Single-Crystal Synchrotron Radiation X-ray Diffraction Study of B and Ga Silicalites Compared to a Purely  Siliceous MFI: A Discussion of the Heteroatom Distribution We report the structure determinations, obtained by synchrotron radiation single crystal X-ray diffraction experiments, of as synthesized orthorhombic MFI boron- and gallium-silicalites compared to an un-substituted defect free silicalite. All carbon and nitrogen atoms of the disordered tetrapropylammonium (TPA+) template molecules have been located. These molecules, located at the intersection of the straight and sinusoidal channels, are similar to those found by Van Koningsveld et al. [Acta Cryst. 1987, B34, 127] in the parent ZSM-5 system. Refinement of the occupation factors of the T sites indicates that random distribution of B and Ga atoms in the MFI framework (see Fugure below) is important, even if a certain degree of preferred substitution does exist (T1 for B and T2 for Ga). Palin, L., Lamberti, C., Kvick, A., Testa, F., Aiello, R., Milanesio, M., Viterbo, D., J. Phys. Chem. B., 107(17), 2003, 4034-4042.

The MFI framework with the 12 T sites that the heteroatom (Ga and B) can occupy

Evolution of the X-ray Powder Diffraction patterns in the 2.5-12.5° 2Theta interval (corresponding to 14.2-2.8 Å d-spacing) as a function of the temperature during the in situ template burning.

Template burning inside TS-1 and Fe-MFI molecular sieves: An in situ XRPD study The high X-ray flux available at European Synchrotron Radiation Facility (ESRF), combined with the use of a suitably designed area detector setup allowed to follow in real time the structural changes occurring during the template burning processes inside TS-1 and Fe-silicalite MFI zeolites with X-ray powder diffraction technique (XRPD). Rietveld analysis of the XRPD patterns collected in the 350-1000 K interval, integrated each 15 K, yields to the determination of the template overall occupancy factor vs. T with an accuracy comparable with that obtained by thermo-gravimetric measurements, routinely employed for this purpose. The evolution of the structural parameters (V, a, b, c, site occupancy factor of the template molecule) vs. T has been obtained. These data allow us to have, for the first time, a complete view of the structural rearrangements induced by the template burning process on the zeolitic framework. The differences caused by the different heteroatom inserted in the MFI lattice (Ti or Fe) are discussed. The kinetic of the reaction was investigated through the Arrhenius plot, to obtain the activation energy of the calcinations process from the non isothermal data from TS-1 and Fe-MFI. For TS-1, the time resolved template burning experiment has been repeated in isothermal conditions at four different temperatures, to obtain the activation energy. Milanesio M, Artioli G, Gualtieri AF, Palin L, Lamberti C., J. Am. Chem. Soc., 125(47), 2003, 14549-14558.

Structural Characterization of Siliceous Spicules from Marine Sponges Siliceous sponges, one of the few animal groups involved in a biosilicification process, deposit hydrated silica in discrete skeletal elements called spicules. A multidisciplinary analysis of the structural features of the protein axial filaments inside the spicules of a number of marine sponges, belonging to two different classes (Demospongiae and Hexactinellida), is presented, together with a preliminary analysis of the biosilicification process. The study was carried out by a unique combination of techniques: fiber diffraction using synchrotron radiation, SEM, TGA, DSC, FTIR and molecular modeling.  From a phylogenetic point of view the main result is the structural difference between the dimension and packing of the protein units in the spicule filaments of the Demospongiae and the Hexactinellida species. Models of the protein organization in the spicule axial filaments, consistent with the various experimental evidences, are given. The three different species of demosponges analyzed have similar general structural features, but they differ in the degree of order. The structural information on the spicule axial filaments can contribute to shed some light on the still unknown molecular mechanisms controlling biosilicification. Croce G., Frache A., Milanesio M., Marchese L., Causà M., Viterbo D., Barbaglia A., Bolis V., Bavestrello G., Cerrano C., Benatti U., Pozzolini M., Giovine M., Amenitsch H., Biophys. J., 86(1), 2004, 526-534.

Structural model of the organization of the filaments in G. cydonium spicules

The Taxol molecule in one of the stable conformations predicted by ab in itio quantum chemical calculations

Ab Initio Conformational Study of the Phenylisoserine Side Chain of Paclitaxel Paclitaxel and related compounds are important anti tumor drugs, currently used for the treatment of several types of  cancer. The flexible amino acidic C13 side chain is a key element of the taxoid pharmacophore, and the identification of the bioactive conformation is a top priority for a better understanding of the mode of action of these anticancer agents. The conformational features of Paclitaxel and of its C(13) side chain have been investigated by  Hartree-Fock DFT and ONIOM ab initio and by semi empirical PM3 calculations. In the light of these data, it is reasonable to assume that, when the drug is bound to the lipophilic pocket of the tubulin receptor, the C13 amino acidic side chain assumes a conformation close to that stable in apolar solvent. These results seems to be confirmed by recent docking experiment on the tubulin-Paclitaxel adduct crystal structure. Milanesio, M., Ugliengo, P., Viterbo, D., Appendino, G., Journal of Medicinal Chemistry, 42, 1999, 291-299.

Other WWW available material on our research activity can be found on the websites we presented to the ECCCx virtual conferences:

1. An electron density study on the Vitamin C structure have been presented at the ECCC3 virtual conference and the results are available on line at the address: http://www1.elsevier.com/homepage/saa/eccc3/paper23/frame.html
2. The interaction between molecules in the crystals and the possibility of driving the synthesis (i.e. crystal engineering) of new materials was investigated and part of the work was presentedhave been presented at the ECCC9 virtual conference and the results are available on line at the address: http://www.mfn.unipmn.it/~chimfis/ECCC9/