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Quadrupole Coupling Constants (quadrupole + coupling_constant)
Selected AbstractsStructural Investigation of a High-Affinity MnII Binding Site in the Hammerhead Ribozyme by EPR Spectroscopy and DFT Calculations.CHEMBIOCHEM, Issue 10 2003Effects of Neomycin B on Metal-Ion Binding Abstract Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity MnIIbinding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Kdof 4.4 ,M in buffer solutions containing 1,M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant,of 0.7 MHz, an asymmetry parameter,of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the MnIIligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by MnIIin crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the MnIIsite in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of,(14N)=+0.80 MHz, ,=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that MnIIis released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 ,M) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry 1995, 34, 11,186). [source] A computational NQR study on the hydrogen-bonded lattice of cytosine-5-acetic acidJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2008Mahmoud Mirzaei Abstract A computational study at the level of density functional theory (DFT) employing 6-311++G** standard basis set was carried out to evaluate nuclear quadrupole resonance (NQR) spectroscopy parameters in cytosine-5-acetic acid (C5AA). Since the electric field gradient (EFG) tensors are very sensitive to the electrostatic environment at the sites of quadruple nuclei, the most possible interacting molecules with the target one were considered in a five-molecule model system of C5AA using X-ray coordinates transforming. The hydrogen atoms positions were optimized and two model systems of original and H-optimized C5AA were considered in NQR calculations. The calculated EFG tensors at the sites of 17O, 14N, and 2H nuclei were converted to their experimentally measurable parameters, quadrupole coupling constants and asymmetry parameters. The evaluated NQR parameters reveal that the nuclei in original and H-optimized systems contribute to different hydrogen bonding (HB) interaction. The comparison of calculated parameters between optimized isolated gas-phase and crystalline monomer also shows the relationship between the structural deformation and NQR parameters in C5AA. The basis set superposition error (BSSE) calculations yielded no significant errors for employed basis set in the evaluation of NQR parameters. All the calculations were performed by Gaussian 98 package of program. © 2007 Wiley Periodicals, Inc. J Comput Chem 2008 [source] Where does Hydrogen Adsorb on Ru Nanoparticles?CHEMPHYSCHEM, Issue 17 2009A Powerful Joint 2H MAS-NMR/DFT Approach Two perspectives: DFT calculations of quadrupole coupling constants of hydrides adsorbed on a pristine Ru(0001) surface allow for secure assignments of subspectra obtained from experimental 2H solid-state NMR data (see picture). [source] Structure and Dynamics of Water Confined in Dimethyl SulfoxideCHEMPHYSCHEM, Issue 1 2006A. Wulf Abstract We study the structure and dynamics of hydrogen-bonded complexes of H2O/D2O and dimethyl sulfoxide (DMSO) by infrared spectroscopy, NMR spectroscopy and ab initio calculations. We find that single water molecules occur in two configurations. For one half of the water monomers both OH/OD groups form strong hydrogen bonds to DMSO molecules, whereas for the other half only one of the two OH/OD groups is hydrogen-bonded to a solvent molecule. The H-bond strength between water and DMSO is in the order of that in bulk water. NMR deuteron relaxation rates and calculated deuteron quadrupole coupling constants yield rotational correlation times of water. The molecular reorientation of water monomers in DMSO is two-and-a-half times slower than in bulk water. This result can be explained by local structure behavior. [source] | ||||||||||