Deuteron nuclear magnetic resonance

Proton and deuteron nuclear magnetic resonance techniques are applied in solid hydrate research both for determining the hydrogen positions and for studying the dynamic processes of the water molecules ". ... 

Surface-Induced Order Detected by Deuteron Nuclear Magnetic Resonance... 

Keywords Calorimetry Deuteron nuclear magnetic resonance orientational order Isotropic-to-nematic transition Liquid-crystalline elastomers Order parameter Phase transition criticality... 

In this chapter we will give a review of recent advances in understanding the nature of the nematic phase transition in LCEs [3-5]. In addition, this chapter explores the possibiUties of controlling the critical behaviour of the nematic transition and, thus, the type of thermomechanical response. In Sect. 1, the nature of the nematic transition will be briefly discussed for pure liquid crystals (LCs) and LCEs. Sections 2 and 3 focus on the application of two essential experimental techniques, high-resolution ac calorimetry and deuteron nuclear magnetic resonance ( H-NMR) spectroscopy, to these systems. Section 4 explains the nature of the nematic transition in LCEs as revealed by the two techniques. Section 5 is devoted to experimental studies that systematically explored the possibilities of tailoring the TM response of LCEs by a variation of the chemical composition and other parameters during the synthesis. 

In addition to mixtures of single-chained anionic and cationic surfactants, mixtures of single-chained anionic surfactants with double-chained cationic surfactants have also been studied. The phase equilibria of the SDS-DDAB-water system have been studied by water deuteron nuclear magnetic resonance (NMR) and polarization microscopy methods at 40°C [27]. Based on particle size measurements, the possibility of vesicle formation has been realized from this study. Spontaneous vesicle formation in the aqueous mixture of didodecyldimethylammonium bromide and sodium dodecyl sulfate has been investigated with differential interference microscopy, transmission electron microscopy, glucose-trapping experiments, -potential measurements, and surface-tension measurements [28]. A solution of DDAB with a small amotmt of SDS is a lamellar phase. Adding more SDS induces surfactant precipitation. Further addition of SDS causes DDAB-SDS precipitate to disperse and results in the vesicle formation. The DDAB and SDS mixtures yield... 

Nuclear magnetic resonance provides means to study molecular dynamics in every state of matter. When going from solid state over liquids to gases, besides mole- cular reorientations, translational diffusion occurs as well. CD4 molecule inserted into a zeolite supercage provides a new specific model system for studies of rotational and translational dynamics by deuteron NMR. 

The mechanism for the bond cleavages indicated in figure 10.1b was clarified by Ronald Breslow. In one of the earliest applications of nuclear magnetic resonance to biochemical mechanisms, he demonstrated that the proton bonded to C-2 in the thiazolium ring is readily exchangeable with the protons of H20 and deuterons of D20 in a base-catalyzed reaction... 

For the investigation of the molecular dynamics in polymers, deuteron solid-state nuclear magnetic resonance (2D-NMR) spectroscopy has been shown to be a powerful method [1]. In the field of viscoelastic polymers, segmental dynamics of poly(urethanes) has been studied intensively by 2D-NMR [78, 79]. In addition to ID NMR spectroscopy, 2D NMR exchange spectroscopy was used to extend the time scale of molecular dynamics up to the order of milliseconds or even seconds. In combination with line-shape simulation, this technique allows one to obtain correlation times and correlation-time distributions of the molecular mobility as well as detailed information about the geometry of the motional process [1]. 

The direct attack of proton from the solvent on the intermediate dihydropyridine as well as the over-all mechanism of the reduction received support from the extent and position of deuterium labeling in the product from the reduction of l-methyl-4-phenyl-pyridinium iodide (7) with sodium borohydride in dimethylformamide and deuterium oxide. The l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (9) formed was shown by nuclear magnetic resonance (NMR) and mass spectral analysis to contain approximately one deuterium atom located at the 3-position.13,14 This is the result to be expected from the pathway shown in Eq. (3) if the electrophile were a deuteron. 

L. Vugmeyster, D. Ostrovsky,. . Ford, S.D. Burton, A.S. Lipton, G.L. Hoatson, R.L. Void, Probing the dynamics of a protein hydrophobic core by deuteron sohd-state nuclear magnetic resonance spectroscopy,. Am. Chem. Soc. 131 (2009) 13651-13658. 

Nuclear magnetic resonance (NMR), in particular, deuterium NMR, has proven to be a valuable technique for determining the nature of molecular organization in liquid crystals. The utility of the NMR technique derives from the fact that the relevant NMR interactions are entirely intramolecular, i.e. the dominant interaction is that between the nuclear quadrupole moment of the deuteron and the local electric-field gradient (EFG) at the deuterium nucleus. The EFG tensor is a traceless, axially symmetric, second-rank tensor with its principal component along the C—D bond. In a nematic fluid rapid anisotropic reorientation incompletely averages the quadrupolar interaction tensor q, resulting in a nonzero projection similar to the result in Eq. (5.6) ... 

There are several experimental tools available for the determination of the H-H distance and the degree of the H-H bonding interaction. Neutron diffraction studies provide an accurate measure of the H-H distance. The measurement of the spin-lattice proton relaxation time, Ti, for an tf -V 2 complex or the proton-deuteron couphng constant, Jhd. for the corresponding isotopically substituted rf -WT) complex via H nuclear magnetic resonance (NMR) spectroscopy provides a quantitative measure of the H-H distance. The frequency of the v(H-H) stretching band, as determined by Raman or infrared (IR) spectroscopy of / -H2 complexes provides semiquantitative information about the strength of the H-H interaction. 

As in the case of hydrogen and tritium, deuterium exhibits nuclear spin isomerism (see Magnetic spin resonance) (14). However, the spin of the deuteron [12597-73-8] is 1 instead of S as in the case of hydrogen and tritium. As a consequence, and in contrast to hydrogen, the ortho form of deuterium is more stable than the para form at low temperatures, and at normal temperatures the ratio of ortho- to para-deuterium is 2 1 in contrast to the 3 1 ratio for hydrogen. 

There are a large number of studies concerned with nuclear spin relaxation [7.45] in liquid crystals. The majority of these involve observation of the total proton magnetization arising from all protons in a mesogen. The experiments usually yield only one relaxation time, which is difficult, if not impossible, to relate to details of motion in the liquid crystalline phase. Deuteron and carbon-13 NMR may be used to study nuclear spin relaxation at several sites in a mesogen. In particular, direct measurement of spectral densities using deuterium resonant lines has made testing of motional models possible in liquid crystals. As yet, there is no report on systematic comparison between the different models of molecular reorientation. 

---