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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

Two sides of the coin. Part 2. Colloid and surface science meets real biointerfaces.

Part 1 revisited developments in lipid and surfactant self assembly over the past 40 years [1]. New concepts emerged. Here we explore how these developments can be used to make sense of and bring order to a range of complex biological phenomena. Together with Part 1, this contribution is a fundamental revision of intuition at the boundaries of Colloid Science and Biological interfaces from a perspective of nearly 50 years. We offer new insights on a unified treatment of self assembly of lipids, surfactants and proteins in the light of developments presented in Part 1. These were in the enabling disciplines in molecular forces, hydration, oil and electrolyte specificity; and in the role of non Euclidean geometries-across the whole gammut of physical, colloid and surface chemistry, biophysics and membrane biology and medicine. It is where the early founders of the cell theory of biology and the physiologists expected advances to occur as D'Arcy Thompson predicted us 100 years ago.

Specific ion effects in polysaccharide dispersions.

The specific effects induced by some strong electrolytes or neutral co-solutes on aqueous mixtures of guar gum (GG), sodium alginate (SA) and sodium hyaluronate (SH) were studied through rheology and DSC experiments. The results are discussed in terms of changes in the polymer conformation, structure of the network and hydration properties. This study is also aimed at controlling the viscosity of the aqueous mixtures for application in green formulations to be used as fracturing fluids for shale gas extraction plants.

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.

Two sides of the coin. Part 1. Lipid and surfactant self-assembly revisited.

Hofmeister, specific ion effects, hydration and van der Waals forces at and between interfaces are factors that determine curvature and microstructure in self assembled aggregates of surfactants and lipids; and in microemulsions. Lipid and surfactant head group interactions and between aggregates vary enormously and are highly specific. They act on the hydrophilic side of a bilayer, micelle or other self assembled aggregate. It is only over the last three decades that the origin of Hofmeister effects has become generally understood. Knowledge of their systematics now provides much flexibility in designing nanostructured fluids. The other side of the coin involves equally specific forces. These (opposing) forces work on the hydrophobic side of amphiphilic interfaces. They are due to the interaction of hydrocarbons and other "oils" with hydrophobic tails of surfactants and lipids. The specificity of oleophilic solutes in microemulsions and lipid membranes provides a counterpoint to Hofmeister effects and hydration. Together with global packing constraints these effects determine microstructure. Another factor that has hardly been recognised is the role of dissolved gas. This introduces further, qualitative changes in forces that prescribe microstructure. The systematics of these effects and their interplay are elucidated. Awareness of these competing factors facilitates formulation of self assembled nanostructured fluids. New and predictable geometries that emerge naturally provide insights into a variety of biological phenomena like anaesthetic and pheromone action and transmission of the nervous impulse (see Part 2).

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.