Norberto Micali

Scaling the Chirality in Porphyrin J-Nanoaggregates

Chiral porphyrin J-aggregates are confined into microemulsions, achieving a fine control of their size and optical properties. The quality of the circular dichroism signal exhibits a remarkable scaling on the dimension from the nano- up to mesoscopic regime.

Self-organizing functional materials via ionic self assembly: porphyrins H- and J-aggregates on synthetic chrysotile nanotubes.

Positively charged, synthetic chrysotile nanotubes act as inorganic tectons supporting H- and J-type aggregates of anionic porphyrins with markedly different optical properties, making these nanohybrid materials of interest for application in nanotechnology.

Nanostructures of cationic amphiphilic cyclodextrin complexes with DNA.

Complexes of cationic amphiphilic cyclodextrins heptakis[2-(ω-amino-oligo(ethylene glycol))-6-deoxy-6-hexadecylthio]-β-cyclodextrin and heptakis[2-(ω-amino-oligo(ethylene glycol))-6-deoxy-6-dodecylthio]-β-cyclodextrin with DNA were examined by small-angle X-ray scattering and dynamic as well as electrophoretic light scattering. The first cyclodextrin forms bilayer vesicles in water, which, in the presence of calf thymus DNA, transform to a multilamellar complex. In this complex, the DNA lies between the two polar layers of the cyclodextrins protonated amino groups in alternation with the lipidic bilayers. The cyclodextrin with shorter lipid chains, in contrast, forms micelles in water, and electrostatic clustering of these about DNA does not affect their intrinsic structure. These results are relevant to the potential of such cyclodextrins in therapeutic gene delivery, showing that their self-assembly modes in isolation influence their complex formation with DNA and possibly their efficiency in promoting cell transfection.

SERS detection of Biomolecules at Physiological pH via aggregation of Gold Nanorods mediated by Optical Forces and Plasmonic Heating

Strategies for in-liquid molecular detection via Surface Enhanced Raman Scattering (SERS) are currently based on chemically-driven aggregation or optical trapping of metal nanoparticles in presence of the target molecules. Such strategies allow the formation of SERS-active clusters that efficiently embed the molecule at the “hot spots” of the nanoparticles and enhance its Raman scattering by orders of magnitude. Here we report on a novel scheme that exploits the radiation pressure to locally push gold nanorods and induce their aggregation in buffered solutions of biomolecules, achieving biomolecular SERS detection at almost neutral pH. The sensor is applied to detect non-resonant amino acids and proteins, namely Phenylalanine (Phe), Bovine Serum Albumin (BSA) and Lysozyme (Lys), reaching detection limits in the μg/mL range. Being a chemical free and contactless technique, our methodology is easy to implement, fast to operate, needs small sample volumes and has potential for integration in microfluidic circuits for biomarkers detection.

Structural properties of macromolecular solutions

We report measurements of viscosity and light scattering in an aqueous solution of BSA. Like the lysozyme solutions, previously investigated, the BSA solutions show thixotropic properties. Optical measurements of both elastic and inelastic light scattering indicate the existence of a structure in which the BSA molecule tends to clusterize, each cluster being correlated to the others. A k‐dependent diffusion coefficient D(k) is found. The static structure factor deduced from the values of DL(k) agrees well with the indications given by the elastically scattered intensity J(k). Also, the statical properties of scattered light appear to be consistent with the proposed model. A qualitative explanation, in terms of a dominant component in the fluctuations of concentration, is briefly sketched.

Probing specific protein recognition by size-controlled glycosylated cyclodextrin nanoassemblies

The balance between hydrophobic and hydrophilic components in amphiphilic β-cyclodextrins, targeted by receptor specific groups (SC6CDGlc, SC6CDGal, SC16CDGlc, SC16CDGal), sensitively influences the structural properties of these systems. The different amphiphilic features of single cyclodextrins generate micellar aggregates and vesicles with an internal aqueous compartment able to encapsulate guests, such as rhodamine 6G. Small-angle light scattering (SAXS), cryo-TEM and AFM investigations describe the size and shape of these self-organized glycoligands. Recognition of the nanoassemblies by a specific receptor has effectively been demonstrated by means of time resolved fluorescence and is addressed in water by the morphological properties of cyclodextrin aggregates. Exclusively galactosylated thiohexyl-cyclodextrin binds specifically lectin from Pseudomonas aeruginosa. β-D-Galactose competes with galactosylated cyclodextrin aggregates by inhibiting lectin binding but does not affect the mesoscopic environment of the protein. The better selectivity of the less hydrophobic cyclodextrins towards lectin should probably be ascribed to the morphology (size and shape) of these cyclodextrin aggregates. The recognition properties of this particular cyclodextrin (SC6CDGal) are probably due to the presence of small micelles which interact more efficiently with the lectin binding site. The modulation of the hydrophobic–hydrophilic balance of the macrocycle labelled with targeting groups allows the design of “active” nanosized carriers for drug delivery.

Percolation and viscoelasticity of triblock copolymer micellar solutions

We report analyses of an extensive set of rheological data from triblock copolymer micelles in aqueous solutions. We investigated Pluronic L64 (PEO13PPO30PEO13)–water system in the vicinity of the percolation threshold. The existence of percolation loci has been suggested by previous light (elastic and quasi-elastic) and neutron scattering (small angle-SANS) experiments and their analyses by using a sticky hard sphere model of Baxter. The rheological properties of the system was measured by an oscillating viscometer of the frequency range 0.1–60 (rad/s). From these measurements scaling exponents were determined for frequency-dependent complex moduli. The exponents satisfy the scaling relations predicted by the theory. But their numerical values agree with those from the scalar elasticity percolation theory only at the lowest micellar concentrations.

Kinetic effects of tartaric acid on the growth of chiral J-aggregates of tetrakis(4-sulfonatophenyl)porphyrin

The kinetics of growth for chiral J-aggregates of H(4)TPPS(4) porphyrin have been investigated under different experimental conditions in the presence of tartaric acid. The observed rate constants and the anisotropy factor g show a defined dependence on the enantiomer used as a chiral templating agent.

Sequence, Stoichiometry, and Dimensionality Control in Porphyrin/Bis‐calix[4]arene Self‐Assemblies in Aqueous Solution

The use of a water-soluble octacationic bis-calix[4]arene with divergent cavities (BC(4)) as a templating agent for the assembly of a tetraanionic porphyrin (CuTPPS) has allowed the noncovalent synthesis of 2D or 3D multiporphyrin assemblies. Self-assembly of CuTPPS and BC(4) molecules proceeded under hierarchical control in a stepwise fashion to yield discrete and isolable supramolecular nanostructures containing up to 33 molecular elements (i.e., the CuTPPS/BC(4) 17:16 assembly, obtained in less than three hours). The formation of these species could be conveniently monitored by means of UV/Vis spectroscopy by following the absorbance of the Soret band at 412 nm. In particular, the attainment of the pivotal CuTPPS/BC(4) 5:4 species with a cruciform structure, as the key fork-point intermediate for the subsequent formation of the higher 2D and 3D assemblies, has been demonstrated by light-scattering studies and by an unequivocal synthesis of mixed-porphyrin/calixarene 5:4 species involving the use of two different types of metallated porphyrins, namely CuTPPS and MnTPPS. The remarkable stability of these assemblies permits a stepwise synthesis that makes it possible to choose the desired porphyrin sequence.

Amphiphilic Cyclodextrins as Nanocarriers of Genistein: A Spectroscopic Investigation Pointing Out the Structural Properties of the Host/Drug Complex System

Nanoggregates of nonionic amphiphilic cyclodextrin (ACyD) modified with hydrophobic chains of intermediate length [(2-oligo-ethyleneoxide-6-hexylthio)-beta-CyD, SC6OH] were prepared by emulsification-diffusion method. They are able to entrap an isoflavone, genistein (Gen), and the complexed species are studied at different host/guest molar ratio. The increased isoflavone solubility in the presence of the aggregates of SC6OH is investigated by UV-Vis spectroscopy, whereas size, charge, and structure of aggregates and their complexes with Gen are measured by means of static and quasi-elastic light scattering, and electrophoretic mobility measurements. On the other hand, preparing samples by the conventional method used for liposomes (hydration of an organic film of SC6OH and sonication) gives rise to aggregates with different sizes and lower colloidal stability. It is shown that the improved stability in water of ACyD aggregates both in the absence and in the presence of Gen, obtained by emulsification-diffusion is due to the existence of nanodomains of organic solvent (R(H) congruent with 120 nm) which cannot be completely removed by evaporation and freeze-drying and in which host/guest complexes are contained. This result shows that residues of organic solvent from preparation step favor the colloidal stability of the aggregate, but their presence must be taken into account in designing systems for drug delivery.