Home About us Contact
|
Home About us Contact | ||
|
|
||
Quadrupole Interaction (quadrupole + interaction)
Selected AbstractsTyr235 of human cytosolic phosphoenolpyruvate carboxykinase influences catalysis through an anion,quadrupole interaction with phosphoenolpyruvate carboxylateFEBS JOURNAL, Issue 23 2008Lakshmi Dharmarajan Tyr235 of GTP-dependent phosphoenolpyruvate (PEP) carboxykinase is a fully invariant residue. The aromatic ring of this residue establishes an energetically favorable weak anion,quadrupole interaction with PEP carboxylate. The role of Tyr235 in catalysis was investigated via kinetic analysis of site-directed mutagenesis-derived variants. The Y235F change lowered the apparent Km for PEP by about six-fold, raised the apparent Km for Mn2+ by about 70-fold, and decreased oxaloacetate (OAA)-forming activity by about 10-fold. These effects were due to an enhanced anion,quadrupole interaction between the aromatic side chain at position 235, which now lacked a hydroxyl group, and PEP carboxylate, which probably increased the distance between PEP and Mn2+ and consequently affected the phosphoryl transfer step and overall catalysis. For the Y235A and Y235S changes, an elimination of the favorable edge-on interaction increased the apparent Km for PEP by four- and six-fold, respectively, and the apparent Km for Mn2+ by eight- and six-fold, respectively. The pyruvate kinase-like activity, representing the PEP dephosphorylation step of the OAA-forming reaction, was affected by the substitutions in a similar way to the complete reaction. These observations indicate that the aromatic ring of Tyr235 helps to position PEP in the active site and the hydroxyl group allows an optimal PEP,Mn2+ distance for efficient phosphoryl transfer and overall catalysis. The Y235A and Y235S changes drastically reduced the PEP-forming and OAA decarboxylase activities, probably due to the elimination of the stabilizing interaction between Tyr235 and the respective products, PEP and pyruvate. [source] Preparation and Photoluminescence Properties of Novel Color-Tunable MgY4Si3O13:Ce3+, Tb3+ Phosphors for Ultraviolet Light-Emitting DiodesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Hau-Yun Chung Oxide-based phosphors MgY4Si3O13 codoped with Ce3+ and Tb3+ were prepared in this study. Broad Ce3+ excitation spectra with the highest intensity at 330 nm were found for MgY4Si3O13:Ce3+, Tb3+ phosphors. Emission lines ranging from 450 to 650 nm originated from the 5D4,7FJ (J=6, 5, 4, 3) transitions of Tb3+ ions. The energy transfer from Ce3+ to Tb3+ occurred effectively in MgY4Si3O13:Ce3+, Tb3+ with a dipole,quadrupole interaction. Codoping Ce3+ with Tb3+ significantly increased the emission intensity of the prepared phosphors. Increasing the Tb3+ concentration led to the chromaticity coordinates of the prepared samples greatly shifting from the blue to the green region, extending the applicability of MgY4Si3O13:Ce3+, Tb3+ phosphors in solid-state lighting. [source] The 14N quadrupole coupling in hexamethylene triperoxide diamine (HMTD)MAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2007John Persons Abstract Using high-field NMR, we have determined the magnitude of the nuclear quadrupole interaction in hexamethylene triperoxide diamine (HMTD), the explosive allegedly used in the London bombings of July 2005. The experimental quadrupolar coupling constant, 5.334 MHz, is in good agreement with quantum chemical calculations. The predicted single zero-field transition frequency should lie in a relatively empty part of the 14N nuclear quadrupole resonance (NQR) spectrum; the spin relaxation rate is reasonably fast. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||