Thermal and Temporal Aging of Silica Gels in Monomer Solutions

In previous work we have introduced the idea of preparing ambient pressure dried silica aerogels by increasing the wet gels' stiffness by aging in a TEOS solution until shrinkage during drying is almost eliminated. The present work elucidates the possibilities for obtaining ambient pressure dried aerogels employing this idea, however, cheap water soluble sodium silicate (water glass) precursors have been used to increase the economic feasibility of the process.We have shown how the G modulus of water glass based gels can be increased by aging in TEOS solution and gels with a density down to 0.2 g/cm3 can be obtained. These wet gels show a higher reactivity towards TEOS compared to TEOS based gels. We have also introduced the idea of aging wet gels in a solution where the monomers are provided from water glass instead of TEOS and some initial results on G modulus and density are included.     

Measurement of specific radioactivity in proteins separated by two-dimensional gel electrophoresis

We report a method to quantify the specific radioactivity of proteins that have been separated by 2-DE. Gels are stained with SyproRuby, and protein spots are excised. The SyproRuby dye is extracted from each spot using DMSO, and the fluorescence is quantified automatically using a plate reader. The extracted gel piece is then dissolved in hydrogen peroxide and radioactivity is quantified by liquid scintillation counting. Gentle agitation with DMSO for 24 h was found to extract all the SyproRuby dye from gel fragments. The fluorescence of the extract was linearly related to the amount of BSA loaded onto a series of 1-D gels. When rat muscle samples were run on 2-DE gels, the fluorescence extracted from 54 protein spots showed a good correlation (r = 0.79, p < 0.001) with the corresponding spot intensity measured by conventional scanning and image analysis. DMSO extraction was found not to affect the amount of radioactive protein left in the gel. When a series of BSA solutions of known specific radioactivity were run on 2-DE gels, the specific radioactivity measured by the new method showed a good correlation (r = 0.98, p < 0.01, n = 5) with the specific radioactivity measured directly before loading. Reproducibility of the method was measured in a series of 2-DE gels containing proteins from the livers of rats and mice that had been injected with [35S]methionine. Variability tended to increase when the amount of radioactivity in the protein spot was low, but for samples containing at least 10 dpm above background the CV was around 30%, which is comparable to that obtained when measuring protein expression by conventional image analysis of SyproRuby-stained 2-DE gels. Similar results were obtained whether spots were excised manually or using a spot excision robot. This method offers a high-throughput, cost-effective and reliable method of quantifying the specific radioactivity of proteins from metabolic labelling experiments carried out in vivo, so long as sufficient quantities of radioactive tracer are used.     

The proteome of maize leaves: use of gene sequences and expressed sequence tag data for identification of proteins with peptide mass fingerprints.

As a first step in establishing a proteome database for maize, we have embarked on the identification of the leaf proteins resolved on two-dimensional (2-D) gels. We detected nearly 900 spots on the gels with a pH 4-7 gradient and over 200 spots on the gels with a pH 6-11 gradient when the proteins were visualized with colloidal Coomassie blue. Peptide mass fingerprints for 300 protein spots were obtained with matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometer and 149 protein spots were identified using the protein databases. We also searched the pdbEST databases to identify the leaf proteins and verified 66% of the protein spots that had been identified using the protein databases. Sixty-seven additional protein spots were identified from expressed sequence tags (ESTs). Many abundant leaf proteins are present in multiple spots. Functions of over 50% of the abundant leaf proteins are either unknown or hypothetical. Our results show that EST databases in conjunction with peptide mass fingerprints can be used for identifying proteins from organisms with incomplete genome sequence information.     

Magnetic resonance investigation of vanadia and vanadium-molybdenum gels synthesized with peroxovanadate precursors

Vanadia gels and vanadium-molybdenum oxide gels were investigated using the magnetic resonance techniques, EPR spectroscopy and (51)V MAS NMR spectroscopy. The vanadium oxide gels were derived from the reaction of H(2)O(2) and V(2)O(5), and the vanadium-molybdenum oxide (VMoO) gels were derived from the reaction of peroxovanadates with an ammonium molybdate solution. EPR spectroscopy was utilized to determine quantitative information about the concentration of V(4+) paramagnetic species present in the samples and additional structural information about the V(4+) coordination environment. (51)V MAS NMR spectroscopy was used to elucidate the V(5+) electronic environment and how it changes as a function of molybdenum content. The observed line broadening of the (51)V NMR signal with increasing molybdenum content was correlated with an increase in the concentration of paramagnetic species as monitored by EPR spectroscopy. The evolution of various vanadium sites during thermal treatment was also investigated. This work provides further support for the hypothesis that the selectivity of VMoO catalysts in the oxidation of 1,3-butadiene to maleic anhydride is due to the presence of paramagnetic V(4+) sites.     

Characterization of Cr(III)-Zr(IV) mixed and Sn(II) doped hydrous oxides

Surface and structural properties of chromium-zirconium mixed and Sn(II)doped hydrous oxide gels have been compared with chromium oxide hydrate gel by the use of thermal analysis, IR spectroscopy, X-ray diffraction, electron microscopy and magnetic measurements. The mixed and doped oxide gels were found to have a hexagonal close packed stacking of O, OH and H₂O ligands with chromium ions distributed in octahedral sites with little degree of order among them. The microstructure of the gels are characterized by the presence of large aggregates of chromium hydroxides, fine granular sheets due to HCrO₂ phase and Cr(OH)₃ microcrystallites. Magnetic susceptibility measurements indicate anti-ferromagnetic behaviour of these gels.     

Study on the NaNp/Al2O3-SiO2 system

Sodium naphthenide (NaNp) deposited on aluminosilicate gels yields systems that exhibit signals in EPR spectra, the multiplicity, g values, and intensities of which depend on the gel composition. The symmetrical singlets (I) of a g(1) value of 2.00 were assigned to the complexed naphthalene anion radicals on the centers occurring on the surfaces of the alumina and silica phases of the gels studied. Those radicals complexed on surface Lewis acid sites are of hard acid/hard base type according to Pearson theory, and are bonded to the sites by ionic forces. The asymmetrical singlets (II) described by the value g(2)=1.95 were assigned to naphthalene anion radicals, which are complexed by the centers of the aluminosilicate phase of the gels studied. Those radicals, complexed on surface Lewis acid sites of this phase, are of soft acid/soft base type and are bonded to the sites by covalent bonds. The highest intensity of the singlet (I) was recorded for the system containing alumina gel. The highest intensity of the singlet (II) was recorded for the system containing Al(2)O(3) in 30 wt%. The structures of Lewis acid sites on aluminosilicate phases are postulated to be different from those on alumina or silica phases.     

Diffusion, relaxation, and chemical exchange in casein gels: a nuclear magnetic resonance study

Water in protein/water mixtures can be described in terms of bound water and free water, by exchange between these two states, and by its exchange with appropriate sites on the protein. 1H-NMR diffusion and relaxation measurements provide insights into the mobility of these states. T2 relaxation-time dispersions (i.e., T2 relaxation times at different echo pulse spacings) reveal additional information about exchange. We present a comprehensive set of diffusion and T2 dispersion measurements on casein gels for which the protein/water ratio ranges from 0.25 to 0.5. The combination of these methods, taken in conjunction with concentration dependence, allows a good estimate of the parameters required to fit the data with Luz/Meiboom and Carver/Richards models for relaxation and chemical exchange. We compare the exchange (a) between water and protein and (b) between free water and bound water. Further, we attempt to distinguish chemical site exchange and diffusion/susceptibility exchange.     

Thermal and Temporal Aging of Two Step Acid-Base Catalyzed Silica Gels in Water/Ethanol Solutions

Dissolution and reprecipitation of silica during aging in water improve the wet gels mechanical stiffness and strength, and hence shrinkage during supercritical drying is reduced. We have investigated how the strength and stiffness of a 2-step TEOS acid-base catalyzed wet gel can be improved by aging in a solution of water/ethanol (20–40 vol%) at various temperatures (20–70°C) and time (2 h and 24 h) and how this influences the aerogels properties. The linear shrinkage during supercritical drying was reduced from 29% to 2% by introducing the aging step in the 20 vol% water/ethanol solution for 24 h at 60°C.We have also in previous works introduced the idea of preparing ambient pressure dried silica aerogels by increasing the wet gels stiffness by aging in a TEOS solution until shrinkage during drying is almost eliminated. The gels aged in the water/ethanol solutions were further aged in a TEOS/ethanol solution and the effect of the increasing water content in the pore liquid was studied. A xerogel density of 0.20 g/cm³ is reported for gels with a shear modulus (G) of 30 MPa.     

Stability and gelation behavior of bovine serum albumin pre-aggregates in the presence of calcium chloride

We study, using wide-angle and small-angle light scattering techniques, the stability and aggregation/gelation behaviors of denatured filamentous bovine serum albumin pre-aggregates (BSA-PAs), induced by CaCl(2). It is observed that transparent filamentous gels can be formed not only at low CaCl(2) concentrations but also at high CaCl(2) concentrations, while turbid gels are obtained at intermediate CaCl(2) concentrations. Although the filamentous gels at low CaCl(2) concentrations and the turbid gels at intermediate CaCl(2) concentrations are consistent with the literature observations, the filamentous gels at high CaCl(2) concentrations have to be explained by different mechanisms. The latter is attributed to the repulsive hydration interactions originating from increased surface dipoles generated by counterion binding. Since such surface dipole-induced hydration is very short-range and occurs mainly on charged or polar patches of proteins (thus protected from aggregation), the aggregation of the filamentous BSA-PAs at hydrophobic patches at the two ends is still possible, leading to formation of the filamentous gels.     

Lycopene/arabinoxylan gels: rheological and controlled release characteristics

Arabinoxylan gels exhibiting different rheological and lycopene transport properties were obtained by modifying the polysaccharide concentration from 3 to 4% (w/v). The apparent lycopene diffusion coefficient decreased from 2.7 × 10?? to 2.4 × 10?? cm2/s as the arabinoxylan concentration in the gel changed from 3 to 4% (w/v). A low amount of lycopene is released by diffusion from arabinoxylan gels. These results indicate that arabinoxylan gels could be carriers for lycopene delivery in specific sites after network degradation. The possibility to modulate lycopene release from arabinoxylan gels makes these biomaterials potential candidates for the controlled delivery of biomolecules.     

Ground-state equilibrium thermodynamics and switching kinetics of bistable [2]rotaxanes switched in solution, polymer gels, and molecular electronic devices

We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a pi-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90 %) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a pi-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs.     

Recent Advances in Supramolecular Gels and Catalysis

Over the past two decades, supramolecular gels have attracted significant attention from scientists in diverse research fields and have been extensively developed. This review mainly focuses on the significant achievements in supramolecular gels and catalysis. First, by incorporating diverse catalytic sites and active organic functional groups into gelator molecules, supramolecular gels have been considered as a novel matrix for catalysis. In addition, these rationally designed supramolecular gels also provide a variety of templates to access metal nanocomposites, which may function as catalysts and exhibit high activity in diverse catalytic transformations. Finally, as a new kind of biomaterial, supramolecular gels formed in situ by self‐assembly triggered by catalytic transformations are also covered herein.     

17O MAS and 3QMAS NMR investigation of crystalline V(2)O(5) and layered V(2)O(5).nH(2)O gels

The environments for oxygen sites in crystalline V(2)O(5) and in layered vanadia gels produced via sol-gel synthesis have been investigated using (17)O MAS and 3QMAS NMR. For crystalline V(2)O(5), three structural oxygen sites were observed: V=O (vanadyl), V(2)O (doubly coordinated), and V(3)O (triply coordinated). Line-shape parameters for these sites were determined from numerical simulations of the MAS spectra. For the vanadia gels at various stages of dehydration, assignments have been proposed for numerous vanadyl, doubly coordinated, and triply coordinated oxygen sites. In addition, by correlating the (17)O MAS and 3QMAS NMR, (51)V MAS NMR, and thermogravimetric analysis data, the coordination of water sites has been established. On the basis of these results, the gel structure and its evolution at various stages of hydration have been detailed. Upon rehydration of the layered gel, we observed a preferred site for initial water readsorption. The oxygen atoms of these readsorbed water molecules readily exchanged into all types of oxygen sites even at room temperature.     

Mass spectrometric imaging of immobilized pH gradient gels and creation of "virtual" two-dimensional gels

We have developed a matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) based technique for the detection of intact proteins directly from immobilized pH gradient gels (IPGs). The use of this technique to visualize proteins from IPGs was explored in this study. Whole cell Escherichia coli extracts of various loadings were separated on IPGs. These IPGs were processed to remove contaminants and to achieve matrix/analyte cocrystallization on the surface of the gel. Mass spectra were acquired by scanning the surface of the gel and were assimilated into a "virtual" two dimensional (2-D) gel. This virtual 2-D gel is analogous to a "classical" 2-D gel, except that the molecular weight information is acquired by mass spectrometry rather than by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). This mass spectrometry (MS) based technology exemplifies a number of desirable characteristics, some of which are not attainable with classical two-dimensional electrophoresis (2-DE). These include high sensitivity, high reproducibility, and an inherently higher resolution and mass accuracy than 2-D gels. Furthermore, there is a difference in selectivity exhibited between virtual 2-D gels and classical 2-D gels, as a number of proteins are visible in the virtual gel image that are not present in the stained gels and vice versa. In this report, virtual 2-D gels will be compared to classical 2-D gels to illustrate these features.     

Catch and Release of DNA in Coacervate‐Dispersed Gels

Summary: We have synthesized novel coacervate‐droplet gels, which were applied to controlling the transportation of DNA in electrophoresis. Coacervate droplets are colloidal particles and they are usually composed of positive and negative polyelectrolytes. However, the polyzwitterion (polyampholyte) PDMAPS can form coacervate droplets in water by itself, since PDMAPS has both positive and negative charges in each side group of main chain. Coacervate droplets have a unique nature and can catch charged macromolecules such as DNA. In order to utilize the nature of the PDMAPS coacervate droplets for the catch and release of DNA, we stabilized PDMAPS droplets in gels. The droplets catch the DNA in electrophoresis and the release of DNA can be controlled by temperature and salt addition.

Electrophoresis of DNA, using coacervate‐dispersed PAAm gels, prepared at various PDMAPS concentrations. The circles indicate the PAAm gels embedded in agarose gels.     

Independent component analysis of 2-D electrophoresis gels

We present a novel application of independent component analysis (ICA), an exploratory data analysis technique, to two-dimensional electrophoresis (2-DE) gels, which have been used to analyze differentially expressed proteins across groups. Unlike currently used pixel-wise statistical tests, ICA is a data-driven approach that utilizes the information contained in the entire gel data. We also apply ICA on wavelet-transformed 2-DE gels to address the high dimensionality and noise problems typically found in 2-DE gels. Also, we use an analysis-of-variance (ANOVA) approach as a benchmark for comparison. Using simulated data, we show that ICA detects the group differences accurately in both the spatial and wavelet domains. We also apply these techniques to real 2-DE gels. ICA proves to be much faster than ANOVA, and unlike ANOVA it does not depend on the selection of a threshold. Application of principal component analysis reduces the dimensionality and tends to improve the performance by reducing the noise.     

Proteomic analysis of the endoplasmic reticulum from developing and germinating seed of castor (Ricinus communis)

Endoplasmic reticulum (ER) has been prepared and analysed from germinating and developing castor bean endosperm. A combination of one- and two-dimensional (1-D and 2-D) gel electrophoresis was used to study the complexity of sample and protein differences between the two stages. The ER of the developing oilseed is central to the synthesis, sorting and storage of protein and lipid reserves while the germinating seed is concerned with their degradation. Sample complexity has been reduced by separation of ER proteins into lumenal, peripheral membrane and integral membrane subfractions. Membrane proteins pose specific problems in aggregation and binding to passive surfaces. We have overcome this by collection of membranes at density gradient interfaces and by silanization of plastic ware. Several major components have been identified from 1-D gels by N-terminal sequencing and matrix-assisted laser desorption/ionization (MALDI) peptide mass fingerprints. These include protein disulphide isomerase (PDI), calreticulin and developing-ER-specific oleate-12-hydroxylase involved in the biosynthesis of ricinoleic acid. In excess of 300 spots are detectable in each developmental fraction by high sensitivity 2-D gels. This is the first 2-D electrophoretic analysis of plant ER. These gels reveal significant differences between germinating and developing ER. Preparative loading 2-D gels of germinating ER have been run and 14 selected spots characterized by quadrupole time of flight tandem mass spectrometry (Q-TOF MS/MS). Ten of these proteins were assigned function on the basis of identity with existing castor database entries, or by homology with other species. Two proteins, aspartate proteinase precursor and N-carbamyl-L-aminohydrolase-like protein, appear to be absent from developing profiles. Most of the proteins identified are concerned with roles in protein processing and storage, and lipid metabolism which occur in the ER. Data from three of the assigned spots included unidentified peptides indicating the presence of more than one protein in these spots following 2-D electrophoresis. More extensive analysis will have to await developments in genomics but the basic separation technologies to simplify sample identity for a plant ER preparation have been established.     

Physico-chemical applications of liquid chromatography II. Investigations of the surface properties of chemically modified silica gels and of the adsorption of cardiac glycosides from solutions

Summary The chemical modification of silica surface using dichlorosilanes with methyl and phenyl groups and triethylamine as donor in the liquid phase was investigated. This modification leads to a dense coverage of the silica surface by the organic functional groups. Liquid chromatography permits the determination of the thermodinamic characteristics of intermolecular interactions of different molecules during adsorption from solutions on the modified surface of the silica. Silica gels modified with dichlorosilanes containing phenyl groups, possess high selectivity () and capacity (k) for the cardiac glycosides G-strophanthin, K-strophanthoside, K-strophanthin- and cymarin using water-alcohol mixture as the mobile phase, and the selectivity and capacity is much higher than observed on silica gels modified with methyl groups only.     

Effect of Shear Flow on the Polymeric Gels Formed by Macroscopic Phase Separation

Summary: Shear‐induced phase behavior of poly(ethylene oxide‐b‐(DL ‐lactic acid‐co‐glycolic acid)‐b‐ethylene oxide) (PEO‐PLGA‐PEO) triblock copolymers in water is investigated using rheology and small‐angle neutron scattering equipped with an in situ Couette shear cell. For gels formed by the macroscopic phase separation, the steady shear experiment reveals that the flow‐induced anisotropy on a nanometer length scale at a critical shear rate and the phase separation on a larger length scale are successively induced with a further increase in the shear rate. In particular, the hard gels show a memory effect inscribed by a pre‐high shear in contrast to the soft gels.

2D SANS patterns clearly show the memory effect of the hard gels at a pre‐high shear.     

Surface-controlled spatially heterogeneous physical properties of a supramolecular gel with homogeneous chemical composition

Controlling supramolecular self-assembly across multiple length scales to prepare gels with localised properties is challenging. Most strategies concentrate on fabricating gels with heterogeneous components, where localised properties are generated by the stimuli-responsive component. Here, as an alternative approach, we use a spiropyran-modified surface that can be patterned with light. We show that light-induced differences in surface chemistry can direct the bulk assembly of a low molecular weight gelator, 2-NapAV, meaning that mechanical gel properties can be controlled by the surface on which the gel is grown. Using grazing incidence X-ray diffraction and grazing incidence small angle X-ray scattering, we demonstrate that the origin of the different gel properties relates to differences in the architectures of the gels. This provides a new method to prepare a single domain (i.e., chemically homogeneous) hydrogel with locally controlled (i.e., mechanically heterogeneous) properties.

A mechanical pattern is created in a hydrogel film by pre-patterning the underlying surface chemistry. This allows spatial variation of the viscous component of the gel, controlling dissipative forces in the gel film without altering gel chemistry.