Anomalous proton NMR relaxation behavior of cell wall materials from Chinese water chestnuts

Proton T-1 NMR relaxation of the cell wall materials from Chinese water che stnuts (CWC) is an order of magnitude more efficient than those from potato es, even though both the major relaxation pathways and the relative proton population of the relaxation groups are similar. This anomalous behavior of CWC can be explained by the detection of a strong ESR signal, which is an order of magnitude larger than that in samples from potatoes. The estimated free radical concentration is about 60 mu M. Spectral properties of the ra dicals (g = 2.00599, linewidth 10.75 G) are consistent with that of semiqui none radicals derived from wall-bound polyphenols in cell wall materials. H ydration led to the drastic reduction of the ESR signal; it virtually disap peared when;Is little as 13% water was added to CWC in the vapor phase. Red rying over phosphorus pentoxide under vacuum followed by exposure to air re sulted in some recovery of the free radical signals. Paradoxically, H-1 T-1 relaxation of a wet CWC (21% D2O) showed sustained efficiency at T > 300 K . T-1, relaxation was only moderately affected by the presence of free radi cals and transverse relaxation showed no effects. All the relaxation behavi or could be accounted for by a spin diffusion model involving low concentra tion of unpaired electron spins. Copyright (C) 2000 John Wiley & Sons, Ltd.