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.

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.

Direct biocatalysed synthesis of first sulfur-, selenium- and tellurium- containing l-ascorbyl hybrid derivatives with radical trapping and GPx-like properties.

6-O-l-Ascorbyl selenoesters, thioesters and telluroesters can be efficiently and directly prepared from l-ascorbic acid and suitable functionalised chalcogenoesters through lipase-catalysed transesterification reactions. Novel synthesised l-ascorbyl derivatives exhibited remarkable chain breaking and glutathione peroxidase-like activities.

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.

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.

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

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.

High-performance and anti-stain coating for porcelain stoneware tiles based on nanostructured zirconium compounds.

The technological characteristics of porcelain stoneware tiles make them suitable for a wide range of applications spanning far beyond traditional uses. Due to the high density, porcelain stoneware tiles show high bending strength, wear resistance, surface hardness, and high fracture toughness. Nevertheless, despite being usually claimed as stain resistant, the surface porosity renders porcelain stoneware tiles vulnerable to dirt penetration with the formation of stains that can be very difficult to remove. In the present work, we report an innovative and versatile method to realize stain resistant porcelain stoneware tiles. The tile surface is treated by mixtures of nanosized zirconium hydroxide and nano- and micron-sized glass frits that thanks to the low particle dimension are able to penetrate inside the surface pores. The firing step leads to the formation of a glass matrix that can partially or totally close the surface porosity. As a result, the fired tiles become permanently stain resistant still preserving the original esthetical qualities of the original material. Treated tiles also show a remarkably enhanced hardness due to the inclusion of zirconium compounds in the glass coating.

Effect of the alkyl chains and of the headgroups on the thermal behavior of ascorbic acid surfactants mixtures.

The role of the alkyl chain length and of the headgroup on the thermal behavior of mixtures of ASC8 (ascorbyl octanoate) and ASC16 (ascorbyl hexadecanoate) was investigated through differential scanning calorimetry, small- and wide-angle X-ray scattering, and Fourier transform infrared spectroscopy experiments. The formation of two eutectics and of a peritectic point was found from the phase diagram, and their structural properties were studied. The results were compared by investigating the thermal behavior of mixtures of octanoic acid and hexadecanoic acid. The findings provide insights into the role of the ascorbyl headgroups on the intermolecular interactions that determine the phase behavior of the two ascorbic acid based surfactants in the solid state.

Symmetric and asymmetric bolaamphiphiles from ascorbic acid.

The properties of novel bolaamphiphiles that carry epimers of vitamin C (L-ascorbic acid and/or D-isoascorbic acid) as hydrophilic head groups, and an interconnecting aliphatic C(12) chain (DD, DL, and LL) were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) in the solid state (anhydrous powders) and in aqueous dispersions as a function of the surfactant concentration. Upon heating, the aqueous dispersions undergo a phase transition from a hydrated semicrystalline "coagel" to a micellar phase. The results suggest that the headgroup chirality determines the formation of either inter- or intramolecular hydrogen bonds between the polar heads, which affect the phase behavior and structural properties of the nanoassemblies produced by these surfactants in water dispersions. The DSC data of aqueous dispersions were analyzed to obtain the size distribution of the pores in the coagel state.

Understanding the properties of the coagel and gel phases: a 2H and 13C NMR study of amphiphilic ascorbic acid derivatives.

The coagel and gel phases formed by the d and l diastereoisomers of ascorbyl-dodecanoate (ASC12) in deuterated water were studied through solid-state NMR techniques. In particular, the dynamic properties of water and surfactant chains were investigated by (2)H and (13)C NMR static spectra, respectively. Two fractions of water with very different dynamics were found in the coagel phases, one solidlike and one liquidlike, assigned to water strongly bound to the surfactant polar heads and bulk water, respectively. Only one kind of "intermediate" water was instead detected in the gel phase suggesting that the merging of the two types of water in the interlayers between the surfactant lamellae occurs at the coagel-to-gel transition. Moreover, the surfactant chains, very rigid in the coagel phase, give rise to fast trans-gauche interconformational jumps in the gel phase, where almost isotropic reorientations of the whole aggregates also occur. A different dynamic behavior was found for the two diastereoisomers in particular for what concerns the surfactant molecules in the gel phase and the water molecules in the coagel presumably ascribable to different inter- and intramolecular interactions that involve the polar heads.

Nanoparticles for cultural heritage conservation: calcium and barium hydroxide nanoparticles for wall painting consolidation.

Nanotechnology provides new concepts and materials for the consolidation and protection of wall paintings. In particular, humble calcium and barium hydroxide nanoparticles offer a versatile and highly efficient tool to combat the main degradation processes altering wall paintings. Clear example of the efficacy and potentiality of nanotechnology is represented by the conservation in situ of Maya wall paintings in the archaeological area in Calakmul (Mexico).

Effect of headgroup chirality in nanoassemblies. 2. Thermal behavior of vitamin C-based surfactants.

l-Ascorbic and d-isoascorbic acids are epimers, and their alkanoyl-esters are surfactant-like in water. These ascorbic acid derivatives retain the same stereogenic configurations of the parent molecules. That circumstance strongly affects their physicochemical properties, both in the solid and in the dispersed states. The thermal behavior of 6-O-l-ascorbyl-dodecanoate (l-ASC12), of 6-O-d-isoascorbyl-dodecanoate (d-ASC12), and of their mixtures was investigated through DSC, XRD, and FTIR experiments. The results indicate that the mixtures of the two epimers produce two eutectics and a 1:1 molecular compound, both in the pure phase and in the coagel state. From the phase diagram data, the activity coefficients of the different species and the main excess thermodynamic functions can be calculated. The results provide insight into the effects of stereochemistry on their intermolecular interactions.

Effect of headgroup chirality in nanoassemblies. Part 1. Self-assembly of D-isoascorbic acid derivatives in water.

L-(+)-Ascorbic acid and D-(-)-isoascorbic acid are epimers, with an opposite configuration at the C5 stereogenic chiral center. Single-chained surfactants that carry a L-ascorbic or d-isoascorbic acid residue as hydrophilic headgroup and an alkanoate tail as hydrophobic chain were synthesized. We refer to these as L-ASCn and D-ASCn, with n=8, 10, or 12. The role of the headgroup configuration in determining the nature of both the pure compounds and their nano assembly in aqueous dispersions were studied. Surface tension, infrared spectroscopy, differential scanning calorimetry, conductivity, small-angle X-ray scattering, and wide-angle X-ray diffractometry were used to characterize surfactant properties as a function of temperature and concentration. The L and D headgroup forms have significantly different hydration. This greatly affects the structure and stability of the aggregates in the micellar and coagel states.

Organogels from a vitamin C-based surfactant.

A new double chained surfactant, 2-octyl-dodecanoyl-6-O-ascorbic acid (8ASC10), with a L-ascorbic acid unit as the polar headgroup was synthesized for the first time. The behavior of the compound in the dry solid state has been characterized through DSC, XRD, and SAXS measurements. The surfactant forms stable viscous organogels in the presence of suitable organic solvents and also water-induced organogels upon addition of water to the organogel. These mixtures show shear-thinning properties and are birefringent. The behavior and properties of the organogels have been studied through rheology, DSC, and SAXS experiments. The organogels possess the same antioxidant properties of the original L-ascorbic acid ring and can be used to solubilize and protect valuable organic molecules.

Nanotubes from a vitamin C-based bolaamphiphile.

A bolaform surfactant, 1,12-diascorbyl dodecanedioate (BOLA12), with ascorbic acid units as the polar headgroups was synthesized for the first time. Once dispersed in water above 0.5% w/w, BOLA12 forms hollow nanotubes as revealed by cryo-TEM experiments. These nanostructures transform into clear micellar solutions on heating. X-ray diffraction and SAXS experiments were performed both on the pure solid and on its aqueous dispersions. The critical aggregation concentration and the phase behavior were determined by conductivity and DSC experiments. The latter technique provided also the amount of strongly bound, solvating water molecules that surround the polar headgroups. BOLA12 shows the same reducing properties of ascorbic acid, as indicated by the antioxidant activity evaluated with the DPPH method. This feature was used for the reduction of Pd(II) ions on the surface of the nanoassemblies, which lead to the formation of large bundles homogeneously coated with palladium as observed in SEM micrographs.

Investigation of the interaction between peanut agglutinin and synthetic glycopolymeric multivalent ligands.

The interaction between synthetic glycoplymers bearing beta-D-galactose side groups and the lectin peanut agglutinin (PNA) was investigated by UV-difference spectroscopy and isothermal titration calorimetry (ITC). UV-difference spectroscopy indicated that the polymer-lectin interaction was stronger than that between PNA and either the corresponding monomer, D-galactose or D-lactose. The thermodynamics of binding (K, DeltaG, DeltaH, DeltaS and n) were determined from ITC data by fitting with a two-site, non-cooperative binding model. It was found that the glycopolymer displayed around a 50 times greater affinity for the lectin than the parent carbohydrate, and around 10 times greater than the monomer, on a valency-corrected basis. Binding was found to be entropically driven, and was accompanied by aggregation and precipitation of protein molecules. Furthermore, interesting differences between polymers prepared either from deacetylated monomers, or by deacetylation of pre-formed polymers, were found.

Lectins: tools for the molecular understanding of the glycocode.

Recent progress in glycobiology has revealed that cell surface oligosaccharides play an essential role in recognition events. More precisely, these saccharides may be complexed by lectins, carbohydrate-binding proteins other than enzymes and antibodies, able to recognise sugars in a highly specific manner. The ubiquity of lectin-carbohydrate interactions opens enormous potential for their exploitation in medicine. Therefore, extraordinary effort is made into the identification of new lectins as well as into the achievement of a deep understanding of their functions and of the precise mechanism of their association with specific ligands. In this review, a summary of the main features of lectins, particularly those found in legumes, will be presented with a focus on the mechanism of carbohydrate-binding. An overview of lectin-carbohydrate interactions will also be given, together with an insight into their energetics. In addition, therapeutic applications of lectins will be discussed.