Cooperative Electrostatic Interactions Research Articles

Regulating the Interface Polarity Distribution of Zr-Based MOFs by Amino Acid-Like Ligand Functionalization Enables Efficient Recovery of Gold.

The recovery of gold from industrial effluents is crucial for environmental conservation, sustainable resource management, and promoting the green development of gold resources. We designed a Zr-based MOF (UKM-78) by incorporating functional organic ligands that resemble amino groups, using MOFs' inherent sieving effect for ion separation. This novel material exhibited enhanced gold recovery under acidic conditions, with an adsorption capacity three times and an adsorption rate four times higher than those of nonfunctionalized UKM-77. Notably, UKM-78 efficiently captured gold solutions at concentrations as low as 1 ppm and achieved an adsorption rate exceeding 90%, owing to the electrostatic interactions and coordination between its functionalized groups and the synergistic effect of its porous structure. Despite multiple regeneration cycles, UKM-78 retains 99.4% of its adsorption capacity. X-ray photoelectron spectroscopy (XPS), kinetic studies, and thermodynamics collectively demonstrated that Au(III) binding on UKM-78 involved cooperative electrostatic interactions and chemical adsorption through coordination. This study highlights the potential of MOFs for efficient and sustainable recovery of gold from complex waste streams.

Self-Assembling Systems Based on Pillar[5]arenes and Surfactants for Encapsulation of Diagnostic Dye DAPI.

In this paper, we report the development of the novel self-assembling systems based on oppositely charged Pillar[5]arenes and surfactants for encapsulation of diagnostic dye DAPI. For this purpose, the aggregation behavior of synthesized macrocycles and surfactants in the presence of Pillar[5]arenes functionalized by carboxy and ammonium terminal groups was studied. It has been demonstrated that by varying the molar ratio in Pillar[5]arene-surfactant systems, it is possible to obtain various types of supramolecular systems: host–guest complexes at equimolar ratio of Pillar[5]arene-surfactant and interpolyelectrolyte complexes (IPECs) are self-assembled materials formed in aqueous medium by two oppositely charged polyelectrolytes (macrocycle and surfactant micelles). It has been suggested that interaction of Pillar[5]arenes with surfactants is predominantly driven by cooperative electrostatic interactions. Synthesized stoichiometric and non-stoichiometric IPECs specifically interact with DAPI. UV-vis, luminescent spectroscopy and molecular docking data show the structural feature of dye-loaded IPEC and key role of the electrostatic, π–π-stacking, cation–π interactions in their formation. Such a strategy for the design of supramolecular Pillar[5]arene-surfactant systems will lead to a synergistic interaction of the two components and will allow specific interaction with the third component (drug or fluorescent tag), which will certainly be in demand in pharmaceuticals and biomedical diagnostics.

Construction of three-dimensional interleaved protein hetero-superlattices in solution by cooperative electrostatic and aromatic stacking interactions

HypothesisHierarchical assembly of naturally occurring assemblies is accurate and responsible for performing various cellular functions. However, Nature’s wisdom in navigating the assembly process to desired protein assemblies by the cooperation of multiple noncovalent interactions has been underexploited for protein superstructures constructions. Owing to the chemical diversity of noncovalent interactions, it should be possible to fabricate protein assemblies with novel properties in high efficiency through the cooperation of different noncovalent interaction. ExperimentsBoth charged residues and aromatic residues are introduced on the exterior surface of ferritin centered at their symmetry axes, mixing of complementary variants forms ordered assemblies through the cooperation of two kinds of chemical-diverse noncovalent interactions. The assemblies were further characterized in terms of their assembly behavior, structure, size, assembly kinetics, properties and stabilities. FindingsWe utilized both electrostatic and π-π stacking interactions between complementary nanocages to cooperatively trigger the self-assembly into predesigned interleaved hetero-superlattices which exhibit high electrolyte stability and thermal stability. The size of the hetero-superlattices can be well controlled with ranges from nanometers to micrometers in solution in response to external stimuli such as pH and salt concentration. The hetero-superlattice may have the potential applications in hybrid bio-templating, light-harvesting and compartmentalized encapsulation.

Novel self-assembling systems based on imidazolium amphiphiles with cleavable urethane fragment for construction of soft nanocontainers for biomedicine application

In the framework of this report the bottom-up strategy has been used for the development of novel soft nanocontainers through self-assembly of homologous series of newly synthesized amphiphilic compounds of N-(2-ethylaminocarbonyloxyethyl)-N-alkylimidazolium bromides. Their aggregation properties, solubilization capacity, antimicrobial activity, membranotropic properties and capability to form lipoplexes have been investigated. Using various physico-chemical techniques it has been demonstrated that introduction of urethane moiety into amphiphile structure results in the 2-3-fold decrease of critical micelle concentration in comparison with their unsubstituted counterparts. It has been suggested, that interaction of amphiphiles with DNA decamer is predominantly driven by cooperative electrostatic interactions. Membranotropic properties of novel amphiphiles could be regulated by the change of the length of hydrophobic tail; with these properties being the more markedly expressed in the case of the lower homologue. Estimation of antimicrobial activity against several strains of microorganisms has revealed, that these amphiphiles were by several-fold more active toward Staphylococcus aureus, Bacillus cereus bacteria and Candida albicans fungi in comparison with reference compounds – norfloxacin and ketoconazole. Hemolytic activity of these amphiphiles has not exceeded 0.9% under bactericide and bacteriostatic concentrations. The combination of advanced characteristics allows us to recommend these amphiphiles for fabrication of soft materials with the wide spectrum of practically useful properties like effective nanocontainers for drug and gene delivery, capable of crossing the cell membrane, and harmless for human agents against pathogenic microorganisms.

Electrostatic lateral interactions drive ESCRT-III heteropolymer assembly.

Self-assembly of ESCRT-III complex is a critical step in all ESCRT-dependent events. ESCRT-III hetero-polymers adopt variable architectures, but the mechanisms of inter-subunit recognition in these hetero-polymers to create flexible architectures remain unclear. We demonstrate in vivo and in vitro that the Saccharomyces cerevisiae ESCRT-III subunit Snf7 uses a conserved acidic helix to recruit its partner Vps24. Charge-inversion mutations in this helix inhibit Snf7-Vps24 lateral interactions in the polymer, while rebalancing the charges rescues the functional defects. These data suggest that Snf7-Vps24 assembly occurs through electrostatic interactions on one surface, rather than through residue-to-residue specificity. We propose a model in which these cooperative electrostatic interactions in the polymer propagate to allow for specific inter-subunit recognition, while sliding of laterally interacting polymers enable changes in architecture at distinct stages of vesicle biogenesis. Our data suggest a mechanism by which interaction specificity and polymer flexibility can be coupled in membrane-remodeling heteropolymeric assemblies.

An "On-Site Transformation" Strategy for Treatment of Bacterial Infection.

To date, numerous nanosystems have been developed as antibiotic replacements for bacterial infection treatment. However, these advanced systems are limited owing to their nontargeting accumulation and the consequent side effects. Herein, transformable polymer-peptide biomaterials have been developed that enable specific accumulation in the infectious site and long-term retention, resulting in enhanced binding capability and killing efficacy toward bacteria. The polymer-peptide conjugates are composed of a chitosan backbone and two functional peptides, i.e., an antimicrobial peptide and a poly(ethylene glycol)-tethered enzyme-cleavable peptide (CPC-1). The CPC-1 initially self-assembles into nanoparticles with pegylated coronas. Upon the peptides are cleaved by the gelatinase secreted by a broad spectrum of bacterial species, the resultant compartments of nanoparticles spontaneously transformed into fibrous nanostructures that are stabilized by enhanced chain-chain interaction, leading to exposure of antimicrobial peptide residues for multivalent cooperative electrostatic interactions with bacterial membranes. Intriguingly, the in situ morphological transformation also critically improves the accumulation and retention of CPC-1 in infectious sites in vivo, which exhibits highly efficient antibacterial activity. This proof-of-concept study demonstrates that pathological environment-driven smart self-assemblies may provide a new idea for design of high-performance biomaterials for disease diagnostics and therapeutics.

Cooperative Electrostatic Interactions Drive Functional Evolution in the Alkaline Phosphatase Superfamily.

It is becoming widely accepted that catalytic promiscuity, i.e., the ability of a single enzyme to catalyze the turnover of multiple, chemically distinct substrates, plays a key role in the evolution of new enzyme functions. In this context, the members of the alkaline phosphatase superfamily have been extensively studied as model systems in order to understand the phenomenon of enzyme multifunctionality. In the present work, we model the selectivity of two multiply promiscuous members of this superfamily, namely the phosphonate monoester hydrolases from Burkholderia caryophylli and Rhizobium leguminosarum. We have performed extensive simulations of the enzymatic reaction of both wild-type enzymes and several experimentally characterized mutants. Our computational models are in agreement with key experimental observables, such as the observed activities of the wild-type enzymes, qualitative interpretations of experimental pH-rate profiles, and activity trends among several active site mutants. In all cases the substrates of interest bind to the enzyme in similar conformations, with largely unperturbed transition states from their corresponding analogues in aqueous solution. Examination of transition-state geometries and the contribution of individual residues to the calculated activation barriers suggest that the broad promiscuity of these enzymes arises from cooperative electrostatic interactions in the active site, allowing each enzyme to adapt to the electrostatic needs of different substrates. By comparing the structural and electrostatic features of several alkaline phosphatases, we suggest that this phenomenon is a generalized feature driving selectivity and promiscuity within this superfamily and can be in turn used for artificial enzyme design.

The N-terminus of α-synuclein is essential for both monomeric and oligomeric interactions with membranes

The intrinsically disordered protein α-synuclein (αSN) is linked to Parkinson’s Disease and forms both oligomeric species and amyloid fibrils. The N-terminal part of monomeric αSN interacts strongly with membranes and αSN cytotoxicity has been attributed to oligomers’ ability to interact with and perturb membranes. We show that membrane folding of monomeric wt αSN and N-terminally truncated variants correlates with membrane permeabilization. Further, the first 11 N-terminal residues are crucial for monomers’ and oligomers’ interactions with and permeabilization of membranes. We attribute oligomer permeabilization both to cooperative electrostatic interactions through the N-terminus and interactions mediated by hydrophobic regions in the oligomer.

Fluorescent detection of coenzyme A by analyte-induced aggregation of a cationic conjugated polymer

A new cationic conjugated polymer was designed and synthesized to optically discriminate coenzyme A(CoA) among structurally similar biomolecules, ATP, ADP and AMP. The analyte-induced aggregation of the conjugated polymer by π-stacking between their main chains leads to the fluorescence quenching. Except for the similar adenosine and phosphate moieties as those in ATP, ADP and AMP, the CoA molecule also includes a long side chain that is favorable for hydrophobic interactions. Thus, CoA can form a complex with oppositely charged conjugated polymer by cooperative electrostatic and hydrophobic interactions, whereas ATP, ADP and AMP form the complexes with oppositely charged conjugated polymer mainly by electrostatic interactions. The increase of the ion strength of the assay solution screens the electrostatic attractions, and the remaining hydrophobic interactions dominate the formation of PFP-PTF/CoA complex. At this case, the quenching efficiency of PFP-PTF by CoA is much higher than that by ATP, ADP and AMP, which impart the PFP-PTF to sense CoA from these interferencing species.

Bistability of Fc-PTM-Based Dyads: The Role of the Donor Strength

Bistability of valence tautomeric donor–acceptor dyads formed by covalently linking a ferrocene-based electron-donor and the perchlorotriphenylmethyl radical, as the electron-acceptor, is tuned via a chemical modification of the ferrocene group. Specifically, the methylation of the ferrocene unit increases the strength of the donor group stabilizing the zwitterionic state in polar solvents and leading to an intriguing coexistence of neutral and zwitterionic species in solvents of intermediate polarity. Bistability in the crystalline phase is demonstrated by temperature dependent Mössbauer spectra. This complex and interesting behavior is quantitatively rationalized in the framework of a bottom-up modeling strategy. Optical spectra in solution are first analyzed to extract and parametrize an effective two-state molecular model, which is then adopted to rationalize the observed bistability in the solid state as due to cooperative electrostatic interchromophore interactions.

Nanofibers Resulting from Cooperative Electrostatic and Hydrophobic Interactions between Peptides and Polyelectrolytes of Opposite Charge

We investigated whether cationic peptides that contain hydrophobic side chains were able to stabilize themselves via hydrophobic interactions between neighboring peptide molecules upon electrostatic binding to oppositely charged polyelectrolytes. The interaction mechanism was examined through a model system consisting of the anionic polyelectrolyte alginate and the cationic decapeptide ozarelix. The interaction resulted in the formation of highly ordered complexes that were noticeable upon visual inspection. These complexes were then investigated by microscopic techniques and shown to exhibit a branched network structure. Cryogenic-temperature transmission electron microscopy (cryo-TEM) and negative staining TEM revealed that the molecular interactions between alginate and ozarelix led to the formation of nanofibers. The rodlike nanofibers had a diameter distribution of 4-8 nm. Isothermal titration calorimetry was used to determine the thermodynamic parameters of the alginate-ozarelix interaction. The binding constant was found to be on the order of 10(6) M(-1), indicating a high binding affinity. The interaction of the peptide with the polyelectrolyte triggered profound changes in the conformation of ozarelix, which was confirmed by UV spectroscopy and circular dichroism. On the basis of these experimental results, a theoretical modeling study of the alginate-ozarelix interaction was conducted to gain a better molecular-level understanding of the complex structure. It revealed that, upon binding of ozarelix to alginate, new intermolecular and intramolecular aromatic interactions between the ozarelix molecules occurred. These interactions changed the conformation of the peptide, a modification in which the aromatic side chains played a major role. Our results indicate that the cationic peptides interact with the polyanions via electrostatic interactions, but are additionally stabilized via hydrophobic interactions. This binding mode may serve as a powerful tool to extend the duration of drug release in hydrogel drug delivery systems.

Partially Glycosylated Dendrimers Block MD-2 and Prevent TLR4-MD-2-LPS Complex Mediated Cytokine Responses

The crystal structure of the TLR4-MD-2-LPS complex responsible for triggering powerful pro-inflammatory cytokine responses has recently become available. Central to cell surface complex formation is binding of lipopolysaccharide (LPS) to soluble MD-2. We have previously shown, in biologically based experiments, that a generation 3.5 PAMAM dendrimer with 64 peripheral carboxylic acid groups acts as an antagonist of pro-inflammatory cytokine production after surface modification with 8 glucosamine molecules. We have also shown using molecular modelling approaches that this partially glycosylated dendrimer has the flexibility, cluster density, surface electrostatic charge, and hydrophilicity to make it a therapeutically useful antagonist of complex formation. These studies enabled the computational study of the interactions of the unmodified dendrimer, glucosamine, and of the partially glycosylated dendrimer with TLR4 and MD-2 using molecular docking and molecular dynamics techniques. They demonstrate that dendrimer glucosamine forms co-operative electrostatic interactions with residues lining the entrance to MD-2's hydrophobic pocket. Crucially, dendrimer glucosamine interferes with the electrostatic binding of: (i) the 4′phosphate on the di-glucosamine of LPS to Ser118 on MD-2; (ii) LPS to Lys91 on MD-2; (iii) the subsequent binding of TLR4 to Tyr102 on MD-2. This is followed by additional co-operative interactions between several of the dendrimer glucosamine's carboxylic acid branches and MD-2. Collectively, these interactions block the entry of the lipid chains of LPS into MD-2's hydrophobic pocket, and also prevent TLR4-MD-2-LPS complex formation. Our studies have therefore defined the first nonlipid-based synthetic MD-2 antagonist using both animal model-based studies of pro-inflammatory cytokine responses and molecular modelling studies of a whole dendrimer with its target protein. Using this approach, it should now be possible to computationally design additional macromolecular dendrimer based antagonists for other Toll Like Receptors. They could be useful for treating a spectrum of infectious, inflammatory and malignant diseases.

TargetingBrucella melitensiswith polymeric nanoparticles containing streptomycin and doxycycline

Treatment and eradication of intracellular pathogens such as Brucella is difficult because infections are localized within phagocytic cells and most antibiotics, although highly active in vitro, do not actively pass through cellular membranes. Thus, an optimum strategy to treat these infections should address targeting of active drugs to the intracellular compartment where the bacteria replicate, and should prolong the release of the antibiotics so that the number of doses and associated toxicity can be reduced. We incorporated streptomycin and doxycycline into macromolecular nanoplexes with anionic homo- and block copolymers via cooperative electrostatic interactions among the cationic drugs and anionic polymers. The approach enabled simultaneous binding of both antibiotics into the nanoplexes, and their use resulted in an improvement in performance as compared with the free drugs. Administration of two doses of the nanoplexes significantly reduced the Brucella melitensis load in the spleens and livers of infected BALB/c mice. The nanoplexes were more effective than free drugs in the spleens (0.72-log and 0.51-log reductions, respectively) and in the livers (0.79-log and 0.42-log reductions, respectively) of the infected mice. Further research regarding the design of optimum nanoplex structures will be directed towards alterations in both the core and the shell properties to investigate the effects of the rates and pathways of entry into immune cells where the brucellae replicate.

A New Paclitaxel Formulation with a Cationic Cyclotriphosphazene

Recently the inter-polyelectrolyte complexes (IPECs) have received considerable attention. IPECs represent a special class of chemical compounds formed as a result of cooperative electrostatic interactions between cations and anions. The properties of IPECs depend strongly on the feeding ratio of the oppositely charged polyions. First studies on the utilization of IPECs were reported on gene delivery in the late 1980s. Paclitaxel is one of the most important antitumor agents currently in clinical use, since it exhibits effective antitumor activity against various cancers. However, its clinical applications are limited due to its extremely low water solubility (< 1 μg/mL) as well as its serious side effects. Therefore, a great deal of efforts has been made to overcome such problems. There are numerous studies on solubilization of paclitaxel by chemical conjugation to hydrophilic polymers or micellar encapsulation using amphiphilic polymers. However, to our knowledge, there is no report on the formulation of paclitaxel based on IPEC. In this paper we report a novel formulation method for paclitaxel by incorporation of 2'succinylpaclitaxel (2'-SPTX) into a cationic cyclotriphosphazene resulting in chemically stable micelles. A cationic and water soluble cyclotriphosphazene drug carrier bearing a hydrophilic poly(ethylene glycol) (PEG) with a molecular weight of 350 and lysine ethyl ester as cationic moiety was prepared according to the same procedure as described in our previous work with modification. Instead of an oligopeptide, lysine ethyl ester (LysEt) was employed as a cationic moiety for electrostatic interaction with anionic 2'-SPTX. The synthetic schemes for the anionic 2'-SPTX (I) and the cationic cyclotriphosphazene carrier (II) are shown along with their final ion paired IPEC in Scheme 1. The final paclitaxel IPEC could easily be prepared by a direct feeding method as follows. The 2'-SPTX (1 mg) solution in ethanol was added to the cyclotriphosphazene carrier (20 mg) in ethanol. The mixed solution was evaporated to dryness and then the residue was dissolved in distilled water. After sonication for 10 min, the resulting solution was filtered with 0.45 μm syringe filter to obtain a clear solution of the paclitaxel-loaded IPEC, which was fully characterized by multinuclear (H, P) NMR spectroscopy along with its dynamic light scattering (DLS) and critical micelle concentration (CMC) measurements. The H-NMR spectra of the paclitaxel IPEC in CDCl3 displayed in Figure 1(a) clearly show all the proton resonances both of the hydrophilic methoxy poly(ethylene glycol) (MPEG) and the LysEt group forming an ionic pair with 2'SPTX with good resolution, but in D2O most proton

Electrostatically “Patchy” Coatings via Cooperative Adsorption of Charged Nanoparticles

Solutions containing oppositely charged nanoparticles (NPs) deposit "patchy" coatings of alternating charge distribution on various types of materials, including polymers, elastomers, and semiconductors. Surface adsorption of the NPs is driven by cooperative electrostatic interactions and does not require chemical ligation or layer-by-layer schemes. The composition and the quality of the coatings can be regulated by the types, the charges, and the relative concentrations of the NPs used and by the pH. Dense coatings form on flat, curvilinear, or micropatterned surfaces, are stable against common chemicals for prolonged periods of time, and can be used in applications ranging from bacterial protection to plasmonics.

Recognition of solvent exposed protein surfaces using anthracene derived receptors

A new class of receptor is described that can selectively bind to the solvent exposed surface of proteins such as cytochrome c and lysozyme with low micromolar affinity over cytochrome c551, alpha-lactalbumin, myoglobin and RNase A, under physiologically relevant conditions (5 mM phosphate, pH 7.4). The use of anthracene as a hydrophobic scaffold allows the receptor to act as a selective chemosensor via fluorescence quenching or FRET. The study reveals that co-operative electrostatic interactions over a large surface area dominate binding. Further investigations reveal that the receptor binds to the solvent exposed heme edge of cytochrome c inhibiting its reaction with small reducing agents and validating the strategy for the disruption of protein function.

Energy versus Entropy in Cooperative Electrostatic Interactions: Comparative Study of Binding of Sodium Poly(Styrenesulfonate), Dodecylbenzenesulfonate, and Methylbenzenesulfonate to Polycations

Electrostatic coupling of sodium 4-dodecylbenzenesulfonate (DDBS), sodium 4-methylbenzene-sulfonate (MBS), and sodium poly(styrenesulfonate) (PSS) with the homopolymers of N-diallyldimethylammonium chloride (DADMAC) and chloride of 2-N-trimethylammonioethylmethacrylate (TMAEMA) or their copolymers with neutral hydrophilic groups were studied using 1H and 35Cl (single- and double-quantum) NMR, relaxations, and pulsed field-gradient (PFG) diffusivity measurements. Both DDBS and PSS were found to react cooperatively with the polycations, in contrast to MBS. However, PSS binds more strongly to the polycations and is thus able to substitute DDBS in its complex with an appropriate polycation. The binding isotherms of DDBS and MBS with DADMAC polymer agree well with the theoretical model suggested by Kuhn, Levin, and Barbosa, providing that the hydrophobic energy parameter χ has the value −3.5kBT for DDBS and 0.0 for MBS. Energy stabilization by hydrophobic interactions is thus suggested to be the determining factor in the cooperative binding of DDBS. This conclusion is supported by clusters of bound DDBS with a mean length of about 30 molecules in its complex with DADMAC polymer, which were indirectly found using 35Cl T23 relaxation. In conclusion, the interaction of DDBS with polycations is suggested to be an example of cooperative electrostatic binding with unfavorable entropy but strong energy stabilization by, e.g., hydrophobic interactions. Entropy change due to liberation of bound counterions into a disordered state, found by us earlier1-3 to be operative in the couplings of complementary polyions, is thus not the only possible driving force of cooperative electrostatic interactions.

The role of a basic amino acid cluster in target site selection and non-specific binding of bZIP peptides to DNA.

The ability of a transcription factor to locate and bind its cognate DNA site in the presence of closely related sites and a vast array of non-specific DNA is crucial for cell survival. The CREB/ATF family of transcription factors is an important group of basic region leucine zipper (bZIP) proteins that display high affinity for the CRE site and low affinity for the closely related AP-1 site. Members of the CREB/ATF family share in common a cluster of basic amino acids at the N-terminus of their bZIP element. This basic cluster is necessary and sufficient to cause the CRE site to bend upon binding of a CREB/ATF protein. The possibility that DNA bending and CRE/AP-1 specificity were linked in CREB/ATF proteins was investigated using chimeric peptides derived from human CRE-BP1 (a member of the CREB/ATF family) and yeast GCN4, which lacks both a basic cluster and CRE/AP-1 specificity. Gain of function and loss of function experiments demonstrated that the basic cluster was not responsible for the CRE/AP-1 specificity displayed by all characterized CREB/ATF proteins. The basic cluster was, however, responsible for inducing very high affinity for non- specific DNA. It was further shown that basic cluster-containing peptides bind non-specific DNA in a random coil conformation. We postulate that the high non- specific DNA affinities of basic cluster-containing peptides result from cooperative electrostatic interactions with the phosphate backbone that do not require peptide organization.

Nonthermally Accessible Phase for CO on the Si(100) Surface

A new phase $\mathrm{BT}\ensuremath{-}\mathrm{C}\mathrm{O}$ on Si(100), not accessible with thermal CO (which leads to the $T\ensuremath{-}\mathrm{C}\mathrm{O}$ phase), has been observed using an energetic molecular beam of CO and characterized by first principles quantum chemical methods. The $\mathrm{BT}$ phase is composed of bridge $(B)$ and terminal $(T)$ sites; it is driven and stabilized by cooperative electrostatic interactions that result because $B$ $(T)$ binding leads to the transfer of charge away from (toward) the surface. Desorption of CO from the $B$ site proceeds through the $T$ configuration.

Effect of charge separation on methyl orange homologue-ionene interaction.

Methyl Orange and Ethyl Orange were used in the study of the effects of charge separation of polyionic amine (ionene) and hydrophobicity of both the dye and ionene on the interaction between the anionic dye and the cationic polymer. The unit structure of x-y ionene was _??_Br-(CH3)2N+(CH2)xN+ (CH3)2(CH2)yBr-_??_. The x-y for seven ionenes used were 3-3, 3-4, 3-6, 3-8, 3-12, 6-6, and 6-12. The amounts of the dye bound to the ionene were determined by means of equilibrium dialysis procedure. One dye molecule was found to occupy one cationic charged site of ionene. The binding occurred due to the positively cooperative electrostatic and hydrophobic interactions. The results were analysed according to the procedure of McGhee and von Hippel. The interaction constants differed widely from one ionene to another ionene. The binding of the dye to the ionene depended strongly on the charge separation and hydrophobicity of both the dye and the ionene. The entropy change of the interaction process suggested strongly that the dye stacked on the polymer.