Nuclear quadrupole resonance

About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.

Cu NMR and NQR Studies of High-Tc Superconductor La2-xSrxCuO4.

Abstract: Results of extensive Cu NMR and NQR studies in the superconducting La 2- x Sr x CuO 4 with x =0.075∼0.24 have been presented. The rapid decrease of the nuclear spin-lattice relaxation rate, 1/ T 1 , and the spin Knight shift below T c confirm microscopically the existence of the superconducting phase with lower T c than 38 K for 0.10 ≤ x ≤0.24. For x =0.10, magnetic anomalies emerge at low- T in some small parts of the sample, e.g . T -independent T 1 and broadening of spectrum, having some relevance to the magnetic order in La 2- x Ba x CuO 4 with x =0.125. For x >0.15, the T 1 T =const. behavior and the existence of the residual spin Knight shift far below T c have revealed that the superconductivity is of a gapless type with a finite density of states at the Fermi level caused by the mixture of different structures, i.e. tetragonal and orthorhombic.

Spectroscopic properties of inorganic and organometallic compounds

Abstract: This book covers literature published up to late 1984. Includes nuclear magnetic resonance; nuclear quadrupole resonance spectroscopy; rotational spectroscopy; characteristic vibrations of compounds of main-group elements; vibrational spectra of transition-element compounds and some co-ordinated ligands; Mossbauer spectroscopy; and gas-phase molecular structures determined by electron diffraction.

Rotational jumps of the tyrosine side chain in crystalline enkephalin. Hydrogen-2 NMR line shapes for aromatic ring motions in solids

Abstract: Deuterium NMR spectra of polycrystalline (tyrosine-3,5-*H2) (Leus)enkephalin show that the aromatic tyrosyl ring of this pentapeptide is executing 180' flips about the Cfl-C' axis in the solid state. Specifically, the axially symmetric powder pattern observed at low temperature collapses to an axially asymmetric pattern with TJ 0.6 at high temperature. Computer simulations of the NMR line shapes, which account for spectral distortions induced by the quadrupole echo technique, indicate that at room temperature the flipping rate is approximately 5 X IO4 s-* and that it increases to about lo6 s-I at 101 "C. In the past few years it has become apparent that solid-state NMR spectra can be employed to investigate the rate and mechanism of molecular reorientation processes in solids, and there are now several examples in the literature which demonstrate this point."" To date these studies have focussed on small crystalline molecules, but the techniques are equally applicable to large molecules such as peptides and proteins, where they can be used to obtain information on phenomena such as the motion of amino acid side chains. As part of a study of side-chain reorientation in peptides and proteins by solid-state NMR, we report here an investigation of the motion of the aromatic tyrosine ring in polycrystalline (Le~~jenkephalin. Specifically, the 2H NMR powder line shapes of ( tyrosine-3 ,S2H2) ( LeuS) enkephalin show that the tyrosyl group is not rigid, but instead is executing jumps of 180' about the Co-Cc axis of the aromatic ring. At room temperature the jump rate is approximately lo4 s-l and inceases to about IO6 s-' at 101 OC. (Le~~lenkephalin is a natural pentapeptide with the sequence Tyr-Gly-Gly-Phe-Leu which has been chemically labeled with (3,5-ZH2)tyrosine for this study as is depicted in Figure 1. The peptide is of considerable interest because of its structural similarity to opiate agonists. Theoretical and experimental evidence from solution measurementsl2 reveal that enkephalin may exist in a relatively rigid conformation in which the phenyl and tyrosyl rings are separated by a distance similar to that of opiates, so that these groups may participate in binding to the receptor. (Leus)enke- phalin has been crystallized, and its structure determined;l3-l5 the X-ray studies have suggested that the orientation of the tyrosyl side chain is not unique, the ring experiencing disorder of either a static or dynamic nature. Because of the possible existence of dynamic disorder, and because NMR can detect this type of disorder and reveal the details of its nature, a solid-state NMR investigation of (Leus)enkephalin appeared promising. Experimental Section ~~-(3,5-2H,)Tyrosine was purchased from Merck, Sharpe, and Dohme (St. Louis, Mo.). The DL form was resolved by treatment of the N-trifluoroacetyl derivative with carboxypeptidase A to yield the L isomer of the free amino acid. The latter was used to synthesize (Leus)enke- phalin by the procedure reported previously.12 The 2H labeled peptide was recrystallized from ethanol. Samples for the NMR experiments typically consisted of approxi- mately 50 mg of the 2H-labeled peptide and were placed in vacuum- sealed glass tubes. The ZH NMR spectra were obtained on a home-built spectrometer operating at 45.1 MHz for 2H, using a quadrupole echo pulse seq~encc.'~~'~ The r/2 pulse width was 2-2.5 ps and the T value in the echo experiment was 30 ps. In order to ensure that the line shapes we obtain are accurate, we have found it necessary to employ quadrature, rather than single sided, phase detection. With the latter method gross

Optically Polarized Atoms: Understanding light-atom interactions

Abstract: I: INTRODUCTION TO LIGHT-ATOM INTERACTIONS 1. Introduction 2. Atomic States 3. A bit of angular-momentum theory 4. Atoms in external electric and magnetic fields 5. Polarized atoms 6. Polarized light 7. Atomic transitions 8. Coherence in atomic systems 9. Optical pumping 10. Light-atom interaction observed in transmitted light II: ADVANCED TOPICS 11. Nonlinear magneto-optical rotation 12. Perturbative analysis of light-atom interactions 13. Polarization effects in transitions with partially resolved hyperfine structure 14. The effect of hyperfine splitting on nonlinear magneto-optical rotation 15. Spectral properties of excitation light ground-state coherence effects revisited 16. Collapse and revival in quantum beats 17. Nuclear quadrupole resonance and alignment-to-orientation conversion 18. Selective addressing of high-rank polarization moments 19. Tensor structure of the DC- and AC-Stark polarizabilities 20. Photoionization of polarized atoms with polarized light Appendix A Constants, units and notations Appendix B Units of energy, frequency and wavelength Appendix C Reference data for hydrogen and the alkali atoms Appendix D Nonlinear magneto-optical rotation with hyperfine structure Appendix E The Atomic Density Matrix software package