Gianluca Croce

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, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetric (DSC), Fourier transform infrared spectroscopy (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 help shed some light on the still unknown molecular mechanisms controlling biosilicification.

Structural characterization and thermal and chemical stability of bioactive molecule–hydrotalcite (LDH) nanocomposites

Layered double hydroxides (LDH) are versatile materials used for intercalating bioactive molecules, both in pharmaceutical and cosmetic fields, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability, and/or obtaining modified release properties. The properties of the intercalation compounds of Mg/Al_LDH and Zn/Al_LDH with different drugs and sunscreens, namely diclofenac, ketoprofen, gliclazide, retinoic acid, furosemide, para-aminobenzoic acid and 2-phenylbenzimidazolsulfonic (Eusolex) acid, have been studied by crystallographic, spectroscopic and thermogravimetric techniques and by solid state NMR, to shed light on their structure, their molecular interactions and their stability from the thermal and chemical viewpoint. The structural features were described with particular attention to the interaction between the organic and inorganic components and to the stability of the intercalation products. For the first time two synchrotron radiation powder diffraction patterns of organic-containing LDH were solved and refined by Rietveld methods to obtain an experimental crystal structure.

Sonochemical Synthesis and Structural Characterization and DFT Calculations of a Novel Nano Flower Pb(II) Coordination Compound [Pb(phen)2(4-abs)2]n

Nano-structures of a new coordination polymer of divalent Pb with the ligands 1,10-phenanthroline (phen) and 4-aminobenzene sulfonic acid (4-abs), [Pb(phen)2(4-abs)2]n (1), were synthesized by a sonochemical method that produced a coordination polymer of nanometer size. The new nano-structure was characterized by scanning electron microscopy, X-ray powder diffraction and IR spectroscopy and elemental analysis. Compound 1 was structurally characterized by single crystal X-ray diffraction and showed that the coordination number of the Pb(II) ions is six; i.e. (PbN4O2). Compound 1 also has a stereochemically active lone pair of electrons and a hemi-directed coordination sphere. The chains interact with each other through π–π stacking to create a 3D framework. The structure of 1 was optimized by density functional theory calculations. The calculated structural parameters and IR spectra of 1 are consistent with the crystal structure.

Rationalization of Dye Uptake on Titania Slides for Dye‐Sensitized Solar Cells by a Combined Chemometric and Structural Approach

A model photosensitizer (D5) for application in dye-sensitized solar cells has been studied by a combination of XRD, theoretical calculations, and spectroscopic/chemometric methods. The conformational stability and flexibility of D5 and molecular interactions between adjacent molecules were characterized to obtain the driving forces that govern D5 uptake and grafting and to infer the most likely arrangement of the molecules on the surface of TiO2. A spectroscopic/chemometric approach was then used to yield information about the correlations between three variables that govern the uptake itself: D5 concentration, dispersant (chenodeoxycholic acid; CDCA) concentration, and contact time. The obtained regression model shows that large uptakes can be obtained at high D5 concentrations in the presence of CDCA with a long contact time, or in absence of CDCA if the contact time is short, which suggests how dye uptake and photovoltaic device preparation can be optimized.

Studying modifications and reactions in materials by simultaneous Raman and X-ray powder diffraction at non-ambient conditions: methods and applications

X-ray powder diffraction played a key role in materials science over the past 25 years. It is now possible to employ powder diffraction at in situ conditions to study solid-state transformations. “Real” materials science samples often show deviations from the “perfectly crystalline” state and hence powder diffraction reaches its limits. Spectroscopic techniques can often provide useful complementary information. With the aim of gaining information from this aspect, we combined Raman spectroscopy with diffraction. A novel experimental setup for simultaneous in situ Raman and XRPD experiments was designed and realized at the SNBL line at ESRF Synchrotron (Grenoble-F). High-resolution XRPD data can be collected with a time resolution in the range of minutes. A permanently installed Raman spectrometer can now be used to measure the same sample at the same spot under the same conditions. A wide variety of non-ambient conditions are available. The setup is described with limitations and potentialities, by describing one example of application. Finally some hints on future improvements are described.

Synthesis, structural and spectroscopic study of the donor–acceptor complexes between fluorene and D2h cyano molecular building blocks

Three solid molecular complexes of fluorene with electron-withdrawing tetracyanoethylene, 1,2,4,5-tetracyanobenzene and 7,7,8,8-tetracyanoquinodimethane were synthesized. Single-crystal X-ray diffraction data elucidated the order–disorder aspects of the crystal structures ascribed to the different molecular symmetries of the employed building blocks. This hypothesis was confirmed by the structural and energetic results of ab initio periodic calculations. Donor–acceptor solid state interactions between molecular counterparts have been highlighted by electron and vibrational IR and Raman solid state spectroscopy, indicating a significant extent of electron density transfer from the fluorene unit towards the cyano-molecules. The experimental evidences of donor–acceptor interactions between molecular counterparts were compared to the lattice energies and solid state band-gaps, obtained by periodic calculations, and to the cluster HOMO–LUMO differences, obtained by isolated cluster calculations. A good agreement between spectral and theoretical data was found.

Development and Characterization of a Novel Bioresorbable and Bioactive Biomaterial Based on Polyvinyl Acetate, Calcium Carbonate and Coralline Hydroxyapatite

Coralina® HAP-200 (coralline hydroxyapatite obtained by hydrothermal treatment of marine corals) and POVIAC® (polymeric matrix based on PVAc), commercial trade marks were mixed with a natural product from the Cuban sea costs, i.e. calcium carbonate from Porites Porites coral, to obtain a novel bioactive composite with potential use as bone restoration material. The samples were characterized by physical-chemical (FTIR, XRD, SEM, EDS) and mechanical studies. It was shown that there is no chemical interaction between the inorganic filler and the polymer matrix, each conserving the original properties of the raw materials. The studied formulation had a compressive strength similar to that reported for trabecular bone. Scanning electron microscopy examination revealed that the addition of CaCO3 induces a change on the morphologic structure of the composite obtained after 30 days of SBF immersion. These composites generate novel biomaterials capable of promoting the deposition of a new phase, a Ca-P layer due to the bioactivity of a Ca2+ precursors.

A Combined High-Resolution X-ray Powder Diffraction, Computational, and XPS Study of the Local Structure of Extra-Framework Copper Ions in Over-Exchanged Cu-MCM22 Zeolite

Local structure and site distribution of extra-framework copper ions in over-exchanged Cu-MCM22 zeolite were determined by a combination of high resolution X-ray powder diffraction and computational analysis. X-ray diffraction data suggested the presence of three Cu sites in six-membered rings and one site in a five-membered ring close to the interlamellar region, inside the MCM-22 supercage, whereas no Cu ions were found within the sinusoidal channels. First principle molecular orbital DFT calculations were employed to obtain, for the first time, an accurate structural description of the Cu(I) sites in the supercage, adding a structural and energetic interpretation to previous IR and EPR studies. The combined experimental and computational study suggested that Cu(I) sites facing 6-MRs are particularly stable. In general 5- or 4-fold coordination sites are located in 6-MRs while 2- or 3-fold coordination sites are located in 5-MRs. Three preferentially occupied sites were found in copper-exchanged MCM-22. X-ray photoelectron spectroscopy suggested the formation of dispersed Cu close to the surface of MCM-22 crystallites, easily reduced to Cu(I) under ultrahigh vacuum conditions.

Rational design of the solid-state synthesis of materials based on poly-aromatic molecular complexes

The possibility of exploiting a thermally-induced solid-state reaction to obtain the formation of a fluorene and TCNQ molecular complex was proposed by some of us (Kumar et al., Cryst. Growth Des., 2009, 9(8), 3396–3404). In this paper, we generalize and rationalize the approach to other charge transfer (CT) molecular complexes with naphthalene and anthracene, changing the size of the donor moiety to propose a general approach for the preparation of this class of materials by exploiting the solid-state synthesis method. Moreover, the kinetic features of the solid state reactions were fully elucidated by Raman spectroscopy and high resolution X-ray Powder Diffraction analysis (in situ Raman/XRPD), exploiting the Avrami equation in isothermal and non-isothermal conditions; rate constants, reaction orders and activation energies were obtained. All the three tested solid-state charge transfer (SS-CT) reactions obeyed a general rule, whereby the most apt reaction temperature was predicted. Finally, a method based on principal component analysis (PCA) for a fast kinetic analysis of in situ XRD synchrotron data was successfully developed, employing a formalism suitable for the analysis of non-isothermal reaction data, thus allowing a high throughput approach for the fast screening of the kinetics of parent reactions. PCA analysis was exploited as an alternative technique to obtain kinetic information in a faster and more efficient way, which can be used for online monitoring and/or in all those cases where Rietveld analysis is not feasible.

Multi-component, regio-selective aldol addition of β-ketoesters to aldehydes: scope and applications

Simple and effective multi-component one-pot aldol addition/protection reactions of β-ketoesters to a series of aldehydes in the presence Me(3)SiCl and i-Pr(2)EtN have been described. The analysis of the scope of the reaction revealed a dramatic dependence of the reactivity on the substrates used. Thus the effect of a catalytic amount of DMF and different reaction conditions was widely investigated. Further transformations of the aldol adducts were particularly useful to give valuable diols and compounds with quaternary stereocenters, while X-ray structural analysis gave also important stereochemical information about this challenging reaction.