Publications

Azathioprine (Imuran), one of the oldest immunosuppressants, having been used in transplantation since the early 1960's, is known to have only two crystal forms: an anhydrous form and a dihydrate phase. We report the crystal structure of a new anhydrous solid-state form of Azathioprine, determined directly form powder X-Ray diffraction data, employing the direct-space genetic algorithm technique for structure solution, followed by Rietveld refinement. The new anhydrous polymorph is accessible only by a solid-state dehydration process of the readily obtained monohydrate form of Azathioprine, the form for which a crystal structure has not previously been reported. The IR and Raman spectra confirmed the results obtained from X-Ray diffraction indicating the presence of all functional groups involved in intermolecular hydrogen bonding which dictates different arrangement of molecules in the structural packing. (C) 2018 Elsevier B.V. All rights reserved.

Bipolar Pulse High Power Impulse Magnetron Sputtering (BP-HiPIMS) was investigated and used in this work to control the ion bombardment process of growing thin films and to improve their structure and properties. Energy-resolving mass spectroscopy was used to investigate the effect of reverse target voltage on the ion energies and fluxes during BP-HiPIMS of a high-purity copper target, in argon gas. It was found that the reverse target voltage provides a wide range of ion energies and fluxes incident to the growing film, which, in turn, produce a wide variety of effects during the deposition process, improving the adhesion strength and influencing both surface and bulk properties. Fast ICCD imaging was used to investigate both HiPIMS and BP-HiPIMS plasma dynamics. The temporal and spatial distributions of plasma potential measurements were performed in order to explain the mechanisms for accelerating the ions. The topological, structural and mechanical properties of the deposited coatings were investigated using atomic force microscopy (AFM), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), thermal desorption spectroscopy (TDS), scanning electron microscopy (SEM), nanoindentation and scratch tests. The obtained results indicate an energy-enhanced deposition process during BP-HiPIMS, the deposited films being characterized by smooth surfaces, dense microstructure, small inert gas inclusions, high elastic strain to failure, scratch resistance and good adhesion to the substrate. These improvements in the films' structure and properties may be attributed to the intense and energetic ion bombardment taking place during the deposition process. During BP-HiPIMS operation, there is no net increase in the deposition rate as compared to the monopolar regime due to the re-sputtering process.

(Y0.87-xLa0.1Zr0.03Ybx)(2)O-3 (x = 0.02, 0.04, 0.05) transparent ceramics were obtained by solid-state reaction and combined sintering procedures with La2O3 and ZrO2 as sintering additives. A method based on two-step intermediate sintering in air followed by vacuum sintering was applied in order to control the densification and grain growth of the samples during the final sintering process. The results indicate that La2O3 and ZrO2 co-additives can improve the microstructure and optical properties of Yb:Y2O3 ceramics at relatively low sintering temperature. On the other hand, the addition of Zr4+ ions leads to the formation of dispersed scattering volumes in the ceramic bodies. Transmittance of 78.8% was measured for the 2.0 at% Yb:Y2O3 ceramic sample at the wavelength of 1100 nm. The spectroscopic properties of Yb:Y2O3 ceramics were investigated at room temperature. The obtained results show that the absorption cross-section at 978 nm is in the range of 2.08 x 10(-20) to 2.36 x 10(-20) cm(2), whereas the emission cross-section at 1032 nm is similar to 1.0 x 10(-20) cm(2).

N-doped, defective graphene obtained by pyrolysis of chitosan at 900 degrees C under Ar exhibits catalytic activity for the Sabatier hydrogenation of CO2 to CH4 at temperatures about 500 degrees C with estimated turnover frequencies and activation energy values of 73.17s(-1) and 24.3 kcal x mol(-1), respectively. It has been found that this enhanced catalytic activity compared to other related doped defective graphenes derives from the presence of pyridinic N atoms that adsorbs CO2 forming carbamate-type adsorbates.

The interaction of proteins with free radicals leads, among other types of damages, to the production of stable carbonyl groups, which can be used as a quantification of oxidative stress at proteins level. The aim of this study was the development of an electrochemical sensor for the detection of carbonyl groups in proteins oxidized by reactive oxygen species. Its working principle is based on the redox properties of dinitrophenylhydrazine (DNPH). BSA was used as a model protein and its oxidation achieved through Fenton reactions. Using differential pulse voltammetry at glassy carbon electrode, the electrochemical behavior of DNPH and of the native and oxidized BSA was investigated in solution. It has been shown that the hydrazine moiety of the DNPH is the electroactive center and is responsible for carbonyl complexation. Special attention was paid to the immobilization of the DNPH in order to retain its redox properties, and this was achieved on a mixed 4-styrenesulfonic acid-nafion matrix. The sensor's surface characterization and the detection of carbonyl groups in oxidized protein were performed by voltammetry, Fourier-transformed infrared spectroscopy and scanning electron microscopy while the voltammetric results were confirmed by surface plasmon resonance measurements. It has been shown that upon interaction with carbonyl groups of the oxidized protein, the oxidation peak of the hydrazine moiety of DNPH decreases as a function of incubation time and protein concentration. The sensor sensitivity was 0.015 nmol carbonyl per mg of oxidized protein and detection limits of 50 mu g oxidized BSA and 0.75 pmol carbonyls.

o-Alkenyl N-triflylanilides underwent rhodium(III)-catalyzed oxidative annulations with alkynes to produce different types of naphthylamides in a process which involves the cleavage of two C-H bonds. Remarkably, besides formal dehydrogenative (4C+2C) cycloadducts, the reaction also produces variable amounts of isomeric naphthylamides, whose formation requires a formal migration of the alkenyl moiety from the ortho to the meta position of the anilide. The annulation reaction can be efficiently carried out in the absence of external oxidants, such as Cu(OAc)(2).

The electro-oxidation mechanism of free methionine and bound within different peptide sequences was investigated by voltammetry, at glassy carbon electrode, and mass spectrometry. It is proposed that the electro-oxidation of free methionine occurs in two steps, each involving the transfer of one electron and turns pH-independent from mild acid to mild alkaline electrolytes. The first oxidation reaction leads to the formation of a cation radical stabilized either through the amino group resulting in the dehydromethionine intermediate, or by interaction with a neutral methionine molecule leading to production of a dimer cationic radical. The dehydromethionine hydrolysis gave methionine sulfoxide as final oxidation product, whereas a future oxidation of methionine dimer cation radical, i.e. the second electro-oxidation step, results in a methionine dimer dication. Moreover, at high acid media, the protonated amino group influence the electro-oxidation process to take place via proton transfer mechanism. The presence of methionine sulfoxide and of the dimer cationic radical as oxidation products of methionine was confirmed by mass spectroscopy.

Calcium carbonate from marble and seashells is an eco-friendly, sustainable, and largely available bioresource for producing natural bone-like calcium phosphates (CaPs). Based on three main objectives, this research targeted the: (i) adaptation of an indirect synthesis route by modulating the amount of phosphorus used in the chemical reaction, (ii) comprehensive structural, morphological, and surface characterization, and (iii) biocompatibility assessment of the synthesized powdered samples. The morphological characterization was performed on digitally processed scanning electron microscopy (SEM) images. The complementary 3D image augmentation of SEM results also allowed the quantification of roughness parameters. The results revealed that both morphology and roughness were modulated through the induced variation of the synthesis parameters. Structural investigation of the samples was performed by Fourier transform infrared spectroscopy and X-ray diffraction. Depending on the phosphorus amount from the chemical reaction, the structural studies revealed the formation of biphasic CaPs based on hydroxyapatite/brushite or brushite/monetite. The in vitro assessment of the powdered samples demonstrated their capacity to support MC3T3-E1 pre-osteoblast viability and proliferation at comparable levels to the negative cytotoxicity control and the reference material (commercial hydroxyapatite). Therefore, these samples hold great promise for biomedical applications.

Titanium dioxide (TiO2) and TiO2 - graphene oxide (GO) composite layers were deposited by spin coating technique onto SiO2 quartz substrates. TiO2 NPs and GO platelets were used as base materials for the preparation of the starting water/acetone dispersions. Polystyrene (PS) buffer layers were deposited by drop-cast method onto the substrates surface to ensure the adherence of the pure TiO2/PS and TiO2-GO/PS composite layer. The surface morphology and physico-chemical properties of the layers have been determined and correlated with their photocatalytic properties. It was found that GO oxygen functional groups are reduced by the presence of TiO2 NPs in the composite materials. Photodegradation activity under UV-visible light irradiation was studied by measuring the concentration changes in time of organic methylene blue dye in aqueous solutions as well as the chemical oxygen demand for real wastewater samples. The obtained results revealed that the photocatalytic properties of the spin coated composites are determined by the graphene oxide concentration. The effect of the spontaneous reduction of GO in the presence of TiO2 NPs on the photocatalytic activity of the TiO2-GO/PS composites is discussed in detail.

We report the successful growth of multiferroic (Nd,Fe)-doped PbTiO3 thin films with the composition (Pb0.88Nd0.08)(Ti0.93Fe0.05Mn0.02)O-3 (PNFT) using pulsed laser deposition. The deposited films have been investigated by XRD, SEM, energy-dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), atomic force microscopy, magnetic force microscopy, piezoforce microscopy, spectroscopic ellipsometry (SE) and dielectric spectroscopy measurements. PNFT films deposited on different substrates (MgO, SrTiO3 and Nb:SrTiO3) are (001) oriented, preserving the orientation of the single-crystal substrates. EDS mapping and SIMS across the film thickness probed the uniform distribution of all the elements. The refractive index and extinction coefficient have been obtained with the SE software package and refined with an optical-graded model. Magnetic domains and ferroelectric domains have been evidenced at microscopic scale. Good dielectric properties and low loss, comparable to those of bulk materials, have been obtained.