzyme membranes were characterized using scanning electron microscopy and proved to be chemically clean, porous, and homogeneous and to have a very narrow particle size distribution. The sol-gel-derived titania-modified electrode retained the enzyme bioactivity and provided for long-term stability of the enzyme in storage. In the presence of catechol as a mediator, the sensor exhibited a rapid electrocatalytic response (less than 5 s), a linear calibration range from 0.08 to 0.56 mM with a detection limit of 1.5 microM and a high sensitivity (61.5 microA mM(-1)) for monitoring of H2O2. Effects of pH and operating potential were also explored for optimum analytical performance by using the amperometric method. The apparent Michaelis-Menten constant of the encapsulated HRP was 1.89 +/- 0.21 mM.     

Poly(aniline) nanowires in sol-gel coated ITO: a pH-responsive substrate for planar supported lipid bilayers

Facilitated ion transport across an artificial lipid bilayer coupled to a solid substrate is a function common to several types of bioelectronic devices based on supported membranes, including biomimetic fuel cells and ion channel biosensors. Described here is fabrication of a pH-sensitive transducer composed of a porous sol-gel layer derivatized with poly(aniline) (PANI) nanowires grown from an underlying planar indium-tin oxide (ITO) electrode. The upper sol-gel surface is hydrophilic, smooth, and compatible with deposition of a planar supported lipid bilayer (PSLB) formed via vesicle fusion. Conducting tip AFM was used to show that the PANI wires are connected to the ITO, which convert this electrode into a potentiometric pH sensor. The response to changes in the pH of the buffer contacting the PANI nanowire/sol-gel/ITO electrode is blocked by the very low ion permeability of the overlying fluid PSLB. The feasibility of using this assembly to monitor facilitated proton transport across the PSLB was demonstrated by doping the membrane with lipophilic ionophores that respond to a transmembrane pH gradient, which produced an apparent proton permeability several orders of magnitude greater than values measured for undoped lipid bilayers.     

Formulation and release behavior of diclofenac sodium in Compritol 888 matrix beads encapsulated in alginate

Sustained-release polymer beads containing diclofenac sodium (DNa) dispersed in Compritol 888 and encapsulated in calcium alginate shell were prepared utilizing 2³ factorial design. The effect of sodium alginate concentration, drug:Compritol 888 weight ratio and CaCl₂ concentration on drug content (%), time for 50% and 80% of the drug to be released, and mean dissolution time (MDT) were evaluated with analysis of variance (ANOVA). An increase in the level of all these factors caused retardation in the release, and t_50%, t_80%, and MDT were increased. The drug release was dependent on the pH of the release media. A formula that gives a release comparable to commercial products was prepared.     

Interaction of two nearby CNTs/nanovoids embedded in a metal matrix using modified nonlocal elasticity

Interaction of Carbon Nanotubes (CNTs) and nanovoids embedded in a metal matrix is studied comparatively. For this purpose, two nearby CNTs/nanovoids are modeled as two similar cylindrical inclusions/holes in an infinite matrix. The nonlocal stresses around the CNTs/nanovoids are obtained by applying the integral constitutive equation of the nonlocal elasticity to the stresses from the complex stress potential method. Also, in order to bring different nonlocality effects of dissimilar media into account, the influence function of the nonlocal elasticity is modified. Effects of the CNTs/nanovoids size and distance as well as far-field loading ratio on the stress state in the matrix are investigated. The CNTs strengthening effect on the matrix is shown through lower stresses at the CNTs and matrix interface in comparison to the applied stress. Furthermore, it is indicated that the modified nonlocal analysis brings out the interaction of CNTs/nanovoids at smaller distances in comparison with those the classical analysis used to predict. In other words, higher volume fraction of the CNTs/nanovoids can be incorporated in the metal matrices without devastating effects of their interactions.