Field-Cycling NMR Relaxometry

NMR field-cycling spectroscopy: principles and a]lications

Indirect detection of magnetic resonance by heteronuclear two-dimensional spectroscopy

Nuclear quadrupole double resonance

Magnetic resonance and relaxation in structurally incommensurate systems

The 14N nuclear quadrupole resonance spectra and spin‐lattice relaxation times of the amino acids histidine, methionine, cystine, cysteine, and tyrosine as well as of the nucleic bases uracil, thymine, cytosine, and guanine have been determined by a 14N‐proton double resonance technique in the laboratory frame. The experiments were performed on polycrystalline samples at 77°K or above this temperature. A theoretical estimate of the sensitivity of this method for a variety of experimental conditions is as well presented. It is shown that in contrast to usual double resonance techniques the method works even in the case of a short proton spin‐lattice relaxation time if only the nitrogen relaxation time is long.

14N NQR Spectroscopy of Some Amino Acids and Nucleic Bases via Double Resonance in the Laboratory Frame

Using proton–nitrogen double resonance and cross relaxation in the laboratory frame, the 14N NQR spectra of solid p‐azoxyanisole (PAA), diheptyloxyazoxybenzene (HOAB), ethoxybenzilidene butylaniline (EBBA), and p‐anisalazine have been measured. The room temperature 14N quadrupole coupling constant of p‐anisalazine is e2qQ/h=4410 kHz whereas the asymmetry parameter is η=0.213. In EBBA, e2qQ/h=3990 kHz and η=0.186. In PAA and HOAB there are more than two chemically nonequivalent nitrogens in the unit cell. The 14N quadrupole coupling constants lie in the range between 4320–4370 kHz (PAA) and 4160–4400 kHz (HOAB) whereas the asymmetry parameters lie between 0.37 and 0.5. A comparison of the results for solid and nematic PAA shows that the largest principal axis of the 14N electric field gradient tensor is very nearly parallel to the N=N bond and that the central part of the PAA molecules containing the N=N bonds is rigid in the solid whereas it rotates around the long molecular axis in the nematic phase.

14N quadrupole resonance of some liquid crystalline compounds in the solid

The technique of nuclear magnetic pulsed double resonance in the rotating frame has been used to study the changes in the 14N quadrupole interactions in a triglycine sulfate (TGS) single crystal on going from the paraelectric to the ferroelectric phase. The 14N electric field gradient tensors have been determined above as well as below Tc. The most significant effect of the ferroelectric transition is a large change in the time averaged value of the C–N bond direction of glycine I and the onset of chemical nonequivalence of glycines II and III due to an ordering of the protons in the short O–H ··· O bond. The results show that the phase transition in TGS is of the order—disorder type as far as the glycine groups are concerned.

R. Osredkar

Papers

14N NQR Spectroscopy of Some Amino Acids and Nucleic Bases via Double Resonance in the Laboratory Frame

14N quadrupole resonance of some liquid crystalline compounds in the solid

Pulsed Nitrogen—Proton Double Resonance Study of the Ferroelectric Transition in Triglycine Sulfate

14N quadrupole coupling in paraelectric (NH4)2 SO4

Orientational Order in Biaxial Liquid Crystals