Proton-driven spin-diffusion

Proton-driven spin diffusion Pulsed field gradient spin-echo Pleckstrin homology Poly(hydroxyethylmethacrylate)... 

Magnetization transfer via proton-driven-spin-diffusion (PDSD) in MAS NMR is not by any means a new experiment. It was introduced in the early 1980s by Maciel and coworkers [136] and later used, described, and analyzed by numerous groups in relation to, e.g., biological solid-state NMR. In its original form, the experiment consists of a couple of oppositely phase n/2 pulses bringing the low-y... 

The main source of conformational information for biopolymers are the easy-to-obtain chemical shifts that can be translated into dihedral restraints. In addition, for fully 13C labeled compounds, proton-driven spin diffusion between carbons [72] can be used to measure quantitatively distances between carbons. The CHHC experiment is the equivalent of the NOESY in solution that measures distances between protons by detecting the resonances of the attached carbons. While both techniques, proton-driven spin diffusion and CHHC experiment [73], allow for some variation in the distance as determined from cross-peak integrals, REDOR [74] experiments in selective labeled compounds measure very accurate distances by direct observation of the oscillation of a signal by the dipolar coupling. While the latter technique provides very accurate distances, it provides only one piece of information per sample. Therefore, the more powerful techniques proton-driven spin diffusion and CHHC have taken over when it comes to structure determination by ss-NMR of fully labeled ligands. 

Figure 46 (Top) Experimental 31P NMR spectra of three component sample crystallised from toluene (A) powdered sample (PS) recorded with CP/MAS sequence and spinning rate 8 kHz (B) three-component single crystal (TCSC) A held in rotor filled with silica gel recorded with CP/MAS sequence and spinning rate of 8 kHz. Note the much better NMR resolution of resonance lines and small distinction of 31P chemical shifts for the monocrystal compared to powdered sample. (Bottom) 31P-31P proton-driven spin diffusion 2D correlation recorded with mixing times of (A) 0.2 and (B) 10 s. Taken from Ref. [229].

The dynamics of the rotor speed can be conveniently analysed and adjusted by feeding a signal from the rotor motion monitor (via an optical fibre) to a console ADC (Fig. 7). The corresponding spectra are shown in Fig. 8. The faster sweep clearly reduces K12, and to a lesser extent K13. Both direct complementary peaks (1-Kmn) and relayed peaks depend on the product of complementary transfer coefficients, and correlate well with the expected influence of the sweep rate variation. The observed relay process can be shorted by proton-driven spin diffusion. Consequently, efficient rotation-speed independent (or carefully synchronized) decoupling is required during the entire mixing period. 

T. The side-chain signal sets of the individual amino acids were identified by 2D proton-driven spin diffusion and dipolar recoupling... 

Relaxation-mediated magnetization transfer is often dominated by the effects of a strongly coupled proton bath. The influence of the corresponding homonuclear and heteronuclear dipolar interactions may indirectly enhance the rate of polarization exchange between rare spins such as by a process called proton-driven spin diffusion... 

There are several ways to enhance spin diffusion in such systems. One can broaden the zero-quantum line to such an extent that the intensity at frequency zero is non vanishing for all relevant chemical-shift differences. However, due to the normalization of the zero-quantum line, a broad line implies that the intensity/,y(0) is low and that the spin diffusion proceeds slowly. A broadening of the zero-quantum line can often naturally be achieved by the coupling to a strongly-coupled proton spin system in so-called proton-driven spin diffusion while the form of the heteronuclear dipolar-coupling Hamiltonian (Equation (4.3)) prevents polarization exchange with the protons, the... 

Proton-driven spin diffusion (see also Appendix A) is the classical spin-diffusion experiment for low abundant spins. The line width of the one- and zero-quantum lines of the S-spins are mainly determined by the heteronuclear dipolar couplings while the homonuclear I-spin dipolar coupling makes the broadening of the levels homogeneous. Suter and Ernst [12] calculated an approximate value for the zero-quantum relaxation time... 

The slow-MAS spin-diffusion experiment (S-MAS) [21] is a modified version of the proton-driven spin-diffusion experiment described above. It is applicable to situations where the chemical-shift differences in the spectrum are mainly due to the orientational dependence of the CSA tensor. In these... 

For proton-driven spin diffusion, the most important difference to abundant high-y spin systems is that the main contribution to the zero-quantum line-width is no longer the homonuclear dipolar coupling, but rather, the hetero-nuclear dipolar coupling to protons or other abundant high-y spins in the sample. Because the zero-quantum lineshape is largely independent of the size of the homonuclear dipolar couplings and, therefore, independent of the... 

In proton-driven spin diffusion, the diffusion constant depends much more on the S-spin density than in r.f.-driven spin diffusion. 

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. 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]). 

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

Fig. 9.18 A 2D C—SQ-SQ correlation achieved using proton-driven spin diffusion a...

As an alternative means, it is a natural consequence to expect that high-resolution sohd-state NMR could be conveniently utilized to reveal the 3D structure and dynamics of a variety of membrane proteins, because the expected NMR line widths available from sohd-state NMR are not any more influenced by motional fluctuation of proteins under consideration as a whole as encountered in solution NMR. For instance, an attempt was made to determine 3D structure of uniformly C-labeled a-spectrin SH3 domain as a globular protein, based on distance constraints estimated from proton-driven spin-diffusion (PDSD) measure-... 

Second-order recoupling may be less sensitive to dipolar truncation, and several methods have been developed, based on the assistance of strongly coupled nuclei. However, many proton-driven spin diffusion experiments fail at ultrafast MAS. Among those that have been tested at ultrafast MAS, we can mention proton-assisted recoupling (PAR), efficient for providing long-range distances in the GBl protein at v = 65 kHz [153] (PAR... 

Finally, structural investigations of a human calcitonin-derived carrier peptide in a membrane enviromnent by solid-state NMR have been reported. The typical axially symmetric powder patterns of NMR spectra were used to confirm the presence of lamellar bilayers in the samples studied. The chemical shift anisotropy of the NMR spectra was monitored in order to reveal weak interaction of the peptide with the lipid headgroups. In addition, paramagnetic enhancement of relaxation rates and NMR order parameters of the phospholipid fatty acid chains in the absence and presence of the carrier peptide were measured. All peptide signals were resolved and fully assigned in 2D proton-driven spin diffusion experiments. The isotropic chemical shifts of CO, C and provided information about the secondary structure of the carrier peptide. In addition, dipolar eoupling measurements indicated rather high amplitudes of motion of the peptide. 

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

Proton-Driven) Spin Diffusion and Second-Order Recoupling for Polarization... 

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