B. Lonetti

Liquid crystalline magnetic materials

This work deals with the synthesis of a new magnetic liquid crystalline material: a side chain liquid crystal silicone, doped with magnetic cobalt nanorods. This new material presents very promising magnetic properties, discussed in terms of the influence of the lateral liquid crystal groups.

Structural arrest in concentrated cytochrome C solutions: the effect of pH and salts

The effect of pH and different anions of sodium salts on concentrated solutions of cytochrome C protein have been investigated by means of small angle neutron scattering and viscosity measurements. The control and a fine tuning of protein–protein interactions leads to the formation of protein clusters that eventually evolve into a structural arrested state. The appearance of a low Q peak in the small angle neutron scattering intensity distributions is also accompanied by a strong increase in the relative viscosity. These phenomena taken together can be considered as the signature of the gelation process. This structural arrest is induced by salt addition and specifically depends on the nature of anions, according to the Hofmeister series.

Viscoelastic and small angle neutron scattering studies of concentrated protein solutionsPresented at the 17th Conference of the European Colloid & Interface Science Society, Firenze, Italy, September 21?26, 2003.

Small angle neutron scattering (SANS) and rheological measurements have been used to study horse heart cytochrome C, a globular protein characterized by approximately spherical shape (a × b × b = 15 × 17 × 17 A3) with a molecular weight of 12 384 Da and a pI = 10.2. Two series of very concentrated protein solutions have been investigated at pD 5.4 and 11.0, respectively, the volume fraction of the protein spanning from 0.1 to 0.5. The Krieger–Dougherty model was applied to describe the relation between relative high shear viscosity of the solution and volume fraction of the protein at both pD in order to elucidate the charge effect on the interaction potential. The SANS intensity distributions at pD 5.4 were fitted using the GOCM model with an excellent agreement between the theory and experiments up to the volume fraction ϕ of 0.4. At pD 11.0 the intensity distribution at ϕ = 0.1 can be fitted with a pure form factor (oblate ellipsoid), suggesting that under this condition the cytochrome C molecules are almost uncharged and preserve the native molecular size. Addition of salt induces the transformation from liquid to a gel. This is a result of formation of ordered fractal clusters internally as evident from appearance of a second interaction peak at very low Q (magnitude of the scattering vector). The appearance of the low Q peak is also accompanied by a strong increase in the relative viscosity. These phenomena taken together can be considered as the signature of the gelation process.

Synthesis of benzothiadiazole-based molecules via direct arylation: an eco-friendly way of obtaining small semi-conducting organic molecules

New A–D–A–D–A unsophisticated small molecules based on benzothiadiazole and thiophene were designed and synthesized in a two-step pathway, involving the coupling of benzothiadiazole with thiophene-, or bithiophene-carboxaldehyde, followed by Knoevenagel condensation. The first step was specifically investigated in comparing different coupling methods and their related green metrics. It is established that the synthesis of benzothiadiazole-based small molecules via direct heteroarylation may be an environmentally attractive procedure. It generates a low amount of polluting waste in a cost-effective way in comparison to the classical Suzuki coupling. Moreover, the direct arylation using low loading of the palladium-catalyst without a ligand or an additive is the method of choice for the present case. The physico-chemical properties of the four target molecules were investigated using electronic absorption spectroscopy, differential scanning calorimetry, cyclic voltammetry, polarized optical microscopy and small angle X-ray scattering analysis. DFT studies have been performed to support the electronic characteristics.

Liquid crystalline polymer-Co nanorod hybrids: structural analysis and response to a magnetic field.

This work deals with the structural analysis of side-chain liquid crystalline polysiloxanes, doped with magnetic cobalt nanorods, and their orientational properties under a magnetic field. These new materials exhibit the original combination of orientational behavior and ferromagnetic properties at room temperature. Here we show that, within the liquid crystal polymer matrix, the cobalt nanorods self-assemble in bundles made of nanorod rows packed in a 2-dimensional hexagonal lattice. This structure accounts for the magnetic properties of the composites. The magnetic and orientational properties are discussed with respect to the nature of the polymer matrix.

A shear-induced network of aligned wormlike micelles in a sugar-based molecular gel. From gelation to biocompatibility assays

A new low molecular weight hydrogelator with a saccharide (lactobionic) polar head linked by azide-alkyne click chemistry was prepared in three steps. It was obtained in high purity without chromatography, by phase separation and ultrafiltration of the aqueous gel. Gelation was not obtained reproducibly by conventional heating-cooling cycles and instead was obtained by shearing the aqueous solutions, from 2 wt% to 0.25 wt%. This method of preparation favored the formation of a quite unusual network of interconnected large but thin 2D-sheets (7nm-thick) formed by the association side-by-side of long and aligned 7nm diameter wormlike micelles. It was responsible for the reproducible gelation at the macroscopic scale. A second network made of helical fibres with a 10-13nm diameter, more or less intertwined was also formed but was scarcely able to sustain a macroscopic gel on its own. The gels were analysed by TEM (Transmission Electronic Microscopy), cryo-TEM and SAXS (Small Angle X-ray Scattering). Molecular modelling was also used to highlight the possible conformations the hydrogelator can take. The gels displayed a weak and reversible transition near 20°C, close to room temperature, ascribed to the wormlike micelles 2D-sheets network. Heating over 30°C led to the loss of the gel macroscopic integrity, but gel fragments were still observed in suspension. A second transition near 50°C, ascribed to the network of helical fibres, finally dissolved completely these fragments. The gels showed thixotropic behaviour, recovering slowly their initial elastic modulus, in few hours, after injection through a needle. Stable gels were tested as scaffold for neural cell line culture, showing a reduced biocompatibility. This new gelator is a clear illustration of how controlling the pathway was critical for gel formation and how a new kind of self-assembly was obtained by shearing.

Room-Temperature, Strain-Tunable Orientation of Magnetization in a Hybrid Ferromagnetic Co Nanorod–Liquid Crystalline Elastomer Nanocomposite

Hybrid nanocomposites based on magnetic nanoparticles dispersed in liquid crystalline elastomers are fascinating emerging materials. Their expected strong magneto-elastic coupling may open new applications as actuators, magnetic switches, and for reversible storage of magnetic information. We report here the synthesis of a novel hybrid ferromagnetic liquid crystalline elastomer. In this material, highly anisotropic Co nanorods are aligned through a cross-linking process performed in the presence of an external magnetic field. We obtain a highly anisotropic magnetic material which exhibits remarkable magneto-elastic coupling. The nanorod alignment can be switched at will at room temperature by weak mechanical stress, leading to a change of more than 50 % of the remnant magnetization ratio and of the coercive field.

Hybrid vesicles from lipids and block copolymers: Phase behavior from the micro- to the nano-scale

In recent years, there has been a growing interest in the formation of copolymers-lipids hybrid self-assemblies, which allow combining and improving the main features of pure lipids-based and copolymer-based systems known for their potential applications in the biomedical field. In this contribution we investigate the self-assembly behavior of dipalmitoylphosphatidylcholine (DPPC) mixed with poly(butadiene-b-ethyleneoxide) (PBD-PEO), both at the micro- and at the nano-length scale. Epifluorescence microscopy and Laser Scanning Confocal microscopy are employed to characterize the morphology of micron-sized hybrid vesicles. The presence of fluid-like inhomogeneities in their membrane has been evidenced in all the investigated range of compositions. Furthermore, a microfluidic set-up characterizes the mechanical properties of the prepared assemblies by measuring their deformation upon flow: hybrids with low lipid content behave like pure polymer vesicles, whereas objects mainly composed of lipids show more variability from one vesicle to the other. Finally, the structure of the nanosized assemblies is characterized through a combination of Dynamic Light Scattering, Small Angle Neutron Scattering and Transmission Electron Microscopy. A vesicles-to-wormlike transition has been evidenced due to the intimate mixing of DPPC and PBD-PEO at the nanoscale. Combining experimental results at the micron and at the nanoscale improves the fundamental understanding on the phase behavior of copolymer-lipid hybrid assemblies, which is a necessary prerequisite to tailor efficient copolymer-lipid hybrid devices.

Simple Synthetic Molecular Hydrogels from Self- Assembling Alkylgalactonamides as Scaffold for 3D Neuronal Cell Growth

In this work, we demonstrated that the hydrogel obtained from a very simple and single synthetic molecule, N-heptyl-galactonamide was a suitable scaffold for the growth of neuronal cells in 3D. We evidenced by confocal microscopy the presence of the cells into the gel up to a depth of around 200 μm, demonstrating that the latter was permissive to cell growth and enabled a true 3D colonization and organization. It also supported successfully the differentiation of adult human neuronal stem cells (hNSCs) into both glial and neuronal cells and the development of a really dense neurofilament network. So the gel appears to be a good candidate for neural tissue regeneration. In contrast with other molecular gels described for cell culture, the molecule can be obtained at the gram scale by a one-step reaction. The resulting gel is very soft, a quality in accordance with the aim of growing neuronal cells, that requires low modulus substrates similar to the brain. But because of its fragility, specific procedures had to be implemented for its preparation and for cell labeling and confocal microscopy observations. Notably, the implementation of a controlled slow cooling of the gel solution was needed to get a very soft but nevertheless cohesive gel. In these conditions, very wide straight and long micrometric fibers were formed, held together by a second network of flexible narrower nanometric fibers. The two kinds of fibers guided the neurite and glial cell growth in a different way. We also underlined the importance of a tiny difference in the molecular structure on the gel performances: parent molecules, differing by a one-carbon increment in the alkyl chain length, N-hexyl-galactonamide and N-octyl-galactonamide, were not as good as N-heptyl-galactonamide. Their differences were analyzed in terms of gel fibers morphology, mechanical properties, solubility, chain parity, and cell growth.