The formation of host–guest complexes between surfactants and cyclodextrins

Cyclodextrins are able to act as host molecules in supramolecular chemistry with applications ranging from pharmaceutics to detergency. Among guest molecules surfactants play an important role with both fundamental and practical applications. The formation of cyclodextrin/surfactant host–guest compounds leads to an increase in the critical micelle concentration and in the solubility of surfactants. The possibility of changing the balance between several intermolecular forces, and thus allowing the study of, e.g., dehydration and steric hindrance effects upon association, makes surfactants ideal guest molecules for fundamental studies. Therefore, these systems allow for obtaining a deep insight into the host–guest association mechanism. In this paper, we review the influence on the thermodynamic properties of CD–surfactant association by highlighting the effect of different surfactant architectures (single tail, double-tailed, gemini and bolaform), with special emphasis on cationic surfactants. This is complemented with an assessment of the most common analytical techniques used to follow the association process. The applied methods for computation of the association stoichiometry and stability constants are also reviewed and discussed; this is an important point since there are significant discrepancies and scattered data for similar systems in the literature. In general, the surfactant–cyclodextrin association is treated without reference to the kinetics of the process. However, there are several examples where the kinetics of the process can be investigated, in particular those where volumes of the CD cavity and surfactant (either the tail or in special cases the head group) are similar in magnitude. This will also be critically reviewed

Effect of non-associated electrolyte solutions on the behaviour of poly(vinyl alcohol)-based hydrogels

The aim of this paper is to present the behaviour of the poly(vinyl alcohol) hydrogels [PVA-HG] in sodium and potassium chlorides aqueous solutions, due to their interactions. The tested [PVA-HG]-s have been obtained by repeated freezing and thawing cycles. White, heterogeneous hydrogels have been obtained. These hydrogels exhibit a mechanical active behaviour at their contact with electrolytes aqueous solutions, manifested by important changing in mass, volume and density of the hydrogel samples. These modifications could be explained by water elimination from the hydrogels that initially reached the equilibrium of swelling. The kinetic of the water desorption and the reversibility of this process, have been studied and some of the factors that influence this behaviour have been evidenced. The sensitivity of PVA hydrogels to electrolyte nature and concentration could be used in sensors design and also could explain some aspects of electrolytes diffusion through PVA membranes and targeted drugs delivery.http://www.sciencedirect.com/science/article/B6TWW-4MM8BMS-3/1/8bdd4617945ac22704313f4540917a4

Thermodynamic analysis of unimer-micelle and sphere-to-rod micellar transitions of aqueous solutions of sodium dodecylbenzenesulfonate

Temperature dependence of specific conductivity of sodium dodecylbenzenesulfonate (NaDBS) aqueous solutions was analyzed. Two breaks on the plot appeared for all temperature, which suggest two micellar transitions. This has been corroborated by surface tension measurements. The first transition concentration occurs at the critical micelle concentration (CMC), whilst the second critical concentration (so-called transition micellar concentration, TMC) is due to a sphere-to-rod micelles transition. The dependence of CMC and TMC on the temperature allows the computation of the corresponding thermodynamic functions: Gibbs free energy, enthalpy and entropy changes. For the CMC, enthalpy and entropy increments were found that decrease with the temperature values. However, an anomalous behavior was obtained for the TMC, where both ΔS0 and ΔH0 values raised with the temperature increase. However, for both transitions, an (enthalpy + entropy) compensation is observed. These results will be compared with similar systems reported in the literature

Plasmid DNA hydrogels for biomedical applications

In the last few years, our research group has focused on the design and development of plasmid DNA (pDNA) based systems as devices to be used therapeutically in the biomedical field. Biocompatible macro and micro plasmid DNA gels were prepared by a cross-linking reaction. For the first time, the pDNA gels have been investigated with respect to their swelling in aqueous solution containing different additives. Furthermore, we clarified the fundamental and basic aspects of the solute release mechanism from pDNA hydrogels and the significance of this information is enormous as a basic tool for the formulation of pDNA carriers for drug/gene delivery applications. The co-delivery of a specific gene and anticancer drugs, combining chemical and gene therapies in the treatment of cancer was the main challenge of our research. Significant progresses have been made with a new p53 encoding pDNA microgel that is suitable for the loading and release of pDNA and doxorubicin. This represents a strong valuable finding in the strategic development of systems to improve cancer cure through the synergetic effect of chemical and gene therapy

Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.http://www.sciencedirect.com/science/article/B6TWW-4DVBFCN-7/1/63e48f8aac1513c35feeaa6c746621e

Enhancing lignin dissolution and extraction: the effect of surfactants

The dissolution and extraction of lignin from biomass represents a great challenge due to the complex structure of this natural phenolic biopolymer. In this work, several surfactants (i.e., non-ionic, anionic, and cationic) were used as additives to enhance the dissolution efficiency of model lignin (kraft) and to boost lignin extraction from pine sawdust residues. To the best of our knowledge, cationic surfactants have never been systematically used for lignin dissolution. It was found that ca. 20 wt.% of kraft lignin is completely solubilized using 1 mol L-1 octyltrimethylammonium bromide aqueous solution. A remarkable dissolution efficiency was also obtained using 0.5 mol L-1 polysorbate 20. Furthermore, all surfactants used increased the lignin extraction with formic acid, even at low concentrations, such as 0.01 and 0.1 mol L-1. Higher concentrations of cationic surfactants improve the extraction yield but the purity of extracted lignin decreases.FCT: UID/QUI/00313/2020, PTDC/AGR-TEC/4814/2014, PTDC/ASP-SIL/30619/2017, UIDB/05183/2020, CEECIND/01014/2018, SFRH/BD/132835/2017, COMPETEinfo:eu-repo/semantics/publishedVersio

PVA−DNA Cryogel Membranes: Characterization, Swelling, and Transport Studies

Double-stranded (ds) DNA from salmon testes has been incorporated into PVA hydrogels obtained by a technique of repeated freezing and thawing. The cryogels obtained are free of potential toxic species like chemical cross-linkers, and consequently, they can be used in pharmaceutical or medical applications. These cryogels show a good mechanical resistance and a white and opaque appearance caused by a heterogeneous porous structure. Encapsulated DNA molecules can be in a compacted or an extended conformation in the PVA matrix and can be controlled by tailoring the degree of crystallinity of the PVA network; this is supported by fluorescence microscopy and UV and FTIR spectroscopic studies. The two forms of encapsulated DNA were observed for different types of matrixes: an extended one in a more crystalline network and a globular one in a more amorphous one. Different associations of base pairs have also been observed. PVA cryogel crystallinity could be tailored by the cryogel contact with different salt solutions. Cryogel surface (scanning electron microscopy) and bulk morphology (porosimetry), swelling, DNA retention, and delivery kinetics have also been studied. All these investigations clearly show strong interactions between PVA and DNA

Synthesis and characterization of new aromatic polyamides bearing crown ethers and acyclic ethylene oxide units in the pendant structure. III. Benzo-18-crown-6 systems and their open-chain counterparts

We report the synthesis and characterization of 10 novel polyamides containing the benzo-18-crown-6 subunit and its dipodal counterpart, along with their properties, and a comparison with homologous polyamides bearing benzo-12-crown-4, benzo-15-crown-5, and the corresponding dipodal systems. The anomalous polymerization of some of the diacid monomers, that leads to insoluble gels under standard Yamazaki polymerization conditions, is described. The gel formation has been attributed to the threading of cyclic oligoamides with a growing polyamide chain to yield rotaxanes, polyrotaxanes, catenanes, or polycatenanes. Polyamide macrocycles have been characterized with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A route to avoid gel formation, consisting of a lower initial monomer concentration, is also described, along with the polymer properties of the polyamides obtained, including the chemical characterization, mechanical behavior, water sorption, morphology, diffusion data, and permeability of membranes prepared with these polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6252-6269, 200

Diffusion Coefficients of Copper Chloride in Aqueous Solutions at 298.15 K and 310.15 K

Mutual diffusion coefficients (interdiffusion coefficients) and molar conductivities have been measured for copper(II) chloride in water at 298.15 K and 310.15 K at concentrations between 0.005 mol·dm-3 and 0.05 mol·dm-3. The diffusion coefficients were measured using a conductometric cell. The experimental data are discussed on the basis of the Onsager−Fuoss model. The Nernst diffusion coefficients derived from diffusion (1.297 × 10-9 and 1.690 × 10-9) m2·s-1 and from conductance (1.282 × 10-9 and 1.663 × 10-9) m2·s-1 at two temperatures (298.15 K and 310.15 K, respectively) are in good agreement

Drug release mechanisms of chemically cross-linked albumin microparticles: effect of the matrix erosion

Albumin (BSA) microparticles were developed as a biotechnological alternative for drug delivery. Vitamin B12 (Vit-B12) was used as a model drug. The microparticles were obtained from maleic anhydride-functionalized BSA and N′,N′-dimethylacrylamide (DMAAm) in a W/O emulsion without and with PVA. The microparticles produced at 15 min of stirring without PVA showed the best results in terms of size, homogeneity, and sphericity. In such a case, BSA played a role as a surface active agent, replacing PVA. For longer stirring times, BSA was unable to act as an emulsifier. These microparticles showed an uncommon release profile, consisting of a two-step release mechanism, at the pH range studied. Considering that a two-step release mechanism is occurring, the experimental data were adjusted by applying modified power law and Weibull equations in order to describe release mechanism n and release rate constant k, respectively. Each one of the release stages was related to a specific value of n and k. The second stage was driven by a super case II transport mechanism, as a result of diffusion, macromolecular relaxation, and erosion. A third model, described by Hixson–Crowell, confirmed the erosion mechanism. Vit-B12 diffusion kinetics in aqueous solutions (i.e., without the microparticles) follows a one-step process, being k dependent on the pH, confirming that the two-step release mechanism is a characteristic profile of the developed microparticles. The microparticles released only 2.70% of their initial drug load at pH 2, and 58.53% at pH 10