Carbon magnetization

The similarity between the cryptands and the first of these molecules is obvious. Compound 7 7 is a urethane equivalent of [2.2.2]-cryptand. The synthesis of 7 7 was accomplished using a diacyl halide and l,10-diaza-18-crown-6 (shown in Eq. 8.13). Since amidic nitrogen inverts less rapidly than a tertiary amine nitrogen, Vogtle and his coworkers who prepared 7 7, analyzed the proton and carbon magnetic resonance spectra to discern differences in conformational preferences. Compound 7 7 was found to form a lithium perchlorate complex. 

However, if side-chain carbon assignments are wanted, C(CC)(CO)NH experiments [33] that start directly with carbon magnetization and transfer it further to the amide proton for detection are available. If protonated substituents, for example methyl groups, have been introduced into the otherwise perdeuterated protein, the usual HC(C)(CO)NH-TOCSY pulse sequence can be used to obtain the proton chemical shifts. These protons can provide a small number of NOEs that, together with residual dipolar couplings and the secondary structure identification from chemical shifts, make the determination of the global fold of large proteins possible. 

Carbon-13 magnetic resonance (CMR) can play a useful role. Since carbon magnetic resonance deals with analyzing the carbon distribution types, the obvious structural parameter to be determined is the aromaticity, fa Direct determination from the various types of carbon environments is one of the better methods for the determination of aromaticity. Thus, through a combination of proton and carbon magnetic resonance techniques, refinements can be made on the structural parameters, and for the solid-state high-resolution carbon magnetic resonance technique, additional structural parameters can be obtained. 

Equation (10) admits a simple interpretation the carbon magnetization rises with... 

Ugeda MM, Brihuega I, Guinea F et al (2010) Missing atom as a source of carbon magnetism. Phys Rev Lett 104 96804... 

The product exhibits the following carbon magnetic resonance spectrum... 

The initial building-up of the carbon magnetization via polarization transfer is characterized with the spin-lock cross-polarization time Tcir It is sensitive to the static interactions, i.e. transfer of the polarization via static dipolar interactions (proportional to e J). Hence, the shortest TCH will have carbons a) in more rigid systems and b) with more directly attached protons, particularly the CH2 (or... 

Fig. 40. Evolution of carbon magnetizations in a cured polystyrylpyridine as a function of the contact time t (reprinted from Ref, 239) with permission)...

The values of, 3C T1 and their temperature dependence are found to be very sensitive to the nature of the build-up of the carbon magnetization directly (by applying a 90° degree pulse), or indirectly by cross-polarization. The 13Clfi vs. 

Figure 4 - Noise decoupled carbon magnetic resonance spectrum of disopyramide phosphate. 

Single Frequency Off-Resonance Proton Decoupled Carbon Magnetic Resonance Spectrum of Disopyramide Phosphate... 

Studies using 14C-labelled precursors and C-l3 carbon magnetic resonance have suggested that the biosynthesis of the benzenic ansamycin geldanamycin follows essentially the same pathway as that of the rifamycins and streptovaricins50. Geldanamycin is composed of 3 acetate and four propionate units which are attached to a C7N unit in the same direction of growth as is found in rifamycins and streptovaricins. The incorporation of three acetate units into the ansa chain, as opposed to two in the naphthalenic ansamycins, excludes the existance of a common precursor. 

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