Ozlem Karahan

Solvent effects on free-radical copolymerization of styrene and 2-hydroxyethyl methacrylate: a DFT study

The free-radical homopolymerization and copolymerization kinetics of styrene (ST) and 2-hydroxyethyl methacrylate (HEMA) in three different media (bulk, DMF, toluene) have been investigated by means of Density Functional Theory (DFT) calculations in combination with the Polarizable Continuum Model (PCM) and the Conductor-like Screening Model for Real Solvents (COSMO-RS). The conventional Transition State Theory (TST) is applied to calculate the rate parameters of polymerization. Calculated propagation rate constants are used to predict the monomer reactivity ratios, which are then used in the evaluation of the copolymer composition following the Mayo–Lewis equation. It is found that copolymerization reactions in bulk and toluene show similar transition geometries; whereas, DMF has a tendency to form H-bonding interactions with the polar HEMA molecules, thus decreasing the reactivity of this monomer during homopolymerization and towards ST during copolymerization. Calculations of copolymer composition further show that the amount of HEMA monomer in the ST–HEMA copolymer system decreases in the polar DMF solution. The calculated spin densities of the radical species are in agreement with the rate parameters and confirm that the copolymerization propagation rate of the ST–HEMA system is in the order: kp(bulk) ≈ kp(toluene) > kp(DMF).

Micro and nanostructural analysis of a human tooth using correlated focused ion beam (FIB) and transmission Electron microscopy (TEM) investigations

In this study, natural molar human tooth specimens were investigated for determining their micro- and nanoscale structural morphology, chemistry and crystallinity. The differences were tracked comparatively for both enamel and dentin layers and at their interfaces. Although dental material structures are hard and tough and the cross-sectioning of these materials using mechanical methods is challenging, FIB-SEM dual-beam instruments serve for preparing ultra-thin homogenous lamella sections. In this work, both FIB-SEM and TEM based advanced characterization methods were applied to reveal different morphological characteristics of dental tissue via complementary imaging and diffraction analysis. In addition, SEM-EDS and Raman spectroscopy techniques provided additional information about the elemental distribution and the chemical composition differences of the dental tissues. According to electron microscopy examinations at the intersection between the enamel and the dentin layers, it was shown that the enamel was denser and polycrystalline, while the dentin layer was porous, fibrillar and of negligible long-range order, due to its tubular structure and organic components. In particular, EDS mapping and linescan analyses showed almost no differences in the elemental distribution. Raman results confirmed that both tissues had similar chemical composition except dentin showed spectral background effects in the spectrum due to its tubular structure and organic components.

Development of Efficient Copper-Based MOF-Derived Catalysts for the Reduction of Aromatic Nitro Compounds: Development of Efficient Copper-Based MOF-Derived Catalysts for the Reduction of Aromatic Nitro Compounds

Two Copper-based Cu3(btc)2 and Cu(Im)2 metal organic frameworks were synthesized and annealed to form nanoporous Cu/Cu2O@C and Cu@N-C nanoparticles for utilization as catalysts in the reduction reaction of aromatic nitro compounds to aromatic amines. All synthesized MOF compounds and MOF-derived nanoparticles were characterized using XRD, Raman, TGA, SEM-EDX and XPS methods. Also, the pore size distribution and surface area of the MOF-derived Cu/Cu2O@C and Cu@N-C nanoparticles were characterized by BJH and BET methods. After characterization, the catalysts Cu/Cu2O@C and Cu@N-C were catalytically tested for the reduction reactions of various aromatic nitro compounds chemically by monitoring via a UV-vis spectrometer. Both catalysts exhibited remarkable results compared with those in the literature. Also, the Cu/Cu2O@C catalyst showed better results than the Cu@N-C catalyst.