Donato Ciccarelli

Synthesis, self-aggregation and bioactivity properties of a cationic aminoacyl surfactant, based on a new class of highly functionalized nucleolipids.

A highly functionalized aminoacyl nucleolipid based on uridine is here proposed as a novel cationic surfactant. To achieve this, a straightforward, high yielding and versatile protocol has been devised, in principle providing synthetic access to a variety of different, related analogs. Self-aggregation properties of this nucleolipid were determined by using a combined approach, including surface tension, conductivity and DLS measurements. Above the critical micellar concentration of 4 × 10(-5) mol kg(-1), large supramolecular assemblies with a counterion condensation degree of 0.25 were observed. The bioactivity profile of this new compound was investigated on cancer and non cancer cell lines.

Microstructural characterization of lysophosphatidylcholine micellar aggregates: The structural basis for their use as biomembrane mimics

Lysophosphatidylcholines are widely used as biomembrane mimics. In order to furnish a structural basis for this application, in this work the self-aggregation behaviour of n-acyl-lysophosphatidylcholines (C(n)lysoPC, n=6,8,10,12), in aqueous solution has been investigated by the PGSTE-NMR and spin probing EPR techniques at 25 degrees C. The experimental data show that C(n)lysoPCs behave as zwitterionic surfactants, and permit evaluation of the influence of the acyl chain length on the phospholipid micellization. For all the C(n)lysoPCs considered, the phospholipid intradiffusion coefficient trend shows a slope change corresponding to the critical micelle concentration (CMC). In the micellar composition range, solubilized tetramethylsilane (TMS) molecules were used to determine the micelle intradiffusion coefficient, from which the aggregate radii and the aggregation numbers were obtained. The solvent intradiffusion coefficient in the C(n)lysoPC aqueous mixtures has been also measured. The results show that the C(n)lysoPC micelles present a thick external layer constituted by strongly hydrated glycerophosphocholine groups. The ability of this layer to embed either anionic or cationic guest molecules has been studied by EPR spectroscopy, employing 3-carboxy-PROXYL in its deprotonated form (CP(-)) or TEMPO-choline (TC) as spin probes. In all the considered systems, the nitrogen isotropic hyperfine coupling constant of the spin probe, A(N), decreases and the correlation time, tau(C), increases with increasing phospholipid molality. The results show that C(n)lysoPC micelles can establish a variety of interaction with different guests. In fact, CP(-) anions interact with the C(n)lysoPC choline groups adsorbing on the micelle surface, while TC cations interacting with the C(n)lysoPC phosphate groups are embedded in thick external layer of the micelles.

Mixed micellar aggregates of nonionic surfactants with short hydrophobic tails

Abstract 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.

Effect of chain length in ethoxylated and sulfonate surfactants upon the limiting diffusion coefficients in water at 25.0°C

Limiting diffusion coefficients of ethoxylated surfactants of general formula CH3(CH2)p−1(OCH2CH2)qOH (CpEq) and sulfonate surfactants of formula CH3(CH2)p−1SO3− Na+(CpSO3Na) were measured at 25°C by the Taylor dispersion technique. The series C6Eq, with 0⩽q⩽5, was studied to evaluate the effect of the length of ethoxylic chain, (–OCH2CH2–)q, on the mobility of the surfactant, the series CpE5 with 0⩽p⩽8 was studied to evaluate the effect of the length of the hydrophobic group, (–CH2–)p. The series CpSO3Na was also studied to compare the experimental results with the intradiffusion coefficients obtained by the NMR-PGSE technique and with the data computed by the Nernst–Hartley equation.

Mutual diffusion coefficients in systems with inclusion compounds: α-cyclodextrin - polyoxyethylene 5 hexylether -water and α-cyclodextrin - sodium 1 hexylsulfonate -water

Abstract Mutual diffusion coefficients were measured with the Gouy technique for two ternary systems: (A) α-cyclodextrin - polyoxyethylene 5 hexylether -water, a non-ionic system, and (B) α-cyclodextrin - sodium 1 hexylsulfonate -water, a ionic system. For both systems the four measured diffusion coefficients allow us to estimate the diffusion coefficients of the actual species present in solution, assuming for the inclusion constant the values obtained from calorimetric data.