L. Monsù Scolaro

Scaling properties in the internal structure of dendrimer systems

In this work, we study the internal density distribution in a dendrimer or “starburst polymers” system at different generations. We have used different techniques like small angle X-ray scattering, quasi-elastic light scattering and a Molecular dynamics simulation. Obtained data, compared with the literature ones, proposed that lower generation dendrimers display an internal self-similar structure, whereas the higher generations tend to exhibit a spherical homogenous dense structure.

Building a model of interaction at the NK-2 receptors: Polycondensed heterocycles containing the pyrimidoindole skeleton†

Summary The pyrazolopyrimidothiazole ring system (compound N, table II) has been previously reported by us as a new competitive antagonist (apparent pA 2 = 7.3 equiv to 55 nM) at NK2-receptors. As part of our investigation on polycondensed heterocycles containing the pyrimidine ring as antagonists of G-protein coupled receptors, pyrimidoindole derivatives were prepared and tested in order to probe the topography of the NK2-receptors and ascertain the pattern of frameworks that result in optimum affinity and specificity. The title indole derivatives 5, 11a-d, 12c, 13a,b and 14b were ‘de novo’ designed or selected from our chemical archives and prepared by up-to-date synthetic routes, thus exploring new synthetic methodologies. According to the established graphic computer model, none of the tested substances exhibited activity as a consequence of the violation of an excluded volume area due the unfavourable position of the aromatic substituents.

Cyclodextrin nanoaggregates and their assembly with protein: a spectroscopic investigation

Light scattering and time-resolved fluorescence spectroscopy results showed that specially designed amphiphilic cyclodextrins are able to bind a specific protein, PA-I lectin. When containing a galactosyl group, the self-assembled cyclodextrins interact with the protein affecting the dynamical properties of the system and the fluorescence lifetimes (as well as the fluorescence anisotropy) of the protein itself. The self-assembled cyclodextrins containing a glucosyl group, on the other hand, do not induce any change in these measured quantities, suggesting no interaction with protein. This binding capability of galactosyl-modified cyclodextrins offers perspectives on exploiting self-assembled supramolecular structures as nano-carriers to deliver drugs to target tissues.

PORPHYRIN AGGREGATION IN AQUEOUS SOLUTIONS : SMALL ANGLE AND QUASIELASTIC LIGHT SCATTERING RESULTS

Abstract The porphyrin trans -bis( N -methylpyridinium-4-yl)diphenylporphyine ( t -H 2 P agg ) is known to form in solution large assemblies and supramolecular structures in the presence of polyanions, such as nucleic acids, as a template support. We have studied the aggregation of the unbound porphyrin in 0.1 M NaCl aqueous solutions. The aggregation process was monitored by a time resolved small angle light scattering apparatus. The intensity profile of the scattered light as a function of the exchanged wavevector q , conforms to a scattered law for fractal aggregates in the range 0.2–31.4 μm −1 . An analysis of the intensity data reveals a value of the fractal dimension d f equal to 2.5. Additional dynamic light scattering measurements confirm the presence of almost monodispersed aggregates in the mesoscopic range.

X-ray photoelectron spectroscopy and x-ray excited Auger spectroscopy studies of manganese thiophosphate intercalated with sodium ions

Polycrystalline powders of Na2xMn1−xPS3 have been synthesized from layered MnPS3 material by successive ion-exchange intercalation of potassium and sodium ions. Their x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger spectroscopy spectra have been measured at room temperature using Mg Kα (1253.6 eV) x-ray source. In particular, the Mn, P, and S 2p and Na 1s and 2p core-level regions and the Na Auger KL23L23 transition have been investigated. All the analyzed XPS core-level spectra display a single-peak structure, suggesting the absence of nonequivalent atoms of Na, Mn, P, and S. The manganese XPS spectrum shows, as observed in MnPS3 and in its cesium and potassium intercalation compounds, typical shake-up satellites, suggesting that the Mn–S bond is yet mainly ionic in nature. The comparison with the XPS spectra relative to MnPS3 and its potassium intercalation compound (K2xMn1−xPS3) does not emphasize any relevant difference in the binding energy positions of the investigated core levels, in...

An XPS analysis of the interaction of meso-tetrakis(N-methylpyridinium-4-yl)porphyrin with exfoliated manganese thiophosphate

Composite thin films of (C72H66N8O12S4)yLi2xMn1−xPS3 have been obtained through a solution approach by interacting the tosylate salt of the cationic water soluble 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin (H2T4) and MnPS3 exfoliated in the presence of lithium ions. The thin films have been investigated through x-ray diffraction (XRD), ultraviolet/visible (UV/vis) absorption and mainly x-ray photoemission spectroscopy (XPS). N 1s core-level XPS spectra emphasize the presence of three non-equivalent nitrogen atoms, similarly to the film of the pure H2T4 salt. This result, together with the interlayer spacing determined by the XRD pattern and the evidence from absorption measurements, indicates that the porphyrin is intercalated into MnPS3 layers in a non-protonated form and substantially flattened with respect to the free molecule. The striking likeness between the N 1s core levels in the XPS spectra of the composite material, of the H2T4 salt and of the neutral meso-tetrapyridylporphyrin (H2TPyP) suggests that H2T4 is present between the MnPS3 nanosheets together with its counter-ion (tosylate). This hypothesis is confirmed by the observation of a structure which can be attributed to the sulfur of the counterion in the S 2p core-level XPS spectra of the composite material. An analysis of the Mn 2p and 3p, S and P 2p core-level regions through XPS reveals a strong similarity between the starting MnPS3 and the composite material, suggesting that no charge transfer occurs from the guest (H2T4-tosylate) to the host species (MnPS3).

Vertical coupled double organic microcavities

A light emitting structure consisting of two coupled microcavities has been realized and studied. One of the two cavities contains a luminescent organic thin film of tetrakis(4-methoxyphenyl)porphyrin, whereas the other microcavity is a dielectric structure coupled to the organic one by means of a LiF/ZnS Bragg mirror. Reflectivity spectra show the presence of two well defined cavity dips. We observe an energy splitting of the two cavity modes. Despite the fact that only one cavity contains the active layer, the photoluminescence spectra display two peaks with comparable intensities at the same energy of the reflectivity dips. These observations indicate the strong coupling of the two cavities. The comparison of the diagonalized effective Hamiltonian with the observed resonances further confirms the strong coupling.

Fractal aggregation in aqueous solutions of porphyrins

We have studied the aggregation of the porphyrin trans-bis(N-methylpyridinium-4-yl)-diphenylporphyrine (t−H2Pagg) in aqueous solutions by means of light scattering (elastic and quasielastic) and UV-visible absorption measurements. Elastic and dynamic light scattering indicate that the aggregation produces large monodisperse clusters having a fractal structure driven by diffusion limited aggregation (DLA). UV-visible absorption measurements have been applied to study the corresponding kinetics, obtaining the time dependence of the monomer concentration and of the mean cluster size. The obtained findings are in agreement with the picture proposed by current theoretical models and molecular dynamics (MD) simulations on DLA.

Unforeseen alkylating effect of triethylorthoformate in the synthesis of pyrazolotriazolopyrimidine derivative

Summary The final ring closure reaction of 2-phenylamino-3-aminopyrazolo[3,4- d ]pyrimidin-4-ones with triethylorthoformate in the synthesis of 1 H -pyrazolo[3,4- d ][1,2,4]-8 H -triazolo[2,3- a ]-4 H -pyrimidin-4-one derivatives, unexpectedly gave both the desired product and its N 2 -ethyl analog. The structure of the latter, which arises from an unexpected alkylating effect of triethylorthoformate, was determined through a combined instrumental mass spectroscopy/NMR study reported elsewhere (S Pucci et al , manuscript in preparation). It was further defined using a comparison between a sample of 4 obtained by synthesis and a sample of 4 isolated by PLC or RP-PLC of the crude reaction product.

Spectroscopic studies on manganese thiophosphate intercalated with cesium ions

Cesium ions have been intercalated by ion exchange into layered manganese thiophosphate to produce Cs2xMn1−xPS3. Investigations have been conducted by x-ray diffraction analysis, IR absorption spectroscopy, x-ray photoemission spectroscopy (XPS), and dielectric spectroscopy. The XPS spectra, recorded at room temperature and at the Mn, P, and S 2p, Mn 3p, and Cs 3d and 4d core-level regions, indicate that no charge transfer occurs from guest species (Cs+) to pure host lattice (MnPS3). The presence of shake-up satellites at the Mn 2p and 3p core levels suggests that the cesium intercalation does not alter the nature of the Mn–S bond which is mostly ionic. Dielectric measurements, carried out between 260 and 375K and in the 20Hz–1MHz frequency range, classify Cs2xMn1−xPS3 as hopping charge carrier systems. The nature of such carriers can be hypothesized on the basis of both the intercalation process by cationic substitution and the comparison with the observed dielectric response of the pure MnPS3.