A Promising Compound for Green Multiresponsive Materials Based on Acyl Carrier Protein.

A gel that exhibits intrinsically multiple-responsive behavior was prepared from an oligopeptide and studied. ACP(65-74) is an active decapeptide fragment of acyl carrier protein. We investigated 3% w/v ACP(65-74)-NH2 self-healing physical gels in water, glycerol carbonate (GC), and their mixtures. The morphology was investigated by optical, birefringence, and confocal laser scanning microscopy, circular dichroism, Fourier transform infrared, and fluorescence spectroscopy experiments. We found that all samples possess pH responsiveness with fully reversible sol-to-gel transitions. The rheological properties depend on the temperature and solvent composition. The temperature dependence of the gels in water shows a peculiar behavior that is similar to that of thermoresponsive polymer solutions. The results reveal the presence of several ß-sheet structures and amyloid aggregates, offering valuable insights into the fibrillation mechanism of amyloids in different solvent media.

The Lyotropic Nature of Halates: An Experimental Study.

Unlike halides, where the kosmotropicity decreases from fluoride to iodide, the kosmotropic nature of halates apparently increases from chlorate to iodate, in spite of the lowering in the static ionic polarizability. In this paper, we present an experimental study that confirms the results of previous simulations. The lyotropic nature of aqueous solutions of sodium halates, i.e., NaClO3, NaBrO3, and NaIO3, is investigated through density, conductivity, viscosity, and refractive index measurements as a function of temperature and salt concentration. From the experimental data, we evaluate the activity coefficients and the salt polarizability and assess the anions' nature in terms of kosmotropicity/chaotropicity. The results clearly indicate that iodate behaves as a kosmotrope, while chlorate is a chaotrope, and bromate shows an intermediate nature. This experimental study confirms that, in the case of halates XO3-, the kosmotropic-chaotropic ranking reverses with respect to halides. We also discuss and revisit the role of the anion's polarizability in the interpretation of Hofmeister phenomena.

Selenated and Sulfurated Analogues of Triacyl Glycerols: Selective Synthesis and Structural Characterization.

The synthesis of sulfur- and selenium-containing isosters of triacyl glycerols is herein described. Regioselective fluoride-induced ring-opening reaction of suitable substituted thiiranes with bis(trimethyl)silyl selenide, followed by in situ S- and Se-acylation with fatty acid acyl chlorides, enables the one pot synthesis of mixed chalcogeno esters in good yield. The key step of this methodology is the functionalization of S-Si and Se-Si bonds of silyl chalcogenides, generated in situ under mild conditions. A related procedure for the synthesis of functionalized selenides, bearing two thiol ester and two ester moieties, was also developed through a fine tuning of the reaction conditions. The physico-chemical properties of these novel fatty acid chalcogeno esters have been investigated through DSC, SAXS, WAXS, FTIR and polarized optical microscopy, and compared to those of the common triglycerides in order to highlight the effect of the replacement of oxygen with other chalcogen elements in the polar head of the lipid.

Organogels from Double-Chained Vitamin†C Amphiphilic Derivatives.

The syntheses and physicochemical characterization of double-chained amphiphilic compounds obtained from vitamin C are reported: dialkanoyl-5,6-O-ascorbic acid esters (Di-ASCn, n=8, 10, and 12). The acetyl-5-dodecanoyl-6-ascorbic acid ester is synthesized and investigated for comparison. These products are quite insoluble in water and in polar solvents, although they form homogeneous dispersions in cyclohexane. Upon cooling, these dispersions turn into a gel-like phase. Differential scanning calorimetry, FTIR spectroscopy, and small- and wide-angle X-ray scattering experiments are performed to investigate the properties of pure solids and their liquid dispersions. Di-ASCn retain the same redox properties of the parent molecule and represent a valid candidate for the production of nanosized protective carriers for valuable guests that are sensitive to oxidative radical attack. Moreover, the contribution of the vitamin C hydroxyl group in position 5 to the overall hydration properties of single- and double-chained amphiphilic derivatives is discussed.

Specific Anion Effects on the Kinetics of Iodination of Acetone.

Specific ion effects on the kinetics of iodination of acetone in an acidic medium are investigated by UV/Vis spectrophotometry as a function of nature of the acid and temperature. The results indicate that the order of the reaction with respect to acetone is practically unaffected by the composition of the acid while the value of the mixed constant k1 K increases according to the sequence HBr

Phase transitions in hydrophobe/phospholipid mixtures: hints at connections between pheromones and anaesthetic activity.

The phase behavior of a mixture of a typical insect pheromone (olean) and a phospholipid (DOPC)/water dispersion is extensively explored through SAXS, NMR and DSC experiments. The results mimic those obtained with anaesthetics in phospholipid/water systems. They also mimic the behavior and microstructure of ternary mixtures of a membrane mimetic, bilayer-forming double chained surfactants, oils and water. Taken together with recent models for conduction of the nervous impulse, all hint at lipid involvement and the underlying unity in mechanisms of pheromone, anaesthetic and hydrophobic drugs, where a local phase change in the lipid membrane architecture may be at least partly involved in the transmission of the signal.

Structure and rheology of gel nanostructures from a vitamin C-based surfactant.

The structure and rheology behaviour of gels produced by water dispersions of a vitamin C-derived surfactant (ascorbyl-6-O-dodecanoate) were investigated by means of SAXS and rheology experiments for the first time. The gel state is formed upon heating and is due to an anisotropic expansion of the tightly compact lamellar structure. The phase transition involves primarily the melting of the alkyl chains and a significant increment in the interlamellar water layer. In particular, our results show that in the gel the hydrophobic chains are in a liquid-like state, as in the core of a micelle, while the head groups release their acidic proton, become negatively charged and determine the onset of strong electrostatic interactions between facing lamellae. The full hydration of the anionic head groups and the uptake of a significant amount of water increase the interlamellar thickness and stabilise the gel structure. Rheology and SAXS measurements together provide an updated picture for the gel state. Moreover, for the first time we show the presence of a concentration threshold, above which the self-assembled aggregates interact more strongly and deplete some of the water that is retained in the interlamellar region.

Specific anion effects on urease activity: A Hofmeister study.

The effects of a range of electrolytes on the hydrolysis of urea by the enzyme urease is explored. The autocatalytic behavior of urease in unbuffered solutions and its pH clock reactions are studied. The concentration dependence of the experimental variables is analyzed in terms of specific ion-enzyme interactions and hydration. The results offer insights into the molecular mechanisms of the enzyme, and on the nature of its interactions with the electrolytes. We found that urease can tolerate mild electrolytes in its environment, while it is strongly inhibited by both strong kosmotropic and strong chaotropic anions. This study may cast light on an alternative therapy for Helicobacter pylori infections and contribute to the design of innovative materials and provide new approaches for the modulation of the enzymatic activity.

Synthesis of Zeolitic Imidazolate Framework-8 Using Glycerol Carbonate.

In this study, we show that glycerol carbonate (GlyC), a bio-based derivative of glycerol, can be used as a suitable green solvent for the synthesis of metal-organic frameworks (MOFs). In particular, a zinc-based zeolitic imidazolate framework-8 (ZIF-8) was synthesized by exploring several different experimental conditions (in terms of temperature, reaction time, and reactants' concentrations) to find that the yield of the reaction and the quality of the products, measured in terms of crystallinity, surface area, and porosity, were in line with those obtained in the most commonly (non-green) used solvents. GlyC was also found to be reusable for several cycles, maintaining the same original quality as a solvent for the synthesis. Finally, some indicators for the assessment of the greenness of a process (E-factor and PMI) revealed a milder environmental impact of GlyC with respect to other solvents.

Physicochemical characterization of green sodium oleate-based formulations. Part 3. Molecular and collective dynamics in rodlike and wormlike micelles by proton nuclear magnetic resonance relaxation.

HYPOTHESIS: Sodium oleate (NaOL) self-aggregates in water forming rodlike micelles with different length depending on NaOL concentration; when KCl is added wormlike micelles form, which entangle giving rise to a viscoelastic dispersion. It is expected that aggregates with different size and shape exhibit different internal and overall molecular motions and collective dynamics. EXPERIMENTS: Two low viscosity NaOL/water and two viscoelastic NaOL/KCl/water formulations with different NaOL concentration (0.23 and 0.43 M) were investigated by 1H fast field cycling NMR relaxometry over broad temperature and Larmor frequency ranges, after a first screening by 1H and 13C NMR spectroscopy at high frequency. FINDINGS: The analysis of the collected data indicated that fast conformational isomerization and rotation of NaOL about its long molecular axis and lateral diffusion of NaOL around the axis of the cylindrical aggregates are slightly affected by the aggregate shape and length. On the other hand, fluctuations of the local order director are quite different in the fluid and viscoelastic systems, reflecting the shape and size of the aggregates. Quantitative information was obtained on activation energy for fast internal and overall motions, correlation times and activation energy for lateral diffusion, and coherence length for collective order fluctuations.

Specific ion effects on copper electroplating.

The main goal of this work is to open new perspectives in the field of electrodeposition and provide green alternatives to the electroplating industry. The effect of different anions (SO42-, ClO3-, NO3-, ClO4-, BF4-, PF6-) in solution on the electrodeposition of copper was investigated. The solutions, containing only the copper precursor and the background electrolyte, were tailored to minimize the environmental impact and reduce the use of organic additives and surfactants. The study is based on electrochemical measurements carried out to verify that no metal complexation takes place. We assessed the nucleation and growth mechanism, we performed a morphological characterization through scanning electron microscopy and deposition efficiency by measuring the film thickness through X-ray fluorescence spectroscopy. Significant differences in the growth mechanism and in the morphology of the electrodeposited films, were observed as a function of the background electrolyte.

Physicochemical characterization of green sodium oleate-based formulations. Part 2. Effect of anions.

HYPOTHESIS: In Part 1 of this work we reported the behavior of a moderately concentrated dispersion of sodium oleate (NaOL) in water that produces elongated wormlike micelles (WLMs). Prompted by the striking effect induced by adding potassium chloride to the original NaOL dispersion, here we investigate the effect of different anions (with fixed cation) on NaOL or KOL-based hydrogels upon addition of different strong electrolytes. The interest in these investigations relies on the fact that they are among the best candidates for the production of eco-friendly stimulus-responsive materials. EXPERIMENTAL: The thermal and rheological properties of a 0.43 M dispersion of NaOL or KOL in water were investigated by steady-state and oscillatory rheology, and DSC experiments in the presence of different potassium or sodium salts at the same concentration (0.54 m), respectively. FINDINGS: This paper highlights the occurrence of a Hofmeister phenomenon in the case of oleate-based WLMs and illustrates the remarkable effect induced by kosmotropic and chaotropic anions in terms of rheology and hydration of the rod-like nanoassemblies, that reflect the different ion adsorption at the WLM interface. We also discuss the different ion condensation of sodium and potassium ions at the interface that can lead to a significant change in the curvature of the elongated rods.

Effect of the Polarity of Solvents on Periodic Precipitation: Formation of Hierarchical Revert Liesegang Patterns.

Liesegang pattern (LP) is one example of self-organized periodic precipitation patterns in nonequilibrium systems. Several studies have demonstrated that the LP morphology can track physicochemical environmental conditions (e.g., temperature); however, the polarity effect has not been explored to date. In this study, a copper chromate system is used to reveal the impact of solvent polarity on the evolving LP structure using water/organic solvent mixtures. In the typical case of using water/dimethyl sulfoxide (DMSO) mixtures, two drastic changes in LP morphology with increasing DMSO contents were found: (i) increasing frequency of the original structure and (ii) formation of a hierarchical pattern with the appearance of another, lower-frequency structure. Furthermore, the simulation model operating with a bimodal size distribution, allowing both homogeneous and heterogeneous precipitations showed good agreement with the experimental results. Therefore, this study demonstrated that LP can be tailored by solvent polarity and can be used for designing hierarchical precipitation patterns in a straightforward manner.

Hofmeister effects: interplay of hydration, nonelectrostatic potentials, and ion size.

The classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloids, and corresponding theories of electrolytes, are unable to explain ion specific forces between colloidal particles quantitatively. The same is true generally, for surfactant aggregates, lipids, proteins, for zeta and membrane potentials and in adsorption phenomena. Even with fitting parameters the theory is not predictive. The classical theories of interactions begin with continuum solvent electrostatic (double layer) forces. Extensions to include surface hydration are taken care of with concepts like inner and outer Helmholtz planes, and "dressed" ion sizes. The opposing quantum mechanical attractive forces (variously termed van der Waals, Hamaker, Lifshitz, dispersion, nonelectrostatic forces) are treated separately from electrostatic forces. The ansatz that separates electrostatic and quantum forces can be shown to be thermodynamically inconsistent. Hofmeister or specific ion effects usually show up above ≈10(-2) molar salt. Parameters to accommodate these in terms of hydration and ion size had to be invoked, specific to each case. Ionic dispersion forces, between ions and solvent, for ion-ion and ion-surface interactions are not explicit in classical theories that use "effective" potentials. It can be shown that the missing ionic quantum fluctuation forces have a large role to play in specific ion effects, and in hydration. In a consistent predictive theory they have to be included at the same level as the nonlinear electrostatic forces that form the skeletal framework of standard theory. This poses a challenge. The challenges go further than academic theory and have implications for the interpretation and meaning of concepts like pH, buffers and membrane potentials, and for their experimental interpretation. In this article we overview recent quantitative developments in our evolving understanding of the theoretical origins of specific ion, or Hofmeister effects. These are demonstrated through an analysis that incorporates nonelectrostatic ion-surface and ion-ion dispersion interactions. This is based on ab initio ionic polarisabilities, and finite ion sizes quantified through recent ab initio work. We underline the central role of ionic polarisabilities and of ion size in the nonelectrostatic interactions that involve ions, solvent molecules and interfaces. Examples of mechanisms through which they operate are discussed in detail. An ab initio hydration model that accounts for polarisabilities of the tightly held hydration shell of "cosmotropic" ions is introduced. It is shown how Hofmeister effects depend on an interplay between specific surface chemistry, surface charge density, pH, buffer, and counterion with polarisabilities and ion size. We also discuss how the most recent theories on surface hydration combined with hydrated nonelectrostatic potentials may predict experimental zeta potentials and hydration forces.

Morphologies and Structure of Brain Lipid Membrane Dispersions.

This study aims to explore the variety of previously unknown morphologies that brain lipids form in aqueous solutions. We study how these structures are dependent on cholesterol content, salt solution composition, and temperature. For this purpose, dispersions of porcine sphingomyelin with varying amounts of cholesterol as well as dispersions of porcine brain lipid extracts were investigated. We used cryo-TEM to investigate the dispersions at high-salt solution content together with small-angle (SAXD) and wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) for dispersions in the corresponding salt solution at high lipid content. Sphingomyelin forms multilamellar vesicles in large excess of aqueous salt solution. These vesicles appear as double rippled bilayers in the images and as split Bragg peaks in SAXD together with a very distinct lamellar phase pattern. These features disappear with increasing temperature, and addition of cholesterol as the WAXD data shows that the peak corresponding to the chain crystallinity disappears. The dispersions of sphingomyelin at high cholesterol content form large vesicular type of structures with smooth bilayers. The repeat distance of the lamellar phase depends on temperature, salt solution composition, and slightly with cholesterol content. The brain lipid extracts form large multilamellar vesicles often attached to assemblies of higher electron density. We think that this is probably an example of supra self-assembly with a multiple-layered vesicle surrounding an interior cubic microphase. This is challenging to resolve. DSC shows the presence of different kinds of water bound to the lipid aggregates as a function of the lipid content. Comparison with the effect of lithium, sodium, and calcium salts on the structural parameters of the sphingomyelin and the morphologies of brain lipid extract morphologies demonstrate that lithium has remarkable effects also at low content.

Physicochemical characterization of green sodium oleate-based formulations. Part 1. Structure and rheology.

HYPOTHESIS: The structure, rheology and other physicochemical properties of dilute aqueous dispersions of sodium oleate (NaOL) are well known. This paper is the first report in which a moderately concentrated (13% w/w) dispersion of NaOL in water is investigated. In fact, at this concentration the phase and rheology behavior of the surfactant remarkably deviates from those of its dilute solutions in water and a significant effect is imparted by the addition of potassium chloride. EXPERIMENTAL: The structural, thermal and rheological properties of a 13% w/w dispersion of NaOL in water were investigated by cryo-TEM, rheology, and DSC experiments with and without the addition of potassium chloride. The system is comprised of elongated wormlike micelles that turn into a gel-like more disordered viscous material upon addition of small amounts of KCl (4% w/w). FINDINGS: This paper illustrates the multifaceted behavior of sodium oleate dispersions at intermediate concentrations that depends on the presence of other cosolutes (such as KCl). The results show that viscoelastic aqueous dispersions of NaOL are excellent candidates for the preparation of stimuli-responsive green materials to be used in a number of different applications. We also discuss the genesis of wormlike micelles (WLMs) in terms of the general theory of self-assembly.

Asymmetric partitioning of anions in lysozyme dispersions.

An aqueous dispersion of lysozyme and sodium dodecyl sulfate phase separates below the cloud point. Two liquid phases are formed. At pH < pI electrolytes change the cloud point temperatures (T(c)). These follow an inverse Hofmeister series. Anions partition asymmetrically between the two phases. At fixed cation, the partitioning depends on the specific anion. In a system of finite volume, a concentrated dispersion of a protein is able to act as a chemical "sponge". No active pump is necessary to maintain concentration differences between concentrated and dilute dispersions.

Unexpected Properties of Degassed Solutions.

Theories of liquids and their simulation ignore any physical effects of dissolved atmospheric gas. Solubilities appear far too low to matter. Long-standing observations to the contrary, like cavitation, the salt dependence of bubble-bubble interactions, and the stability of degassed emulsions, continue to call that assumption into question, and these questions multiply. We herein explore more unexpected effects of dissolved gas that are inexplicable by classical theory. Electrical conductivities of different salts in water were measured as a function of concentration before and after degassing the liquid. The liquid/liquid phase separation of binary mixtures containing water, n-hexane, or perfluorooctane was significantly retarded after degassing. We anticipate that preliminary attempts at explaining these effect probably lie in self-organization of dissolved gas, like nanobubbles and cooperativity in gas molecular interactions. These are salt- and liquid-dependent.

Hofmeister Effect in Self-Organized Chemical Systems.

We studied the effect of spectator ions in the prototype of far-from-equilibrium self-organized chemical systems, the Belousov-Zhabotinsky (BZ) reaction. In particular, we investigated the specific ion effect of alkali metal cations, connoted for their kosmotropic and chaotropic properties. By means of combined experimental and numerical approaches, we could show a neat and robust evidence for the Hofmeister effect in this system. Spectator cations induce a marked increment of the induction period that preludes regular oscillations and decrease the oscillation amplitude following the sequence Li+ < Na+ ≪ K+ ∼ Cs+. These ions affect the system kinetics by interfering in the interaction between the oxidized form of the catalyst and the organic substrate, responsible for resetting the BZ system to pre-autocatalytic (reduced) conditions. The specific ion effect on these key reactive steps is systematically characterized and correlated with different parameters which describe the interaction of the cations with the solvent.

Preparation and Characterization of Ascosome Vesicles Loaded with Khellin.

Ascorbic acid has a unique role in the prevention and treatment of a large number of chronic diseases, including skin disorders but it can hardly penetrate the skin due to its solubility in water and its high instability. This study explored the formation of phosphatidylcholine-based vesicles upon addition of ascorbyl octanoate or decanoate, and their potential value as drug delivery systems. Khellin, a natural furanochromone with numerous applications in skin pathologies was loaded as model drug in ascosomes. Ascosomes had narrow size distribution, adequate encapsulation efficiency, long-term stability, and antioxidant properties. Increasing amounts of loaded khellin resulted in a reduction of the vesicle average size, without affecting the polydispersity, suggesting a stabilizing effect. Ascorbyl alkanoates produced remarkably different bilayer organizations and different capabilities to accommodate khellin in the hydrophobic pocket of the vesicles. The addition ascorbyl alkanoates reduced the amount of water molecules strongly bound to the polar headgroups. Moreover, the loading of khellin did not induce any significant hydration change in the unilamellar vesicular systems. The narrow size distribution, adequate encapsulation efficiency and long-term stability of ascosomes loaded with khellin, make these nanostructures suitable for dermatological use and other routes of administrations, preserving the biological properties of ascorbic acid.