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LL-III is an anticancer peptide and has the ability to translocate across tumor cell membranes, which indicates that its action mechanism could be non-membranolytic. However, the exact mechanism through which the peptide gains access into the cell cytoplasm is still unknown. Here, we use a plethora of physico-chemical techniques to characterize the interaction of LL-III with liposomes mimicking the lipid matrix of the tumor cell membrane and its effect on the microstructure and thermotropic properties of the membrane. Furthermore, the effect of the presence of Ca

The search for new synthetic melanin-related pigments that maintain the antioxidant and photoprotective properties of naturally occurring dark eumelanins, while overcoming their unfavorable solubility, and molecular heterogeneity is presently a very active issue for dermo-cosmetic purposes. In this work, we explored the potential of a melanin obtained from the carboxybutanamide of a major eumelanin biosynthetic precursor, 5,6-dihydroxyindole-2-carboxylic acid (DHICA), by aerobic oxidation under slightly alkaline conditions. Analysis of the pigment by EPR, ATR-FTIR and MALDI MS indicated a substantial structural similarity to DHICA melanin, while investigation of the early intermediates confirmed unchanged regiochemistry of the oxidative coupling. The pigment exhibited a UVA–visible absorption even more intense than that of DHICA melanin, and a noticeable solubility in polar solvents of dermo-cosmetic relevance. The hydrogen- and/or electron-donor ability, and the iron (III) reducing power as determined by conventional assays provided evidence for marked antioxidant properties not merely ascribable to the more favorable solubility profile, while the inhibitory action of the radical- or photosensitized solar light-induced lipid peroxidation was more marked compared to that of DHICA melanin. Overall, these results hint at this melanin, which remarkable properties are, in part, due to the electronic effects of the carboxyamide functionality as a promising functional ingredient for dermo-cosmetic formulations.

The need to protect human and environmental health and avoid the widespread use of substances obtained from nonrenewable sources is steering research toward the discovery and development of new molecules characterized by high biocompatibility and biodegradability. Due to their very widespread use, a class of substances for which this need is particularly urgent is that of surfactants. In this respect, an attractive and promising alternative to commonly used synthetic surfactants is represented by so-called biosurfactants, amphiphiles naturally derived from microorganisms. One of the best-known families of biosurfactants is that of rhamnolipids, which are glycolipids with a headgroup formed by one or two rhamnose units. Great scientific and technological effort has been devoted to optimization of their production processes, as well as their physicochemical characterization. However, a conclusive structure–function relationship is far from being defined. In this review, we aim to move a step forward in this direction, by presenting a comprehensive and unified discussion of physicochemical properties of rhamnolipids as a function of solution conditions and rhamnolipid structure. We also discuss still unresolved issues that deserve further investigation in the future, to allow the replacement of conventional surfactants with rhamnolipids.

The functional properties of metal oxide semiconductors depend on intrinsic and extrinsic defects. The population of intrinsic defects is strongly affected by the synthesis method and subsequent treatments of the material, while extrinsic defects can originate from suitable doping. Stoichiometric ZrO2 is a nonreducible oxide with a large band gap. Therefore, controlling and modulating its defect profile to induce energy states in the band gap is the sole possibility to make it a photocatalyst responsive to visible light. We report a method, based on low temperature sol−gel synthesis coupled with treatments performed in mild conditions, to obtain undoped visible light-responsive ZrO2−x. The electronic structure of these materials is interpreted in relation to their oxygen vacancy defect population. On the basis of a wide set of experimental measurements (X-ray photoelectron, steady-state and time-resolved photoluminescence, electron paramagnetic resonance, and UV−visible diffuse reflectance spectroscopy) and supported by density functional theory calculations, we demonstrate, for the first time, the predominance of positively charged F-center oxygen vacancies that do not give rise to Zr3+ species.

In recent years, interest in the class of water-soluble polymers—hydrophobically modified alkali soluble emulsion (HASE)—has increased on a surprising scale. With respect to other associative polymers, they have several advantages in terms of cost and ease of handling and utilization. In addition, unlike the solvent-based formulations, these water-soluble systems do not contain volatile solvents and hence do not contribute to environmental problems. In solutions, HASE polymers form a transient network through molecular associations between the hydrophobic groups. Due to these hydrophobic interactions, they have been increasingly used as rheology modifiers for various applications, such as paints, cosmetics, and personal care and paper coating products. These associative polymers have an architectural richness that allows the fine tuning of several physicochemical properties, and their optimal use requires controlling polymer concentration, molecular weight, size of the hydrophobic groups, and characteristics of the polymeric backbone. We give an overview of several studies on HASE polymers reported in the literature, focusing on the molecular structure, the synthetic methodologies, and—more specifically—on the factors that affect the rheology of their aqueous mixtures. As a general rule for the optimal HASE design and formulative exploitation, we highlight that the hydrophobic hanging groups are responsible for the rheological changes in the liquid phase, while the steric hindrance of the polymeric backbone and of the hydrophobic groups causes the stiffness.

pH-sensitive surfactants find applications in many fields, including responsive drug delivery and smart material design. The rational design of the surfactant molecular structure leads to species presenting strong variations of the micellization parameter (e.g., critical micelle concentration, cmc, and aggregate dimension) in a controlled pH range. In the present work, the micellization of the branched amine oxide surfactant N,N-dimethyl-2-propylheptan-1-amine oxide (C10DAO-branched) is studied as a function of pH in dilute aqueous mixtures. Its behavior is compared with that of the linear isomer N,N-dimethyldecan-1-amine oxide (C10DAO-linear). The samples are investigated by potentiometric titrations, fluorescence spectroscopy, and Dynamic Light Scattering (DLS). With increasing pH, micellized C10DAO-branched presents a higher tendency to remain in the protonated/cationic form with respect to the linear isomer. As a consequence, the minimum cmc value, observed when the protonated and the deprotonated/zwitterionic forms of the surfactant coexist in the micelles, is shifted to higher pH values. The volume of these C10DAO-branched “mixed micelles” is more than one order of magnitude higher than that of completely protonated or deprotonated aggregates. This is a singularity of the branched surfactant, not observed for the linear isomer. Overall, the results highlight that the branched molecular architecture of the surfactant tail, favoring the formation of low-curvature aggregates, enhances H-bonding between the protonated and deprotonated headgroups, which synergistically stabilizes the flatter surface of bulkier aggregates. Taking into account the good biodegradability of surfactants with a limited number of short side chains, purposely designed branched surfactants appear as a suitable option to accurately tune supramolecular aggregation in pH-responsive formulations.

Gold nanoparticles (AuNPs) are considered suitable systems for drug delivery and diagnostics with several applications in biomedicine. Size, shape and surface functionalization of these nanoparticles are important parameters influencing their behavior in a biological environment. This study describes the preparation and the characterization of lysophosphocholine coated AuNPs by means of Small Angle Neutron Scattering (SANS), Electron Paramagnetic Resonance (EPR) and Fluorescence Spectroscopy. In particular the structure of the functionalized AuNP suspension, as well as the physical properties, of the nanoparticle organic coating are discussed. The experimental results indicated that functionalized lysophosphocholine-AuNPs form aggregates, which are composed by nanoparticles with core-shell structure. Nevertheless, the nanoparticle suspension resulted to be stable, without significant structural rearrangements even when the temperature was increased to 50 °C. At the same time, experimental evidences also suggested that the 18LPC layer around AuNPs presented a reduced chain packing compared to pure 18LPC aggregates.

The mechanism of conversion of globular native proteins into amyloid fibrils represents one of the most attractive research topics in biophysics, because of its involvement in the development of severe pathologies and in various biotechnological processes. Aqueous medium properties, such as pH and ionic strength, as well as interactions with other species in solution, play a key role in tuning the fibrillization process. Here, we describe a comparative study of the influence of different ions from the Hofmeister series on the thermal unfolding and aggregation propensity of MNEI, a model protein, selected because of its tendency to form amyloid aggregates at acidic pH, even at temperatures well below its melting temperature. By selecting a temperature at which only negligible amounts of protein are unfolded, we have focused on the effect of ions on fibril formation. ThT fluorescence experiments indicated that all the salts examined increased the rate and the extent of fibrillization. Moreover, we found that anions, particularly sulfate, strongly influence the process, which instead is only marginally affected by different cations. Finally, a specific link to the chloride concentration was detected.

Formulations for industrial applications are often mixtures of different surfactants and additives, including salts; thus, it is crucial to understand the reciprocal effects of the different components on the properties of the system such as cmc and morphology of the aggregates in solution. In this respect, we have studied the effects of anions occupying different positions within the so-called Hofmeister series, namely Cl−, Br−, SCN−, on the aggregation properties of mixtures containing a cationic and a non-ionic surfactant largely employed in formulation chemistry: dodecyltrimethyl ammonium bromide (DTAB) and pentaethylenglycol mono octyl ether (C8E5). We determined the cmc of the mixtures with different relative content of the two surfactants, as well as of pure DTAB and C8E5 systems, in water and in the presence of salts. Dynamic light scattering measurements were used to evaluate the hydrodynamic size of the aggregates, while small-angle neutron scattering to determine their morphology, as a function of increasing DTAB content, at constant salt concentration. We found no significant effect of salts on the cmc or aggregate dimensions of C8E5. On the other hand, increasing DTAB content, the salt effect is clearly detectable and ion-dependent: salt addition decreases the cmc in the order SCN− ≫ Br− > Cl−; moreover, halides seem to affect structural properties of mixed C8E5-DTAB systems very slightly whereas SCN− leads to a morphological change from a spherical to a cylindrical aggregate shape. Thus, this study well demonstrates how formulation properties can be fine-tuned by salt addition through a proper choice of ions species.

Hybrid Melanin-TiO2 nanoparticles are promising bioinspired antibacterial agents for biomedical coatings and food-packaging fields. However, due to a very low colloidal stability, they showed a high tendency to self-aggregate and rapidly precipitate, making not easy their use in aqueous medium to produce homogeneous antimicrobial coatings or nanocomposites. A valid strategy to improve their dispersion is the combination with a hydrophilic water-soluble polymer such as poly-vinyl-alcohol (PVA), which is a good choice to improve the colloidal stability of nanoparticles and to modulate their agglomeration. In this work, we propose an in-situ synthetic approach based on the hydrothermal route, by which the hybrid Melanin-TiO2 nanoparticles were prepared starting from the inorganic and organic precursors in the presence of PVA. Combined approach of TEM, XRD, TG/DSC, EPR and DLS techniques allows for assessing the PVA role in the formation of hybrids and on their morphological features as well as colloidal stability and aqueous dispersion. Antibacterial tests demonstrated the biocide activity of PVA/Melanin-TiO2 nanoparticles against Escherichia coli bacterial cultures, which resulted partially influenced by the PVA content. This study provides key information on the mutual influence of organic/inorganic components on the functional properties of the final hybrid nanocomposites, contributing to define a much more far-reaching implementation in the synthesis of bioinspired polymer-based nanocomposites.

Marine microorganisms represent a reservoir of new promising secondary metabolites. Surface-active proteins with good emulsification activity can be isolated from fungal species that inhabit the marine environment and can be promising candidates for different biotechnological applications. In this study a novel surface-active protein, named Sap-Pc, was purified from a marine strain of Penicillium chrysogenum. The effect of salt concentration and temperature on protein production was analyzed, and a purification method was set up. The purified protein, identified as Pc13g06930, was annotated as a hypothetical protein. It was able to form emulsions, which were stable for at least one month, with an emulsification index comparable to that of other known surface-active proteins. The surface tension reduction was analyzed as function of protein concentration and a critical micellar concentration of 2 &mu, M was determined. At neutral or alkaline pH, secondary structure changes were monitored over time, concurrently with the appearance of protein precipitation. Formation of amyloid-like fibrils of SAP-Pc was demonstrated by spectroscopic and microscopic analyses. Moreover, the effect of protein concentration, a parameter affecting kinetics of fibril formation, was investigated and an on-pathway involvement of micellar aggregates during the fibril formation process was suggested.

Amine-oxide surfactants have emerged as highly stable, nontoxic, and cost-effective constituents of detergent formulations, specifically as wetting agents and foam boosters. With the aim of enhancing their functional behavior, a new member of this family, N,N-dimethyl-2-propylheptan-1-amine oxide, bearing a branched alkyl tail (C 10 DAO-branched) was synthesized and purified using a simple and easily scalable strategy starting from 2-propylheptan-1-ol. 2D-nuclear magnetic resonance (NMR) and mass spectrometry confirm the obtainment of the desired product in high yield and purity. The protonation behavior of the branched surfactant is not affected by alkyl tail branching, as shown by potentiometric titrations. In contrast, surface activity and aggregation behavior of C 10 DAO-branched is dramatically different from that of the linear analog N,N-dimethyldecyl-1-amine oxide (C 10 DAO-linear), in that it occupies a higher area at the solution interface and aggregates at much higher concentration, forming larger aggregates, as detected using tensiometry and dynamic light scattering (DLS), respectively. Aggregation behavior of C 10 DAO-branched is less sensitive to pH variations. Foaming tests show that C 10 DAO-branched is a more effective foam booster than its linear analog, in both acidic and basic solutions. The experimental results indicate that the branched surfactant can be used in applications that require enhanced and pH-independent surface activity and foamability.

The oxidative polymerization of 5,6-dihydroxybenzothiophene (DHBT), the sulfur analog of the key eumelanin building block 5,6-dihydroxyindole (DHI), was investigated to probe the role of nitrogen in eumelanin build-up and properties. Unlike DHI, which gives a typical black insoluble eumelanin polymer on oxidation, DHBT is converted to a grayish amorphous solid (referred to as thiomelanin) with visible absorption and electron paramagnetic resonance properties different from those of DHI melanin. Mass spectrometry experiments revealed gradational mixtures of oligomers up to the decamer level. Quite unexpectedly, nuclear magnetic resonance (NMR) analysis of the early oligomer fractions indicated linear, 4-, and 7-linked structures in marked contrast with DHI, which gives highly complex mixtures of partially degraded oligomers. Density functional theory (DFT) calculations supported the tendency of DHBT to couple via the 4- and 7-positions. These results uncover the role of nitrogen as a major determinant of the structural diversity generated by the polymerization of DHI, and point to replacement by sulfur as a viable entry to regioregular eumelanin-type materials for potential applications for surface functionalization by dip coating. Fil: Iacomino, Mariagrazia. Università degli Studi di Napoli Federico II; Italia Fil: Mancebo Aracil, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universitat Autònoma de Barcelona; España. Consejo Superior de Investigaciones Científicas; España Fil: Guardingo, Mireia. Barcelona Institute of Science and Technology; España. Universitat Autònoma de Barcelona; España Fil: Martín, Raquel. Universitat Autònoma de Barcelona; España Fil: D’Errico, Gerardino. Università degli Studi di Napoli Federico II; Italia Fil: Perfetti, Marco. Università degli Studi di Napoli Federico II; Italia Fil: Manini, Paola. Università degli Studi di Napoli Federico II; Italia Fil: Crescenzi, Orlando. Università degli Studi di Napoli Federico II; Italia Fil: Busqué, Félix. Universitat Autònoma de Barcelona; España Fil: Napolitano, Alessandra. Università degli Studi di Napoli Federico II; Italia Fil: d’Ischia, Marco. Università degli Studi di Napoli Federico II; Italia Fil: Sedó, Josep. Consejo Superior de Investigaciones Científicas; España. Barcelona Institute of Science and Technology; España Fil: Ruiz Molina, Daniel. Consejo Superior de Investigaciones Científicas; España. Barcelona Institute of Science and Technology; España

The four diffusion coefficients of the ternary system human serum albumin (HSA,1)–sodium cholate (NaC,2)–water (W,0) were determined at three average compositions with constant protein concentration, C 1 o , and variable bile salt concentration, C 2. Various types of solute–solute interactions are present in this ternary system: electrostatic, co-ions–protein, and unspecific volume interactions due to the large difference in size of the two solutes. Each type of interaction has a different effect in determining the values and the sign of the experimental diffusion coefficients, exp D ij . To simplify the analysis of the dependence of the exp D ij s on C 2, we considered three model systems where different types of solute–solute interaction are present individually. The overall analysis allows highlighting which kinds of solute–solute interaction predominates in determining the value of each diffusion coefficient.

In commercial formulations, surfactants are often co-formulated with inorganic electrolytes, which are included as inexpensive thickeners. Salts affect the surfactant’s aggregative and functional behavior. However, while the electrolyte effect on the self-aggregation of ionic surfactants can be rationalized in terms of electrostatic interactions, in the case of nonionic surfactants the molecular determinants are still unclear. In this work, we investigate the effects of alkali and alkaline–earth metal chlorides on the micellization of the nonionic surfactant hexyl penta(oxyethylene) ether, C6E5, in aqueous solution. To this aim, the C6E5 intradiffusion (also named self-diffusion) coefficient in aqueous mixtures of various alkali and alkaline–earth metal chlorides was measured by pulsed gradient spin-echo NMR. The results show that all the considered electrolytes cause a decrease of the surfactant critical micellar concentration, cmc, while the micellar size is almost unaffected. The experimental evidence can be interpreted in terms of de-hydration of the apolar alkyl tails with a minor contribution arising from the dehydration of the poly(ethylene oxide) headgroups. The order of effectiveness of the different cations follows the Hofmeister series, some aspects of which are briefly discussed.

A combination of biomedical and technological applications is generating, over the past decades, the wellestablished interest toward melanins and melanogenesis. Several compounds have been explored to promote/catalyze oxidative polymerization of melanogenic precursors, such as 5,6-dihydroxyindole-2-carboxylic acid (DHICA), to melanin-like biopolymers in vitro. TiO2 has shown a photocatalytic activity driving DHICA polymerization and leading to the formation of melanin−TiO2 hybrid nanostructures with unique biocide behavior even under visible light. However, the mechanism of melanin formation in those hybrids is not yet well understood although a ligand to metal charge transfer (LMCT) process involving DHICA and Ti4+ ions was hypothesized. Here, we focus on melanin formation and apply a complementary analysis, by using photoluminescence (PL), UV−vis, electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) spectroscopy to reveal the mechanism of DHICA polymerization in the presence of a TiO2-sol. This study discloses TiO2 potentialities to drive and template DHICA polymerization to melanin via LMCT-based photo-oxidative process.

The infinite dilution partial molar volumes $\bar{V}^{\infty}$ of poly(acrylic acid), at different degrees of neutralization α N with sodium hydroxide, have been experimentally determined in aqueous solutions. Analysis of the data indicates that, to a good approximation, the observed decrease of $\bar{V}^{\infty}$ with α N can be interpreted in terms of the electrostriction of the water molecules involved in the hydration cospheres of the –RCOO− groups. The presence of PVA does not significantly affect the value of $\bar{V}^{\infty}$ for the undissociated acid, but causes a large decrease for the sodium salt. This aspect has been discussed in terms of direct interaction between the two polymers.

The mutual diffusion coefficients, Dij, of the ternary system sodium cholate (NaC, component 1) + sodium deoxycholate (NadC, component 2) + water have been determined at five average compositions (c1, c2) keeping c1 constant and varying c2. The possibility to obtain expressions for the four diffusion coefficients in term of the micellization parameters and of the diffusivity of the species in solution is discussed. Data have been qualitatively interpreted. Results for the main term diffusion coefficients have been used in the much more difficult analysis of the cross term diffusion coefficients.

The molar conductivities of NaCl in several poly(ethylene glycol)(PEG)–water “mixed solvents” are presented as a function of the PEG content in solution. Three different PEG samples, a monodispersed one and two polydispersed ones, have been used. The comparison between the molar conductivity values in the mixed solvents and the corresponding ones in pure water shows that the only effect of PEG on the ions’ motions is an obstruction effect despite the variation of the macroscopic dielectric constant induced by PEG itself. A comparison between the molar conductivities and the corresponding mutual main diffusion coefficients shows a tight correlation between the two quantities. This correlation is possible only in the absence of electrostatic effects due to the presence of PEG.

Herein we report density measurements for the binary system 2-methyl-2,4-pentanediol(MPD,1)-water(0), and for the ternary system MPD(1)-NaCl(2)-water(0), at several fixed MPD/water ratios and at varying NaCl concentrations. The partial molar volume of MPD in the binary system has been discussed according to the McMillan-Meyer theory. At low MPD concentrations, the non-bonding MPD-MPD interactions are related to the overlapping of the hydrophobic parts of the hydration cospheres, whereas at higher concentrations the hydrophilic moieties are also involved in the solute-solute interactions. The ternary density data allowed us to determine the salt partial molar volume at infinite dilution. The trend of this quantity as a function of the MPD content in the MPD-water “mixed solvent” has been interpreted on the basis of the water partial molar volume in the binary MPD-water system.

Measurements of osmotic coefficients, mutual diffusion coefficients, and conductivity were performed on the binary system sodium n-octyl sulfonate (C8SO3Na)-water at 25degreesC both below and above the micellar composition range. The osmotic coefficient data were obtained through vapor-pressure osmometry, while the Taylor dispersion method was used to measure diffusion coefficients. The mass equilibrium model was applied to this self-aggregating system, taking into account the deviation of the activity coefficients from the Debye-Huckel limiting law by using the Guggenheim corrective terms for mixed electrolyte solutions. The expressions derived from the model fit the experimental osmotic and diffusion coefficient data well, when the same values of aggregation number, fraction of condensed counterions, and equilibrium constant are used. Osmotic coefficients were also used to determine the thermodynamic factor required to compute the solute mobility from diffusion data. Conductivity data were used to test two theoretical models, namely, the Onsager-Fuoss and the Mean Spherical Approximation theories. Both models have been found to yield unsatisfactory fits to our experimental data and some arbitrary terms had to be applied to the theoretical expressions to obtain good agreement between experiment and theory.

The ternary system water–pentaethyleneglycol monooctyl ether (C8E5)–octyltrimethyl ammonium bromide (C8TAB) has been studied at 25 °C. Accurate c.m.c. values have been determined through spectrofluorimetric measurements, by using DL-tryptophan as a molecular probe. The surfactant intradiffusion coefficients have been measured through the PGSE-NMR technique. Experimental data show the formation of mixed micelles. The compositions of the aqueous and micellar pseudo-phase have been computed over the whole micellar composition range; they indicate that C8E5 has a larger tendency to form aggregates than C8TAB. The aggregation number and the Gibbs energy of mixed micelle formation are calculated and interpreted in terms of interactions among the surfactants in the micellar aggregates. The experimental results have been compared with those predicted by the regular solution model finding reasonable agreement.

Mixed micelle formation by aqueous mixtures of pentaethylene glycol monohexyl ether (C6E5) and diethylene glycol monohexyl ether (C6E2) has been investigated by determining the temperature-composition phase diagrams and measuring the intradiffusion coefficients. In binary aqueous solutions, C6E5 shows a high tendency to micellize, while C6E2, because of its too short hydrophilic head, presents a macroscopic phase separation in a water-rich and a surfactant-rich phases. The temperature-composition phase diagrams obtained for the ternary water-C6E5C6E2 mixtures present a micellar region in which both surfactants co-aggregate. The dimensions of this micellar region depend on the relative ratio between the two surfactants molalities. By analysing the micelle intradiffusion coefficient, measured through the PGSE-NMR technique, the hydrodynamic radius of the aggregates has been estimated at 25 °C. It is similar to that of triethylene glycol monohexyl ether (C6E3) in binary aqueous solution. The experimental evidences suggest that in mixed ethoxylated surfactants the micellar behaviour is mainly determined by the mean number of ethoxylic units per surfactant molecule, independently of their distribution.

The micellization process of three sulfonate surfactants [CH3(CH2)n−1SO3Na (n = 6,8,10), CnSO3Na] has been studied by electron paramagnetic resonance (EPR) spectroscopy by employing TEMPO-choline [4-(N,N-dimethyl-N-(2-hydroxyethyl))ammonium-2,2,6,6-tetramethylpiperidine-1-oxyl chloride, TC) as a spin label. The dependence of both the nitrogen isotropic hyperfine coupling constant (〈AN〉) and the correlation time (τC) of the label on the surfactant molality have been analysed. In order to allow a correct interpretation of the experimental evidence a preliminary study on the factors influencing the EPR spectrum of TC in solution has been performed. EPR spectra of TC in various solvents show that the 〈AN〉 value increases with increasing the solvent polarity and, especially, H-bonding ability. The experimental values have been compared with those obtained by a composite ab initio computational approach, in which 〈AN〉 is determined by a suitable combination of post-Hartree–Fock and density functional calculations. Solvent effects are modelled by using the polarizable continuum model (PCM) and, for solvents with H-bonding ability, by including a few explicit solvent molecules. The experimental and computed values are in good agreement, confirming the reliability of the adopted computational strategy. The effect of the ionic strength on the EPR spectrum of TC in NaCl and Na2SO4 aqueous solution has been also investigated, finding that the 〈AN〉 value is almost constant, whereas τC increases with the electrolyte molality. In surfactants' aqueous solution, both 〈AN〉 and τC of TC, plotted as a function of the surfactant molality, show a slope change, corresponding to the critical micellar composition (c.m.c.). The τC increase can be interpreted in terms of a reduction of the label mobility determined by the strong electrostatic interaction between the TC positive charge and the anionic micelles' surface. The 〈AN〉 decrease can be ascribed to the embedding of the NO moiety of TC in the outer part of the micellar hydrophobic core. By comparing the data collected for the different surfactants, it can be seen that the variation of both τC and 〈AN〉 upon micellization increases with the surfactant chain length. This evidence can be interpreted in terms of an increasing strength of the TC-micelle surface interaction, and of an increasing hydrophobic behaviour of the outer part of the micellar core in which the NO moiety of TC is solubilized. The TC affinity for the micellar pseudo-phase has been estimated by evaluating the distribution coefficient, Kd, of the spin label between the micelles and the aqueous medium. The Kd value increases with the length of the surfactant hydrophobic chain.

A simple mathematical model based on bistationary autocatalytic kinetics is proposed to describe a possible progression of prion disease. The model accounts for both the sporadic and the infectious manifestation of the disease. Peculiarly, it shows how the disease grows if the concentration of the infectious agent (the prion PrPSc) is added to the metabolic system over a threshold concentration, while for a lower concentration the disease cannot grow.

Intradiffusion coefficients of binary mixtures, water-polyethyleneglycol (PEG) (molecular weight 200, 400, 2000, 3400, 10 000 Da), were measured by pulsed gradient spin echo (PGSE)-NMR to determine the mass and concentration effects. The properties of polydisperse samples are compared with those of oligomers, and the e†ect of polydispersity is discussed. The PEG diffusion coefficients approach a constant value at high concentration, indicating the formation of a dynamic network between water and PEG molecules. The stochiometry of this network is evaluated and compared with the result of a model derived from an extension of gelation theory. It was found that at infinite dilution limiting self and mutual diffusion coefficients are not equal : this has been interpreted as an effect of polydispersity.

Mutual diffusion coefficients have been measured for several average compositions of the system sodium cholate-sodium deoxycholate-water at 25 °C. The experiments have been grouped in different sets having constant concentration of one component and variable concentration of the other one. Following this approach, it has been found that the trends of the main- and cross-term diffusion coefficients can be interpreted on the basis of the diffusion and equilibrium results of similar experiments performed on the two binary systems sodium cholate-water and sodium deoxycholate-water. Implications of the presented results in the transport of lipids operated by bile salt aggregates are mentioned. The method proposed in this work, able to connect the diffusivities of an n-component system to those of the related n-1 subsystems, can be extended to obtain qualitative prediction on the diffusion coefficient trends for mixtures of other surfactants, of both industrial and biological interest.

Viscosity, density, diffusion and self-diffusion data have been collected on the system N-methylpyrrolidone–water at 20 °C over the entire composition range. From density and vapour pressure data, affinities, Gαβ(α,β= 1, 2), were computed and compared with the velocity cross-correlation coefficients, fαβ. Good agreement was found between the interpretation of dynamic, fαβ, and thermodynamic, Gαβ, data. Both data are in favour of preferential solute–solvent interactions leading to short-lived hydration aggregates.

Viral fusion glycoproteins present a membrane-proximal external region (MPER) which is usually rich in aromatic residues and exhibits a marked tendency to stably reside at the membrane interfaces, leading, through unknown mechanisms, to a destabilization of the bilayer structure. This step has been proposed to be fundamental for the fusion process between target membrane and viral envelope. In the present work, we investigate the interaction between an octapeptide (C8) deriving from the MPER domain of gp36 of feline immunodeficiency virus and POPC bilayers by combining experimental results obtained by neutron reflectivity, electron spin resonance, circular dichroism, and fluorescence spectroscopy with molecular dynamics simulations. Our data indicate that C8 binds to the lipid bilayer adsorbing onto the membrane surface without deep penetration. As a consequence of this interaction, the bilayer thickness decreases. The association of the peptide with the lipid membrane is driven by hydrogen bonds as well as hydrophobic interactions that the Trp side chains form with the lipid headgroups. Upon peptide-bilayer interaction, C8 forms transient secondary structures ranging from 3(10) helices to turn conformations, while acyl chains of the peptide-exposed POPC molecules assume a more ordered packing. At the same time, lipid headgroups' hydration increases. The asymmetric lipid bilayer perturbation is proposed to play a fundamental role in favoring the membrane fusion process.

Sodium cholate (NaC) and sodium deoxycholate (NaDC) in binary and ternary aqueous mixtures were investigated by means of surface tension, electron paramagnetic resonance spectroscopy (EPR), small angle neutron scattering (SANS) and mutual diffusion coefficient analysis. Concerning the NaC-H(2)O and NaDC-H(2)O binary mixtures, the surface tension, EPR and diffusion measurements confirmed the formation of micelles above a well detectable critical concentration. The SANS data indicated for both systems, the formation of ellipsoidal micelles whose major axis increased with concentration and minor axis remained constant. The data were interpreted under the assumption that aggregate growth occurred via hydrogen bonding of small aggregates along one preferential direction. For the NaC-NaDC-H(2)O ternary mixtures, the surface tension and EPR results were in good agreement with the Clint model prediction for the ideal mixed micellization. Based on this model, the SANS data enabled a complete description of the mixed aggregates in terms of dimensions, composition and concentration. In turn, this strategy allowed for a satisfactory interpretation of the main and cross-term diffusion coefficient trends, which are quite complex.

The mutual diffusion coefficients for two aqueous ternary systems, both containing a protein, human serum albumin (HSA, component 1), were measured. The first system contained a neutral polymer, polyethylene glycol (PEG, component 2), and the second an "organic solvent", 2-methyl-2,4-pentanediol (MPD, component 3). Both PEG and MPD are used as co-precipitants in HSA crystallization protocols. Measurements were performed at constant protein concentration, with increasing precipitant content. The results obtained for the two systems were discussed and compared. In both cases, the two main diffusion coefficients, relative to the motion of the protein and of the precipitant under their own concentration gradient, can be interpreted in terms of non-specific volume interactions between the solutes. Particularly, it was showed that any possible direct HSA-MPD interaction may not have a significant effect on the values of these two diffusion coefficients. Differences arise between the cross precipitant's diffusion coefficients, relative to the motion of the precipitant under the protein concentration gradient, D(i1) with i = 2, 3. In the case of PEG, the D(21) trend vs. c(2) can be simply interpreted in terms of an "exclude volume" effect. In contrast, in the case of MPD, the D(31)vs. c(3) trend seems to indicate a more complex mechanism of transport. Because the cross precipitant's diffusion coefficient plays an important role in the crystallization process, the implication of the observed difference on the crystallization procedure was also discussed.

Large unilamellar liposomes formed by the Re LPS (from here below named LOS) from Salmonella enterica serotype minnesota strain 595 (Re mutant) have been prepared by the extrusion techniques. The physico-chemical investigation of these systems has been performed by a combined experimental strategy, which has allowed a characterization at different observation scales, from the morphological to the micro-structural level. Particularly, dynamic light scattering (DLS) measurements have revealed the formation of liposomes with a narrow dimension distribution; small-angle neutron scattering (SANS) measurements have led to an estimation of the thickness of the LOS bilayer, which is consistent with an extended conformation of the acyl chains; electron paramagnetic resonance (EPR) measurements have allowed to investigate the bilayer fluidity, as determined by LOS acyl chain conformation and packing; Pulsed-field-gradient stimulated echo nuclear magnetic resonance (PGSTE-NMR) measurements have shown that water permeability through the LOS bilayer is low. The effect of temperature has been considered. Liposome dimension does not change; however, centered at 30-35 degrees C, a progressive transition of the acyl chain self-organization from a gel to a liquid crystalline phase is detected. Above this temperature, the water permeability through the bilayer increases. The effect of introducing the zwitterionic phospholipid dilauroyl phosphatidylcholine (DLPC) in the liposome formulation have been also analysed. A comparative analysis of the results points out a clear relation between the microstructure of LOS molecules in the bilayer and liposome functional properties.

The structure of chemically-crosslinked chitosan and chitosan-poly(vinylpyrrolidone) (PVP) hydrogels is investigated by means of the combined use of small-angle neutron scattering (SANS), electron paramagnetic resonance spectroscopy (EPR), intradiffusion, and swelling degree measurements. These hydrogels may be described in terms of an inhomogeneous structure composed by polymer-rich and polymer-poor regions. The polymer-rich regions, whose correlation distance zeta is ranged between approximately 600 and approximately 850 A, are, in turn, characterized by the presence of a network formed by the chemical crosslinks, with a mean correlation distance xi approximately 90 A. The structures of chitosan and chitosan-PVP hydrogels have also been analyzed in the presence of sodium decylsulfate micelles that could provide a multidomain system useful, in principle, for drug delivery applications. Both SANS and EPR measurements show that sodium decylsulfate micelles do not significantly interact with both the gels. Finally, intradiffusion and swelling degree measurements show an improved hydrophilicity of chitosan-PVP gels, even further magnified by the presence of C10OS surfactant.

The structure of poly(vinyl alcohol) (PVA) hydrogels formed as a result of freeze/thaw treatments of aqueous solutions of the polymer (11 wt % PVA) in the freshly prepared state is analyzed through the combined use of small (SANS) and ultrasmall (USANS) angle neutron scattering techniques. The structure of these hydrogels may be described in terms of polymer rich regions, with dimensions of the order of 1-2 microm, dispersed in a water rich phase, forming two bicontinuous phases. The PVA chains in the polymer rich phase form a network where the cross-linking points are mainly crystalline aggregates of PVA having average dimensions of approximately 45 A. The structural organization of freeze/thaw PVA hydrogel membranes does not change either after rehydration of dried gels or in the presence of a tensile force. Finally, addition of surfactant micelles inside the gel provides a formulation with both hydrophobic and hydrophilic regions, which demonstrates the potential of the system for drug delivery. Both SANS and EPR measurements show that sodium decylsulfate (C10OS) micelles do not significantly interact with the PVA gel. Variation of the gel structure by the number of freeze/thaw cycles should modulate the rate of release of an active constituent, for example, in a dermal patch.

Mixtures containing water, bovine serum albumin (BSA), and sodium taurodeoxycholate (NaTDC), a component of the bile in mammals, have been investigated in a wide range of composition and pH. Depending on the concentration of both solutes and the pH, solutions, precipitates, and gels are formed. Under spontaneous pH conditions, the transport properties in dilute solutions indicate the occurrence of significant interactions between BSA and the surfactant. Conversely, acidic media favor the formation of nonsoluble protein-surfactant complexes, with subsequent precipitation. The nucleation kinetics of the protein-surfactant complexes in solid form and the related precipitation processes can be slow or fast, depending on the overall solute content and the mole ratio. At high concentrations, a gel, extending on both sides of the charge neutralization line, and two-phase regions are observed. Gels shrink in open air and swell in the presence of excess water. Depending on concentration and temperature, the gels transform from an essentially liquidlike behavior to that peculiar to true gels (when G' >= G ''). The thermal gelation threshold, the temperature above which G' >= G '', depends on BSA and NaTDC content and is concomitant to moderate heat effects, inferred by differential scanning calorimetry (DSC). The above data also indicate that the protein thermal denaturation in the gel is shifted to higher temperatures compared to water. Such a stabilizing effect is presumably related to the occurrence of both electrostatic and hydrophobic interactions with NaTDC. Water self-diffusion in the gels is slightly slower than that in the bulk and poorly sensitive to composition: it is about 65% the value of neat H2O in a wide concentration range, irrespective of the BSA, or NaTDC, concentration. A peculiar behavior is also observed in Na-23 longitudinal and transverse relaxation rates. The T-1 and T-2 values, measured at 105.75 MHz on BSA-NaTDC gels, indicate that the motions determining the NMR relaxation of the sodium ions in the hydration layer of the protein-surfactant aggregates are not slow, having frequencies comparable with the Larmor one. The above properties, especially the rheological and the spectroscopic ones, are important for understanding the behavior of gels based on protein-surfactant mixtures.

The self-aggregation process of five alkyltrimethylammonium bromide surfactants [CH3(CH2)(n-1)N(CH3)(3)Br (n = 6,8,10,12,16), C(n)TAB] in aqueous solution at pH = 7 has been studied by electron paramagnetic resonance (EPR) spectroscopy by employing 3-carboxy-PROXYL in its deprotonated form [2,2,5,5-tetramethyl-3-carboxypyrrolidinyloxy sodium salt, CP-] as a spin probe. In all the considered systems, the nitrogen isotropic hyperfine coupling constant of CP-, A(N)), decreases and the correlation timed tau(C), increases with increasing surfactant molality. Concerning the surfactants with long hydrophobic tails (n = 8,10,12,16), both (A(N)) and tau(C) present a slope change corresponding to the critical micellar composition, c.m.c. In these cases the tau(C) increase can be interpreted in terms of a reduction of the spin probe mobility determined by the strong electrostatic interaction between the CP- charge and the cationic micelles' surface. Particularly, the tau(C) values show that the microviscosity experienced by CP- in C(16)TAB micelles is much higher in respect to that found in the other micellar systems, thus suggesting a different structural organization of the aggregates' surface. The (A(N)) decrease can be ascribed to a partial embedding of the NO moiety of CP- in the outer part of the micellar hydrophobic core. The CP- affinity for the micellar pseudo-phase has been estimated by evaluating the distribution coefficient, K-d, of the spin probe between the micelles and the aqueous medium. The K-d value increases with the length of the surfactant hydrophobic chain. Because of the short hydrophobic tail, the C(6)TAB aqueous mixtures exhibit a peculiar behaviour: (A(N)) smoothly decreases and tau(C) of CP- increases with increasing surfactant molality without any abrupt slope change. This experimental evidence suggests that C(6)TAB association can be described in terms of a gradual change, with increasing surfactant molality, from solvent-mediate to direct surfactant-surfactant interactions.

In the present work the mixtures water - sodium decylsulfate (C10OS)- poly(vinylpyrrolidone) (PVP) and water - sodium decylsulfonate (C10S) - PVP have been investigated by electron paramagnetic resonance (EPR) spectroscopy employing 4-(N, N-dimethyl-N-(2-hydroxyethyl)) ammonium-2,2,6,6-tetramethyl-piperidine-1-oxyl chloride (TEMPO-choline, TC) as spin probe. TC cations condense on the surface of the aggregates formed by anionic surfactants, acting as counterions, and fit their NO moiety in the outer shell of the hydrophobic core. In water - C10OS - PVP mixtures the nitrogen isotropic hyperfine coupling constant of TC ([A(N)]), reported as a function of the surfactant molality at constant PVP composition, shows two breakpoints: the former ( critical aggregation concentration, c. a. c.) corresponds to the formation of surfactant - polymer clusters while the latter (c(2)) corresponds to the formation of free surfactant micelles. The trend of the correlation time (tau(C)) of the nitroxides in the same system shows that the electrostatic repulsion among the clusters formed onto the PVP macromolecules favours a broadening of the polymer coil and a stiffening of its chain. In contrast, in water - C10S - PVP mixtures no surfactant - polymer interaction could be detected. The effect of the molecular structure of the surfactant headgroup on the surfactant - polymer interaction has been discussed in terms of charge density distribution. In order to further highlight the importance of the headgroup molecular structure on the surfactant association behaviour, the micellisation process of the sodium alkylsulfates (CnOS, n = 6,8,10) has been investigated by the same experimental approach, and the results have been compared with those, previously reported (A. M. Tedeschi, G. D'Errico, E. Busi, R. Basosi and V. Barone, Phys. Chem. Chem. Phys., 2002, 4, 2180, ref. 46), relative to the sodium alkylsulfonates (CnS). CnOS micelles are more ordered and compact with respect to the CnS ones. For the former class of surfactants the electrostatic interaction with TC is stronger and the hydrophobic behaviour of the TC solubilization site is higher.

The interactions in aqueous solution between poly(vinylpyrrolidone) (PVP) and sodium nonanoate (C8COONa), sodium octylsulfonate (C8SNa), lithium perfluorononanoate ( C8FCOOLi), respectively, were investigated. In all the studied systems, the presence of PVP induces a lowering of the aggregation number of the surfactant as evidenced by fluorescence quenching measurements. However, no direct surfactant-polymer interaction has been found for the systems C8COONa PVP and C8SNa PVP. Strong hydrophobic interaction in the system C8FCOOLi PVP has been shown by the fluorescent behavior of pyrene used as a probe. The presence of the fluorinated surfactant induces an increment of similar to14% of the polymer gyration radius, as shown by viscosimetry. Calorimetry confirms the experimental results obtained through fluorescence and shows that the adsorption of C8FCOOLi on PVP is an endothermic process.

The modulation induced by different solvents and by pH on the nitrogen isotropic hyperfine coupling consts. (AN) of 2,2,5,5-tetramethyl-3-carboxypyrrolidine (3-carboxy-PROXYL,CP) and 2,2,6,6-tetramethyl-4-carboxypiperidine (4-carboxy-TEMPO,CT) nitroxides was studied through ab initio quantum mech. computations and by EPR spectroscopy. The geometry of the neutral and deprotonated forms and the corresponding dissocn. consts. are computed by using the hybrid PBE0 functional. With these structures, accurate AN values were obtained by an integrated post-Hartree-Fock/PBE0 approach. Specific solvent effects are modeled by including a few solvent mols. (strongly bound to the solute), whereas bulk contributions are taken into account by the polarizable continuum model (PCM). Both EPR spectra and quantum mech. computations point out that AN increases with increasing solvent polarity and, esp., H-bond ability. The AN values obtained by the authors' computational model both for the neutral and deprotonated forms in aq. soln. are in good agreement with EPR values. However, the computed pKa values(4.97 and 5.25 for CP and CT, resp.) are significantly larger than the value reported in the literature for CP (3.4). New potentiometric and spectroscopic measurements lead to values (4 and 4.30 for CP and CT, resp.) in better agreement with quantum mech. computations and chem. intuition. Also the calcd. magnetic titrn. curves in aq. soln. are in quite good agreement with the authors' new EPR curves.

The effect of urea, N-monomethylurea, and N,N′-dimethylurea on the micellization of the nonionic ethoxylated tenside pentaethyleneglycolmonohexyl ether (C6E5) was investigated through intradiffusion coefficient measurements (Pulsed-gradient spin-echo-NMR method) at 25 °C. The presence of the additive causes, in all cases, an almost linear increase in the critical micellar composition (cmc), while a decrease in the aggregation number occurs. Furthermore, both the monomer-monomer and micelle-micelle interactions increase. The analysis of the intradiffusion coefficients shows the presence of additive molecules in the hydration shell of the tenside, in both its monomeric and micellar forms. A comparison with the results obtained for the water- pentaethyleneglycol (PEG5)-urea or alkylurea systems suggests that the additive molecules are mainly positioned near the tenside ethoxylic chain. The number of alkylurea molecules in the solvation shell of each C6E5 and PEG5 molecule was computed and commented. The experimental cmc values in water-C6E5-urea mixtures are in quite good agreement with those predicted through a molecular thermodynamic model.

Intradiffusion coefficients were measured at 25°C by the PGSE-NMR technique for the binary systems: water-urea, water-(N-methylurea), water-(N,N′-dimethylurea). The collected data have been combined with osmotic and mutual diffusion coefficients present in the literature to calculate the velocity correlation coefficients (VCC). The results have been interpreted in terms of molecular interactions, showing that alkylureas have a structuring effect on the aqueous medium. The hydration number of the solutes were estimated.

Density and viscosity of binary systems water-nonionic surfactants poly(ethylen-oxide) alkyl alcohols type, [CnH2n+1(OCH2CH2)mOH, CnEm], have been studied. The partial molar volumes in the dilute solution range and the viscosity B-coefficients were calculated. The nonionic surfactants partial molar volumes were compared with those of ethylene glycol and poly(ethylenglycol) (PEG). The comparison shows that the ethoxy unit volume,\(\bar V^O \) (OCH2CH2), seems to be independent of the particular system. The consequences of this are discussed. A model for interpreting the experimental B values has been proposed. The model treats the macroscopic viscosity as the superimposition of different local effects. The following surfactants have been considered: C5E1, C5E2, C6E1, C6E2, C6E3, C6E4.

The self-diffusioncoefficients of HDO and some surfactants in aqueous mixtures at different concentrations, below the critical micelle concentration, have been determined by means of the NMR, spin-echo pulsed field gradient method. The surfactant solutes chosen were ethylene glycol-pentyl alcohol (diethylene glycol- pentylalcohol, ethylene glycol-hexyalcohol, diethylene glycol-hexyl alcohol, tri- ethylene glycol-hexyl alcohol, tetraethylene glycol-hexyl alcohol, pentaethylene glycol-hexyl alcohol). The interactions in solution are studied by analyzing the solute self-diffusion coefficients extrapolated to infinite dilution. These values are comparedwith those of 1-alkanols.The slope of the self diffusioncoefficients vs. the solute concentration are correlated with the microscopic friction coeffi- cients. A model for interpreting the experimental data is suggested.

Self-diffusion coefficients for binary systems containing water and an oligomer of ethylene glycol [HO-(CH2CH2-O)nH, n = 1-5], have been measured at 25 °C in the whole concentration range by the pulsed gradient spin-echo NMR technique. Upon adding oligomer to pure water, both the oligomer and water self-di†usion coefficients decrease until a certain composition is reached, after which they remain approximately constant. This evidence is interpreted in terms of molecular interactions, especially hydrogen-bond formation. A relation between mutual and self-diffusion coefficients for these systems is found and commented upon.