Giuseppe Colafemmina

A novel approach for determining the droplet size distribution in emulsion systems by generating function

We present a novel approach that allows us to figure out the size distribution of an isolated collection of droplets of a liquid dispersed in another one (emulsion) using NMR pulsed gradient spin echo (PGSE) measurements. The echo decay coming from the ensemble of droplets with different radii was related to the particle size distribution function and to the echo attenuation of an isolated sphere. This latter term was evaluated according to the second cumulant approximation, while the unknown distribution was approximated using a generating function series. The coefficients of the series are evaluated, using a least squares procedure, fitting the obtained relationship to the experimental data. We find that when the volume fraction distribution is contained in the range of lengths determined by the parameters of the PGSE measurement, the experimental data (echo attenuation) contain enough information to describe the distribution function in all the details. The method has been tested on both experimental a...

General methods for determining the droplet size distribution in emulsion systems

We present a general method that allows us to figure out the size distribution of an isolated collection of droplets of dilute emulsion system using nuclear magnetic resonance pulsed gradient spin echo measurements. We show that the expression to obtain the volume fraction distribution function is equivalent to a Fredholm integral equation of the first kind. We prove, using the Dirac notation, that a solution of this equation can be easily found if its kernel has a complete biorthogonal system of eigenvectors. Two numerical procedures are discussed. The first, termed indirect, is based on the expansion of the unknown distribution function in the eigenfunctions of the kernel. The second one, called direct, uses the properties of shifted Legendre polynomials to integrate numerically the integral equation and evaluates the unknown distribution by means of a constrained least square procedure. The computational limits are analyzed. To extract the distribution’s form directly by experimental data we have const...

Nucleotides and nucleolipids derivatives interaction effects during multi-lamellar vesicles formation.

In this paper a micellar interface, constituted by the cationic surfactant CTAB, in presence of 1,2-epoxydodecane and nucleotides was used for catanionic multi-lamellar vesicles (MLVs) formation. The micellar solution of CTAB is able to disperse the 1,2 epoxydodecane in the micellar core promoting the reaction of this reagent with the nucleotide attracted by the positive surface charge of the micellar aggregates. The alkylation of AMP and UMP nucleotides leads to the synthesis of nucleolipids. The behaviour of the supramolecular structures formed depends on the starting reagents (AMP, UMP and AMP+UMP) and on the assembly capabilities of the products. In particular nucleotides and nucleotides derivatives interaction effects are evaluated during the multi-lamellar vesicles formation. NMR spectroscopy and UV-vis measurements performed on MLVs showed strong aryl interactions. Interestingly, NMR spectra revealed prevailing stacking interactions between complementary nucleolipids. The assembly of complementary nucleotides affects the course of the reaction during the MLVs formation. Moreover the MLVs supramolecular stability has been tested by means of turbidity and UV-vis measurements. In particular, an enhanced stability has been found in systems prepared with complementary nucleotides confirming that in these systems the self-assembly process is influenced by nucleolipids interactions. Furthermore by following the hypocromic effect during the micellar catalysis, we showed that even in the earlier stages of the reaction significant differences are detectable.

The role of the cosurfactant in the CTAB/water/n-pentanol/n-hexane system: Pentanol effect on the phase equilibria and mesophase structure

We report on the effect of 1-pentanol loading on the phase behaviour of mixtures of CTAB/water/n-hexane at fixed mole ratios 1∶80∶47. The cosurfactant induces changes in the interfacial film curvature. By increasing the pentanol/CTAB mole ratio, the system evolves from oil-in-water to water-in-oil structures. For very large 1-pentanol loading some water is expelled from the reverse micelles resulting in a L2plus water equilibrium (emulsification failure). In the range of compositions investigated most of the phase equilibria reveals the coexistence of liquid crystals and hexane/pentanol solutions. In these cases, we estimate the interface composition by assuming a constant 1-pentanol concentration in all the oil domains, and by tacking into account the alcohol solubility in water. In the case of single-phase sample the interfacial composition was determined by means of turbidimetric titration. The adsorption of cosurfactant at the interface of direct micelles, planar lamellae, bicontinuous microemulsions, and spherical reverse micelles follows the same adsorption isotherm (independently from the curvature of the interface). Moreover, the results obtained unambiguously show that the interface composition dictates the spontaneous curvature of interfacial film. Actually positive, null, and negative curvatures correspond to different compositions of the interfacial film. Once the influence of cosurfactant on the spontaneous curvature of the interface is understood, the appearance of the emulsification failure upon pentanol loading can be rationalised within the framework of the flexible surface model.

Phyto-liposomes as nanoshuttles for water-insoluble silybin-phospholipid complex.

Among various phospholipid-mediated drug delivery systems (DDS) suitable for topic and oral administration, phytosome technology represents an advanced innovation, widely used to incorporate standardized bioactive polyphenolic phytoconstituents into phospholipid molecular complexes. In order to extend their potential therapeutic efficiency also to other routes of administration, we proposed a novel phytosome carrier-mediated vesicular system (phyto-liposome) as DDS for the flavonolignan silybin (SIL), a natural compound with multiple biological activities related to its hepatoprotective, anticancer and antioxidant (radical scavenging) effects. We screened the optimum fraction of its phytosome, available in the market as Siliphos™, into liposomes prepared by extrusion, such that vesicle sizes and charges, monitored through dynamic light scattering and laser doppler velocimetry, satisfied several quality requirements. Special emphasis was placed on the study of host-guest interaction by performing UV-vis absorption, spectrofluorimetry and NMR experiments both in aqueous and non-polar solvents to probe the effect of the presence of phospholipids on the electronic properties of SIL and its propensity to engage H bonding with the lipid headpolar groups. Finally, fluorescence microscopy observations confirmed the ability of phyto-liposomes to be internalized in human hepatoma cells, which was promising for their potential application in the treatment of acute or chronic liver diseases.

Characterization of the Solutol® HS15/water phase diagram and the impact of the Δ9-tetrahydrocannabinol solubilization

Here, the phase behavior of the commercial non-ionic surfactant Solutol® HS15 in water was investigated. The focus was on the evolution of the system nanostructure at low water content. Particularly, it was demonstrated that spherical micelles found in dilute surfactant solutions coalesce at a surfactant volume fraction close to 0.5. As consequence, a heterogeneous pseudo-binary mixture occurs. No liquid crystalline phases were detected even at the highest HS15 concentrations in water. Alteration of the micellar morphology induced by the addition of Δ(9)-tetrahydrocannabinol to the surfactant/water binary system was also investigated. It was found that the cannabinoid molecules become entrapped within the surfactant hydrophobic tails, thus increasing the surfactant effective packing parameter and inducing a radical change of the micelle shape. At sufficiently low water content (18-35 wt.%), such alteration of the interfacial packing results in a lamellar organization of the surfactant molecules.

CHLOROPHYLL A SELF-ORGANIZATION IN MICROHETEROGENEOUS SURFACTANT SYSTEMS

Abstract Study on the factors affecting the chlorophyll a (Chl a) organization with neutral, positively and negatively charged surfactants has been performed by using UV-Vis absorption spectroscopy and circular dichroism. NMR techniques have been employed to investigate the role played in the surfactant reorganization by the state of aggregation of the Chl a host. Micelles and lamellar phases have been used during the investigation, carried out at different surfactant and pigment concentrations. Ionic surfactants in micellar phases always promote the Chl a aggregation. By varying the non-ionic surfactant concentration, it is possible to modulate the amounts of the aggregated and monomeric forms of Chl a. The pigment accelerates the lamellar phase formation and influences the phase organization only above a surfactant concentration of 30%.

Resolving complex mixtures by means of pulsed gradient spin-echo NMR experiments

We present a method to analyse pulsed gradient spin-echo (PGSE) NMR data from a mixture of compounds sharing the same NMR resonance (e.g. polymer solutions or mixtures of aliphatic compounds). If all the spin-bearing species undergo Brownian motion, their contribution to the experimental echo decay is exponential (i.e. e−sD, with s a function of the parameters of the PGSE-NMR experiment and D the self-diffusion coefficient). For the case of more than one diffusing species at a given chemical shift, the (normalized) echo attenuation is the Laplace transform of the distribution function of the self-diffusion coefficients. The Laplace transform can be reduced to a Fredholm integral equation of the first kind in the variable z ∝ e−sD (in the interval [0,1]). Applying the algorithm previously developed by us (L. Ambrosone, A Ceglie, G. Colafemmina and G. Palazzo, J. Chem. Phys. 1999, 110, 797) we solve the integral equation, obtaining the distribution function of the diffusion coefficients. The method is tailored for small data sets (10–30 points) typical of PGSE-NMR measurements. Moreover, the relevant variable (z) being an exponential function of the self-diffusion coefficient, it allows insight on the fine structure of the diffusion spectrum. The method was successfully tested on a three-component solution and on an aqueous solution of seven PEG oligomers. In the latter case an estimate of the molecular mass distribution function was obtained. The reported results indicate that such an approach permits determination of self-diffusion coefficients differing by 15% with a high accuracy (6–3%).

23Na NMR relaxation study of sodium dodecyl sulphate in some aqueous and nonaqueous systems

Abstract The analysis of the 23Na NMR spin-lattice (R1) and spin-spin (R2) relaxation rates was performed on several two-, three-, and four-component systems of the surfactant sodium dodecyl sulphate in water, formamide, N-methyl formamide and N,N-dimethyl formamide. n-pentanol or n-octanol was used as cosurfactant, while p-xylene was added as oil to obtain some aqueous and nonaqueous microemulsions. In several systems R1 = R2, thus indicating that Na+ ions are not tightly bound to any structured interface. Whenever R1 ≠ R2 the use of a two-site model gives a reliable estimate of the dynamic parameters characterizing the motion of the Na+ ions in the bound state. It is worth noting that while, in the aqueous systems, the Na+ ions retain an octahedral coordination (Oh symmetry), a tetrahedral coordination (Td symmetry) of the Na+ ions by FM, NMF, and DMF molecules has been proposed as a reasonable explanation of the observed high-field shifts and increase in the quadrupolar coupling constant.

The impact of alkanes on the structure of Triton X100 micelles

Here we investigate the structural evolution of TX100 micelles upon loading with several linear and cyclic alkanes by DLS, PGSE-NMR, 2D NOESY NMR, viscosity measurements, and molecular dynamic simulations. Our results confirm that TX100 alone forms spherical, onion-like micelles made of several partially interpenetrating surfactant layers where the polyethylene glycol chains are in contact with the tetramethyl-butyl-phenyl moieties. Loading with non-penetrating oils larger than decane induces a decrease in micellar size and hydration because the alkane molecules compete with both water and tetramethyl-butyl-phenyl groups for the polyethylene glycol chains. This results in the partial peeling of the “onion” and in the dehydration of polyethylene glycol chains so that the micelles increase in number and decrease in size upon alkane loading. In contrast, small and penetrable oils (mainly cyclo-alkanes) first swell the onion-like micelles (inducing an increase in size) and only above a critical oil/surfactant ratio does the oil induce the weakening of the multilayer structure and the dehydration of polyethylene glycol chains found in long linear alkanes.