C-terminal processing of yeast Spt7 occurs in the absence of functional SAGA complex

Background  

Spt7 is an integral component of the multi-subunit SAGA complex that is required for the expression of ~10% of yeast genes. Two forms of Spt7 have been identified, the second of which is truncated at its C-terminus and found in the SAGA-like (SLIK) complex.     

Reduction of hematite with ethanol to produce magnetic nanoparticles of Fe3O4, Fe1 − x O or Fe0 coated with carbon

The production of magnetic nanoparticles of Fe₃O₄ or Fe⁰ coated with carbon and carbon nanotubes was investigated by the reduction of hematite with ethanol in a Temperature Programmed Reaction up to 950°C. XRD and Mössbauer measurements showed after reaction at 350°C the partial reduction of hematite to magnetite. At 600°C the hematite is completely reduced to magnetite (59%), wüstite (39%) and metallic iron (7%). At higher temperatures, carbide and metallic iron are the only phases present. TG weight losses suggested the formation of 3–56 wt.% carbon deposits after reaction with ethanol. It was observed by SEM images a high concentration of nanometric carbon filaments on the material surface. BET analyses showed a slight increase in the surface area after reaction. These materials have potential application as catalyst support and removal of spilled oil contaminants.     

Vibrational spectra of Na, K, Mn2+, Ni2+ and Zn2+ salts of 1,2,4,5-benzenetetracarboxylic (pyromellitic) acid--a short hydrogen bond evidence

Five salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C6H2(COO)4H4], have been synthesized and investigated by infrared and Raman spectroscopy and by single crystal X-ray diffraction methods: sodium salt [Na2(H2O)2][C6H2(COO)4H2], potassium salt [K(H2O)3][C6H2(COO)4H3] and transition metal salts [M(H2O)6][C6H2(COO)4H2], which M = Mn, Ni and Zn. Crystal structures of all five compounds show short intramolecular asymmetric hydrogen bonds (SHB) between adjacent carboxyl groups with O...O distance average of 2.40 A. The Raman and infrared spectra reported indicate the presence of short hydrogen bonds in all salts, in agreement with the X-ray data. The O-H stretching mode [nu(OH)] had been observed at about 2500 cm(-1). Deuterated analogues were synthesized and their Raman spectra show that nu(OH)/nu(OD) ratio average is about unit. The symmetric [nu(sym)(O..H..O)] and asymmetric [nu(asym)(O..H..O)] stretching modes have been attributed about 300 and 870 cm(-1), respectively, in all salts, and for deuterated analogues, the ratio nu(OH)/nu(OD) to nu(sym)(O..H..O, O..D..O) is close to unit like it occurs in nu(OH). The vibrational modes, mainly SHB modes, are tentatively assigned by molecular orbital ab initio calculations of pyromellitic acid and anions [C6H2(COO)4H3]- and [C6H2(COO)4H2]2-. Geometry optimizations showed a good agreement with experimental data. Frequency calculation confirms the assignment of specific vibrational modes. Ab initio calculations show that nu(C=O) and nu(sym)(COO) are strongly coupled with in plane OH bending [delta(OH)]. In Raman spectra of deuterated analogues is observed a frequency shift of these bands.     

A short hydrogen bond investigation by polarized Raman spectra of Co2+ and Zn2+ salts of pyromellitic acid

Cobalt and zinc salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C(6)H(2)(COO)(4)H(4)], have been synthesized and investigate by polarized Raman spectroscopy. These compounds present short intramolecular hydrogen bonds (SHB) between adjacent carboxyl groups. Raman spectra indicate the presence of this interaction in both salts. Three specific vibrational of SHB modes have been investigated: O-H-O symmetric [nu(sym)(OHO)] and asymmetric [nu(asym)(OHO)] stretching modes and O-H stretching mode [nu(O-H)], which they were observed around 300, 850 and 2500 cm(-1), respectively. In crystallographic point of view, the cobalt salt presents a symmetric SHB while the zinc salt presents an asymmetric SHB. In cobalt salt all three vibrational modes of O-H-O groups in polarized Raman spectra occur in A(g) orientation although in zinc salts two of them are observed in A(g) orientation and one in B(g). Spectra analysis indicate that nu(sym)(OHO) mode is observed as A(g) to cobalt salt and B(g) to zinc salt. This mode occurs in a crowded spectral region and its identification was made by deconvolution techniques. Comparing spectra of the two salts, it is observed a small difference in relative intensity and wavenumber shift of nu(sym)(OHO) (deviance of 43 cm(-1)) and nu(OH) (deviance of 21 cm(-1)) modes due probably to differences in O...O distance between salts and in orientation of pyromellitate anion in unit cell. The nu(asym)(OHO) mode does not present significant wavenumber shift due difference in SHB. The nu(OH) band presents a great potential for hydrogen bond studies due to the fact that in its vibrational region (around 2500 cm(-1)) it is not observed other vibrational modes of these compounds.