Complex Formation between Dodecylpyridinium Chloride and Multicharged Anionic Planar Substances

Abstract

The complex formation between dodecylpyridinium chloride (DPC) and multicharged anionic planar substances, 14 azo dyes and 3 benzene- or naphthalenesulfonates, has been studied by the potentiometric titration using a surfactant selective electrode. The agreement between the observed maximum binding number and the number of anionic charges (n) on dye molecules showed n:1 complex formation. The binding isotherms were found to be composed of two types of binding; one is the noncooperative binding observed at low surfactant concentrations and the other is the cooperative binding at the higher concentrations. The microscopic binding constant for the noncooperative binding was found to take the values in the range of 50-200 mol(-)(1) dm(3) for many of the substances, but, takes more large values up to 2500 mol(-)(1) dm(3) for the substances which have a large hydrophobic part or the structure of separate hydrophobic and hydrophilic regions. A multiple regression analysis showed that the data of the corresponding standard free energy change of binding were well interpreted by the equation (in unit of kJ mol(-)(1)) DeltaG degrees = - 5.85 log P(S) - 1.68 log P(D) - 2.12z + 28.4, where P(S) and P(D) are the partition coefficients of the surfactants and planar substances in the 1-octanol/water system and z is the number of anionic charges on the planar molecules. At the beginning of the cooperative binding, precipitate formation was observed for almost all of the present systems. Among these, some of the dyes having the structure of separate hydrophobic and hydrophilic regions formed a needlelike crystal, which was accompanied by a hysteresis phenomenon in the binding isotherm. The stable complex formation by both the hydrophobic and electrostatic interactions between the surfactant and the planar substances was found to be important for the crystal formation. Depending on the manner of arrangement of the charged groups on the planar substances, the origin of the binding cooperativity was ascribed to the interactions between surfactants bound to one planar-substance molecule or to the association of the complexes. It was also found that the present small binding systems are useful as the model of ligand binding to protein local structures.

Molecular Structure Encodes Nanoscale Assemblies: Understanding Driving Forces in Electrostatic Self-Assembly

“…After the initial exothermal data point, which can be attributed to adsorption of the dye molecules to the ITC cell wall, the dilution is almost athermal; i.e., no dye self-aggregation occurs. The reason for this can be found in the structure of the molecule, as in general azo dye molecules with separated hydrophilic and hydrophobic or π–π-interacting moieties are more prone to self-interact . The benzene moiety in RAcA is sufficient to enable the dye to develop mutual interactions, whereas NHSSuA does have a charged sulfonate group on the benzene moiety and a charged group on the naphthalene moiety located near the center of the molecule.…”

“…The reason for this can be found in the structure of the molecule, as in general azo dye molecules with separated hydrophilic and hydrophobic or πÀπ-interacting moieties are more prone to self-interact. 72 The benzene moiety in RAcA is sufficient to enable the dye to develop mutual interactions, whereas NHSSuA does have a charged sulfonate group on the benzene moiety and a charged group on the naphthalene moiety located near the center of the molecule. Therefore, no efficient interaction of the aromatic moieties is possible, as electrostatic repulsion is stronger than for RAcA due to this unfavorable geometry.…”

“…That is as adjacent dye binding is favored in a cooperative binding process for the first set of dyes, which is most likely not present for this second class of dyes. 72 Further, the initial monovalent counterions have to be displaced from the dendrimer, which is only possible for dye counterions with high binding strengths as the buffer leads to a hundredfold excess of the formiate anions. 74 Thus, the counterion exchange of multivalent dye ions for monovalent ions is not expected to be complete for dyes with low binding strengths.…”

Influencing Particle Size and Stability of Ionic Dendrimer−Dye Assemblies

“…We found this to lead to elongated structures for Ar26 and isotropic (core−shell) or flatlike (vesicle wall) structures for Ar27. Interestingly, it was found in a very different system based on a dye−surfactant combination that elongated structures were formed only if the hydrophobic moiety of the azo dye is spatially separated from the hydrophilic part of the molecule . The structural difference in the dye molecules and thereby the different interplay of interactions thus represents a code for a particular assembly shape.…”

Thermal Behavior of Dodecylpyridinium-Based Surfactant Salts with Varied Anionic Constituent

“…1 Exploration of new amphiphilic building blocks is an important task since this makes it possible to diversify supramolecular architectures and physicochemical properties of systems. 1 surfactant complexes in forms of stretched networks, 22 bind with three dimensional coordination polymers and anionic planar substances such as dyes, 17,23 naphthalene or benzenesulfonates. 23 Besides this, they are also used for making novel surfactants, 24-29 very often in their catanionic form that could be used in various applications mentioned previously.…”