A rapid method for the assay of alginates in solution using polyhexamethylenebiguanidinium chloride

A rapid method for the quantitative assay of alginate in solution over a wide concentration range (0.01–0.5 percent) has been developed using the polymetric cation poly(hexamethylenebiguandinium chloride) [PHMBH⁺Cl⁻]. The procedure consists of the addition of a known excess amount of PHMBH⁺Cl⁻ to alginate solutions to precipitate the sample quantitatively and therafter measuring the u.v. absorption of residual PHMBH⁺C1⁻ in the supernatant. The working range of the assay can be altered by simply adjusting the excess quantity of PHMBH⁺Cl⁻ which is added during the assay. Assay response is easily reproducible and insensitive to variation in salt concentration (up to 2.5 per cent), pH (5.5–7.6) and temperature (10–60°C). The PHMBH⁺Cl⁻ method shows good agreement with another recognised method for the assay of alginate solutions. The simplicity of this new method and the short time required to perform it, enhances its suitability as a quick analytical procedure for alginates. Preliminary evidence suggests that assay response is independent of the D-mannuronic acid/L-guluronic acid ratio of alginate.     

Kinetics of oxidation of butadiene to crotonaldehyde

The oxidation of butadiene to crotonaldehyde has been investigated using an aqueous catalyst solution containing palladium chloride–cupric chloride in dilute hydrochloric acid. Unlike the oxidation of ethylene, propylene, etc., this oxidation was found to be a zero-order reaction with respect to butadiene. The effects of temperature and the concentration of Pd²⁺, Cu²⁺, Cl^? and H⁺ ions on the reaction rate were studied. The order of reaction with respect to Cl^? and H⁺ ions in this case (approximately 1.5 and ?0.25, respectively) is different from that observed in the case of lower alkenes.     

Solvent effect on the dissociation of o-nitroanilinium ion in methanol-propylene glycol media at 25°C

The dissociation constants (K_s) of o-nitroanilinium ion have been determined at 25° in methanol, propylene glycol and mixtures of the two components containing 10, 30, 50, 70 and 90 wt. % propylene glycol by spectrophotometric measurements. Standard free energies of transfer, ΔG°_t(B) of o-nitroaniline from methanol to the other solvents have been evaluated from the measurement of solubilities at 25°C. The solvent effect on the proton transfer process of this acid: ΔG°_t[BH⁺?B]_sys = 2.303RT[p(K_s?p(K_m)] has been discussed in terms of the free energies of transfer ΔG°_t from methanol to other solvents, of the uncharged based B, of the hydrochloride of the base (BHCl) computed from the corresponding values for HCl and also of the individual ions assessed from the previous knowledge of ΔG°_t(Cl^?). The corresponding data for the protonated tris(hydroxymethyl)methyl amine [TrisH⁺] and p-nitroanilinium ion in the same solvent system obtained from the literature are also compared. ΔG°_t[BH⁺?B]_sys values for the dissociation of o-nitroanilinium ion have been found to increase less readily with wt.% propylene glycol compared to p-nitroanilinium ion and are in contrast with the decreasing nature of the corresponding values for the TrisH⁺ ion of different chemical nature. Electrostatic effect being negligible in this solvent system, the overall behaviour of these acids is found to be dictated by specific chemical nature of solute-solvent interactions besides the effect of relative solvent basicities.     

Etude des phenomenes electrochimiques et des transports de matiere d'un systeme metal electrolytique: cas d'un disque tournant en cuivre dans des solutions aqueuses d'acide chlorhydrique

In the first two areas of the curves I = F(E) corresponding to Cu/CuCl_x^1?x and Cu/CuCl/CuCl_x^1?x redox systems we study the diffusion of Cl^?, Cu⁺ Cu²⁺ and CuCl_x^1?x species: in acidic chloride media (0,1 Ml^?1 ?HCl ? 3 Ml^?1) the diffusion of Cl^? does not exist because the amount of ions consumed is negligible compared to the large quantities contained in the solution, these HCl solutions behave like supporting electrolyte. Cu⁺ and Cu²⁺ does not exist in the diffusion layer on account of the high Cl^? concentration. At all events the diffusion of CuCl_x^1?x complex is the rate determining step. Experimental current is a pure diffusion current because the transference number tCuCl_x^1?x is negligible compared to one and the charge transfer step is very fast. The electrode surface seems to be uniformly reactive although for the Cu/CuCl/CuCl_x^1?x system we can assume there may be a partially blocked electrode surface constituted by independent sites.     

Novel PVA-based polymers showing an anti-Hofmeister Series property

A series of poly(vinyl alcohol)-trimellitate (PVA-T) polymers with different esterification degrees (ED: 82, 61, and 32 mol%) were prepared through the esterification of PVA and trimellitic anhydride (TA). Solubilities of these polymers and the swelling properties of PVA-T hydrogels, which were prepared by crosslinking with ethylene glycol diglycidyl ether (EGDGE), were investigated in various salt solutions comprising of SO₄²⁻, Cl⁻, SCN⁻ and Li⁺, Na⁺, K⁺, Cs⁺. The PVA-T polymers proved to have larger solubilities in salt solutions (1 M) than in pure water, and the ionic “salting-in” effect was significant in order of SO₄²⁻ > SCN⁻ > Cl⁻ for anions, and Li⁺ > Na⁺ > K⁺ > Cs⁺ for cations, regardless of their ED values. The PVA-T hydrogels also showed corresponding swelling properties; they significantly swelled in sulfate solutions of medium concentration (0.1-1 M), while in other salt solutions no appreciable swelling occurred. The marked salting-in effects exerted by sulfate anion, which is otherwise a typical “salting-out” agent, means that PVA-T polymers have an “anti-Hofmeister Series” (anti-HS) property. This is naturally ascribed to the trimellitic acid group because the degree of swelling in sulfate solutions was more significant for PVA-T with higher ED values; the combination of π-electron system and acidic protons seems to be essential to endow polymers with the anti-HS property.     

Kinetics of armco iron dissolution in an anhydrous methanol and hydrochloric acid solution

The polarization behaviour of Armco iron in anhydrous solutions of CH₃OH+HCl and CH₃OH+HCl+LiCl was studied by the potentiostatic method. The following reaction orders were found for the anodic process: Z_a(Cl^?) = 1.7 –1.82 and Z_a(H⁺) = 0. The following mechanism of dissolution is proposed: Fe+Cl^? ? FeCl^?_ads, FeCl^?_ads+Cl^? → FeCl₂+2e (rate-determining step), FeCl₂?FeP²⁺ + 2Cl^?.     

Effect of electron density on the catalysts for copolymerization of propylene oxide and CO<Subscript>2</Subscript>

Copolymerization of propylene oxide and carbon dioxide (CO₂) has been studied using different R-salophenCoOBzF₅ (OBzF₅ = pentaflorobenzoate, R = CH₃, H, Cl, Cl₂) based catalysts. The central moiety of the catalysts R-salophenCoOBzF₅ has been kept the same and effect of the catalyst electron density on the copolymerization reaction has been studied. It has been observed that introduction of an electron withdrawing group (like Cl, Cl₂) on the o-phenylenediamine backbone moiety of the catalyst makes it more selective for poly(propylene carbonate) synthesis. On the other hand, introduction of an electron donating group (like CH₃) makes the catalyst selective for cyclic carbonate conversion. The effect of different type of co-catalysts has also been investigated using tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, [PPN]⁺Cl^? ([PPN]⁺ = bis(triphenylphosphine)iminium), DMAP and tetrabutyl ammonium bromide.     

Synthesis of Chitosan/Gelatin granule containing amine derivated octa(ammonium chloride) substituted Polyhedral Oligomeric Silsesquioxane and investigating its application as a drug carrier

In this work, we have prepared a new granule hydrogel composites of natural biocompatible polymeric chitosan and gelatin (C-G). The gelatin side groups (hydroxyl and carboxyl) can attach with amine groups of chitosan, which improve the interlink crosslinking in the final nanocomposites. The diameter of the granuls is around 3?mm to 6?mm. Furthermore, in order to reinforce the mechanical properties of granules, for the first time, octa(ammonium chloride) substituted Polyhedral Oligomeric Silsesquioxane (POSS-(NH₃⁺Cl^?)₈) has been used as a nanofiller in the structure of this nanocomposite. The effect of POSS-(NH₃⁺Cl^?)₈ on mechanical stability and swelling behavior of hydrogels has been investigated in three pH of 1.2, 7.4 and 9.5, respectively. Results demonstrate that the C-G/POSS-(NH₃⁺Cl^?)₈ granules in acidic pH has the maximum swelling percent. The encapsulation efficiency (EE) values for C-G granules in three pH of 1.2, 7.4 and 9.5 are obtained 65%, 58% and 53% and for C-G/POSS-(NH₃⁺Cl^?)₈ sample are 59%, 52% and 48%, respectively, which conform with the swelling behavior of these hydrogels. According to the obtained results from Metronidazole (MTZ) release, the as-synthesized hydrogels may have intrinsic ability in the controlled release of drugs. The as-prepared hydrogels are characterized via FT-IR, SEM, TGA and XRD analysis.     

Investigations on esterification reactions of starches in 1‐N‐butyl‐3‐methylimidazolium chloride and resulting substituent distribution

The ionic liquid (IL) 1‐N‐butyl‐3‐methylimidazolium chloride ([C₄mim]⁺Cl^?) was used as solvent for different esterification reactions of the biopolymer starch. Therefore, maize starches with varying content of amylose were used. Different carboxylic acid anhydrides were applied to esterify starch with a degree of substitution (DS) in the range of 0.7–3.0. For example, starch acetates with the mentioned DS are accessible within 30 min at a 105°C‐reaction temperature. The DS distribution of starch acetates synthesized in IL was compared with the common starch acetate synthesis of Mark and Mehltretter. Also, a consideration of starch acetates and cellulose acetates synthesized in [C₄mim]⁺Cl^? is given. The starch esters were characterized by means of Raman spectroscopy for qualitative‐ and nuclear magnetic resonance spectroscopy for quantitative determination of the functionalization pattern. Moreover, the molecular mass distribution was determined after saponification by means of GPC‐MALLS. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of acidic pumice and determination of its electrokinetic properties in water

In this study some characterization tests of acidic pumice were performed using various techniques such as Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Thermal Analysis (DTA–TG), FTIR and its electrokinetic properties in water such as zeta potential (ZP), isoelectrical point (IEP), indifferent, specifically adsorbing and potential determining ions were determined. The results showed that (i) pore dimensions of the irregular or oval and fibrous cavities of the pumice varied between 0.05 μm and 2 mm depending on its particle size and these cavities usually did not intersect each other; (ii) as the pumice particle size decreases, both total pore volume and total pore surface area significantly decrease as well; (iii) pumice maintained its thermal stability approximately up to 900 °C; (iv) pumice had a negative surface charge between pH 1.8 and 11.4; and (v) Cl^?, Br^? SO₄^2?, Na⁺, Al(OH)₂⁺ and Ca²⁺ ions were indifferent, C₁₆H₃₃(CH₃)₃N⁺, Al³⁺ and Al(OH)²⁺ cations were specifically adsorbing and, H⁺ and OH^? ions were potential determining ions for acidic pumice.     

Ethylene carbonate—propylene carbonate mixed electrolytes for lithium batteries

Electrolytic characteristics of propylene carbonate (PC)ethylene carbonate (EC) mixed electrolytes were studied, compared with those in PC electrolytes. Conductivity and Li charge—discharge efficiency values increased with EC contents increasing. For example, 1 M LiClO₄ECPC (EC mixing molar ratio; [EC]/[PC] = 4) showed the conductivity of 8.5 ohm^?1 cm^?1, which value was 40% higher than that in PC. Also, 1 M LiClO₄ECPC([EC]/[PC] = 5) showed the Li charge—discharge efficiency of 90.5% at 0.5 mA cm^?2, 0.6 C cm^?2, which value was ca. 25% higher than that in PC. ECPC mixed electrolytes were considered to be practically available for ambient lithium batteries in regard to the high Li⁺ ion conductivity and also high Li charge—discharge efficiency.     

Insertion des ions PF6−, AsF6− et SbF6− dans le graphite par methode electrochimique. caracterisation des produits obtenus

PF₆^?, AsF₆^? and SbF₆^? ions were intercalated into graphite from a propylene carbonate electrolyte by an electrochemical method. During the intentiostatic charging of the system Li-Al/P.C., LiX (molar)/graphite one can observe a continuous increase of potential up to 5.2 V. This value is reached for a C₂₄⁺ charge of the graphite (Fig. 3). The discharge from the intercalated compound of graphite (I.C.G.) presents three plateaus: at 4.7 V until C₄₈⁺, 4 V between C₄₈⁺ and C₉₆⁺ and 2.5 V between C₉₆⁺ and graphite (Fig. 4).X-Ray powder studies (Fig. 5) of C₄₈⁺X^?χ P.C.I.C.G. show that such compound is a second stage one. The anion is solvated by four molecules of propylene carbonate between the layers of graphite. This solvation causes the considerable thickness of the inserted layers (10.6 A for PF₆^? 4 P.C., 10.9 Å for SbF₆^? 4 P.C.). The detailed structure (Fig. 8) of these layers is clarified by intensity line calculations. The presence of four molecules of solvent was confirmed by thermogravimetric measurements (Fig. 6).The first stage compound C₂₄⁺X^? 4 P.C. could not be obtained outside of the cell. The C, P, As and Sb analysis in the I.C.G. provided a composition in good agreement with the formula C_24n⁺ P.C., where n is the stage.Owing to their high potential of 5.2 V against lithium, these compounds are of great interest for their utilisation as cathodes in high energy density batteries.     

Silica-Supported Ionic Liquids Prompted One-Pot Four-Component Synthesis of Pyrazolopyranopyrimidines, 3-methyl-4-aryl-4,5-dihydro-1H-pyrano[2,3-c]pyrazol-6-ones,and 1,6-diamino-2-oxo-1,2,3,4-tetrahydropyridine-3,5-dicarbonitriles

Three methods have been used for synthesis of pyrazolopyranopyrimidines, 3-methyl-4-aryl-4,5-dihydro-1H-pyrano[2,3-c]pyrazol-6-ones, and 1,6-diamino-2-oxo-1,2,3,4-tetrahydropyridine-3,5-dicarbonitrile derivatives via four-component reactions under solvent-free conditions. Silica-bonded 5-n-propyl-octahydro-pyrimido[1,2-a]azepiniumchloride (SB-DBU⁺Cl^?), silica-bonded n-propyl-4-aza-1-azoniabicyclo[2.2.2]octane chloride (SB-DABCO⁺Cl^?), and nano silica-bonded 5-n-propyl-octahydro-pyrimido[1,2-a]azepinium chloride (NSB-DBU⁺Cl^?) as silica-supported ionic liquids catalyzed these reactions. These green, heterogeneous catalysts are separated from the reactions by simple filtration. The catalysts were recovered for at least four times without significant loss of their catalytic activities.     

Gelation of pectinic acids in the presence of calcium counterions

Pectins are polysaccharides which are able to gel in the presence of calcium ions if their degree of esterification is lower than 40%. From a purified pectin, a de-esterification was carried out by alkali and by enzymes in order to obtain samples with a different charge density and esterification pattern (random or blockwise distribution of carboxylic acid sites). The pectin-calcium interactions were studied in a dilute solution of calcium pectinates by conductimetry. If the concentration of highly charged polymer is increased, a multichain association can occur: the same process is observed with dilute solutions (c_p≤10-3 eq. 1^?1) but in the presence of an excess of calcium ions. This first step of the gelation was followed by light scattering and by viscometry. The gelling system can be described by a power law including a critical ratio (equivalent concentration of calcium ions/pectin carboxylic sites) and quasi-critical exponents. The values of these critical parameters have been discussed as a function of charge density of the pectins, their esterification pattern, their concentration, and the nature of the divalent counterion.     

Performance and cycling of the iron-ion/hydrogen redox flow cell with various catholyte salts

A redox flow cell utilizing the Fe²⁺/Fe³⁺ and H₂/H⁺ couples is investigated as an energy storage device. A conventional polymer electrolyte fuel cell anode and membrane design is employed, with a cathode chamber containing a carbon felt flooded with aqueous acidic solution of iron salt. The maximum power densities achieved for iron sulfate, iron chloride, and iron nitrate are 148, 207, and 234 mW cm^?2, respectively. It is found that the capacity of the iron nitrate solution decreases rapidly during cycling. Stable cycling is observed for more than 100 h with iron chloride and iron sulfate solutions. Both iron sulfate and iron chloride solutions display moderate discharge polarization and poor charge polarization; therefore, voltage efficiency decreases dramatically with increasing current density. A small self-discharge current occurs when catholyte is circulating through the cathode chamber. As a result, a current density above 100 mA cm^?2 is required to achieve high Coulombic efficiency (>0.9).     

Synthesis of amphiphilic (meth)acrylates with oligo(ethylene glycol) and (or) oligo(propylene glycol) blocks by the esterification of (meth)acrylic acid

Thermoresponsive PEG-based (PEG stands polyethylene glycol) polymers are unique for use in medicine because of their low toxicity, good biocompatibility and biodegradability, but usually more hydrophobic and more toxic comonomers are used to adjust lower critical solution temperature (LCST). A convenient way to overcome this problem and to finely tune LCST is to use alkoxy oligo(ethylene glycol)- or alkoxy oligo(propylene glycol) (meth)acrylates as starting comonomers. Here we report on the conditions for the simple and affordable synthesis of methoxy oligo(propylene glycol) (meth)acrylate- and methoxy oligo(propylene glycol)-block-oligo(ethylene glycol) (meth)acrylate-based macromonomers with high yields (80%–98.7%) by the acid-catalyzed esterification of (meth)acrylic acid with alkoxy oligo(alkylene glycols) containing oligo(ethylene glycol) (OEG) and/or oligo(propylene glycol) (OPG) blocks. p-Toluene sulphonic acid (pTSA), alkyl(C₁₂–C₁₄)benzene sulfonic acid (ABSA) and H₂SO₄ were used as catalysts. It has been shown that pTSA and ABSA are practically the same in catalytic activity and are superior to sulfuric acid. The reaction orders with respect to catalyst was found to be close to 1 in all cases. It has been shown that the reaction is actually insensitive to the lengths of OEG and OPG blocks, as well as to the structure of the terminal alkyl group, while the esterification of acrylic acid (AA) proceeds much faster compared to methacrylic acid (MAA) one under the same conditions. The influence of temperature on the equilibrium conversions of alcohols was determined, which were found to be 89%–93% for the esterification of AA and 61%–86% for MAA in the temperature range of 60–120°C. A further increase in conversion was achieved by introducing an azeotropic agent (toluene), its optimal concentration was found to be 10%–15%.     

Effect of amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solutions polluted with Cl−, F− and Fe3+ ions–behaviour near and at the corrosion potential

Research on non‐toxic inhibitors is of considerable interest in investigations into the replacement of hazardous classical molecules. This paper reports the action of four amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solution with and without Cl^?, F^? and Fe³⁺ ions near and at the corrosion potential (E_corr) using both the polarization resistance method and electrochemical impedance spectroscopy (EIS). Both cysteine and N‐acetylcysteine (ACC) showed higher inhibition efficiency than methionine and cystine. Adsorption of methionine onto a mild steel surface obeys the Frumkin adsorption isotherm and has a free energy of adsorption value (ΔG °_ads) lower than those obtained in the presence of cystine, cysteine and ACC whose adsorption isotherms follow that of Langmuir. Both F^? and Fe³⁺ ions stimulate mild steel corrosion while Cl^? ions inhibit it. The binary mixtures of methionine, cysteine or ACC with Cl^? or F^? ions are effective inhibitors (synergism) while the combinations of the amino acid with Fe³⁺ or the ternary Cl^?/F^?/Fe³⁺ mixture have low inhibitive action (antagonism). EIS measurements revealed that the charge transfer process mainly controls the mechanism of mild steel corrosion in phosphoric acid solution in the absence and presence of the investigated additives. The mechanism of corrosion inhibition or acceleration is discussed. © 2002 Society of Chemical Industry     

Influence of H+ and Cl− ions on inhibitive performance of poly(aniline) for iron corrosion in acid

The inhibition effect of poly(aniline) on pure iron corrosion in 1M HCl and with various H⁺ ions and Cl^? ions concentrations was investigated by the polarization and electrochemical impedance spectroscopy methods. The results showed that poly(aniline) suppressed both cathodic and anodic processes of iron dissolution in 1M HCl by its adsorption on the iron surface according to Langmuir's adsorption isotherm. The inhibition efficiency of poly(aniline) was found to increase with the inhibitor concentrations. Further, it was observed that, there was no significant variation in corrosion potential (E_corr) values in the presence of inhibitors suggesting that, this polymer behaved as mixed type inhibitor. Similar studies for the inhibitor at 500 ppm in various concentrations of H⁺ and Cl^? ions, have shown that the inhibition efficiency decreases with decrease in concentrations of H⁺ ions and Cl^? ions in aqueous solution. It reveals that, the adsorption of inhibitor on iron surface is by more cationic form of inhibitor and higher efficiency at higher H⁺ and Cl^? ions is due to enhanced adsorption of cat ionic form of inhibitor molecules. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Voltammetric and impedance studies of the electropolishing of type 316 stainless steel in a choline chloride based ionic liquid

We demonstrate the first practical alternative to the use of phosphoric and sulphuric acid mixtures for the electropolishing of stainless steel. In this paper, efficient electropolishing of type 316 stainless steel is demonstrated in an ionic liquid composed of ethylene glycol (HOCH₂CH₂OH) and choline chloride (HOC₂H₄N(CH₃)₃⁺Cl⁻). Linear sweep voltammetry, chronoamperometry, scanning electron microscopy, atomic force microscopy and AC impedance methods were used to investigate the steel dissolution mechanism and the results are compared to polishing done in aqueous acidic solutions. It is shown that the quality of the polish is related to the breakdown of the oxide film and preliminary data suggest that the polishing process may be controlled by the diffusion of chloride ions. The dissolution is different from that found in aqueous acid solutions, and oxide breakdown is shown to be slower, which can lead to pitting at low current densities.