Physicochemical and macromolecular properties of sodium amylose xanthate in dilute solution

Sodium amylose xanthate has been studied in dilute solution. Potato starch was fractionated for this purpose into amylose and amylopectin fractions. Amylose was xanthated in solution under alkaline conditions and the Na amylose xanthate was then characterized by reaction with I₂ solution and ultraviolet spectra of the xanthate groups determined. Stability of the xanthate in alkaline condition under both oxygen and nitrogen atmospheres was also investigated. From light scattering measurements of dilute salt solutions of Na amylose xanthate, the weight-average molecular weight M _w as well as the molecular dimensions were determined. In 0.11M NaCl, which conforms to the θ solvent, Na amylose xanthate molecules appear to have a random-coil configuration. Two other configurational parameters, such as the effective bond length b, and the steric factor σ, i.e., (R₀²)^1/2/(R_f² )^1/2, where (R₀²)^1/2 is the Root-mean-square end-to-end distance in the unperturbed state and (R_f² )^1/2 is the unperturbed value calculated on the assumption of free rotation about each intermonomer C? O bond of the amylose chain were also calculated and found to be 6.24 and 1.020, respectively. It is thus concluded that the amylose chain in Na amylose xanthate behaves as a typical flexible coil in dilute salt solution.     

Polyelectrolyte Configuration of Low Molecular Weight Sodium Amylose Xanthate in Aqueous and Salt Solutions

The polyelectrolyte chain configuration of low molecular weight sodium amylose xanthate (NaAX) in aqueous and salt solutions has been studied by viscometry and light scattering. The viscometric results in aqueous solution have been found to be in accordance with the Fuoss's modified equation. The intrinsic viscosities of NaAX in salt solutions from 0.00125 to 0.25 M NaCl have been determined and the expansion factor a at each ionic strength has been determined. The dependence of a on ionic strength has been studied according to the theories of Hermans and Overbeek, Flory, etc. But though qualitative agreement between experimental and theoretical results has been found, quantitative agreement was far from expectations. The frictional coefficient per monomer unit | has been calculated from the relationship of Kirkwood and Riseman. The NaAX macromolecule has been found to have the polydispersed random coil chain configuration in 0.25 M NaCl. Some macromolecular configurational parameters such as effective bond length b, Kuhn-Kuhn equivalent chain length A_m, and steric factor α has been determined.     

Degradation of Na amylose xanthate in dilute caustic soda solution during ripening

Na amylose xanthate was prepared from potato starch by xanthation of amylose in dilute NaOH solution. Pure xanthate was then isolated and viscometric and turbidimetric studies on its ripening characteristics were carried out for a period of about 200 hrs. Prolonged ripening in air degraded the amylose chain without formation of gel. To study the nature of ripening more precisely, it was carried out in an identical way under N₂ and followed both viscometrically and turbidimetrically. The refractive-index increment (dn/dc) of the xanthate solutions during ripening under both air and nitrogen was continuously measured so as to avoid any possible error in computing correct molecular weights during ripening. Light-scattering molecular weights (M?_w) thus computed during the course of degradation of Na amylose xanthate extending for about 200 hr under both air and nitrogen were found to obey a first-order rate equation, In (M₀/M_t) = Kt where M_o is the initial molecular weight, M_t the molecular weight at time t of ripening, and K the rate constant of the degradation process.     

Dilute solution properties of sodium amylopectin xanthate

Sodium amylopectin xanthate, prepared by xanthation of potato amylopectin in alkaline medium, was fractionated and the fractions in 1M NaOH were characterized by viscometry and light scattering. The expansion factor α was determined from the expression due to Orofino and Flory. The value of a of the Mark-Houwink relation, [η] = KM^a, was also determined. Its weight-average molecular weight, end-to-end distance, branching, and other parameters in alkali solution were also evaluated. From the data, it was concluded that the sodium amylopectin xanthate molecule had a polydisperse random-coil chain configuration in 1M NaOH and had no tendency to aggregate in this medium.     

Polymers containing quaternary ammonium groups based on poly(N-vinylimidazole)

A poly(N-vinylimidazole) (PNVI)—based poly(carboxybetaine) with two methylene groups between the opposite charges was achieved by the nucleophilic addition reaction of the mentioned aminic polymer to the carbon-carbon double bond of acrylic acid (AA). Treatment of poly(carboxybetaine) with concentrated HCl (2 N) for long time leads to the corresponding cationic polyelectrolyte. The poly(carboxybetaine) is soluble in both water and aqueous solutions of salts such as: LiCl, NaCl, NaHCO₃, CaCl₂, Na₂SO₄. In water and in the first three salts, poly(carboxybetaine) exhibits a non-polyelectrolyte behaviour (a linear dependence of reduced viscosities on polymer or salt concentration), while in the remaining two salts, a slight polyelectrolyte behaviour is observed. The cationic polyelectrolyte is soluble in water and aqueous solutions of LiCl, NaCl, CaCl₂ and NaHCO₃, except Na₂SO₄. It has a polyelectrolyte behaviour in all solutions. Also, the binding trends of the added salts by polymers are discussed.     

Laser light scattering studies of poly(L-lysine HBr) in aqueous solutions

A simple theory for the relaxation of concentration fluctuations in polyelectrolyte solutions is presented, and particular results for the high-salt and no-salt limiting cases are discussed. Autocorrelation functions for the fluctuating intensity of scattered light from dilute aqueous solutions of poly(L -lysine HBr) (PLL-HBr) with and without added salt have been observed over a wide range of pH. The observed autocorrelation functions are in general very satisfactorily represented by single exponentials except at high pH (>10.5), where considerable aggregation is manifested. Solutions of PLL HBr without added salt exhibit extraordinary behavior, evident at low pH, involving a species with a very slowly decaying autocorrelation function. Though this species is readily annealed to a more ordinary individual free-molecule form by cycling the pH to 9.5 or higher and back, the resulting molecules are found to require unusually long times to reach internal configuration equilibrium under low pH conditions. Solutions of PLL-HBr in 0.2M NaBr and 0.1M NaCl are apparently free of similar extraordinary effects and show the normal isothermal helix–coil transition accompanied by a 15–30% rise in the diffusion coefficient to a maximum at pH 10.5, which is interpreted in terms of a change in molecular dimension of an interrupted helix. The predicted K² dependence of the reciprocal relaxation time and enhancement of the apparent diffusion coefficient of the polyelectrolyte in the absence of salt is confirmed.     

Interactions between Adsorbed Layers of a Low Charge Density Cationic Polyelectrolyte on Mica in the Absence and Presence of Anionic Surfactant

Interactions between two negatively charged mica surfaces across aqueous solutions containing various amounts of a 10% charged cationic polyelectrolyte have been studied. It is found that the mica surface charge is neutralized when the polyelectrolyte is adsorbed from a 10–50 ppm aqueous solution. Consequently no electrostatic double-layer force is observed. Instead an attractive force acts between the surfaces in the distance regime 250–100 Å. We suggest that this attraction is caused by bridging. Additional adsorption takes place when the polyelectrolyte concentration is increased to 100 and 300 ppm, and a long-range repulsion develops. This repulsive force is both of electrostatic and steric origin. The polyelectrolyte layer adsorbed from a 50 ppm solution does not desorb when the polyelectrolyte solution is replaced with an aqueous polyelectrolyte-free solution. Injection of sodium dodecyl sulfate (SDS) into the measuring chamber to a concentration of about 0.01 CMC (8.3 × 10⁻⁵M) does not affect the adsorbed layers or the interaction forces. However, when the SDS concentration is increased to 0.02 CMC (0.166 mM) the adsorbed layer expands dramatically due to adsorption of SDS to the polyelectrolyte chains. The sudden swelling suggests a cooperative adsorption of SDS to the preadsorbed polyelectrolyte layer and that the critical aggregation concentration between the polyelectrolyte and SDS at the surface is about 0.02 CMC. The flocculation behavior of the polyelectrolyte in solution upon addition of SDS was also examined. It was found that 0.16–0.32 mol SDS/mol charged segments on the polyelectrolyte is enough to make the solution slightly turbid.     

A study of the composition of polyacrylamide-polyaluminum chloride polymer-colloid complexes

The behavior of aqueous solutions of polymer-colloid complexes based on polyacrylamide (M ～ 5.2 × 10⁵) and colloid particles of polyaluminum chloride depending on the initial component ratio and the concentration of a low-molecular-mass electrolyte (NaCl) was studied by means of viscometry and turbidimetry. It was suggested that the composition of polymer-colloid complexes, ? (the number of colloid particles attached to one macromolecule), depends on the component ratio. At ? > 1, the polymer-colloid complexes take on the polyelectrolyte properties, namely, repulsion in the case of overlap of the diffuse layers of counterions of colloid particles bound to the polymer chain leads to unfolding of macromolecular coils. Correspondingly, as the concentration of a low-molecular-mass salt increases, the coil size diminishes and the solubility of the complex drops. At ? = 1, the concentration of low-molecular-mass salt has no effect on the solubility of the complex and the viscosity of its solution.     

Molecular weight and aggregation of Aeromonas gum treated with dimethyl sulfoxide in aqueous solution

Aeromonas (A) gum, an acidic hetero polysaccharide, in 0.2 M LiCl/dimethyl sulfoxide (DMSO) was fractionated satisfactorily according to the nonsolvent addition method. Eight fractions were chosen to examine their aggregation behavior in aqueous solution. The weight‐average molecular weight (M_w), radius of gyration 〈S²〉^1/2, and intrinsic viscosities [η] of the fractions in 0.2 M LiCl/DMSO and 0.5 M NaCl aqueous solution at 25 °C were measured by static light scattering and viscometry. The results indicated that the A gum was aggregated in 0.5 M NaCl aqueous solution at 25 °C, and the aggregates were broken in 0.2 M LiCl/DMSO. The apparent weight‐average aggregation number (N_ap) of the fractions increased with the process of fractionation, that is, N_ap increased from 1.1 to 15 with decreasing M_w of the single chain. The fractions obtained by treating with DMSO were more easily dissociated in the aqueous solution, and its N_ap was lower than that of the A gum fractions that were not treated with DMSO. Moreover, the A gum molecules with relatively low M_w aggregated easily to form a compact spherelike structure in the aqueous solution. Elemental analysis and ¹³C NMR spectroscopy indicated that DMSO was adsorbed on the A gum molecules caused by the fractionation program; DMSO not only prevented the polysaccharide aggregation but also increased the solubility. A model has been proposed to describe the aggregation behavior of the A gum chains with DMSO overcoat in the aqueous solution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2269–2276, 2002     

Activity coefficients of NaCl in polyelectrolyte solutions from EMF measurements

Electromotive force (EMF) data were measured at 298.15 K for the cell, Na–ISE |polyelectrolyte(m_p), NaCl(m_s)| AgCl, Ag, where a salt NaCl with different concentrations is added in aqueous poly(diallyl dimethyl ammonium chloride), poly(anethole sulfonic acid, sodium salt) and sodium polyacrylate solutions, respectively. ISE means ion-selective electrode. Mean activity coefficients of the salt NaCl in these aqueous polyelectrolyte solutions were calculated correspondingly. The standard cell potential needed for calculations were obtained from EMF measurements of an another cell, Na–ISE |NaCl(m)| AgCl, Ag, where the solution contains only a single electrolyte. Activity coefficients of the electrolyte NaCl in this cell were estimated by Pitzer model. For poly(diallyl dimethyl ammonium chloride) solutions with different concentrations, mean activity coefficients of the salt NaCl decrease monotonically as the concentration of NaCl increases. However, for poly(anethole sulfonic acid, sodium salt) solutions and sodium polyacrylate solutions, the salt-concentration dependence of the mean activity coefficients of NaCl exhibit a maximum.     

Phase Transition of Acrylamide‐Based Polyampholyte Gels in Water

The swelling behavior of acrylamide (AAm)–based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. [(Methacrylamido)propyl]trimethyl‐ammonium chloride (MAPTAC) and acrylic acid (AAc) were used as the ionic comonomer in the hydrogel preparation. Three sets of hydrogels containing 70 mol% AAm and 30 mol% ionic comonomers of varying mole ratios were prepared. The variations of the hydrogel volume in response to changes in pH, and salt concentration were measured. As pH increases from 1, the hydrogel volume V _eq in water first increases and reaches a maximum value at a certain pH. Then, it decreases again with a further increase in pH and attains a minimum value around the isoelectric point (IEP). After passing the collapsed plateau region, the gel reswells again up to pH=7.1. The reswelling of the collapsed gels containing 10 and 4% MAPTAC occurs as a first‐order phase transition at pH=5.85 and 4.35, respectively, while the hydrogel with 1% MAPTAC reswells continuously beyond its IEP. Depending on pH of the solution, the hydrogels immersed in salt solutions exhibit typical polyelectrolyte or antipolyelectrolye behavior. The experimental swelling data were compared with the predictions of the Flory‐Rehner theory of swelling equilibrium including the ideal Donnan equilibria. It was shown that the equilibrium swelling theory qualitatively predicts the experimental behavior of polyampholyte hydrogels.     

Characterization of Silicate Complexes in Aqueous Sodium Sulfate Solutions by FAB-MS

When the sodium ion (Na⁺) concentration is increased above 0.5 mol-dm⁻³ (M), the concentrations of dissolved silica in aqueous sodium chloride (NaCl) and sodium nitrate (NaNO₃) solutions decrease because of the salting out effect. On the other hand, the concentration of the dissolved silica in aqueous sodium sulfate (Na₂SO₄) solutions increases monotonously as the concentration of Na⁺ is increased above 0.5 M. The purpose of this study is to determine the reasons why the salting-out effect is not observed in Na₂SO₄ solutions. FAB-MS (Fast Atom Bombardment Mass Spectrometry) was used to sample directly the silica species dissolved in aqueous Na₂SO₄, NaCl, and NaNO₃ solutions. In the FAB-MS spectra of these solutions, the peak intensity ratios of the linear tetramer to the cyclic tetramer largely increased for Na⁺ concentrations between (0.1 and 1) M. This shows that some characteristics of the Na₂SO₄ solutions are similar to those of the NaCl and NaNO₃ solutions. In Na₂SO₄ solutions, however, when the concentration of Na⁺ is higher than 1 M, the peak intensity of the dimer is much higher than those of the other silicate complexes. In Na₂SO₄ solutions, the SO₄²⁻ ion undergoes partial hydrolysis to form HSO⁻₄ and OH⁻ is produced. In particular, in the range where the concentration of SO₄²⁻ is high, the pH of the solution increases slightly. This higher pH yields more dimers from the hydrolysis of silicate complexes. This increase in dimer production agrees with the observation that silica dissolves in sodium hydroxide (NaOH) solutions mainly as a dimer when the concentration of NaOH is less than 0.1 M. In Na₂SO₄ solutions at high concentrations, a salting-out effect is not observed for silica. This is due to the increase in the concentration of OH⁻, which accelerates the hydrolysis of silica and results in dimer formation.     

Effect of concentration regime on rheological properties of sodium polymethacrylate and its complexes with polystyrene-poly(N-ethyl-4-vinylpyridinium bromide) block copolymer in aqueous salt solution

The effect of concentration on the behavior of high-molecular-mass sodium polymethacrylate (M _w = 3.9 × 10⁵) in a 0.1 M NaCl aqueous solution was studied by the methods of dynamic and static light scattering, and capillary and rotational viscometry. It was shown that the concentration corresponding to the formation of fluctuation network of polyelectrolyte entanglements (6.4%) is substantially higher than the crossover concentration (0.25%). This fact indicates the existence of a wide concentration interval for a semidilute unentangled polyanion solution. The introduction of minor amounts of micelles of cationic amphiphilic polystyrene-poly(N-ethyl-4-vinylpyridinium bromide) diblock copolymer is accompanied by the development of the network of an interpolyelectrolyte complex. The junctions of this network are diblock copolymer micelles that are linked to polyanion macromolecules via salt bonds. The formation of interpolyelectrolyte network leads to the additional structuring of the sodium polymethacrylate solution and an increase in its viscosity. The growth in viscosity is most pronounced in the concentration region above the concentration corresponding to the formation of entanglement network of the free polyanion.     

Thermodynamic properties of aqueous-alcoholic solutions of sodium chloride. H<Subscript>2</Subscript>O-2-C<Subscript>3</Subscript>H<Subscript>7</Subscript>OH-NaCl

The temperature-concentration dependences of the NaCl activity coefficient in aqueous solutions of isopropanol (propanol-2) at temperatures of 298.15 and 323.15 K (solution ionic force, 0.01 to 3m; alcohol content, 10–60 wt %) were determined through the electromotive force method with an ion-selective electrode. A Pitzer model was used to mathematically describe the thermodynamic properties. The integral Gibbs energy of the solution formation of the H₂O-2-C₃H₇OH-NaCl ternary system was performed according to Darken’s method. The dissociation degree of salt in the investigated solutions was estimated using the literature data on the association constant of NaCl in aqueous-isopropanol solution.     

Amylose and amylopectin as reagents for the flow-injection determination of elemental iodine

The complexation reactions of elemental iodine with amylopectin and amylose were studied under flow conditions with spectrophotometric signal detection. It was found that the average hydrodynamic molecular weights of amylose and amylopectin are 260 000 and 430 000, whereas the coefficients of sedimentation are 3.44 × 10^?13 and 7.15 × 10^?13 s, respectively. It was demonstrated that the optimum configuration of a flow system depends on the properties of polymer reagent solutions, their viscosity, and the different effects of clath-rate formation with iodine. It was found that the reaction somewhat accelerated in the presence of iodide ions, and amylose as a reagent exhibited the best properties, when the calibration function was described by a linear regression equation. The throughput capacity of this technique was as high as 220 or 140 samples per hour with the use of amylose or amylopectin, respectively. The technique is suitable for the direct determination of elemental iodine in seawater and salt. The detection limit of iodine with amylose was as low as 40 ng/mL.     

Entanglement properties of cellulose and amylose in an ionic liquid

Concentrated solutions of cellulose and amylose were prepared with an ionic liquid 1‐butyl‐3‐methylimidazolium chloride (BmimCl), which was chosen as a good solvent for these polysaccharides. Dynamic viscoelasticity of the concentrated solutions was examined to obtain the molecular weight between entanglements, M_e. The value of M_e in the molten state (M_e,melt), a material constant that reflecting the entanglement properties, was determined for cellulose and amylose by extrapolating M_e to the “melt.” A marked difference in M_e,melt was found: 3.2 × 10³ for cellulose and 2.5 × 10⁴ for amylose. The value of M_e,melt for cellulose, which is composed of β‐(1,4) bonding of D ‐glucose units, is very close to those for polysaccharides with a random‐coil conformation such as agarose and gellan in BmimCl. The much larger M_e,melt for amylose can be attributed to the helical nature of the amylose chain, α‐(1,4)‐linked D ‐glucose units. The effect of concentration on the zero‐shear viscosity for the solutions of cellulose and amylose was also examined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Effect of borax additives on the rheological properties of sodium hyaluronate aqueous solutions

The rheological properties of sodium hyaluronate aqueous solutions are studied, and the effect of borax additives on them is investigated. It is shown that, at low concentrations, sodium hyaluronate behaves as a typical linear polyelectrolyte in the limit of a high concentration of the salt in both a 0.1 M NaCl aqueous solution and a salt-free solvent. The addition of 1 mole of borax per base-mole of the polymer to the solution of sodium hyaluronate significantly decreases the specific viscosity of the solution if no salt is added and has practically no effect on the viscosity of the solution in 0.1 M NaCl. The viscosity of a semidilute solution of sodium hyaluronate without the added salt decreases as the shear rate is increased in the range 1.5–656 s^?1. With an increase in temperature, viscosity decreases and its dependence on shear rate becomes less pronounced. The same effect is exerted by small amounts of borax. The properties of salt-free solutions are explained by the presence of admixtures of low-molecular-mass ions in them that screen the Coulomb repulsion of charges linked to sodium hyaluronate chains, and the effect of borax may be rationalized by the screening effect of ions resulting from the hydrolysis of borax.     

Calculation of solvation free energy using RISM theory for peptide in salt solution

We developed a robust, highly efficient algorithm for solving the full reference interaction site model (RISM) equations for salt solutions near a solute molecule with many atomic sites. It was obtained as an extension of our previously reported algorithm for pure water near the solute molecule. The algorithm is a judicious hybrid of the Newton–Raphson and Picard methods. The most striking advantage is that the Jacobian matrix is just part of the input data and need not be recalculated at all. To illustrate the algorithm, we solved the full RISM equations for a dipeptide (NH₂(SINGLE BOND)CHCH₃(SINGLE BOND)CONH(SINGLE BOND)CHCH₃(SINGLE BOND)COOH) in a 1 M NaCl solution. The extended simple point charge (SPC/E) model was employed for water molecules. Two different conformations of the dipeptide were considered. It was assumed for each conformation that the dipeptide was present either as an un-ionized form or as a zwitterion. The structure of the salt solution near the dipeptide and salt effects on the solvation free energy were also discussed. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1724–1735, 1998     

Water‐soluble hyperbranched polyelectrolytes with high fluorescence quantum yield: Facile synthesis and selective chemosensor for Hg2+ and Cu2+ ions

New water‐soluble hyperbranched polyfluorenes bearing carboxylate side chains have been synthesized by the simple “A2 + B2 + C3” protocol based on Suzuki coupling polymerization. The linear polyfluorene analogue LPFA was also synthesized for comparative investigation. The optical properties of the neutral precursory polymers in CHCl₃ and final carboxylic‐anionic conjugated polyelectrolytes in buffer solution were investigated. The obtained hyperbranched polyelectrolyte HPFA2 with lower content of branch unit (2%) showed excellent solubility and high fluorescence quantum yield (?_F = 89%) in aqueous solution. Fluorescence quenching of HPFA2 by different metal ions was also investigated, the polyelectrolyte showed high selectivity for Hg²⁺ and Cu²⁺ ions relative to other various metal ions in buffer solution. The Stern‐Volmer constant K_sv was determined to be 0.80 × 10⁶ M^?1 for Hg²⁺ and 3.11 × 10⁶ M^?1 for Cu²⁺, respectively, indicating the potential application of HPFA2 as a highly selective and sensitive chemosensor for Hg²⁺ and Cu²⁺ ions in aqueous solution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3431–3439, 2010     

Rheological properties of native and hydrolyzed starches in dependence on composition and concentration

The structure formation of starch polysaccharides in aqueous solutions is determined by the ratio of amylose to amylopectin and the molecular properties of these components. Our research is focused on establishing defined correlations between composition, molecular structure in diluted solutions and rheological properties of concentrated aqueous starch polysaccharide solutions. Diluted solutions were investigated by size exclusion chromatography with multi angle laser light scattering detector. Measurements of concentrated aqueous solutions were carried out by a Bohlin cs-rheometer with programmed stress using a cone-plate geometry of 40 mm diameter and a cone angle of 4 degrees. Gels were characterized by oscillatory measurements taking into account the frequency dependence of the storage and loss moduli and the influence of a stress sweep on the moduli. The concentration dependence was investigated with starches of potato, wheat, maize and wrinkled pea. Starches with quite similar amylose content as from potato, wheat and maize, show different behavior in rheological properties. Further differences in structure formation were obtained by enzymatic hydrolysis of potato and wheat starch with bacterial α-amylase. The hydrolyzing conditions were chosen such that the degradation led to molecular weights between 5*10⁵ and 10⁷ g/mol. Detailed information about molecular composition was obtained by fractionation of degraded starches. The amylopectin was found to be degraded more strongly than the contained amylose. In comparison to native starch polysaccharide fractions the amylopectin hinders the gelation process in dependence on its molecular weight distribution and the length of the outer chains.