Multifold curdlan gel formation by dialysis into aqueous solutions of metal salts

We have found that the dialysis of curdlan dissolved in alkaline solution into aqueous solutions of metal salts yielded multifold gel structures. Aqueous sodium chloride and potassium chloride as well as pure water induced isotropic gels. Aqueous calcium salts induced liquid crystalline gel with refractive index gradient/amorphous gel alternative structure. Aqueous salts of trivalent aluminum and ferric cations induced a rigid liquid crystalline gel, which shrank above a threshold concentration of each salt. On the other hand, Liesegang ring-like pattern was observed with aqueous solutions of mixed salts of calcium chloride and magnesium chloride. The patterns have been classified to discuss the mechanism of forming the variety of structures.     

Liquid crystalline gel beads of curdlan

Curdlan beads consisting of liquid crystalline gel (LCG) and amorphous gel (AG) in alternating layers in a wide range of diameters were newly prepared by interfacial insolubilization reactions using calcium chloride as the setting reagent. The thickness of the liquid crystalline layer was proportional to the diameter of the gel bead, and the proportional constant agreed with that determined for the cylindrical gel prepared by a dialysis method. The proportional constant initially increased with increasing calcium concentration of the dispersing medium and saturated at a high concentration limit. These results suggest that the mechanisms for forming the alternating LCG/AG structures prepared with different boundary conditions are the same. The LCG/AG structure could be controlled by calcium concentration.     

Dynamics in dialysis process for liquid crystalline gel formation

The processes of gelation and liquid crystalline formation in the dialysis of Curdlan solution have been observed under crossed nicols, and the calcium concentration and pH of the inner solution were traced. The results showed that the gelation and the liquid crystalline formation occurred simultaneously to form liquid crystalline gel (LCG), but the birefringence of the LCG increased even after the gelation, suggesting further ordering of the Curdlan molecules. On the basis of the calcium ion diffusion, a simple theory for the time development of the thickness of the LCG layer was developed. The experimental and theoretical results agree very well until an amorphous gel (AG) ring appears. The whole process was expressed by a master curve by reducing time and distance data for different radius dialysis tubes by those at the final state; a scaling behavior with respect to the dialysis tube radius was found. The experimental analysis for the calcium concentrations and the pH indicates that forming Curdlan LCG with high ordering of Curdlan molecules consists of two steps: the diffusion of calcium ions inducing the ordering of Curdlan molecules and yielding cross-links simultaneously, and the local relaxation of the Curdlan molecules increasing the ordering degree further.     

Comparison of the structure and the transport properties of low-set and high-set curdlan hydrogels

Curdlan, a bacterial polysaccharide, can form different types of thermogels, having the very same chemical composition, but whose structures depend on the incubation temperature. Structural characterization of 10% (w/v) low-set and high-set curdlan gels was carried out by Fourier transformed infrared (FT-IR) imaging and environmental scanning electron microscopy (eSEM) in the hydrated state. Considerable differences were observed between the two gels, the high-set one being overall more homogeneous. The self-diffusion coefficients of a series of analytes of different sizes (water, phosphate, glucose-6-phosphate, polyphosphate, polyethylene glycol, and dextran labelled with rhodamine B) were measured in aqueous solution (D(s)(sln)) and in both types of curdlan gels (D(s)(gel)) using (1)H and (31)P pulsed field gradient nuclear magnetic resonance (PFG NMR) spectroscopy. The mutual-diffusion coefficients (D(m)(gel)) of dextran in the curdlan gels were determined from release experiments based on fluorescence spectroscopy. The dependence of the relative diffusion coefficient (D(s)(gel)D(s)(sln)) on the size of the analyte, expressed by its hydrodynamic radius (R(h)), could be expressed by D(s)(gel)D(s)(sln) ∝ exp(-R(h)(0.46)), valid for both types of gels. The self-diffusion measurements for the largest investigated analytes were not compatible with a single diffusion coefficient and, therefore, were analysed using an approach based on a normal distribution of self-diffusion coefficients. In the hydrogels, broadening of the self-diffusion coefficient distribution increased as a function of the analyte size. This phenomenon was associated with the limited distance travelled by the analytes during the measurements, and it is inferred that the distribution of diffusion coefficients is representative of the distribution of local environments of the individual analyte. It was found that the structural differences observed between both types of curdlan gels are not correlated with the gel transport properties, highlighting the complexity of the relationship between structural details and transport properties in gels.     

室温离子液体中合成方钠石的研究

本文以离子液体为溶剂, 在常压下采用离子液体热合成方法合成了方钠石分子筛.     

The Cross‐Sectional Structure of Vanadium Oxide Nanotubes Studied by Transmission Electron Microscopy and Electron Spectroscopic Imaging

Vanadium oxide nanotubes (VO_x‐NTs) are easily accessible in pure form from vanadium(V) alkoxides and amines by a sol‐gel reaction and a subsequent hydrothermal treatment. The wall structure of VO_x‐NTs containing hexadecylamine or dodecylamine as the structure‐directing template has been characterised by transmission electron microscopy (TEM). A standard method for preparing TEM specimens was modified in order to investigate the cross‐sectional structure of the tubes. The elemental distribution in the layered structure inside the tube walls has been visualised by electron spectroscopic imaging: vanadium oxide builds up the layers that appear with dark contrast in the TEM images while carbon, i. e., the organic template, is present in between. The bent VO_x layers inside the tube walls are preferentially scrolls rather than concentric cylinders. Moreover, some tubes are formed by a combination of both types. The layer structure inside the tube walls is frequently disordered, and several types of defects appear.     

DNA liquid-crystalline gel as adsorbent of carcinogenic agent

DNA liquid crystalline gel (LCG) has been newly prepared by a dialysis of concentrated DNA solutions into concentrated metal cation solutions. The condition for forming DNA LCG is examined by means of the insolubilization reaction. The shrinking ratio and the ratio of the thickness of LCG layer, delta, and the diameter of the dialysis tube, d0, do not depend on d0. The adsorption of one of carcinogenic agents, acridine orange is demonstrated. From the experimental results, the mechanism for forming DNALCG is discussed.     

Conformation of curdlan as observed by tapping mode atomic force microscopy

Tapping mode atomic force microscopy was used to study the bacterial polysaccharide curdlan deposited from dimethyl sulfoxide (Me₂SO) and NaOH aqueous solutions. For curdlan in Me₂SO, flexible single chains corresponding to a disordered conformation were observed at a concentration of 5 mg/l, and the chain diameter was measured to be 0.65±0.05 nm, which showed good agreement with the expected value of the single polysaccharide chain. Because the concentration of curdlan increased, the chains became more rigid and aggregated, subsequently, the network structures of curdlan appeared. However, curdlan samples deposited from a 5 mM NaOH solution showed entirely different conformations. The chains observed were almost in the form of micelles of several nanometers, which were supermolecular assemblies. The heterogeneously dense zones were observed as the curdlan concentration increased to 40 mg/l. When the concentration of curdlan was above 100 mg/l, which might cause the real concentration of curdlan on the mica substrate after drying treatment exceeding some critical value of gelation, gel network structures were formed. Keeping on increasing the concentration of curdlan, the image showed a more homogeneous fibrous network.     

Structure formation of the mixed gels of zirconium oxyhydrate and silicic acid produced with different sequencing of reagents

The physicochemical characteristics of single and mixed zirconia and silica gels produced by the sol-gel technique at different synthesis pH and sequence of introducing the reagents in the mother liquid are presented. As a result of comparing the data obtained by different research methods, it is found that in the mixed gels, irrespective of the synthesis technique, Si-O-Zr bonds are present. The introduction of a zirconium salt in the mother liquid containing a silicate salt leads to the preferred formation of zirconia gel granules of 20–30 nm in diameter enclosed in the matrix of silica gel. The inverse sequence of introducing the gel-forming components in the reaction mixture promotes the formation of large gel aggregates containing the particles of less that 10 nm and having a high degree of polymerization. Mixed gels of zirconium oxyhydrate and silicic acid have an order higher sorptive capacity for yttrium (III) and calcium cations, as compared to single silica gels and zirconia gels.     

Quantitative separation of biological lipids by successive chromatographic runs on juxtaposed thin layers (author's transl)]

During a study on incorporation of 14C-labeled precursors in biological lipids, we had to elaborate a method of quantitative separation of lipid classes, based upon three successive chromatographic runs on juxtaposed thin layers. The first thin layer, on which the lipid extract is applied, consists of silica gel alkalised by means of sodium hydroxide solution. The second thin layer is constituted only by silica gel G. The three one-dimensional migrations are respectively carried out in the following solvent systems: diethyl ether-hexane-benzene (55:30:15), hexane-benzene (80:20) and diethyl ether-benzene-acetic acid (62:20:18). The lipid fractions are scraped out and counted by liquid scintillation. The reproducibility of the whole operation is discussed.     

Phase relationship and dynamics of anisotropic gelation of carboxymethylcellulose aqueous solution

Anisotropic gelation of carboxymethylcellulose (CMC) in aqueous NaOH sandwiched between two circular cover glasses by immersing it in aqueous CaCl₂ has been studied. In the course of dialysis, gelation and phase separation occurred simultaneously to make turbid stripes arranged radially. The time course of the gel layer width was well expressed in scaled linear plots predicted by a theory based on “moving boundary picture” at low CMC concentrations. On the other hand, at high CMC concentrations, the time course was expressed by a two-stage dynamics. The time course did not depend on the initial thickness of the CMC solution and the diameter of the cover glasses, whereas the rate of gelation decreased with increasing CMC concentration. It was attributed to the change in the calcium cation concentration required for forming the gel in the process. The universality and the individuality of the present system in the gelation dynamics are discussed.     

Perrhenate ion uptake by aluminium hydroxide gels

The adsorption of perrhenate ions onto aluminium hydroxide gels was investigated. These gels were prepared by the sol-gel method in non aqueous solutions using a tertiary amine as template. They were amorphous and presented high specific surface areas. The amount of perrhenate ions adsorbed from aqueous solutions depended on the specific surface area of the gels. Removal of perrhenate ions up to 84% could be achieved without reaching saturation.     

Multi-gradient hydrogels produced layer by layer with capillary flow and crosslinking in open microchannels

This technical note describes a new bench-top method for producing anisotropic hydrogels composed of gradient layers of soluble factors, particles, polymer concentrations or material properties. Each gradient layer was produced by a previous gradient method in which a droplet of one precursor solution was added to a thin layer of a second solution. The ensuing rapid capillary flow along the open channel generated a gradient precursor solution, which was then crosslinked to form a gradient gel. Repeating these steps allowed a layered gel to be iteratively constructed with as many gradient layers as desired. This technique renders the synthesis of multi-layered gradient gels accessible to virtually any researcher and should help simplify the production of more biologically relevant cellular microenvironments.     

IPAAm凝胶在丙酮水溶液中溶胀行为的关联与预报

基于Maurer和Prausnitz的凝胶相平衡条件，建立了凝胶的溶胀模型.模型假设凝胶是以凝胶组分及凝胶吸收的溶液为核心，以弹性半渗透膜为壳的复合体.并采用UNIQUAC方程计算凝胶相及与之共存液相的Gibbs过剩自由能，采用“phantomnetwork”理论计算凝胶的弹性自由能，采用“自由体积”计算分子的尺度效应.同时以N-异丙基丙烯酰胺（IPAAm）为单体合成了IPAAm凝胶.研究了25 ℃时IPAAm凝胶在丙酮水溶液中的溶胀行为，并测定了丙酮在胶体相和与之共存液相中的分配，以检验模型的关联与预报能力.结果表明,模型预报的单体总量和交联剂浓度对凝胶溶胀的影响与实验符合得很好.而且凝胶溶胀时，能很好地预测丙酮在两相中的分配,表明模型具有很好的关联和预报能力.     

Quantitative turbidity assay for lipolytic enzymes in microtiter plates

A clearing assay for lipolytic enzymes has been realized in 96-well microtiter plates. A thin layer containing emulsified tributyrin as turbidity-generating substrate was placed on a thicker supporting aqueous layer. Both layers were stabilized by a gel-forming agent. Enzyme addition leads to clearing of the emulsion detected with a standard microtiter plate reader as a decrease of extinction. Dependencies of the signal kinetics on the substrate and enzyme concentrations were studied. For 0.5–1 % tributyrin content the reaction rate is not substrate-limited. An initial slope of the signal kinetics is proportional to the lipase activity. A detailed characterization of the assay was performed. Lipolysis of tributyrin was confirmed by glycerol detection. Various gel-forming agents were compared and diffusion conditions in these gels were analyzed. Agar and agarose were found to be the most suitable gel-forming agents, which do not affect enzyme diffusion whereas polyacrylamide gels block lipase diffusion and therefore are not suitable for the assay. The optimized assay prepared from 1 % tributyrin emulsion in 2 % agar gel was tested with six microbial lipases and porcine pancreatic lipase. The detection limit is 20–60 ng/well which is equivalent to 30 μU/well for T. lanuginosus lipase.

Determination of Surface Silanols of Silica Gels and HPLC Bonded Phases

Abstract

A rapid method determining the surface silanols of silica gels and HPLC bonded phases involves a titration of silica gel with sodium hydroxide, in a medium of any of the following 10% aqueous salts: sodium chloride, sodium nitrate, sodium sulfate, potassium chloride, potassium nitrate and potassium sulfate. The silanols are quantified as m eg/g. It is possible to determine cation exchange capacity of a cation-exchanger due to an acid as an end group and surface silanols separately.     

Stable sensor layers self-assembled onto surfaces using azobenzene-containing polyelectrolytes.

Polyelectrolytes functionalized with photoisomerizable azobenzene chromophores were multi-layered onto inorganic and metal surfaces, by the repeated adsorption from dilute aqueous solution, alternating between oppositely charged polymers. These layer-by-layer ionically self-assembled thin films were investigated for their suitability as sensor host materials with respect to the criteria of control over physical layer properties, versatility to different substrates and adsorption geometries, and stability of the formed layers to heat, solvent, and sonication. Layer thickness was found to be controllable between 5 A and 500 nm by varying the total number of layers deposited, from a single monolayer to 1000 layers. Control over individual layer thickness was achieved by varying the pH of the adsorption solutions. This multi-layer self-assembly was demonstrated to be suitable for a wide range of metal and inorganic substrates, and achievable with surfaces of high curvature (r = 50 nm), and confined geometry. The deposited layers exhibited good stability to desorption in a range of organic solvents, aqueous temperatures to 100 degrees C, and cleaning protocols such as sonication. The laser-induced geometric isomerization of the azobenzene chromophores was shown to be strongly dependent on aqueous solution properties, demonstrating an application as a hydroxide ion sensor in highly alkaline media.     

Preparation of a pinhole-free Pd–Ag membrane on a porous metal support for pure hydrogen separation

A pinhole-free palladium membrane with a thickness of 3 μm has been prepared on the surface of a porous sintered stainless steel tube coated with a thin silver layer as a diffusion barrier. Filling of aluminum hydroxide gel in the surface pores of the tube is effective in preventing defect formation during electroless plating of the palladium layer, while the volume of the hydroxide beneath the membrane decreases greatly upon thermal treatment up to 500 °C. The hydrogen flux at 400–500 °C is reasonably proportional to the pressure difference between the two sides of the membrane. Addition of a 2 μm Pd_0.8Ag_0.2 alloy layer on the membrane by electroplating does not greatly decrease the hydrogen permeability.     

Milk protein interfacial layers and the relationship to emulsion stability and rheology

The properties of milk protein-stabilised, oil-in-water emulsions are determined by the structure and surface rheology of the adsorbed layer at the oil-water interface. Analysis of the segment density profiles normal to the surface show differences in the structure between adsorbed layers of disordered casein and globular whey protein. Systematic studies of stability and rheology of model oil-in-water emulsion systems made with milk proteins as sole emulsifiers give insight into the relation between adsorbed layer properties and bulk emulsion stability. Of particular importance are effects of pH, temperature, calcium ions and protein content. Colloidal interactions between adsorbed layers on different surfaces can be inferred from an analysis of dynamic collisions of protein-coated emulsion droplets in shear flow using the colloidal particle scattering technique. The role of competitive adsorption on emulsion properties can be derived from experiments on systems containing mixtures of milk proteins and small-molecule surfactants. Shear-induced destabilisation is especially influenced by the presence of fat crystals in the emulsion droplets. Aggregated gel network properties are dependent on the balance of weak and strong interparticle interactions. In heat-set whey protein emulsion gels, the rheological behaviour is especially sensitive to surfactant type and concentration. Rearrangements of transient caseinate-based emulsion gels can have a profound influence on the quiesent stability behaviour. Computer simulation provides a general link between particle interactions, microstructure and rheological properties.     

Study of the role of ceramic filler in composite gel electrolytes based on microporous polymer membranes

The presented contribution aims at reconsidering the role of filler in affecting the ionic transport in composite gel electrolytes for Li-ion cells based on microporous polymer membranes. The gels have been prepared by swelling thin PVdF/HFP membranes either with conventional liquid electrolyte or with pure propylene carbonate solvent. The membranes contained dispersed submicron-size modified silica filler added in a wide range of weight ratios. The effect of filler content on the kinetics of liquid phase absorption and evaporation from the composite membranes, as well as on the conductivity of the corresponding gel electrolytes, has been studied and discussed in terms of the “colloidal” and “soggy sand” electrolyte concepts. It has been found that conductivity increase of composite gels is not directly correlated with the liquid electrolyte uptake. On this basis it is concluded that important part of ionic transport in this type of composite gel polymer electrolytes is realized on the filler grain boundaries, through overlapping space charge layers of the silica grains.