Effect of chemical substitution in Rh17S15

Rh17S15 has recently been shown to be a strongly correlated superconductor with a transition temperature of 5.4 K. In order to understand the nature of strong correlations we study the effect of substitution of some of the Rh and S atoms by other elements such as Fe, Pd, Ir and Ni on the Rh side and Se on the S side in this work. We find that while substitution of Ir and Se lower the transition temperature considerably, that of Fe, Pd and Ni destroy superconductivity down to 1.5 K. The resistivity data in these doped samples show a minimum which is presumably disorder induced. A reduction of Tc is always accompanied by a reduction of electron correlations as deduced from heat capacity and magnetization data. Interestingly, the Fe doped sample shows some possible antiferromagnetic ordering at low temperatures.Comment: Published in Journal of Physics Condensed Matte

Structural and Dynamic Features of F-recruitment Site Driven Substrate Phosphorylation by ERK2

The F-recruitment site (FRS) of active ERK2 binds F-site (Phe-x-Phe-Pro) sequences found downstream of the Ser/Thr phospho-acceptor on cellular substrates. Here we apply NMR methods to analyze the interaction between active ERK2 (ppERK2), and a 13-residue F-site-bearing peptide substrate derived from its cellular target, the transcription factor Elk-1. Our results provide detailed insight into previously elusive structural and dynamic features of FRS/F-site interactions and FRS-driven substrate phosphorylation. We show that substrate F-site engagement significantly quenches slow dynamics involving the ppERK2 activation-loop and the FRS. We also demonstrate that the F-site phenylalanines make critical contacts with ppERK2, in contrast to the proline whose cis-trans isomerization has no significant effect on F-site recognition by the kinase FRS. Our results support a mechanism where phosphorylation of the disordered N-terminal phospho-acceptor is facilitated by its increased productive encounters with the ppERK2 active site due to docking of the proximal F-site at the kinase FRS

PHOTOLYSIS OF SOME CYCLIC DISULFIDES

Author Institution: Coates Chemical Laboratories, Louisiana State UniversityThe photolysis of tetra- and pentamethylene disulfides and 1,4-butanedithiol has been investigated for the pure liquids and for the liquids doped with alkali. The courses of the photochemical reactions were followed by observing the UV absorption in the region of $1850-2300 {\AA}$ of the vapors in equilibrium with the photolized liquid. Photolysis of the disulfides produced the corresponding dithiols whereas addition of alkaki resulted in formation of the respective cyclic monosulfides at a much faster rate. The 1,4-butanedithiol also produced a cyclic monosulfide with the rate of formation being greatly enhanced by the addition of NaOH. Reaction mechanisms are proposed as well as a somewhat general photochemical rule for solutions or any condensed medium to the effect that in those cases where photodecomposition occurs, it will proceed primarily from the lowest excited state unless the irradiation energy exceeds the ionization limit; furthermore, dependent on the magnitude of intersystem crossing rate constants, this lowest excited state may be either singlet, triplet, or both

The effect of chemical substitution in Rh<SUB>17</SUB>S<SUB>15</SUB>

Rh17S15 has recently been shown to be a strongly correlated superconductor with a transition temperature of 5.4 K. In order to understand the nature of the strong correlations we study the effect of replacement of some of the Rh and S atoms by other elements such as Fe, Pd, Ir and Ni on the Rh side and Se on the S side in this work. We find that while replacements of Ir and Se lower the transition temperature considerably, those of Fe, Pd and Ni destroy the superconductivity down to 1.5 K. The resistivity data for these doped samples show a minimum which is presumably disorder induced. A reduction of Tc is always accompanied by a reduction of electron correlations, as deduced from heat capacity and magnetization data. Interestingly, the Fe doped sample shows evidence of spin glass formation at low temperatures

ORIENTAL JOURNAL OF CHEMISTRY Investigation of Physico-Chemical and Biological Characteristics of Various Lake Water in Coimbatore District, Tamilnadu, India

ABSTRACT Lake water quality degradation has been apparent for decades, especially in those lakes situated in the vicinity of cities which have anthropogenic activities. The present investigation was carried out for determining the various physico-chemical and biological characteristics of surface water quality of various lakes at Coimbatore, India. The sampling points were selected on the basis of their importance. Six sampling locations namely at Perur Lake (L 1 ), Selvachinthamani Lake (L 2 ), Ukkadam Lake (L 3 ), Kurichi Lake (L 4 ), Valankulam Lake (L 5 ), and Singanallur Lake (L 6 ) were selected and water samples were collected mostly from open wells in and around Coimbatore district. The physico-chemical parameters like Dissolved oxygen, Faecal coliforms, pH, Electrical conductivity, Biochemical oxygen demand, Chemical oxygen demand, Turbidity, Total dissolved solids, Sulphate, Nitrate, Phosphate, Chlorides and Alkalinity were analyzed. The results suggested that, the lake water samples collected from various sites in and around Coimbatore citywere above the limits of WHO standards

Suppression of electron correlations in the superconducting alloys of Rh<SUB>17-x</SUB>Ir<SUB>x</SUB>S<SUB>15</SUB>

We have studied the effect of Iridium doping (Rh17-xIrxS15) in the rhodium sites of the strongly correlated superconductor Rh17S15. Even at low levels of doping (x = 1 and 2) we see a drastic change in the superconducting properties as compared to those of the undoped system. We deduce that there is a reduction in the density of states at the Fermi level from reduced Pauli susceptibility and Sommerfeld coefficient in the doped samples. Moreover, the second magnetization peak in the isothermal magnetization scan ('fishtail') which was very prominent in the magnetization data of the undoped crystal is suppressed in the doped samples. The temperature dependence of resistivity of the doped crystals show a remarkably different behavior from that of the undoped crystal with the appearance of a minima at lower temperatures, the position of which is fairly constant at different fields. Our data supports the notion that Iridium, which is a bigger atom than rhodium expands the lattice thereby, reduces the electron correlations that existed due to the interaction between closer lying rhodium atoms in the undoped system