2H-NMR

Further support for this pathway was provided by competition feeding studies. If 104 were not a true biosynthetic intermediate and were incorporated due to some flexibility in the biosynthetic enzymes, then its incorporation would be expected to be reduced by an equivalent concentration of the true substrate 102 or 103. If it were a real intermediate, then it would be expected that incorporation of earlier intermediates would be reduced by an equivalent concentration of 104. Precursor 104, labeled with deuterium at the O-methyl group, was co-fed with an approximately equal concentration of either 102 or 103 labeled with deuterium at the C-5 methyl group, and relative incorporation levels were compared by measurement of the CD3 peak intensities in the 2H NMR spectrum of the labeled azinomycin B. In each case, there was approximately twice as much deuterium labeling at the O-methyl group as at the other methyl group, consistently with 104 being a true biosynthetic intermediate. 

Fig. la-c. Theoretical 2H NMR line shapes for axially symmetric FGT (r = 0) in rigid solids, cf. Equ. (1). a Line shapes for the two NMR transitions b 2H spectrum (Pake diagram) in absorption mode as obtained by Fourier transform methods c 2H spectrum in derivative mode as obtained by wide line methods... 

Fig. 3. Calculated 2H NMR line shapes for planar and conical distributions, respectively, for different angles between the direction of order and the magnetic field, for details see text...

In presence of molecular motion the NMR line shape will change. A particularly simple situation arises, if the motion is rapid on timescale defined by the inverse width of the spectrum in absence of motion 6 1. In this fast exchange limit, which in 2H NMR is reached for correlation times tc < 1CT7 s, the motion leads to a partially averaged quadrupole coupling and valuable information about the type of motion can directly be obtained from analysis of the resulting line shapes. The NMR frequency is then given by... 

Fig. 5a-c. Theoretical 2H NMR spectra in the rapid exchange limit for the motional mechanisms depicted schematically in Fig. 4 a Kink-3-bond motion b crankshaft-S-bond motion c 180° jump of phenyl ring... 

Fig. 7. Theoretical line shapes resulting from an interchange between two NMR frequencies

In Fig. 7 actual numbers for the correlation times of the motion are included that apply for 2H NMR of deuterons in C—H bonds. It is evident that the line shape analysis of deuteron spectra should, in principle, provide a means to determine accurate values for the correlation times in a range of at least three orders of magnitude, the limits... 

Fig. 8. Calculated solid echo 2H NMR powder spectra for jumps between two sites related by the tetrahedral angle for ij =0, i.e. true absorption spectrum and Tj = 200 ps. xc is the correlation time of motion. R is the reduction factor, giving the total normalized intensity of the spectra for x, = 200 ps. (For x, = 0 all the spectra have total intensity 1)...

Fig. 14.2H NMR spectra of LPE, isothermally crystallized from the melt at 396 K (Mw as 100000, Mw/Mn as 10, Merck, Darmstadt) at 55 MHz obtained from a complex FT of the solid echo for various temperatures...

Fig. 16. Sketch of selected chain in the amorphous layers of LPE, subject to localized constraints of the motion (O) due to the interaction with neighboring chains. Through these constraints the chain is divided into flexible units. A selected deuteron 2H on unit j is shown for convenience Fig. 17. Fractions of flexible units in the amorphous layers of LPE as obtained from the analysis of 2H NMR line shapes displayed in Fig. 15...

Polycarbonate (PC) serves as a convenient example for both, the direct determination of the distribution of correlation times and the close connection of localized motions and mechanical properties. This material shows a pronounced P-relaxation in the glassy state, but the nature of the corresponding motional mechanism was not clear 76 80> before the advent of advanced NMR techniques. Meanwhile it has been shown both from 2H NMR 17) and later from 13C NMRSI) that only the phenyl groups exhibit major mobility, consisting in 180° flips augmented by substantial small angle fluctuations about the same axis, reaching an rms amplitude of 35° at 380 K, for details see Ref. 17). 

Fig. 27 a and b. Schematic representation of the molecular structure of a side chain polymeric liquid crystals b polymer model membranes studied by 2H NMR... 

Fig. 28. Room temperature 2H NMR spectra of the smectic liquid crystalline polymer (m = 6), oriented in its nematic phase by the magnetic field (8.5 T) of the NMR spectrometer with director ii parallel (left) and perpendicular (right) to the magnetic field...

Fig. 29. Observed and calculated 2H NMR spectra for the mesogenic groups of a) the nematic (m = 2), b) the smectic (m = 6) liquid crystalline polymer in the glassy state, showing the line shape changes due to the freezing of the jump motion of the labelled phenyl ring. The exchange frequency corresponds to the centre of the distribution of correlation times. Note that the order parameters are different, S = 0.65 in the frozen nematic, and S = 0.85 in the frozen smectic system, respectively...

In summary the results of our 2H NMR investigation illustrate the spacer model for liquid crystalline polymers, indicating, however, that the decoupling of the mesogenic groups from the main chain, while effective, is not complete. 

H NMR 38,39,42, 50-55 Hole capacity constant 205 Homogeneous distribution of correlation times 37 Humic acids 17 Humidity of plastics 119 Humins 17 Hydrogen bond 200 Hydrophilic 191, 194, 206... 

Fig. 2.8.12 2H NMR spectra obtained at the stress is highest, a quadrupole splitting is...

Fig. 2.8.17 Director orientation 0 obtained from 2H NMR spectra from the polysiloxane backbone polymer with liquid-crystal side-chain 4-methoxyphenyl-4 -butenyloxybenzoate, as a function of the apparent extension rate, i. The...

Westman, J. Boulanger, Y. Ehrenberg, A. Smith, I. C. P., Charge and pH dependent drug binding to model membranes A 2H-NMR and light absorption study, Biochim. Biophys. Acta 685, 315-328 (1982). 

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

Proton NMR and deuteron NMR spectra of soluble fractions and spent solvent mixtures were obtained by using a JE0L FX60Q FT NMR Spectrometer. A flip angle of 45° was used which corresponds to 14 ms for and 75 ms for 2H. The pulse repetition times were 6.0 and 9.0 s, respectively. Chloroform-d was used as the NMR solvent, and chloroform was used as the 2H NMR solvent. 

H NMR and 2H NMR spectra of fractionated coal products from El0 and El9 were recorded and analyzed to determine and 2H composition for each structural position. In our study, y y and 2Hx,v are defined as the fraction of the JH and 2H determined from the integrals of the NMR spectra of a given soluble fraction where y equals HS, BS or BMS and x = y-alkyl, 0-alkyl, a-alkyl or aromatic structural positions. The spectral range of the NMR integrations are given in Table V. 

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