Characterization of the Fe site in iron-sulfur cluster-free hydrogenase (Hmd) and of a model compound via nuclear resonance vibrational spectroscopy (NRVS)

We have used (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the iron site in the iron-sulfur cluster-free hydrogenase Hmd from the methanogenic archaeon Methanothermobacter marburgensis. The spectra have been interpreted by comparison with a cis-(CO)2-ligated Fe model compound, Fe(S2C2H4)(CO)2(PMe3)2, as well as by normal mode simulations of plausible active site structures. For this model complex, normal mode analyses both from an optimized Urey-Bradley force field and from complementary density functional theory (DFT) calculations produced consistent results. For Hmd, previous IR spectroscopic studies found strong CO stretching modes at 1944 and 2011 cm(-1), interpreted as evidence for cis-Fe(CO)2 ligation. The NRVS data provide further insight into the dynamics of the Fe site, revealing Fe-CO stretch and Fe-CO bend modes at 494, 562, 590, and 648 cm(-1), consistent with the proposed cis-Fe(CO)2 ligation. The NRVS also reveals a band assigned to Fe-S stretching motion at approximately 311 cm(-1) and another reproducible feature at approximately 380 cm(-1). The (57)Fe partial vibrational densities of states (PVDOS) for Hmd can be reasonably well simulated by a normal mode analysis based on a Urey-Bradley force field for a five-coordinate cis-(CO)2-ligated Fe site with additional cysteine, water, and pyridone cofactor ligands. A "truncated" model without a water ligand can also be used to match the NRVS data. A final interpretation of the Hmd NRVS data, including DFT analysis, awaits a three-dimensional structure for the active site.     

Synthesis and electropolymerization studies of non-aggregated (4-{3-[3-(dimethylamino,diethylamino)phenoxy]propoxy}phenyl)propanoxy substituted silicon naphthalocyanines

In this study, 3-(4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)propan-1-ol, 3-(4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)propan-1-ol and axially disubstituted silicon naphthalocyanines (SiNc) bearing electropolymerizable bis-[(4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)propanoxy] and bis-[(4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)propanoxy] units were synthesized for the first time. Aggregation behavior of SiNcs was examined in different solvents and concentrations in DMSO. In all solvents and concentrations, SiNcs were non-aggregated. Also, electrochemical studies of SiNcs were investigated by cyclic and square wave voltammetry. While SiNcs gave only naphthalocyanine-based reduction process during the cathodic potential scans, they were electropolymerized on the working electrode during the anodic potential scan because of the oxidative electropolymerization of (4-{3-[3-(dimethylamino)phenoxy]propoxy}phenyl)propanoxy and (4-{3-[3-(diethylamino)phenoxy]propoxy}phenyl)propanoxy groups on the substituents of the complexes.     

Investigation of DTS effect on r.f. magnetron sputtered ZnO thin films

The aim of this study depends on understanding the effect of target‐to‐substrate distance (D_TS) on ZnO thin films deposited by r.f. magnetron sputtering on to glass substrates at room temperature conditions. The D_TS was changed from 35 mm to 65 mm with steps of 5 mm at 165 W and 0.2 Pa. The deposition rate of the films were ranged from 76 Ǻ / min to 146 Ǻ / min, while 10^‐3 Ω.cm was obtained as the resistivity value with the help of four point probe technique. The structural investigations were carried out by using both the x‐ray diffraction (XRD) and high resolution transmission electron microscopy. According to XRD observations, the films were (002) oriented. Surface behaviour of the ZnO films was examined with atomic force microscopy and scanning electron microscopy. The root mean square (RMS) values were varied from 4.6 nm to 22.8 nm. Also, optical properties were obtained from UV–visible spectrophotometer and the transmittances as around 80 %. At 45 mm D_TS value, the minimum resistivity measured as 9 × 10^{− 4} Ω.cm with 76 Ǻ / min deposition rate. The RMS was obtained as 4.9 nm and transmission was measured as 85.30 %, while band gap was 3.45 eV.     

Tuning Photoinduced Intramolecular Electron Transfer by Electron Accepting and Donating Substituents in Oxazolones

The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31?+?G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the π-electron mobility, however, the 3,5-dinitro substituent decreased the π-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the π-conjugated linker and may find applications in photovoltaic cells and light emitting diodes.     

Structural and photophysical characterization, topological and conformational analysis of 2-o-tolyl-4-(3-N,N-dimethylaminophenyl-methylene)-oxazol-5-one

A novel oxazole-5-one derivative 2-o-tolyl-4-(3-N,N-dimethylaminophenylmethylene)-oxazol-5-one (TDPO) C₁₉H₁₈N₂O₂ is synthesized and characterized and the crystal structure is determined by X-ray crystallography. TDPO is monoclinic in the P2₁/c space group. The molecule adopts the Z configuration. To enlighten the flexibility of TDPO, the selected torsion angle is varied from −180° to 180° in each 10° separately, and the molecular energy profile is calculated and analyzed by density functional calculations. In addition, Bader’s QTAIM analysis is performed to investigate the intramolecular weak interactions.