Observation of a narrow hyperon state of mass 3.17 GeV

We present evidence for a narrow Y¹ with a mass of 3.17 GeV and a width ? 20 MeV decaying to ΣKK? + pions, ΛKK? + pions and ΞK + pions. The data come from two high statistics K^?p bubble chamber experiments with a sensitivity of ≈100 eV/μbat 8.25 GeV/c and ≈ 45 eV/μbat 6.5 GeV/c.     

Anharmonic effects in a Jahn-Teller phase transition

A mechanism is proposed to explain the double phase transitions found in K₂PbCu(NO₂)₆ and Tl₂PbCu(NO₂)₆. The higher temperature transition is caused by the cooperative Jahn-Teller effect. The lower temperature transition occurs as the fourth order anharmonic interaction restabilizes the lattice against instabilities caused by static distortions in the third order anharmonic interaction. Calculated curves of the order parameter and heat capacity reproduce all the features in the experimental curves.     

Synthesis, structure, and reactivity of a dinuclear metal complex with linear M-H-M bonding

Reaction of two equiv of 1-adamantylzinc bromide with (dippm)NiBr2 (dippm = bis(di-isopropylphosphino)methane) led to a dinuclear metal complex containing a unique linear bridging hydride ligand. The hydride was characterized by neutron diffraction methods, which confirmed a linear bonding mode. Preliminary reactivity studies of this unusual dimer are reported.     

Direct evidence for neutrino flavor transformation from neutral-current interactions in the Sudbury Neutrino Observatory

Observations of neutral-current nu interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard 8B shape, the nu(e) component of the 8B solar flux is phis(e) = 1.76(+0.05)(-0.05)(stat)(+0.09)(-0.09)(syst) x 10(6) cm(-2) s(-1) for a kinetic energy threshold of 5 MeV. The non-nu(e) component is phi(mu)(tau) = 3.41(+0.45)(-0.45)(stat)(+0.48)(-0.45)(syst) x 10(6) cm(-2) s(-1), 5.3sigma greater than zero, providing strong evidence for solar nu(e) flavor transformation. The total flux measured with the NC reaction is phi(NC) = 5.09(+0.44)(-0.43)(stat)(+0.46)(-0.43)(syst) x 10(6) cm(-2) s(-1), consistent with solar models.     

Mechanism of glutaredoxin-ISU [2Fe-2S] cluster exchange

Exchange of [2Fe-2S] centers between Grx2 and the cluster scaffold protein ISU, and characterization of two mutually exclusive Grx2 binding sites on ISU by isothermal titration calorimetry supports a direct link for Grx and glutathione involvement in ISU promoted Fe-S cluster biosynthesis.     

Dynamics of photogenerated holes in nanocrystalline α-Fe2O3 electrodes for water oxidation probed by transient absorption spectroscopy

Transient absorption spectroscopy on the μs-s time scale is used to monitor the yield and decay dynamics of photogenerated holes in nanocrystalline hematite photoanodes. In the absence of a positive applied bias, these holes are observed to undergo rapid electron-hole recombination. The application of a positive bias results in the generation of long-lived (3 ± 1 s lifetime) photoholes.     

(TMTSF)2(2,5-Tcnqbr2): Structure and Physical Properties

The 2:1 charge-transfer salt (TMTSF)₂(2,5-TCNQBr2) has been prepared and its physical properties investigated. Its crystal structure consists of segregated stacks of TMTSF donors (ring-over-bond overlap pattern; mean interplanar spacing of 3.6A) and chains of edge-on and disordered 2,5-TCNQBr2 acceptors. Infrared data are suggestive of unit charge on the 2,5-TCNQBr2 molecule and, therefore, half charge on the TMTSF donor. Resistivity data are successfully interpreted on the basis of a percolation construction. Magnetic data are also presented.     

Control of cytochrome C redox potential: axial ligation and protein environment effects

Axial iron ligation and protein encapsulation of the heme cofactor have been investigated as effectors of the reduction potential (E degrees ') of cytochrome c through direct electrochemistry experiments. Our approach was that of partitioning the E degrees ' changes resulting from binding of imidazole, 2-methyl-imidazole, ammonia, and azide to both cytochrome c and microperoxidase-11 (MP11), into the enthalpic and entropic contributions. N-Acetylmethionine binding to MP11 was also investigated. These ligands replace Met80 and a water molecule axially coordinated to the heme iron in cytochrome c and MP11, respectively. This factorization was achieved through variable temperature E degrees ' measurements. In this way, we have found that (i) the decrease in E degrees ' of cytochrome c due to Met80 substitution by a nitrogen-donor ligand is almost totally enthalpic in origin, as a result of the stronger electron donor properties of the exogenous ligand which selectively stabilize the ferric state; (ii) on the contrary, the binding of the same ligands and N-acetylmethionine to MP11 results in an enthalpic stabilization of the reduced state, whereas the entropic effect invariably decreases E degrees ' (the former effect prevails for the methionine ligand and the latter for the nitrogenous ligands). A comparison of the reduction thermodynamics of cytochrome c and the MP11 adducts offers insight on the effect of changing axial heme ligation and heme insertion into the folded polypeptide chain. Principally, we have found that the overall E degrees ' increase of approximately 400 mV, comparing MP11 and native cytochrome c, consists of two opposite enthalpic and entropic terms of approximately +680 and -280 mV, respectively. The enthalpic term includes contributions from both axial methionine binding (+300 mV) and protein encapsulation of the heme (+380 mV), whereas the entropic term is almost entirely manifest at the stage of axial ligand binding. Both terms are dominated by the effects of water exclusion from the heme environment.