Cross polarization dynamics

For the study of complex cuticular mixtures, measurements of cross-polarization dynamics proved to be especially informative. The equality of Ti/>(H) values in cutin-wax assemblies demonstrated that these cuticular materials were mixed intimately. By contrast, Ti >(H) measurements showed that the polymeric components of suberized cell walls were present in distinct domains, suggesting that suberin was attached at a few structural sites rather than being embedded in the polysaccharide wall. 

Zumbulyadis N (1987) H/ Si cross-polarization dynamics in amorphous hydrogenated sUicon. J Chem Phys 86 1162-1166... 

The intensities of the lines(Figure 4a) are in the approximate ratio 5 5 1 for a, 3. and y carbons respectively and do not reflect the true 2 2 1 ratio. This must arise from a difference in rotating frame relaxation times for the protons and/or carbons such that the Cross-polarization dynamics of the a and 3 carbons are not the same as for the y carbon(5 ). Further, sidebands introduced by the sample rotatk>n(2.8 kHz) appear to low field of the main resonances, indicating that the inherent chemical shift anisotropy of the planar molecules is not averaging by thermal motion. These data are consistent with restricted overall motion and perhaps a preferential rotation about the C 2 symmetry axis of the pyridine. 

I.S. Chuang, and G.E. Maciel, Probing Hydrogen Bonding and the Local Environment of Silanols on Silica Surfaces via Nuclear Spin Cross Polarization Dynamics, J. Am. Chem Soc., 118, pp. 401-406, 1996. 

The inclusion complexes formed by a-CD and y-CD with PCL have been characterized by DSC, FTIR and X-ray diffraction [3,11]. These studies showed that complexes are formed and adopt channel structures. PCL and PEO chains of the triblock copolymer are included in both a- and y-CD/ICS, while the PS chains in the diblock copolymer are excluded from the channels of a-and y-CD/ICs. In the bulk PCL-PS diblock the PCL blocks do not crystallize, and so rubbery, amorphous PCL blocks are bonded to glassy, amorphous PS blocks. Figure 1 shows the 100 MHz solid-state NMR spectra for a-CD, PCL and the a-CD/PCL inclusion complex. The signals from PCL are easily identified and are well resolved from the a-CD signals in the complex. The chemical shifts for PCL in the inclusion complex are similar to those observed in the semicrystalline sample, suggesting that the PCL in a-CD channels adopts an extended all-trans conformation [3]. We can observe similar characteristics in the complex between PCL and y-CD. However, the cross polarization dynamics indicates that the maximum intensity for the PCL peaks was observed with a 4 ms cross polarization time, rather than the shorter 1 ms contact time used for the a-CD complex. 

Chuang, I.-S. and Maciel, G.E. 1996. Probing hydrogen bonding and the local environment of silanols on silica surfaces via nuclear spin cross polarization dynamics. J. Am. Chem. Soc. 118 401-406. 

In general, crystalline materials, including membrane proteins as the subject of this article, are an ideal target to be studied by solid-state NMR owing to the expected narrow line widths and efficient cross-polarization dynamics. From this... 

The 15N spectral peaks of fully hydrated [15N]Gly-bR, obtained via cross-polarization, are suppressed at 293 K due to interference with the proton decoupling frequency, and also because of short values of T2 in the loops.208 The motion of the TM a-helices in bR is strongly affected by the freezing of excess water at low temperatures. It is shown that motions in the 10-j-is correlation regime may be functionally important for the photocycle of bR, and protein-lipid interactions are motionally coupled in this dynamic regime. 

Polymer Dynamics. 13C spin-lattice relaxation times (Ti) were determined with either an inversion-recovery sequence (16) (for carbons observed by direct polarization) or with a modified cross-polarization experiment (17). 13C rotating-frame relaxation times (Tip(C)) were derived from measurements of the carbon signal that remained after a Tjp(C) hold time of... 

Table II highlights the 3C NMR relaxation times that reflect molecular motions and help define the physical properties of the cutin polymer. For those solid-like carbons that cross polarized, considerable motional freedom was evidenced for (CH2)n and CH2OCOR groups, on both MHz and kHz timescales, by the short values of Tj(C) and Tip(C), respectively. By contrast, the CHOCOR moiety was more restricted dynamically as judged from its long value of TX(C) low-frequency motions in particular were implicated by the strong dependence of Tip(C) on Bi. These latter groups...

The cross-polarization (CP), i.e. the transfer of I-spin polarization to the dilute spins (S), is a double resonance experiment in which the I and S spins are coupled by a certain interaction, determined by the cross relaxation time tb. From the dynamics of the CP process, usually described with the spin temperature concept, the following equation for the time dependence of S-spin polarization could be derived ... 

Section 6 reviews developments in cross-polarization and spin diffusion/ exchange. This section is closely related to Section 4 because of the interplay between these spin dynamics processes and the recoupling schemes at highspeed spinning, which now is almost invariably used for high resolution. Actually, many recoupling techniques were motivated by effecting crosspolarization and spin diffusion under fast MAS. 

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