Longitudinal spin relaxation

Carbon-13 Heteronuclear Longitudinal Spin Relaxation for Geometrical (and Stereochemical) Determinations in Small or Medium Size Molecules... 

In mixed solutions of ferro- and ferri-cytochrome c cross saturation effects could be observed by this technique. For example when the methyl resonance at +23.2 ppm of ferricytochrome c (Fig. 19) was irradiated, saturation effects were also observed in the methyl resonance of ferro-cytochrome c at +3.3 ppm (Fig. 27). This cross relaxation was shown to arise from an exchange of protein molecules, and hence also the saturated spins, between the ferrous and ferric oxidation states. The life-time in either oxidation state then has to be comparable to or shorter than the longitudinal spin relaxation time of the observed protons. Besides... 

Longitudinal spin relaxation requires a stimulus in the form of a magnetic field fluctuating at a frequency equal to the frequency (energy) of the transition. In the case of dipolar relaxation, this arises from the time-dependent field a spin experiences from its dipolar coupled neighbour as the molecule rotates or tumbles in solution. The NOE in turn is dependent upon the rates of molecular tumbling. 

Fig. 1. The FC principle for measurements of the longitudinal spin relaxation time T at different Larmor frequencies (i ) or Zeeman fields (Bq), i e. of the relaxation dispersion 7 ](t ) or The upper diagram illustrates the Bo t) cycle with finite...

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