Solid proton component relaxation

The usefulness of NMR in such analysis is because the proton spin-relaxation time constants are different for different components, such as water, liquid fat and solid fat. For example, the signal from solid fat is found to decay rapidly while the liquid signals decay much slower. This phenomenon is the basis for an NMR technique to determine the solid fat content [20], However, as the relaxation time constant of water, for example, could depend on its local environment, such as protein concentration, it may overlap with that of oil and other components. As a result, it could be difficult to formulate a robust and universal relaxation analysis. It... 

The T2 decay curves revealed two-component behaviour of the dried samples with distinct relaxation times of the single components for both the samples dried with and without sorbitol. One component relates to a solid proton fraction with a very low T2 relaxation time in the range of 10 ps that is independent on residual water content (data not shown). The second component relates to a more mobile proton fraction with a T2 relaxation time in the order of 100 ps that is dependent on water content and becomes lower with decreasing water content. It is assumed that the solid protons mainly relate to the protons of the biomass and... 

Note also that the finite time needed to encode the NMR magnetization in fe-space requires that the nuclear spin relaxation time, T2, be sufficiently long. T2 is determined predominantly by internuclear interactions, which in turn are motionally averaged by molecular tumbling. This means in effect that molecules in the liquid state have long proton T2 values (10-1000 ms) while those in the solid state may have relaxation times as short as 10 ps. This results in a sharp discrimination of the signal in which the solid state component is entirely filtered out, unless special... 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

Top) Solid-state proton (left) and deuterium (right) NMR spectra for freeze-dried media systems containing 14% mannitol indicating narrow (rapidly exchanging) and broad (slowly exchanging) components. (Bottom) Tj and T2 deuterium relaxation times for freeze-dried xanthan-locust bean gum with (solid circles) and without (solid squares) 14% mannitol. 

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