Proton spin echo spectra

Fig. 1. Proton spin echo spectra of 4- -pentyl-dn-4 -cyanobiphenyI-d4. (a) Experiment (b) calculated. From Ref. 8.

An example of the spin echo technique is shown in Fig. 1 which is the proton spin echo spectrum of the four protons on 4-w-pentyl-du-4 -cyanobiphenyl-d4 (5CB-di5),... 

The period of the pinning SDW potential has been derived from two sets of NMR experiments which have been performed recently in a sliding SDW state. First, measurement of the SDW velocity from the proton spin echo amplitude of (TMTSF)2PF6 [119] (Fig. 37) as a function of the dc current (above threshold field) and comparison with the SDW noise spectrum lead to a pinning potential period that is half the SDW wavelength (namely, a = 2). Second, the result a = 1 is inferred from a study of the amplitude of the motionally narrowed 13C spectrum in (TMTSF)2PF6 and of a SDW current and noise spectrum [111] (Fig. 38). 

Figure 5.42. The 2D C, H COSY NMR spectrum of erythromycin in CDCIj as a contour plot beneath the corresponding ID C spin-echo NMR spectrum. The spin-echo spectrum (pulse sequence 90°-(r-I80°-x) -data acquisition) was acquired with broadband proton decoupling during the second period and data accumulation. With x = 8 ms CH2 and C resonances are inverted relative to CHj and CH resonances. The small triangles (A) indicate the two outer lines of the solvent triplet. The contour plot levels are higher than the cross-peaks due to methylene moieties.

The location of TMB within the micelles was studied by Kevan et al. [132] with the spin-echo technique. In the deuterated SDS solution in the spin-echo spectrum of TMB" one can observe both the proton modulation from the hydrogen atoms of SDS and the deuterium atoms of water. The conclusion was that TMB" is located at the micelle-water interface. As discussed above, parent TMB is located in hydrophobic micelle nuclei. So the location of TMB changes within its lifetime and it transfers from the hydrophobic region of the micelle to the interface. The evolution of TMB" in CTAB and SDS micelles was studied by Beck and Brus with pulse Raman spectroscopy [132]. They found that TMB is formed in CTAB micelles with a delay and yields TMB and TMB in the millisecond range. TMB formed in SDS micelles is stable for several days [134]. The anionic micelles seem to stabilize TMB" and the cationic ones to destabilize it. 

Figure 12.1 Clearance of small-molecule impurities from process buffers in a formulated protein product. Trace A the NMR spectrum of a control sample containing a mixture of three components (succinate, tetraethylammonium, and tetramethylammonium) in the final formulation buffer (sodium acetate). These three components were used in the recovery process for a biopharmaceutical product. Traces B and D the proton NMR spectra of the formulated protein product. No TEA or TMA were detected, but a small amount of succinate was observed in this sample. Traces C and E the proton NMR spectra of a formulated protein product spiked with 10 jag/ml of succinate, TEA, and TMA. Traces D and E were recorded with CPMG spin-echo method to reduce the protein signals. The reduction of NMR signals from the protein allows for better observation of the small-molecule signals.

Figure 12.3 Clearance of MES in a formulated protein product. Trace A the proton NMR spectrum of a formulated protein product spiked with 8 jig/ml of MES. Trace B the proton NMR spectrum of a formulated protein product. The arrows indicate the positions where MES signals would be detected if present. Trace C the difference of traces A and B (A-B). Trace D proton NMR spectrum of 8 ftg/ml of MES in the formulation buffer. The NMR spectra in traces A, B, and D were recorded with the CPMG spin-echo method to reduce protein signals. Only the region where MES signals appear is shown.

Fig. 2.42. I3C NMR spectra of D-camphor in tetradeuteriomelhanol at 15.08 MHz (a). /-modulation of aliphatic carbon signals depending on the decoupling delay z, a verification of Fig. 2.41 (b) proton broadband decoupled spectrum (c-e). /-modulated spin-echo experiments with z = 4, 6, and 8 ms for CH multiplicity analysis (f-g) spectra with off-resonance (0 and gated decoupling of protons (g) for comparison.

The antiphase relationship of the C13 —C13 doublet signals in the INADEQUATE spectrum can be eliminated by an additional spin-echo sequence (— 1/4Jcc — 180° — 1 /4 Jcc —) before the 90 monitor pulse [58]. The sensitivity of the experiment may be improved by the application of stronger magnetic fields or by using proton polarization transfer techniques [59]. 

This used to be a common way of distinguishing methyl, methylene and methine carbons. However, as can be seen in the spectrum above, it is not a clean experiment methylene carbons with non-equivalent protons attached often give particularly messy results ( 8.2.2). /-modulated spin-echoes, INEPT or DEPT provide much more reliable ways of determining multiplicities ( 3.3.2 and 8.5). 

FIG. 11. J-spectrum obtained by Fourier transformation of the spin-echo envelope from the protons of 1,1,2-trichloroethane. The interval between echoes is 2r = 40 milliseconds and echoes have been sampled for 30 seconds. Responses are observed at 0 Hz, 2-97 Hz, and 5-94 Hz. From ref. 145. 

J/2) from the CH2 protons and the other at 5-94 Hz from the CH proton whose resonance in a normal spectrum is a 1 2 1 triplet with outer components which precess at twice the rate of the components of the CH2 doublet. (148) In fact each spin-echo normally contains a number of different frequency components which can be separated by electronic filtration or by Fourier transformation to yield a set of J-spectra which can then be conveniently displayed in a two-dimensional plot. In practice the second approach is normally used, and thus the set of spin-echoes is subjected to a double Fourier transformation according to equation (2) in which cafe must be taken to combine correctly the real and imaginary transforms. (26)... 

The second refocusing period again is a spin echo in which chemical shifts are focused by the 180° pulses. The spin roles, however, are reversed in the second set, so that I magnetization is refocused back to two positive peaks for the CH case. The decoupling of protons during carbon acquisition thus does not result in the cancelation of any peaks. The spectrum that is obtained contains decoupled peaks with enhanced intensity. Figure 5-22 compares the various experiments for chloroform. 

Left two-pulse [(a) primary ESEEM] and three-pulse [(b) stimulated echo ESEEM] sequences t is the (fixed) delay time between pulses one and two and T is a variable delay time. Right frequency domain and time domain (inset) of the two-pulse EESEM spectrum of VO - vanabin, recorded at the m = — 1 /2 line, at 77 K and a pulse width of 20 ns.P l The superhyperfine coupling constant = 4.5 MHz (obtained from the N double-quantum lines at 3.9 and 7.1 MHz) is in accord with amine nitrogen provided by lysines of the vanadium-binding protein. The spin echo due to proton coupling, at 13.7 MHz, was also observed. Reproduced from K. Eukui et al., J. Am. Chem. Soc. 125, 6352-6353. Copyright (2003), with permission from the American Chemical Society. 

---