2H NMR experiments

Sepiolite (SepSp-1) was obtained from the Source Clay Mineral Repository (University of Missouri) and was used without additional purification. Thermal treatment was carried out for 19-20 hours under air in a baffle furnace, using 0. l-0.2g sepiolite that had been gently ground in a mortar and passed through a 100-mesh sieve. The vials containing dried sepiolite were transferred into capped bottles containing a few milliliters of acetone (acetone-d6 for the broad line 2H NMR experiments) and then remained in contact with the acetone vapor at room temperature for 4 days. 

There is a long history of controversy in the literature regarding the mode of action of general anesthetics. Experimental results derived from model systems of lipids alone or lipid-cholesterol are somewhat controversial. To mention just a few, using Raman spectroscopy it was found that, at clinical concentrations, halothane had no influence on the hydrocarbon chain conformations, and it was concluded that the interaction between halothane and the lipid bilayer occurs in the head group region [57]. This idea was also supported by 19F-NMR studies. The chemical shifts of halothane in a lipid suspension were similar to those in water and differed from those in hydrocarbons. In contrast, from 2H-NMR experiments, it was concluded that halothane is situated in the hydrocarbon region of the membrane (see also chapter 3.3). 

Siminovitch, D.I. (1998) Solid-state NMR studies of proteins the view from static 2H NMR experiments, Biochemistry and Cell Biology 76, 411-422. 

Fig. 14. Effects of small-amplitude reorientation on 2H NMR experiments, as calculated by means of RW simulations. In the model, C-2H bonds (<5 = 2n 125 kHz, rj = 0) perform rotational random jumps on the surface of a cone with a full opening angle % = 6°. (a) 2H NMR spectra for various solid-echo delays tp (tj = t = 30 pis), and (b) 2H NMR correlation functions Fcos(tm) for various evolution times tp (tj = t = 10ms). (Adapted from Ref. 76.)...

Powder and single-crystal 2H NMR experiments were also carried out to study the phase transitions of l,2,3-trichloro-4,5,6-trimethylbenzene TCTMB d3203 and o -dich 1 o rotelramethylbenzene DCTMB <712.204 which show considerable dynamical disorder in their room temperature phase. 

In polymers one will often particularly be interested in very slow dynamic processes. The solid echo technique just described is still limited by the transverse relaxation time T being of the order of a few ps at most. The ultimate limitation in every NMR experiment however, is not T but the longitudinal relaxation time T, which for 2H in solid polymers typically is much longer, being in the range 10 ms to 10 s. The spin alignment technique (20) circumvents transverse relaxation and is limited by Tx only, thus ultraslow motions become accessible of experiment. 

The coal residue was separated into a THF-soluble fraction and a THF-insoluble residue. The wt % yields and atom % 2H compositions are given in Table I. The coal residue was 6 wt % soluble in tetrahydrofuran. The soluble fraction had 23 atom % 2H content. Evaluation of the 2H NMR data showed that 85 wt % of this fraction was derived from the coal and that its deuterium content was 10%. The chemically-bonded naphthalene-d8 content of the THF-soluble fraction, estimated from the 2H NMR data, was about 15 wt % or approximately 1 wt % of the coal. The insoluble residue had 6 atom % 2H content. This indicates that the residue contained approximately 1 wt % chemically-bonded naphthalene which was estimated from the difference in the atom % 2H content of the insoluble residue and recovered naphthalene-d8. This gives a total chemically-bonded naphthalene-d8 content of approximately 2 wt %. Similar results were obtained in extraction experiments made with phenanthrene (30), where it was found that 3-7 wt % of the phenanthrene was chemically linked to the coal product. 

In the solid, dynamics occurring within the kHz frequency scale can be examined by line-shape analysis of 2H or 13C (or 15N) NMR spectra by respective quadrupolar and CSA interactions, isotropic peaks16,59-62 or dipolar couplings based on dipolar chemical shift correlation experiments.63-65 In the former, tyrosine or phenylalanine dynamics of Leu-enkephalin are examined at frequencies of 103-104 Hz by 2H NMR of deuterated samples and at 1.3 x 102 Hz by 13C CPMAS, respectively.60-62 In the latter, dipolar interactions between the 1H-1H and 1H-13C (or 3H-15N) pairs are determined by a 2D-MAS SLF technique such as wide-line separation (WISE)63 and dipolar chemical shift separation (DIP-SHIFT)64,65 or Lee-Goldburg CP (LGCP) NMR,66 respectively. In the WISE experiment, the XH wide-line spectrum of the blend polymers consists of a rather featureless superposition of components with different dipolar widths which can be separated in the second frequency dimension and related to structural units according to their 13C chemical shifts.63... 

Lyotropic polymeric LC, formed by dissolving two aromatic polyamides in concentrated sulphuric acid, have been studied using variable-director 13C NMR experiments.324 The experimental line shapes at different angles w.r.t the external field were used to extract macromolecular order and dynamic in these ordered fluids. An interesting application of lyotropic LC is for the chiral discrimination of R- and S-enantiomers, and has recently been demonstrated by Courtieu and co-workers.325 The idea was to include a chiral compound 1-deutero-l-phenylethanol in a chiral cage (e.g., /1-cyclodextrin) which was dissolved and oriented by the nematic mean field in a cromolyn-water system. Proton-decoupled 2H NMR spectrum clearly showed the quad-rupolar splittings of the R- and S-enantiomers. The technique is applicable to water-soluble solutes. 

Fig. 22. Relaxation map for PBLG side chain motion. Experiments except 2H NMR measurements are open symbols, and PBLG-Kdi (filled circle) and PBLG-fd2 (filled triangle).

Sepiolite clay (<100 mesh) was heated in air at 120°C in order to remove the zeolitic and surface bound water molecules. The partially dehydrated clay mineral was subsequently exposed to acetone vapor at room temperature for a period of four days. H and 29Si CP MAS-NMR experiments revealed that the acetone molecules penetrated into the microporous channels of the sepiolite structure. Broad line 2H NMR studies using acetone-d6 revealed that, in addition to fast methyl group rotations, the guest acetone-d6 molecules were also undergoing 2-fold re-orientations about the carbonyl bond. The presence of acetone-d6 molecules adsorbed on the exterior surfaces of the sepiolite crystals was also detected at room temperature. 

Representative broad line 2H NMR spectra obtained at -140, 30 and 60°C are presented in Fig. 5a, 5b and 5c, respectively. Differences in the signal to noise ratios of the spectra that appear in Fig. 5 may be attributed to the different number of transients that were observed during each experiment. Note that the surface bound acetone-d6 molecules, which would give rise to a very intense peak at the isotropic frequency, have been removed with gentle heating (60°C) prior to collecting the NMR spectra that are presented in Fig. 5. The shapes of the powder patterns are therefore dependent solely upon the motional state of the acetone-d6 molecules that are present within the microporous channels. 

For /er/-butyl alcohol, we have observed (8f) with l3C CP/MAS and 2H NMR spectroscopy, the formation of tert-butyl silyl ether (TBSE) at temperatures as low as 296 K. In these experiments,, 3C and 2H-labeled tert-butyl alcohols were used ... 

In order to get more detailed information about the motions associated with the p relaxation in PET and to understand the differences observed between mechanical and dielectric data, 13 C NMR was used, as well as 2H NMR on PET samples selectively deuterated either on the phenyl rings or on the ethylene glycol units [12]. Due to the higher frequency range corresponding to NMR experiments (105 Hz), the extrapolation of the dielectric results leads to the occurrence of the motions involved in the f3 relaxation around 25 °C, which is effectively observed. 

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