Interaction of Ethylene Oxide−Propylene Oxide Copolymers with Ionic Surfactants Studied by Calorimetry: Random versus Block Copolymers

Synergistic enhancement in the drug sequestration power and reduction in the cytotoxicity of surfactants

Surfactants in supramolecular assemblies show a significant increase in their drug sequestration power with a remarkably reduced cytotoxicity.

Interaction of cationic dodecyl-trimethyl-ammonium bromide with oxy-HbGp by isothermal titration and differential scanning calorimetric studies: Effect of proximity of isoelectric point

In this work, isothermal titration and differential scanning calorimetric methods, in combination with pyrene fluorescence emission and dynamic light scattering have been used to investigate the interaction of dodecyltrimethylammonium bromide (DTAB) with the giant extracellular Glossoscolex paulistus hemoglobin (HbGp) in the oxy-form, at pH values around the isoelectric point (pI ≈ 5.5). Our ITC results have shown that the interaction of DTAB with the hemoglobin is more intense at pH 7.0, with a smaller cac (critical aggregation concentration) value. The increase of protein concentration does not influence the cac value of the interaction, at both pH values. Therefore, the beginning of the DTAB-oxy-HbGp premicellar aggregates formation, in the cac region, is not affected by the increase of protein concentration. HSDSC studies show higher Tm values at pH 5.0, in the absence and presence of DTAB, when compared with pH 7.0. Furthermore, at pH 7.0, an aggregation process is observed with DTAB in the range from 0.75 to 1.5 mmol/L, noticed by the exothermic peak, and similar to that observed for pure oxy-HbGp, at pH 5.0, and in the presence of DTAB. DLS melting curves show a decrease on the hemoglobin thermal stability for the oxy-HbGp-DTAB mixtures and formation of larger aggregates, at pH 7.0. Our present data, together with previous results, support the observation that the protein structural changes, at pH 7.0, occur at smaller DTAB concentrations, as compared with pH 5.0, due to the acidic pI of protein that favors the oxy-HbGp-cationic surfactant interaction at neutral pH.

Use of isothermal titration calorimetry to study surfactant aggregation in colloidal systems

BACKGROUND

Isothermal titration calorimetry (ITC) is a general technique that allows for precise and highly sensitive measurements. These measurements may provide a complete and accurate thermodynamic description of association processes in complex systems such as colloidal mixtures.

SCOPE OF THE REVIEW

This review will address uses of ITC for studies of surfactant aggregation to form micelles, with emphasis on the thermodynamic studies of homologous surfactant series. We will also review studies on surfactant association with polymers of different molecular characteristics and with colloidal particles.

GENERAL SIGNIFICANCE

ITC studies on the association of different homologous series of surfactants provide quantitative information on independent contribution from their apolar hydrocarbon chains and polar headgroups to the different thermodynamic functions associated with micellization (Gibbs energy, enthalpy and entropy). Studies on surfactant association to polymers by ITC provide a comprehensive description of the association process, including examples in which particular features revealed by ITC were elucidated by using ancillary techniques such as light or X-ray scattering measurements. Examples of uses of ITC to follow surfactant association to biomolecules such as proteins or DNA, or nanoparticles are also highlighted. Finally, recent theoretical models that were proposed to analyze ITC data in terms of binding/association processes are discussed.

MAJOR CONCLUSIONS

This review stresses the importance of using direct calorimetric measurements to obtain and report accurate thermodynamic data, even in complex systems. These data, whenever possible, should be confirmed and associated with other ancillary techniques that allow elucidation of the nature of the transformations detected by calorimetric results, providing a complete description of the process under scrutiny.

Block versus Random Amphiphilic Glycopolymer Nanopaticles as Glucose-Responsive Vehicles

To explore the effect of polymer structure on their self-assembled aggregates and their unique characteristics, this study was devoted to developing a series of amphiphilic block and random phenylboronic acid-based glycopolymers by RAFT polymerization. The amphiphilic glycopolymers were successfully self-assembled into spherically shaped nanoparticles with narrow size distribution in aqueous solution. For block and random copolymers with similar monomer compositions, block copolymer nanoparticles exhibited a more regular transmittance change with the increasing glucose level, while a more evident variation of size and quicker decreasing tendency in I/I0 behavior in different glucose media were observed for random copolymer nanoparticles. Cell viability of all the polymer nanoparticles investigated by MTT assay was higher than 80%, indicating that both block and random copolymers had good cytocompatibility. Insulin could be encapsulated into both nanoparticles, and insulin release rate for random glycopolymer was slightly quicker than that for the block ones. We speculate that different chain conformations between block and random glycopolymers play an important role in self-assembled nanoaggregates and underlying glucose-sensitive behavior.

Calorimetric and Light Scattering Investigations of the Transition from Spherical to Wormlike Micelles of C₁₄TAB Triggered by Salicylate

Although wormlike micelles (WLM) were first described more than 30 years ago, many aspects of their formation process are still unclear. Herein, a systematic experimental investigation of the process for wormlike micelle (WLM) formation in mixtures of tetradecyltrimethylammonium bromide (C14TAB) and salicylate (2-hydroxybenzoate) was carried out. This system was used as a model to investigate the conditions for the formation of the giant aggregate. For comparison, the other two isomers of salicylate (3- and 4-hydroxybenzoate) were also investigated, once in these cases wormlike micelles are not formed. The studies were based on calorimetric titration, static light scattering, and rheological measurements. Enthalpy changes upon titration of C14TAB into 2-hydroxybenzoate solutions revealed a highly cooperative and exothermic process that was associated with micelle growth. The size of the aggregates, obtained by static light scattering measurements, confirms the shape transition. In addition, the correlation of these two sets of results with measurements of micelle charge surface indicates that this transition occurs around the point of charge neutralization.

How does the ethoxylated grafting of polyelectrolytes affect the self-assembly of polyanion-cationic surfactant complex salts?

A cationic surfactant and different anionic copolymers randomly grafted with side chains of ethylene oxide were used to prepare stoichiometric complex salts. Variations in the length or proportion of side chains were shown to be responsible for affecting the surfactant phase behavior in water, resulting in the observation of a number of structures characterized by small angle X-ray scattering measurements, including a hierarchical micellar system and different liquid-crystalline phases. Additionally, although aqueous mixtures of stoichiometric complex salts usually phase separate, the presence of a sufficiently high weight fraction of ethylene oxide side chains can enhance the solubility of the complex salt aggregates in water over a wide range of concentration. Moreover, a dispersion of an isotropic concentrated solution of complex salts is formed at higher temperatures in a reversible process. In summary, this study proves the importance of the polyion structure for tuning the properties of systems of complex salts.

Polymers containing hydroxamate groups: nanoreactors for hydrolysis of phosphoryl esters

A polyhydroxamicalkanoate (PHA) polymer containing the functional groups hydroxamic acid and carboxylic acid with the ability to accelerate dephosphorylation reactions is proposed. The methodology used to prepare this polymer favored the position of the two functional groups next to each other, which allows for the cooperativity between these groups. This cooperative effect has an important role when one wants to mimic enzymes. The catalytic effect promoted by the polymer was evaluated on the cleavage of the bis(2,4-dinitrophenyl) phosphate (BDNPP) and diethyl 2,4-dinitrophenyl phosphate (DEDNPP) esters. Indeed, PHA was very efficient and promiscuous because it increased the rate of both reactions by a factor of up to 10(6)-fold. Isothermal titration calorimetry (ITC) experiments showed that the presence of PHA aids the formation of cetyltrimethylammonium bromide (CTABr) micelles. Thus, the effect of the cationic surfactant CTABr on the dephosphorylation of BDNPP by PHA was also investigated, and it was observed that, when CTABr is added to PHA, the reaction is ca. 15-fold faster compared to the reaction when only PHA is present.