Carbon-13 spin-lattice magnetic

Figure Bl.13.2. Spin-lattice and spin-spm relaxation rates (R and/ 2> respectively) for a carbon-13 spin directly bonded to a proton as a fiinction of correlation time at the magnetic fields of 7 and 14 T.

When carbon (S) spins are locked following a CP 90° pulse, the HB term becomes nonsecular and, after these oscillations vanish, the S spin-lock magnetization is fractionally reduced. Thus, the observed decay is generally a sum of two Weibull functions, usually exponentials (Equation 20 p = 1) the initial slope reflects a Tle dominated by a spin-lattice process and the final slope yields a Tt dominated... 

A complementary article by Dais (Iraklion, Crete) addresses the theoretical principles underlying the phenomenon of carbon-13 nuclear magnetic relaxation, encompassing spin-lattice (Tt) and spin-spin (T2) relaxation times, the nuclear Overhauser enhancement, and their relation to the motional behavior of carbohydrates in solution. With examples broadly selected from simple sugar derivatives, oligosaccharides, and polysaccharides, the author shows how qualitative treatments have provided useful interpretations of the gross mobility of molecules in solution, but demonstrates how a quantitative approach may be of greater ultimate value. 

At the same time the proton magnetization is being partially transferred to the carbon spins it relaxes to the lattice proton spin lattice relaxation in... 

For effective spin-lattice relaxation, the tumbling magnetic nuclei must be spatially close to the resonating nucleus. For attached protons provide effective spin-lattice relaxation. A carbonyl carbon or a carbon attached to four other carbons thus relaxes very slowly and is more easily saturated because the attached atoms are nonmagnetic ( C and... 

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