Interaction of the low-molecular weight salts with cationic polyelectrolytes

The interaction of several mono-, di-, and trivalent anions with cationic polyelectrolytes having different contents in N,N-dimethyl-2-hydroxypropylen ammonium chloride units (polymer A) or tertiary amine N-atoms and PEG (polymer PEGA) in the main chain was studied by viscosimetric and conductometric measurements. Both methods have shown a stronger interaction for tri- and bi- than for univalent counterions. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2571–2581, 1997     

Macromolecular design of new cationic polyelectrolytes

Methods were elaborated for the synthesis of new monomers, derivatives of diallylguanidine and macromers, which contain fragments of polytetrahydrofuran and diallylic nitrogencontaining end groups (diallylamine, alkyldiallylammonium, diallylguanidine both in base and acetate forms). Alkylation of a macromer with a diallylamine end group was carried out with methyl iodide in various organic solvents. The possibility of synthesis of diallylguanidine acetate homopolymer as well as its statistical copolymer with diallyldimethylammonium chloride was shown. For the first time, block copolymers based on synthesized macromers were obtained.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1976–1982, November, 1994.The work was supported in part by the Russian Foundation For Basic Research (project code 94-03-08924a).     

Surfactant polymer interactions between strongly interacting cationic surfactants and anionic polyelectrolytes from conductivity and turbidity measurements

The interactions between oppositely charged surfactant/polymer mixtures have been studied using conductivity and turbidity measurements. The dependence of aggregation phenomenon on the chain length and head group modifications of conventional cationic surfactants, i.e., hexadecyl- (HTAB), tetradecyl- (TTAB), and dodecyltrimethylammonium bromides (DTAB) and dimeric cationic surfactants, i.e., decyl- (DeDGB) and dodecyldimethylgemini bromides (DDGB), is investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolytes at critical aggregation concentration (cac). The cac values are considerably lower than the critical micelle concentration (cmc) values for the same surfactant. After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in aqueous polyelectrolyte than in pure water. Among the conventional and dimeric cationic surfactants, DTAB and DeDGB, respectively, have been found to have least interactions with oppositely charged polyelectrolytes.     

The effect of the amphiprotic nature of human hair keratin on the adsorption of high charge density cationic polyelectrolytes

Adsorption of the cationic polymers poly(methacrylamidopropyltrimethyl ammonium chloride) (PMAPTAC) and poly(1,1-dimethylpiperidinium-3,5-diallylmethylene chloride) (PDMPDAMC) on human hair was studied by measurements of the amount of polymer adsorbed and by the streaming potential method. Results reflect the amphoteric nature of the keratin surface and show that the excess of anionic sites at pH values above 4 is the main driving force for the adsorption of cationic polyelectrolytes. Lowering the pH below 4 or addition of neutral salt (KCl) reduces the amount of adsorbed polymer. It was shown that the adsorption of cationic polymer in the concentration range 0.01 to 0.1 % and at neutral pH reverses the overall character of the surface from anionic to cationic. Keratin fibers modified in this manner do not exhibit amphoteric character and bear excess positive charge in the pH range 2–9.5. The value of the amount of the polymer adsorbed at saturation concentration (2 mg/g) as well as the lack of molecular weight effect in the range (5 · 10⁴ – 10⁶) on the amount of polymer adsorbed suggest that polymer chains adopt a rather extended conformation on the fiber surface. Some data concerning the formation of a complex between adsorbed cationic polymer and anionic detergents or polyelectrolytes are also presented.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Benzylic and pyridinium head groups controlled surfactant-polymer aggregates of mixed cationic micelles and anionic polyelectrolytes

The oppositely charged electrostatic interactions between cationic single and mixed micelles of benzyldimethylhexadecylammonium chloride (BHDACl), hexadecylpyridinium bromide (HPyBr), hexadecylpyridinium chloride (HPyCl), and their mixtures with anionic polyelectrolytes, namely carboxymethylcellulose sodium salt (CMC) and polystyrene sulfonate sodium salt (PSS) were studied with the help of conductivity (), viscosity (), turbidity (), and NMR studies. showed single aggregation process, which was represented by apparent critical micelle concentration, acmc, of each surfactant in aqueous polyelectrolyte solution. Both and demonstrated strong electrostriction effects in the case of BHDACl-polyelectrolyte systems due to weak electrostatic interactions in view of steric hindrances created by benzylic group of BHDACl. ¹H NMR results showed that the head group proton resonances of BHDACl upon incorporation of HPyBr or HPyCl in the presence of CMC or PSS remained identical to that in pure water, which demonstrated very weak interactions between BHDACl and polyelectrolytes. A less shielding of pyridinium head group protons by BHDACl in the presence of polyelectrolytes in comparison to that in pure water indicated favorable electrostatic interactions between pyridinium head groups and anionic polyelectrolytes. HPyBr in comparison to HPyCl showed stronger interactions with polyelectrolytes.     

Synthesis of green nanocatalysts and industrially important green reactions

Abstract

There is a growing interest in applying green chemistry for nanocatalysis applications. On the basis of a Scifinder Scholar search, the field of applying green chemistry to catalysis with nanoparticles has undergone an explosive growth from year 2002 to present. It can be seen that green chemistry applied to nanocatalysis is a relatively hot area with much room for growth. I discuss several review articles written about the use of green nanocatalysts as well as green reactions. I discuss studies involving the synthesis of green nanocatalysts and application of metal nanocatalysts in green reactions. I have organized the discussion of green nanocatalysts by the type of nanoparticles that are synthesized and used as catalysts. I have organized discussions of green reactions by the type of green reaction that is being conducted. Overall, our review article discusses developments in new types of green nanocatalysts as well as developments in green catalytic reactions.     

Adsorption of linear and star-shaped polyelectrolytes to monolayers of charged amphiphiles

Adsorption of polyelectrolytes has been studied employing monolayers of ionic amphiphiles at the air water interface as model surfaces. The adsorption of polyelectrolytes from a solution brought into contact with the amphiphile monolayer results in changes of the monolayer structure and properties. Monitoring these changes can be done by recording the changes in surface pressure. The kinetics of the adsorption depends strongly on the nature of the polyelectrolyte. Depending on the structure of the polyelectrolyte a purely diffusion controlled adsorption or a sequence of diffusion controlled adsorption and ordering processes have been identified to determine the kinetics. The influence of the molecular architecture on the polyelectrolyte adsorption has been further studied employing linear and star shaped poly(acrylic acid) and poly(N-propyl-4-vinyl pyridinium bromides), respectively. An unexpected behavior with an induction period in the adsorption kinetics of both polymers has been found. Furthermore, the degree of branching has only very minor effects on the adsorption kinetics.     

Hydrophobically modified polyelectrolytes used as reducing and stabilizing agent for the formation of gold nanoparticles

This paper is focused on the synthesis and characterization of hydrophobically modified polyelectrolytes and their use as reducing as well as stabilizing agents for the formation of gold nanoparticles. Commercially available poly(acrylic acid) has been hydrophobically modified with various degrees of grafting of butylamine introduced randomly along the chain. Different analytical methods are performed, i.e., IR and ¹H-NMR spectroscopy in combination with elemental analysis to determine the degree of grafting. The modified polymers can successfully be used for the controlled single-step synthesis and stabilization of gold nanoparticles. The process of nanoparticle formation is investigated by means of UV-vis spectroscopy. The size and shape of the particles obtained in the presence of unmodified or modified polyelectrolytes are characterized by dynamic light scattering, zeta potential measurements and transmission electron microscopy. The polyelectrolytes were involved in the crystallization process of the nanoparticles, and in the presence of hydrophobic microdomains at the particle surface, a better stabilization at higher temperature can be observed.     

Polyelectrolyte titration using fluorescent indicator. I. Direct titration of anionic and cationic polyelectrolytes with 10−4N standard solutions

The polyelectrolyte titration, which was originally called colloid titration, is based on the stoichiometric reaction between positively charged colloidal particles and negatively charged ones. In the conventional method, the metachromatic color change of the indicator, toluidine blue, from blue to red-purple has been applied for the determination of the end point in the titration. 2.5 × 10^?3N potassium polyvinylsulfonate (KPVS) is usually used as the standard titrant. In this work, fluorescent indicators such as 6-(p-toluidino)-2-naphthalene sulfonate (TNS), acridine orange, etc., have been introduced. The fluorescence intensity was measured using the spectrophotometer equipped with magnetic stirrer and connected with a vinyl tube attached to the hand piston burette. For example, TNS is practically nonfluorescent, but it exhibits strong fluorescence when it is bound to a cationic polyelectrolyte (CP). The fluorescence of the TNS–CP complex is diminished by titration with KPVS standard solution since TNS is liberated from the complex by substitution with KPVS. After the equivalent point, the fluorescence intensity becomes constant and the end point can thus be detected by that point. It has been elucidated that the very dilute standard solution like 1 × 10^?4N can be used because the sensitivity of fluorescence detection is extremely high. © 1993 John Wiley & Sons, Inc.     

Interaction between anionic polyelectrolytes and anion exchange membranes and change in membrane properties

Electrodialytic transport properties of anion exchange membranes were measured after formation of anionic polyelectrolyte layers on the membrane surfaces: relative transport number of various anions to chloride ions, current efficiency and apparent diffusion coefficients of neutral molecules. The anionic polyelectrolyte layers were formed by immersing the membrane into an aqueous solution of polycondensation product of sodium naphthalene sulfonate and formaldehyde or polystyrene sulfonic acid.

The change in the relative transport number between anions was remarkable in the anion exchange membrane with high ion exchange capacity by forming the layer. Results were: the relative transport number of sulfate ions to chloride ions decreased and those of nitrate ions to chloride ions, fluoride ions to chloride ions and bromide ions to chloride ions increased compared with the corresponding membrane. Although the apparent diffusion coefficient of neutral molecules suggested clogging of the membrane pores by the polyelectrolyte, anions with higher hydrated ionic diameter were able to permeate through the membrane easily. This means that difference of electrostatic repulsion force against two anions is effective on the change in the relative transport number of anions.     

酞菁铜衍生物与聚电解质的自组装

用原子力显微镜研究了阿利新蓝(Alcian Blue)和聚电解质自组装膜的表面形貌结构以探讨染料小分子的静电自组装途径。并通过将氯甲基酞菁小分子挂接在高分子链上，制备了一种高分子染料，然后和聚电解质组装成一种高分子复合物。     

Treating the polyelectrolytes as polymers with a draining effect. II. The behavior in the gel permeation chromatography

The behavior of the polyelectrolytes in the gel permeation chromatography (GPC) can be better understood if the modified universal calibration (log([η]M/Φ) vs. elution volume) is used instead of the “classical” universal calibration (log[η]M vs. elution volume). The value of Flory's parameter Φ is obtained from an equation established for nonionic polymers presenting a draining effect, considering that polyelectrolytes also behave as polymers with a draining effect. The modified universal calibration does not apply as successfully to polyelectrolytes as to nonionic polymers, because of their electrostatic exclusion in the pore surface of the GPC columns. Nevertheless, when polyelectrolytes are found in a high salt concentration solution, the modified universal calibration can be used to obtain their molecular mass, using nonionic hydrosoluble polymers as standard polymers. Moreover, considering polyelectrolytes as polymers presenting a draining effect and applying the modified universal calibration provides a better explanation for the electrostatic exclusion of these polymers from the pores of the GPC columns, using the Dubin–Tecklenburg model. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1106–1113, 2006     

Application of magnetically recoverable nanocatalysts in synthesis of imidazole,thiazole, and oxazoles

Abstract

Imidazoles, thiazoles, and oxazoles have been identified as valuable molecules in pharmaceutical and agriculture chemistry. Molecules containing these scaffolds are excited in many natural products and biologically active molecules. During the last decade, magnetic nanomaterials have appeared as highly efficient catalysts in chemical science in general organic chemistry, because of their simple preparation, modification, and large surface area ratio. This article assists to review the application of magnetically reusable nanocatalysts in synthesis of biologically active imidazoles, thiazoles, and oxazoles.     

Determination of cationic polyelectrolytes using a photometric titration with crystal violet as a color indicator

The reaction of the cationic dye, crystal violet (CV) with the anionic polyelectrolytes such as potassium poly (vinyl sulfate) (PVSK) results in a decrease of the absorbance of CV at the maximum absorption wavelength (590 nm). This change of the absorption spectra of the CV has been already applied to the determination of anionic polyelectrolytes using flow injection analysis method. In this paper, CV was applied to the indicator for the determination of cationic polyelectrolytes such as poly (diallyldimethylammonium chloride) (Cat-floc) by photometric titration, using a PVSK solution as a titrant. The end-point of the titration is detected as the break point of the titration curve. A linear relationship between the concentration of cationic polyelectrolyte and the end-point volume of the titrant exists in the concentration range from 0 to 5×10⁻⁵ eq. mol dm⁻³ for Cat-floc, glycol chitosan and methylglycol chitosan. The effects of the concentration of CV and coexisting electrolytes in the sample solution and the effect of pH of the sample solution on the degree of the change of absorbance at the end-point were also examined.     

Fully charged: Maximizing the potential of cationic polyelectrolytes in applications ranging from membranes to gene delivery through rational design

Polyelectrolytes have found utility across various applications in materials science, from electrochemical devices to biotechnology, due to their facile processing and tunable properties. Through chemistry, rational manipulation of molecular structure enables individual families of polyelectrolytes to be used in emerging advanced applications. In this perspective, we focus on cationic systems, and we describe how various structural motifs influence macromolecular properties for anion exchange membranes and gene delivery vectors. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3167–3174     

Treating the polyelectrolytes as polymers with a draining effect. I. The statistical segment length

The statistical segment length of polyelectrolytes, A, in aqueous salt solutions is derived from the unperturbed dimensions parameter, K_θ, that is obtained from the graphical representations based on the Stockmayer–Fixman–Burchard and Dondos–Benoît equations. In order to obtain A from K_θ we use values of the Flory's parameter, Φ, which are given from an empirical equation established for the polymers presenting a draining effect, such as the wormlike polymers. With these values of Φ, the obtained values of A for different polyelectrolytes in aqueous salt solutions of different ionic strength are found very close to the values obtained from other more complicated methods. This result shows that the polyelectrolytes can be considered as polymers presenting a draining effect. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4225–4229, 2004     

Synthesis and properties in solution of rodlike polyelectrolytes

Efficient synthetic strategies are described for the preparation of rodlike polyelectrolytes based on the intrinsically rigid poly(p-phenylene). Uncharged precursors were first prepared via the Suzuki coupling and then characterized by different methods of polymer analysis. Finally, they were transformed into polyelectrolytes using macromolecular substitution reactions. Depending on the substitution pattern, the obtained polyelectrolytes are either soluble or insoluble in water. Using water-soluble derivatives, the Poisson-Boltzmann cell model was tested by osmotic measurements and small-angle X-ray scattering. It is shown that the cell model provides a good first approximation of the distribution of the counterions around the macroion but still underestimates their correlation. Moreover, the PPP polyelectrolytes show a very pronounced polyelectrolyte effect. Since the rodlike PPPs are very rigid in shape, this observation proves that the polyelectrolyte effect is caused by long-range intermolecular electrostatic repulsion of the dissolved macroions rather than due to conformational changes.     

Conjugated polyelectrolytes and neutral polymers with poly(2,7‐carbazole) backbone: Synthesis,characterization, and photovoltaic application

Poly(2,7‐carbazole) neutral polymers (PC‐N, PC‐NOH, and PC‐P) and polyelectrolytes (PC‐NBr and PC‐SO₃Na) with hydrophilic pendant groups of ammonium, phosphonate, and sulfonate were synthesized as interlayers for cathode modifications in bulk‐heterojunction photovoltaic cells (BHJ PVCs). The absorptions of the polymers were determined by the poly(2,7‐carbazole) backbone, showing absorption peaks at ～390 nm for their solutions and films. Because of large intermolecular interactions, excimer emissions with wavelengths higher than 500 nm were found in the photoluminescence spectra of the films of the polymers, which weakened the light emissions of the polymers. PC‐N, PC‐NBr, PC‐NOH, and PC‐P possessed comparable HOMO levels of ?5.23 eV and LUMO levels of ?2.4 eV, but HOMO and LUMO levels of PC‐SO₃Na were up‐lying to ?4.91 and ?2.12 eV, respectively. PC‐N, PC‐NBr, PC‐NOH, and PC‐P were selected to construct thin interlayers in BHJ PVCs with PFO‐DBT35:PCBM = 1:4 as the active layer. Compared with traditional Al cathode, bilayer cathodes with the interlayers showed improvements of open‐circuit voltages and short‐circuit currents of the PVCs. PC‐NOH was the best for the photovoltaic performances and over 20% increase of power conversion efficiency (PCE) was achieved. The bilayer cathodes would have great potential to further elevate PCE of BHJ PVCs with other active layer materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Interactions between nonpolar surfaces in mixed solutions of cationic and nonionic surfactants

The interaction energy between hydrophobic SiO₂ particles in aqueous solutions of a cationic surfactant (dodecylpyridinium bromide, DDPB), a nonionic surfactant (Triton X-100, TX-100), and their mixed solutions was measured as a function of concentration. Synergism has been observed in mixed surfactant solutions: the surfactant concentration required for achieving the set interaction energy in the mixed solutions was lower than in the solutions of the individual surfactants. The molecular interaction parameters in surfactant mixtures were calculated using the Rosen model. Chain-chain interactions between nonionic and cationic surfactants were suggested as the main reason for the synergism.