Spectroscopy slow tumbling

Correlation times with time scales of 10 to 10 s are determined by the above method and are said to be in the fast tumbling region. In the slow tumbling region (lO" to 10 s) more sophisticated theoretical approaches [79], [80] are used. The very slow region (1 O to 10 s) cannot be studied by conventional ESR and requires special techniques such as saturation transfer spectroscopy (see Section 18.6.5.4). 

For a long time, magic-angle spinning (MAS A has helped biomolecular NMR applications in cases where slow molecular tumbling or susceptibility effects prohibit high-resolution spectroscopy under static conditions. For example, the benehcial effect of MAS has been observed for structural studies on biopolymers, model membranes,... 

The unique capability of NMR spectroscopy to differentiate by means of molecular mobility makes it a perfect tool to assign chemical constituents to structural elements of a particle dispersion. This is most straightforward in the case of dispersed nanospheres every constituent which is part of the solid matrix will exhibit the slow particle tumbling, while all components of the liquid continuous phase undergo rapid rotational diffusion. 

Flavoprotein radicals have been extensively studied by ESR [139] and ENDOR [140] spectroscopies. Their ESR spectra, with few exceptions, are broad and featureless because of the slow rate of tumbling of the radicals, even in fluid solution. Nevertheless, some structural information is available based on the width of the observed ESR line. The spectra observed fall into three classes, having widths of about 19,15 and 12 G. Non-covalently bound semiquinones have linewidths of either 19 or... 

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