Spin-diffusion spectra

Fig. 85. Two-dimensional, 3C spin diffusion spectra of mixtures of adamantane and 2,2,3,3-tetramethylbutane at 75.4 MHz (424) (a) Mixture of powders (b) mixture by melt. Note the absence of cross-peaks between signals belonging to different species in the heterogeneous sample in (a).

Fig. 4.11. Proton driven spin-diffusion spectra of l- C glycine and alanine-labeled Nephila madagascariensis dragline silk at T = 150 K. A mixing time of 10 s was used. The spectrum was acquired with 128 transients per data point in ti, 96 spectra have been recorded in the Fi domain. The data matrix of 96 x 128 points was zero-filled to 256 x 256. As inset, the contour plot of the same data is shown. (Figure adapted from Ref. [63]).

Fig. 10.20. Spin-diffusion spectra taken after the indicated spin-diffusion times for PS(OH)/PBMA = 60/40 the Mo spectrum is given as a reference lineshape corresponding to full internal spin equilibrium. (Reprinted with permission from Ref. [116]. 1992 American Chemical Society, Washington, DC.)...

Figure 9 Experimental 2D "P NMR spin-diffusion spectra of hydrated VPI-5 recorded with 3-s mixing time at various MAS speeds 77 (a) 4.9 kHz (b) 6.5 kHz and (c) 10.1 kHz. The three spectra are not on the same intensity scale, so only the relative intensities within each can be compared.

Fig. 7. Experimental 2D P spin diffusion spectra of hydrated VPl-5 recorded with the mixing time of 3 s and MAS speeds of 4.9 kHz (top), 6.5 kHz (middle) and 10.1 kHz (bottom), respectively (used from Koiodziejski et with permission).

Figure 20 Comparison of proton-driven spin diffusion spectra obtained using...

Peptides. The correlation of deuterium quadrupolar tensors by spin diffusion under slow magic-angle-spinning conditions can provide accurate measurements of their relative orientation. This work showed the technique applied to the cyclo-P-peptide cyclo[(5)- 3-homoalanyl-(R)-P-homoalanyl-(S)-P-homoalanyl-(i )-P-homoalanyl] with its amide hydrogens labeled by deu-terons. From the 2D spin-diffusion spectrum, the mutual orientation of the amide deuteron quadrupolar coupling tensors were found. Eight conformations that are all consistent with the NMR measurement were determined. 

Fig. 4.6. Spin-diffusion spectrum (or TOSSY spectrum) of uniformly labeled calcium acetate monohydrate. Intramolecular as well as intermolecular cross-peaks are detected. The mixing time in the presence of a RIL mixing sequence with Lee-Goldburg proton decoupling was 20 ms. 512 ti experiments were performed with 16 scans each. Contour levels are shown for constant intervals between 2 and 15% of the maximal signal intensity. The signals marked by a star are assigned to a second crystal form present as a contamination. (Figure adapted from Ref. [2]).

The application of proton-driven CSA correlation spectroscopy to amino-acid specifically carboxylic-labeled spider silk [63] is shown in Fig. 4.11. Spider silk is known to consist of alanine- and glycine-rich domains [64, 65] and is known to be semicrystalline. The assignment of alanine to the (crystalline) /3-sheet domains [66] is clearly supported by the chemical-shift correlation spectrum of Fig. 4.11. Because the tensors in a j8-sheet structure are almost parallel, or antiparallel, with the tensors in spatial proximity, a diagonal spin-diffusion spectrum is expected for that structure and is indeed found. In contrast, the glycine spectrum shows considerable off-diagonal intensity. Simulations have shown that the spectrum is compatible with a local 3i-helical structure [63]. 

Fig. 4.12. (a) 2D quasi-equilibrium proton-driven spin-diffusion spectrum at 295 K of amorphous, atactic polystyrene C-enriched at the aromatic carbon Ci. The mixing time was set to 10 s. Within this time frame, a completely disordered environment is sampled (see Fig. 4.8(c)). (b) Rate-constants for r.f.-driven spin-diffusion obtained from mixing times smaller than 4 ms from the same compound, (c) Structure of a microstructure, constructed by Rapold et al. [71] to describe amorphous atactic polystyrene. The rate constants in (b) can be well explained by a set of such microstructures. From the microstructures, in turn, the weighted distributions p( 8)/sin /3 can be extracted. The result is given in (d). (Figure adapted from Refs. [30, 70]). 

Figure 5. Contour plot of the 2D spin diffusion spectrum of the hydroxyl protons of SAPO-5.

Spectral spin diffusion in the solid state involves simultaneous flipflop transitions of dipolar-coupled spins with different resonance frequencies 11,39,63-76], whereas spatial spin diffusion transports spin polarization between spatially separated equivalent spins. In this review we deal only with the first case. The interaction of spins undergoing spin diffusion with the proton reservoir provides compensation for the energy imbalance (extraneous spins mechanism) [68,70,73,74]. Spin diffusion results in an exchange of magnetization between the nuclei responsible for resolved NMR signals, which can be conveniently detected by observing the relevant cross-peaks in the 2D spin-diffusion spectrum [63-65]. This technique, formally analogous to the NOESY experiment in liquids, is already well established for solids and can also be applied to the study of catalysts. 

Figure 11 C NMR spin-diffusion spectrum of products of the conversion of meth-...

Table 3 Assignment of the 2D C NMR Spin-Diffusion Spectrum Shown in Fig. 11 [10]...

Fig. 4 proton-driven spin diffusion spectrum of OmpG-GAFY recorded at 900 MHz... 

FIGURE 12.16 (a) 2D H- H spin-diffusion spectrum of thymol. Boxes indicate the regions used for integration of each cross-peak. Asterisks indicate the carrier frequency artifacts (b) H- H spin-diffusion build-up curves. Experimental data points are represented by circles the best fit from the rate matrix analysis using the X-ray structure is shown using solid lines. Adapted with permission from Ref. [71]. Copyright 2009, RSC Publishing. 

Figure 19 (A) CRAMPS NMR spectrum of the slow-spin unannealed thin film P3HT PCBM blend. Also, CRAMPS NMR spin diffusion spectrum representing a physical P3HT-PCBM (50-50 by mass) mixture at tm = 2 ms (B), and that of the slow-spin unannealed thin film blend for f,n=(C)2, (D) 30, (E) 60, and (F) 240 ms. All experiments were performed at 7.0 T using a spinning frequency of 2525 Hz. Copyright 2012 Wiley. Used with permission from Ref. [55].

Figure 8. NMR spin diffusion spectrum of products of methanol conversion into gasoline over zeolite ZSM-5 with the projection onto the F2 axis (corresponding to a conventional spectrum) at the top [51]. Carbon atoms to which individual resonances are assigned are highlighted. For signal assignment see Table 2.

Table 2. Assignment of the 2D NMR spin-diffusion spectrum in Figure 8.

Self-Diffusion of Desmopressin and Monoolein by NMR. The self-diffusion coefficient was measured with the NMR diffusion technique using a Bruker MSL 100 spectrometer. Two magnetic field gradient pulses were applied at either side of the 180-degree pulse in a [90x-T-180y-T-echo] spin echo sequence (7,8) (Figure 2). Due to diffusion, the amplitude of a component in the spin-echo spectrum is attenuated according to (7)... 

To continue the investigation, carbon detected proton T relaxation data were also collected and were used to calculate proton T relaxation times. Similarly, 19F T measurements were also made. The calculated relaxation values are shown above each peak of interest in Fig. 10.25. A substantial difference is evident in the proton T relaxation times across the API peaks in both carbon spectra. Due to spin diffusion, the protons can exchange their signals with each other even when separated by as much as tens of nanometers. Since a potential API-excipient interaction would act on the molecular scale, spin diffusion occurs between the API and excipient molecules, and the protons therefore show a single, uniform relaxation time regardless of whether they are on the API or the excipients. On the other hand, in the case of a physical mixture, the molecules of API and excipients are well separated spatially, and so no bulk spin diffusion can occur. Two unique proton relaxation rates are then expected, one for the API and another for the excipients. This is evident in the carbon spectrum of the physical mixture shown on the bottom of Fig. 10.25. Comparing this reference to the relaxation data for the formulation, it is readily apparent that the formulation exhibits essentially one proton T1 relaxation time across the carbon spectrum. This therefore demonstrates that there is indeed an interaction between the drug substance and the excipients in the formulation. 

Fig. 9 TrNOESY and QUIET-trNOESY spectra of the peptide DRPVPY in the presence of the antibody SA-3. A Regions of a trNOESY spectrum (r = 200 ms) showing Val-4 HN-Pro-3,-5 H8 cross-peaks and Pro-3,-5 H5-H5 cross-peaks. B Corresponding regions of a QUIET-trNOESY spectrum (r = 200 ms) with inversion of 0.75 ppm wide bands centered at 4.15 ppm and 8.1 ppm within the intersection of the quiet bands (quiet window), the Val HN-Pro-5 U8 cross-peaks are still present, while the Val HN-Pro-3 B.82 crosspeak is absent, indicating cancelation due to spin diffusion. Reproduced with permission from [125]. 2002 American Chemical Society...

In conclusion, if temperature can be chosen freely, the best one is around the high-temperature maximum of a". Then, the NOESY spectrum has the highest possible sensitivity but is still free of spin diffusion. Low-temperature spectroscopy can increase sensitivity immensely, but quantitative data analysis requires either the full matrix or the buildup curve analysis. 

In practice, the full matrix analysis is rarely applicable because of spectral overlap and because of the global error propagation. In full matrix analysis all the elements are interconnected and the error in one volume element propagates into all cross-relaxation rates. This property is not favorable in practical situations in which a part of the spectrum may be ill-defined although a good portion of the spectrum is of a satisfactory quality. Then, the more favorable analysis is localized, i.e., errors are confined within respective cross-relaxation rates. However, such analysis is possible only on data in which spin diffusion is not dominant. 

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