Aliphatic Ionenes Research Articles

Synthesis and characterization of poly(tetramethylene oxide)-based segmented ionenes block copolymer with aliphatic or DABCO hard segments

In this study, the effects of the contents of the soft and hard segments as well as the type of hard segments (linear aliphatic and DABCO) on the properties of PTMO-based segmented ionenes were investigated. DSC revealed that soft segment weight fractions up to 75 wt% induced heterogeneous crystallization while the melting temperature decreased due to the lower degree of crystallization. DMA showed the formation of a higher degree of ionic aggregates in both linear aliphatic and DABCO-based PTMO ionenes with 25 wt% of soft segment resulting from strong Coulombic interactions between hard segments. DABCO-based ionenes showed a higher degree of phase separation compared to linear aliphatic analogs and displayed a long-range ordered lamellar structure. In contrast, linear aliphatic ionenes showed the formation of random ionic domains, which was confirmed by SAXS and AFM. TGA showed that the PTMO-based ionenes were thermally stable up to 250 °C and suggested that the DABCO hard segment has a weaker protective effect against the degradation of the PTMO soft segment at elevated temperatures compared to the linear aliphatic hard segment. Uniaxial tensile tests exhibited stress-induced crystallization of PTMO-based ionenes, high elongation at break with linear aliphatic hard segment compared to the DABCO hard segment, and the opposite trend of Young's modulus and ultimate tensile strength by changing the type of the hard segment.

Influence of the hydrophobic groups and the nature of counterions on ion-binding in aliphatic ionene solutions

Transport and binding capabilities in aqueous solutions of 3,3-, 6,6-, and 6,9-ionene fluorides and bromides at 25°C were explored through the experimentally determined values for transport numbers of counterions and polyion constituents, along with the data for electrical conductivity in these solutions. Within the association theory, the fractions of free counterions and the effective linear charge densities of polyions were calculated. Experimental data were compared with the predictions of the Manning theory of polyelectrolyte solutions. It was determined that binding of the counterions to the polyion critically depends (i) on charge density of the polyion and (ii) on the chemical nature of the counterion in question. The effects of the charge density are the strongest in solutions of ionene bromides. Differences in the behavior of solutions of ionene fluorides and bromides are the consequence of different hydration capabilities of these ions. The effective linear charge density was found to be much lower than the one predicted from structural parameters of ionenes. The study addresses questions important to the biomedical field, in particular that of binding of ligands to charged macromolecules.

Thermodynamics of Dilution and the Hofmeister Series in Aqueous Solutions of Aliphatic Ionenes with Halide Counterions

Enthalpies of dilution of aqueous solutions of aliphatic x,y-ionene fluorides and iodides, with x,y being equal to 3,3-, 4,5-, 6,6-, and 6,9-, were measured in the concentration range from 0.1 mol·kg−1 to 0.0016 mol·kg−1. The results were combined with previously obtained data for ionene chlorides and bromides to discuss the ion-specific and charge density effects in these solutions. The comparison with theoretical results, based on Manning's limiting law and cylindrical cell model founded on the solution of Poisson−Boltzmann's equation, is presented. These theories imply the enthalpy of dilution to be exothermic. Of all the solutions studied here, only those with fluoride ions as counterions agree with theoretical predictions. Solutions of 3,3-, 4,5-, and 6,6-ionene with bromide, chloride, and iodide counterions yield endothermic effect upon dilution. For the most hydrophobic 6,9-ionene, heat is released when adding water in the low concentration regime. Using the previously measured data for 3,3-, 4,5-,...

Dielectric Relaxation Spectroscopy of Aliphatic Ionene Bromides and Fluorides in Water: The Role of the Polyion’s Charge Density and the Nature of the Counterions

Dielec. relaxation spectroscopy (DRS) has been chosen to study the dielec. properties of ionene bromides and fluorides in water. The best model for describing the exptl. data in the range of frequencies 0.05 < v/GHz < 89 was the one that considered two relaxing species: (i) counterions and (ii) the bulk water. From the redn. of the water amplitude, S2, effective hydration nos. could be derived. Relaxation times of counterions, τ1, decreased with the increasing concn., which was a consequence of stronger electrostatic screening in more concd. solns. Fluoride counterions were to a lesser extent affected by the polyion than bromide counterions. It seemed that charged sites of the polyions had a much greater influence on the F- counterions than the chains of -CH2- units between them. For ionene bromides, however, the influence of polyion's charges and of hydrophobic parts of the backbone manifested itself in a more complex manner. High hydration nos. in the case of Br- counterions as well as the insensitivity of τ1 on the charge d. of the polyion indicated that the role of the solvent could not be disregarded in these systems.

Polyelectrolyte hydration: Theory and experiment

AbstractA short review of recent theoretical and experimental advances in studies of polyelectrolyte solutions is presented. The focus is on ion-specific effects as revealed in measurements of osmotic pressure and enthalpy of dilution. We review the experimental results for two different polyelectrolyte systems: (i) salts of polyanetholesulfonic acid, and (ii) aliphatic ionenes (polycations) in aqueous solution with various counterions. A theoretical approach based on the extension of Wertheim's integral equation theory [J. Stat. Phys.35, 19 (1984)] is used to analyze the experimental data. Preliminary results, based on the all-atom simulation of model 3,3 ionene oligomers, are discussed in the light of polyelectrolyte hydration.

A Molecular Dynamics study of short-chain polyelectrolytes in explicit water: Toward the origin of ion-specific effects

We present all atom explicit water Molecular Dynamics simulation results for the structure of short (six monomer units) aliphatic ionenes in mixtures with a low-molecular weight electrolyte. The SPC/E model was used to describe water. Long-range effects were taken into account via the Ewald summation procedure. The results indicate that strongly hydrated ions such as F − cannot approach the nitrogen atom on the oligoion. In contrast, weakly hydrated I − ions accumulate close to the oligoion. These findings are consistent with the thermodynamic data and ongoing measurements of the dielectric relaxation in ionene solutions.

Polystyrene immobilized ionenes as novel stationary phase for ion chromatography

Several aliphatic ionenes (2-6-, 6-6-, 10-6-ionene) have been prepared as ion exchangers for the development of novel high-performance stationary phases for anion chromatography (IC). A macroporous polystyrene/divinylbenzene (PS/DVB) resin with adjusted cation exchange capacity was used as support. Therefore the immobilization of ionenes to polystyrene carriers with remaining positive surface charge became possible for the first time. Strong ion-exchange interactions, resulting in high retention times, between the stationary phase and inorganic as well as organic anionic analytes have been observed. The influence of different ionenes on the retention behaviour during the ion chromatographic separation was investigated. Additionally, partly aromatic and polar ionene backbones were prepared and their retention behaviour as anion exchanger was investigated. The highest number of theoretical plates obtained was about 90.000 per meter. The signal asymmetries were generally lower than obtained for surface functionalized anion exchangers.

Recognition and Selective Binding of DNA by Ionenes of Different Charge Density

The ability of aliphatic ionenes to recognize and bind DNA or poly(methacrylic acid) (PMA) in the equimolar mixture of these polyanions was studied by fluorescence quenching technique. Within a particular system, the selectivity of competitive interactions was shown to be determined by a component with the lowest degree of polymerization (DP). Ionene polycations with lowest DP values did not exhibit pronounced selectivity in binding DNA or PMA with higher values of DP. Increase in ionene DP resulted in a steady increase in selectivity of interaction and ultimately in almost exclusive binding of one of the two polyanions. The ability of the ionene to recognize and bind DNA in the mixture of polyanions was shown not to correlate with the affinity of the ionene to DNA in their binary mixture. Although ionenes with a higher charge density exhibited preferential binding to PMA, the ionenes with the lowest charge density selectively bound DNA.

Electrophoretic evidence for a new type of counterion condensation

AbstractA systematic capillary electrophoresis study uncovered how polyelectrolyte effective charge density varies with backbone charge spacing and solvent dielectric constant. The study primarily focused on aliphatic ionenes, a special class of polyelectrolytes, which possess regularly spaced quaternary ammonium groups in the backbone. Complete ionization of functional units and good solvency in water or mixtures of water with lower dielectric constant solvents (methanol, acetonitrile) enabled continuous measurements of ionene effective charge density through the onset of counterion condensation. Ionenes with both uniform and alternating charge spacing were examined. As expected, effective charge density rose linearly with fixed charge density to a critical value, above which effective charge density remained constant. Deviating from expectation, the onset of condensation did not occur at a critical fixed charge density. Instead, condensation initiated at a constant critical Bjerrum length. The same onset condition was found for quaternized poly(vinyl pyridine)s. These experimental results suggest a new form of condensation, one driven by ion‐pairing of polyelectrolyte with counterions. In support of this hypothesis, the onset of condensation appeared to correlate with counterion size. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3616–3627, 2004

Conformation of Polyelectrolyte Chains in Dilute Aqueous Solutions Investigated by Conductometry. 4. Influence of Molecular Mass and Charge Density of the Chains on Conformation of Symmetrical Aliphatic Ionene Bromides

Samples of 3,3-, 4,4-, 6,6-, and 10,10-ionene bromides of different degree of polymerization (DP) were synthesized, fractionated, and characterized. Salt-free dilute aqueous solutions of the sample...

Polyelectrolytic Behavior of a Novel Fluorine-Containing Ionomer, PPFNA

Solution properties of a novel fluorine-containing ionomer PPFNA were studied by pH titration, conductivity, and viscosity measurements. This polymer is a poly(carboxylic acid) but dissociates strongly, resulting in a low pH value and a high specific conductance at low degrees of neutralization. When the solution was neutralized with NaOH, the conductance decreased sharply at first and then decreased gradually until full neutralization. This conductometric titration profile indicates that this polymer is a fairly strong polyelectrolyte but not a typical strong one such as poly(styrene sulfonic acid) or aliphatic ionenes. The pH measurement showed that this polymer is a strong polyacid, although the titration profile changed slightly upon the addition of salt. The reduced viscosity of the salt-free solution was well fitted to Fuoss' equation, specific to polyelectrolyte solutions. Upon the addition of salt, however, the viscosity−neutralization profile became rather similar to that of weak polyacid, and th...

Factors Controlling Phase Separation in Water−Salt Solutions of DNA and Polycations

Factors affecting phase separation in water-salt solutions of polyelectrolyte complexes (PECs), formed by DNA and integral or pendant polycations with a quaternary amino group in every monomer unit, have been studied. When no salt was added, quantitative DNA precipitation occurred at a stoichiometric charge ratio, = [+]/[-] 1. In DNA mixtures with poly(N,N'-dimethyldiallylammonium chloride) (PDMDAAC, a pendant polycation), insoluble PECs formed in the range 0.7 2. For different aliphatic ionene bromides (integral polycations), the range of corresponding to insoluble PECs was significantly broader, mainly due to the poor ability of the ionenes to form soluble, positively charged PECs. The range was also relatively broad for poly(N-ethyl-4-vinylpyridinium bromide) (a pendant polycation) and became broader with decreasing degree of polymerization of the polycation. The formation of insoluble PECs was favored by the addition of salt (NaCl), and the effect was more pronounced when decreasing the relative content of the solubilizing component, i.e., the nucleic acid at 1. At moderate ionic strength, 0.12 M < [NaCl] < 0.6 M, quantitative precipitation of DNA was attained by addition of PDMAAC in the whole region studied: 1 < < 4.5. The data obtained strongly suggest that phase separation in solutions of DNA-containing PECs follows general rules revealed by studying PECs formed by flexible vinyl polyanions. However, the high rigidity of the DNA double helix appears to be responsible for the key feature revealed in the phase diagrams, i.e., significant broadening of the region for insoluble PECs at the expense of the region in which soluble DNA-containing PECs are formed. This feature may severely limit the application of DNA-containing PECs in medicine and biology but could be beneficial in the development of simple and effective procedures for DNA separation in biotechnology.

Conformational Changes of Aliphatic Ionenes in Water-Salt Solutions as a Factor Controlling Stability of Their Complexes with Calf Thymus DNA

Fractions of symmetrical X,X-ionenes (X = 3, 6 and 10) with degrees of polymerization DP = 30−250 and nonsymmetrical 2,Y-ionenes (Y = 4, 6, 8, and 10), DP = 4−30, were used as positively charged partners of calf thymus DNA in polyelectrolyte complexes (PEC). The determined values of salt concentration, C*salt, corresponding to the complete dissociation of PEC increased with the lengthening of ionenes of both families. C*NaCl for PEC formed by relatively short 2,Y-ionenes of the same DP increased markedly with Y decrease. However the impact of this factor was substantially diminished upon lengthening of the 2,Y-ionenes. For the long-chained X,X-ionenes a more than 3-fold increase in X resulted only in moderate decrease in C*NaCl. These finding suggest that the effective charge density of different ionenes releasing from PEC at relatively high C*salt becomes comparable owing to their pronounced compaction. This assumption was supported by the results of treatment of the experimental data using the developed model of PEC dissociation in water−salt media, which established the conformations of the releasing chains as slightly more swollen than θ-coil for 3,3-ionenes, θ-coil for 6,6-ionenes, and close to globule for 10,10-ionenes. The findings appear to be of particular interest to gain a better insight into the mechanism of DNA interaction with positively charged counterpart in vivo and in vitro.

Recent progress in adsorbed stationary phases for capillary electrochromatography.

This review surveys the recent progress in the adsorbed stationary phases for capillary electrochromatography (CEC). Adsorption-based methods for preparation of stationary phase are novel approaches in CEC, which allow rapid and facile preparing stationary phases with desirable selectivity onto an open-tubular fused-silica capillary, a bare-silica or ion-exchange packed column or a monolithic silica or polymer column. A variety of adsorbing agents have been developed as adsorbed stationary phases, including ionic long-chain surfactant, protein, peptide, amino acid, charged cyclodextrin (CD), basic compound, aliphatic ionene, and ion-exchange latex particle. The adsorbed stationary phases have been applied to separation of neutral, basic and acidic organic compounds, inorganic anions and enantiomers. They have also been applied to on-line sample concentration, fast separation and study of the competitive binding of enantiomers with protein.

Aliphatic ionenes as gene delivery agents: elucidation of structure-function relationship through modification of charge density and polymer length.

Polycation-based gene delivery agents are generally polydisperse populations whose properties are averaged among the different molecular weight species. Therefore, to understand the physicochemical properties of polycations and their relationships to cellular gene transfer, one needs to control the molecular weight of the polymer as well as its cationic charge density. To investigate the structure-function correlation of polycations with respect to the degree of polymerization (DP) and charge density, a series of model materials based on aliphatic ionenes was synthesized and fractionated into distinct molecular weight fractions with DP range from 14 to 32. The aliphatic ionene fractions and their polyelectrolyte complexes (PEC) with DNA were studied using physicochemical and biological methods. Ionene polymers were shown to possess low cytotoxicity (minimal viability of the P388D1 murine macrophage cells 80%). DP and charge density of the ionenes were shown to be the factors of effective control of PEC dissociation in water-salt solutions, with a diminished role of charge density upon lengthening the ionene chain. These polymer characteristics were also important for DNA-ionene PEC resistivity to DNase activity and the ability of ionenes to serve as gene delivery vectors in vitro and exhibited good correlation with the results of salt-induced dissociation of PEC. These data may be useful for developing correlations and mathematical models to predict synthetic gene delivery vector efficiency.

Polyelectrolyte Complexes Formed by Calf Thymus DNA and Aliphatic Ionenes: Unexpected Change in Stability upon Variation of Chain Length of Ionenes of Different Charge Density

The formation of polyelectrolyte complexes (PECs) between aliphatic 2,4- and 2,8-ionenes and calf thymus DNA in water–salt solutions is monitored by a fluorescence-quenching technique using an ethidium bromide probe. As expected, the tolerance of PEC to dissociation in water–salt solutions increased with an increase in both the number of charged groups, i. e., degree of polymerization of the ionenes (DP), and in the charge density of their chains. However, the latter tendency weakened markedly upon the lengthening of the ionenes chains and ceased to hold at DP ≈ 25. Comparison of the stability of PECs formed by DNA and poly(methacrylate) anion, respectively, with the ionenes, disclosed that relatively short ionene chains formed noticeably less stable DNA-containing PECs, whereas upon lengthening of the ionenes the difference in the stability of the PEC successively decreased and evened out at DP ≈ 25, in the case of 2,8-ionene. All these findings imply that in such systems the role of charge–charge conformity of the partners in DNA-containing PECs is evident only for rather short ionenes. The unexpected changes in PEC stability revealed suggest that the short chains of the ionenes are of special interest for the design of self-assembling polyelectrolyte systems with controllable stability attractive for biomedical applications and bioseparation.

Modified Aliphatic Ionenes. Influence of Charge Density and Length of the Chains on Complex Formation with Poly(methacrylic acid)

Modified ionenes were obtained by alkylation of terminal amino groups of aliphatic ionenes with p-nitrotoluene bromide. The modification endowed the ionenes with relatively high absorbance in UV-range of spectrum. The advantages of the modified ionenes were demonstrated, i.e. the possibility of highly accurate determination of the ionene concentration in dilute aqueous solutions from UV-spectra, fractionation of the sample by ion-exchange chromatography in NaCl gradient with UV-detection, estimation of a polymerization degree of the obtained fractions by “end groups” method and studying of polyelectrolyte complex formation with pyrenyl-tagged poly(methacrylic acid) by fluorescence quenching technique. Chain length and charge density of the ionene were shown to be the factors controlling both solubility and dissociation of the polyelectrolyte complexes in water-salt media. The data obtained strongly suggest that the main regularities ascertained for polyelectrolyte complexes are applicable to the ionene-containing systems, even though the ionene samples contained at most 32 charges in the chains. The revealed possibility of preparing ionene-containing PEC of desired stability, which can be varied in a wide range of ionic strength, including physiological one demonstrates potential of the modified ionenes as components of self-assembly and self-adjustment systems attractive for biomedical applications.

Ionene-coated sulfonated silica as a packing material in the packed-capillary mode of electrochromatography

An aliphatic ionene (2–10-ionene) has been selected as a modifier to prepare a novel polymer-coated packing material for capillary electrochromatography. The packing material was produced by dynamical modification of a commercially available sulfonated silica Exsil-100 SCX. Strong ion-exchange interactions in the capillary packed with ionene-modified sulfonated silica have been demonstrated by the example of the retention of p-aminobenzoic acid. The total calculated anion-exchange capacity of the sorbent in the capillary was about 4·10 −9 mol. A fast separation (about 15 min) of several aromatic acids was achieved with the packing material. The highest number of theoretical plates obtained was about 120 000. Limits of detection of the aromatic acids were 2–5 μg/ml. The advantages and lacks of the approach are discussed briefly.

Ion-chromatographic selectivity of polyelectrolyte sorbents based on some aliphatic and aromatic ionenes

An aliphatic ionene with hydroxyl group (2HP-8 ionene), mixed aliphatic–aromatic ionenes (3-X and 6-X ionenes), aromatic ionene (Ph-X ionene), and viologen (Dp-X ionene) – polymers with quaternary nitrogen atoms in the main chain – served as modifiers in synthesising polyelectrolyte sorbents for ion chromatography. The selectivity of produced and several previously prepared anion exchangers was compared with those of aliphatic ionenes. It was found that aromatic ionenes having a rigid structure of polymer chains are similar to their aliphatic analogues with shorter chains with a high charge density. Polyelectrolyte sorbents based on aromatic ionenes show higher selectivity to aromatic acids (e.g., 1-naphthalenesulfonic acid) as compared with aliphatic ionenes due to specific π–π interactions.

Polyelectrolyte sorbents based on aliphatic ionenes for ion chromatography

2-4, 3-4, 2-8, 3-8, 3-6, 4-6, 6-8, 6-10-ionenes (polymers with quaternary nitrogen atoms in the main chain) served as modifiers in synthesizing polyelectrolyte sorbents for ion chromatography. The approaches to the synthesis and their stability are discussed. Cluster analysis was applied to separate aliphatic ionenes to three groups as chromatographic modifiers, namely hydrophilic, hydrophobic, and intermediate. Each group is characterized by a certain selectivity to sulfate, perchlorate, iodide and thiocyanate. The sorbents show high selectivity and efficiency up to 15 000 theoretical plates per meter.