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Double Resonance (double + resonance)
Kinds of Double Resonance Selected AbstractsElectron paramagnetic resonance and electron-nuclear double resonance of nonequivalent Yb3+ centers in stoichiometric lithium niobatePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Galina Malovichko Abstract Lithium niobate crystals doped with ytterbium were studied using Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR). The tremendous narrowing of EPR lines in nearly stoichiometric samples, when compared to those in congruent samples, allowed us to distinguish nine non-equivalent centers, as well as line splitting caused by the hyperfine interaction of ytterbium electrons with the nuclear spins of two magnetic isotopes, 171Yb and 173Yb. Eight of the nine centers are described for the first time. It was found that three of the centers have axial C3 symmetry, and all others have the lowest C1 symmetry due to the presence of intrinsic defects and/or charge compensation defects in the near neighborhood of Yb3+. Characteristics of the g -tensor for all of the centers and hyperfine tensors for axial centers were determined. The ENDOR observations of Nb nuclei in the nearest neighborhood of Yb13+ gave direct evidence that the dominated axial Yb1 center has no charge compensator in its nearest surroundings (distant charge compensation mechanism). Both the EPR and ENDOR data for the main axial ytterbium center are explained by a supposition that Yb3+ ions substitute for Li+. Possible models for low-symmetry centers are discussed. The obtained numerous spectroscopic parameters can be used as cornerstones for model calculations of Yb3+ centers in lithium niobate. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conformational heterogeneity of transmembrane residues after the Schiff base reprotonation of bacteriorhodopsinFEBS JOURNAL, Issue 9 200515N CPMAS NMR of D85N/T170C membranes bR, N-like and O-like intermediate states of [15N]methionine-labelled wild type and D85N/T170C bacteriorhodopsin were accumulated in native membranes by controlling the pH of the preparations. 15N cross polarization and magic angle sample spinning (CPMAS) NMR spectroscopy allowed resolution of seven out of nine resonances in the bR-state. It was possible to assign some of the observed resonances by using 13C/15N rotational echo double resonance (REDOR) NMR and Mn2+ quenching as well as D2O exchange, which helps to identify conformational changes after the bacteriorhodopsin Schiff base reprotonation. The significant differences in chemical shifts and linewidths detected for some of the resonances in N- and O-like samples indicate changes in conformation, structural heterogeneity or altered molecular dynamics in parts of the protein. [source] A solid-state 23Na NMR study of monovalent cation binding to double-stranded DNA at low relative humidityMAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2008Alan Wong Abstract We report a solid-state 23Na NMR study of monovalent cation (Li+, Na+, K+, Rb+, Cs+ and NH4+) binding to double-stranded calf thymus DNA (CT DNA) at low relative humidity, ca 0,10%. Results from 23Na31P rotational echo double resonance (REDOR) NMR experiments firmly establish that, at low relative humidity, monovalent cations are directly bound to the phosphate group of CT DNA and are partially dehydrated. On the basis of solid-state 23Na NMR titration experiments, we obtain quantitative thermodynamic parameters concerning the cation-binding affinity for the phosphate group of CT DNA. The free energy difference (,G° ) between M+ and Na+ ions is as follows: Li+ (,1.0 kcal mol,1), K+ (7.2 kcal mol,1), NH4+ (1.0 kcal mol,1), Rb+ (4.5 kcal mol,1) and Cs+ (1.5 kcal mol,1). These results suggest that, at low relative humidity, the binding affinity of monovalent cations for the phosphate group of CT DNA follows the order: Li+ > Na+ > NH4+ > Cs+ > Rb+ > K+. This sequence is drastically different from that observed for CT DNA in solution. This discrepancy is attributed to the different modes of cation binding in dry and wet states of DNA. In the wet state of DNA, cations are fully hydrated. Our results suggest that the free energy balance between direct cation,phosphate contact and dehydration interactions is important. The reported experimental results on relative ion-binding affinity for the DNA backbone may be used for testing theoretical treatment of cation-phosphate interactions in DNA. Copyright © 2008 John Wiley & Sons, Ltd. [source] Conformational constraints in solid-state NMR of uniformly labeled polypeptides from double single-quantum-filtered rotational echo double resonance,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2007Nathan A. Oyler Abstract A solid-state nuclear magnetic resonance (NMR) technique is described for obtaining constraints on the backbone conformation of a protein or peptide that is prepared with uniform 15N,13C labeling of consecutive pairs of amino acids or of longer segments. The technique, called double single-quantum-filtered rotational echo double resonance (DSQ-REDOR), uses frequency-selective REDOR to prepare DSQ coherences involving directly bonded backbone 13CO and 15NH sites, to dephase these coherences under longer-range 15NH13CO dipole-dipole couplings in a conformationally dependent manner, and to convert the remaining DSQ coherences to detectable transverse 13C-spin polarization. The efficacy of DSQ-REDOR is demonstrated in experiments on two isotopically labeled samples, the helical peptide MB(i + 4)EK and the amyloid-forming peptide A,11,25. Published in 2007 John Wiley & Sons, Ltd. [source] An ENDOR study of oxomolybdenum(V) tris(pyrazolyl)borate complexes; identification of couplings to boron and other heteroatomsMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2002Robert D. Farley Abstract 11B hyperfine and quadrupolar couplings have been observed by the electron magnetic resonance techniques electron nuclear double resonance and hyperfine sublevel correlation spectroscopy for some tris(pyrazolyl)borato-oxomolybdenum(V) and related nitrosyl complexes including a dinuclear B,B linked complex. The spectra are interpreted according to the electron delocalization onto the ligands, especially the pyrazolylborate. Copyright © 2002 John Wiley & Sons, Ltd. [source] Electron paramagnetic resonance and electron-nuclear double resonance of nonequivalent Yb3+ centers in stoichiometric lithium niobatePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Galina Malovichko Abstract Lithium niobate crystals doped with ytterbium were studied using Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR). The tremendous narrowing of EPR lines in nearly stoichiometric samples, when compared to those in congruent samples, allowed us to distinguish nine non-equivalent centers, as well as line splitting caused by the hyperfine interaction of ytterbium electrons with the nuclear spins of two magnetic isotopes, 171Yb and 173Yb. Eight of the nine centers are described for the first time. It was found that three of the centers have axial C3 symmetry, and all others have the lowest C1 symmetry due to the presence of intrinsic defects and/or charge compensation defects in the near neighborhood of Yb3+. Characteristics of the g -tensor for all of the centers and hyperfine tensors for axial centers were determined. The ENDOR observations of Nb nuclei in the nearest neighborhood of Yb13+ gave direct evidence that the dominated axial Yb1 center has no charge compensator in its nearest surroundings (distant charge compensation mechanism). Both the EPR and ENDOR data for the main axial ytterbium center are explained by a supposition that Yb3+ ions substitute for Li+. Possible models for low-symmetry centers are discussed. The obtained numerous spectroscopic parameters can be used as cornerstones for model calculations of Yb3+ centers in lithium niobate. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Determination of intermolecular distance for a model peptide of Bombyx mori silk fibroin, GAGAG, with rotational echo double resonanceBIOPOLYMERS, Issue 2 2002Tsunenori Kameda Abstract Rotational echo double resonance NMR spectroscopy is applied for the determination of the distance of intermolecular chains of pentapeptide, GAGAG (G: Gly, A: Ala), a model typical of the crystalline domain in Bombyx mori silk fibroin. 1:4 mixture of G[1- 13C]AGAG and GAG[15N]AG with antiparallel ,-sheet structure was used to determine the distance of intermolecular hydrogen bonding between adjacent molecules within pleated sheet and the 13C,15N interatomic distance was determined to be 4.3 Å. On the other hand, 1:4 mixture of GAG[1- 13C]AG and GAG[15N]AG gave information on the interpleated sheet arrangement. When we assumed the same distances between two interpleated sheets, the distance was calculated to be 5.3 Å and the angle 15N,13C,15N was 180°. © 2002 Wiley Periodicals, Inc. Biopolymers 64: 80,85, 2002 [source] Self-Assembled Amphotericin,B Is Probably Surrounded by Ergosterol: Bimolecular Interactions as Evidenced by Solid-State NMR and CD SpectraCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2008Yusuke Kasai Dr. Abstract Amphotericin,B (AmB) is thought to exert its pharmacological effects by forming a barrel-stave assembly with ergosterol in fungal membranes. To examine the interaction between AmB and ergosterol (Erg) or cholesterol (Cho), 13C- and 19F-labelled covalent conjugates were prepared as reported previously (N. Matsumori et,al. Chem. Biol.2004, 11, 673,679). The CD spectra of the conjugates in a membrane-bound form suggested that the distance between the heptaene moieties of the ergosterol conjugates AmB,C2,(6-F)Erg 2 and AmB,C2,Erg 3 is similar to that of AmB in ergosterol-containing membranes, but significantly larger than that of AmB in nonsterol or cholesterol-containing membranes. These observations suggest that, as is the case with ergosterol-containing membranes, the conjugated sterol moiety prevents the close contact between the heptaene moieties within the membrane that would reduce channel conductivity of the AmB assemblies. To further investigate this bimolecular interaction, we recorded the solid-state NMR spectra of conjugates 2 and AmB,C2,(6-F)Cho 4, which are composed of uniformly 13C-labelled AmB and 6-fluorinated ergosterol or cholesterol; the conjugates were expected to facilitate the estimation of distances between the fluorine and carbon atoms. By using rotor-synchronous double resonance (rotational echo double resonance of X cluster; RDX) experiments, we deduced the distance between the fluorine atom and its nearest carbon atom in the heptaene moiety of 2 to be less than 8.6,Å. This indicates that the B,ring of ergosterol comes close to the AmB polyene moiety. A conformational search of the AmB,ergosterol conjugate by using distance constraints derived from the RDX results suggested that ergosterol molecules possibly surround the AmB assembly, which is in contrast with the conventional image in which ergosterol is inserted into AmB molecules. [source] A novel spectroscopic probe for molecular chiralityCHIRALITY, Issue 3 2006Na Ji Abstract Recent advances in developing sum frequency generation (SFG) as a novel spectroscopic probe for molecular chirality are reviewed. The basic principle underlying the technique is briefly described, in comparison with circular dichroism (CD). The significantly better sensitivity of the technique than CD is pointed out, and the reason is discussed. Bi-naphthol (BN) and amino acids are used as representatives for two different types of chiral molecules; the measured chirality in their electronic transitions can be understood by two different molecular models, respectively, that are extensions of models developed earlier for CD. Optically active or chiral SFG from vibrational transitions are weaker, but with the help of electronic-vibrational double resonance, the vibrational spectrum of a monolayer of BN has been obtained. Generally, optically active SFG is sufficiently sensitive to be employed to probe in-situ chirality of chiral monolayers and thin films. © 2006 Wiley-Liss, Inc. Chirality [source] | ||||||||||