Vernetzung von Phenolcarbonsäureestern von Polysacchariden durch oxydative phenolische Kupplung

Guaran, a watersoluble polysaccharide, was esterified with various phenolic acids. Solutions of these esters formed gels upon oxidation. In these gels the phenolic ester groups were crosslinked by oxidative phenolic coupling, the corresponding dimeric phenolic acids being liberated by saponification.     

All-small-molecule dynamic covalent gels with antibacterial activity by boronate-tannic acid gelation

Reversible boronate-catechol linkage was widely used to construct two-dimensional coatings and threedimensional nanostructures or hydrogels.The construction of these functional materials usually requires the pre-synthesis of macro molecular building blocks,and direct gelation between natural polyphenols and small molecule boranic acids is yet to be investigated.In this study,we fabricated a family of allsmall-molecule dynamic covalent gels consisting of tannic acid and boronic acids.Transparent and thixotropic gels were formed by boronate affinity towards catechol groups abundant on natural polyphenols.The gels showed multi-responsiveness,such as acid-,base-,reduction-and oxidantsensitive depending on the used boronic acid building blocks.The chemistry for gel formation and stimuli-responsiveness was characterized by11B NMR spectroscopy.The multi-stimuli responsiveness,green processing and facile modular design make the boronic acid-tannic acid gels promising candidates for the development of smart soft materials.     

Matrices for capillary gel electrophoresis--a brief overview of uncommon gels

This article gives an overview of uncommon replaceable matrices (gels) for capillary gel electrophoresis. This electrophoretic technique is useful mainly for the separation and analysis of biopolymers-nucleic acids and their fragments, and proteins/peptides. Commonly used gels are not reviewed. Those mentioned and discussed here are gels containing saccharides, newly developed acrylamide-based gels and thermoadjustable viscosity polymers, namely triblock copolymers and grafted polyacrylamide.     

Sensitive fluorescence detection of polyphosphate in polyacrylamide gels using 4',6-diamidino-2-phenylindol

PAGE is commonly used to identify and resolve inorganic polyphosphates (polyP). We now report highly sensitive and specific staining methods for polyP in polyacrylamide gels based on the fluorescent dye, 4',6-diamidino-2-phenylindol (DAPI). DAPI bound to polyP in gels fluoresced yellow while DAPI bound to nucleic acids or glycosaminoglycans fluoresced blue. Inclusion of EDTA prevented staining of glycosaminoglycans by DAPI. We also identified conditions under which DAPI that was bound to polyP (but not nucleic acids or other anionic polymers) rapidly photobleached. This allowed us to develop an even more sensitive and specific negative staining method that distinguishes polyP from nucleic acids and glycosaminoglycans. The lower LOD using DAPI negative staining was 4 pmol (0.3 ng) phosphate per band, compared to conventional toluidine blue staining with a lower LOD of 250 pmol per band.     

Catanionic aggregates formed from drugs and lauric or capric acids enable prolonged release from gels

The aim of this study was to add to the range of charged surfactants that can be used to form catanionic aggregates with oppositely charged surface active drug substances; and to apply these aggregates to prolong drug release from gels. The surfactants used in this study, lauric and capric acids are of natural origin-unlike traditionally used, synthetic, surfactants. The mixtures of drug substances and oppositely charged surfactants were studied visually and with cryogenic transmission electron microscopy. Drug release from gels was studied with a modified USP paddle method. This study shows that lauric and capric acids are as, or even more, active in forming catanionic aggregates than traditionally used surfactants such as sodium dodecyl sulfate. It is shown that the length of the hydrophobic part of the surfactant plays an important role in the formation of pharmaceutically interesting catanionic aggregates. As seen in previous studies, using catanionic vesicles prolongs the drug release from gels and decreases the apparent diffusion coefficient by a factor of 10-50, compared to a gel containing only drug substance.     

Application of Protonic Acid-Doped Silica Gels to Electric Double-Layer Capacitors

Silica gels doped with several protonic acids such as HClO₄, H₂SO₄ and H₃PO₄ have been prepared by the sol-gel method and totally solid electric double-layer capacitors have been successfully fabricated using the highly proton-conductive silica gels as an electrolyte and activated carbon powder (ACP) hybridized with the silica gels as a polarizable electrode. It was found that the addition of HClO₄, which had the highest value of acid dissociation constant among these three acids, most effectively increased the proton conductivity of the resultant acid-doped silica gels. Tablets of the HClO₄-doped silica gels exhibited conductivities as high as 10^–5–10^–2 S cm^–1 at room temperature in dry N₂ atmosphere. One of the capacitors fabricated using the protonic acid-doped silica gels had a capacitance of 44 F/(gram of total ACP in the capacitor), which was comparable to those of conventional capacitors using liquid electrolytes.     

Enhanced radiation crosslinking of carboxymethylated chitosan in the presence of acids or polyfunctional monomers

Carboxymethylated chitosan (CMCt) hydrogels were synthesized by γ-ray radiation-induced crosslinking in the presence of acids or polyfunctional monomers. Compared with that of CMCt hydrogels synthesized without additives, the gel fraction was improved and the gelation dose was decreased obviously after incorporating acids or polyfunctional monomers into CMCt hydrogels. The diffusion behavior of water in the CMCt gels prepared at different conditions was Fickian diffusion, and the swelling of the CMCt gels displayed characteristic pH sensitivity, which was analyzed by fluorescence molecular probes. Preliminary mechanism of radiation-induced crosslinking of CMCt in the presence of acids or polyfunctional monomers was discussed based on the FTIR and sol-gel analysis. Furthermore, it was found that CMCt hydrogels were hydrodegradable with high temperature (>60 °C), and incorporating polyfunctional monomers into the CMCt hydrogels also could improve the thermal stability of the CMCt hydrogels obviously.     

Microscopic Imaging of Chiral Amino Acids in Agar Gel through Circularly Polarized Luminescence of EuIII Complex

We recently found that [Eu(pda)₂]^? (pda: 1,10‐phenanthroline‐2,9‐dicarboxylic acid), which has an achiral structure in crystals, exhibits circularly polarized luminescence (CPL) in aqueous solutions containing chiral amino acids such as arginine and histidine. CPL measurements were performed for agar gel, which includes an aqueous solution of [Eu(pda)₂]^? and chiral arginine or histidine. The spectral shape, concentration, and pH dependences on CPL intensity in the agar gels were very close to those in aqueous solutions, indicating that the CPL of the Eu^III complex in the agar gels was induced by mechanism similar to that in aqueous solutions. We performed spatially resolved CPL measurements using a laboratory‐built microscopic CPL spectroscopic system for agar‐gel samples, where d ‐ and l ‐ amino acids were separately dispersed. We successfully recorded CPL imaging maps showing spatial dispersions of d ‐ and l ‐amino acid in the agar gels.     

Fixation of amino acids and oligopeptides by freeze-drying in polyacrylamide gel electrophoresis

Following polyacrylamide gel electrophoresis in an acetic/formic acid buffer, pH 2.0, in fabric reinforced gels, amino acids and oligopeptides could successfully be fixed in the gel by freeze-drying. Lyophilization of the fabric reinforced polyacrylamide gel after electrophoresis resulted in a dry film which absorbed ninhydrin solution quickly and uniformly, thus improving the detection limit for amino acids and oligopeptides with molecular weights ranging from 189-1045. Most amino acids were detected with a sensitivity of 0.1-0.25 microgram and for oligopeptides the detection limit was found to be 0.5-5 microgram.     

Manual and automated enrichment procedures for biological samples using lipophilic gels

Aspects of the use of lipophilic gels in manual sample preparation procedures are reviewed. Neutral gels with a controlled hydrophobicity are used for sorbent extraction of non-polar and medium polarity compounds from biological fluids. Acidic amphiphilic compounds can be extracted as ion-pairs with decyltrimethylammonium ions. Solvent or detergent extracts of tissues or faeces can be mixed with hydrophobic gels for transfer of analytes from a solvent to a gel phase, permitting subsequent sample preparation in gel bed systems. Hydrophobic gels, alkyl-bonded silica and polystyrene matrices can be used in series for extraction of compounds with a wide range of polarities. Group fractionations are performed on neutral and ion-exchanging lipophilic gels to yield fractions of neutral, basic and acidic metabolites within selected polarity ranges. Selective isolation of phenolic acids on a strong anion exchanger, of ethynylic steroids on a strong cation exchanger in silver form and of oximes of ketonic steroids on a strong cation exchanger in hydrogen form is possible. A computerized system for automatic sample preparation is also described. It consists of an extraction bed, a cation-exchange column and an anion-exchange column. The pumps and switching valves are arranged so that the columns can operate in series or parallel for isolation of neutral, basic and acidic metabolites of amphiphilic compounds and for regeneration of the column beds. Fractions can be collected, or the effluent from the column beds can be diluted with water to permit sorption on a solid phase. The applicability of the automated method to the analysis of bile acids and metabolites of mono(2-ethylhexyl) phthalate is demonstrated.     

An evaluation of some simple sulfonic acids as nonaqueous titrants

The simple aliphatic and aromatic sulfonic acids show evidence of possibilities as new titrants in a glacial acetic acid medium. Excellent precision is obtained in potentiometric titrations with both ethane- and methane sulfonic acids with a standard deviation of 0.2%. Benzenemonosulfonic and naphthalenesulfonic acids both give an average precision of 0.4%. In visual titrations with with crystal violet indicator, the color changes at the end-point are very sharp. The chief advantage of these acids as titrants lies in the fact that they dissolve readily in glacial acetic acid and can be titrated to give reproducible results with the glass-calomel electrode system. None of the sulfonic acids tested was as strong a titrant as perchloric acid, but, unlike perchloric acid, they did not form precipitates or gels in the titration with potassium acid phthalate.     

Inhibation of crystal growth during drying in gels derived from a cheap,mixed metal oxide precursor

The influence of addition of small amounts of either citric acid or lactic acid on the formation of crystalline matter in dried gels derived from a multi-component industrial sol–gel silica precursor has been studied. The sols were water-based and had formic acid as the main acid constituent. A pronounced decrease in the extent of crystallization was observed for both acids, with citric acid being more effective than lactic acid. The results are discussed based on the complexation behavior of the corresponding acids under the studied conditions, and the complexation behavior in solution can be directly linked to the extent of crystallization in the dried gels. However, the sol–gel kinetics followed that expected for a purely silica-based sol, which suggests that the kinetics is mainly controlled by the silica portion of the sol. The results are suggested to be of importance for the industrial use of these sols as binders, as pronounced crystallization in the gels upon drying may lead to mechanical stresses, and thus to a decreased binder performance.     

Sustainable Green Processing of Grape Pomace Using Micellar Extraction for the Production of Value-Added Hygiene Cosmetics

This study sought to evaluate the possibility of using grape pomace, a waste material from wine production, for the preparation of cosmetic components. Following the existing clear research trend related to improving the safety of cleansing cosmetics, an attempt was made to determine the possibility of preparing model shower gels based on grape pomace extract. A new method for producing cosmetic components named loan chemical extraction (LCE) was developed and is described for the first time in this paper. In the LCE method, an extraction medium consisting only of the components from the final product was used. Thus, there were no additional substances in the cosmetics developed, and the formulation was significantly enriched with compounds isolated from grape pomace. Samples of the model shower gels produced were evaluated in terms of their basic parameters related to functionality (e.g., foaming properties, rheological characteristics, color) and their effect on the skin. The results obtained showed that the extracts based on waste grape pomace contained a number of valuable cosmetic compounds (e.g., organic acids, phenolic compounds, amino acids and sugars), and the model products basis on them provided colorful and safe natural cosmetics.     

ENZYME CATALYSIS IN DIFFERENT GELATIN GELS

Enzymes in microemulsions, liposomes, aqueous monomer surfactant solutions or pure water have been entrapped in gelatin-based gels. These gels have been used as minireactors for stereoselective resolution of racemic 2-octanol in esterifications with alkanoic acids or in transesterifications with vinyl butyrate. The microstructures were stabilized by the anionic surfactant sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT) or the zwitterionic surfactant soybean lecithin. The enzymes used were commercial lipases from Chromobacterium viscosum or Candida antarctica (SP 525). The incubation temperature was 298.2 K. The enantiomeric excess (e.e.) values were high in all systems studied, but the reaction rates depended on the gel used. In AOT-stabilized and in ethanol-free lecithin-stabilized gels the conversion was close to 0.45. However, in the ethanol-containing lecithin gels, the conversion was lower and decreased with increased ethanol content, due to competing reactions. In the hydrogels, the conversion and e.e. values were high, but the reaction rates were low.     

Versatile protonic acid mediated preparation of partially deacetylated chitin nanofibers/nanowhiskers and their assembling of nano-structured hydro- and aero-gels

The partially deacetylated α-chitin nanofiber/nanowhisker (DEChN) aqueous dispersions were prepared by alkali deacetylation. The following mechanical treatment under acidic conditions was mediated by five different organic protonic acids, including acetic acid, gluconic acid, itaconic acid, citric acid and ascorbic acid. Thereafter, these acidic DEChN dispersions were transformed into hydrogels under an alkali gas phase coagulation bath. After solvent exchange and freeze drying, the DEChN-based aerogels were prepared. Previous research showed that the kinds of acid used for the adjustment of the pH value during the fibrillation process influenced the nanofibrillation efficiency. In this study, it was discovered that the types of protonic acid also influenced the properties of the DEChN hydrogels and aerogels under the same mass concentration (0.6%) of DEChNs, including the appearance, strength of hydrogels, the pore size and specific surface area of aerogels, as well. Nevertheless, all of the hydrogels showed good mechanical strength and all of the aerogels possessed a porous nanostructure sustained by nanofibrillar networks. The highly porous chitin aerogels showed a broad size mainly distribution from 2 to 100 nm, and the specific surface area of chitin aerogels ranged from 90 to 170 m²g^?1. Although it was not clear how the types of protonic acids influenced the properties of the hydrogel and aerogel, we were able to obtain DEChN dispersions and gels by mechanical treatment of partially deacetylated chitin at acidic conditions mediated by versatile acids. In the meantime, the observed differences among the gels provided the possibility to use the acid medium to select the gels with certain mechanical strength, porosity or specific surface area for the prospective desired applications.     

The parameter of binary interaction in weakly crosslinked polyelectrolyte gels near the collapse threshold

The behavior of partially ionized weakly crosslinked gels based on polyacrylamide that undergo a discrete phase transition-collapse in water-acetone mixtures and the behavior of gels of polyacrylic and poly(methacrylic acids) for which gradual contraction is observed under the same conditions are studied experimentally. The concentration dependences of the enthalpy of swelling for the gels in the mixtures with volume concentrations of acetone of 0, 20, 30, and 40% are measured via isothermal calorimetry and are used to calculate the parameter of interaction between a polymer network and a medium during the approach toward the threshold concentration of collapse. In sharply collapsing gels based on polyacrylamide at an acetone concentration up to 40%, the enthalpy parameter of interaction does not exceed 0.2, a value that is significantly smaller than the critical value. In contrast, in the gels based on polyacids, for which gradual contraction is observed, the enthalpy parameter is as high as 0.6 at the same content of acetone. The experimental data testify that a reduction in the energetics of interaction between a weakly charged polymer network and a medium is not the decisive cause of the discrete phase transition-collapse.     

热敏性印迹水凝胶的合成及对甘草酸分离性能的研究

以甘草酸分子为印迹分子,N-异丙基丙烯酰胺作为温度响应性单体,和甲基丙烯酸共同为甘草酸的吸附性单体,在大量交联剂存在下,N-甲基吡咯烷酮中经自由基模板聚合,制备了一种热敏性印迹凝胶,对水凝胶的热收缩动力学进行了表征;用红外光谱证实了甘草酸分子与单体分子间的相互作用,以旁证其模板作用的存在：同时还与没有模板作用所合成的同种凝胶作了实施对比,发现模板聚合所得的水凝胶可以富集水溶液中的甘草酸,并对它表现出特殊的选择性分离作用,分配系数约为非模板聚合水凝胶的11倍。     

Chromatographic amino acid analysis of protein hydrolysed in polyacrylamide after removal of ammonia

Summary A simple method for the removal of NH₃ from amino acids is presented. The method is based on a cation-exchange resin from which amino acids are eluted with NH₄OH. The eluent is then removed under reduced pressure. The method allows the ninhydrin-based detection of amino acids after hydrolysis of stained protein bands in polyacrylamide gels. This was previously not possible since NH₃ produced by the hydrolysis of polyacrylamide interferes with the ninhydrin-detection of basic amino acids. The method should also be applicable to the detection of amino acids with o-phthalaldehyde.     

Investigation on the coacervation of fish scale gelatin hydrogel with seafood waste hydrolysates for the development of artificial fish bait: Physico-chemical,thermodynamic, and morpho-structural properties

The study dealt with the development of biopolymer based hydrogel artificial fish bait with hydrolysates derived from fish processing wastes. Fish scale gelatin (FSG) was used for the development of a hydrogel to which bioattractants extracted from seafood processing wastes of fish, squid and shrimp were added to prepare composite gels such as FSG-FH, FSG-SH and FSG-SPH, respectively. To understand the homogenesity and cross linking complexation of composite gels, the study aimed at investigating physico-chemical, thermodynamic, molecular and structural properties were analysed. The gel strength, melting point and thermal stability of the composite hydrogels were found to decrease marginally compared to the control gel, FSG. It could be understood that the crystalline structure at 2θ = 23° of the FSG-SH, and FSG-FH were not much altered compared to FSG gel. However, alteration in the crystalline structure in FSG-SPH was evident at 2θ = 27.3°. The TGA and DSC analysis revealed the reduction in the thermal stability of FSG on the addition of protein hydrolysates in the process of coacervation to get hydrogel based fish bait. Further, FESEM and AFM analysis indicated FSG-SH as the composite hydrogel with most compact and smooth surface was evident by Ra and Rq values. Among the composite gels, FSG-SH was found to have higher hydrophobicity due to enhanced gel structure. FTIR spectra of FSG and composite gels exhibitted similarity corresponding to amide-A, B, I, II and III bands. However, NMR analysis revealed the existence of notable difference with respect to chemical shift in the range of 7.0–7.75 ppm expressing the presence of aromatic protons of the amino acid phe and N–H protons of amide in all the composite gels. Further, NMR analysis confirmed the role of imino acids (δ CH₂ & β CH₂ protons) and hydrophobic amino acids (α-CH₂ protons) in decrease the physical and thermal properties of the composite gels. The addition of protein hydrolysates with FSG was found to decrease the physical, thermal and structural properties, however improve the aromatic compounds of the composite gels.     

pH and temperature-sensitive N-isopropylacrylamide ampholytic networks incorporating L-lysine

Ampholytic polymer gels based on N-isopropylacrylamide (NIPA) and natural amino acid L-lysine were prepared by free radical polymerization in aqueous solutions. To make amino acids attachable to the polymer chain, the acrylic group was added to the epsilon-amino group of lysine to obtain N-epsilon-acrylic-lysine (Z). Finally, a new temperature- and pH-sensitive (NIPA-Z) hydrogel was obtained. The presence of amino and carboxylic groups of amino acids gave us a possibility to control the amount and sign of the excessive charge on the polymeric network with respect to pH. The swelling behavior of the NIPA-Z hydrogels with respect to the amount of Z (0-4%), temperature, and pH was investigated. Temperature and pH were changed in the ranges of 20-50 degrees C and 2-12, respectively. To eliminate the influence of ionic strength on the swelling behavior, this parameter was kept constant in all experiments. It was found that the pH dependence of the degree of swelling for the NIPA-Z gels, measured at constant temperature, exhibits a minimum. Such a minimum was seen for the ampholyte networks with independent acidic and basic groups attached to the polymer chains. For the NIPA-Z gels, the minimum was wide, and the pH range over which it was spread corresponded well to the pH distribution of the zwitterions. The way the gel volume changed with an increase in temperature depends on the amino acid amount. It is initially discontinuous and turns to the continuous one for the higher percentage of amino acid. The temperature dependence of the swelling process obtained for different pH values clearly shows that for the pH region where the zwitterions dominate, the polymer networks collapse more efficiently.