Synthesis of a new potassium-substituted lead fluorapatite and its structural characterization.

Prismatic crystals of partially potassium substituted lead fluorapatite Pb5.09Ca3.78K1.13(PO4)6F0.87 were grown through a solid-state reaction. The structural study conducted by single-crystal X-ray diffraction revealed that the compound crystallizes in the hexagonal P63/m space group, with unit cell parameters a = b = 9.7190(5) Å, c = 7.1700(6) Å and V = 587.37(7) Å3(Z = 1), as well as final values amounting to R and wR of 0.0309 and 0.0546, respectively. The structural refinement demonstrated that Pb occupies both the (6h) and (4f) structural sites of hexagonal fluorapatite, K occupies the (6h) site, and Ca is placed on the (4f) site. Powder X-ray diffraction study indicated the absence of additional phases or impurities. Chemical analysis using atomic absorption spectrometry and energy-dispersive X-ray spectroscopy confirmed the expected chemical formula. The electrical conductivity measured over a wide temperature range was found to be governed by the ion mobility mechanism in the tunnel along the c axis (probably attributed to the fluorine ion located there). We, therefore, could infer from the analysis of the complex impedance spectra that the electrical conductivity of our apatite depends essentially on the temperature and frequency, which produces a relaxation phenomenon and semiconductor-like behavior. Moreover, the strong absorption in the UV-Visible region was substantiated through studies of the optical properties of the developed sample. Fluorescence spectra exhibited emissions in the orange regions when excited at 375 nm. The findings of the phenomena resulting from the emission and conduction of the apatite in question suggest its potential for application in various technological fields such as photovoltaic cells, optoelectronics, photonics, LED applications, catalysis and batteries.

Influence of Intramineral Proteins on the Growth of Carbonate Crystals Using as a Scaffold Membranes of Ratite Birds and Crocodiles Eggshells.

The lack of information on structural basis where proteins are involved, as well as the biomineralization processes of different systems such as bones, diatom frustules, and eggshells, have intrigued scientists from different fields for decades. This scientific curiosity has led to the use of methodologies that help understand the mechanism involved in the formation of these complex structures. Therefore, this work focuses on the use of eggshell membranes from different species of ratites (emu and ostrich) and reptiles (two species of crocodiles) as a model to differentiate biocalcification and biosilicification by introducing calcium phosphate or silica inside the membrane fiber mantles. We performed this to obtain information about the process of eggshell formation as well as the changes that occur in the membrane during crystal formation. In order to identify and understand the early processes leading to the formation of the microstructures present in the eggshell, we decided to carry out the synthesis of silica-carbonate of calcium, barium, and strontium called biomorph in the presence of intramineral proteins. This was carried out to evaluate the influence of these proteins on the formation of specific structures. We found that the proteins on untreated membranes, present a structural growth similar to those observed in the inner part of the eggshell, while in treated membranes, the structures formed present a high similarity with those observed in the outer and intermediate part of the eggshell. Finally, a topographic and molecular analysis of the biomorphs and membranes was performed by scanning electron microscopy (SEM), Raman and Fourier-transform Infrared (FTIR) spectroscopies.

Electrochemical and Structural Characterization of Lanthanum-Doped Hydroxyapatite: A Promising Material for Sensing Applications.

In the quest to find powerful modifiers of screen-printed electrodes for sensing applications, a set of rare earth-doped Ca10-xREx(PO4)6(OH)2 (RE = La, Nd, Sm, Eu, Dy, and Tm and x = 0.01, 0.02, 0.10, and 0.20) hydroxyapatite (HAp) samples were subjected to an in-depth electrochemical characterization using electrochemical impedance spectroscopy and cyclic and square wave voltammetry. Among all of these, the inorganic phosphates doped with lanthanum proved to be the most reliable, revealing robust analytical performances in terms of sensitivity, repeatability, reproducibility, and reusability, hence paving the way for their exploitation in sensing applications. Structural data on La-doped HAp samples were also provided by using different techniques, including optical microscopy, X-ray diffraction, Rietveld refinement from X-ray data, Fourier transform infrared, and Raman vibrational spectroscopies, to complement the electrochemical characterization.

Improved Synthesis of Larger Resorcinarenes.

The synthesis of the larger resorcin[5 and 6]arene macrocycles [5](OMe) and [6](OMe) has been realized by a Lewis acid-catalyzed condensation of 1,3-dimethoxy-2-methylbenzene with paraformaldehyde in o-dichlorobenzene as the solvent. The methoxy-resorcin[5 and 6]arenes were quantitatively demethylated by treatment with BBr3 to obtain the corresponding macrocycles with free OH groups. X-ray studies showed that in the solid state both the conformation and the packing of [6](OMe) and [5](OMe) are driven by C-H···O, C-H···π, and π···π interactions.

Stacked naphthyls and weak hydrogen-bond interactions govern the conformational behavior of P-resolved cyclic phosphonamides: a combined experimental and computational study.

P-Enantiomerically pure cyclic phosphonamides have been synthesized via a cyclization reaction of (S,S)-aminobenzylnaphthols with chloromethylphosphonic dichloride. The reaction is highly stereoselective and gives almost exclusively (S,S,SP)-cyclic phosphonamides in good yields. Analysis of the X-ray crystal structures shows clearly that the cyclization reaction forces the two naphthyl rings into a stable parallel displaced stacking assembly and indicates also the existence of intramolecular CH···π interactions and weak forms of intermolecular hydrogen bondings, involving the oxygen and the chlorine atoms. QM computations and NMR spectra in solution confirm the stacked molecular assembly as the preferred arrangement of the two naphthyl groups.

A combined theoretical and experimental investigation on the enantioselective oxidation of aryl benzyl sulfides in the presence of a chiral titanium catalyst.

An experimental investigation of the enantioselective oxidation of aryl benzyl sulfides by tert-butyl hydroperoxide in the presence of a titanium/hydrobenzoin catalyst has shown that these sulfides are ideal substrates for this catalytic system, with negligible interference by the substituents on the aryl groups. A reaction mechanism based on DFT computations has been proposed. The DFT MPWB1K functional was used in the theoretical investigation to account for weak hydrogen-bonding and pi interactions. The computed reaction profile explains the experimentally observed enantioselectivity, which is determined by the thermodynamics of the first phase of the reaction. A detailed discussion of the hydrogen-bonding and pi interactions that drive the reaction along the observed stereochemical path is given.

A new dinuclear platinum complex with a nitrogen-containing geminal bisphosphonate as potential anticancer compound specifically targeted to bone tissues.

The paper describes the synthesis and characterization of a new platinum dinuclear complex (2) bearing a nitrogen-containing geminal bisphosphonate (NBP, 1), structurally related to the commercial drug risedronate. NBPs themselves have shown in quite a few cases to be endowed with anticancer activity, therefore the new platinum complex has two potential antitumor moieties (the NBP ligand and the platinum residue) and could have high affinity for bone tumors or metastases (due to the presence of NBP). The free bisphosphonate (1) has been crystallized by a sol-gel method and characterized by X-ray diffraction analysis. The platinum complex (2) has been found to have a dinuclear structure with the bisphosphonate bridging two platinum moieties in a W conformation.

Highly selective metal mediated ortho-alkylation of phenol. First platinum containing organometallic chromane analogues.

We were able, for the first time, to synthesize and characterize Pt derivatives with a structural shape similar to vitamin E, having a metalla-chromane core. The formation reaction mechanism includes an unexpected highly selective ortho aromatic electrophilic substitution on phenol, operated by [PtCl(eta(1)-C(2)H(4)OR)(N-N)], R = Me or Ph, and a final cyclization step. The X-ray structure of one of the new metalla-chromane complexes [Pt(EtPh)(phen)],1a, (EtPh = 2-(ethan-2'-yl-kC(1))-1-phenolato-k0(1), phen = 1,10-phenanthroline) is reported. Cytotoxicity and Pt uptake measurements, performed on HeLa cancer cells, show an interesting structure-activity correlation for the new metalla-chromane analogues 1a and [Pt(MeOEtPh)(phen)], 1b, (MeOEtPh = 2-(ethan-2'-yl-kC(1))-4-(methoxy)-1-phenolato-k0(1)), being the structurally closest to vitamin E and also the most active.

Sterically hindered complexes of platinum(II) with planar heterocyclic nitrogen donors. A novel complex with 1-methyl-cytosine has a spectrum of activity different from cisplatin and is able of overcoming acquired cisplatin resistance.

A very interesting series of water soluble platinum compounds violating some of the classical structure-activity relationships, but still showing antitumor activity, was reported by Hollis and collaborators some 25 years ago [L.S. Hollis, A.R. Amundsenm, E.W. Stern. J. Med. Chem. 32 (1989) 128-136]. The compounds, having formula [PtClA(2)L](+) (A(2)=two monodentate or a bidentate amine, L=a secondary or tertiary amine or a N-donor heterocycle), were characterized by a positive charge and three non-labile N-donor ligands. We have extended the investigation to analogous compounds in which 2,9-dimethyl-1,10-phenanthroline has taken the place of the A(2) ligand(s) and L is 2-picoline (1), 6-amino-2-picoline (2), or 1-methyl-cytosine (3). The X-ray analysis of 2 has revealed a bow-like distortion of the phenanthroline plane, a sloping of the phenanthroline plane with respect to the coordination plane, and an overall shielding of the metallic core by the ortho substituents of the phenanthroline and pyridine ligands. In vitro grow inhibition assays have been performed on the most water soluble complex 3. The results indicate that this complex is characterized by a potent growth inhibitory activity with mean IC(50) value (in a panel of 11 human tumor cell lines) of 1.1 microM to be compared with a mean value of 3.8 microM for cisplatin. The same compound also appears to completely overcome the acquired cisplatin resistance stemming from reduced uptake or a multifocal mechanism, thus pointing to a mechanism of action distinctly different from that of cisplatin.