Isothermal calorimetric titrations of aqueous solutions of poly(ethylene glycol) (PEG) with sodium dodecyl sulfate (SDS) are known to exhibit a peculiar trend consisting of endothermic and exothermic effects. This behavior was explained with the formation of two different mixed micellar aggregates, one characterized by hydrophobic interactions and the second by ion-dipole association. Present NMR measurements on 13C, 1H, and 23Na nuclei do not support the formation of a number of PEG-SDS aggregates characterized by interactions of different nature. Our data are rather in accordance with the initial formation, at low surfactant concentration, of a polymer-surfactant aggregate in which the polymeric chain assumes a strained conformation in order to bind a small micellar cluster. The subsequent growing of the aggregate with increasing surfactant concentration allows the polymer to relax to a more expanded, energetically favored, conformation. Further calorimetric titrations with a set of PEG samples of different molecular weight (200 to 20000 Daltons) allowed to establish a few points so far unclear. The minimum molecular weights necessary for observing the onset and the settling, respectively, of polymer-surfactant interaction were identified and the characteristic multiple peak curve of the titration of the polymer with molecular weight of 8000 Dalton was found related to the discrete binding of two successive SDS micellar clusters on the same polymeric chain

A series of water-soluble fullerene C(60) derivatives has been investigated for their cytotoxic and hemolytic properties, with the aim to correlate structure with toxicity. We observed that cationic chains induce significant toxicity while the presence of neutral or anionic moieties did not produce any response in our model. A validation of these experimental observations has been performed by theoretical studies in which hydrophilic and hydrophobic surface areas were correlated quantitatively with hemolytic properties.

The importance of Interpenetrating Polymer Networks (IPNs) in biomedical and pharmaceutical fields is continuously growing because of their mechanical and drug carrier tailoring opportunities. This paper deals with the physico-chemical characterization of an IPN hydrogel based on calcium-alginate and a dextran methacrylate derivative. The attention is focused on the determination of IPN mesh size distribution. For this purpose, two different approaches were applied, namely using a combination of rheological and low field NMR characterization, and cryoporosimetry. Appropriate mathematical models were developed for the interpretation of the experimental data. Both approaches led to a monomodal mesh size distribution spanning the same size range but characterized by different mean values (25 nm, Rheo-NMR; 44 nm, cryoporosimetry). This is probably due to mesh widening upon water freezing. Moreover, release experiments of a model protein -myoglobin -from the IPN were performed and the obtained data were combined with the results of the two above mentioned approaches. Release tests yielded an estimation of the mean mesh size that is closer to that obtained according to the rheology-NMR approach than that resulting from cryoporosimetry measurements.

Chitlac is a biocompatible modified polysaccharide composed of a chitosan backbone to which lactitol moieties have been chemically inserted via a reductive N-alkylation reaction with lactose. The physical-chemical and biological properties of Chitlac that have been already reported in the literature suggest a high accessibility of terminal galactose in the lactitol side chain. This finding may account for its biocompatibility which makes it extremely interesting for the production of biomaterials. The average structure and the dynamics of the side chains of Chitlac have been studied by means of NMR (nuclear Overhauser effect and nuclear relaxation) and molecular dynamics to ascertain this hypothesis. A complete assignment of the (1)H and (13)C NMR signals of the modified polysaccharide has been accomplished together with the determination of the apparent pKa values of the primary and secondary amines (6.69 and 5.87, respectively). NMR and MD indicated a high mobility of Chitlac side chains with comparable average internuclear distances between the two techniques. It was found that the highly flexible lactitol side chain in Chitlac can adopt two distinct conformations differing in the orientation with respect to the polysaccharide chain: a folded conformation, with the galactose ring parallel to the main chain, and an extended conformation, where the lactitol points away from the chitosan backbone. In both cases, the side chain resulted to be highly hydrated and fully immersed in the solvent.

The synthesis of four classes of bisadduct derivatives of C60 is reported. The solubility of the new compounds in aqueous solvents is enhanced and is among the highest ever reported for fullerene derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The optical response of nanoplasmonic colloids in disperse phase is strictly related to their shape. However, upon self-assembly, new optical features, for example, bonding or antibonding modes, emerge as a result of the mutual orientations of nanoparticles. The geometry of the final assemblies often determines which mode is dominating in the overall optical response. These new plasmon modes, however, are mostly observed in silico, as self-assembly in the liquid phase leads to cluster formation with a broad range of particle units. Here we show that low-symmetry clustering of gold nanorods (AuNRs) in solution can also reveal antibonding modes. We found that UV-light irradiation of colloidal dispersions of AuNRs in N-methyl-2-pyrrolidone (NMP), stabilized by poly(vinylpyrrolidone) (PVP) results in the creation of AuNRs clusters with ladderlike morphology, where antibonding modes can be identified. We propose that UV irradiation induces formation of radicals in solvent molecules, which then promote cross-linking of PVP chains on the surface of adjacent particles. This picture opens up a number of relevant questions in nanoscience and is expected to find application in light induced self-assembly of particles with various compositions and morphologies.

Functionalized carbon nanotube (CNT) derivatives are currently under thorough investigation in different biomedical investigations. In this field of research, the composition of sample either in terms of covalently attached or physisorbed moieties can greatly affect the observed results and hamper the comparison between different studies. Therefore, the availability of a fast and reliable analytical technique to assess both the type of interaction (covalent vs noncovalent) and the composition of CNT conjugates is of great importance. Here we describe that the two-dimensional diffusion-ordered (DOSY) NMR spectroscopy is extremely useful to discriminate between conjugated and unconjugated polyethylene glycol groups in samples obtained by condensation with oxidized single-walled carbon nanotubes (SWNTs). This fast and nondestructive technique allows us to follow the removal of unconjugated polyethylene glycol chains during the purification. In particular, DOSY analysis reveal that about 1/3 (wt %) of the polyethylene glycol used for the condensation remained physisorbed to functionalized SWNTs after dialysis. Complete elimination of physisorbed polyethylene glycol was achieved using diafiltration.

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